links between southwestern tropical indian ocean sst and precipitation over southeastern africa over the last 17 kyr abstract time series of mg ca ba ca and 18o analyzed in tests of surface dwelling planktonic foraminifer globigerinoides ruber from two marine sediment cores recovered in the mozambique channel off the zambezi river southwestern tropical indian ocean reveal climate variability over the last 17 kyr analysis of samples collected from the water column of the mozambique channel validates that mg ca in g ruber reflects calcification temperatures at 0 30 m water depth and that the surface water of the southwestern indian ocean is very sensitive to dissolved ba input from adjacent rivers foraminiferal ba ca and mg ca time series are used to reconstruct hydrological and thermal changes over southeastern african and southwestern tropical oceans the mg ca based sea surface temperature sst estimates indicate that the thermal evolution of the tropical southwestern indian ocean followed within age model uncertainties climate changes over antarctica the trend of the sst record is marked by a gradual warming from 24 7 0 6 c at 17 0 0 2 kyr bp to 26 4 0 3 c at 10 11 kyr bp interrupted by two prominent coolings of 1 5 0 2 c and 1 c centered at 15 0 1 kyr bp and 13 4 0 2 kyr bp respectively declining ssts in the early holocene reach their minimum 25 c at 8 7 0 2 kyr bp and give way to stable thermal conditions over the middle and late holocene the ba ca record indicates that the zambezi basin experienced relatively wet conditions during the early phase of the last deglaciation bolling allerod and the early holocene these wet phases coincide with an increase of sst in the mozambique channel in contrast relatively dry conditions throughout the middle and late holocene epoch are accompanied by relatively cold mozambique channel surface water these shifts likely reflect a response to meridional shifts of the austral westerlies and subtropical front these hypothesized shifts would have modulated the advection of cold southern ocean water into the mozambique channel changes in sst in the mozambique channel and possible resultant changes in the zonal gradient in the tropical indian ocean in turn had a strong impact on the precipitation over southeastern africa

bioerosion structures in crepidula mollusca gastropoda as indicators of latitudinal palaeoenvironmental changes example from the marine quaternary of argentina abstract late quaternary marine skeletal concentrations from argentina are rich in molluscs exhibiting a great variety of bioerosion structures the shells of crepidula a characteristic gastropod occurring along more than 2000 km of coastline between the rio de la plata margin and southern patagonia show traces of dwelling predation and anchoring activities made by porifers bryozoans annelids other gastropods and brachiopods caulostrepsis entobia maeandropolydora iramena oichnus finichnus pennatichnus pinaceocladichnus podichnus and renichnus occur on the outer shell surface finichnus and oichnus are the only traces present along the entire area and the full time span considered the most characteristic structures are produced by bryozoans polychaetes and predatory gastropods traces produced by annelids and predatory gastropods occur preferentially in the central shell sector where predators gained access to the soft parts of the prey by contrast encrusting or branching bryozoan colonies are widely distributed as they can attach to any sector regardless of shell features available no strict correlation is evident between ichnodiversity and either time or latitude but ichnodiversity is linked to local oceanographical biotic controls for patagonia with a great majority of ichnotaxa made by bryozoans the general trend of higher bioerosion degree and ichnodiversity at higher latitudes is controlled by sea surface temperature productivity for the modern and the holocene several ichnodiversity peaks match with well constrained conditions substrate salinity thermal fronts by contrast this does not hold for the pleistocene dissimilar conditions probably prevailed especially during the last interglacial colder waters richer in nutrients

equatorial vertical drift modulation by the lunar and solar semidiurnal tides during the 2013 sudden stratospheric warming during the 2013 stratospheric sudden warming ssw period the jicamarca unattended long term investigations of the ionosphere and atmosphere julia radar at jicarmarca peru observed low latitude vertical drift modulation with lows of 0 12 m s daytime maximum drifts between 6 13 and 22 25 january and enhanced drifts up to 43 m s between 15 snd 19 january the ncar thermosphere ionosphere mesosphere electrodynamics general circulation model reproduces the prevailing vertical drift feature and is used to examine possible causes the simulations indicate that the modulation of the vertical drift is generated by the beating of the semidiurnal solar sw2 and lunar m2 tides during the ssw period the beating is observable since the magnitudes of lunar and solar semidiurnal tidal amplitudes are comparable the theoretical beating frequency between sw2 and m2 is 1 15 13 day which may be modified due to phase changes this study highlights the importance of the lunar tide during ssw periods and indicates that the equatorial vertical drift modulation should be observable at other longitudes as well

can we probe the conductivity of the lithosphere and upper mantle using satellite tidal magnetic signals thesis s m massachusetts institute of technology department of earth atmospheric and planetary sciences 2015

electrical conductivity of the earth s mantle from the first swarm magnetic field measurements we present a 1 d electrical conductivity profile of the earth s mantle down to 2000 km derived from l1b swarm satellite magnetic field measurements from november 2013 to september 2014 we first derive a model for the main magnetic field correct the data for a lithospheric field model and additionally select the data to reduce the contributions of the ionospheric field we then model the primary and induced magnetospheric fields for periods between 2 and 256 days and perform a bayesian inversion to obtain the probability density function for the electrical conductivity as function of depth the conductivity increases by 3 orders of magnitude in the 400 900 km depth range assuming a pyrolitic mantle composition this profile is interpreted in terms of temperature variations leading to a temperature gradient in the lower mantle that is close to adiabatic

role of continents in driving the hadley cells gcm simulations are used to investigate how forcing that originates over land surfaces influences the hadley circulation the presence of continental surfaces is found to approximately double the intensity of the winter hemisphere hadley cell and to halve the intensity of the summer cell the strengthening of the winter cell occurs because the increase in surface friction associated with land enhances the angular momentum flux into the atmosphere the development of strong monsoon circulations in the northern hemisphere summer and the convergence zones of the southern hemisphere south pacific south atlantic and south indian convergence zones shifts mass out of the subtropics lowers the zonal mean subtropical highs and weakens the summer cells the responses of the summer and winter cells are different signs and occur by different processes because heating of the land surfaces in the summer is effectively communicated through the depth of the atmosphere whereas cooling in the winter is not also the higher surface wind speeds and shears of the winter hemisphere trade winds make the winter cell more sensitive to surface friction than the summer cell these results suggest that the axisymmetric models that have provided a theoretical basis for the understanding of the hadley circulation do not capture some of the important physical processes that determine the intensity of the mean meridional circulation

