Search

Gridded precipitation (PRP) data have been largely used in diagnostic studies on the climate variability in several time scales, as well as to validate model results. The three most used gauge-based PRP datasets are from the Global Precipitation Climatology Centre (GPCC), University of Delaware (UDEL), and Climate Research Unit (CRU). This paper evaluates the performance of these datasets in reproducing spatiotemporal PRP climatological features over the entire South America (SA) for the 1901–2015 period, aiming to identify the differences and similarities among the datasets as well as time intervals and areas with potential uncertainties involved with these datasets. Comparisons of the PRP annual means and variances between the 1901–2015 period and the non-overlapping 30-year subperiods of 1901–1930, 1931–1960, 1961–1990, and the 25-year subperiod of 1991–2015 for each dataset show varying means of the annual PRP over SA depending on the subperiod and dataset. Consistent patterns among datasets are found in most of southeastern SA and southeastern Brazil, where they evolved gradually from less to more rainy conditions from 1901–1930 to the 1991–2015 subperiod. All three datasets present limitations and uncertainties in regions with poor coverage of gauge stations, where the differences among datasets are more pronounced. In particular, the GPCC presents reduced PRP variability in an extensive area west of 50° W and north of 20° S during the 1901–1930 subperiod. In monthly time scale, PRP time series in two areas show differences among the datasets for periods before 1941, which are likely due to spurious or missing data: central Bolivia (CBO), and central Brazil (CBR). The GPCC has less monthly variability before 1940 than the other two datasets in these two areas, and UDEL presents reduced monthly variability before 1940 and spurious monthly values from May to September of the years from 1929 to 1941 in CBO. Thus, studies with these three datasets might lead to different results depending on the study domain and period of analysis, in particular for those including years before 1941. The results here might be relevant for future diagnostic and modelling studies on climate variability from interannual to multidecadal time scales. [ABSTRACT FROM AUTHOR]

On a hemispheric scale, it is now well established that stratospheric ozone depletion has been the principal driver of externally forced atmospheric circulation changes south of the Equator in the last decades of the 20th Century. The impact of ozone depletion has been felt over the entire hemisphere, as reflected in the poleward drift of the midlatitude jet, the southward expansion of the summertime Hadley cell and accompanying precipitation trends deep into the subtropics. On a regional scale, however, surface impacts directly attributable to ozone depletion have yet to be identified. In this paper we focus on South Eastern South America (SESA), a region that has exhibited one of the largest wetting trends during the 20th Century. We study the impact of ozone depletion on SESA precipitation using output from 6 different climate models, spanning a wide range of complexity. In all cases we contrast pairs of model integrations with and without ozone depletion, but with all other forcings identically specified. This allows for unambiguous attribution of the computed precipitation trends. All 6 climate models consistently reveal that stratospheric ozone depletion results in a significant wetting of SESA over the period 1960-1999. Taken as a whole, these model results strongly suggest that the impact of ozone depletion on SESA precipitation has been as large as, and quite possibly larger than, the one caused by increasing greenhouse gases over the same period. [ABSTRACT FROM AUTHOR]

This paper examines moisture transport on intraseasonal timescales over the continent and over the South Atlantic convergence zone (SACZ) during the South America (SA) summer monsoon. Combined Empirical Orthogonal Function analysis (EOFc) of Global Precipitation Climatology Project pentad precipitation, specific humidity, air temperature, zonal and meridional winds at 850 hPa (NCEP/NCAR reanalysis) are performed to identify the large-scale variability of the South America monsoon system and the SACZ. The first EOFc was used as a large-scale index for the South American monsoon (LISAM), whereas the second EOFc characterized the SACZ. LISAM (SACZ) index showed spectral variance on 30-90 (15-20) days and were both band filtered (10-100 days). Intraseasonal wet anomalies were defined when LISAM and SACZ anomalies were above the 75th percentile of their respective distribution. LISAM and SACZ wet events were examined independently of each other and when they occur simultaneously. LISAM wet events were observed with the amplification of wave activity in the Northern Hemisphere and the enhancement of northwesterly cross-equatorial moisture transport over tropical continental SA. Enhanced SACZ was observed with moisture transport from the extratropics of the Southern Hemisphere. Simultaneous LISAM and SACZ wet events are associated with cross-equatorial moisture transport along with moisture transport from Subtropical Southwestern Atlantic. [ABSTRACT FROM AUTHOR]

