migrating and nonmigrating semidiurnal tides in the upper atmosphere excited by tropospheric latent heat release migrating and nonmigrating semidiurnal tides

sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

a study of a self generated stratospheric sudden warming and its mesospheric lower thermospheric impacts using the coupled time gcm ccm3 1 a stratospheric sudden warming episode was self consistently generated in the coupled national center for atmospheric research thermosphere ionosphere mesosphere and electrodynamics general circulation model climate community model version 3 time gcm ccm3 taking advantage of the unique vertical range of the coupled model ground to 500 km we were able to study the coupling of the lower and upper atmosphere in this warming episode planetary wave 1 is the dominant wave component in this warming event analysis of the wave phase structure and the wave amplitude indicates that the wave may experience resonant amplification prior to the peak warming the mean wind in the high latitude winter stratopause and mesosphere decelerates and reverses to westward due to planetary wave forcing and forms a critical layer near the zero wind lines the wind deceleration and reversal also change the filtering of gravity waves by allowing more eastward gravity waves to propagate into the mesosphere and lower thermosphere mlt which causes eastward forcing and reverses the westward jet in the mlt this also changes the meridional circulation in the upper mesosphere from poleward downward to equatorward upward causing a depletion of the peak atomic oxygen layer at 97 km and significant reduction of green line airglow emission at high latitudes and midlatitudes planetary waves forced in situ by filtered gravity waves in the mlt grow in the warming episode their growth and interaction with tides create diurnal and semidiurnal variabilities in the zonal mean zonal wind

goce gradiometer measurements response to ionospheric dynamics with the launch of dedicated satellite gravity missions starting with challenging minisatellite payload champ in 2000 with gravity recovery and climate experiment grace in 2002 and gravity field and steady state ocean circulation explorer goce in 2009 the accuracy and spatial resolution of the earth s global gravity field models have been improved highly sensitive accelerometer measurements have not only been useful for gravity field modeling but have also been contributing to the studies of thermospheric dynamics while improving the sensitivity of the accelerometer measurements the new instrumentation used on board goce brings different challenges in understanding the data and developing sophisticated data processing our analyses reveal that the goce gravitational gradient measurements were affected by highly variable ionospheric dynamics that did not only degrade the quality of the goce electrostatic gravity gradiometer egg measurements but also proved that some characteristics of ionospheric dynamics can be measured by goce accelerometers and other low earth orbiters in this paper we show how goce retrieved neutral winds respond to main ionospheric currents and we develop the impulse response relation between intense ionospheric dynamics plasma drift represented by poynting energy flux and the gravity gradiometer tensor trace disturbances observed over the north geomagnetic polar region

stereo and wind observations of a fast icme flank triggering a prolonged geomagnetic storm on 5 7 april 2010 1 on 5 april 2010 an interplanetary ip shock was detected by the wind spacecraft ahead of earth followed by a fast average speed 650 km s ip coronal mass ejection icme during the subsequent moderate geomagnetic storm minimum dst 72 nt maximum kp 8 communication with the galaxy 15 satellite was lost we link images from stereo secchi to the near earth in situ observations and show that the icme did not decelerate much between sun and earth the icme flank was responsible for a long storm growth phase this type of glancing collision was for the first time directly observed with the stereo heliospheric imagers the magnetic cloud mc inside the icme cannot be modeled with approaches assuming an invariant direction these observations confirm the hypotheses that parts of icmes classified as 1 long duration mcs or 2 magnetic cloud like mcl structures can be a consequence of a spacecraft trajectory through the icme flank

enso related rainfall changes over the new guinea region 1 the large scale nature of el nino southern oscillation enso impacts on rainfall in the western pacific region is generally well known but in some regions where there are relatively few observations and the terrain is mountainous the details of the impacts are less obvious here we analyze rainfall data for the new guinea region comprising station observations reanalysis products and satellite based estimates in order to better understand some of these details we find that most gridded products are limited due to their relatively coarse horizontal resolutions that fail to resolve topographic effects however the relatively fine resolution tropical rainfall measurement mission satellite based product appears to provide reliable estimates and linear correlations between the data and the nino34 sea surface temperature index provides an insight into the pattern of enso rainfall impacts the first major finding is that the correlation patterns reveal that some highland regions are impacted differently to other surrounding regions most likely because of the interaction between winds and topography second we find that the association between enso and rainfall for stations in the new ireland new britain region tends to be nonlinear in the sense that warm el nino cool la nina events cause a decrease in rainfall the strong 2010 2011 la nina event being a clear example both findings help explain why previous studies have tended not to identify a simple large scale response of new guinea rainfall to enso

an investigation of the influence of data and model inputs on assimilative mapping of ionospheric electrodynamics the geospace environment modeling gem substorm challenge event of november 24 1996 has been used as a test case to investigate the influence of different data and model inputs on the assimilative mapping of ionospheric electrodynamics amie outputs during that period the interplanetary magnetic field imf went from northward to southward and then returned to northward in the later part of the day a moderate substorm with al 600 nt took place the amie convection patterns derived from the super dual auroral radar network superdarn data alone are generally similar to those derived using ground magnetometer alone especially during the relatively stable southward imf period however some differences are found during the northward imf period and during the substorm namely the reversed convection configuration near local noon imaged by superdarn is absent in the magnetometer observations while the strong convection on the nightside recorded by the magnetometers during the substorm expansion phase is not seen by the radars different conductance models do not seem to have a big effect on the large scale distributions of ionospheric convection and joule heating but they do alter the cross polar cap potential drop and the hemispheric integrated joule heating rate by nearly a factor of 2 when the amie derived electric potential drop was compared with the in situ measurements along the satellite track it is found that amie underestimated the potential drop by 20 kv amounting to a 22 underestimation the analysis of the amie results based on the superdarn and ground magnetometer data reiterates the view that the response of ionospheric convection to a sudden imf southward turning is global and nearly simultaneous

the normality of el nino the amplitude of the el nino southern oscillation enso would be normally distributed if the coupled pacific ocean atmosphere were a linear system forced by gaussian weather noise moment estimates of skewness and kurtosis demonstrate that this is not the case for monthly mean anomalies in pacific sea surface temperatures during 1950 97 the noted predominance of el nino events compared to la nina events is related to the high skewness in the eastern pacific skewness and kurtosis both exhibit an intriguing geographical variation from positive in the eastern to negative in the western pacific we have also examined nino 3 indices generated by three climate models having widely different complexity these exhibit a wide range of skewness and kurtosis values rather different from those found for the observations skewness and kurtosis can be used to diagnose non linear processes and provide powerful tools for validating models and for testing observed sea surface temperatures for the presence of possible climate change

a 21 year record of arctic sea ice extents and their regional seasonal and monthly variability and trends satellite passive microwave data have been used to calculate sea ice extents over the period 1979 1999 for the north polar sea ice cover as a whole and for each of nine regions over this 21 year time period the trend in yearly average ice extents for the ice cover as a whole is 32 900 6 100 sq km yr 2 7 0 5 decade indicating a reduction in sea ice coverage that has decelerated from the earlier reported value of 34 000 8 300 sq km yr 2 8 0 7 decade for the period 1979 1996 regionally the reductions are greatest in the arctic ocean the kara and barents seas and the seas of okhotsk and japan whereas seasonally the reductions are greatest in summer for which season the 1979 1999 trend in ice extents is 41 600 12 900 sq km yr 4 9 1 5 decade on a monthly basis the reductions are greatest in july and september for the north polar ice cover as a whole in september for the arctic ocean in june and july for the kara and barents seas and in april for the seas of okhotsk and japan only two of the nine regions show overall ice extent increases those being the bering sea and the gulf of st lawrence for neither of these two regions is the increase statistically significant whereas the 1079 1999 ice extent decreases are statistically significant at the 99 confidence level for the north polar region as a whole the arctic ocean the seas of okhotsk and japan and hudson bay

pore water pressure effects on the detachment of cohesive streambeds seepage forces and matric suction erosion of cohesive channel materials is not fully understood but is assumed to occur largely as a result of hydraulic shear stress however field and laboratory observations of pore water pressures in cohesive streambed materials reveal the presence of positive and negative pore water pressure effects that may significantly affect the erosion process as contributing and resisting forces respectively measurements of pore water pressures below cohesive streambeds in the loess area of the midwestern usa were conducted in situ and in undisturbed cores with a digital miniature tensiometer results disclosed matric suction values in the range of 15 50 kpa in eastern nebraska and northern mississippi repetitive tests in soft materials verified a change from positive pore water pressures in the upper 10 15 cm to negative pore water pressures to depths of at least 50 cm in firm materials the entire sampled profile was unsaturated laboratory experiments were carried out in which synthetic hydrographs were imposed on undisturbed streambed cores from the same sites miniature tensiometers in the cores monitored the resulting pattern of pore water pressures and revealed upward directed seepage forces on the recessional limb of the hydrograph maximum calculated values of the force ranged from 10 to 275 kn for the materials and heads tested the maximum value obtained after application and release of a 2 5 m head was 119 kn with 275 kn after a 5 0 m head these results were supported independently by subsequent simulations using a finite element hydrology model coupled with a stress deformation model a numerical scheme was developed to calculate the forces acting on cohesive aggregates in an idealized streambed and to evaluate the potential for their detachment the scheme added upward directed seepage as an additional driving force and matric suction as an additional resisting force to the commonly applied factors of particle weight fluid drag and lift force results demonstrate that upward directed seepage forces of the magnitude measured in the laboratory with 5 0 m stages have the potential to detach particles larger than 10 cm in diameter without requiring fluid drag and lift forces when added to these hydraulic forces erosion thresholds are lowered enabling erosion at lower hydraulic stresses a hypothesis for detachment of chips or blocks of cohesive bed material is proposed 1 large 5 m rises in stage increase pore water pressures or decrease matric suction dramatically in the region just below the bed surface 2 a relatively rapid decrease in stage causing a loss of water pressure above the bed combined with low rates of excess pore water pressure dissipation just below the bed surface result in steepened hydraulic gradients and 3 a resulting net upward seepage force is great enough to contribute to detachment of cohesive bed material or rupture the bed by exceeding the available strength and confining stress published in 2001 by john wiley sons ltd

