intraseasonal modulation of the north pacific storm track by tropical convection in boreal winter abstract the modulation of the north pacific storm track by tropical convection on intraseasonal time scales 30 90 days in boreal winter december march is investigated using the ncep ncar reanalysis and noaa satellite outgoing longwave radiation olr data multivariate empirical orthogonal function meof analysis and case compositing based upon the principal components pcs of the eofs reveal substantial changes in the structure and intensity of the pacific storm track quantified by vertically 925 200 mb averaged synoptic eddy kinetic energy seke during the course of a typical madden julian oscillation mjo event the storm track response is characterized by an amplitude varying dipole propagating northeastward as the center of the anomalous tropical convection moves eastward across the eastern indian ocean and the western central pacific a diagnosis of the seke budget indicates that the storm track anomaly is induced primarily by changes in the convergence of energy flux baroclinic conversi

stationary rossby wave propagation in a baroclinic atmosphere observational studies of teleconnections in both soisticial seasons have suggested various patterns of behaviour linked mainly to westerly jets and equatorial westerlies these have been interpreted using barotropic rossby wave theory and simulated using stationary forcing in barotropic models linearized about 300 hpa flows in this paper the relevant propagation behaviour is investigated using a baroclinic model with three dimensional climatological basic states time integrations are performed using localized thermal forcing as a wavemaker the propagation results are qualitatively very similar to those obtained with the barotropic model though there are quantitative differences the westerly jets still act as strong waveguides the shorter wavelengths and smaller wave activity speeds found with the baroclinic model are generally in better agreement with observation propagation into and from the upper tropospheric equatorial westerlies in the east pacific propagation across north america and propagation from europe across the arabian gulf are all found the extent to which upper tropospheric westerlies reach towards the equator influences the propagation into those regions barotropic models can only represent such behaviour if the basic state reflects the near equatorial upper tropospheric zonal wind structure

impact of high potential vorticity intrusions into the tropical upper troposphere in south atlantic on precipitation over northeast brazil 1 interannual variations of high potential vorticity intrusions at 10 s in the upper troposphere during ndjfm are shown to be negatively correlated with rainfall over northern northeast brazil neb that is higher intrusions associated with stronger equatorial westerlies may provoke droughts higher intrusions lead to the formation of an anomalous cyclonic vortex over neb which causes convergence in the upper troposphere and sinking motion at lower levels the number of intrusions in ndjfm has highest correlation significant at 99 confidence level with the rainfall of the principal rainy season in fmam

tropical extratropical interactions associated with an atlantic tropical plume and subtropical jet streak abstract tropical plumes tps are elongated bands of upper and midlevel clouds stretching from the tropics poleward and eastward into the subtropics typically accompanied by a subtropical jet stj streak and a trough on their poleward side this study uses ecmwf analyses and high resolution university of wisconsin nonhydrostatic modeling system trajectories to analyze the multiscale complex tropical extratropical interactions involved in the genesis of a pronounced tp and stj over the nh atlantic ocean in late march 2002 that was associated with extreme precipitation in arid northwest africa previous concepts for tp genesis from the literature are discussed in the light of this case study analysis of the upper level flow prior to the tp formation shows a northeastward propagation and a continuous acceleration of the stj over the atlantic ocean equatorward of a positively tilted upper level trough to the west of northwest africa both dynamic and advective processes contribute to the generation of th

observations of rossby waves linked to convection over the eastern tropical pacific rossby wave activity propagating into the eastern tropical pacific from the midlatitudes during northern winter is examined in some detail these waves are associated with the intrusion of high potential vorticity air into low latitudes and they modulate cloudiness stability and vertical motion in the vicinity of the itcz in the upper troposphere and lower stratosphere the horizontal phase and group propagation of the wave activity are qualitatively like those of a nondivergent barotropic rossby wave as the waves move equatorward they become more shallow and propagate upward into the stratosphere the horizontal and vertical propagation is consistent with the tilts of the waves the large scale three dimensional background flow and with the signatures of momentum and heat fluxes associated with the wave activity in the lower troposphere paired cyclonic anomalies on either side of the equator accompany the upper level wave activity to the west of the itcz cloudiness signal these waves amplify following the peak in the itcz cloudiness and propagate westward along the equator this suggests that the upper level wave activity and possibly the associated convective heating can trigger the excitation of the equatorially trapped rossby modes the transient wave activity appears to be a crucial component of the momentum balance of the eastern tropical pacific circulation there is substantial interannual variability in the wave activity consistent with observed changes in the large scale basic state associated with the southern oscillation

effect of the hadley circulation on the reflection of planetary waves in three dimensional tropospheric flows the nonlinear behavior of quasi stationary planetary waves excited by midlatitude orographic forcing is considered in a three dimensional primitive equation model that includes a representation of the hadley cir culation the hadley circulation is forced by newtonian cooling to a zonally symmetric reference temperature and vertical diffusion on the zonally symmetric component of the flow to quantify the effect of the hadley circulation on wave propagation breaking and nonlinear reflection an initial state with no meridional flow but with the same zonal flow as the hadley state is also considered in order to allow the propagation of large scale waves over extended periods rayleigh friction is applied at low levels to delay the onset of baroclinic instability as in the absence of a hadley circulation the waves in the hadley state propagate toward low latitudes where the background flow is weak and the waves are therefore likely to break potential vorticity fields on isentropic surfaces are used to diagnose wave breaking nonlinear pseudomomentum conservation relations are used to quantify the absorption reflection behavior of the wave breaking region in the presence of a hadley circulation representative of winter conditions the nonlinear reflection requires more forcing to get established but a reflected wave train is still present in the numerical simulations both for a longitudinally symmetric forcing and for the more realistic case of an isolated forcing the effect of the thermal damping on the waves is more severe in the current three dimensional simulations than in the shallow water case considered in an earlier study both the directly forced wave train and the reflected wave train are quite barotropic in character however in the shallow water case one is essentially assuming an infinite vertical scale

stationary wave reflection as a mechanism for zonalizing the atlantic winter jet at the lgm abstractcurrent estimates of the height of the laurentide ice sheet lis at the last glacial maximum lgm range from around 3000 to 4500 m modeling studies of the lgm using low end estimates of the lis height show a relatively weak and northeastward tilted winter jet in the north atlantic similar to the modern jet while simulations with high end lis elevations show a much more intense and zonally oriented jet here an explanation for this response of the atlantic circulation is sought using a sequence of lgm simulations spanning a broad range of lis elevations it is found that increasing lis height favors planetary wave breaking and nonlinear reflection in the subtropical north atlantic for high lis elevations planetary wave reflection becomes sufficiently prevalent that a poleward directed flux of wave activity appears in the climatology over the midlatitude north atlantic this entails a zonalization of the stationary wave phase lines and thus of the midlatitude jet

chemical and dynamical discontinuity at the extratropical tropopause based on start08 and waccm analyses 1 using isentropic trace gas gradients of o3 and co the discontinuity in the chemical composition of the upper troposphere ut and lower stratosphere ls is examined on middle world isentropes from 300 to 380 k the analysis is a follow up study of the dynamical discontinuity as represented by the potential vorticity pv gradient based tropopause which is based on the product of isentropic pv gradients and wind speed overall there is fairly good consistency between the chemical discontinuity in trace gas distributions and the pv gradient based tropopause trace gas gradients at the pv gradient based tropopause are stronger in winter than in summer revealing the seasonal cycle of the tropopause transport barrier the analysis of the trace gas gradients also identifies atmospheric transport pathways in the upper troposphere lower stratosphere utls several regions where trace gas gradients are found to be decoupled from the dynamical field indicate preferred transport pathways between the ut and ls in particular anomalous co and o3 gradients above eastern africa eastern asia and the west pacific are likely related to convective transport and anomalous o3 gradients over the north atlantic and north pacific are related to isentropic transport connected to frequent wave breaking the results indicate that the pv gradient based tropopause definition provides a good identification of the dynamical and chemical discontinuity and is therefore effective in locating the physical boundary in the utls

intrusions into the tropical upper troposphere three dimensional structure and accompanying ozone and olr distributions abstract the evolution and structure of stratospheric intrusions into the upper troposphere ut over the northern tropical pacific is examined in terms of both potential vorticity pv and ozone o3 analysis of 20 years of ncep ncar reanalysis pv shows that the intrusion events have remarkably similar evolution and structure at 350 k with all events producing narrow tongues of high pv that have an almost north south orientation and last around 3 days nearly all events extend up into the lower stratosphere but only for a small percentage is there deep downward penetration the intrusions explain a large amount of the observed variability in upper tropospheric o3 above hilo hawaii with large values occurring when a tongue of high pv passes over hilo and low values when hilo is just upstream of a high pv tongue there is also an increase in total column ozone within the pv tongues but for most intrusions the increase is relatively small the relationship between deep convection as diagnosed by sate