The global impacts of El Niño on precipitation have been long‐recognized, but more understanding of the mechanisms behind this influence is needed. For instance, previous studies have largely overlooked the potential impacts of El Niño on terrestrial moisture recycling (TMR). We perform a 40‐year forward tracking simulation to derive a global climatology of recycled precipitation and use a composite analysis to investigate how El Niño affects TMR. We identify seven regions where the El Niño impact on TMR is most significant and find that, in these regions, changes in precipitation and TMR are directly related: they increase or decrease together. In addition, we find a marked latitudinal contrast between the Southern Hemisphere, where TMR increases during El Niño, and the Northern Hemisphere and the tropics, where it decreases. Our results indicate that the weakening and strengthening of TMR can be behind precipitation changes caused by El Niño globally. Plain Language Summary: El Niño is recognized as a climate variability phenomenon with significant impacts on precipitation worldwide. However, the mechanisms behind these impacts are not fully understood. Here we use model simulations to argue that one of those mechanisms is the effect of El Niño on terrestrial moisture recycling (TMR), that is, the fraction of precipitation fed by atmospheric moisture originating not in the ocean but on the continents. We show that El Niño significantly affects TMR globally, especially in seven regions of South America, Africa, North America, Europe, and Asia. In these regions, precipitation and TMR increase or decrease together. We find a contrast between the South and North of the planet: during El Niño, TMR increases in the Southern Hemisphere while decreasing in the Northern Hemisphere and the tropics. Overall, our results indicate that TMR weakening or strengthening are previously overlooked mechanisms behind precipitation changes caused by El Niño globally. Key Points: El Niño exerts significant effects on terrestrial moisture recycling worldwideEl Niño's impacts on terrestrial moisture recycling are most significant in seven regions worldwidePrecipitation and terrestrial moisture recycling increase or decrease together due to El Niño [ABSTRACT FROM AUTHOR]

In the present study, five-year of precipitation features (PFs) datasets, based on Global Precipitation Measurement (GPM), are used to investigate the global and regional characteristics of extreme rainfall events (EREs). The EREs are defined based on the PFs area, depth (maximum height of radar reflectivity), and the rain rate and called them largest, deepest, and intense EREs, respectively. The EREs are divided into top 10%, 1%, 0.1%, and 0.01% based on their frequency of occurrences. It is observed that occurrences of EREs belonging to less than top 0.01% EREs follow the tropical rainfall climatology over the tropics based on all the parameters. Subtropical oceanic areas consist of a higher frequency of largest EREs, whereas tropical land areas consist of the higher number of deepest EREs. The most intense EREs (top 0.01%) are uniformly distributed over tropical areas and subtropical oceans, and spatial distribution shows that a deepest ERE belongs to intense EREs in the tropical land areas. Large differences between the precipitation contribution from the largest and deepest EREs are seen; for example, the top 1% of largest EREs contribute to ∼80.7% of Earth's precipitation, whereas the corresponding percentage for deepest EREs is only 53%. On the regional and seasonal scale, South Asia (SAsia) and South America (SA) nearly show common features, as oceanic and land areas consist of largest and deepest EREs, respectively, and contribute to higher precipitation. Subtropical latitudes over South America, including Sierra de Cordoba and La Plata basin, consist of deepest and intense EREs and match with those of the Indo-Gangetic plain over South Asia, which also shows the similar characteristics. EREs based on various parameters are strongly linked over SAsia compared to SA. For example, the largest top 10% EREs have a higher probability to be part of the top 10% deepest and intense EREs over SAsia. The seasonal and regional water budget reveals different characteristics, as in the southern hemisphere, the deeper EREs contribute to the higher fraction of rainfall, but over SAsia, the shallower EREs could also contribute to significant rainfall. [ABSTRACT FROM AUTHOR]

