Eduardo Agosta Scarel | Universidad Nacional de La Plata (original) (raw)

Papers by Eduardo Agosta Scarel

Meteorologica, Apr 25, 2024

RESUMEN Algunos autores encuentran que la variabilidad de la precipitación en distintas escalas s... more RESUMEN Algunos autores encuentran que la variabilidad de la precipitación en distintas escalas sobre Argentina subtropical puede ser vinculada a las condiciones de la temperatura superficial del mar (TSM) en el Atlántico Sur (Venegas et al., 1998, Robertson y Mechoso 1998, Doyle y Barros 2002). Particularmente, la precipitación estival en el Centro-Oeste de Argentina (COA) presenta también vinculación con las TSMs en latitudes medias en el sector sudoeste del Atlántico Sur (Compagnucci y Agosta 2006). Las variaciones en la TSM sobre esta área oceánica está modulada por el flujo de masa de aire en superficie en torno a 40°S (Wainer y Venegas 2002). Por tanto el objetivo de este trabajo es estudiar los procesos en baja frecuencia del sistema atmósfera/océano sobre el sector sudoeste del Atlántico Sur que se asocian a la precipitación estival del COA. Los resultados muestran que la circulación de la atmósfera tiene un centro de acción sobre el sudoeste del Atlántico Sur, en torno a 45°S-60°O, durante gran parte del siglo XX, que modula las fluctuaciones interanuales a multidecádicas (cuasi-ciclo de 18 años) de la precipitación en el COA, estudiadas por Compagnucci et al. (2002). Este centro de acción de la atmósfera es el forzante común para la precipitación y la TSM sobre el sector sudoeste del Atlántico Sur.

AGU Spring Meeting Abstracts, May 1, 2013

AGU Fall Meeting Abstracts, Dec 1, 2013

Se estudia el ciclo anual de precipitación en la región Pampa Amarilla (RPA). La mayor parte de l... more Se estudia el ciclo anual de precipitación en la región Pampa Amarilla (RPA). La mayor parte de la RPA presenta máximo en marzo, seguido de noviembre y diciembre, y mínimo en invierno. El acumulado octubre-marzo (verano) resulta significativamente distinto al acumulado abril- septiembre (invierno). Se analizan las variaciones, tendencias y cambios de las series temporales en verano e invierno. Las series más largas seleccionadas sobre el centro y norte de La Pampa, muestran cambio positivo y significativo por tendencia lineal, del orden del 44% de la media regional en verano. Tras una prolongada sequía (1930-1950) el cambio estival irrumpe en la década de los setenta (centro-norte de La Pampa), y en la década de los sesenta (centro-este de La Pampa). Este cambio brusco ha producido una larga fase húmeda extendida hasta comienzos de los dos mil. El cambio de la década del setenta puede estar asociado al cambio de las condiciones medias de la Temperatura superficial del mar (TSM) del Pacífico central ecuatorial. Para el período de prolongada fase húmeda (1969-2009) en el sector centro y norte de la RPA hay un aumento (disminución) de las precipitaciones de verano (invierno) mientras que hacia el centro-sudoeste de la RPA, los cambios son negativos y significativos. La exploración de la circulación troposférica y la TSM revela que la variabilidad interanual de la precipitación está modulada por teleconexiones remotas trópico-extratrópico. Se descarta cualquier posible relación con el Modo Anular del Sur. En verano, el mecanismo de interacción es la modulación de la corriente en chorro subtropical en el Pacífico Sur hacia Sudamérica, generada por anomalías en la circulación de la celda de Hadley sobre el Pacifico ecuatorial central. El mecanismo podría estar asociado a la baja y la alta frecuencia del fenómeno El Niño. En invierno, la teleconexión está dada por la propagación de ondas cuasi estacionarias de Rossby desde la región ecuatorial del Pacifico occidental. Los centros de acción en las inmediaciones de Sudamé [...]