global ionospheric and thermospheric response to the 5 april 2010 geomagnetic storm an integrated data model investigation we present a case study of the 5 april 2010 geomagnetic storm using observations and numerical simulations the event was driven by a fast moving coronal mass ejection and despite being a moderate storm with a minimum dst near 50 nt the event exhibited elevated thermospheric density and surges of traveling atmospheric disturbances tads more typically seen during major storms the thermosphere ionosphere mesosphere electrodynamics general circulation model timegcm was used to assess how these features were generated and developed during the storm the model simulations gave rise to tads that were highly nonuniform with strong latitude and longitude local time dependence the tad phase speeds ranged from 640 m s to 780 m s at 400 km and were 5 lower at 300 km and approximately 10 15 lower at 200 km in the lower thermosphere around 100 km the tad signatures were nearly unrecognizable due to much stronger influence of upward propagating atmospheric tides the thermosphere simulation results were compared to observations available from the gravity field and steady state ocean circulation explorer goce challenging minisatellite payload champ and gravity recovery and climate experiment grace satellites comparison with goce data shows that the timegcm reproduced the cross track winds over the polar region very well the model data comparison also revealed some differences specifically the simulations underestimated neutral mass density in the upper thermosphere above 300 km and overestimated the storm recovery tome by 6 h these discrepancies indicate that some heating or circulation dynamics and potentially cooling processes are not fully represented in the simulations and also that updates to some parameterization schemes in the timegcm are warranted

a model of channel response in disturbed alluvial channels dredging and straightening of alluvial channels between 1959 and 1978 in west tennessee caused a series of morphologic changes along modified reaches and tributary streams degradation occurred for 10 to 15 years at sites upstream of the area of maximum disturbance and lowered bed levels by as much as 6 1 m following degradation reaches upstream of the area of maximum disturbance experienced a secondary aggradation phase in response to excessive incision and gradient reduction aggradation downstream of the area of maximum disturbance reached 0 12 m per year with the greatest rates occurring near the stream mouths the adjustment of channel geometry and phases of channel evolution are characterized by six process oriented stages of morphologic development premodified constructed degradation threshold aggradation and restabilization down cutting and toe removal during the degradation stage causes bank failure by mass wasting when the critical height and angle of the bank material is exceeded threshold stage channel widening continues through the aggradation stage as the slough line develops as an initial site of lower bank stability the bank profile develops three dynamic elements 1 vertical face 70 to 90 2 upper bank 25 to 50 and 3 slough line 20 to 25 alternate channel bars form during the restabilization stage and represent incipient meandering of the channel

how well do current climate models simulate two types of el nino in this study we evaluate the fidelity of current climate models in simulating the two types of el nino events using the pre industrial output in cmip3 archives it is shown that a few climate models simulate the two types of el nino events to some extent while most of the models have serious systematic problems in simulating distinctive patterns of sea surface temperature sst and precipitation anomaly associated with the two types of el nino that is they tend to simulate a single type of el nino it is shown that the ability of climate models in simulating the two types of el nino is related to the sensitivity of the atmospheric responses to the sst anomaly patterns models whose convective location is shifted to the east west as the sst anomaly center moves to the east west tends to simulate the two types of el nino events successfully on the other hand models whose location of convective anomaly is confined over the western or central pacific tends to simulate only the single type of el nino event it is also shown that the confinement of the convective anomaly over the western or central pacific is closely linked to the dry bias and the associated cold bias over the eastern pacific that is because positive el nino sst anomalies over the eastern pacific cannot increase local convection effectively when the total ssts are still too cold due to a cold bias this implies that the realistic simulation of climatology especially over the equatorial eastern pacific is essential to the successful simulation of the two types of el nino

decadal amplitude modulation of two types of enso and its relationship with the mean state in this study we classified two types of el nino southern oscillation enso events within the decadal enso amplitude modulation cycle using a long term coupled general circulation model simulation we defined two climate states strong and weak enso amplitude periods and separated the characteristics of enso that occurred in both periods there are two major features in the characteristics of enso the first is the asymmetric spatial structure between el nino and la nina events the second is that the el nino la nina asymmetry is reversed during strong and weak enso amplitude periods el nino events during strong weak enso amplitude periods resemble the eastern pacific central pacific el nino in terms of the spatial distribution of sea surface temperature anomalies ssta and physical characteristics based on heat budget analysis the spatial pattern of the thermocline depth anomaly for strong weak el nino is identical to that for weak strong la nina but for an opposite sign and slightly different amplitude the accumulated residuals of these asymmetric anomalies dominated by an east west contrast structure could feed into the tropical pacific mean state moreover the residual pattern associated with el nino la nina asymmetry resembles the first principal component analysis pca mode of tropical pacific decadal variability indicating that the accumulated residuals could generate the change in climate state thus the intensified enso amplitude yields the warm residuals due to strong el nino and weak la nina over the eastern tropical pacific this linear relationship between enso and the mean state is strong during the mature phases of decadal oscillation but it is weak during the transition phases furthermore the second pca mode of tropical pacific decadal variability plays an important role in changing the phase of the first mode consequently the feedback between enso and the mean state is positive feedback to amplify the first pca mode whereas the second pca mode is a negative feedback to lead the phase change of the first pca mode due to their lead lag relationship these features could be regarded as evidence that the decadal change in properties of enso could be generated by the nonlinear interaction between enso and the mean state on a decadal to interdecadal time scale

insights into river bank erosion processes derived from analysis of negative erosion pin recordings observations from three recent uk studies recent studies of river bank erosion in three catchments in the uk have been characterized by the persistent occurrence of negative erosion pin results the cause of these negative recordings is considered with reference to field data from the afon trannon nant tanllwyth and river arrow and to a laboratory study of freeze thaw and desiccation processes it seems that there is potential for and in some cases evidence of a number of different circumstances that generate negative results but none of these alone is sufficient to explain all incidents factors considered include deposition of sediment during high flows soil fall from the upper parts of the bank on to lower erosion pins loosening of the soil surface and expansion contraction of the soil mass with fluctuations in temperature and moisture content movement of the erosion pin within the bank and human interference each has its own implications for the use of erosion pins further issues arise when including negative data in subsequent data analysis and it is demonstrated that attempts to correlate erosion rates with hydro meteorological data in order to ascertain causes of erosion will be influenced by the way in which negative data are handled it is thus suggested that any study of river bank erosion using erosion pins should state whether or not negative data were obtained and if so how they were included in data analysis failure to include this information could lead to comparison of mean erosion rates that reflect bank processes very differently the studies presented here offer a clear example of the value of anomalous field data results which do not appear to fit expected patterns can reveal as much about the processes in operation as those that do

morphology of large scale traveling atmospheric disturbances in the polar thermosphere using a fully coupled thermosphere ionosphere plasmasphere model we investigate the morphology of modelled large scale traveling atmospheric disturbances ls tads hereinafter tads propagating both poleward and equatorward from auroral sources we confirm observational evidence of daytime ion drag reducing equatorward far field tad activity we further suggest an additional source dependent mechanism that associates tads propagating preferentially poleward with an auroral electric field burst that contains an eastward rather than a westward component these poleward tads are superimposed on the high speed neutral air winds in the polar cap originating from the day night plasma convection and exhibit speed and spatial resonance effects with the neutral wind the direction of propagation is affected by coriolis forcing due to the earth s rotation