The Atlantic Intertropical Convergence Zone (A-ITCZ) exhibits variations on several time-scales and plays a crucial role in precipitation regimes of northern South America and western Africa. Here we investigate the variability of the A-ITCZ on intraseasonal time-scales during austral summer (November-March) and winter (May-September) based on a multivariate index that describes the main atmospheric features of the A-ITCZ and retains its variability on interannual, semiannual, and intraseasonal time-scales. This index is the time coefficient of the first combined empirical orthogonal function mode of anomalies (annual cycle removed) of precipitation, and zonal and meridional wind components at 850 hPa from the climate forecast system reanalysis (1979-2010). We examine associations between the intraseasonal variability of the A-ITCZ and the activity of the Madden-Julian oscillation (MJO). We show that during austral summer intraseasonal variability of the A-ITCZ is associated with a Rossby wave train in the Northern Hemisphere. In austral winter this variability is associated with the propagation of a Rossby wave in the Southern Hemisphere consistent with the Pacific-South American pattern. Moreover, we show that intense A-ITCZ events on intraseasonal time-scales are more frequent during the phase of MJO characterized by convection over western Pacific and suppression over the Indian Ocean. These teleconnection patterns induce anomalies in the trade winds and upper level divergence over the equatorial Atlantic that modulate the intensity of the A-ITCZ. [ABSTRACT FROM AUTHOR]

This work focuses on the evaluation of different sources of uncertainty affecting regional climate simulations over South America at the seasonal scale, using the MM5 model. The simulations cover a 3-month period for the austral spring season. Several four-member ensembles were performed in order to quantify the uncertainty due to: the internal variability; the definition of the regional model domain; the choice of physical parameterizations and the selection of physical parameters within a particular cumulus scheme. The uncertainty was measured by means of the spread among individual members of each ensemble during the integration period. Results show that the internal variability, triggered by differences in the initial conditions, represents the lowest level of uncertainty for every variable analyzed. The geographic distribution of the spread among ensemble members depends on the variable: for precipitation and temperature the largest spread is found over tropical South America while for the mean sea level pressure the largest spread is located over the southeastern Atlantic Ocean, where large synoptic-scale activity occurs. Using nudging techniques to ingest the boundary conditions reduces dramatically the internal variability. The uncertainty due to the domain choice displays a similar spatial pattern compared with the internal variability, except for the mean sea level pressure field, though its magnitude is larger all over the model domain for every variable. The largest spread among ensemble members is found for the ensemble in which different combinations of physical parameterizations are selected. The perturbed physics ensemble produces a level of uncertainty slightly larger than the internal variability. This study suggests that no matter what the source of uncertainty is, the geographical distribution of the spread among members of the ensembles is invariant, particularly for precipitation and temperature. [ABSTRACT FROM AUTHOR]

The objective of this study is to assess the climate projections over South America using the Eta-CPTEC regional model driven by four members of an ensemble of the Met Office Hadley Centre Global Coupled climate model HadCM3. The global model ensemble was run over the twenty-first century according to the SRES A1B emissions scenario, but with each member having a different climate sensitivity. The four members selected to drive the Eta-CPTEC model span the sensitivity range in the global model ensemble. The Eta-CPTEC model nested in these lateral boundary conditions was configured with a 40-km grid size and was run over 1961-1990 to represent baseline climate, and 2011-2100 to simulate possible future changes. Results presented here focus on austral summer and winter climate of 2011-2040, 2041-2070 and 2071-2100 periods, for South America and for three major river basins in Brazil. Projections of changes in upper and low-level circulation and the mean sea level pressure (SLP) fields simulate a pattern of weakening of the tropical circulation and strengthening of the subtropical circulation, marked by intensification at the surface of the Chaco Low and the subtropical highs. Strong warming (4-6°C) of continental South America increases the temperature gradient between continental South America and the South Atlantic. This leads to stronger SLP gradients between continent and oceans, and to changes in moisture transport and rainfall. Large rainfall reductions are simulated in Amazonia and Northeast Brazil (reaching up to 40%), and rainfall increases around the northern coast of Peru and Ecuador and in southeastern South America, reaching up to 30% in northern Argentina. All changes are more intense after 2040. The Precipitation-Evaporation (P-E) difference in the A1B downscaled scenario suggest water deficits and river runoff reductions in the eastern Amazon and São Francisco Basin, making these regions susceptible to drier conditions and droughts in the future. [ABSTRACT FROM AUTHOR]