cross equatorial response to middle latitude forcing in a zonally varying basic state abstract a nonlinear model based on the shallow water equations is used to study cross equatorial propagation of forced waves in the presence of a longitudinally varying time mean basic state zonal wind field it is found that global scale planetary waves are unable to propagate past a critical latitude where the mean zonal wind speed vanishes however if the longitudinally asymmetric basic state includes a duet in which the zonal winds are westerly waves of zonal scale less than the zonal scale of the westerly duct may propagate from one hemisphere to the other even though the zonally symmetric mean zonal wind remains easterly in the equatorial region the amplitude of the response in one hemisphere to forcing in the opposite hemisphere increases strongly with the magnitude of the westerlies in the equatorial duct the existence and annual variations of a westerly duct region in the upper troposphere in the eastern pacific appear to account for some features of the low frequency variability in the no

critical bed shear stress and threshold of motion of maerl biogenic gravel abstract a determination of the critical bed shear stress of maerl is a prerequisite for quantifying its mobility rate of erosion and deposition in conservation management the critical bed shear stress for incipient motion has been determined for the first time for samples from biogenic free living maerl beds in three contrasting environments open marine intertidal and beach in galway bay west of ireland the bed shear stress was determined using two methods law of the wall and turbulent kinetic energy in a rotating annular flume and in a linear flume the velocity profile of flowing water above a bed of natural maerl grains was measured in four runs of progressively increasing flow velocity until the flow exceeded the critical shear stress of grains on the bed the critical shields parameter and the mobility number are estimated and compared with the equivalent curves for natural quartz sand the critical shields parameters for the maerl particles from all three environments fall below the shields curve along with a previously reported correlation between maerl grain shape and settling velocity these results suggest that the highly irregular shapes also allow maerl grains to be mobilised more easily than quartz grains with the same sieve diameter the intertidal beds with the roughest particles exhibit the greatest critical shear stress because the particle thalli interlock and resist entrainment in samples with a high percentage of maerl and low percentage of siliciclastic sand the lower density lower settling velocity and lower critical bed shear stress of maerl results in its preferential transport over the siliciclastic sediment at velocities 10 cm s 1 higher than the threshold velocity of grain motion rarely documented subaqueous maerl dunes formed in the annular flume

connections between potential vorticity intrusions and convection in the eastern tropical pacific abstract the connections between intrusions of stratospheric air into the upper troposphere and deep convection in the tropical eastern pacific are examined using a combination of data analysis potential vorticity pv inversion and numerical simulations analysis of ncep ncar reanalyses and satellite measurements of outgoing longwave radiation during intrusion events shows increased cloudiness lower static stability upward motion and a buildup of convective available potential energy cape at the leading edge of the intruding tongue of high pv potential inversion inversion calculations show that the upper level pv makes the dominant contribution to the changes in the quantities that characterize convection this supports the hypothesis that upper level pv anomalies initiate and support convection by destabilizing the lower troposphere and causing upward motion ahead on the pv tongue the dominant role of the upper level pv is confirmed by simulations using the fifth generation pennsylvania state u

the effect of model bias on the equatorward propagation of extratropical waves the effect of model bias on the equatorward propagation of extratropical waves in a gcm simulation is assessed within the context of simple wave guiding principles the modes representing these waves are identified through the use of empirical orthogonal function analysis performed on the 200 mb zonal wind filtered to retain variations between 6 and 30 days the temporal evolution and vertical structure of these modes are examined through the use of time lagged composite analysis the differences between observed and simulated wave propagation is examined in relationship to the theoretical wave guiding properties associated with the observed and simulated time mean flow the utility of simple wave guiding theory for describing the observed and modeled wave propagation is assessed the model bias in the time mean flow is closely associated with the differences in the propagation of the transient waves the excessively strong wave guiding properties associated with the simulated pacific jet appear to inhibit the proper meridional propagation of wave energy into the tropical central and eastern pacific in the simulation waves that do propagate into the tropical pacific either dissipate or are reflected near the equator while in the observations wave energy propagates into the southern hemisphere on the other hand the wave guiding by the subtropical and midlatitude jets over the atlantic is weaker in the simulation than in the observations in this region wave energy propagates primarily into the tropics in the simulation while some of the observed wave energy is reflected toward the east and northeast over the atlantic and northern africa the locations of the theoretical critical lines and wave guides of the time mean flow although based on many simplifying assumptions are remarkably consistent with the propagation characteristics of these waves

horizontal and vertical structure of observed tropospheric equatorial rossby waves equatorial rossby er waves are identified in an 8 year data set of national meteorological center operational analyses the westward moving waves have symmetric circulations about the equator and eastward energy dispersion with maximum zonal wind perturbations along the equator and meridional wind maxima roughly 10 15 off the equator they have maximum amplitude in the lower troposphere and are associated with convective signals at roughly the mean latitude of the tropical convergence zones the circulations thus possess many of the features of the equatorially trapped n 1 rossby modes derived by matsuno 1966 they are generally around zonal planetary wavenumber 6 scale and have a deep nearly equivalent barotropic structure up to 100 mbar this is in contrast with the madden julian oscillation and mixed rossby gravity waves which generally have a first baroclinic mode vertical structure during the intensive observing period iop of the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare and in other years westward propagating er disturbances along the equator are observed by using 6 to 30 day filtered circulation data at 850 mbar zonal wind anomalies at 850 mbar are preferentially associated with like signed anomalies in a deep layer at this frequency as was observed during coare the er waves are most common during northern winter in the central pacific although they can be detected sporadically over the other ocean basins and in other seasons as well one source for the equatorial rossby waves appears to be upper level extratropical rossby wave activity propagating into the eastern pacific although the equatorial waves are sometimes present during the northern summer when the extratropical source is absent we cite evidence that propagation of er wave activity from the central into the western pacific is related to occurrences of westerly wind bursts

soil co2 flux in hydrothermal areas of the tatun volcano group northern taiwan abstract we measured soil co2 flux in the representative hydrothermal areas of the tatun volcano group tvg to better understand the volcano s dynamic nature and to estimate its soil co2 degassing output results show that the average soil co2 fluxes obtained at da you keng dyk geng tze ping gtp she haung ping shp and tatun natural park tnp were 128 g m 2 d 1 518 g m 2 d 1 420 g m 2 d 1 and 25 g m 2 d 1 respectively the range is comparable to other active volcanic hydrothermal areas in the world along with liu huang ku lhk where the soil co2 flux is known the total soil co2 output from measured areas is evaluated at 82 t d 1 furthermore a first total soil co2 output from the whole hydrothermal areas of the tvg is roughly estimated at 113 t d 1 which includes 15 t d 1 mantle contribution considering the mantle derived co2 flux and h2o co2 ratio of fumarolic gas thermal energy associated with the diffuse degassing at the tvg hydrothermal area is estimated at 8 2 mw carbon 13c and helium 3he 4he isotopic ratios of soil samples of the studied areas ranged from 4 4 to 6 7 and 2 45 to 6 98 ra respectively the extent of air involvement in the soil degassing system as constrained by the helium and carbon isotopic compositions provides essential information for depicting regional degassing features of the hydrothermal areas

le roux j p 2001 a simple method to predict the threshold of particle transport under oscillatory waves sedimentary geology 143 2001 59 70 reply to discussion

grains in motion a review abstract this review paper aims to present a practical integrated procedure for the prediction of sediment transport rates in both the continental and marine environment based on the settling velocity of particles such studies have important applications in diverse fields such as civil and coastal engineering sedimentology and environmental geology where they can assist in flood control and the prevention of contaminant dispersal by wind and water as well as the siltation of dams and harbours the formation of placer deposits including gold diamonds and other heavy minerals is also controlled by sediment transport processes so that these studies can form the basis for more efficient exploration programs the first part of the paper discusses some basic principles important in sediment transport followed by an overview of published methods to determine the settling velocity of differently shaped particles including natural grains the application of settling velocity to predict the entrainment threshold of sediments on plane horizontal and inclined beds by unidirectional currents and oscillatory waves is then discussed which finally leads to the determination of sediment transport rates over plane and rippled beds the validity of this approach to natural conditions is tested against published field data where possible other widely used methods are also critically discussed pointing out severe problems in current sampling technology and the calculation of bedload transport in natural environments