effects of riparian vegetation on stream bank subaerial processes in southwestern virginia usa riparian vegetation is frequently used for stream bank stabilization but the effects of vegetation on subaerial processes have not been quantified subaerial processes such as soil desiccation and freeze thaw cycling are climate related phenomena that deliver soil directly to the stream and make the banks more vulnerable to fluvial erosion by reducing soil strength this study compares the impact of woody and herbaceous vegetation on subaerial processes by examining soil temperature and moisture regimes in vegetated stream banks soil temperature and water tension were measured at six paired field sites in southwestern virginia usa for one year results showed that stream banks with herbaceous vegetation had higher soil temperatures and a greater diurnal temperature range during the summer compared to forested stream banks daily average summer soil water tension was 13 to 57 per cent higher under herbaceous vegetation than under woody vegetation probably due to evapotranspiration from the shallow herbaceous root system on the bank in contrast to summer conditions the deciduous forest buffers provided little protection for stream banks during the winter the forested stream banks experienced diurnal temperature ranges two to three times greater than stream banks under dense herbaceous cover and underwent as many as eight times the number of freeze thaw cycles during the winter the stream banks under the deciduous forests were exposed to solar heating and night time cooling which increased the diurnal soil temperature range and the occurrence of freeze thaw cycling study results also indicated that freeze thaw cycling and soil desiccation were greater on the upper stream bank due to thermal and moisture regulation of the lower bank by the stream therefore subaerial erosion and soil weakening may be greater on the upper stream banks additional research is needed on the influence of subaerial processes on both subaerial and fluvial erosion copyright 2006 john wiley sons ltd

a physically based model to predict hydraulic erosion of fine grained riverbanks the role of form roughness in limiting erosion hydraulic erosion of bank toe materials is the dominant factor controlling the long term rate of riverbank retreat in principle hydraulic bank erosion can be quantified using an excess shear stress model but difficulties in estimating input parameters seriously inhibit the predictive accuracy of this approach herein a combination of analytical modeling and novel field measurement techniques is employed to improve the parameterization of an excess shear stress model as applied to the lower mekong river boundary shear stress is estimated using a model kean and smith 2006a 2006b for flow over the irregular bank topography that is characteristic of fine grained riverbanks bank erodibility parameters were obtained using a cohesive strength meter tolhurst et al 1999 the new model was used to estimate annual bank erosion rates via integration across the mekong s annual flow regime importantly the simulations represent the first predictions of hydraulic bank erosion that do not require recourse to calibration thereby providing a stronger physical basis for the simulation of bank erosion model predictions as evaluated by comparing simulated annual rates of bank toe retreat with estimates of bank retreat derived from analysis of aerial photographs and satellite imagery indicate a tendency to overpredict erosion root mean square error equals 0 53 m yr form roughness induced by bank topographic features is shown to be a major component 61 85 of the spatially averaged total shear stress and as such it can be viewed as an important factor that self limits bank erosion

an empirical electric field model derived from chatanika radar data plasma convection velocity observations obtained with the chatanika alaska incoherent scatter radar have been used to prepare a quantitative empirical model of the convection electric field at auroral latitudes between 58 and 75 vector averaging of the individual days data and smoothing across 2 5 hours of local time were used to reduce substorm perturbations tables of the vector electric field components at 300 km altitude have been prepared for moderately disturbed kp 3 summer conditions resolution of the model is 0 5 of invariant latitude and one half hour of magnetic local time the model field is asymmetric with the afternoon convection cell dominant in magnitude and spatial extent and corresponds to conditions in which the cross polar cap potential is approximately 70 kv

asymmetry in the duration of el nino and la nina abstract el nino and la nina are not a simple mirror image but exhibit significant differences in their spatial structure and seasonal evolution in particular sea surface temperature sst anomalies over the equatorial pacific cold tongue are larger in magnitude during el nino compared to la nina resulting in positive skewness of interannual sst variations the associated atmospheric deep convection anomalies are displaced eastward during el nino compared to la nina because of the nonlinear atmospheric response to sst in addition to these well known features an analysis of observational data for the past century shows that there is a robust asymmetry in the duration of el nino and la nina most el ninos and la ninas develop in late boreal spring summer when the climatological cold tongue is intensifying and they peak near the end of the calendar year after the mature phase el ninos tend to decay rapidly by next summer but many la ninas persist through the following year and often reintensify in

reversed spatial asymmetries between el nino and la nina and their linkage to decadal enso modulation in cmip3 models abstractthis study examines preindustrial simulations from coupled model intercomparison project phase 3 cmip3 models to show that a tendency exists for el nino sea surface temperature anomalies to be located farther eastward than la nina anomalies during strong el nino southern oscillation enso events but farther westward than la nina anomalies during weak enso events such reversed spatial asymmetries are shown to force a slow change in the tropical pacific ocean mean state that in return modulates enso amplitude cmip3 models that produce strong reversed asymmetries experience cyclic modulations of enso intensity in which strong and weak events occur during opposite phases of a decadal variability mode associated with the residual effects of the reversed asymmetries it is concluded that the reversed spatial asymmetries enable an enso tropical pacific mean state interaction mechanism that gives rise to a decadal modulation of enso intensity and that at least three cmip3 models realistically simu

streambank erosion rates and loads within a single watershed bridging the gap between temporal and spatial scales abstract the importance of streambank erosion to watershed scale sediment export is being increasingly recognized however few studies have quantified bank erosion and watershed sediment flux at the basin scale across temporal and spatial scales in this study we evaluated the spatial distribution extent and temporal frequency of bank erosion in the 5218 ha walnut creek watershed in iowa across a seven year period we inventoried severely eroding streambanks along over 10 km of stream and monitored erosion pins at 20 sites within the watershed annual streambank recession rates ranged from 0 6 cm yr during years of hydrological inactivity to 28 2 cm yr during seasons with high discharge rates with an overall average of 18 8 cm yr the percentage of total basin export attributed to streambank erosion along the main stem of walnut creek ranged from 23 to 53 large variations in individual site annual rates and percentage of annual load suggested that developing direct relationships between streambank erosion rates and total sediment discharge may be confounded by the timing and magnitude of discharge events storage of sediments within channel system and the remobilization of eroded material

vertical distribution of total carbon nitrogen and phosphorus in riparian soils of walnut creek southern iowa abstract subsurface lithology plays an important role in many riparian zone processes but few studies have examined how sediment nutrient concentrations vary with depth in this study we evaluated concentrations of nutrients n c and p with depth in a riparian zone of the glaciated midwest a total of 146 sediment samples were collected from 24 cores that extended to a maximum depth of 3 6 m at eight sites in the riparian zone of walnut creek subsurface deposits were predominantly silt loam becoming coarser and more variable with depth nitrogen and carbon content ranged from

ionospheric scintillation over antarctica during the storm of 5 6 april 2010 on 5 april 2010 a coronal mass ejection produced a traveling solar wind shock front that impacted the earth s magnetosphere producing the largest geomagnetic storm of 2010 the storm resulted in a prolonged period of phase scintillation on global positioning system signals in antarctica the scintillation began in the deep polar cap at south pole just over 40 min after the shock front impact was recorded by a satellite at the first lagrangian orbit position scintillation activity continued there for many hours on the second day significant phase scintillation was observed from an auroral site 81 degrees s during the postmidnight sector in association with a substorm particle data from polar orbiting satellites provide indication of electron and ion precipitation into the antarctic region during the geomagnetic disturbance total electron content maps show enhanced electron density being drawn into the polar cap in response to southward turning of the interplanetary magnetic field the plasma enhancement structure then separates from the dayside plasma and drifts southward scintillation on the first day is coincident spatially and temporally with a plasma depletion region both in the dayside noon sector and in the dayside cusp on the second day scintillation is observed in the nightside auroral region and appears to be strongly associated with ionospheric irregularities caused by e region particle precipitation

high latitude thermospheric vertical wind activity from dynamics explorer 2 wind and temperature spectrometer observations indications of a source region for polar cap gravity waves 1 the large scale distribution of thermospheric vertical wind activity from 250 to 650 km altitude was studied using observations from the wind and temperature spectrometer on the dynamics explorer 2 satellite we calculated the vertical velocity standard deviation vz within a sliding window of width 120 s corresponding to an along track distance of 900 km maps of vz in local magnetic time and invariant latitude reveal a high latitude region of enhanced activity that largely fills the polar cap maximizing in the midnight dawn sector separating the data by altitude suggests that most of the vertical wind energy present at 250 450 km is dissipated within a few hundred vertical kilometers northern and southern hemisphere high latitude vz fields were found to be very similar indicating no significant hemispheric differences no strong correlation was found between solar illumination and vz at high latitudes although the dayside vertical wind activity may be slightly reduced compared to night and twilight intervals however a clear relationship to geomagnetic activity as measured by the ae index was found vertical wind activity increases with increasing ae we interpret these results as a possible signature of polar cap gravity waves with sources in or near the midnight dawn auroral oval we use the probability density functions of vz separated by ae to infer the temporal characteristics of the wave source and consequently to provide preliminary estimates of the production rates of polar cap gravity waves