The present work aims to analyze the tropospheric circulation in the Southern Hemisphere (SH) ass... more The present work aims to analyze the tropospheric circulation in the Southern Hemisphere (SH) associated with anomalously cold summers (ACS, Dec-Feb) in the period 1981-2010 over northernmost Antarctic Peninsula (AP). A quartile criterion is used to identify ACSs, and a wave-activity flux for stationary quasi-geostrophic (QG) eddies on a zonally varying basic flow is used as a diagnostic tool to study wave-train propagation from the Pacific Ocean. It is shown that the summer of 2010 was singularly cold, so this summer is studied separately from the ACS composites previous to 2010. The ACSs prior to 2010 are characterized by a Pacific-South American (PSA)-like quasi-stationary wave (QSW) train that extends barotropically through the troposphere up to the lower stratosphere. It is emanated from a region of anomalous convection in New Zealand and it is directed towards the South Pacific. The wave train leads to an anomalous stationary cyclone that is located to the northwest of the AP. The easterly wind anomalies induced by this local anomalous stationary cyclone together with higher cloudiness anomalies are found to be associated with ACS events over the northern AP. The 2010 cold summer not only shows an anomalous stationary cyclone to the northwest of the AP, but singularly also shows a mid-latitude anomalous anticyclone over the southeastern South Pacific. From there, a shorter QSW regionally propagates towards southern South America. In this case there is no PSA-like wave structure crossing the South Pacific. The short regional QSW seems to emanate from a region of positive sea surface temperature (SST) anomalies in the middle of the southern South Pacific. The SST anomalies can be related to the generation of locally increased mean-flow baroclinicity. Hence, this QSW propagation is related to anomalous transient activity. In turn, these SST anomalies could be induced by a PSA-like QSW propagation during the previous spring (Sep-Nov) of 2009.

Atmospheric Research, Sep 1, 2020

Homogeneity is an important characteristic of time series that must be checked before doing any a... more Homogeneity is an important characteristic of time series that must be checked before doing any analysis. Breakpoints in meteorological time series are very common due to climatic jumps caused by natural forcing and/or human activity but also, and mainly, produced by inhomogeneities which are erratic in nature. In this work, five breakpoint tests are analyzed to evaluate their performance in detecting breakpoints for different lengths of time series and intensity of breakpoint, among other features, through the realization of numerical experiments of sensitivity. These tests are: Student's, Mann-Whitney, Buishand-R, Pettit and SNHT. The Student's and Mann-Whitney tests show high probability of false breakpoint detection and problems to reproduce the date when a breakpoint occurs. In addition, the Buishand-R and Pettit are more efficient to reproduce the date of breakpoint when it occurs in the middle of a time series while the SNHT does it for breakpoints in its borders. In this sense, the Pettit, Buishand-R and SNHT tests show better performance than the Mann-Whitney and Student's. Furthermore, an original methodology to detect multi-breakpoints based on the aforementioned tests is applied to precipitation time series from sixty-two rain-gauge stations in subtropical Argentina. A breakpoint around 1976 is detected in the wet season (austral warm season), highly likely linked to the well-documented 1976/77 climate transition, by all the used tests and for most of the stations. To a lesser extent, another breakpoint occurred in the mid-1950's. Other breakpoints are also detected in the early 1980s and the early 2000s, though in few stations and by one or two tests. For the breakpoints found in the mid-1950's and in the early 1980's, a strong relationship with two ENSO's indices is found which suggests that changes in long-term ENSO variability could be the cause of these breakpoints.

Climate Research, Feb 5, 2015

Westerlies are the main climatic feature in the mid-latitudes of the Southern Hemisphere (SH), dr... more Westerlies are the main climatic feature in the mid-latitudes of the Southern Hemisphere (SH), driving the amount and distribution of precipitation. Patagonia is a vast region in South America's mid-latitudes, which encompasses 2 sub regions with highly distinct precipitation features. These two regions include wet Western Patagonia extending from the Pacific coast to the Andean highs (i.e. maximum elevations), and dry Eastern Patagonia situated leeward of the Andes in the Argentine steppe plains. Patagonia is influenced by strong mid-latitude westerlies throughout the year. Westerlies have been considered the unique driver of climate both in Western and Eastern Pata gonia. This research is focused on the Lago Cardiel catchment area in central Eastern Patagonia. A significant link between precipitation in that region and local zonal moisture transport from the Atlantic was established. A fraction of intense precipitation was related to strong local westward moisture transport, partly as a consequence of slow-moving weather systems crossing over Patagonia. As long as a dipolar pattern of long-term precipitation anomaly was observed between dry central Western/Southern Patagonia and wet central Eastern Patagonia, it could be interpreted as due to enhanced synoptic easterly moisture flux from the Atlantic. Thus, the westerlies rule was broken at least under blocking-like flows, which induced moist easterlies. The relatively wet 1940s exemplified this phenomenon. Such a conceptual framework can be applied to palaeoclimatic proxy record reconstructions as well as to general circulation model (GCM) outcomes for the late and mid-Holocene.