nonlinear barotropic response to a localized topographic forcing formation of a tropical surf zone and its effect on interhemispheric propagation abstract the nonlinear response of a barotropic nondivergent spherical flow representative of the upper troposphere but without a tropical hadley cell to localized extratropical topographic forcing is examined using high resolution contour surgery calculations the response is shown to vary greatly with forcing amplitude and can be significantly different from the linear response at large amplitude rossby wave breaking occurs in the tropics irrespective of the direction of the equatorial winds and leads to small scale stirring and the formation of a tropical surf zone which inhibits the meridional propagation of the disturbance

convective destabilization by a tropopause fold diagnosed using potential vorticity inversion there is observational evidence to suggest that at the time tropopause folds in extra tropical cyclones are descending into the mid troposphere there is frequently a destablization of the lower troposphere to moist convection here we consider the dynamical reasons for such a linkage using so called potential vorticity pv attribution concepts in particular pv inversion is used to find the wind shear attributable to the tropopause fold itself then this shear is used to quantify the tendency to generate regions of potential instability for an observed case of a modest tropopause fold it is found that the pv anomaly contained in the tropopause fold contributed substantially to the instantaneous convective destabilization in the sense of increasing the potential instability indeed at some locations it overcame a tendency to stabilize by the atmosphere without the fold on the other hand only a fraction of the region with increased potential instability experienced sufficient large scale ascent to lead to convection and it remains to be seen whether folds in general make a significant contribution to the generation of potential instability that can actually be realized the importance of tropopause folds or indeed of tropopause depressions in general in the context of convection is that their small horizontal scale has the potential to focus and amplify any convective destabilization locally this may account for the localization of outbreaks of severe convective weather which it is important to forecast accurately currently numerical weather prediction models often do not handle these small scales very accurately

planetary scale tropopause folds in the southern subtropics daily measurements of tropospheric ozone at la reunion island 55 e 21 s in july 1998 show that ozone layers are quasi permanent in the troposphere between 6 and 10 km with values reaching 80 to 100 ppbv meridional cross sections of potential vorticity reveal that these layers are related to tropopause folds beneath the subtropical jet folding is persistent and extends over a considerable longitude range from mid atlantic to mid pacific we suggest that this structure is due to the convergent flow associated to the descent branch of the hadley circulation during austral winter

surface heat flow and co2 emissions within the ohaaki hydrothermal field taupo volcanic zone new zealand abstract carbon dioxide emissions and heat flow have been determined from the ohaaki hydrothermal field taupo volcanic zone tvz new zealand following 20 a of production 116 mw e soil co 2 degassing was quantified with 2663 co 2 flux measurements using the accumulation chamber method and 2563 soil temperatures were measured and converted to equivalent heat flow w m 2 using published soil temperature heat flow functions both co 2 flux and heat flow were analysed statistically and then modelled using 500 sequential gaussian simulations forty subsoil co 2 gas samples were also analysed for stable c isotopes following 20 a of production current co 2 emissions equated to 111 6 7 t d observed heat flow was 70 6 4 mw compared with a pre production value of 122 mw this 52 mw reduction in surface heat flow is due to production induced drying up of all alkali cl outflows 61 5 mw and steam heated pools 8 6 mw within the ohaaki west thermal area ohw the drying up of all alkali cl outflows at ohaaki means that the soil zone is now the major natural pathway of heat release from the high temperature reservoir on the other hand a net gain in thermal ground heat flow of 18 mw from 25 mw to 43 3 5 mw at ohw is associated with permeability increases resulting from surface unit fracturing by production induced ground subsidence the ohaaki east ohe thermal area showed no change in distribution of shallow and deep soil temperature contours despite 20 a of production with an observed heat flow of 26 7 3 mw and a co 2 emission rate of 39 3 t d the negligible change in the thermal status of the ohe thermal area is attributed to the low permeability of the reservoir beneath this area which has limited production mass extraction and sheltered the area from the pressure decline within the main reservoir chemistry suggests that although alkali cl outflows once contributed significantly to the natural surface heat flow 50 they contributed little 2 emissions due to the loss of 99 of the original co 2 content due to depressurisation and boiling as the fluids ascended to the surface consequently the soil has persisted as the major 99 pathway of co 2 release to the atmosphere from the high temperature reservoir at ohaaki the co 2 flux and heat flow surveys indicate that despite 20 a of production the variability in location spatial extent and magnitude of co 2 flux remains consistent with established geochemical and geophysical models of the ohaaki field at both ohw and ohe carbon isotopic analyses of soil gas indicate a two stage fractionation process for moderate flux 60 g m 2 d 1 sites boiling during fluid ascent within the underlying reservoir and isotopic enrichment as co 2 diffuses through porous media of the soil zone for high flux sites 300 g m 2 d 1 the 13 co 2 signature 7 4 0 3 ohw and 6 5 0 6 ohe is unaffected by near surface soil zone fractionation processes and reflects the composition of the boiled magmatic co 2 source for each respective upflow flux thresholds of 2 d 1 for purely diffusive gas transport between 30 and 300 g m 2 d 1 for combined diffusive advective transport and 300 g m 2 d 1 for purely advective gas transport at ohaaki were assigned 13 co 2 values and cumulative probability plots of co 2 flux data both identified a threshold of 15 g m 2 d 1 by which background atmospheric and soil respired co 2 may be differentiated from hydrothermal co 2

a rapid method to determine the critical shear stress for sphere entrainment under unidirectional fluid flow abstract empirical equations are presented which allow the rapid calculation of critical shear stresses for spherical particles of any size and density in any given fluid this eliminates the more cumbersome graphical methods employed to date the approach is based on the relationship of the dimensionless grain size dd to the dimensionless critical shear stress c and the grain reynolds number re re 2 c 3 equals dd which plots against c in a curve described by two simple equations

identifying blind geothermal systems with soil co2 surveys abstract diffuse soil co2 flux surveys are a widely applied approach for delineating zones of elevated heat and mass transfer in areas with geothermal surface features including hot springs mud pools and geysers however many geothermal systems are capped by relatively impermeable layers that diminish the surface expression of potential resources present at depth here we report diffuse soil co2 flux survey results with complementary 13co2 values and shallow soil temperatures for the ngatamariki geothermal system taupo volcanic zone new zealand a largely surface blind system in an effort to explore the utility of such data as indicators of magmatic carbon emission in geothermal systems with low co2 flux our results include that 1 the majority 54 of the soil co2 flux measurements are below background levels 15 gco2 m 2 day 1 2 only 5 6 of the shallow 10 cm soil temperatures exceed 30 c and 3 no correlation is present between soil temperature and co2 flux at ngatamariki these results belie the fact that a recently developed geothermal resource is present beneath ngatamariki yet 13co2 values when interpreted in the context of soil gas co2 concentrations demonstrate that the magmatic hydrothermal system beneath ngatamariki can be distinguished from soil zone carbon sources using diffuse soil gas geochemical tracers modeling the ngatamariki co2 system as a simple mixture of geothermal biogenic and atmospheric end members allows for the apportionment of co2 flux at different locations across the field based on these findings we suggest that delineating potential geothermal sites and assessing the relative contributions of mixed fluid end members is possible even with low diffuse co2 flux and limited surface expression of geothermal systems at depth

entrainment threshold of natural grains in liquids determined empirically from dimensionless settling velocities and other measures of grain size abstract grain size plays a crucial role in sediment transport but different methods of size analysis do not yield comparable results particle diameters obtained by settling tube for example cannot be employed in equations based on sieve sizes although the majority of experiments on the initiation of sediment motion has been based on sieve data settling tube analysis is probably superior as both the settling rate and the entrainment threshold of grains are determined by the same factors of size shape and density in this paper empirical equations are provided which allow the determination of a non dimensional critical shear stress directly from the equivalent sedimentation diameter the equations apply to the entrainment of well sorted grains with a high sphericity on flat sediment beds and are valid for particles and liquids of different densities

initiation of motion in overland flow this article reports the results of an experimental study concerning the initial movement of sediment in overland flow experiments were carried out in a small flume using water and quartz materials of various grain sizes the comparison of our experimental results with classic criteria showed that the shields curve and the criterion of yang can also be used for turbulent overland flow generally higher shear stresses are necessary to provoke bed instability under laminar flow conditions especially at higher shear velocity particle reynolds numbers a relative roughness effect also exists in laminar flow contrary to the observations by savat on fixed beds laminar flow does not show an uncommon selectivity when loose homogeneous beds are considered