The majority of precipitation in central Chile falls during austral winter with the passage of surface and upper-level low pressure systems and their associated surface fronts. Earlier studies have found the presence of a terrain-parallel, low-level barrier jet during cold front passage and low-level wind convergence in the region of heaviest precipitation. This study advances these findings by developing multiyear climatologies for a rainfall event in central Chile using a broad cross section of observational datasets: the Tropical Rainfall Measuring Mission (TRMM), the Atmospheric Infrared Sounder (AIRS), the National Climatic Data Center (NCDC) Global Surface Summary of the Day (GSOD), the Integrated Global Radiosonde Archive (IGRA), the Quick Scatterometer (QuikSCAT), and the NCEP-NCAR reanalysis. For this study, a precipitation event was defined as daily rainfall exceeding a certain threshold at a Santiago observing station (Pudahuel). Climatologies were developed for a five-day period surrounding the precipitation event: the three days leading up to the day of precipitation at Pudahuel, the day of the precipitation itself, and the day after. Precipitation was found to move northeastward over the southeast Pacific toward central Chile and increase in intensity upon reaching reached the coast between 33° and 40°S. At middle levels, a pronounced 500-hPa trough moved eastward and amplified during the same period, and at the surface, an area of low pressure deepened and followed the same path to the east. In the boundary layer and lower troposphere, winds at 925 and 850 hPa became exclusively north-northwesterly, suggesting the existence of a low-level jet, and surface winds backed with time and increased in speed ahead of a well-defined cold front wind shift. As these winds became more northwesterly ahead of the upper-level trough and surface low, precipitable water values increased, and a tongue of high precipitable water air intersected the coast at the same location as the region of heaviest precipitation. These climatologies, based on hundreds of cases, together provide strong confirmation that forcing associated with an eastward-progressing upper-level trough, a terrain-parallel low-level wind maximum, and an advancing surface cold front together constitute the complex, complementary mechanisms for precipitation in central Chile. [ABSTRACT FROM AUTHOR]

We summarize the recent progress in regional climate modeling in South America with the Rossby Centre regional atmospheric climate model (RCA3-E), with emphasis on soil moisture processes. A series of climatological integrations using a continental scale domain nested in reanalysis data were carried out for the initial and mature stages of the South American Monsoon System (SAMS) of 1993–92 and were analyzed on seasonal and monthly timescales. The role of including a spatially varying soil depth, which extends to 8 m in tropical forest, was evaluated against the standard constant soil depth of the model of about 2 m, through two five member ensemble simulations. The influence of the soil depth was relatively weak, with both beneficial and detrimental effects on the simulation of the seasonal mean rainfall. Secondly, two ensembles that differ in their initial state of soil moisture were prepared to study the influence of anomalously dry and wet soil moisture initial conditions on the intraseasonal development of the SAMS. In these simulations the austral winter soil moisture initial condition has a strong influence on wet season rainfall over feed back upon the monsoon, not only over the Amazon region but in subtropical South America as well. Finally, we calculated the soil moisture–precipitation coupling strength through comparing a ten member ensemble forced by the same space–time series of soil moisture fields with an ensemble with interactive soil moisture. Coupling strength is defined as the degree to which the prescribed boundary conditions affect some atmospheric quantity in a climate model, in this context a quantification of the fraction of atmospheric variability that can be ascribed to soil moisture anomalies. La Plata Basin appears as a region where the precipitation is partly controlled by soil moisture, especially in November and January. The continental convective monsoon regions and subtropical South America appears as a region with relatively high coupling strength during the mature phase of monsoon development. [ABSTRACT FROM AUTHOR]

The temporal stability of the southern annular mode (SAM) impacts on Southern Hemisphere climate during austral spring is analyzed. Results show changes in the typical hemispheric circulation pattern associated with SAM, particularly over South America and Australia, between the 1960s–70s and 1980s–90s. In the first decades, the SAM positive phase is associated with an anomalous anticyclonic circulation developed in the southwestern subtropical Atlantic that enhances moisture advection and promotes precipitation increase over southeastern South America (SESA). On the other hand, during the last decades the anticyclonic anomaly induced by the SAM’s positive phase covers most of southern South America and the adjacent Atlantic, producing weakened moisture convergence and decreased precipitation over SESA as well as positive temperature anomaly advection over southern South America. Some stations in the Australia–New Zealand sector and Africa exhibit significant correlations between the SAM and precipitation anomalies in both or one of the subperiods, but they do not characterize a consistent area in which the SAM signal can be certainly determined. Significant changes of SAM influence on temperature anomalies on multidecadal time scales are observed elsewhere. Particularly over the Australia–New Zealand sector, significant positive correlations during the first decades become insignificant or even negative in the later period, whereas changes of opposite sign occur in the Antarctic Peninsula between both subperiods. [ABSTRACT FROM AUTHOR]

