intraseasonal interactions between the tropics and extratropics in the southern hemisphere abstract the mechanics of the interaction between tropical beating estimated from outgoing longwave radiation olr and southern hemisphere sh subtropical and extratropical circulations on intraseasonal time scales are discussed base points are selected from teleconnectivity and teleconnection maps between olr and zonal wind heights and meridional component of the divergent wind then composites are formed for pentads with olr anomalies at the base point greater in magnitude than one standard deviation enhanced convection over indonesia is found to be associated with increases of both the southward component of the meridional divergent wind and of the westerly zonal wind to the south of the heating region during the sh summer the increased westerly wind gradients resulting to a certain extent from strengthened northerly flow together with increased values of the southward component of the divergent wind lead to an enhancement of the rossby wave source in the vorticity equation in the vicinit

global climatic anomalies associated with extremes in the southern oscillation abstract composite temperature and precipitation anomalies during various stages of an event in the southern oscillation so have been computed for several hundred stations across the globe large regions of coherent significant signals are shown to exist for both extremes of the so with warm event signals generally opposite to those during cold events in addition during the year preceding the development of an event in the so year 1 climatic anomalies tend to be opposite to those during the following year year 0 this confirms that the biennial tendency of the so over the pacific indian ocean sectors is also present in more remote regions with climatic signals related to the so many of the signals are consistent enough from event to event to be useful for extended range forecasting purposes

circulation anomalies associated with tropical convection during northern winter abstract lagged cross correlations between outgoing longwave radiation olr and national meteorological center global analyses are utilized to isolate the preferred upper level and surface circulation anomalies associated with tropical convection during northern winter three intraseasonal time scales are studied 30 70 14 30 and 6 14 days in the 30 70 day band the upper level circulation signals are zonally elongated with zonal wavenumbers 0 2 dominant higher frequency signals are dominated by zonal wavenumbers 5 and 6 in the 14 30 day band convection over the eastern hemisphere is associated with upper level anticyclones in the subtropics and appears to be linked in some cases to midlatitude wave trains the strongest signals are for convection over africa australia and the eastern indian ocean only weak signals are seen for convection over indonesia in these regions of upper level easterlies olr anomalies peak prior to the maximum anomalies in wind suggesting forcing of the circulation b

interannual and decadal cycles in river flows of southeastern south america abstract the time series of annual streamflow of four rivers in southeastern and south central south america the negro paraguay parana and uruguay rivers for the period 1911 93 are analyzed application of the multitaper method shows that the following features are significant at the 95 level 1 a nonlinear trend 2 a near decadal component and 3 interannual peaks with enso timescales the trend and near decadal components are most marked in the two more central rivers the paraguay and parana with enso timescale variability most pronounced in the negro and uruguay rivers in the southeast composites of sst are made for each of the statistically significant oscillatory components of river flow by reconstructing each component using singular spectrum analysis these composites confirm the influence of enso on the streamflow variability of the negro and uruguay rivers with el nino associated with enhanced streamflow on the decadal timescale high river runoff is associated with anomalously coo

large amplitude short scale stationary rossby waves in the southern hemisphere observations and mechanistic experiments to determine their origin abstract studies by van loon and jenne van loon et al trenberth and others indicate that stationary waves in the southern hemisphere are dominated by planetary scales kalnay and halem reported the presence of large amplitude short scale stationary waves during the month of january 1979 in the lee of south america and their disappearance in february 1979 in this paper we present further observational evidence of the january waves we also perform two 15 day forecast experiments with the glas fourth order general circulation model and initial conditions corresponding to 5 january and 4 february 1979 these factors reproduce reasonably well the presence of the january waves and their absence in february several mechanistic experiments to determine the origin of the waves are then performed the principal conclusions are a large amplitude stationary rossby waves with zonal wavenumber 7 were present between 20 and 40 s both in the south pacific and east of south america during january 1979 they app

formation of stationary alternate bars in a steep channel with mixed size sediment a flume experiment alternate bars were formed by sediment transport in a flume with froude modelled flow and relative roughness characteristic of gravel boulder channels with steep slopes the flume 0 3 m wide 7 5 m long was filled with a sand gravel mixture which was also fed into the top of the flume at a constant rate under constant discharge channel slope was set at 0 03 initially coarse particles accumulated on incipient bar heads near one side of the flume and diverted flow and bedload transport across the flume toward a pool scoured against the opposite flume wall downstream sorting in the pool directed coarse particles onto the next bar head downstream alternate sequences of pools and coarse bar heads were thereby linked down the entire flume by interactions of sediment sorting flow and channel morphology during episodes of bar construction unsorted bedload invaded interior bar surfaces and was deposited persistent deposition of coarse particles on bar heads prevented downstream migration of bars by inhibiting bar head erosion and bedload transport over bars likely factors leading to bar head stabilization in modelled gravel bed channels are coarse mixed size sediment steep channel gradients and shallow depths