measuring streambank erosion due to ground water seepage correlation to bank pore water pressure precipitation and stream stage limited information exists on one of the mechanisms governing sediment input to streams streambank erosion by ground water seepage the objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow erosion with precipitation stream stage and soil pore water pressure the streambank site was located in northern mississippi in the goodwin creek watershed soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity ks with depth but differences between lateral ks of a concretion layer and the vertical ks of the underlying layers contributed to the propensity for lateral flow goodwin creek seeps were not similar to other seeps reported in the literature in that eroded sediment originated from layers underneath the primary seepage layer subsurface flow and sediment load quantified using 50 cm wide collection pans were dependent on the type of seep intermittent low flow lf seeps flow rates typically less than 0 05 l min 1 persistent high flow hf seeps average flow rate of 0 39 l min 1 and buried seeps which eroded unconsolidated bank material from previous bank failures the timing of lf seeps correlated to river stage and precipitation the hf seeps at goodwin creek began after rainfall events resulted in the adjacent streambank reaching near saturation i e soil pore water pressures greater than 5 kpa seep discharge from hf seeps reached a maximum of 1 0 l min 1 and sediment concentrations commonly approached 100 g l 1 buried seeps were intermittent but exhibited the most significant erosion rates 738 g min 1 and sediment concentrations 989 g l 1 in cases where perched water table conditions exist and persistent hf seeps occur seepage erosion and bank collapse of streambank sediment may be significant copyright 2007 john wiley sons ltd

effects of silt clay content on the susceptibility of river banks to subaerial erosion abstract the aim of this paper is to demonstrate how subaerial processes vary with the silt clay content of river bank soil and to consider this variation in the context of erosion observed in the field in particular spatial and temporal variations in erosion interactions with other bank erosion processes and the implications for bank morphology are explored a number of soil blocks of known silt clay content were subjected to a series of freeze thaw and drying wetting cycles changes in the dimensions of the soil blocks were recorded and the mass of soil eroded from each block together with maximum size of eroding aggregates were measured limitations to this methodology are acknowledged including a limited ability to replicate the forces to which a river bank may be subject restrictions imposed by the available equipment in producing temperature and humidity cycles which reflect those occurring in the field and issues of scale the results indicate that river banks with high silt clay contents are the most susceptible to erosion by subaerial processes high susceptibility may influence spatial variations in bank erosion processes and rates including downstream changes in the effectiveness and significance of subaerial erosion a vertical zoning of processes on a river bank is recognised whereby the upper part of the bank is subject to subaerial erosion and the lower part to fluvial erosion given that a high silt clay content tends to indicate increased susceptibility to subaerial erosion but increased resistance to fluvial erosion this vertical zoning may have implications for bank morphology

high resolution basin extent observations and implications for understanding river form and process fifty years of fluvial studies have posited a variety of conceptual frameworks for characterizing river forms and processes throughout entire basins including hydraulic geometry the river continuum concept self organized criticality and sediment links this article uses basin extent high resolution observations of fluvial forms in the nueces river basin texas and yellowstone national park to evaluate the ability of these frameworks to characterize system behavior across a multitude of scales the nueces data were collected with remote sensing methods and the yellowstone data were collected through extensive field surveys the data resolution spatial extent and quality of these data sets allow direct comparison between the two areas the hyperscale comparison supports using of each these frameworks at specific scales but also indicates an irreducible amount of variation in both datasets across many different scales that is not captured by the conceptual frameworks moreover the scales and locations where one framework such as hydraulic geometry works well are often not the same scales and locations where another framework such as the river continuum concept works well because the conceptual frameworks appear to operate at scales and locations distinct from one another the measurement approaches necessary to observe them must also be at different scales and locations for example seeing self organized criticality in a river system is difficult without an extensive survey through space whereas the recognition of sediment links requires quite intense sampling in specific river regions we suggest that these separations between measurement scales represent an incommensurability issue in river studies making it very difficult to both communicate among and test between two or more competing theories making simultaneous hyperscale observations of the river is one approach to minimizing the theory ladeness of observation as deviations from different predictions can be plotted at every scale copyright 2010 john wiley sons ltd

river width adjustment i processes and mechanisms in 1993 a task committee tc of the asce was established to study the hydraulics bank mechanics and modeling of width adjustment in alluvial channels the work of the tc in reviewing width adjustment processes and mechanisms is reported in this paper a companion paper presents the findings of the tc with regard to width adjustment modeling this paper first establishes the geomorphic context within which width adjustments occur and it demonstrates that width adjustment may take place over a wide range of scales in time and space in the past engineering analyses of channel width have tended to concentrate on prediction of the equilibrium width for stable channels most commonly the regime extremal hypothesis and rational mechanistic approaches are used and these are reviewed herein more recently attention has switched to channels that are adjusting their morphology either due to natural instability or in response to changes in watershed land use river regulation or channel engineering chara

global thermospheric neutral density and wind response to the severe 2003 geomagnetic storms from champ accelerometer data 1 measurements of atmospheric density near 410 km from the star accelerometer on the champ satellite are used to illustrate the spatial temporal dependence of the thermospheric response to the severe solar storms occurring during 29 october to 1 november 2003 this interval includes periods of elevated magnetic activity with kp values of 5 9 as well as undisturbed intervals that serve to define quiet time baseline densities measurements are available from 87 to 87 latitude during both day and night at local times near 1300 and 0100 hours respectively during times of maximum geomagnetic activity for this study density measurements exhibit enhancements of 200 300 northern hemisphere daytime responses are much larger than in the southern hemisphere the origins of this effect are unknown nighttime density disturbances more readily propagate to equatorial latitudes possibly facilitated by the predominant equatorward flow in both hemispheres due to the diurnal tides driven by in situ euv heating the champ density measurements are compared with density predictions from the nrl msise00 empirical density model and demonstrate some model shortcomings measurements of cross track accelerations provide the opportunity to estimate zonal winds from the equator to about 60 latitude transitioning to a measure of purely meridional winds at the turning point of the orbit near 87 latitude a periodic variation in cross track winds with an apparent period of 24 hours appears at high latitudes and exhibits similar amplitudes and temporal latitudinal structures to the empirical hwm 93 wind model when projected into the cross track direction this periodicity is due to the displacement of geomagnetic and geographic coordinates at low latitudes champ and hwm 93 both yield westward winds of order 100 ms 1 during midday under quiet magnetic conditions however during severely disturbed periods the hwm 93 winds generally show a greater westward intensification to 250 ms 1 than the champ measurements at night champ winds are near zero under quiet conditions whereas hwm 93 indicates eastward winds of order 50 100 ms 1 under disturbed conditions the champ winds shift to westward values of order 200 to 250 ms 1 while hmw 93 values do not exceed about 50 ms 1 in the westward direction the physical origins of the observed effects are difficult to isolate and unequivocal interpretation will require sophisticated numerical modeling taking into account self consistent interactions between the neutral winds drifts and ionization densities

morphological evolution of a rural headwater stream after channelisation in recent decades stream valleys have been profoundly modified by the construction of weirs and dams and by channelisation channelisation modifies the morphology of streams and induces changes in their energy regime and sediment transport capacity these types of changes in the channel morphology have to be quantified to allow the implementation of management strategies to regulate sediment transfer however studies over an entire stream using historical comparisons remain scarce and the associated uncertainties have not yet been resolved in this study the sedimentary response to channelisation on a medium time scale 42 years of a french river known as the ligoire is investigated this river is the main channel of a small rural headwater catchment that has been channelised over 21 km we have used the historical cross sections before and after channelisation and the current ones and the objectives of this study were as follows 1 to develop a methodology of cross section superposition and the associated uncertainties 2 to quantify the erosion and aggradation processes in the bed and on the banks along the bed profile and 3 to calculate a sediment budget for the entire stream and determine the relative contributions of the banks and the streambed to this budget a comparison of the cross sections before and after the channelisation shows that the morphology of the stream has been completely altered the main channel length was reduced by 10 the bankfull width was increased on average by 63 and the slopes were smoothed a total of 60 000 m3 of sediments was excavated during the channelisation works our results indicate that erosion is the dominant process over 63 of its length the streambed was incised by 0 41 m on average and over 60 of its length the banks were eroded by 0 20 m on average the successive patterns of erosion and deposition along the stream are the result of the cumulative effects of channelisation and of the presence of weirs and artificial knickpoints in the ligoire channel the vertical uncertainty of the elevation of the historical cross section is an important parameter for controlling the areas and sediment budget values using monte carlo methods we found that 1000 sediment budgets from different profile shiftings are necessary to obtain a variation coefficient below 0 1 the overall mean stream sediment budget for the period 1970 2012 is 9358 412 m3 with 66 originating from the banks and 34 from the streambed relative to the ligoire watershed surface the stream sediment yield is 2 71 0 12 m3 km 2 y 1 the approach developed in this study is easily replicable and relatively cheap and provides an integrated quantified overview of the morphological adjustments after channelisation works on a stream