tidal signals in ocean bottom magnetic measurements of the northwestern pacific observation versus prediction summary motional induction in the ocean by tides has long been observed by both land and satellite measurements of magnetic fields while these signals are weak 10 nt when compared to the main magnetic field their persistent nature makes them important for consideration during geomagnetic field modelling previous studies have reported several discrepancies between observations and numerical predictions of the tidal magnetic signals and those studies were inconclusive of the source of the error we address this issue by 1 analysing magnetometer data from ocean bottom stations where the low noise and high signal environment is most suitable for detecting the weak tidal magnetic signals 2 by numerically predicting the magnetic field with a spatial resolution that is 16 times higher than the previous studies and 3 by using four different models of upper mantle conductivity we use vector magnetic data from six ocean bottom electromagnetic obem stations located in the northwestern pacific ocean the obem tidal amplitudes were derived using an iteratively re weighted leastsquares irls method and by limiting the analysis of lunar semidiurnal m2 lunar elliptic semidinurnal n2 anddiurnal o1 tidalmodestothenight time usinga3 delectromagnetic induction solver and the tpx07 2 tidal model we predict the tidal magnetic signal we use earth models with non uniform oceans and four 1 d mantle sections underneath taken from kuvshinov and olsen shimizu et al and baba et al to compare the effect of upper mantle conductivity we find that in general the predictions and observations match within 10 70percent across all the stations for each of the tidal modes the median normalized percent difference npd between observed and predicted amplitudes for the tidal modes m2 n2 and o1were15percent 47percentand98percent respectively forallthestationsandmodels at the majority of stations and for each of the tidal modes the higher resolution 0 25 0 25 modelling gave amplitudes consistently closer to the observations than the lower resolution 1 1 modelling the difference in lithospheric resistance east and west of the izu bonin trench system seems to be affecting the model response and observations in the o1 tidal mode this response is not seen in the m2 and n2 modes thereby indicating that the o1 mode is more sensitive to lithospheric resistance

on the likelihood of tropical extratropical cloud bands in the south indian convergence zone during enso events abstractthe southern hemisphere subtropical convergence zones are important regions of rainfall in the subtropics the south indian ocean convergence zone sicz has the strongest seasonality and exhibits substantial interannual variability in strength and position during austral summer on synoptic time scales the sicz is a preferred region for the formation of tropical extratropical te cloud bands with local maxima over the southern african mainland and madagascar this study investigates how the seasonality in satellite observed cloud band frequency emerges from the interplay between the asynchronous seasonal cycles in convective instability and upper level flow as represented by reanalysis data these atmospheric mean states are diagnosed with a gross convective instability metric and a method to distinguish between subtropical and eddy driven jet axes month by month analysis of these diagnostics elucidates how mean state perturbations during enso events modify cloud band likelihood typically 1

land atmosphere ocean interactions in the southeastern atlantic interannual variability land atmosphere ocean interactions in the southeastern south atlantic and their connections to interannual variability are examined using a regional climate model coupled with an intermediate level ocean model in austral summer zonal displacements of the south atlantic subtropical high sash can induce variations of mixed layer currents in the benguela upwelling region through surface wind stress curl anomalies near the namibian coast and an eastward shifted sash is related to the first pacific south american mode when the sash is meridionally displaced mixed layer vertically integrated ekman transport anomalies are mainly a response to the change of alongshore surface wind stress the latitudinal shift of the sash tends to dampen the anomalous alongshore wind by modulating the land sea thermal contrast while opposed by oceanic diffusion although the position of the sash is closely linked to the phase of el nino southern oscillation enso and the southern annular mode sam in austral summer an overall relationship between benguela upwelling strength and enso or sam is absent during austral winter variations of the mixed layer ekman transport in the benguela upwelling region are connected to the strength of the sash through its impact on both coastal wind stress curl and alongshore surface wind stress compared with austral summer low level cloud cover change plays a more important role although wintertime sea surface temperature fluctuations in the equatorial atlantic are strong and may act to influence variability over the northern benguela area the surface heat budget analysis suggests that local air sea interactions dominate

cm5 a pre swarm comprehensive geomagnetic field model derived from over 12 yr of champ orsted sac c and observatory data a comprehensive magnetic field model named cm5 has been derived from champ rsted and sac c satellite and observatory hourly means data from 2000 august to 2013 january using the swarm level 2 comprehensive inversion ci algorithm swarm is a recently launched constellation of three satellites to map the earth s magnetic field the ci technique includes several interesting features such as the bias mitigation scheme known as selective infinite variance weighting sivw a new treatment for attitude error in satellite vector measurements and the inclusion of 3 d conductivity for ionospheric induction sivw has allowed for a much improved lithospheric field recovery over cm4 by exploiting champ along track difference data yielding resolution levels up to spherical harmonic degree 107 and has allowed for the successful extraction of the oceanic m2 tidal magnetic field from quiet nightside data the 3 d induction now captures anomalous solar quiet features in coastal observatory daily records cm5 provides a satisfactory continuous description of the major magnetic fields in the near earth region over this time span and its lithospheric ionospheric and oceanic m2 tidal constituents may be used as validation tools for future swarm level 2 products coming from the ci algorithm and other dedicated product algorithms

variability of the south atlantic convergence zone simulated by an atmospheric general circulation model interannual and decadal variability of the south atlantic convergence zone sacz during austral summer season january february march jfm is investigated an attempt is made to separate the forced variability from the internal variability this is accomplished by applying a signal to noise optimization procedure to an ensemble of multidecadal integrations of the latest version of the ncar community climate model ccm3 forced with observed sst the result yields two dominant forced atmospheric responses a local response to atlantic sst anomalies with interannual decadal timescales and a remote response to pacific sst anomalies at interannual timescales the former is localized within the south atlantic ocean with almost no signal over land consisting of a dipolelike structure in precipitation close to the coast of south america accompanied by a clockwise anomalous circulation of surface winds the latter manifests itself mainly in the upper level circulation consisting of a northeastward shift of the sacz with associated rainfall anomalies during warm enso events

extracting ocean generated tidal magnetic signals from swarm data through satellite gradiometry ocean generated magnetic field models of the principal lunar m2 and the larger lunar elliptic n2 semidiurnal tidal constituents were estimated through a comprehensive inversion of the first 20 5 months of magnetic measurements from european space agency s esa swarm satellite constellation mission while the constellation provides important north south along track gradiometry information it is the unique low spacecraft pair that allows for east west cross track gradiometry this latter type is crucial in delivering an m2 estimate of similar quality with that derived from over 10 years of champ satellite data but over a shorter interval at higher altitude and during more magnetically disturbed conditions recovered n2 contains nonoceanic signal but is highly correlated with theoretical models in regions of maximum oceanic amplitude thus satellite magnetic gradiometry may eventually enable the monitoring of ocean electrodynamic properties at temporal resolutions of 1 to 2 years which may have important implications for the inference of ocean temperature and salinity

