Predictability of extratropical upper-tropospheric circulation in the Southern Hemisphere by its main modes of variability

The predictability and forecast skill of the models participating in the Climate Historical Forecast Project (CHFP) database is assessed through evaluating the representation of the upper-tropospheric extratropical circulation in the Southern Hemisphere (SH) in winter and summer and its main modes of variability. In summer, the predictability of 200-hPa geopotential height anomalies mainly comes from the ability of the multimodel ensemble mean (MMEM) to forecast the first three modes of interannual variability with high fidelity. The MMEM can reproduce not only the spatial patterns of these modes but also their temporal evolution. On the other hand, in JJA only the second and fourth modes of variability are predictable by the MMEM. These seasonal differences in the performance of the MMEM seem to be related to the role that the sea surface temperature (SST) anomalies have in influencing the variability of each mode. Accordingly, modes that are strongly linked to tropical SST anomalies are better forecast by the MMEM and show less spread among models. The analysis of both 2-m temperature and precipitation anomalies in the SH associated with the predictable modes reveals that DJF predictable modes are accompanied by significant temperature anomalies. In particular, temperatures at polar (tropical) latitudes are significantly correlated with the first (second) mode. Furthermore, these links obtained with observations are also well forecast by the MMEM and can help to improve seasonal forecast of climate anomalies in those regions with low skill.Fil: Osman, Marisol. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Vera, Carolina Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentin

Plausible Drying and Wetting Scenarios for Summer in Southeastern South America

Summer rainfall trends in southeastern South America (SE-SA) have received attention in recent decades because of their importance for climate impacts. More than one driving mechanism has been identified for the trends, some of which have opposing effects. It is still not clear how much each mechanism has contributed to the observed trends or how their combined influence will affect future changes. Here, we address the second question and study how the CMIP6 summer SE-SA rainfall response to greenhouse warming can be explained by mechanisms related to large-scale extratropical circulation responses in the Southern Hemisphere to remote drivers (RDs) of regional climate change. We find that the regional uncertainty is well represented by combining the influence of four RDs: tropical upper-tropospheric amplification of surface warming, the delay in the stratospheric polar vortex breakdown date, and two RDs characterizing recognized tropical Pacific SST warming patterns. Applying a storyline framework, we identify the combination of RD responses that lead to the most extreme drying and wetting scenarios. Although most scenarios involve wetting, SE-SA drying can result if high upper-tropospheric tropical warming and early stratospheric polar vortex breakdown conditions are combined with low central and eastern Pacific warming. We also show how the definition of the SE-SA regional box can impact the results since the spatial patterns characterizing the dynamical influences are complex and the rainfall changes can be averaged out if these are not considered when aggregating. This article’s perspective and the associated methodology are applicable to other regions of the globe. Significance Statement: Summer rainfall in southeastern South America (SE-SA) affects an area where around 200 million people live. The observed trends suggest long-term wetting, and most climate models predict a wetting response to greenhouse warming. However, in this work, we find that there is a physically plausible combination of large-scale circulation changes that can promote drying, which means SE-SA drying is a possibility that cannot be ignored. We also show that the definition of the SE-SA regional box can impact regional rainfall analysis since the spatial patterns characterizing the dynamical influences are complex and the changes can be averaged out if these are not considered when aggregating. This perspective and the associated methodology are applicable to other regions of the globe

Intraseasonal and low frequency processes contributing to the December 2013 heat wave in Southern South America

In the second fortnight of December 2013, the longest heat wave registered until then occurred in Buenos Aires city and over a large region of Argentina, with large socio-economic impacts. Excess heat indexes were used to characterize this heat wave, which occurred within the warm season with largest number of heat wave days. This extreme event resulted in the longest consecutive period of heat wave conditions between 1979 and 2014. This event was the result of the combined activity of short intraseasonal (10–30 days), long intraseasonal (30–90 days) and larger (more than 90 days) time scales. Accounting for the lower frequency, dry soil moisture anomalies were observed in Argentina during autumn, winter and spring of 2013 probably favoring more extreme values in the temperature anomalies. Weekly geopotential heights anomalies computed during the event showed that the combination of the negative phase of the Southern Annular Mode and a wave-4 pattern at midlatitudes favored the development of positive geopotential height anomalies over southern South America which promoted subsidence motions there. Intraseasonal variability played a key role in the persistence of the heat wave. The development of an MJO event over the Indian Ocean (RMM phase 3) 12 days prior to the beginning of the heat wave may have contributed to organize the extratropical wave train which in turn favored the anticyclonic upper-level anomaly development over southern South America. Furthermore, an intense SACZ event during the first 12 days of the heat wave favored clear-sky conditions and diabatic heating as well as subsidence, while during the last days it was the northerly advection of warmer air in the 10–30-day time scale that maintained the intensity of the temperature anomalies.Fil: Alvarez, Mariano Sebastián. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Cerne, Silvia Bibiana. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Osman, Marisol. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Vera, Carolina Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; Argentin

Assessment of ECMWF subseasonal temperature predictions for an anomalously cold week followed by an anomalously warm week in central and Southeastern South America during July 2017