interannual and interdecadal variability of the south atlantic convergence zone interannual variations of the summertime january march atmospheric circulation over subtropical south america are examined during the period 1958 97 using the national centers for environmental prediction national center for atmospheric research reanalysis data it is found from an empirical orthogonal function analysis that an anomalous upper tropospheric large scale stationary eddy in the lee of the andes tends to accompany a dipole in anomalous vertical motion an anomalous cyclonic anticyclonic eddy accompanies an intensified diffuse south atlantic convergence zone sacz with anomalous descent ascent to the southwest the cold core equivalent barotropic vertical structure of the anomalous cyclonic eddy and the 200 hpa vorticity balance are both characteristic of a stationary rossby wave the tendency for the eddy to be advected downstream by the mean westerlies is compensated by meridional advection of planetary vorticity and stretching associated with vertical motion the anomalous cyclonic flow at low levels reinforces the thermally direct circulation associated with the sacz a weak funneling of submonthly rossby wave activity into this descent region is also identified the interannual time series of the eddy is significantly correlated with north south dipolar sea surface temperature sst anomalies over the southwest atlantic one standard deviation 200 hpa wind speed anomalies of up to 5 m s21 are accompanied by sst anomalies of up to 0 38c a near cyclic 15 yr component is identified which the authors corroborate from independent analyses of southwest atlantic ssts and river flows both are

subpolar high anomaly preconditioning precipitation over south america abstract the mechanisms associated with the intraseasonal variability of precipitation over south america during the spring season are investigated with emphasis on the influence of a quasi stationary anomalous circulation over the southeastern south pacific ocean sep a spectral analysis performed to the bandpass filtered time series of daily precipitation anomalies for the la plata basin lpb and the south atlantic convergence zone sacz regions revealed several statistically relevant peaks corresponding to periods of roughly 23 days and 14 16 days with the lower higher frequency peaks more prevalent for the sacz lpb the large scale circulation patterns preconditioning precipitation variability over both regions were explored by means of a regression analysis performed on the daily 500 hpa geopotential anomaly field provided by the ncep ncar reanalysis dataset the most prominent feature of the regression fields is the presence of a quasi stationary anomalous anticyclonic cyclonic circulation

large scale circulation patterns and related rainfall in the amazon basin a neuronal networks approach this study describes the main circulation patterns cp in the amazonian basin over the 1975 2002 period and their relationship with rainfall variability cps in the amazonian basin have been computed for each season from the era 40 daily 850 hpa winds using an approach combining artificial neural network self organizing maps and hierarchical ascendant classification a 6 to 8 cluster solutions depending on the season considered is shown to yield an integrated view of the complex regional circulation variability for austral fall winter and spring the temporal evolution between the different cps shows a clear tendency to describe a cycle with southern wind anomalies and their convergence with the trade winds progressing northward from the la plata basin to the amazon basin this sequence is strongly related to eastward moving extra tropical perturbations and their incursion toward low latitude that modulate the geopotential and winds over south america and its adjoining oceans during austral summer cps are less spatially and temporally organized compared to other seasons principally due to weaker extra tropical perturbations and more frequent shallow low situations each of these cps is shown to be associated with coherent northward moving regional rainfall patterns both in in situ data and era 40 reanalysis and convective activity however our results reveals that precipitation variability is better reproduced by era 40 in the southern part of the amazonian basin than in the northern part where rainfall variability is likely to be more constrained by local and subdaily processes e g squall lines that could be misrepresented in the reanalysis dataset this analysis clearly illustrates the existing connections between the southern and northern part of the amazonian basin in terms of regional circulation rainfall patterns the identification of these cps provide useful information to understand local rainfall variability and could hence be used to better understand the influence of these cps on the hydrological variability in the amazonian basin