Journal of Climate, Sep 1, 2008

Previous works suggest that more El Niño-like conditions can be expected over the South American ... more Previous works suggest that more El Niño-like conditions can be expected over the South American (SA) climate and atmospheric circulation because of the similarity of the predominately warm conditions in the sea surface temperature (SST) over the central-equatorial Pacific after the 1976/77 summer with those of the SSTs during El Niño events. Here, the summer (October to March) low-level atmospheric circulation over southern SA is studied in order to determine the specific changes that can be related with the global climate transition 1976/77. The rotated principal component analysis is applied to the daily 850-hPa geopotential height fields from the NCEP-NCAR reanalysis I for the periods before and after 1976/77. The second and third principal patterns reveal changes both in the order of explained variances and in some of their spatial features. They can be associated with an expansion of the subtropical South Atlantic anticyclone over SA and lower midlatitude cyclone activity after the 1976/77 summer. The latter is partly associated with the actual tendency toward the positive phase of the southern annular mode. The main patterns can even explain some changes in the observed precipitation over subtropical central-west Argentina as well as for other subtropical regions. Different inhomogeneity tests applied to the atmospheric circulation climatology support the changes. Results suggest that the atmospheric circulation change could be somewhat unique (not observed in the twentieth century) and, thus, it could not be thoroughly ascribed to the El Niño-like variability.

International Journal of Climatology, Mar 27, 2020

Precipitation anomalies over subtropical Argentina in eastern subtropical South America (ESSA) sh... more Precipitation anomalies over subtropical Argentina in eastern subtropical South America (ESSA) show significant signatures of the El Niño Southern Oscillation (ENSO) during the SONDJ (from September to January) season. The correlation maps between seasonal precipitation anomalies and the C‐index show a dipole structure with positive correlation over eastern ESSA and negative over South American convergence zone. Based on principal component analysis, precipitation anomalies within the SONDJ season during ENSO events were discriminated into three categories typical, atypical and nontypical, regarding their precipitation response. Typical (atypical) stands for precipitation anomalies similar (inverse) in comparison to the linear expected anomalies for El Niño or La Niña events. In the period 1979–2016, five (five) typical seasons, two (zero) atypical seasons and six (six) nontypical seasons were recorded under El Niño (La Niña) events. During typical SONDJ seasons under El Niño, precipitation over ESSA is mainly modulated by regional tropospheric circulation anomalies induced by quasi‐stationary Rossby wave propagation from the western South Pacific towards South America. The precipitation anomalies during the two atypical SONDJ seasons in El Niño were overall partly owing to shifts of the sea surface temperature (SST) gradient in the equatorial Pacific, and changes in the Atlantic basin SST anomalies.

Atmospheric Research, Jun 1, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

International Journal of Climatology, Jul 17, 2013

This work shows statistical evidence for lunar nodal cycle influence on the low-frequency summer ... more This work shows statistical evidence for lunar nodal cycle influence on the low-frequency summer rainfall variability over the plains to the east of subtropical Andes, in South America, through long-term sea surface temperature (SST) variations induced by the nodal amplitude of diurnal tides over southwestern South Atlantic (SWSA). In years of strong (weak) diurnal tides, tide-induced diapycnal mixing makes SST cooler (warmer) together with low (high) air pressures in the surroundings of the Malvinas/Falklands Islands in the SWSA, possibly through mean tropospheric baroclinicity variations. As the low-level tropospheric circulation anomalies directly affect the interannual summer rainfall variability, such an influence can be extended to the bi-decadal variability present in the summer rainfall owing to the nodal modulation effect observed in the tropospheric circulation. The identification of the nodal periodicity in the summer rainfall variability is statistically robust.