dominant anomaly patterns in the near surface baroclinicity and accompanying anomalies in the atmosphere and oceans part i north atlantic basin abstract variability in the monthly mean flow and storm track in the north atlantic basin is examined with a focus on the near surface baroclinicity b bxi byj dominant patterns of anomalous b found from empirical orthogonal function eof analyses generally show patterns of shift and changes in the strength of b composited anomalies in the monthly mean wind at various pressure levels based on the signals in the eofs display robust accompanying anomalies in the mean flow up to 50 hpa in the winter and up to 100 hpa in other seasons anomalous eddy fields accompanying the anomalous bx patterns exhibit broadly speaking structures anticipated from linear theories of baroclinic instabilities and suggest a tendency for anomalous wave fluxes to accelerate decelerate the surface westerly accordingly atmospheric anomalies accompanying by anomalies have patterns different from those that accompany bx anomalies but are as large as those found for bx anomalies in the sea surface temperature sst found for

on the effects of the hadley circulation and westerly equatorial flow on planetary wave reflection the nonlinear behaviour of quasi stationary planetary waves that are excited by mid latitude orographic forcing is considered in a global shallow water model taken to represent the upper troposphere the waves propagate toward low latitudes where the background flow is normally weak and the waves are therefore likely to break nonlinear pseudomomentum conservation relations are used to quantify the absorption reflection behaviour of the wave breaking region two different flow scenarios are represented i initial states without a representation of the hadley circulation but where the axisymmetric equatorial background flow changes from being weak and easterly to moderate westerly ii initial states that include a representation of the hadley circulation and that have weak equatorial easterlies based on linear arguments both i and ii are expected to influence the progression of the wave train the nonlinear behaviour in the presence of low latitude westerly background flows is different from linear predictions for large amplitude forcing wave breaking takes place even though there is no zero wind line in the initial state and the cross equatorial wave propagation that took place for small amplitude forcing is stopped before it can reach the equator nonlinear reflection is found to take place back into the hemisphere of origin but not across to the other hemisphere in the presence of a hadley circulation representative of winter conditions the nonlinear reflection takes longer to get established i e it requires more forcing but a reflected wave train is still present in the numerical simulations both for a longitudinally symmetric forcing and for the more realistic case of an isolated forcing a summer hadley circulation allows wave activity to get to the winter hemisphere as the forcing is increased wave breaking occurs and eventually nonlinear reflection

longitudinal variation of the stratospheric quasi biennial oscillation the longitudinal dependence of interannual variations of tropical stratospheric wind is examined in a detailed general circulation model simulation and in the limited observations available a version of the skyhi model is run with an imposed zonally symmetric zonal momentum source that forces the zonal mean zonal wind evolution in the tropical stratosphere to be close to an estimate of the observed zonal wind based on radiosonde observations at singapore during the period 1978 99 this amounts to a kind of simple assimilation model in which only the zonal mean wind field in the tropical stratosphere is assimilated and other quantities are allowed to vary freely a total of five experiments were run one covering the full 1978 99 period and four for 1989 99 the results at and above about 30 hpa are fairly simple to characterize when the zonal mean wind near the equator at a particular level is easterly the monthly mean wind has only very small zonal contrasts when mean westerlies are present near the equator significant zonal asymmetries occur at low latitudes most notably easterly anomalies over south america and westerly anomalies in the eastern pacific region these anomalies generally display a continuous meridional phase propagation with the extratropical quasi stationary eddy field in the winter hemisphere the net result is a significantly weaker peak to peak amplitude of the quasi biennial oscillation qbo in zonal wind over the south american sector than over the rest of the equatorial band the zonal contrast in qbo amplitude near 10 hpa exceeds 10 in the lower stratosphere the zonal asymmetries in the prevailing wind are fairly small asymmetries seem to reflect the upward extension of the tropospheric walker circulation and are less strongly modulated by the quasi biennial oscillation in zonal mean circulation the model results were checked against limited station observations at nairobi 1 38s 36 78e singapore 1 48n 103 98e rochambeau 4 88n 52 48w and bogota 4 78n 74 18w overall reasonable agreement was found between the monthly mean zonal winds in the model simulation and these station data the low latitude wind field in monthly mean ncep gridded analyses was also examined these analyses have some obviously unrealistic features in the tropical stratosphere but some of the behavior seen in the skyhi model simulations can be identified as well in the ncep analyses

climatology of intrusions into the tropical upper troposphere regions of upper tropospheric equatorial westerly winds observed over the pacific and atlantic oceans during northern fall to spring are important for extratropical tropical interactions this paper focuses on one feature of these westerly ducts that has received relatively little attention to date the occurrence of rossby wave breaking events that transport tongues of extratropical air deep into the tropics mix tropical and subtropical air and can affect deep convection a climatology of these intrusion events formed from 20 years of meteorological analyses shows a strong dependence on the basic state flow notably intrusion events are found to occur almost exclusively within westerly ducts with more events in the presence of stronger equatorial westerlies it is also found that there is strong interannual variability in the frequency of pacific events with fewer events during the warm phases of enso consistent with the changes in the basic flow since these intrusion events laterally mix trace constituents and have been linked to tropical convection their spatial and temporal variability may cause related variability in the distribution of trace constituents and tropical convection

wave friction factor as related to the shields parameter for steady currents abstract the wave friction factor fw is an important dimensionless parameter used to estimate wave induced bed shear stress which together with current induced bed shear stress controls sediment transport in the marine and lacustrine environment however fw is either overestimated or underestimated by existing equations the matter is complicated by the fact that different equations must be used for hydrodynamically smooth or rough flows but the limit between these two boundary conditions is still poorly defined some equations also require estimated values for the nikuradse roughness length and the wave boundary layer thickness neither of which can be derived accurately it is therefore not surprising that fw values as calculated by existing equations differ by as much as a factor of 3 in the present paper fw is related to the shields parameter for unidirectional currents which not only facilitates the direct comparison and summation of bed shear stresses but also yields a more accurate equation valid for grains of different density in any fluid irrespective of the boundary condition

persistent north pacific circulation anomalies and the tropical intraseasonal oscillation abstract a composite analysis of multiyear 1985 93 global reanalyses produced by the ncep ncar and the nasa dao is used to show that the development of persistent north pacific pnp circulation anomalies during nh winter is linked to tropical intraseasonal oscillations the development is initiated over the tropical west pacific by anomalous convection characterized by an east west dipole structure one to two weeks prior to the extratropical onset time in both reanalyses as tropical heating moves eastward toward the central pacific anomalous divergent outflow associated with the local hadley circulation generates an anomalous rossby wave sink source in the subtropics consistent with the retraction extension of the pacific jet prior to onset the signature of the forced anomalies is a pair of cyclonic anticyclonic circulation anomalies centered near the node of the tropical heating dipole wave trains extending from the region of anomalous convection into the extratropics set the stage for th

the link between cut off lows and rossby wave breaking in the southern hemisphere the climatological link between cut off low col pressure systems that occur from 20 to 50 s and rossby wave breaking rwb in the southern hemisphere sh is examined for 1979 2008 it is shown that cols are associated with either rwb events 89 or with potential vorticity pv intrusions where there is north south advection of high pv air 11 in the vast majority of cols the rwb events occur upstream on or before the day of the col formation the evolution of the pv geopotential heights static stability absolute vorticity and temperature advection fields during the cols are consistent with the formation of high pv anomalies that induce cyclonic circulations as predicted by theory rwb plays a key role in producing the split flow associated with cols in the sh which in turn produces absolute vorticity anomalies by shear curvature vorticity conversion and creates static stability anomalies the cols associated with rwb at 330 k are deeper and more persistent than those associated with 350 k rwb and surface processes differ depending on the isentropic surface on which the associated rwb occurs the seasonality of the rwb and cols are similar and is linked to the seasonal march of the westerly jets copyright 2010 royal meteorological society

tropical upper tropospheric potential vorticity intrusions during sudden stratospheric warmings abstractthe intrusion of lower stratospheric extratropical potential vorticity into the tropical upper troposphere in the weeks surrounding the occurrence of sudden stratospheric warmings ssws is examined the analysis reveals that ssw related pv intrusions are significantly stronger penetrate more deeply into the tropics and exhibit distinct geographic distributions compared to their climatological counterparts while climatological upper tropospheric and lower stratospheric utls pv intrusions are generally attributed to synoptic scale rossby wave breaking it is found that ssw related pv intrusions are governed by planetary scale wave disturbances that deform the extratropical meridional pv gradient maximum equatorward as these deformations unfold planetary scale wave breaking along the edge of the polar vortex extends deeply into the subtropical and tropical utls in addition the material pv deformations also reorganize the geographic structure of the utls waveguide which alters where synopti