paleozoic brachiopod symbioses testing the limits of modern analogues in paleoecology paleoecologic interpretations involving symbiotic interactions begin with a determination that the partners were simultaneously alive criteria for recognizing live live interactions among benthic suspension feeders include 1 preferred locations of symbionts on encrusting or in boring or embedding the host 2 preferred orientations of elongate symbionts or clustering of symbiont apertures and feeding structures in relation to host induced currents and 3 growth abnormalities and or distortions of the host the symbiont or both interpretations of the nutritional aspects of ancient symbioses involve establishment of feeding locations and methods and the diets of holocene descendants however use of living analogues and hence their value in paleoecology commonly invoke the unwarranted assumption that the host symbiont interaction and the foods available to the partners have not evolved in concert with their skeletons these nutritional uncertainties are compounded further in symbioses involving fossils of unknown biological affinities or taxa that have evolved by different rules analyses of paleozoic brachiopod symbioses spanning the gamut from symbionts of undoubted ancestor descendent relations e g spirorbis to trace fossils e g trypanites exemplify these nutritional uncertainties most of these symbionts suggest that in life spiriferaceans were attached to the substrate by a thick short pedicle and that the hinge line and or umbo of the brachial valve acted as a fulcrum to elevate the commissure into the water column for efficient suspension feeding conversely the same symbionts provide equivocal results when used to infer the circulation pattern of spiriferacean mantle cavity currents these analyses also exemplify the great limitations of uniformitarian concepts in evolving biological systems

spherical harmonic analysis of geomagnetic tides 1964 1965 the mathematical forms chosen for analyses of s q and l by seventeen different authors are reviewed on the basis of the review and on consideration of the ionospheric dynamo theory and the hough function structure of wind velocities in the upper atmosphere a mathematical model is chosen that includes two more terms than the recent analysis by malin 1973 hourly mean values from 130 magnetic observatories for the i q s ys international quiet solar years 1964 and 1965 were prepared in machine readable form and analysed the solar and lunar transient magnetic variations were evaluated together with the lunar elliptic magnetic tide and the seasonal change at one and two cycles per year for all magnetic tides spherical harmonic analyses were made of the phase law tides and the smaller partial tides altogether 94 different spherical harmonic analyses were completed for a total of ten different magnetic tides two of the ten tides are the solar and lunar magnetic tides usually denoted s and l respectively the results are tabulated in a form that distinguishes between eastward and westward moving terms which is suitable for the evaluation of phase angle differences and amplitude ratios between internal and external parts malin s ocean dynamo calculation has been applied to the lunar and lunar elliptic magnetic tides the spherical harmonic coefficients are compared in some detail with those of malin 1973 for years of high sunspot activity the magnetic tidal potential associated with a given atmospheric tidal mode is derived theoretically and used to obtain an estimate of the hough function components of the solar and lunar semi diurnal atmospheric tides at ionospheric levels from the corresponding magnetic tidal potential

lunar tidal winds between 80 and 110 km from uars hrdi wind measurements 1 recent observations and models show the considerable effects of upward propagating lunar atmospheric tides on many aspects of the ionosphere thermosphere system a key aspect of atmosphere ionosphere coupling is the wind field in the ionospheric e region circa 100 150 km where the dynamo generation of electric fields occurs yet global specifications of lunar tidal winds exist only in theoretical predictions although years of satellite observations on atmospheric winds exist with almost global coverage in the present paper we report on quasi global semidiurnal lunar tidal winds up to 115 km from data gathered by the high resolution doppler imager hrdi on board the upper atmosphere research satellite during the early years from 1991 to 1999 the observed lunar semidiurnal tidal winds are consistent with global scale wave model gswm simulations in both amplitude and phase with maximum amplitudes located between about 40 n 60 n around the solstices the peak amplitudes of the lunar tidal winds lie in the 10 15 ms 1range whereas those simulated by gswm lie between 15 and 25 ms 1 the smaller hrdi amplitudes are likely due in part to amplitude suppression in construction of the climatological mean resulting from year to year phase variability in the lunar tide it is also possible that wave dissipation is underestimated to some degree in the gswm

lunar daily geomagnetic variations in new zealand summary lunar daily geomagnetic variations l exhibit distinctive behaviour at many sites near coasts in this study data from an array of three component magnetometers that operated for a four month summer period at 22 sites throughout new zealand are used to examine l the chapman miller method is used to determine the four main luni solar harmonics of l at each site analysis of 3 5 years of data from the geomagnetic observatory at eyrewell indicates that the array data produce representative values of l separation of the dominant lunar semidiurnal harmonic l2 into parts of oceanic and ionospheric origin indicates near uniform ionospheric contributions to the x and y field components at all sites with peak values occurring within 3 hours of lunar transit the ionospheric contribution to the 2 field component is smaller and suggests secondary electric currents flowing in the deep water to the north east and south west of new zealand the oceanic contribution to l tends not to be significant for x and y its amplitude for 2 is greatest in the eastern north island and in the south western south island and its phase angle for z is locally consistent throughout the north island and in the south western south island the difference between the phase angles that characterize these northern and southern regions is about 180 this pattern suggests near parallel in phase electric currents flowing in the deep water to the north east and south west of new zealand in response to tidal flows this is in agreement with both the general pattern seen in the united kingdom and lunar daily geomagnetic variations observed under the tasman sea and in eastern australia where the magnetic effects of tidal flows in shallow coastal waters are secondary to those from more distant deep waters the oceanic contribution to l2 might be used to estimate the poorly known tidal flows in the deep water off new zealand

a global climatology of tropical moisture exports in a recent paper a climatology of tropical moisture exports tmes to the northern hemisphere nh was constructed on the basis of 7 day forward trajectories started daily from the tropical lower troposphere which were required to reach a water vaporflux of at least 100 g kg 21 ms 21 somewhere north of 358n it was shownthattmescontributesignificantlytoregionalprecipitation here theauthorscomplement andextend this work by i using 6 hourly european centre for medium range weather forecasts ecmwf interim re analysis era interim data from 1979 to 2010 instead of the earlier 40 yr ecmwf re analysis era40 ii extending the climatology to the southern hemisphere sh and iii relating tme events to atmospheric rivers ars previously discussed in the literature the main conclusions are as follows first the tme climatology is not sensitive to the reanalysis dataset second sh tme shows four activity centers the central and eastern pacific ocean 1708 908w near the south pacific convergence zone eastern south america and the adjacent atlantic ocean 608w 08 near the south atlantic convergence zone the western indian ocean 308 808e and western australia 1108 1408e third tme activity in the sh peaks in austral summer because of highermoisture contents and possiblybecause of increased rossby wave activityfrom the

characterizing the synoptic expression of the angola low the angola low is a key feature of the southern africa wet season atmosphere that influences precipitation across the continent this paper uses era interim to show that the synoptic expression of the angola low is a combination of dry heat lows and moist tropical low pressure systems the angola heat low and angola tropical low composites are contrasted against similar lows observed in other continental tropical regions and found to be broadly comparable the implications that the distinction between dry and moist events has for the interannual relationship among the angola low precipitation and enso are examined the tropical lows exhibit unusual semistationary behavior by lingering in the angola region rather than traveling offshore this behavior is proposed to be caused by an integrated sea breeze anabatic wind that enhances inhibits cyclonic vorticity stretching and convection inland near the coast the combined effect of the heat lows and the anchored tropical lows creates the angola low in the climatological average by elucidating the mechanisms of the angola low this research improves the foundation of process based evaluation of southern africa present and future climate in cmip and amip models

