87 research outputs found
Regionalisation of heat waves in southern South America
No full textThis study describes the climatological characteristics of regional heat waves (HWs) over southern South America (SSA) for the warm seasons (October–March) of 1979–2018 based on daily maximum temperature series from 131 weather stations. Clustering of stations with high co-occurrence of simultaneous HW days is employed to identify regional HW events over five homogeneous regions: northern, central-eastern and southern SSA regions, central Argentina, and central Chile. When all regions are considered, we find a mean frequency of ∼4 HWs per year. Transitional regions (northern SSA, central-eastern SSA and central Argentina) are characterised by longer, albeit less intense, HWs than the southernmost region (southern SSA), whereas central Chile events display the lowest duration, intensity and extension. By aggregating these single HW attributes into a combined severity index, a ranking of historical HWs has been obtained, with the March 1980 event standing as the most severe one of SSA. The assessment of long-term changes reveals significant increases in the frequency of regional HW days over central Argentina and central Chile only. Trends in HW characteristics are also region dependent, and the southernmost region is the only one where HW severity has increased significantly.We report similarities and differences in the synoptic circulation patterns associated with regional HW events. Southern SSA HWs have the most distinctive signatures, related to extratropical high-pressure systems blocking the westerly flow. In the remaining regions, HWs are associated with anomalies in the South Atlantic (northern SSA, central-eastern SSA and central Argentina) or South Pacific (central Chile) High, and the intensification of the northerly low-level flow by regional thermal lows and South American Low Level Jet events. Regional HWs often migrate from northern to central-eastern SSA and central Argentina, following the displacement/intensification of the South Atlantic High, which partially explains the similarity of their associated patterns
Construction of a daily precipitation grid for southeastern South America for the period 1961-2000
No full textDaily station precipitation totals are used to develop a gridded dataset for the region (14°–40°S, 45°–70°W) on a 0.5° × 0.5° latitude/longitude grid, primarily for comparison with regional climate model (RCM) simulations. The gridded dataset covers the period 1961–2000. Much of the paper discusses the quality control of the basic station precipitation series. Although the primary aim of the development has been RCM validation, we have assessed trends in seasonal precipitation totals as well as trends in two measures of precipitation extremes (R95p, the daily precipitation amount exceeded only 5% of the time and Rx5day, the maximum 5-d precipitation total during each season). Relatively few regions across the large domain have statistically significant trends, but those that do tend to be located in the eastern two thirds of the grid, particularly over southeastern Brazil and Uruguay. Significant trends are also more evident in the DJF and MAM seasons. There is good spatial agreement between the trends in seasonal totals and trends in the extreme indices.Fil: Jones, P. D.. University Of East Anglia; Reino UnidoFil: Lister, D. H.. University Of East Anglia; Reino UnidoFil: Harpham, C.. University Of East Anglia; Reino UnidoFil: Rusticucci, Matilde Monica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rusticucci, Matilde Monica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Variability and trends in indices of quality-controlled daily temperature extremes in Uruguay
No full textA 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.Fil:Rusticucci, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Renom, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Temperature extremes in the south of South America in relation to Atlantic Ocean surface temperature and Southern Hemisphere circulation
No full textThe 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.Fil:Barrucand, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Rusticucci, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Vargas, W. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Analysis of interdecadal variability of temperature extreme events in Argentina applying EVT