focused and diffuse effluxes of co2 from mud volcanoes and mofettes south of mt etna italy abstract several sites with anomalous emissions of carbon dioxide were investigated in the region south of mt etna volcano in order to assess the types of emission focused and or diffuse their surface extension and the total output of co 2 most of the studied emissions are located on the southwest boundary of mt etna near the town of paterno they consist of three mud volcanoes known as salinelle one spring with bubbling gas acqua grassa and one area of diffuse degassing pescheria another site naftia lake with remarkable gas emissions bubbling gas into a lake as well as adjacent areas of diffuse soil degassing is located further southwest of mt etna in an area of extinct quaternary volcanism on the northwest margin of hyblean mts in all of these areas the origin of the highest co 2 emissions is clearly magmatic and degassing to the atmosphere occurs mostly through tectonic structures probably at a regional scale the magmatic source that feeds anomalous degassing in the above areas is likely to be the same that feeds volcanic activity at mt etna focused degassing was measured at each emission vent using devices that measure the air speed whereas diffuse soil degassing was measured using the accumulation chamber method in total 712 measurements were carried out 146 in focused degassing vents 566 on diffuse degassing areas single co 2 output values ranged from 1 8 10 5 to 1 68 kg s 1 in the case of diffuse degassing areas statistical analyses allowed to discriminate between biogenic co 2 and co 2 deriving from a magmatic hydrothermal source only the efflux values from the latter source were considered in the output estimates the total estimated output thus obtained was about 2 61 kg s 1 relevant to a total surface of about 146 500 m 2 which includes only the magmatic co 2 emissions this value is comparable with that of most non volcanic emissions from geothermal and or faulted areas of central southern italy as well with the co 2 output from some of the volcanic areas of italy

the signature of the annular modes in the tropical troposphere the extratropical annular modes are coupled with a distinct pattern of climate anomalies that spans the circulation of the tropical troposphere the signature of the annular modes in the tropical troposphere exhibits a high degree of equatorial symmetry it is associated with upper tropospheric zonal wind anomalies centered about the equator midtropospheric temperature anomalies located 208n and 208s and opposing mean meridional circulation anomalies that span the subtropics of both hemispheres the linkages between the annular modes and the tropical circulation are only evident during the cold season months and are most robust in association with the northern hemisphere annular mode nam the coupling between the annular modes and the circulation of the tropical troposphere is consistent with forcing by waves originating at extratropical latitudes both annular modes are characterized by anomalies in the eddy momentum flux convergence at tropical latitudes that act to reinforce the changes in the tropical wind and temperature fields the most pronounced tropical anomalies lag indices of the annular modes by 2 weeks and are found over the eastern tropical pacific where climatological westerlies permit extratropical waves to propagate into the deep tropics the linkages between the nam and the tropical tropospheric circulation are

the 1985 86 intraseasonal oscillation and the role of the extratropics abstract an intraseasonal oscillation that occurred in the 1985 86 northern winter is documented in this study the tropical convection of this event is dominated by the mixture of a standing oscillation over the maritime continent and an eastward moving feature from the indian ocean into the central pacific the time evolution of the upper tropospheric circulation patterns instead of propagating eastward along the equator as suggested in the existing composites of the intraseasonal oscillation is characterized by a series of wave patterns in the northern hemisphere and does not complete the cycle around the globe the familiar moist kelvin wave explanation for the intraseasonal oscillation receives little support from diagnosis of this event using zonal wind height field streamfunction and potential vorticity only in the lower troposphere near the date line is the convincing evidence for its existence found a scenario for the intraseasonal oscillation which is suggested by the analysis includes

relationship between aerodynamic entrainment threshold and hydrodynamic settling velocity of particles abstract data on the critical shear stress c at incipient grain motion under air flow have been carefully selected from the literature it is shown that the non dimensional shields entrainment threshold c in air is an exponential function of the dimensionless settling velocity wds in water of a sphere with a diameter equal to the sieve size as wd5 can be related to the measured dimensionless settling velocity wdm of natural grains wdm can be used directly to calculate c for quartz grains in air the equations are valid for sizes between 0 01 and at least 0 166 cm i e silt to very coarse sand the method is applicable to well sorted grains with a relatively high sphericity entrained on flat surfaces

a simple method to predict the threshold of particle transport under oscillatory waves abstract various methods of predicting the incipient motion of sediments under oscillatory waves have been proposed in the past but most require that at least the wave orbital diameter d o be known methods based on the oscillatory shields parameter ws need the wave friction factor f w in order to calculate the critical threshold velocity for which d o is also required other existing methods not requiring d o are only applicable to quartz grains and yield highly inaccurate results in this paper a new dimensionless threshold orbital velocity based on all the important variables playing a role in wave transport is plotted against the dimensionless settling velocity this yields a relationship that allows the prediction of the threshold velocity from the wave period and grain size alone the method has the advantages that it is valid for grains of varying size and density in laminar or turbulent fluids of different density and viscosity does not require the wave orbital diameter and is more accurate than previous equations

interactions between enso transient circulation and tropical convection over the pacific abstract the interannual variability of transient waves and convection over the central and eastern pacific is examined using 30 northern winters of ncep ncar reanalyses 1968 69 1997 98 and satellite outgoing longwave radiation data starting in 1974 there is a clear signal associated with the el nino southern oscillation such that differences in the seasonal mean basic state lead to statistically significant changes in the behavior of the transients and convection with periods less than 30 days which then feed back onto the basic state during a warm event el nino phase the northern hemisphere subtropical jet is strengthened over the central pacific the region of upper tropospheric mean easterlies over the tropical western pacific expands eastward past the date line and the upper tropospheric mean westerly duct over the tropical eastern pacific is weakened the transients tend to propagate along the almost continuous waveguide of the subtropical jet equatorward propagation into the westerly

invigoration and capping of a convective rainband ahead of a potential vorticity anomaly abstractdeep convection frequently occurs on the eastern side of upper level troughs or potential vorticity pv anomalies this is consistent with uplift ahead of a cyclonic pv anomaly and consequent reduction in static stability and increase of convective available potential energy cape nevertheless the causal link between upper level pv and deep convection has not been proven and given that lift moisture and instability must all be present for deep convection to occur it is not clear that upper level forcing is sufficient in this paper a convective rainband that intensified ahead of a cyclonic pv anomaly in an environment with little cape 10 j kg 1 is examined to determine the factors responsible for its intensification the key feature was a low level convergence line arising from the remnants of an occluded front embedded in the low level cyclonic flow the rainband s intensity and morphology was influenced by the remnants of a tropopause fold that capped convection at midlevels in the

turbulence based measurements of wave friction factors under irregular waves on a gravel bed very few studies have quantified the wave friction factor fw for coarse sediments at field scale to address this shortcoming high frequency measurements of turbulence obtained within the boundary layer of irregular waves over gravel in the delta flume have been used to calculate values of fw using different evaluation methods in the field scale laboratory experiments reported here three velocimeters were deployed on the seaward side of a 4 m high 5 m wide and 55 m long gravel barrier subject to a jonswap spectrum of waves with significant wave heights ranging from 0 8 m to 1 3 m and peak periods of 3 0 s to 10 s and offshore water depths ranging from 1 75 m to 3 75 m the deployment area was essentially flat with little or no predicted or observed sediment movement under the wave conditions investigated the turbulent kinetic energy method was found to be the most suitable approach for calculating the bed shear stress which can be related to fw wave friction factor values under the conditions tested here fell in the range 0 01 and 0 27 although fw predicted by an existing equation agrees well with the mean measured fw value the application of a new predictor for fw is recommended for improved parameterisation of skin friction over the range of relative roughness values encountered in this study this approach combines the wave reynolds number wave steepness and relative depth to provide a simple expression to assist assessments of coarse sediment transport by waves for uses within a range of practical engineering applications