joint inversion of satellite detected tidal and magnetospheric signals constrains electrical conductivity and water content of the upper mantle and transition zone we present a new global electrical conductivity model of earth s mantle the model was derived by using a novel methodology which is based on inverting satellite magnetic field measurements from different sources simultaneously specifically we estimated responses of magnetospheric origin and ocean tidal magnetic signals from the most recent swarm and champ data the challenging task of properly accounting for the ocean effect in the data was addressed through full three dimensional solution of maxwell s equations we show that simultaneous inversion of magnetospheric and tidal magnetic signals results in a model with much improved resolution comparison with laboratory based conductivity profiles shows that obtained models are compatible with a pyrolytic composition and a water content of 0 01 wt and 0 1 wt in the upper mantle and transition zone respectively

the angola low relationship with southern african rainfall and enso the main states of the angola low al are identified using clustering analysis applied to daily anomalous patterns of 700 hpa wind vorticity over angola and adjacent countries from november to march for the 1980 81 2014 15 period at the daily timescale we examine the extent to which the main states of the al modulate daily rainfall over southern africa at the interannual timescale we assess both the relationship between the occurrence of these al states and el nino southern oscillation enso and the role of the al in explaining enso s failure in driving southern african rainfall at times three reanalyses are considered to account for uncertainties induced by the scarcity of data available for assimilation over southern africa three preferential states of the angola low are identified al state close to its seasonal climatology with slight zonal displacements anomalously weak al state and anomalously strong al state with meridional displacements these different states all significantly modulate daily southern african rainfall near climatological al state promotes wet rainfall anomalies over eastern subtropical southern africa and dry rainfall anomalies over its western part a slight westward shift in the near climatological position of the al leads to reversed zonal gradient in rainfall the remaining regimes significantly modulate the meridional gradient in southern african rainfall anomalously weak and anomalously northward al states promote wet rainfall anomalies over tropical southern africa and dry rainfall anomalies over subtropical southern africa the reverse prevails for anomalously southward al at the interannual timescale enso significantly modulates the seasonal occurrence of most al states in the three reanalyses anomalously weak and southward al states are more strongly correlated with regional rainfall than enso in all reanalyses suggesting that accounting for al variability may improve seasonal forecasts case study analysis of the major 1982 83 and 1997 98 el nino events suggests that the weak rainfall anomalies and strong seasonal al in 1997 98 may result from counteracting effects between enso and indian ocean coupled modes of variability

a world without greenland impacts on the northern hemisphere winter circulation in low and high resolution models to investigate the effect of greenland s orography on the northern hemisphere winter circulation experiments with an atmospheric gcm are conducted a perturbed integration where standard orography is reduced to sea level in the greenland area is compared to a standard orography control integration the outcome of these experiments suggests that the existence of high mountains at greenland causes a reinforcement of the stationary wave field in the atlantic sector colder temperatures to the west of greenland and warmer temperatures to the east and south over the north atlantic the impact on the flow field cannot be understood in the framework of standing rossby waves but it indicates a resonance between remotely forced stationary waves and local thermo dynamics the pattern of the north atlantic oscillation nao in particular the northern centre lies further to the east in the flat greenland experiment compared to the control run and the observations together with the fact that the climatological low pressure system around iceland hardly shifts this suggests that the location of the nao is not necessarily tied to the time mean pressure distributions considering the model resolution as a parameter experiments with a high resolution t106 suggest that the near field changes are represented sufficiently by a t42 resolution a standard resolution used in state of the art coupled climate models in contrast far field changes depend critically on model resolution hemispheric circulation and temperature changes differ substantially from low to high resolution and generalized statements about the impact of greenland s orography cannot be made

understanding the seasonality of orographically forced stationary waves interaction between mechanical and thermal forcing abstract idealized simulations of the atmosphere s stationary response to the rockies tibetan plateau and the greenland ice sheet are made using a nonlinear quasigeostrophic model and are compared to observations observational data indicate low level heating cooling occurs above the rockies and tibet in the summer winter low level cooling is found above greenland in both seasons the atmosphere responds to both diabatic heating termed thermal forcing and low level flow being obstructed by the mountain s presence termed mechanical forcing the response to thermal and mechanical forcing together can be very different from the response to either forcing individually the presence of modest low level heating or cooling 1 5 k day 1 causes significant changes to the mechanical forcing and thereby to the stationary wave response for example while the nonlinear response to mechanical forcing and low level heating is characterized by a cyclone over the orography the response to mechanical forc

monsoons itczs and the concept of the global monsoon earth s tropical and subtropical rainbands such as intertropical convergence zones itczs and monsoons are complex systems governed by both large scale constraints on the atmospheric general circulation and regional interactions with continents and orography and coupled to the ocean monsoons have historically been considered as regional large scale sea breeze circulations driven by land sea contrast more recently a perspective has emerged of a global monsoon a global scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation this results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone regional subsystems are embedded in this global monsoon localized by surface boundary conditions parallel with this much theoretical progress has been made on the fundamental dynamics of the seasonal hadley cells and convergence zones via the use of hierarchical modeling approaches including aquaplanets here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings after summarizing the dynamical and energetic balances that distinguish an itcz from a monsoon we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets limitations of current theories are discussed including the need for a better understanding of the influence of zonal asymmetries and transients on the large scale tropical circulation

a southern hemisphere wave response to enso with implications for southern africa precipitation ensemble gcm simulations with an imposed idealized warming of the eastern pacific ocean reveal two wave anomalies in the southern hemisphere one in the eastern and one in the western hemisphere both are statistically significant at the 99 confidence level application of a steady state linear model and a rossby wave source analysis is used to diagnose the causes of the waves the western hemisphere wave is forced by the advection and stretching of planetary vorticity by the divergent flow from the southern hemisphere component of the central pacific twin anticyclones that straddle the equator during warm events the eastern hemisphere wave is a result of the northeastward shift of the south indian convergence zone sicz that in turn is forced from the upper troposphere by convergence to the north an upper level convergence maximum over the equatorial indian ocean induces divergence to the south encouraging vertical motion and precipitation to the northeast of the sicz s normal position the resulting anomalous upper level convergence in the climatological position of the sicz as well as the anomalous vorticity flux convergence by the transients associated with an equatorward shift of the storm track behind the sicz force the eastern hemisphere rossby wave since a shift of the sicz is a fairly robust observed consequence of enso events these results suggest the mechanism by which drought conditions develop over southern africa at the height of many warm events seasonal prediction capabilities in this region can be improved by monitoring and understanding the details and consequences of the adjustment of the walker circulation near the equator outside of the pacific ocean basin

large scale atmospheric circulation related to frequent rossby wave breaking near japan in boreal summer abstractrossby wave propagation along asian jet during boreal summer such as silk road pattern frequently causes wave breaking near the asian jet exit region this study examines statistical rela

