Descripción: Fil:Saraceno, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: Eighteen year (1985-2002) sea surface temperature (SST) data are used to study the intraseasonal variability of the Patagonian shelf break front (SBF) in the SW South Atlantic Ocean between 39° and 44°S. The cross-shelf break SST gradients reveal distinct, previously undocumented thermal fronts located both, offshore and inshore of the SBF. Throughout the year the main SBF, identified as a band of negative SST gradient maxima (relatively strong offshore temperature decrease), forms a persistent feature located closed to the 200 m isobath, while two distinct negative gradient maxima are located inshore and offshore of this location. Daily SST images reveal the presence of three branches of cold waters whose edges delineate the above mentioned fronts. The two offshore branches closely follow lines of constant potential vorticity (f/h) and appear to be associated with the Malvinas Current, while a third branch, located further onshore, is not steered by the bottom topography. South of 40°S the onshore branch forms a quasi permanent front parallel to the SBF. Copyright 2008 by the American Geophysical Union.

Descripción: A Singular value decomposition (SVD) analysis was performed jointly on the daily intensity of extreme rainfall (DIER) over Argentina and the sea surface temperature (SST) of all the oceans from 17.5°N to 90°S in order to identify the large-scale variability of the SSTs related to extreme rainfall, in the period 1962-2005. The main objective of the article is to objectively recognize regions of the tropical and subtropical oceans that could be related with the extreme rainfall over Argentina. Spring is the season that is best represented by the first mode, accounting for up to 45% of the covariance between the DIER and SST. The first SVD mode of spring, summer and autumn presents a pattern of SST relating to the El Niño-Southern Oscillations (ENSO) phenomena with an enhanced DIER in different zones of centre and east of Argentina. In the second SVD mode of spring and summer, the SST patterns show cold conditions in the tropical and subtropical Atlantic and near Indonesia with an enhancement of the DIER in the centre and east of Argentina. These modes show a significant decadal variability. In the third SVD mode of spring and summer, the SST patterns present warm and cold conditions in the Indian Ocean and the centre and western Pacific Ocean (PO) with decreased rainfall in the northern and eastern portion of Argentina, respectively. This mode shows a significant period of temporal variability of around 14 years. The third mode of autumn presents warm conditions in the tropical Atlantic and the southwest PO with a low DIER in the centre and east of Argentina. This mode also presents temporal variability of around 14 years. The correlation between each mode derived from analysis of SVD and climate indices related with SST were computed. © 2012 Royal Meteorological Society.

Descripción: A Singular Value Decomposition (SVD) analysis was performed jointly on extreme temperature events in Argentina and sea surface temperature (SST) in the South Atlantic and South Pacific. Sea level pressure (SLP) patterns associated with the first SVD coupled mode were also analyzed. Winter is the season of the year that is best represented by the first mode, accounting for up to 70% of the winter covariance between temperature events and SST. The warm and cold events in Argentina are essentially a consequence of the creation of meridional atmospheric circulations over the continent. Such atmospheric patterns result from displacements and intensity changes of the subtropical anticyclones over the oceans and of the continental low-pressure center in northwestern Argentina. The temperature events in southern Argentina are also closely related to the warming and cooling of the coastal waters in the South Atlantic and South Pacific. The analysis suggests that in summer and winter, high (low) occurrence of warm events and low (high) occurrence of cold events are related to similar oceanic and atmospheric circulation situations. The temperature events in Argentina show higher correlation with the Atlantic than with the Pacific, which reflects the importance of the "orographic barrier" of the Andes Mountains in driving the atmospheric circulation. The only exception to this rule concerns the warm events in spring, for which the warming of the equatorial Pacific (the ENSO pattern) appears as the dominant mode. The temporal patterns of the temperature events in Argentina exhibit significant interannual variability in fall, winter, and spring, with periods of 3 to 5 years. The summer patterns suggest a very low-frequency variation with a period longer than 20 years. Copyright 2003 by the American Geophysical Union.