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

atmospheric circulation anomalies during episodes of enhanced and reduced convective cloudiness over uruguay abstract regional and large scale circulation anomalies associated with periods of enhanced and reduced convective cloudiness over uruguay are studied for austral spring and summer when rainfall associated with deep convection is more frequent in this region the analysis was performed at a submonthly timescale considering that the essential nature of the mechanisms producing rainfall is not well captured by anomalies calculated on a monthly or seasonal basis in regions where precipitation is highly episodic periods of enhanced and reduced convective cloudiness over uruguay are characterized by a marked dipolar structure in the outgoing longwave radiation anomaly field along eastern south america from 10 to 40 s with the centers of the dipole located over the south atlantic convergence zone sacz and over a broad region including uruguay southern brazil and northeastern argentina this dipole which corresponds to one of the key factors of climate dynamics in south america during spring and summer

solar terrestrial signal record in tree ring width time series from brazil this work investigates the behavior of the sunspot number and southern oscillation index soi signal recorded in the tree ring time series for three different locations in brazil humaita in amazonia state porto ferreira in sao paulo state and passo fundo in rio grande do sul state using wavelet and cross wavelet analysis techniques the wavelet spectra of tree ring time series showed signs of 11 and 22 years possibly related to the solar activity and periods of 2 8 years possibly related to el nino events the cross wavelet spectra for all tree ring time series from brazil present a significant response to the 11 year solar cycle in the time interval between 1921 to after 1981 these tree ring time series still have a response to the second harmonic of the solar cycle 5 5 years but in different time intervals the cross wavelet maps also showed that the relationship between the soi x tree ring time series is more intense for oscillation in the range of 4 8 years

climate variability in southern south america associated with el nino and la nina events a comprehensive view is given of the precipitation and circulation anomalies associated with the various stages of el nino en and la nina ln events all over southern south america ssa this view comprises the delineation of coherent regions with respect to precipitation anomalies the identification of the seasons of maximum anomalies the indication of their magnitude and the assessment of their consistency during those events in addition the spatial and temporal variability of these anomalies is detailed by calculating the expected precipitation percentiles and the consistency of wet and dry anomalies for each station and each three month running season during en and ln events composites of circulation anomalies and an assessment of their consistency are also presented and their connection with the precipitation anomalies is discussed southern brazil presents the strongest average signal in en events the general behavior toward opposite signals in the precipitation and circulation anomalies over ssa during almost the same periods of the en and ln events indicates a large degree of linearity in the response to these events the timing of the anomalies changes throughout ssa leading to the identification of eight different coherent regions in the en case and six in the ln case this regionalization is mostly caused by different processes leading to precipitation anomalies in ssa during those events all these regions show a significant response in some part of each event the magnitude and consistency of this response show a large spatial variability and some areas present very strong and consistent anomalies sometimes not disclosed when large coherent regions are analyzed in spite of the differences in timing some features of the precipitation anomalies are rather uniform throughout the region during en and ln events in en episode there is a tendency to lower than median precipitation in the year before the event which continues until march of the year of the event in a vast region east of the andes the strongest positive precipitation anomalies occur in spring of this year when the circulation anomalies concur to enhance rainfall over several regions during the summer of the mature stage the positive precipitation anomalies almost disappear and then reappear in some regions in late summer early autumn and in winter of the year following the starting year of the event this description holds partially for the ln event but with opposite signs although there is a larger spatial variability in the ln related anomalies in the following year and some shifts in timing as for precipitation the symmetry of the geopotential height anomaly fields with opposite signs between ln and en cases is also remarkable especially during the year 0

mineralogy and paragenesis of the co ni arsenide ores of bou azzer anti atlas morocco the co ni arsenide ore deposits at bou azzer morocco represent an uncommon type of co mineralization several co ni as au ag mines are active in bou azzer and adjacent areas the co ni arsenide ores are structurally controlled and concentrated mainly within quartz carbonate veins along the boundaries of neoproterozoic serpentinized mantle peridotites quartz diorite and precambrian volcanic rocks they have varying shapes and sizes however all deposits have the same general mineralogy in decreasing order of abundance arsenides sulfarsenides and sulfides arsenide minerals include skutterudite coas3 safflorite coas2 loellingite feas2 nickeline nias rammelsbergite nias2 and s rich ni co diarsenide co rich ores are predominant over ni rich ones in almost all deposits arsenopyrite and to a lesser extent gersdorffite are the main sulfarsenide minerals in almost all samples studied bornite an unidentified cu zn sulfide chalcocite chalcopyrite pyrite pyrrhotite sphalerite and tetrahedrite in decreasing order of abundance are the main sulfide minerals present in bou azzer ores gold silver alloys with about 15 wt percent ag on average are commonly associated with ni co arsenides and or disseminated in quartz veins in the ni rich assemblage pure nickeline with high ni content 48 wt and very low co content 0 1 wt grades outward to compositions with less ni 20 wt and very high co up to 18 wt this suggests a depositional sequence from ni monoarsenide nickeline to ni co diarsenide to cobalt triarsenides i e a progressive increase in co and as the ore forming elements co ni fe and as were originally leached from serpentinites by acidic magmatic fluids under moderately reducing conditions at high fluid rock ratios deposition of ore minerals occurred in response to increasing ph and decreasing oxygen fugacity of the mineralizing fluids caused by mixing between the magmatic brines and meteoric water the predominance of co over ni arsenide minerals in the bou azzer mineralization despite the high ni co ratio of the serpentinites may be attributable to the different solubilities of ni and co in the hydrothermal system