orographically induced stationary waves dependence on latitude abstract a general circulation model gcm with idealized boundary conditions is used to study the effects of a mountain s latitudinal position on the stationary wave response in each of a series of experiments the only asymmetry in the boundary conditions is a gaussian shaped mountain with an e folding width of 15 latitude placed at 0 15 30 45 and 60 latitude in separate integrations the stationary wave response in the gcm is analyzed using a linearized primitive equation model a 3d wave flux vector and a barotropic ray tracing technique stationary waves in the gcm are generated by modifications to the diabatic heating field termed thermal forcing and by obstructing the surface winds termed mechanical forcing with a mountain at 0 latitude latent heating anomalies provide the forcing mechanism in the 15 mountain experiment forcing by anomalous latent heating is also found but mechanical forcing which occurs within the easterlies seems to dominate in the 30 45 and 60 mounta

an investigation of interannual rainfall variability in africa abstract interannual variations in african rainfall are examined using rotated principal component analysis pca applied to anomalies from the annual mean as well as seasonal anomalies the rotated pca loading patterns suggest several preferred continental scale rainfall anomaly patterns the dominant features of year to year variations in african rainfall appear to be the high spatial coherence of rainfall anomalies over large portions of the continent in addition several dipole regions that is adjacent regions which tend to experience rainfall anomalies of opposite sign are found and discussed one dipole region the sub saharan region appears to have a relationship with a characteristic atlantic sea surface temperature anomaly pattern during boreal summer during austral summer the tendency for a large scale dipole pattern in southeast africa is apparent as is an association of this pattern with the warm and cold phases of the el nin southern oscillation enso phenomenon normalized rainfal

lunar tide in the equatorial electrojet in relation to stratospheric warmings 1 the relationship between sudden stratospheric warmings ssws and large amplitude lunar tides in the equatorial electrojet eej is studied analysis of ground magnetometer data shows that the lunar tide in the eej is maximum during the northern winter season except in the pacific ocean region since ssws are also a northern winter phenomenon it is suggested that the relation between the large lunar tide in the eej and the ssw may possibly be coincidental the lunar tide in the geomagnetic variations at huancayo is anomalously large compared with other eej stations an examination of geomagnetic variations at eej stations during ssw events shows that afternoon counter electrojets are frequently present at new moon and full moon though the relationship is sometimes broken the observation of large lunar eejs when no ssw is present and of various different delay times suggests that other atmospheric processes are likely to be in play

first record of podichnus in orthide brachiopods from the lower ordovician tremadocian of nw argentina and its relation to the early use of an ethological strategy abstract well preserved etchings from the pedicle attachment of brachiopods occur on orthide brachiopod shells from lower ordovician tremadocian of nw argentina under the name podichnus conicus isp n this trace fossil is interpreted as a fixichnia produced by the attachment of brachiopod pedicles upon hard substrates the trace is characterized by an irregular and asymmetrical cluster of circular pits each individual pit has a typical conical shape and presents the external mean diameter length ratio close to 1 the occurrence of p conicus isp n in the tremadocian is the oldest record of this ichnogenus and points to orthide brachiopods as podichnus producers for the first time the presence of this structure provides new information regarding colonization of biogenic hard substrates during the early ordovician and an adaptive strategy of its use by orthide brachiopods

3 d modelling the electric field due to ocean tidal flow and comparison with observations 1 the tidal motion of the ocean water through the ambient magnetic field generates secondary electric field this motionally induced electric field can be detected in the sea or inland and has a potential for electrical soundings of the earth a first goal of the paper is to gain an understanding of the global distribution of the electric signal due to tidal ocean flow we simulate the electric signals for two tidal constituents lunar semidiurnal m2 and diurnal o1 tides we assume a realistic earth s conductivity model with a surface thin shell and 1 d mantle underneath simulations demonstrate that in some coastal regions the amplitudes of the electric field can reach 100 mv km and 10 mv km for m2 and o1 tides respectively the changes of lithosphere resistance produce detectable changes in the tidal electric signals we show that our predictions are in a good agreement with observations

ionosphere variability during the 2009 ssw influence of the lunar semidiurnal tide and mechanisms producing electron density variability to investigate ionosphere variability during the 2009 sudden stratosphere warming ssw we present simulation results that combine the whole atmosphere community climate model extended version and the thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm the simulations reveal notable enhancements in both the migrating semidiurnal solar sw2 and lunar m2 tides during the ssw the sw2 and m2 amplitudes reach 50 m s 1 and 40 m s 1 respectively in zonal wind at e region altitudes the dramatic increase in the m2 at these altitudes influences the dynamo generation of electric fields and the importance of the m2 on the ionosphere variability during the 2009 ssw is demonstrated by comparing simulations with and without the m2 time gcm simulations that incorporate the m2 are found to be in good agreement with jicamarca incoherent scatter radar vertical plasma drifts and constellation observing system for meteorology ionosphere and climate cosmic observations of the maximum f region electron density the agreement with observations is worse if the m2 is not included in the simulation demonstrating that the lunar tide is an important contributor to the ionosphere variability during the 2009 ssw we additionally investigate sources of the f region electron density variability during the ssw the primary driver of the electron density variability is changes in electric fields changes in meridional neutral winds and thermosphere composition are found to also contribute to the electron density variability during the 2009 ssw the electron density variability for the 2009 ssw is therefore not solely due to variability in electric fields as previously thought

upper mesospheric lunar tides over middle and high latitudes during sudden stratospheric warming events in recent years there have been a series of reported ground and satellite based observations of lunar tide signatures in the equatorial and low latitude ionosphere thermosphere around sudden stratospheric warming ssw events this lower atmosphere ionosphere coupling has been suggested to be via the e region dynamo in this work we present the results of analyzing 6 years of hourly upper mesospheric winds from specular meteor radars over a midlatitude 54 n station and a high latitude 69 n station instead of correlating our results with typical definitions of ssws we use the definition of polar vortex weaking pvw used by zhang and forbes 2014 this definition provides a better representation of the strength in middle atmospheric dynamics that should be responsible for the waves propagating to the e region we have performed a wave decomposition on hourly wind data in 21 day segments shifted by 1 day in addition to the radar wind data the analysis has been applied to simulations from whole atmosphere community climate model extended version and the thermosphere ionosphere mesosphere electrodynamics general circulation model our results indicate that the semidiurnal lunar tide m2 enhances in northern hemispheric winter months over both middle and high latitudes the time and magnitude of m2 are highly correlated with the time and associated zonal wind of pvw at middle high latitudes m2 in the upper mesosphere occurs after before the pvw at both latitudes the maximum amplitude of m2 is directly proportional to the strength of pvw westward wind we have found that m2 amplitudes could be comparable to semidiurnal solar tide amplitudes particularly around pvw and equinoxes besides these general results we have also found peculiarities in some events particularly at high latitudes these peculiarities point to the need of considering the longitudinal features of the polar stratosphere and the upper mesosphere and lower thermosphere regions for example during ssw 2009 we found that m2 enhances many days before pvw which is not in agreement with most of our results