This study investigates the capabilities of two regional models (the ICTP RegCM3 and the climate version of the CPTEC Eta model – EtaClim) in simulating the mean climatological features of the summer quasi-stationary circulations over South America. Comparing the results with the NCEP/DOE reanalysis II data it is seen that the RegCM3 simulates a weaker and southward shifted Bolivian high (BH). But, the Nordeste low (NL) is located close to its climatological position. In the EtaClim the position of the BH is reproduced well, but the NL is shifted towards the interior of the continent. To the east of Andes, the RegCM3 simulates a weaker low level jet and a weaker basic flow from the tropical Atlantic to Amazonia while they are stronger in the EtaClim. In general, the RegCM3 and EtaClim show, respectively a negative and positive bias in the surface temperature in almost all regions of South America. For both models, the correlation coefficients between the simulated precipitation and the GPCP data are high over most of South America. Although the RegCM3 and EtaClim overestimate the precipitation in the Andes region they show a negative bias in general over the entire South America. The simulations of upper and lower level circulations and precipitation fields in EtaClim were better than that of the RegCM3. In central Amazonia both models were unable to simulate the precipitation correctly. The results showed that although the RegCM3 and EtaClim are capable of simulating the main climatological features of the summer climate over South America, there are areas which need improvement. This indicates that the models must be more adequately tuned in order to give reliable predictions in the different regions of South America. [ABSTRACT FROM AUTHOR]

This study investigates the capabilities of two regional models (the ICTP RegCM3 and the climate version of the CPTEC Eta model – EtaClim) in simulating the summer quasi-stationary circulations over South America during two extreme cases: the 1997–1998 El Niño and 1998–1999 La Niña. The results showed that both the models are successful in simulating the interannual variability of summer quasi-stationary circulation over South America. Both the models simulated the intensification of subtropical jet stream during the El Niño event, which favoured the blocking of transient systems and increased the precipitation over south Brazil. The models simulated the increase (decrease) of precipitation over north (west) Amazonia during the La Niña (El Niño) event. The upper level circulation is in agreement with the simulated distribution of precipitation. In general, the results showed that both the models are capable of capturing the main changes of the summer climate over South America during these two extreme cases and consequently they have potential to predict climate anomalies. [ABSTRACT FROM AUTHOR]

The regional Eta workstation (WS) model with horizontal resolution of 40 km has been integrated over South America for January 2003. The NCEP–DOE Reanalysis II was used for initial and lateral boundary conditions. The comparison of the model-simulated and satellite-derived values of monthly mean incident solar radiation at the surface demonstrates that the former values are larger by 20%–30% over the entire region. To improve the surface flux representation in the model, a new solar radiation scheme has been implemented in it. An offline comparison of the original and the new radiation schemes with the detailed line-by-line method demonstrates a higher accuracy for the new scheme. With the new scheme, the model-simulated incident solar radiation at the surface is in a better agreement with the satellite-derived data. Nevertheless, a noticeable systematic difference of 10%–20% still remains, probably because of the incorrect description of cloud parameters in the model. The lower incident solar radiation in the new version of the model causes a decrease of near-surface air temperature by 0.1°–1°C and a decrease of precipitation rate by up to 20%–30% over most of the continent. The increase in the simulated incident solar radiation and temperature is found in the region of the South Atlantic convergence zone, which is responsible for the enhanced cloudiness and precipitation in the central and southeastern parts of Brazil during summer. The model results are compared with observational data of meteorological stations, the Global Precipitation Climatology Project (GPCP), and the South American Low-Level Jet Experiment (SALLJEX) and are discussed. [ABSTRACT FROM AUTHOR]

The article reports on the availability of a gridded dataset of historical daily precipitation for South America. The dataset is a substantial improvement over what heretofore has been easily accessible because it contains data from numerous sources. It help in improving the understanding of precipitation variability, a fundamental and difficult problem of meteorology and climatology. Research into the causes of precipitation variability is seriously impeded by a frequent lack of adequate observational data.