precipitation anomalies in southern brazil associated with el nino and la nina events the impact of el nino and la nina events warm and cold phases of the southern oscillation on rainfall over southern brazil is investigated through the use of a large dataset of monthly precipitation from 250 stations this region is partly dominated by rough orography and presents different climatic regimes of rainfall as previous global studies on southern oscillation precipitation relationships used data from only two stations in southern brazil this region was not included in the area of consistent southern oscillation related precipitation in southeastern south america the present analysis is based on the method by ropelewski and halpert the sensitivity of which is assessed for this region the spatial structure of the rainfall anomalies associated with warm cold events is analyzed and subregions with coherent anomalies are determined their distribution indicates the influence of relief latitude and proximity to the ocean these areas are subjected to further analysis to determine the seasons of largest anomalies and assess their consistency during warm cold events the whole of southern brazil was found to have strong and consistent precipitation anomalies associated with those events their magnitude is even larger than in argentina and uruguay all of the subregions have consistent wet anomalies during the austral spring of the warm event year with a pronounced peak in november the southeastern part also shows a consistent tendency to higher than average rainfall during the austral winter of the following year there is also a consistent tendency to dryness in the year before a warm event during the spring of cold event years strong consistent dry anomalies prevail over the whole region also with maximum magnitude in november they are even stronger and more consistent than the wet anomalies in warm event years consistent anomalies do not occur over large areas in the years before and after cold events the wet anomalies during the austral spring of the warm event year weaken and even reverse during the following january the same tendency though not so clear is observable in the dry anomalies of cold events the seasons of largest anomalies disclosed by this study differ from those found by previous global studies for other regions in southeastern south america this study expands the area of consistent warm cold event related precipitation defined by previous studies in southeastern south america by including a region of larger anomalies and provides a spatial and temporal refinement to the warm cold event precipitation relationship

midsummer low level circulation and precipitation in subtropical south america and related sea surface temperature anomalies in the south atlantic abstract the midsummer interannual variability of the low level tropospheric circulation and of the precipitation field in subtropical south america sa associated to the sea surface temperature sst anomalies in the western subtropical south atlantic ocean wssa is investigated using reanalyses regional precipitation datasets and monthly ssts the region of the wssa where sst has the strongest relation with precipitation in subtropical sa was identified using canonical correlation analysis this region extends from 20 to 30 s and from 30 to 50 w composites corresponding to extreme ssts in this area show two well differentiated patterns in the low level circulation and in the precipitation fields in the composite corresponding to the more positive sst anomalies in this area the mainstream of the low level flow and of the moisture transport from the continental low latitudes starts to follow a southeastward direction at 10 s and converges with the west flow at 35 s over the atlantic ocean on t

a climatology of anticyclones and blocking for the southern hemisphere abstract an automated procedure for locating and tracking high pressure centers is applied to 10 years of twice daily ecmwf analyses during 1980 89 to survey the behavior of anticyclones in the southern hemisphere anticyclones are concentrated in the 25 45 s band with preferred regions consistent with previous studies except in the new zealand nz south pacific sector where a double occurrence maximum noted in earlier studies was only weakly evident marked interannual variability was found in this region with the poleward branch of maximum occurrence south of 50 s present in only 3 out of 10 years mean central pressure maximized about 10 south of the time averaged ridge with highest values in winter anticyclones poleward of 50 s involve an anomalous breakdown of the westerlies with mean central pressures there 20 30 hpa higher than climatology highs tend to form and intensify in western regions of ocean basins and weaken and dissipate in the east of these oceans regions southeast of australi

transient behavior of the meridional moisture transport across south america and its relation to atmospheric circulation patterns the transient behavior of meridional moisture transport across the south american continent is examined with the reanalysis data provided by the european centre for medium range weather forecasts ecmwf the results show clearly the effects of the valley between the andes and the brazilian plateau in canalizing the southward moisture transport an intense jet is episodically formed in this valley the synoptic variability of this low level jet and its relation to the large scale atmospheric circulation are studied