modeling and observations of martian stationary waves abstract a linear coordinate model is used in conjunction with a mars gcm northern hemisphere winter zonal mean circulation to study the orographically forced stationary disturbances on mars the disturbances are compared to their counterparts on earth and to the bright streak data from the mariner 9 and viking images diabatic heating on mars is predominantly radiative and inversion near the surface causes mountains to cool and depressions to heat the atmosphere due to the short radiative timescales and large meridional surface pressure gradient the atmosphere responds to radiative forcing by changing its temperature and pressure gradient the strong meridional flow near the equator and short radiative timescales combine to make responses to mechanical and thermal forcing of the same order in the tropics and in parts of the northern midlatitudes in the subtropics small zonal and meridional flows allow the response to radiative forcing to dominate all these factors contribute to making the martian

sclerobionts on biogenic substrates from the monte leon formation lower miocene in santa cruz province argentina taphonomic and paleoenvironmental considerations abstract study of hard substrate communities in a paleoenvironmental and taphonomic context contributes towards increasing knowledge on the depositional environments and on the history of the substrate colonized before final burial in this work we study traces produced by sclerobionts on biogenic substrates from two shell concentrations in the monte leon formation lower miocene exposed at cabeza de leon southern patagonia argentina the aims of this study are to describe the bioerosion traces and to infer the taphonomic history of the hard substrates mollusk shells based on ichnodiversity and sclerobiont distribution together with other preservational features fifteen ichnotaxa were identified at different taxonomic ranks one ichnofamily three ichnogenera and eleven ichnospecies traces produced by bryozoans were highly predominant followed by those produced by sponges foraminifera and polychaetes the biogenic substrates on which the sclerobionts settled were gastropod and bivalve shells showing different taphonomic signatures shells with high fragmentation and surface alteration are dominant suggesting that they were reworked by wave action before deposition and final burial on the other hand well preserved shells reflect less reworking and shorter transport distance the mixture of these elements could be the result of short term high energy events such as storms yet these taphonomic signatures were modified later by biologic factors mainly bryozoan bioerosion in a quiet and shallow environment with a low sedimentation rate and abundant nutrient availability bioerosion valuation in conjunction with other taphonomic attributes allowed identifying the concentrations as of mixed origin biogenic sedimentologic and including elements that underwent different taphonomic histories the results contribute to improve the knowledge about marine hard substrate communities in middle to high latitudes of the southern hemisphere in addition they highlight the importance of conducting studies on these communities in conjunction with other taphonomic data when elucidating the history of colonized substrates

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

a multiscale framework for the origin and variability of the south pacific convergence zone the diagonal south pacific convergence zone spcz is the major climatological precipitation feature over the pacific region during the northern hemisphere winter however the basic mechanisms that control its structure and variability are only partly understood here an analysis of the spcz is carried out in a multiscale framework this identifies two modes that dominate a westward shifted spcz and an enhanced spcz which occur independently of each other within both modes the primary mechanism for the initiation of precipitation is a transient synoptic wave propagating along the subtropical jet which is then refracted by the basic state toward the westerly duct over the central equatorial pacific individual vorticity centres in the wave become elongated with a diagonal northwest southeast tilt convection then occurs in a diagonal band in the poleward flow ahead of the cyclonic vorticity anomaly in the wave however latent heat release in the convection leads to upper tropospheric divergence and anticyclonic vorticity forcing which dissipates the wave shutting off the convective forcing and stopping the precipitation hence each individual wave or event only lasts a few days and contributes a discrete pulse of diagonally oriented precipitation to the region the sum of these events leads to the diagonal climatological spcz event occurrence is a stochastic process the probability of which is modified by lower frequency variability of the basic state including the madden julian oscillation mjo and el nino southern oscillation enso for example during periods of enhanced convection over the eastern indian ocean to western pacific mjo phases 3 6 and la nina the westerly duct expands westwards allowing synoptic waves to refract equatorwards earlier and increasing the probability of westward shifted spcz events hence both the existence and variability of the spcz depend fundamentally on scale interactions between dynamical processes on time scales ranging from daily to interannual copyright 2011 royal meteorological society

mechanisms by which surface drying perturbs tropical precipitation fields abstract the observed precipitation climatology in austral summer has a pronounced longitudinal gradient across africa and south america a low resolution general circulation model gcm with a simple continent centered on the equator is used to understand how the presence of the land surface generates this gradient and the role of surface wetness in determining its magnitude in the model precipitation is enhanced on the east coast of the continent in the summer hemisphere tropics with magnitude and location independent of surface wetness precipitation rates are lower in the continental interior and in the west as the surface becomes drier resulting in a longitudinal precipitation gradient that is similar to observations modeled low level moisture convergence and wind convergence anomalies mimic the precipitation anomalies over all but the driest land surfaces a linearized primitive equation model is used to identify the physical mechanisms responsible for the gcm s dynamical response dry convecti

diabatic rossby waves in the southern hemisphere diabatic rossby waves drws are a special type of low level cyclone with a self maintaining mechanism given an environment of moderate or strong baroclinicity and abundant moisture under certain conditions these shallow cyclones associated with a cyclonic low level pv anomaly can serve as precursors for explosive cyclone intensification the present study is the first to investigate drws in the southern hemisphere sh two typical drw case studies are presented and a sophisticated algorithm is used to detect drws in operational analysis data from 2001 to 2012 drws occur in all ocean basins and seasons with a maximum in summer on average about four drws are found per month and 12 intensify explosively thereby they contribute 6 to the total set of explosively deepening extratropical cyclones in the sh drw tracks originate slightly closer to the equator than normal extratropical cyclones and they follow the convergence zones eastward and poleward this results in a climatological drw track density similar to a spiral from the western south pacific ending in the eastern south indian ocean broken only by the andes typical synoptic situations associated with drw genesis are identified the categories include i low level pv generation by upper level induced lifting ii low level jet induced diabatic pv generation and iii transformation of the low tropospheric pv anomaly from another system

extratropical forcing of tropical wave disturbances along the indian ocean itcz the role of extratropical waves in the excitation of tropical waves on submonthly timescales is explored along the indian ocean intertropical convergence zone itcz during the austral summer using japanese reanalysis products and noaa outgoing longwave radiation data the analysis period is december february of 1979 1980 to 2008 2009 the submonthly tropical waves are regarded as a type of rossby wave propagating along the mean monsoon westerly flow they play an important role in modulating the indian ocean itcz convection the linkage between the tropical and extratropical waves which is responsible for the formation and strengthening of tropical waves is examined composite analysis results linked to the tropical wave train development show that the midlatitude rossby wave train progresses eastward and northeastward from the south atlantic into the subtropical indian ocean as a trough and ridge that form part of the midlatitude wave train approach the southern africa southwest indian ocean swio region a southwest northeast oriented wave train is subsequently established originating from this feature and is strengthened across the tropical indian ocean the midlatitude wave propagation toward the subtropics induces the growth of the trough and ridge over the swio wave activity flux diagnostics indicate that the amplified trough and ridge over the swio act as an energy source for northeastward amplification of the tropical waves through the wave energy dispersion process the results suggest that the propagation of the midlatitude wave toward the swio is the fundamental mechanism behind the development of the tropical waves along the indian ocean itcz