analysis of the non linearity in the pattern and time evolution of el nino southern oscillation in this study the observed non linearity in the spatial pattern and time evolution of el nino southern oscillation enso events is analyzed it is shown that enso skewness is not only a characteristic of the amplitude of events el ninos being stronger than la ninas but also of the spatial pattern and time evolution it is demonstrated that these non linearities can be related to the non linear response of the zonal winds to sea surface temperature sst anomalies it is shown in observations as well as in coupled model simulations that significant differences in the spatial pattern between positive el nino versus negative la nina and strong versus weak events exist which is mostly describing the difference between central and east pacific events central pacific events tend to be weak el nino or strong la nina events in turn east pacific events tend to be strong el nino or weak la nina events a rotation of the two leading empirical orthogonal function modes illustrates that for both el nino and la nina extreme events are more likely than expected from a normal distribution the bjerknes feedbacks and time evolution of strong enso events in observations as well as in coupled model simulations also show strong asymmetries with strong el ninos being forced more strongly by zonal wind than by thermocline depth anomalies and are followed by la nina events in turn strong la nina events are preceded by el nino events and are more strongly forced by thermocline depth anomalies than by wind anomalies further the zonal wind response to sea surface temperature anomalies during strong el nino events is stronger and shifted to the east relative to strong la nina events supporting the eastward shifted el nino pattern and the asymmetric time evolution based on the simplified hybrid coupled rechoz model of enso it can be shown that the non linear zonal wind response to sst anomalies causes the asymmetric forcings of enso events this also implies that strong el ninos are mostly wind driven and less predictable and strong la ninas are mostly thermocline depth driven and better predictable which is demonstrated by a set of 100 perfect model forecast ensembles

the salience of nonlinearities in the boreal winter response to enso north pacific and north america the prominence of nonlinearities in the response to el nino as compared to la nina to moderate el nino events as compared to extreme el ninno events and to different flavors of el nino events are analyzed using the nasa goddard earth observing system chemistry climate model in the central north pacific region where the sea level pressure response to el nino southern oscillation enso peaks nonlinearities are relatively muted in contrast changes to the east of this region i e the far northeastern pacific and to the north of this region over alaska in response to different enso phases are more clearly nonlinear and become statistically robust after more than 15 events are considered the relative prominence of these nonlinearities is related to the zonal wavenumber of the tropical precipitation response associated with these nonlinearities over the far northeastern pacific are nonlinearities in precipitation over western united states and surface temperature over northwest north america and midwestern united states in all regions at least 15 events of each type are necessary before nonlinearities can be identified as statistically significant at the 95 confidence level due to the presence of internal atmospheric variability as there have only been a similar number of enso events to the total needed for significance since 1920 it is not surprising that it has been difficult to establish statistically significant nonlinearities using observational data

nonlinear reconstruction of global climate leading modes on decadal scales a nonlinear decomposition method is applied to the analysis of global sea surface temperature sst time series in different epochs related to the pacific decadal oscillation pdo since the end of 19th century to present time this method allows one to extract an optimal small number of global nonlinear teleconnection patterns associated with distinct dominant time scales from the original high dimensional spatially extended data set in particular it enables us to reveal enso teleconnection patterns corresponding to different pdo cycles during the last 145 years to uncover four climate shifts connected with pdo phase changes and to reconstruct the corresponding global pdo patterns we find that sst teleconnections between the enso region extra tropical pacific regions and the indian ocean became fundamentally nonlinear since the second half of 20th century

distinct winter patterns of tropical pacific convection anomaly and the associated extratropical wave trains in the northern hemisphere in this paper distinct patterns of boreal winter convection anomalies over the tropical pacific and associated wave trains in the extratropics are addressed the first leading mode eof1 of convection anomalies as measured by outgoing longwave radiation demonstrates an east west oscillation of deep convection with centers over the equatorial central pacific cp and over the tropical western north pacific and the maritime continent the second leading mode eof2 is also a dipole pattern with opposite centers straddling 170 w possibly modifying eof1 to some extent combining the first two leading modes five major categories of tropical convection anomalies can be identified for the period 1979 80 2012 13 the comparison between these five categories and the corresponding sst anomaly patterns indicates a nonlinear relationship between convection and sst the combination of eof1 and eof2 with in phase pcs exhibits an east west dipole pattern with opposite signs over west of the dateline and the maritime continent the negative phase of the two pcs named la nina pattern induces a negative pacific north american positive north atlantic oscillation teleconnection in the extratropics approximately opposite responses can be detected in its positive phase named cp el nino pattern the negative pc2 superposing positive pc1 named ep el nino pattern shows the strongest convection anomalies with enhanced depressed convection over the eastern western pacific and leads to a tropical northern hemisphere like teleconnection pattern and an anomalous anticyclone extending from the north pacific to the north atlantic the positive pc2 with neutral pc1 named western cp pattern shows weakly enhanced convection to the west of the dateline as a response to local sst warming around the dateline this convection anomaly pattern although weak is important and excites a northeastward wave train from the tropics to greenland resulting in surface air temperature cooling covering the northeastern north america and warmer and wetter conditions over western europe

comparison of sea ice extent and ice edge location estimates from passive microwave and enhanced resolution scatterometer data passive microwave sea ice concentration fields provide some of the longest running and most consistent records of changes in sea ice scatterometry based sea ice fields are more recently developed data products but now they provide a record of ice conditions spanning several years resolution enhancement techniques applied to scatterometer fields provide much higher effective resolutions 10km than are available from standard scatterometer and passive microwave fields 25 50km here we examine ice extent fields from both sources and find that there is general agreement between scatterometer data and passive microwave fields though scatterometer estimates yield substantially lower ice extents during winter comparisons with ice edge locations estimated from avhrr imagery indicate that enhanced scatterometer data can sometimes provide an improved edge location but there is substantial variation in the results depending on the local conditions a blended product using both scatterometer and passive microwave data could yield improved results

thermosphere density response to the 20 21 november 2003 solar and geomagnetic storm from champ and grace accelerometer data 1 densities in the 400 500 km height region inferred from accelerometer measurements on the champ and grace satellites are utilized to study the response to the isolated and severe geomagnetic storm of 20 21 november 2003 the champ and grace satellites provide data at approximate local times of 1110 2310 and 1430 0230 hours respectively in a global sense density increases of order 300 800 occur during this storm with relatively little time delay at high latitudes and with about 4 hour delay at the equator significant latitudinal asymmetries in the response are discussed in the context of neutral wind patterns and enhanced summer versus winter joule heating rates at high latitudes comparisons with the nrlmsise 00 empirical model densities during this period show marked differences in amplitude of the response as well as latitudinal and temporal structures evidence for a tight coupling between solar wind and neutral density variability is found for the high latitude summer hemisphere near noon in that densities near 410 km are very responsive to increases in solar wind dynamic pressure even during periods when both bz and by are near zero or positive filtering of the data reveals regional scale 1000 2000 km density anomalies that are common between the champ and grace measurements during the geomagnetic disturbance alternating regions of density enhancements 50 and depressions 50 exist between the pole and low to middle latitudes that have the appearance of a standing wave pattern during magnetically quiet intervals before and after the storm daytime density depressions 4 8 are seen that track the magnetic equator while density enhancements 10 track the latitudes of the ionospheric appleton anomaly peaks large scale 1000 km wave like structures are also prevalent during both day and night during the magnetic disturbance and extend throughout both hemispheres consistent with the concept that these are associated with the so called direct gravity waves forced in the auroral regions and propagating far from the source substantial variability is also present at medium scales 300 500 km but these structures are confined mainly to middle to high latitudes in accord with theoretical expectations grace a and grace b data are used in a feasibility study of the detection of small scale wave activity by taking advantage of the 30 s separation of the satellites in the same orbital plane despite the large amount of maneuvers which are not always recorded this first analysis is promising amplitude variations of order 10 20 and wave speeds of 1000 1500 m s 1 are observed

the influence of nonlinearities and different sst spatial patterns on the summertime anomalies in subtropical south america during strong enso events in this study we analyze the impacts of the strongest enso events on subtropical south america ssa rainfall during the austral summer in the period 1979 2014 we consider reanalysis data and model experiments for the strongest el nino events the precipitation pattern over ssa presents a monopole structure the reanalysis shows a short rossby wave train that causes an increase of the baroclinicity and advection of cyclonic vorticity toward ssa together with an increase in the moisture transport by the south american low level jet sallj they induce strong positive precipitation anomalies over ssa the model reproduces this rainfall anomaly as consequence of a strengthening of the upper level jet and of the sallj although it does not simulate the short wave train from the pacific for the strongest la nina events the precipitation pattern presents a tripole like structure with centers located over 1 uruguay 2 the continental part of the south atlantic convergence zone c sacz and 3 the northwestern argentina nw arg in both cases reanalysis and model experiments the tripole is associated with a weakening of the sallj that increases reduces rainfall anomalies over c sacz uruguay and with an anomalous increase of the lower level moisture convergence over nw arg that increases precipitation over there differences in precipitation responses to the strongest enso events are mainly associated to changes in the spatial pattern of the sea surface temperature anomalies however there is also a contribution of nonlinearities