The Paraná-Plata basin is the second largest hydrological basin in South America and is of great importance for the countries of the region (Argentina, Bolivia, Brazil, Paraguay and Uruguay). The present study focuses on the long-term trends in basin-scale precipitation with special emphasis on the role of distribution changes in extreme large-scale precipitation events and on the characteristics and evolution of ENSO teleconnections over the last 50 years. First, we defined a Paraná-Plata basin total precipitation index (PTPI) as the precipitations spatially averaged over the hydrological basin. On interannual time scales, such an index is mainly representative of anomalous monsoon precipitations in the northern part of the basin and large convective precipitation anomalies in the center of the basin (Paraguay-southern Brazil-Uruguay-northern Argentina) typical of the canonical ENSO teleconnection pattern. Our major findings clearly highlight a positive trend in yearly averaged PTPI mainly from the late 1960s to the early 1980s with a strong dependence from month-to-month. The largest precipitation increase is observed from November to May in southern Brazil and Argentina. A close examination of PTPI distributions during the two halves of the period 1950-2001 shows that the changes in the mean state from 1950-1975 to 1976-2001 result from significant changes in each calendar month mean state and in the tails of the PTPI anomaly distributions in May with lesser and weaker large-scale dry events and stronger large-scale wet events. Further studies will be needed to assess whether the observed trend in large-scale extreme precipitation conditions can be related to natural climate variability or anthropogenic activities and whether it is associated to changes in local/regional extreme events. The stronger wet conditions in different months seem to be associated to changes in ENSO characteristics (amplitude, propagation, spatial structure, ...) since the 1982-1983 El Niño. Indeed, spatial ENSO teleconnections (stronger in November and April-May) have greatly evolved from 1950-1975 to 1976-2001. Moreover, we demonstrate that there is a strong modulation and displacement of the teleconnection patterns from one event to another, impeding the definition of robust statistical relationship between ENSO and precipitation in the Paraná-Plata basin (except maybe over a very limited area near the common border between Paraguay, Argentina and Brazil). Finally, the non-antisymmetrical patterns of precipitation between El Niño and La Niña conditions and the non-linear relationship between precipitation and either Niño3.4 or Niño1+2 sea surface temperature indices show that linear statistical forecast systems are actually of very limited use for impact predictions on society on a local or regional scale. [ABSTRACT FROM AUTHOR]

Seasonal linear trends of precipitation from South American station data, which have been averaged onto grids, are examined, with emphasis on the central continent. In the period 1976–99, the largest trend south of 20°S occurs during the January–March season, is positive, and is centered over southern Brazil. From 1948 to 1975 the trend is also positive, but with less than half the slope. The trend is not due to a systematic change in the timing of the rainy season, which almost always starts before January and usually ends after March, but rather results from an increase in the percent of rainy days, and an increase in the rainy day average. The dynamic causes of the trend are not obvious. It does not appear to be accounted for by an increase in synoptic wave activity in the region. The precipitation trend is related to a positive sea surface temperature trend in the nearby Atlantic Ocean, but apparently not causally. The trend in the Atlantic seems to result from a decrease in mechanical stirring and coastal upwelling associated with a decrease in the strength of the western edge of the circulation associated with the South Atlantic high. [ABSTRACT FROM AUTHOR]

The influence of heating over Africa on the South American precipitation climatology, and the influence of South America on Africa, is examined through the application of GCM simulations with idealized boundary conditions and perpetual solstice (January and July) conditions. The presence of Africa is associated with a pronounced (up to 4 mm day-1) decrease in precipitation in Brazil's Nordeste region during austral summer. Low-level moisture divergence and dry-air advection associated with the downbranch of a Walker circulation induced by heating over southern Africa is amplified over the Nordeste due to the response of the land surface. The response is much smaller during austral winter due to differences in the heat source over Africa and a reduced sensitivity in the surface heat balance over tropical South America. Forcing from South America in January shifts the position of the South Indian convergence zone (SICZ) to the southwest over southern Africa in association with the formation of the South Atlantic convergence zone (SACZ). In July, a Rossby wave train generated over South America induces a response in the surface temperature of Africa that leads to stronger precipitation in central and western Africa. This study suggests a zonal mode of variability for South American and African circulation and precipitation fields. The resulting perturbations depend as much on land surface–atmosphere interactions as on the direct forcing from the adjacent continent, and the mechanisms are highly nonlinear. [ABSTRACT FROM AUTHOR]