interaction of extratropical rossby waves with westerly quasi biennial oscillation winds the role of laterally radiating stratospheric rossby waves from the winter hemisphere in the momentum balance of the quasi biennial oscillation qbo remains an unresolved issue observations of extratropical rossby waves penetrating close to the equator suggest that rossby wave absorption in the tropics must occur at least occasionally this paper presents numerical simulations using a global shallow water model to examine the pattern of wave absorption at low latitude during the westerly wind phase of the qbo earlier results indicating that extratropical rossby waves radiating to the equator do not break there when the qbo phase is westerly are reproduced it is shown that the westerly qbo jet can persist undiminished at its core over seasonal length integrations because the laterally radiating rossby waves are absorbed along the qbo jet s flanks where easterly acceleration occurs the net effect of the rossby waves on the westerly qbo jet is a reduction in the width of its meridional profile but not its core strength this behavior is interpreted by considering the filtering of equatorward radiating rossby waves by critical layer absorption a process that depends on the background zonal mean wind and the waves phase speed and amplitude the simulations also show that adequate horizontal resolution is needed to capture the suppression of wave breaking at the qbo jet core and persistence of the jet core strength over seasonal timescales the implications of this result for simulations of the qbo in general circulation models are considered

identification and era 15 climatology of potential vorticity streamers and cutoffs near the extratropical tropopause abstract a novel approach is introduced to identify potential vorticity pv streamers and cutoffs as indicators of rossby wave breaking near the extratropical tropopause and to compile climatologies of these features on different isentropic surfaces the method is based on a contour searching algorithm that identifies the dynamical tropopause 2 potential vorticity units pvu pvu 1 10 6 k kg 1 m2 s 1 isoline on isentropic surfaces the contour is then analyzed to search for cutoffs and filament like streamers whereas the identification of cutoffs is unambiguous the one for streamers requires the specification of two parameters that determine the width and length of the contour feature to be classified as a streamer this technique has been applied to the pv distribution in the northern hemisphere on isentropes from 295 to 360 k during the time period from 1979 to 1993 using the 15 yr european centre for medium range weather forecasts ecmwf re analysis era 15 the climatology reveals a pronou

the early development of the 2015 16 quasi biennial oscillation disruption abstractan unprecedented disruption of the quasi biennial oscillation qbo started to develop from late 2015 the early development of this event is analyzed using the space time spectra of eddies

dry intrusions lagrangian climatology and dynamical impact on the planetary boundary layer abstractdry air intrusions dis are dry deeply descending airstreams from the upper troposphere toward the planetary boundary layer pbl the significance of dis spans a variety of aspects including the interaction with convection extratropical cyclones and fronts the pbl and extreme surface weather here a lagrangian definition for di trajectories is used and applied to ecmwf interim reanalysis era interim data based on the criterion of a minimum descent of 400 hpa during 48 h a first global lagrangian climatology of di trajectories is compiled for the years 1979 2014 allowing quantitative understanding of the occurrence and variability of dis as well as the dynamical and thermodynamical interactions that determine their impact dis occur mainly in winter while traveling equatorward from 40 50 latitude dis typically reach the lower troposphere with maximum frequencies of 10 in winter in the storm track regions as well as over the mediterranean sea arabian sea and eastern north pa

local mixing events in the upper troposphere and lower stratosphere part ii seasonal and interannual variability the lyapunov diffusivity is used to investigate local isentropic mixing events in the upper troposphere lower stratosphere utls region the diagnostic highlights the seasonal cycle of the longitudinally varying mixing properties in particular those associated with the monsoon circulations and the westerly ducts in the subtropics the results are broadly consistent with studies of rossby wave breaking frequencies the mixing structure is shown to be modulated by modes of atmospheric variability el nino southern oscillation enso is found to strongly influence the mixing structure throughout the tropics and subtropics the sub tropical jet is associated with longitudinal bands of mixing minima isentropic mixing barriers separated by synoptic scale regions of strong mixing activity the greatest enso modulation in december february is confined to the pacific sector where the barriers associated with the subtropical jets extend farther into the eastern pacific and in the western pacific a barrier is found at the equator during the positive phase during june august the influence is seen to extend beyond the pacific region with the barrier at the subtropical jet in the southern hemisphere increasing in strength at all longitudes and with an increase in strength and isolation of monsoon related mixing over asia and north america the local influence of the north atlantic oscillation in wintertime is investigated during the positive phase a double barrier structure is associated with the subtropical jet the northern branch crosses the atlantic toward scandinavia and the southern branch tends toward north africa the antarctic oscillation is shown to influence whether the subvortex region is isolated from midlatitudes

testing the tunable diode laser system in extreme environments measuring high and low co2 concentrations in both active volcanic and geothermal settings abstract measuring co2 emissions in geothermal and volcanic areas is sometimes difficult because of large areas to cover and sites often inaccessible measuring high levels of co2 concentration can provide information on hidden structure in geothermal areas and recording changes in co2 concentration on volcanic areas can help monitor the level of volcanic activity the purpose of this study was to use the tunable laser diode tdl absorption spectroscopy method to test levels of co2 concentrations at two extreme environments white island volcano the most active volcano of new zealand with large and concentrated gas fluxes and ngapouri geothermal area a small geothermal area in the taupo volcanic zone new zealand with relatively low and diffuse gas emissions in 2017 for the first time using tdl at white island co2 concentration measurements performed across the active fumarole fields had the highest co2 concentrations of 657 ppm tdl survey measurements were also conducted across fault strands near the ngapouri geothermal area and the results complemented co2 flux results obtained with the accumulation chamber method higher co2 concentrations were measured close to the mapped ngapouri splays with a maximum of 484 ppm the maximum co2 flux measured in the same area was 100 g m 2 day 1 however the highest co2 fluxes measured along the transects and by the mapped faults were less clear but the co2 concentrations increased closer to the fault splays advantages and disadvantages of using a tdl system have been described and compared to the accumulation chamber method the results from the tdl system demonstrated that co2 concentrations can be used as a tool with other geophysical tools for both detecting and highlighting geological structures where no obvious thermal activity is present and for monitoring purposes on active volcanoes

quasi biweekly oscillations of the south asian monsoon and its co evolution in the upper and lower troposphere the upper tropospheric quasi biweekly oscillation uqbw of the south asian monsoon is studied using the potential vorticity field on the 370 k isentrope the uqbw is shown to be a common occurrence in the upper troposphere during the monsoon and its typical evolution is described we suggest that the uqbw is a phenomenon of both the middle and tropical latitudes owing its existence to the presence of the planetary scale upper tropospheric monsoon anticyclone the uqbw is first identified as rossby waves originating in the northern flank of the monsoon anticyclone these rossby waves break when reaching the pacific ocean and their associated cyclonic pv anomalies move southward to the east of asia and then westward across the indian ocean and africa advected by the monsoon anticyclone a strong correlation or co evolution between the uqbw and quasi biweekly oscillations in the lower troposphere qbw is also found in particular analysis of vertically integrated horizontal moisture transport 850 hpa geopotential and outgoing long wave radiation show that the uqbw is usually observed at the same time as and co evolves with the lower tropospheric qbw over south asia we discuss the nature of the uqbw and its possible physical link with the qbw

the structure of the mokai geothermal field based on geophysical observations abstract the mokai geothermal area about 25 km northwest of taupo has only minor thermal manifestations with a natural heat output of about 6 mw in late 1976 a roving dipole resistivity survey was made in the area surrounding mokai springs since then an extensive schlumberger resistivity survey has been made using two spacings nominally 600 m and 1200 m covering an area of about 4 b v n 2 around the mokai area interpretation of all the resistivity data suggests the area of mokai geothermal field below which high temperatures may be expected at depth is about 12 16 km 2 low resistivities from soundings within this area indicate highly conductive saline geothermal fluids at a depth of about 60 m although below this the resistivity increases suggesting a lowering of porosity the interpretation of resistivity measurements suggests a considerable subterranean flow of geothermal fluids northward from the mokai geothermal field and a further 76 mw of heat is estimated to be carried by springs and seeps into the deeply incised waipapa stream a second low resistivity region occurs at the waikato river about 12 km north of the geothermal field with an area of 3 4 km 2 there are indications that this anomaly is caused by hot geothermal fluids and it is suggested here that these geothermal fluids have their origin at the mokai geothermal field on this basis an estimate of the total heat output of the mokai geothermal area is 400 160 mw temperature in a drill hole within the geothermal field as outlined by this study reach a maximum of 290 c