Journal of Climate, Mar 1, 2012

The interannual-to-multidecadal variability of central-west Argentina (CWA) summer (October-March... more The interannual-to-multidecadal variability of central-west Argentina (CWA) summer (October-March) precipitation and associated tropospheric circulation are studied in the period 1900-2010. Precipitation shows significant quasi cycles with periods of about 2, 4-5, 6-8, and 16-22 yr. The quasi-bidecadal oscillation is significant from the early 1910s until the mid-1970s and is present in pressure time series over the southwestern South Atlantic. According to the lower-frequency spectral variation, a prolonged wet spell is observed from 1973 to the early 2000s. The precipitation variability shows a reversal trend since then. In that wet epoch, the regionally averaged precipitation has been increased about 24%. The lower-frequency spectral variation is attributed to the climate shift of 1976/77. From the early twentieth century until the mid-1970s, the precipitation variability is associated with barotropic quasi-stationary wave (QSW) propagation from the tropical southern Indian Ocean and the South Pacific, generating vertical motion and moisture anomalies at middle-to-subtropical latitudes east of the Andes over southern South America. The QSW propagation could be related to anomalous convection partly induced by tropical anomalous SSTs in the western Indian Ocean (WIO). It could also be linked to another midlatitude source along the storm tracks, to the east of New Zealand. After 1976/77, the precipitation variability is associated with equatorial symmetric circulation anomalies linked to El Niñ o-Southern Oscillation (ENSO)-like warmer conditions. Positive moisture anomalies are consistently observed at lower latitudes in association with inflation of the western flank of the South Atlantic anticyclone. Outside of this, the precipitation variability is unrelated to ENSO.

Atmospheric Research, Apr 1, 2023

Springer earth system sciences, 2016

The climate in the North Atlantic Ocean during the Marine Isotope Stage 3 (MIS 3)—roughly between... more The climate in the North Atlantic Ocean during the Marine Isotope Stage 3 (MIS 3)—roughly between 80,000 years before present (B.P.) and 20,000 years B.P., within the last glacial period—is characterized by great instability, with opposing climate transitions including at least six colder Heinrich (H) events and fourteen warmer Dansgaard–Oeschger (D-O) events. Periodic longer cooling cycles encompassing two D-O events and ending in a colder Heinrich episode occurred lasting about 10 to 15 ky each, known as the Bond cycle. Heinrich events occurred less frequently than D-O events. These were recurrent every 1.5 ky on average, while ~10 ky elapsed between two H events. Neither of the two types of events is strictly periodical, however. After H events abrupt shifted to warmer climate, the D-O events followed immediately. During an H event, abnormally large amounts of rock debris transported by icebergs were deposited as layers at the bottom of the North Atlantic Ocean. The various theories on the causes include factors internal to the dynamics of ice sheets, and external factors such as changes in the solar flux and changes in the Atlantic Meridional Overturning Circulation (AMOC). The latter is the most robust hypothesis. At certain times, these ice sheets released large amounts of freshwater into the North Atlantic Ocean. Heinrich events are an extreme example of this, when the Laurentide ice sheet disgorged excessively large amounts of freshwater into the Labrador Sea in the form of icebergs. These freshwater dumps reduced ocean salinity enough to slow down deep-water formation and AMOC. Since AMOC plays an important role in transporting heat northward, a slowdown would cause the North Atlantic Ocean to cool. Later, as the addition of freshwater decreased, ocean salinity and deep-water formation increased and climate conditions recovered. During the D-O events, the high-latitude warming occurred abruptly (probably in decades to centuries), reaching temperatures close to interglacial conditions. Even though H and D-O events seemed to have been initiated in the North Atlantic Ocean, they had a global footprint. Global climate anomalies were consistent with a slowdown of AMOC and reduced ocean heat transport into the northern high latitudes. The bipolar pattern with warming conditions in the Northern Hemisphere (NH) and cooling in the Southern Hemisphere (SH) is discussed from the information published by various authors who have used the limited data available for the SH, and palaeoclimatic simulations obtained by numerical modelling. Results show that the SH mid-latitude anomalies presented much smaller magnitude than those of the NH.