Descripción: A database of daily extreme temperature was created for as many stations as possible for Uruguay, as far back as possible. This is the first attempt to gather all the different data sources together, perform a quality control and homogeneity assessment. We work with seven stations; it should be taken into account that Uruguay is a small country (around 177 000 km2) and this represents most of the available data. There are three old series with starting dates in 1930, and four that start around 1950. From this database, a set of four extreme temperature indices was constructed for the oldest five stations, warm days (TX90), cold days (TX10), warm nights (TN90) and cold nights (TN10). The index TN10 shows the largest significant negative trend for the period 1960-2002, while TN90 shows a positive but not significant trend for this period indicating a strong warming of nighttime temperature. A spectral analysis was performed using the multi taper methods (MTM) to the de-trended annual, summer Dec-Feb (DJF) and winter Jun-Aug (JJA) indices time-series. This analysis shows that on inter-annual timescales, the most significant range of frequencies is from 2 to 2.5 years and from 3 to 6 years. Low frequencies of variability were detected when the MTM was applied to de-trended smoothed annual time-series, around the range of frequencies of 15-25 years for almost all the indices analysed. Links with global sea surface temperature (SST) were studied for two stations (Paysandu and Rocha), and it was found that the indices showed largest correlations with SST anomalies in the Pacific Ocean. We detected changes in the response of the TN10 index for Rocha station when the series was split up into two different periods (1942-1976 and 1977-2005). Copyright © 2007 Royal Meteorological Society.

Descripción: The objective of this research is to study the main variability modes of the frequency of extreme temperatures in the south of South Amenica, their relation to sea surface temperatures (SSTs), and some indices of atmospheric circulation in the Southern Hemisphere. Observational data and reanalysis data were used for this purpose over the 1964-2003 period. An initial analysis showed that between the months of March and June, the frequency of wann events (especially warm nights) is highly associated with the SST in coastal zones. A wavelet analysis showed that the main variability mode found at a seasonal scale was an 8-year wave signal present in spning that remains active until the 1990s; it was noticeable in the analysis of cold nights, Atlantic SSTs, Pacific SSTs, and the Southern Annular Mode (SAM). A cross-wavelet analysis among them reflected this signal as a common variability mode, with the positive phase of the SAM congruent with the warmest conditions in the coastal zones of the Atlantic Ocean and lower cases with cold nights at the reference meteorological stations analyzed. Although longer series are desirable for low-frequency variability analysis, the results agree with previous studies that take into account an 8-year periodicity of the baroclinic waves at the Southern Hemisphere, supporting the relevance of the 8-year signal. Copyright 2008 by the American Geophysical Union.

Descripción: The response of altered sex ratio in southern elephant seals due to environmental stress was analysed. Data were collected at King George Island from 1980 to 1994. Significant retreats in the ice cover during El Niño events strongly suggest environmental stress during this period along the Bellingshausen Sea, a zone where female elephant seals from King George Island feed during their pregnancy. Randomly chosen weaning elephant seal pups (n = 1178) were sexed at Stranger Point (King George Island, 62° 14' S, 58° 30' W) over 5 km of beach from 1985 to 1994. Adult sex ratio was also determined annually from 1980 to 1994 as the ratio between maximum number of bulls and females on land. The theoretical pup sex ratio was assumed as 1:1 according to background information. Adult sex ratio was calculated as 1:6. To define the occurrence of El Niño Southern Oscillation (ENSO) during the study period, a sea surface temperature (SST) index called 'Niño 3.4' for the region 5°N to 5° S, 120° E to 170° W was considered. Monthly SST anomalies were obtained from the Climate Prediction Center (CPC, NOAA). To provide an annual index of anomaly strength (IAS), the monthly adjusted oscillation index climatology (AOIC) was averaged. Accumulated values during the whole study period showed that during El Niño years (1987, 1991, 1992) the proportion of pups was significantly biased in favour of females (p < 0.01). During normal years (1986, 1990, 1993, 1994) and La Niña years (1985, 1988, 1989), accumulative values showed a greater proportion of male pups to females (p < 0.05), Using the 1:1 hypothesis, we found during El Niño years a 9% reduction in the male segment, whereas in non-El Niño years a recovery of 7 % was observed (3 % during normal years and 4 % during La Niña years. To see the influence of accumulative values of pup sex ratio in adult sex ratio, a theoretical adult proportion was calculated as 1:6. To test this hypothesis, information on adult sex ratio taken from King George Island between 1980 and 1994 (n = 14 yr) was analysed. The average adult sex ratio for King George Island was 1:7. This value seems to confirm the hypothesis that this population has had a balanced production of male and female pups in the long term. Comparisons with Pacific and Indian declining seal populations were made.