classification of atmospheric river events on the u s west coast using a trajectory model author s ryoo jm waliser de waugh dw wong s fetzer ej fung i abstract 2015 american geophysical union all rights reserved we investigate transport pathways of water vapor associated with landfalling atmospheric river ar events that result in precipitation along the west coast of the u s for winters of 1997 2010 the water vapor transport pathways are determined by computing back trajectories with a trajectory model using the modern era retrospective analysis for research and applications reanalysis data set the majority of ar events 86 over the west coast of the u s are grouped into three trajectory types and two of them are closely associated with the ar events we designate the first type as ascending near landfall and of tropical origin at the second type as ascending near landfall and of extratropical origin ae and the third type as descending or parallel near landfall and of extratropical origin de which is accompanied but not directly associated with the ar events the magnitude and spatial distribution of precipitation of a given ar event are found to be strongly determined by the type of trajectories in general ar events composed of both at and ae trajectories have more frequent precipitation over a broad region of the western u s and ar events composed of both at and de trajectories have intense precipitation over the southwestern u s due to at trajectories ar events of at only trajectories have intense precipitation especially over the northwestern u s but are less frequent compared to those of at ae trajectories in addition different patterns of trajectory types among ar events are closely linked to upper level potential vorticity pv anomalies 66 of ar events are associated with anticyclonic rossby wave breaking events

extratropical forcing of tropical pacific convection during northern winter abstract statistical evidence is presented to support the notion that tropical convection in the eastern pacific and atlantic intertropical convergence zone itcz during northern winter can be forced by disturbances originating in the extratropics the synoptic scale transients in these regions are characterized at upper levels by strong positive tilts in the horizontal and appear to induce vertical motions ahead of troughs as in midlatitude baroclinic systems two case studies of such interactions are examined one for the eastern north pacific itcz and another somewhat different type of interaction for the south pacific convergence zone spcz over the western south pacific both cases are associated with upper level troughs strong cold advection deep into the tropics and the formation of a frontal boundary at low levels the itcz case is characterized by the advection of anomalously high isentropic potential vorticity air southward a strong poleward flux of heat and westerly momentum and the devel

potential influence of the november december southern hemisphere annular mode on the east asian winter precipitation a new mechanism as the leading mode of the global atmospheric mass inter annual variability the southern hemisphere annular mode sam may exert potential influences to the northern hemisphere nh climate but the related physical mechanism is not yet clear in this study it is found that the november december nd sam exhibits a significant inverse relationship with the winter precipitation over east asia particularly southern china observational and numerical evidences show that anomalous nd sam is usually associated with a south atlantic pacific dipole sea surface temperature anomaly ssta which persists into ensuring winter the dipole ssta can modulate the variability of the inter tropical convergence zone itcz in pacific subsequently a distinguished atmospheric tele connection pattern is induced and prevails over the nh mid latitude region as a response to the anomalous itcz large areas of high pressure anomalies are triggered at upper troposphere over east asia and centered over southern china which favors less precipitation over east asia particularly southern china and vice versa through such a physical mechanism the notable influence of the nd sam can sustain through the following season and impact on the nh winter climate

observations of 2 4 day inertia gravity waves from the equatorial troposphere to the f region during the sudden stratospheric warming event of 2009 1 we have observed strong 2 4 day wave activity in the f region peak critical frequency fof2 at 7 5 n obtained from gps radio occultation measurements of the constellation observing system for meteorology ionosphere and climate cosmic satellites and the horizontal component of geomagnetic field variations over tirunelveli 8 7 n 77 8 e 1 75 n dip angle during the sudden stratospheric warming ssw event of 2009 a similar wave is observed strongly in the meridional winds observed by the mf radar at tirunelveli the meridional winds at 9 n and the equator obtained from era interim which is the latest global atmospheric reanalysis produced by the european centre for medium range weather forecasts shows clearly the 2 4 day wave propagating eastward with zonal wave number 6 over the central and eastern pacific both before and during the ssw event and over the indian sector during the ssw event only the potential vorticity pv intrusion at 200 hpa to lower latitudes is near the central pacific before the onset of the ssw event however during the ssw event the pv intrusion is observed more strongly near the indian sector in addition to the weaker intrusion near the central pacific it clearly indicates the rossby wave propagation to equatorial latitudes in the form of pv intrusion and it selectively enhances the periodicities generated owing to equatorial convective heating these waves could propagate to upper heights and cause variations in the mesosphere thermosphere ionosphere system

chemical discontinuity at the extratropical tropopause and isentropic stratosphere troposphere exchange pathways diagnosed using aura mls data 1 the chemical discontinuity at the extratropical tropopause extp and stratosphere troposphere exchange ste pathways are investigated using the long lived chemical species carbon monoxide co and ozone o3 measured by the aura microwave limb sounder mls a relative coordinate tropopause latitude tplat is developed based on potential vorticity pv from the goddard earth observing system version 5 geos 5 data assimilation system tplat is defined as the shortest geographic distance along an isentropic surface from the extratropical tropopause extp to an observation location our results show that this coordinate highlights the sharp chemical discontinuities at the extp more clearly than the widely used equivalent latitude coordinate geographical distributions of ste pathways and barriers are investigated based on meridional gradients in o3 abundances in the new tplat coordinate in conjunction with analysis of rossby wave breaking between 330 k and 360 k in northern hemispheric nh winter dec jan feb nh ste pathways are seen mainly above the northeast pacific in nh summer jun jul aug the nh pathway covers all longitudes at 330 k however it is mainly located above asia at 340 k and above the atlantic and the north pacific at 350 k and 360 k in the southern hemisphere sh there is a weaker ste region above the eastern indian ocean and the southwestern pacific at and above 350 k in sh winter and a stronger ste region over the southeastern pacific at these levels during sh summer in addition this study shows nh pv gradients are slightly stronger near the extp in summer than in winter even though the subtropical jet is weaker and rossby wave breaking is stronger in summer than in winter

attribution and its application to mesoscale structure associated with tropopause folds it is important in meteorology to be able to establish a link between various features this link in its strongest form would be referred to as cause and effect but this is extremely difficult to establish for atmospheric flows a weaker but nonetheless powerful link is attribution which attempts to provide a way to associate various fundamental features such as potential vorticity anomalies to weather events involving regions of ascent attribution is not new and it is implicit in the way that atmospheric evolution is usually described in this paper an attempt is made to define more precisely what are the steps and assumptions being made in such a method these ideas become more concrete by applying them to a simple model of a two dimensional front at which there is a tropopause fold the aim is to find the vertical motion attributable to the descended tropopause fold in an extra tropical cyclone this is the first step in a longer programme of research designed to provide a test of the hypothesis that such a descended tropopause can trigger mesoscale phenomena such as convection and cyclones

horizontal and vertical structure of cross equatorial wave propagation abstract observational evidence of interhemispheric wave propagation through the equatorial upper tropospheric mean westerlies in the eastern pacific ocean is found in nine years 1980 81 to 1988 89 of european centre for medium range weather forecasts analyses during boreal winter using time mean standard deviation and one point correlation fields of potential vorticity on isentropic surfaces ipv it is found that waves associated with local fluctuations with periods between 6 and 30 days propagate from the northern hemisphere extratropics cross the equator and continue into the southern hemisphere extratropics this result is in agreement with hypotheses that claim regions of time mean westerlies in the tropics act as ducts allowing extratropical rossby waves to propagate into and through the tropics horizontal structure of the waves appears to change little during the course of the interhemispheric propagation however in the lower troposphere where the mean zonal wind is easterly the lowe

synoptic scale rossby waves and the geographic distribution of lateral transport routes between the tropics and the extratropics in the lower stratosphere atmospheric transport between the tropics and the extratropics in the lowest part of the stratosphere during northern hemisphere winter is investigated the role of synoptic scale disturbances that propagate laterally into the tropics is examined using the middle atmosphere version of the national center for atmospheric research community climate model version 3 general circulation model in the lower stratosphere synoptic scale rossby waves propagate vigorously from the northern i e winter extratropics through two westerly ducts where the westerly zonal mean winds near the equator are favorable to rossby wave propagation the waves break in the westerly ducts and modify the mean potential vorticity pv structure to connect subtropical and equatorial regions of sharp pv gradients frequent wave breaking and the wave induced pv structure create distinct routes where transport occurs vigorously between the tropics and the northern extratropics interhemispheric transport also occurs through regions associated with the westerly ducts in the southern summer hemisphere lower stratosphere synoptic scale disturbances propagate mainly as tongues of pv elongated from extratropical disturbances the transport between the tropics and the southern extratropics has a strong geographic preference but is dominated by the monsoon circulation as was shown for the upper troposphere by chen 1995 pv tongues and other transient anomalies are of secondary importance