No full textThe frequency of occurrence of temperature extreme events has changed throughout the last century: significant positive trends in warm nights and negative trends in cold nights have been observed all over the world. In Argentina, the probability of occurrence of warm annual extremes of maximum temperature has decreased in the last decades, while there has been an increase in warm annual extremes of minimum temperature. The main objective of this paper is to evaluate observed interdecadal changes in the distribution of temperature events that exceed a fixed threshold in five meteorological stations from Argentina over the period 1941-2000, by applying the extreme value theory (EVT). The availability of daily data allows fitting a generalized Pareto distribution (GPD) to daily temperature anomalies over the 90th or below the 10th percentile, in order to estimate return values of extreme events. Daily temperature anomalies are divided into three consecutive and non-overlapping subperiods of 20 years. GPD is fitted to each subperiod independently and a comparison is made between return values estimated in each subperiod. Results show that there is a decrease in the intensity of warm extreme events during the whole period, together with anincrease in its frequency of occurrence during the last 20 years of the twentieth century. Cold extremes alsoshow a decrease in their intensity. However, changes in their frequency of occurrence are not so consistentbetween the different stations analyzed.La frecuencia de ocurrencia de los eventos extremos de temperatura ha sufrido variaciones a lo largo del último siglo: se han observado tendencias positivas significativas en las noches cálidas y tendencias negativas en las noches frías en todo el mundo. En Argentina, la probabilidad de ocurrencia de extremos cálidos anuales de la temperatura máxima disminuyó en las últimas décadas, mientras que hubo un incremento en la probabilidad de ocurrencia de extremos cálidos anuales de la temperatura mínima. El objetivo principal de este trabajo es evaluar la variabilidad interdecadal observada en la distribución de los eventos de temperatura que superan un determinado umbral en cinco estaciones meteorológicas de Argentina durante el periodo 1941-2000, mediante la aplicación de la teoría de valores extremos. La disponibilidad de datos diarios permite el ajuste de la distribución generalizada de Pareto (DGP) a las anomalías diarias de temperatura que exceden el percentil 90 o que no alcanzan el percentil 10 con el propósito de estimar los valores de retorno de los eventos extremos. Las series de anomalías diarias de temperatura se dividen en tres subperiodos consecutivos sin superposición de 20 años cada uno. La DGP se ajusta en cada uno de los tres subperiodos en forma independiente y se comparan los valores de retorno estimados en cada subperiodo. Los resultados muestran que hay una disminución en la intensidad de eventos extremos cálidos durante todo el periodo de estudio, junto con un incremento en su frecuencia de ocurrencia durante los últimos 20 años del siglo XX. Los extremos fríos también muestran una disminución en intensidad. Sin embargo, los cambios en su frecuencia de ocurrencia no son tan consistentes entre las diferentes estaciones estudiadas
The international surface temperature initiative's global land surface databank
No full textThe International Surface Temperature Initiative (ISTI) consists of an end-to-end process for land surface air temperature analyses. The foundation is the establishment of a global land surface Databank. This builds upon the groundbreaking efforts of scientists in the 1980s and 1990s. While using many of their principles, a primary aim is to improve aspects including data provenance, version control, openness and transparency, temporal and spatial coverage, and improved methods for merging disparate sources. The initial focus is on daily and monthly timescales. A Databank Working Group is focused on establishing Stage-0 (original observation forms) through Stage-3 data (merged dataset without quality control). More than 35 sources of data have already been added and efforts have now turned to development of the initial version of the merged dataset. Methods have been established for ensuring to the extent possible the provenance of all data from the point of observation through all intermediate steps to final archive and access. Databank submission procedures were designed to make the process of contributing data as easy as possible. All data are provided openly and without charge. We encourage the use of these data and feedback from interested users.Fil: Lawrimore, J. H.. National Oceanic and Atmospheric Administration; Estados UnidosFil: Rennie, J.. Nansen Environmental and Remote Sensing Center; NoruegaFil: Gambi de Almeida, W.. Centro de Previsao de Tempo e Estudos Climáticos. Instituto Nacional de Pesquisas