summertime precipitation variability over south america role of the large scale circulation abstract the observed large scale circulation mechanisms associated with summertime precipitation variability over south america are investigated particular attention is paid to the altiplano where a close relationship has been observed between rainfall and the position and intensity of the bolivian high empirical orthogonal function eof correlation and composite analyses suggest that on intraseasonal timescales typically 5 20 days rainy periods on the altiplano are associated with at least three types of circulation anomalies involving either extratropical cyclones cold core lows or the westward enhancement of the south atlantic high in each instance the primary support for high rainfall rates is a moist poleward flow at low levels along the eastern flank of the central andes in association with the south atlantic convergence zone sacz the warm low level flow along the sacz also inflates the overlying atmospheric column resulting in an intensification and southward shift of the bolivi

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

analysis of tropical extratropical interactions with influence functions of a barotropic model abstract influence functions ifs of a linear barotropic vorticity equation model are computed in order to determine the regions in which anomalous divergence at upper levels related to tropical heating anomalies has the largest impact on certain prominent low frequency anomalies the present computation differs from that of branstator in two aspects a the model includes the effects of the basic flow divergence and the advection by anomalous divergent wind and b the influence functions directly assess the influence of upper level divergence anomalies rather than sources of vorticity the ifs are applied to the study of low frequency tropical extratropical interactions at the interannual enso and intraseasonal 30 60 day oscillation timescales the origin of well known teleconnection patterns is explored through the identification of comma influence regions in the tropics and subtropics for their main action centers the subtropical west and central east pacific north of the equator is an impo

a strong control of the south american seesaw on the intra seasonal variability of the isotopic composition of precipitation in the bolivian andes water stable isotopes d in tropical regions are a valuable tool to study both convective processes and climate variability provided that local and remote controls on d are well known here we examine the intra seasonal variability of the event based isotopic composition of precipitation ddzongo in the bolivian andes zongo valley 16 20 s 67 47 w from september 1st 1999 to august 31st 2000 we show that the local amount effect is a very poor parameter to explain ddzongo we thus explore the property of water isotopes to integrate both temporal and spatial convective activities we first show that the local convective activity averaged over the 7 8days preceding the rainy event is an important control on ddzongo during the rainy season 40 of the ddzongo variability is captured this could be explained by the progressive depletion of local water vapor by unsaturated downdrafts of convective systems the exploration of remote convective controls on ddzongo shows a strong influence of the south american seesaw sass which is the first climate mode controlling the precipitation variability in tropical south america during austral summer our study clearly evidences that temporal and spatial controls are not fully independent as the 7 day averaged convection in the zongo valley responds to the sass our results are finally used to evaluate a water isotope enabled atmospheric general circulation model lmdz iso using the stretched grid functionality to run zoomed simulations over the entire south american continent 15 n 55 s 30 85 w we find that zoomed simulations capture the intra seasonal isotopic variation and its controls though with an overestimated local sensitivity and confirm the role of a remote control on d according to a sass like dipolar structure 2011 elsevier b v

blocking over the south pacific and rossby wave propagation abstract atmospheric blocking events over the south pacific are investigated using a 39 yr record of 500 hpa height fields from the ncep ncar reanalysis dataset the analysis extends earlier work using a 16 yr record and confirms that the occurrence of blocking over the southeast pacific is strongly modulated by the enso cycle during austral spring and summer comparison of results at 500 hpa with the 300 hpa meridional wind component showed that blocking events are associated with large scale wave trains lying across the south pacific from the region of australia to southern south america similar wave trains are evident in both hemispheres in singular value decomposition analyses between 300 hpa meridional wind components and tropical pacific outgoing longwave radiation olr anomalies the hypothesis that the divergence associated with tropical olr anomalies forces an extratropical wave response that results in enhanced blocking over the southeast pacific was tested using a linearized barotropic vorti

on the functioning of the southern oscillation in the south american sector part i surface climate abstract the functioning of the southern oscillation so over south america and the surrounding tropical atlantic and eastern pacific oceans is studied through analyses of bimonthly patterns of correlation between an so index and the fields of pressure wind temperature and rainfall hydrometeorological anomalies being further ascertained from river discharge and lake level records and measurements of outgoing longwave radiation most pronounced is the anomalously low pressure over the eastern pacific during the negative so phase defined by anomalously low high pressure at tahiti darwin consistently positive so pressure correlations over the eastern tropical pacific extend eastward into the north atlantic region and southern south america during the respective winter semester during the austral winter the tendency for anomalously abundant rainfall in central chile during the negative so phase appears related to an anomalously weak and northward displaced south pacific subtropical high while relativ