el nino and la nina sea surface temperature anomalies asymmetry characteristics associated with their wind stress anomalies 1 the asymmetric nature of el nino and la nina sea surface temperature sst anomalies is investigated by the use of national centers for environmental prediction reanalysis data and various ocean and atmosphere models it is demonstrated that the relatively weak sst anomalies during la nina compared with those of el nino are related to the westward shift of wind stress anomalies by 10 15 the asymmetric characteristics of atmospheric responses are confirmed by the general circulation model experiments with the two different sst anomalies which have equal amplitude but are of opposite sign from each other the experiments with an intermediate ocean model and a hybrid coupled model clearly show that the sst anomalies over the equatorial pacific become weaker as the zonal wind stress shifts to the west not only the amplitude but also the oscillation timescale of the sst anomaly is shown to be sensitive to the location of wind stress anomalies the duration of la nina which is rather shorter than that of el nino is also related to the longitudinal displacement of the wind stress anomaly

effects of agricultural drainage systems on sediment connectivity in a small mediterranean lowland catchment abstract traditional drainage systems combining man made channels and subsurface tile drains have been used since roman times to control water excess in mediterranean lowland regions favouring adequate soil water regime for agriculture purposes however mechanization of agriculture abandonment or land use changes lead to a progressive deterioration of these drains in the last decades the effects of these structures on hydrological and sediment dynamics have been previously analyzed in a small mediterranean lowland catchment can revull mallorca spain 1 4 km2 by establishing an integrated sediment budget with a multi technique approach moreover the recent advances in morphometric techniques enable the completion of this analysis by the accurate identification of active areas i e sources pathway links and sinks and improve the understanding of de coupling mechanisms of water and sediment linkages in this study the borselli s index of connectivity ic cavalli et al 2013 s version derived from a lidar based high resolution dem 1 pt m 2 rmse

stable isotope o h s c and n systematics of quartz vein systems in the turbidite hosted central and north deborah gold deposits of the bendigo gold field central victoria australia constraints on the origin of ore forming fluids the central and north deborah gold deposits are located in one of 15 mining centers of the bendigo gold field central victoria australia a major world class gold province developed in a turbidite terrane gold mineralization occurs primarily within domes and reverse fault systems in multiply deformed lower ordovician metaturbidites deformation and thrusting occurred between 450 and 420 ma coevally with regional metamorphism at zeolite to greenschist facies in the central and north deborah deposits six stages of quartz veining each with characteristic geometry and mineral paragenesis developed sequentially stages 1 2 and 4 are gold bearing whereas stages 3 5 and 6 are barren gold related quartz veins were deposited at temperatures of 350 25 c based on oxygen isotope geothermometry of silicate phases quartz muscovite and sulfur isotope compositions of coexisting sulfide mineral pairs sphalerite galena this result is consistent with temperatures inferred from fluid inclusions the 18o values of gold bearing vein quartz and coexisting hydrothermal muscovite are uniform within and between the six vein stages ranging from 15 9 to 17 2 per mil and 11 6 to 12 8 per mil respectively the d values of hydrothermal muscovites are also uniform at 68 to 55 per mil ore fluids have calculated 18o values of 8 to 11 per mil and d values of 37 to 17 per mil pyrite of synsedimentary diagenetic origin in slate and sandstone displays sulfur isotope compositions of 23 5 to 8 0 per mil and 0 1 to 11 9 per mil respectively sulfides from gold bearing quartz veins have a range of 7 4 to 8 1 per mil median ca 2 5 the relatively uniform vein pyrites indicate a large uniform sulfur source most likely from desulfidation reactions of sulfide minerals interaction of the ore forming fluid with depleted sulfides at the site of deposition may have shifted the sulfur isotope signatures of source sulfides to more negative values carbon isotope compositions of carbonates range from 5 1 to 9 0 per mil median ca 6 5 nitrogen concentrations and nitrogen isotope compositions of hydrothermal muscovite from quartz veins are 652 to 895 ppm and 2 84 to 4 49 per mil respectively collectively the data define a band in n content vegh rsus 15n coordinate space from higher n and lower 15n in the phanerozoic metasedimenary hosted central and north deborah gold deposits to lower n and higher 15n in predominantly meta igneous hosted neoarchean gold provinces collectively the h o s c and n isotope compositions of ore related hydrothermal minerals indicate that the dilute aqueous carbonic and n bearing ore forming fluids were generated from metamorphic dehydration reactions at deeper crustal levels and were variably influenced by exchange with wall rocks during transport to the site of deposition this genetic model for the central and north deborah gold deposits is consistent with other turbidite hosted lode gold deposits and counterparts in volcanic plutonic terranes in contrast these data are not consistent with either mantle derived fluids or magmatic fluids nor do they support a deeply circulated meteoric surface water model for vein formation

a dayside ionospheric positive storm phase driven by neutral winds 1 this paper presents observations and numerical simulations of ionospheric and thermospheric disturbances associated with a moderate geomagnetic storm on 10 september 2005 during the event the incoherent radars located in millstone hill and arecibo observed a dayside positive storm phase as manifested by the enhanced electron density in the f region the universal time ut altitude profile of electron density measured by both radars displayed a structure that closely resembles the greek letter a similar structure is also reproduced by the thermosphere ionosphere electrodynamics general circulation model tiegcm this peculiar electron density distribution is found to be associated with vertical ion drift which initially was upward and then became downward using realistic time dependent ionospheric convection and auroral precipitation as inputs the tiegcm reveals that the primary cause of the positive storm response was the enhanced meridional neutral wind rather than the penetration magnetospheric electric field this study reiterates the importance of neutral wind effects on ionospheric disturbance

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

the tropospheric pathway of the enso north atlantic teleconnection abstractel nino southern oscillation enso exerts an influence on the north atlantic european nae region however this teleconnection is nonlinear and nonstationary owing to the superposition a

asymmetry and nonlinearity of the influence of enso on the northern winter stratosphere 1 observations the el nino southern oscillation enso has significant effects on the extratropical stratosphere this study explores the nonlinearity and the asymmetry of these influences by distinguishing the different effects of four types of enso moderate el nino strong el nino moderate la nina and strong la nina it is revealed that the moderate el nino and the strong la nina are much more efficient than the strong el nino and the moderate la nina respectively in modulating the northern winter stratospheric variability resulting in significant nonlinearity and asymmetry the tropical rainfall anomalies induced by a moderate el nino or a strong la nina are centered over the central equatorial pacific region near the dateline while the convection responses to a strong el nino or a moderate la nina are centered farther eastward accordingly the anomalous pacific north america wave train pattern is modulated by enso in a nonlinear and asymmetric way which leads the large nonlinear and asymmetric components of the vertical eliassen palm e p flux responses to enso the increase of planetary wave activity in the extratropical stratosphere in moderate el nino winters is thus greater than in strong el nino winters whereas a strong la nina gives a larger decrease in propagation than a moderate la nina the relatively strong weak e p flux responses to moderate strong el nino and strong moderate la nina explain the remarkable nonlinearity and asymmetry in the response of the extratropical stratosphere to enso

characteristics of the large scale traveling atmospheric disturbances during geomagnetically quiet and disturbed periods simulated by a whole atmosphere general circulation model 1 we have investigated characteristics of the large scale traveling atmospheric disturbances ls tads generated during geomagnetically quiet and disturbed periods using a whole atmosphere general circulation model gcm the gcm simulations show that various tads appear in association with passages of regions with large temperature gradients near the solar terminator midnight temperature anomaly and auroral oval which move with the earth s rotation these tads which are superimposed on each other appear even when a geomagnetically quiet period the tads generated during a geomagnetically quiet period show structures extending in the longitudinal direction at high latitude and in the latitudinal direction at mid and low latitude these structures disappear after their short range propagations the tads generated during a geomagnetically disturbed period show structures extending widely in the longitudinal direction and propagate from high to low latitude these simulation results suggest the different generation mechanisms and features between the tads generated during geomagnetically quiet and disturbed periods

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

combined impacts of pdo and two types of la nina on climate anomalies in europe abstractcombined impacts of the pacific decadal oscillation pdo and two types of la nina on climate anomalies in europe are studied particularly the conjunction of the negative pdo phase and two different types of la nina events favors strong and significant north atlantic oscillation nao pattern anomalies with opposite polarity for the central pacific cp la nina a clear positive nao signal can be detected which is accompanied by positive surface air temperature sat anomaly and a dipolar structure of precipitation anomalies in europe in addition a typical negative pacific north america pna teleconnection pattern forms including a high pressure anomaly over the southeastern united states which may contribute to the development and maintenance of the nao anomaly by strengthening the baroclinicity and the local eddy mean flow interaction however for the eastern pacific ep la nina a zonal wave train in the high latitudes can be observed which is quite different from the typical pna st

a large scale traveling ionospheric disturbance during the magnetic storm of 15 september 1999 enhancement of gps total electron content 1 0 10 16 m 2 multipoint and imaging observations of these parameters show that the lstid moved equatorward over japan with a velocity of 400 450 m s from a comparison with the sheffield university plasmasphere ionosphere model supim we conclude that an enhancement 250 300 m s of poleward neutral wind that is propagating equatorward caused these observational features of the lstid at midlatitudes to investigate generation of the lstid by auroral energy input we have used auroral images obtained by the polar uvi instrument magnetic field variations obtained at multipoint ground stations and the empirical joule heating rate calculated by the assimilative mapping of ionospheric electrodynamics amie technique intense auroral energy input was observed at 0800 1100 ut 4 6 hours before the lstid probably causing equatorward neutral wind at lower latitudes it is likely that the poleward wind pulse that caused the observed lstid was generated associated with the cessation of this equatorward wind the effect of lorentz force is also discussed index terms 0310 atmospheric composition and structure airglow and aurora 2427 ionosphere ionosphere atmosphere interactions 0335 2435 ionosphere ionospheric disturbances 2437 ionosphere ionospheric dynamics 2788 magnetospheric physics storms and substorms keywords large scale traveling ionospheric disturbance thermosphere ionosphere coupling magnetic storm airglow imaging gps network ionosonde