the impact of enso on southern african rainfall in cmip5 ocean atmosphere coupled climate models we study the ability of 24 ocean atmosphere global coupled models from the coupled model intercomparison project 5 cmip5 to reproduce the teleconnections between el nino southern oscillation enso and southern african rainfall in austral summer using historical forced simulations with a focus on the atmospheric dynamic associated with el nino overestimations of summer rainfall occur over southern africa in all cmip5 models abnormal westward extensions of enso patterns are a common feature of all cmip5 models while the warming of the indian ocean that happens during el nino is not correctly reproduced this could impact the teleconnection between enso and southern african rainfall which is represented with mixed success in cmip5 models large scale anomalies of suppressed deep convection over the tropical maritime continent and enhanced convection from the central to eastern pacific are correctly simulated however regional biases occur above africa and the indian ocean particularly in the position of the deep convection anomalies associated with el nino which can lead to the wrong sign in rainfall anomalies in the northwest part of south africa from the near surface to mid troposphere cmip5 models underestimate the observed anomalous pattern of pressure occurring over southern africa that leads to dry conditions during el nino years

late ordovician brachiopod distribution and ecospace partitioning in the tvaren crater system sweden abstract patterns of distribution and ecospace utilization of late ordovician brachiopods in a recently formed contemporary meteorite crater are described and analyzed rhynchonelliformean brachiopod communities dominated by a wide range of orthides and strophomenides colonized the newly formed crater at the crater rim communities were established early on although the crater depression was not inhabited until deposition of the upper third of the remaining crater fill the crater formed a protected but restricted microenvironment where sediments four times the thickness of the nearby basinal succession accumulated within this narrow space environments varied from shallow water to deeper waters about 200 m in depth and from well oxygenated to hypoxic such varied environments generated a rough ecological landscape facilitating niche partitioning across a relatively small geographic area analysis of the guild structure of the fauna permits explanation of a local biodiversity hotspot in otherwise low diversity strata elsewhere in the scandinavian region the tvaren impact event had an important palaeobiologic effect upon the fossil record as it served as a local pump and reservoir for biodiversity moreover the development of new community types and narrowly defined niches helped further drive both and biodiversity during a critical phase of the great ordovician biodiversification event

daily geomagnetic variations on the iberian peninsula summary mean hourly values of the horizontal and vertical components of the geomagnetic field at six observatories on the iberian peninsula were analysed to study seasonal and spatial behaviour of the solar and lunar ionospheric and oceanic daily geomagnetic variations the results are tabulated and their characteristics are discussed the influence of local oceanic effects on the lunar oceanic contribution at the peninsular observatories is noted in particular the spatial behaviour of the lunar oceanic contribution is considered whereas the mean value for the peninsula is consistent with that expected according to an existing model for electric currents in the eastern atlantic ocean individual values are not the influence of tide in the mediterranean sea of water currents in the strait of gibraltar and of local effects in the atlantic ocean is proposed as the reason for this behaviour

influence of the madden julian oscillation on southern african summer rainfall composite maps of outgoing longwave radiation olr anomalies over the madden julian oscillation mjo cycle show marked intraseasonal fluctuations over southern africa south of 15 s large scale convective clusters are seen to propagate eastward and then northward over the continent mainly between 10 and 20 s the corresponding response of the rainfall field presents the alternation over the cycle of dry and humid phases which are both significant moisture flux anomalies indicate an intraseasonal modulation of the midtropospheric easterly flow over the congo basin at 700 hpa these fluctuations are coupled to meridional flux anomalies that extend from the tropical to the subtropical austral latitudes and favor occurrences of wet or dry conditions over the domain though statistically significant the influence of the mjo on southern africa is however not homogeneous spatially and only the tropical areas exhibit sharp periodicities in the 30 60 day period range the olr dipole observed in previous studies at the interannual and synoptic time scales between the hinterland parts of southern africa and the southwestern indian ocean in the north of madagascar is investigated next as it also shows strong fluctuations at the intraseasonal time scale the study points out that the dipole is partly influenced by the mjo though the strongest periodicities are found for slightly longer periods 35 80 days than those typically associated with the oscillation the forcing of the mjo on the olr dipole though significant remains thus partial

the south indian convergence zone and interannual rainfall variability over southern africa abstract the south indian convergence zone sicz is identified in this paper as a region of enhanced precipitation extending off the southeast coast of southern africa during austral summer unlike the south pacific convergence zone the sicz is a land based convergence zone lbcz with position and intensity at least partially determined by surface conditions over southern africa an idealized gcm simulation is used to explore the basic dynamics of lbczs in the tropics and subtropics output from a realistic gcm simulation and the national centers for environmental prediction national center for atmospheric research 40 year reanalysis are analyzed to apply this basic dynamical framework to the case of the sicz in contrast to the intertropical convergence zone where column moisture convergence is primarily due to meridional wind convergence in the moist environment precipitation within the sicz and the lbczs in general is also supported by zonal wind convergence moisture convergence by transient eddy

millennial scale oscillations of the westerly jet path during the last glacial period abstract it has been established that east asian summer monsoon intensity varies with dansgaard oeschger cycles suggesting a connection between the climates of east asia and the north atlantic on a millennial timescale however the dynamics of such a connection are still unsolved here we demonstrate that temporal changes in the provenance of aeolian dust in japan sea sediments which we interpret to reflect changes in the westerly jet path over east asia exhibit variations in harmony with dansgaard oeschger cycles the dominance of dust with a mongolian gobi provenance during stadials suggests a westerly jet axis located to the south of the himalaya tibetan plateau throughout most of the year whereas the co dominance of dust from both the taklimakan desert and the mongolian gobi during interstadials suggests that the westerly jet axis jumped to the north of the tibetan plateau at latest in summer as the shift of the westerly jet axis to the north of the tibetan plateau is closely related to the onset of the east asian summer monsoon changes of the westerly jet path apparently critically affect the teleconnection between the climates of asia and north atlantic on a millennial timescale

roles of the brazilian plateau in the formation of the sacz abstractthe role of the brazilian plateau bp in maintaining the south atlantic convergence zone sacz has been examined by statistical analysis and numerical experiments statistical analysis using 27 years of data showed that the sacz is most intense when it is over the bp in this case low level cyclonic circulation appears over the southwestern part of the bp and forms westerly flow which intensifies low level convergence along the sacz with northeasterly flow from the amazon and northerly flow along the western edge of the south atlantic subtropical high a vorticity budget analysis indicates that precipitation over the bp that accompanies stretching maintains the cyclonic circulation sensitivity experiments using a regional atmospheric model for two different cases indicate that precipitation over the bp plays a dominant role as an atmospheric heat source in maintaining the cyclonic circulation and the sacz in model experiments in which rain was stopped around the bp but the topography was kept