Espaciais; BrasilFil: Christy, J.. University of Alabama; Estados UnidosFil: Flannery, M.. Bureau of Meteorology; AustraliaFil: Gleason, B.. National Oceanic and Atmospheric Administration; Estados UnidosFil: Klein Tank, A.. Royal Netherlands Meteorological Institute; Países BajosFil: Mhanda, A.. frican Centre of Meteorological Applications for Development; NigeriaFil: Ishihara, K.. Japan Meteorological Agency; JapónFil: Lister, D.. Climatic Research Unit; Reino UnidoFil: Menne, M. J.. National Oceanic and Atmospheric Administration; Estados UnidosFil: Razuvaev, V.. Russian Research Institute of Hydrometeorological Information; RusiaFil: Renom, M.. Universidad de la República; UruguayFil: Rusticucci, Matilde Monica. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tandy, J.. Met Office Hadley Centre; Reino UnidoFil: Thorne, P. W.. Nansen Environmental and Remote Sensing Center; NoruegaFil: Worley, S.. National Center for Atmospheric Research; Estados Unido
Interannual variability of temperature spells over Argentina
No full textThis work is aimed at studying the interannual variability of surface temperature cold spells and warm spells due to cold-and warm-air incursions. The effect of the ENSO event on the occurrence of extreme spells having three different indices was studied In order to track changes during the 1959/96 period, spell parameters, persistence and intensity, have been studied from daily temperatures. The number of extreme spells per year show low frequency variability plus a biennial variability, which is more important in its intensity than in its persistence, and in summer rather than in winter. The number of extreme warm spells increases until the end of the sixties and seventies, reflecting an increase of northeasterly flow. From then onwards, the trend starts to decline significantly over northern Argentina. The interannual variability of extreme winter cold spells increases from the 80's onwards, indicating the variation of anticyclone permanence over the country. Cases are more numerous in the latest years. Extreme spell occurrence in northern Argentina is closely linked to the El Nino phenomenon. Winter warm spells are more persistent in an El Niño (0) year and more intense and persistent in the year following El Niño. In summer, however, these is either no difference or the relationship is reversed, resulting in more intense situations in November and December in the case of La Nina. Cold spells reaching the northeastern most part of the country are more persistent when La Niña occurs, the conclusion being that the region would be affected by extreme cold spells when La Niña is active.EN ESTE TRABAJO SE ESTUDIA LA VARIABILIDAD INTERANUAL DE LAS OLAS DE CALOR Y FRIO EXTREMAS SOBRE LA ARGENTINA COMO LA MANIFESTACIÓN DE IRRUPCIONES EXTREMAS DE AIRE TROPICAL Y POLAR. SE CONSIDERAN LAS TEMPERATURAS DE SUPERFICIE DIARIAS EN EL PERIODO 1959/96, A PARTIR DE LAS CUALES SE CALCULAN DOS PARÁMETROS PARA DEFINIR LAS OLAS: PERSISTENCIA E INTENSIDAD. LA CANTIDAD DE LAS OLAS EXTREMAS POR AÑO MUESTRA DOS ESCALAS DE VARIABILIDAD: BIANUAL Y DE FRECUENCIA MAYOR A 10 AÑOS, LO QUE ES MAS IMPORTANTE EN VERANO QUE EN INVIERNO, Y EN LA INTENSIDAD DE LAS OLAS QUE EN SU PERSISTENCIA, LA CANTIDAD DE OLAS DE CALOR EXTREMAS AUMENTA HASTA EL FINAL DE LOS AÑOS SESENTA LO QUE REFLEJA EL AUMENTO DE FLUJO DEL NORESTE, DE AHÍ EN ADELANTE, DISMINUYE SIGNIFICATIVAMENTE, LA VARIABILIDAD INTERANUAL DE LAS OLAS DE FRÍO ES MAYOR A PARTIR DE LOS AÑOS OCHENTA, INDICANDO UNA MAYOR VARIABILIDAD DE LA PERMANENCIA DE UN SISTEMA ANTICICLÓNICO SOBRE EL PAÍS. HAY MAYOR CANTIDAD DE CASOS DE ESTAS OLAS EN LOS ÚLTIMOS AÑOS. SE ANALIZA EL POSIBLE EFECTO DE EL NIÑO EN LA OCURRENCIA DE LAS MISMAS, MEDIANTE TRES ÍNDICES DIFERENTES. LAS OLAS DE CALOR DE INVIERNO SON MÁS PERSISTENTES EN EL AÑO 0 DE EL NIÑO Y MÁS INTENSAS EN EL INVIERNO SIGUIENTE. EN LOS MESES MAS CALIDOS (ESPECIALMENTE EN NOVIEMBRE Y DICIEMBRE) ESTAS OLAS SE PRESENTAN MAS INTENSAS EN CASO DE LA NIÑA. LAS OLAS DE FRÍO EXTREMAS QUE ALCANZAN AL NORTE DEL PAÍS SON MAS PERSISTENTES EN MESES DE LA NIÑA, CON EL RIESGO CONSECUENTE DE QUE LAS MASAS DE AIRE FRÍO ALCANCEN LATITUDES MENORES EN ESTA FASE DE ENSO
Propiedades y procesos dominantes de una serie cuatridiurna de temperatura
No full textSe estudia la serie de temperaturas cuatridiurnas (hora 02, 08 14 y 20), de la estación Ezeiza (34° 49'S, 59° 32'W) en el período 1968-1980, con el objetivo final de obtener un diagnóstico que pueda servir a posteriori para el ajuste de un modelo de pronóstico para la serie. Se investiga el grado de variabilidad o contribución a la serie que introducen los meses, las horas y los años.