storms channel changes and a sediment budget for an urban suburban stream difficult run virginia usa abstract determining erosion and deposition rates in urban suburban settings and how these processes are affected by large storms is important to understanding geomorphic processes in these landscapes sediment yields in the suburban and urban upper difficult run are among the highest ever recorded in the chesapeake bay watershed ranging from 161 to 376 mg km2 y erosion and deposition of streambanks channel bed and bars and deposition of floodplains were monitored between 1 march 2010 and 18 january 2013 in upper difficult run virginia usa we documented the effects of two large storms tropical storm lee september 2011 a 100 year event and super storm sandy october 2012 a 5 year event on channel erosion and deposition variability in erosion and deposition rates for all geomorphic features temporally and spatially are important conclusions of this study tropical storm lee was an erosive event where erosion occurred on 82 of all streambanks and where 88 of streambanks that were aggrading before tropical storm lee became erosional statistical analysis indicated that drainage area explains linear changes cm y in eroding streambanks and that channel top width explains cross sectional area changes cm2 y in eroding streambanks and floodplain deposition mm y a quasi sediment budget constructed for the study period using the streambanks channel bed channel bars and floodplain measurements underestimated the measured suspended sediment load by 61 2130 mg y underestimation of the sediment load may be caused by measurement errors and to contributions from upland sediment sources which were not measured but estimated at 36 of the gross input of sediment eroding streambanks contributed 42 of the gross input of sediment and accounted for 70 of the measured suspended sediment load similar to other urban watersheds the large percentage of impervious area in difficult run and direct runoff of precipitation leads to increased streamflow and streambank erosion this study emphasizes the importance of streambanks in urban suburban sediment budgets but also suggests that other sediment sources such as upland sources which were not measured in this study can be an important source of sediment

the eastward shift of the walker circulation in response to global warming and its relationship to enso variability this study investigates the global warming response of the walker circulation and the other zonal circulation cells represented by the zonal stream function in cmip3 and cmip5 climate models the changes in the mean state are presented as well as the changes in the modes of variability the mean zonal circulation weakens in the multi model ensembles nearly everywhere along the equator under both the rcp4 5 and sres a1b scenarios over the pacific the walker circulation also shows a significant eastward shift these changes in the mean circulation are very similar to the leading mode of interannual variability in the tropical zonal circulation cells which is dominated by el nino southern oscillation variability during an el nino event the circulation weakens and the rising branch over the maritime continent shifts to the east in comparison to neutral conditions vice versa for a la nina event two thirds of the global warming forced trend of the walker circulation can be explained by a long term trend in this interannual variability pattern i e a shift towards more el nino like conditions in the multi model mean under global warming further interannual variability in the zonal circulation exhibits an asymmetry between el nino and la nina events el nino anomalies are located more to the east compared with la nina anomalies consistent with this asymmetry we find a shift to the east of the dominant mode of variability of zonal stream function under global warming all these results vary among the individual models but the multi model ensembles of cmip3 and cmip5 show in nearly all aspects very similar results which underline the robustness of these results the observed data era interim reanalysis from 1979 to 2012 shows a westward shift and strengthening of the walker circulation this is opposite to what the results in the cmip models reveal however 75 of the trend of the walker circulation can again be explained by a shift of the dominant mode of variability but here towards more la nina like conditions thus in both climate change projections and observations the long term trends of the walker circulation seem to follow to a large part the pre existing dominant mode of internal variability

enso influence on the north atlantic european climate a non linear and non stationary approach el nino southern oscillation enso impact on the north atlantic european sector nae is still under discussion recent studies have found a non stationary feature of this teleconnection suggesting an effective modulating role of the ocean mean state nevertheless physical explanations about the underlying mechanisms have been little studied in the available literature in addition enso events show different sst spatial patterns phases and amplitudes which can also influence on the related remote impacts in view of all this in the present study a set of partially coupled experiments have been performed with a global atmospheric general circulation model in which different sst enso patterns are superimposed over distinct pacific and atlantic sst mean states these sst background conditions are constructed according to the observational difference between periods with a distinct impact of enso on the leading euro mediterranean rainfall mode in late winter early spring our results point to two distinct mechanisms associated with enso that can be modulated by the sst mean state 1 the thermally driven direct circulation walker and hadley cells connecting the atlantic and pacific basins and 2 the rossby wave propagation from the tropical pacific to the north atlantic the former elucidates that the positive nao like pattern usually related to la nina events could be only valid for selected decades the latter explains a reinforced signature of eastern pacific ninos on the euro mediterranean rainfall when the tropical pacific is warmer than usual and the north atlantic is colder than usual this feature is consistent with the changing enso impact identified in previous studies and demonstrates how the enso teleconnection with the nae climate at interannual timecales could be modulated by multidecadal changes in the sst according to our results the assumption of stationarity which is still common to many studies of enso teleconnections clearly has to be questioned

needle ice processes and sediment mobilization on river banks the river ilston west glamorgan uk abstract this paper examines the role of needle ice processes in the bank erosion system of a site on the river ilston west glamorgan south wales uk bank retreat rates were monitored with erosion pins over a 2 25 year period concurrent detailed data were also obtained on river flow levels and ambient air and stream temperatures unique data on river bank thermal regimes are presented along with rare information on the morphological properties and sediment yield characteristics of needle ice growths needle ice occurred even with mild freezing temperatures if sufficient bank moisture was present with average growth rates of approximately 1 mm h 1 bank material incorporation and mobilization within needle ice was significant sediment yields of up to 4 02 kg m 2 of bank face were observed and represented between 32 and 43 of total bank erosion recorded most sediment was incorporated within needle ice when growth became stressed because of overrapid cooling and or limited moisture supplies which supports the models of outcalt and fukuda four mechanisms of direct needle ice sediment transport on river banks were identified direct particle fall sediment laden rivulets sliding failures and toppling failures however the indirect preparatory role of needle ice and frost disturbance of bank surfaces is also emphasized and the enhanced fluvial erosion which takes place when bank materials have first been conditioned by frost related processes is noted both indirect and direct effects are expressed in a simple conceptual model and a number of the important system linkages examined combinations of needle ice action and subsequent fluid entrainment of weakened bank material appear to be the dominant mechanism for bank erosion here pronounced and persistent erosional notches in the lower parts of the bank profile were observed showing that in winter even single low magnitude flow events can effect significant channel width adjustment here

bank and near bank processes in an incised channel abstract gravitational forces acting on in situ bank material act in concert with hydraulic forces at the bank toe to determine rates of bank erosion the interaction of these forces control streambank mechanics hydraulic forces exerted by flowing water on in situ bank toe material and failed cohesive material at the bank toe are often sufficient to entrain materials at relatively frequent flows and to maintain steep lower bank profiles seepage forces exerted on in situ bank material by groundwater downward infiltration of rainwater and lateral seepage of streamflow into and out of the bank are critical in determining bank strength data from a study site on goodwin creek ms usa clearly show the temporal variability of seepage forces and the lag time inherent in reductions in shear strength due to losses of matric suction and generation of positive pore water pressures negative pore water pressures matric suction have also been shown to increase the resistance of failed cohesive blocks to entrainment by fluid shear a stable bank can be transformed into an unstable bank during periods of prolonged rainfall through 1 increase in soil bulk unit specific weight 2 decrease or complete loss of matric suction and therefore apparent cohesion 3 generation of positive pore water pressures and therefore reduction or loss of frictional strength 4 entrainment of in situ and failed material at the bank toe and 5 loss of confining pressure during recession of stormflow hydrographs relatively small frequent flows during the winter have the ability to erode failed bank materials maintain oversteepened unstable bank surfaces and promote prolonged periods of bank retreat channel migration and high yields of fine grained sediment confining pressures provided by stormflow are not as significant in maintaining bank stability as the counteracting force of fluid shear on the bank toe which steepens the bank for example more than 2 m of bank retreat occurred during the study period at the research site on goodwin creek northern mississippi the loss of matric suction negative pore pressures due to infiltrating precipitation has been found to be as significant as the development of excess pore pressures in contributing to mass bank instability apparent cohesion friction angle soil bulk unit weight and moisture content were measured in situ matric suction was measured continuously in situ with a series of five pressure transducer tensiometers a bank failure algorithm which combines the mohr coulomb approach for saturated conditions and the fredlund modification for unsaturated conditions was developed for layered cohesive streambanks the resulting equation has been used successfully to investigate the role of matric suction positive pore water pressures and confining pressure for layered streambanks composed of cohesive materials

soil properties controlling seepage erosion contributions to streambank failure the majority of sediment leaving catchments may be from streambank failure seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks the objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern mississippi using field observations as a guide the soil profile conditions of a shallow 45 cm streambank consisting of 30 cm of topsoil a 10 cm conductive layer and a 5 cm restrictive layer were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head the time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer seepage erosion began within minutes of flow initiation and resulted in substantial 3 to 34 cm undercutting of the bank sediment concentrations of seeps were as high as 660 g l 1in situ and 4500 g l 1 in the lysimeters sediment concentrations were related to the layer slope thereby indicating the importance of detailed site characterization the usda ars streambank stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks published in 2006 by john wiley sons ltd

extratropical cyclogenesis changes in connection with tropospheric enso teleconnections to the north atlantic role of stationary and transient waves abstractthis study investigates mechanisms for changes in wintertime extratropical cyclogenesis over north america and the north atlantic during different phases of el nino southern oscillation en