satellite observations of magnetic fields due to ocean tidal flow the ocean is an electrically conducting fluid that generates secondary magnetic fields as it flows through earth s main magnetic field extracting ocean flow signals from remote observations has become possible with the current generation of satellites measuring earth s magnetic field here we consider the magnetic fields generated by the ocean lunar semidiurnal m2 tide and demonstrate that magnetic fields of oceanic origin can be clearly identified in satellite observations

ocean tidal signals in observatory and satellite magnetic measurements 1 ocean flow moves sea water through the earth s magnetic field inducing electric fields currents and secondary magnetic fields these motionally induced magnetic fields have a potential for the remote sensing of ocean flow variability a first goal must be to gain a better understanding of magnetic field generation by tidal ocean flow we predict the motionally induced magnetic fields for the six major tidal constituents and compare their amplitudes with the spectra of night time observatory and satellite magnetic measurements for the indian ocean the magnetic variations at the solar s2 kl and p1 periods turn out to be dominated by unrelated external fields in contrast observed lunar m2 and n2 tidal signals are in fair agreement with predictions from motional induction the lunar diurnal o1 signal visible at some observatories could be caused by ocean flow but disagrees in amplitude with our predictions

interactions between synoptic intraseasonal and interannual convective variability over southern africa after removing the annual cycle a principal component analysis is applied to the daily outgoing longwave radiation anomaly field used here as a proxy for atmospheric convection the analysis is carried out over the southern african region 7 5 e 70 e 10 s 40 s for austral summer november through february for the period 1979 1980 to 2006 2007 the first five principal components pc are retained the first two pcs describe spatial patterns oriented north west to south east from tropical southern africa sa to the mid latitudes they are interpreted to be different possible locations for synoptic scale tropical temperate troughs ttt one dominant rainfall producing synoptic system in the region the phase relationship between these two pcs describes a tendency for these ttt to propagate eastwards from sa to the mozambique channel and southern madagascar the next three pcs describe convective fluctuations respectively located over the north west the south and the centre of sa their time series are significantly associated with madden julian oscillation mjo activity in the tropics however we find that ttt systems are statistically independent of the mjo i e they are equally liable to occur during any phase of the mjo three pcs out of five also show a significant association with el nino southern oscillation confirming that el nino years mostly coincide with suppressed convection at the intraseasonal time scales a result consistent with its impact on seasonal averages diagnosed in previous studies

regional atmospheric circulation and rainfall variability in south equatorial africa abstractthis study examines daily precipitation data during december march over south equatorial africa sea and proposes a new zonal asymmetric pattern zap that explains the leading mode of weather scale precipitation variability in the region the eastern and western components of the zap separated at about 30 e appear to be a consequence of an anomalous zonal atmospheric cell triggered by enhanced low level westerly winds the enhanced westerlies are generated by a diagonal interhemispheric pressure gradient between the southwestern indian and north tropical atlantic oceans in eastern sea these winds hit the east african plateau producing low level convergence and convection that further intensifies the westerlies in western sea a subsiding branch develops in response closing the circulation cell the system gradually dissipates as the pressure gradient weakens through this mechanism simultaneous changes in two hemispheres generate a regional zonally oriented circulation that relies on clima

tropical extratropical interactions over southern africa three cases of heavy summer season rainfall abstract the synoptic evolution of three tropical extratropical te interactions each responsible for extreme rainfall events over southern africa is discussed in detail along with the consideration of previously studied events common features of these heavy rainfall producing tropical temperate troughs ttts over southern africa are discussed it is found that 2 days prior to an event northeasterly moisture transports across botswana set up by the angola low are diverted farther south into the semiarid region of subtropical southern africa the ttts reach full maturity as a te cloud band rooted in the central subcontinent which is triggered by upper level divergence along the leading edge of an upper tropospheric westerly wave trough convection and rainfall within the cloud band is supported by poleward moisture transports with subtropical air rising as it leaves the continent and joins the midlatitude westerly flow it is shown that these systems fit within a theoretical framework describing

recurrent daily olr patterns in the southern africa southwest indian ocean region implications for south african rainfall and teleconnections a cluster analysis of daily outgoing longwave radiation olr anomalies from 1979 to 2002 over the southern africa southwest indian ocean swio region for the november to february season reveals seven robust and statistically well separated recurrent patterns of large scale organized convection among them are three regimes indicative of well defined tropical temperate interactions linking the hinterland parts of southern africa to the mid latitudes of the swio preferred transitions show a tendency for an eastward propagation of these systems analysis of daily rainfall records for south africa shows that six of the olr regimes are associated with spatially coherent and significant patterns of enhanced or reduced daily rainfall over the country atmospheric anomalies from the ncep doe ii reanalysis dataset show that the olr regimes are associated with either regional or near global adjustments of the atmospheric circulation the three regimes representative of tropical temperate interactions being in particular related to a well defined wave structure encompassing the subtropical and temperate latitudes featuring strong vertical anomalies and strong poleward export of momentum in the lee of the location of the cloud band the time series of olr regimes seasonal frequency are correlated to distinctive anomaly patterns in the global sea surface temperature field among which are shown to be those corresponding to el nino and la nina conditions the spatial signature of el nino southern oscillation s enso influence is related to the combination of an increased decreased frequency of these regimes it is shown in particular that the well known dipole in convection anomalies contrasting southern africa and the swio during enso events arises as an effect of seasonal averaging and is therefore not valid at the synoptic scale this study also provides a framework to better understand the observed non linearities between enso and the seasonal convection and rainfall anomalies over the region

remote effects of el nino and modoki events on the austral summer precipitation of southern africa abstractremote effects modulating the austral summer precipitation over southern africa during el nino el nino modoki events are investigated by analyzing the observed events during december february of the years from 1982 83 to 2010 11 based on the composite analyses it is found that southern africa experiences significantly below normal precipitation during el nino events compared to el nino modoki events during these latter events precipitation anomalies are not so significant although southern africa as a whole receives below normal precipitations the differences in the spatial distribution of precipitation over southern africa are seen to be related to the sea surface temperature sst anomalies of the equatorial pacific through atmospheric teleconnections the low level 850 hpa matsuno gill response to anomalously high precipitation over the pacific during el nino events results in an anomalous anticyclone extending from the equatorial to the subtropical south indian ocean these anomalous ant

deducing anomalous wave source regions during the life cycles of persistent flow anomalies abstract anomalous wave source regions are identified during the life cycles of persistent flow anomalies occurring over the north pacific and north atlantic oceans during boreal winter these cases project strongly upon the pacific north american and eastern atlantic teleconnection patterns respectively and represent two of the primary modes of intraseasonal low frequency variability in the northern hemisphere wintertime circulation in the upper troposphere these cases are manifested by wave trains of large scale and large amplitude flow anomalies extending downstream from key regions near the aleutian islands and south of iceland respectively the occurrence of persistent flow anomalies is closely linked to persistent extremes in surface weather and to variations in the skill of extended range weather forecasts black and dole performed a detailed diagnostic analysis of the onset of persistent cyclonic flow anomalies over the north pacific a key result of their study was that wave activity flux di