origin of warm springs in banks peninsula new zealand abstract thermal springs present rare opportunities to locate and interpret the geological drivers of upper crustal fluid flow interpreting the conditions through which crustal fluids are heated and released to the surface is important for advancing our understanding of crustal deformation and geothermal resource potential across tectonic contexts in new zealand the majority of thermal springs are associated with magmatic hydrothermal systems in the central north island or with the rapidly uplifting bedrock in the south island s convergent fault systems however low enthalpy systems outside of these areas represent attractive targets for potential geothermal resource development the low enthalpy warm springs of banks peninsula located immediately adjacent to christchurch represent a highly understudied but potentially significant resource to the south island s most densely populated metropolitan area hosted within the eroded 11 5 8 ma volcanic complex of banks peninsula these warm springs 14 5 33 6 c represent an anomalous hydrothermal system that has been perturbed by the 2010 2016 canterbury earthquake sequence ces the february 22 2011 mw 6 2 earthquake induced observable changes to the banks peninsula warm springs system including the appearance of new warm springs within the peninsula s north western hillsborough valley we assess the origins of the volcanically hosted banks peninsula warm springs post ces using an integrated isotopic geochemical and soil gas flux approach additionally we elucidate the tectonic context and geological drivers of upper crustal fluid flow in the banks peninsula warm spring system aqueous phase emissions from the springs predominantly plot within the na k hco3 type waters and exhibit 18 o d and 13 c values of 8 30 to 9 26 v smow 60 15 to 64 19 v smow and 12 37 to 15 06 v pdb respectively soil gas flux surveys of the springs at rapaki bay revealed co2 fluxes that average 6 93 10 gm 2 day 1 with an average 13 c value of 19 81 5 v pdb and ch4 fluxes that average 5 58 12 gm 2 day 1 with an average 13 c value of 59 52 1 v pdb our results suggest that the banks peninsula warm springs are a structurally controlled upper crustal metamorphic hydrothermal heated system sourced from high altitude southern alps derived meteoric waters carbon isotope compositions of gaseous emissions associated with the banks peninsula thermal springs are consistent with an upper crustal metamorphic decarbonation and decarboxylation carbon source based on their geochemistry we propose that the banks peninsula warm springs should be considered an outboard extension of the south island s plate boundary hydrothermal system such connectivity implies that long lived low enthalpy geothermal resources may be associated with permeable and distributed fault networks in the periphery of convergent margins

water vapor isotopic composition of a stratospheric air intrusion measurements from the chajnantor plateau chile measurements of water vapor isotopic composition in stratospheric air intrusions can be used to constrain the dilution of the intrusion as it mixes into the middle troposphere the intrusion studied here occurred on 17 and 18 august 2012 with measurements obtained at an altitude of 5 km in the chilean andes at the atacama large millimeter array astronomical observatory on the chajnantor plateau surface ozone concentrations rose 16 ppb in 6 h and were associated with a potential vorticity intrusion on the 330 k isentropic surface a simulated stratospheric ozone tracer reaching chajnantor also supports the interpretation of a stratospheric intrusion beginning around 18 00 utc on 17 august the mixing ratio dropped from 3000 ppmv to 430 ppmv as the water vapor d values dropped from 153 to 438 over 13 h while the 18o values dropped from 20 to 63 the average mixing ratio d and 18o values during august 2012 were measured to be 1500 ppmv 250 and 34 respectively the minimum water vapor concentration during the intrusion was in the driest 5 of measurements made during that month while the minimum d and 18o values were within the lowest 0 5 of measurements made during that month simple two component models of mixing between stratospheric or upper tropospheric air with boundary layer air fail to reproduce observations but a three component mixing model in which the stratospheric intrusion mixes with an upper tropospheric background air mass as it mixes with boundary layer air on chajnantor matches the observations

wave breaking and mixing at the subtropical tropopause abstract this paper discusses rossby wave breaking on the isentropic surfaces that intersect the subtropical tropopause using winds and isentropic potential vorticity from high resolution meteorological analysis the focus is both on particular aspects of individual wave breaking events as well as on more general aspects such as the spatial and temporal distribution of the mixing associated with these events the direction and intensity of wave breaking is shown to exhibit the same dependence on stagnation points in the wind field as that seen in previous highly idealized numerical model studies wave breaking that results in stratospheric intrusions into the troposphere can be categorized as weak or strong depending on the development of filaments or larger coherent vortices or cutoff lows the events presented show a deep vertical structure that approximately spans the region between the 330 k and 370 k isentropic surfaces where the tropopause is steeply sloping through the subtropical jets this i

sealing capacity of clay cap units above the cerro pabellon hidden geothermal system northern chile derived by soil co2 flux and temperature measurements abstract cerro pabellon is a hidden high enthalpy geothermal system reservoir temperature up to 250 c located in the pampa apacheta northern chile where the first geothermal power plant in south america is currently operating a fumarolic field located on the summit of apacheta volcano about 3 5 km w of pampa apacheta is the only evidence of the presence of a degassing magma connected to the surface co 2 soil flux and temperatures on a grid of 400 points were measured to understand the absence of any other thermal manifestations more than 90 of the measured co 2 flux values were below background estimated at 1 35 g m 2 day 1 whereas the associated soil temperatures mean value 19 4 c carried out at 10 cm depth were related at least partially to an endogenous though weak thermal anomaly no spatial correlation was observed between soil co 2 flux and temperature measurements suggesting a minimal role played by the volcano tectonic structures in the circulation of geothermal fluids soil temperature gradients measured on a grid of 85 points in the active fumarolic field where acid waters and magmatic gases are discharged revealed the only strong thermal anomaly temperatures up to 83 c of the area the thick argillic clay cap 300 m located above the geothermal reservoir has a pivotal role in preventing the resurgence of fluids whereas an efficient interaction between the rising magmatic fluids and the liquid dominated reservoir favours acidic gas scrubbing processes thus allowing the ascent of a steam depleted in magmatic compounds this steam interacts with the shallower discontinuous aquifer s below pampa apacheta with the consequent nearly complete dissolution of co 2 and h 2 s and heating of the shallow groundwater this results in low co 2 fluxes and extended slight thermal anomaly at the surface finally an integrated conceptual model using our results and available geological mineralogical geochemical and geophysical data of the cerro pabellon hidden geothermal system is presented with the aim of providing criteria for geothermal exploration of similar high enthalpy geothermal systems in the andes that also exhibit a lack of thermal surface features

dynamics of an interhemispheric teleconnection across the critical latitude through a southerly duct during boreal winter abstractin this study an interhemispheric teleconnection pattern across the critical latitude from southern africa through south asia to the north pacific was revealed in boreal winter monthly averaged 250 hpa streamfunction fields obtained from both the 40 yr ecmwf re analysis era 40 and the ncep ncar reanalysis data from 1957 58 to 2001 02 classical rossby wave theory for zonally varying flow in which the effects of the basic state meridional wind are ignored predicts that stationary rossby waves cannot propagate across easterlies to elucidate the underlying mechanisms responsible for this interhemispheric teleconnection the theoretical basis for stationary wave propagation across the critical latitude is considered taking into account meridional ambient flow the theoretical results suggest that the southerly flow over east africa the western indian ocean and south asia creates a path for the northward propagation of stationary waves across the critical latitude stationary wavenumber and grou

soil δ13c co2 and co2 flux in the h2s rich rotorua hydrothermal system utilizing cavity ring down spectroscopy abstract diffuse soil co2 flux and stable carbon isotope surveys facilitate interpretation of the nature and structure of hydrothermal systems although soil co2 flux measurements are completed in the field isotopic carbon in co2 i e 13c co2 analyses are more commonly performed in a stable isotope mass spectrometry laboratory thereby increasing the effort time and resources required to complete the survey cavity ring down spectroscopy crds overcomes these challenges by enabling both co2 isotopic and flux analyses in field settings however h2s interference has limited crds applications in h2s rich hydrothermal settings here we assess the application of a mobile crds system equipped with a simple cu wire trap to complete 13c co2 and co2 flux surveying in the relatively high h2s rotorua hydrothermal system rhs north island new zealand laboratory experiments demonstrate that the cu trap was able to remove h2s 250 ppmv enabling accurate and precise 13c co2 measurements in the rhs the cu trap successfully removed h2s concentrations during in situ soil gas analyses carbon dioxide fluxes determined using the crds were found be 102 of those values produced by a traditional soil gas flux meter i e licor carbon dioxide flux determined by crds was similar to previous studies in the rhs however zones of high co2 flux in central kuirau park have moved 100 200 m in the past twelve years isoscapes of 13c co2 for the rhs were constructed from our soil gas survey results and were used to assess the apportionment of magmatic hydrothermal versus biogenic co2 release our findings demonstrate that a crds enabled system allows for faster in field survey measurement lower cost and reactive sampling for both 13c co2 and co2 flux measurement in h2s enriched hydrothermal systems