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

stress and seismicity changes on the sunda megathrust preceding the 2007 mw 8 4 earthquake abstract the bengkulu m w 8 4 earthquake on 12 september 2007 close in time and space to the 2004 m w 9 2 sumatra andaman and 2005 m w 8 7 nias megathrust events suggests that it could be a triggered earthquake it was located in the southern portion of the historic 1833 m w 8 9 rupture however it appears perplexing that the portion of the sunda subduction zone between the nias and bengkulu rupture patches which last ruptured in a 1797 m w 8 7 event did not recur first coulomb failure stress cff modeling of the 2004 and 2005 megathrust earthquakes and subsequent postseismic relaxation processes fails to explain why the 2007 patch ruptured before the northern 1797 segment surprisingly the much smaller 2000 m w 8 0 enggano earthquake produced a much larger positive cff change at the 2007 hypocenter and may help to explain the southern location of the 2007 earthquake investigation of changes in seismicity rates in the region following the 2004 2005 events shows that the megathrust earthquakes may have dynamically triggered slip near the northern end of the 2007 rupture zone a large increase in seismicity levels following the 2000 earthquake may also have influenced the eventual initiation point of the 2007 earthquake regrettably the section of the sunda megathrust near siberut that last ruptured in 1797 still poses a great seismic hazard to the region as the only segment not to have ruptured in the sequence of twenty first century megathrust earthquakes

patterns of tropical pacific convection anomalies and associated extratropical wave trains in amip5 in this paper the performance of 18 coupled model intercomparison project phase 5 cmip5 models forced by observational ssts in simulating the tropical pacific convective variation and the atmospheric responses in the extratropics are assessed the multi model ensemble mean results of 18 cmip5 models show that five major patterns of tropical pacific convection anomaly in winter can indeed be well reproduced however the simulation of the corresponding extratropical responses for each pattern exists some deficiency except for the la nina pattern compared with observations we defined an optimized subset of well performing models access1 0 canam4 ccsm4 cmcc cm hadgem2 a mpi esm mr in tropical pacific deep convection according to the ranking of model skill score these models exhibit approximately identical convection anomaly patterns in both amplitude and spatial structure to the observation which potentially might improve the representation of extratropical teleconnections with the tropical pacific especially for the cp el nino cpen ep el nino epen and western cp w cp patterns both evident atmospheric anomalies of cpen and epen patterns over the na e sector and the northeastward propagating wave trains of w cp pattern can be quite well simulated in the high skilled models

ground observation and amie tiegcm modeling of a storm time traveling ionospheric disturbance 1 this paper reports the first comparison between comprehensive observations of equatorward moving traveling ionospheric disturbance at midlatitudes and thermospheric general circulation model with high latitude energy input based on data assimilation a prominent traveling ionospheric disturbance tid was observed during the major magnetic storm of 31 march 2001 the tid propagated from north to south over japan with phase speeds of 370 640 m s the assimilative mapping of ionospheric electrodynamics amie technique was used as input to the thermosphere ionosphere electrodynamics general circulation model tiegcm to investigate generation and propagation of the observed tid in the model two joule heating enhancements in the high latitude dayside sector produced two distinct traveling atmospheric waves tads which propagated to japan in the midnight sector as enhancements in thermospheric temperature and southward wind speed the phase speed of the tads was much faster 1100 m s in the model probably due to the overestimation of joule heating in the model the second tad corresponds to the observed prominent tid while signatures of the first tad were also seen in the observed ionosonde data the observed tid was characterized by a decrease in southward wind speed causing a significant f layer height decrease and a temporal enhancement of f layer peak density these characteristics were reproduced by the model as a rarefaction of the second tad the temporal enhancement of f layer peak density was because of the vertical shear of meridional wind the absolute value of f layer electron density in the model was several factors smaller than that observed probably because of the underestimation of the supply of o ions from the plasmasphere

migration of atmospheric convection coupled with ocean currents pushes el nino to extremes the warm phase of el nino southern oscillation can grow much stronger than the cold phase but the associated dynamics are not well understood here we show that the anomalous zonal advection of warm water is the major process that pushes el nino to extremes and that this anomalous advection results from the coupling of oceanic currents with eastward migration of the atmospheric convection a greater zonal advection is associated with a greater extent of the eastward migration by contrast there is a limited extent for westward migration during la nina climate models that successfully simulate the amplitude asymmetry display a systematic linkage of a greater longitudinal movement of the convection center with a stronger zonal advection and greater el nino amplitude in a warming world the longitudinal migration of convection response increases as does the role of zonal advection increasing the frequency of future extremes of el nino

the measurement of river bank erosion and lateral channel change a review a detailed review and chronological survey is presented of the various techniques which have been used for the measurement of river bank erosion and channel change the techniques are classified according to the time scales involved long intermediate and short and each is discussed with respect to accuracy and repeatability the methods covered include sedimentological evidence botanical evidence historical sources planimetric resurvey repeated cross profiling erosion pins and terrestrial photogrammetry prospects for future developments are also discussed

understanding mass fluvial erosion along a bank profile using peep technology for quantifying retreat lengths and identifying event timing this study provides fundamental examination of mass fluvial erosion along a stream bank by identifying event timing quantifying retreat lengths and providing ranges of incipient shear stress for hydraulically driven erosion mass fluvial erosion is defined here as the detachment of thin soil layers or conglomerates from the bank face under higher hydraulic shear stresses relative to surface fluvial erosion or the entrainment of individual grains or aggregates under lower hydraulic shear stresses we explore the relationship between the two regimes in a representative us midwestern stream with semi cohesive bank soils namely clear creek ia photo electronic erosion pins peeps provide for the first time in situ measurements of mass fluvial erosion retreat lengths during a season the peeps were installed at identical locations where surface fluvial erosion measurements exist for identifying the transition point between the two regimes this transition is postulated to occur when the applied shear stress surpasses a second threshold namely the critical shear stress for mass fluvial erosion we hypothesize that the regimes are intricately related and surface fluvial erosion can facilitate mass fluvial erosion selective entrainment of unbound exposed mostly silt sized particles at low shear stresses over sand sized sediment can armor the bank surface limiting the removal of the underlying soil the armoring here is enhanced by cementation from the presence of optimal levels of sand and clay select studies show that fluvial erosion strength can increase several fold when appropriate amounts of sand and clay are mixed and cement together hence soil layers or conglomerates are entrained with higher flows the critical shear stress for mass fluvial erosion was found to be an order of magnitude higher than that of surface fluvial erosion and proceeded with higher approximately 2 4 times erodibility the results were well represented by a mechanistic detachment model that captures the two regimes copyright 2017 john wiley sons ltd

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

analysis of the nonlinearity of el nino southern oscillation teleconnections abstractel nino southern oscillation enso has significant variations and nonlinearities in its pattern and strength enso events vary in their position along the equator with some located in the central pacific cp and others in the east pacific ep to study how these variations are reflected in global enso teleconnections both observations and idealized atmospheric general circulation model agcm simulations are analyzed clear nonlinearities exist in observed teleconnections of sea level pressure slp and precipitation however it is difficult to distinguish if these are caused by the different signs strengths or spatial patterns of events strong el nino events mostly being ep events and strong la nina events mostly being cp events or by combinations of these therefore sensitivity experiments are performed with an agcm forced with idealized ep and cp enso sea surface temperature sst patterns with varying signs and strengths the response is generally stronger for warm events than for c

enso regimes reinterpreting the canonical and modoki el nino 1 we propose that the first two empirical orthogonal function eof modes of tropical pacific sea surface temperature sst anomalies do not describe different phenomena i e el nino southern oscillation enso and el nino modoki but rather the nonlinear evolution of enso we introduce two new uncorrelated indices e and c based on the leading eofs that respectively account for extreme warm events in the eastern and cold moderate warm events in the central equatorial pacific corresponding to regimes with different evolution recent trends in enso can be described as an increase in the central pacific c variability that is associated with stronger cold events as well as a reduction in the eastern pacific e variability within the cold moderate warm regime consistent with model projections however little can be said observationally with respect to the extreme warm regime