The precipitation variability over South America south of 20° S (5A205) has been investigated at a decadal (DD) and non-DD time scales. The results suggest that the space-time particularities of the ENSO-related precipitation anomalous patterns depend on the time scales considered. The precipitation patterns in the 5A205 associated with the non-DD episodes exhibit a space-time coherent characteristics during ONDJ (0)-JJAS (+1) period such that a prominent area of positive (negative) anomalies is observed in the central 5A205 and displaced northeastward with the time for the non-DD El Niños (La Niñas). On the other hand, the precipitation anomalous patterns associated with the DD episodes feature more complex horizontal structures and larger anomalies than those of the non-decadal episodes. It is also worthwhile noting that the 5A205 climate experiences the strongest and more extensive effects of the DD episode during the austral summer of the year following the onset of the DD episodes. [ABSTRACT FROM AUTHOR]

We classified 34 years of winter daily 500 hPa geopotential height patterns over the eastern South Pacific-South America-South Atlantic region using the K-means clustering method. We found a significant classification into five weather regimes (WRs) defined as the most frequent large-scale circulation anomalies: WR1 (trough centred downstream of the Drake Passage), WR2 (trough over the SW Pacific and ridge downstream), WR3 (ridge over the SE Pacific and NW–SE trough downstream), WR4 (trough over the SE Pacific and NW–SE ridge downstream) and WR5 (weak ridge to the west of southern South America). We also analysed their persistence and temporal evolution, including transitions between them and development around onsets and breaks of each regime. The preferred transitions, WR1→WR3→WR2→WR4→WR1 and also WR1→WR3→WR2→WR1, suggest the progression of a Rossby wave-like pattern in which each of the regimes resemble the Pacific-South America modes. Significant influence of the WRs on local climate over Argentina was found. The preferred transitions WR1→WR3 and WR3→WR2 induce sustained cold conditions over Patagonia and over northern Argentina, respectively. The most significant change in precipitation frequency is found for WR3, with wetter conditions over all the analysed regions. Finally, the interannual to interdecadal significant variations in the occurrence of these regimes were discussed. WR1 and WR3 are more frequent and WR2 is less frequent during El Niño, and WR2 and WR5 are more frequent and WR1 is less frequent during La Niña. A significant decrease in WR2 and increase of WR4 and WR5 during the 1970s and early 1980s were found. [ABSTRACT FROM AUTHOR]

Evolving aspects of the dominant high-frequency modes of the 925-hPa v-component and precipitable water in the Tropical South American and Atlantic sector are studied for the austral summer and winter seasons. Their relations to the precipitation anomalies over the equatorial South America are also investigated. The highest percentages of the total variance contained in the high-frequency time-scale for the 925-hPa v-component have a clear seasonal dependency such that they are confined in the Tropical South Atlantic (TSA) during the austral summer and in the Tropical North Atlantic (TNA) during the austral winter. The high-frequency variability for the TSA during the austral summer stems from the combined effects of equatorward incursions of midlatitude synoptic and transient wave systems, equatorial trades and westward traveling disturbances in equatorial latitudes. All these systems together have a pronounced effect in modulating the summer precipitation over northeastern South America, though the isolated effect of the easterly waves is weak. In contrast, the high-frequency variability for the TNA during the austral winter is mainly due to wave-type westward traveling tropical disturbances. These disturbances have an important role in modulating the daily precipitation of northern part of the South America during the austral winter. [ABSTRACT FROM AUTHOR]

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 the other hand, in the composite corresponding to the more negative SST anomalies, the low-level flow and the moisture transport from the continental low latitudes turn eastward toward the South Atlantic convergence zone (SACZ) at about 20°S, converging with the flow from the north driven by the South Atlantic high. In this composite, there is an anticyclonic circulation with a westward flow between 25° and 35°S, which turns southward after reaching the proximity of the Andes Mountains. In the composite of the more positive anomalies, there are two regional maximums in the precipitation field. One maximum stretches along the continental extension of a southwardly displaced SACZ and another is centered at about 30°S and 55°W, in the path of the main stream of the low-level moisture transport. In the other composite, there is only one regional maximum in precipitation, which coincides with the continental extension of the SACZ... [ABSTRACT FROM AUTHOR]

Examines the relationship between precipitation and cross-equatorial flow over the western Amazon in South America. Variability of the cross-equatorial flow; Indicator for precipitation change over tropical and subtropical; Analysis on the singular value decomposition.