Los procesos estadísticos dominantes en las series, sean estas cuatridiurnas o diarias, son esencialmente Markovianos, según lo detecta la estimación de las funciones de autocorrelación y espectros de poder. Como se postula que la serie filtrada cuatridiurna puede describirse mediante un mismo proceso, se estudia el espectro hora a hora con el objeto de medir la homogeneidad. Se encuentra que las causas de inhomogeneidad serían provocadas por ondas mayores que 14 días.
En función de todas las propiedades que la serie presenta, es factible suponer que un modelo autorregresivo puede ser ajustado con fines de diagnóstico y pronóstico.The series of quartan temperatures of the station Ezeiza (34° 49'S, 59° 32'W) in the period 1968-1980 is being studied, with the final aim to obtain a diagnostic model for the series. The degree of variability or contribution to the series introduced by months, hours and years is being investigated.
The statistic processes dominant in the series, be these quartan or daily, are essentially Markovian, according is being revealed by the estimation of the functions of autocorrelation and power spectra. As it is being postulated that the filtered quartan series can be described by means of the same process, the spectrum is being studied hour by hour with the aim to measure homogeneity. It is found that the un-homogeneity is caused by waves longer than a fortnigth.
Based on the properties of the series, it is possible to assume that an autorregressive model can be adjusted for diagnostic and forecasting purposes.Asociación Argentina de Geofísicos y Geodesta
Predictibilidad estacional de los extremos de temperatura en Argentina a partir de la circulación atmosférica de gran escala
No full textLas variaciones en la temperatura de la superficie del mar (SST), en particular del Océano Atlántico y Pacifico, tienen influencia sobre el sistema climático provocando cambios en los patrones de circulación atmosférica. El Niño – Oscilación del Sur (ENSO), es el mayor modo de variabilidad en el Pacifico Tropical, causando variaciones interanuales en el clima de todo el mundo. Sin embargo, existen otros modos de variabilidad que también son importantes ya que influyen sobre la temperatura y precipitación de Sudamérica. En el presente trabajo se analizó la habilidad para predecir extremos de temperatura en la Argentina al norte de 40°S de los siguientes modos de variabilidad climáticos: Modo anular del Sur (SAM), Dipolo del Océano Indico (IOD), Oscilación Decadal del Pacífico (PDO) y la Oscilación Multidecádica del Atlántico (AMO). Para ello, se calcularon y testearon estadísticamente las correlaciones desfasadas entre cada uno de los modos climáticos y distintos índices representativos de los extremos de temperatura promediados trimestralmente en el periodo 1970-2015. Estos índices de extremos de temperatura, globalmente utilizados, son: noches frías (TN10), noches cálidas (TN90), días fríos (TX10), días cálidos (TX90) y el número de días con heladas (NDH).Eje: Ciencias de la Atmósfera y los Océanos.Facultad de Ciencias Astronómicas y Geofísica
Variabilidad cada seis horas de la temperatura de superficie
No full textEn este trabajo se estudia el comportamiento del cambio de la temperatura cada seis horas en una estación ubicada en la periferia de la ciudad de Buenos Aires. Ese cambio se representa con la "diferencia" de temperatura en seis horas.
Se observa mayor cantidad de calentamientos que de enfriamientos pero de menor intensidad. Todas las distribuciones presentan una leve asimetría.
Estas "diferencias" pertenecen a ondas de período muy corto, lo que muestra que estos procesos se debilitan rápidamente.
En el análisis de valores extremos absolutos, se nota que su ocurrencia tiene horas preferenciales, a pesar de estar filtradas las ondas astronómicas. Es en el intervalo entre las 08 y las 14 donde se producen los mayores calentamientos y enfriamientos.The behavior of the temperature change each six hours, in a station near the city of Buenos Aires is studied. This change is explained by the difference between 6-hourly temporatures.
The distributions are slightly assimetric because there are more heatings than coolings but less intense.
It can be seen that those "differences" belong to short waves. They show that the processes weaken quickly.
A preferent interval occured in the absolute extrem values analysis, in spite of the astronomics waves have been filtered. The mayor heatings and coolings are produced between 08:00 and 14:00.Asociación Argentina de Geofísicos y Geodesta
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