The demand of subseasonal predictions (from one to about four weeks in advance) has been consid-erably increasing as these predictions can potentially help prepare for the occurrence of high-impact events such as heat or cold waves that affect both social and economic activities. This study aims to assess the subseasonal temperature prediction quality of the European Centre for Medium-Range Weather Forecasts (ECMWF) against the Japan Meteorological Agency reanalyses. Two consecutive weeks of July 2017 were analyzed, which presented anomalously cold and warm conditions over central South America. The quality of 20 years of hindcasts for the two investigated weeks was compared to that for similar weeks during the JJA season and of 3 years of real-time forecasts for the same season. Anomalously cold temperatures observed during the week of 17–23 July 2017 were well predicted one week in advance. Moreover, the warm anomalies observed during the following week of 24–30 July 2017 were well predicted two weeks in advance. Higher linear association and discrimination (ability to distinguish events from nonevents), but reduced reliability, was found for the 20 years of hindcasts for the target week than for the hindcasts produced for all of the JJA season. In addition, the real-time forecasts showed generally better performance over some regions of South America than the hindcasts. The assessment provides robust evidence about temperature prediction quality to build confidence in regional subseasonal forecasts as well as to identify regions in which the predictions have better performance.Fil: Alvarez, Mariano Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Coelho, C.A.S.. Centro de Previsao de Tempo e Estudos Climáticos. Instituto Nacional de Pesquisas Espaciais; BrasilFil: Osman, Marisol. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Firpo, M.Â.F.. Centro de Previsao de Tempo e Estudos Climáticos. Instituto Nacional de Pesquisas Espaciais; BrasilFil: Vera, Carolina Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentin

Are We at Risk of Losing the Current Generation of Climate Researchers to Data Science?

Climate model output has progressively increased in size over the past decades and is expected to continue to rise in the future. Consequently, the research time expended by Early Career Researchers (ECRs) on data-intensive activities is displacing the time spent in fostering novel scientific ideas and expanding the frontiers of climate sciences. Here, we highlight an urgent need for a better balance between data-intensive and foundational climate science activities, more open-ended research opportunities that reinforce the scientific freedom of the ECRs, and strong coordinated action to provide infrastructure and resources to the ECRs working in under-resourced environments

Are We at Risk of Losing the Current Generation of Climate Researchers to Data Science?

Climate model output has progressively increased in size over the past decades and is expected to continue to rise in the future. Consequently, the research time expended by Early Career Researchers (ECRs) on data-intensive activities is displacing the time spent in fostering novel scientific ideas and expanding the frontiers of climate sciences. Here, we highlight an urgent need for a better balance between data-intensive and foundational climate science activities, more open-ended research opportunities that reinforce the scientific freedom of the ECRs, and strong coordinated action to provide infrastructure and resources to the ECRs working in under-resourced environments

Aplicación del índice LISAM en el monitoreo del monzón sudamericano

Fil: Vera, Carolina Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-Argentino sobre Estudios de Clima y sus Impactos; Argentina.Fil: Skansi, María de los Milagros. Servicio Meteorológico Nacional. Gerencia de Investigación, Desarrollo y Capacitación. Departamento de Climatología; Argentina.Fil: Ferreira, Lorena Judith. Servicio Meteorológico Nacional. Gerencia de Investigación, Desarrollo y Capacitación. Departamento de Hidrometeorología; Argentina. Servicio Meteorológico Nacional. Gerencia de Gerencia de Investigación, Desarrollo y Capacitación. Departamento de Agrometeorología; Argentina.Fil: Osman, Marisol. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Godoy, Alejandro Aníbal. Servicio Meteorológico Nacional. Gerencia de Investigación, Desarrollo y Capacitación. Departamento de Investigación y Desarrollo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmosfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmosfera; Argentina.En este trabajo se muestra la implementación del índice LISAM (Large-Scale Index for the South American Monsoon) con el fin de incluir una nueva herramienta para el monitoreo del Monzón Sudamericano y su impacto en las regiones subtropicales. Este índice está basado en la componente principal obtenida a partir de un análisis de Funciones Ortogonales Empíricas (EOF) realizado en forma “combinada” a partir de las anomalías de precipitación, humedad específica, temperatura del aire, viento zonal y meridional en el nivel de 850 hPa, calculado en un dominio en el norte de Sudamérica. La implementación del índice reprodujo en forma satisfactoria los resultados de otras investigaciones. Por otro lado, se analizó la sensibilidad del índice a diferentes dominios extendidos hacia regiones extratropicales, observándose pocos cambios en su estructura. Además, se encontró que al extender el dominio donde se calcula el índice, las fechas de inicio y fin del monzón se modifican. Por último, se utilizó el índice LISAM para monitorear el monzón durante el año 2017. Los resultados muestran la enorme utilidad de esta herramienta para detectar el rompimiento y la intensificación del sistema monzónico como así también el inicio y finalización del mismo.We describe the implementation of the LISAM index (Large‐scale index for South America Monsoon) to be added as a new tool for monitoring the South American Monsoon and its impact on subtropical regions. This index is based on the first “combined” component of the Empirical Orthogonal Functions (EOFs) that is performed from the anomalies of precipitation, specific humidity, air temperature, zonal wind and meridional wind at 850 hPa, calculated in a domain in northern South America. The implementation of the index reproduced satisfactorily results from other investigations. It is also shown that the index displays little sensitivity to the choice of different domains when extended towards extratropical regions, although the start and end dates of the monsoon do change. In addition, we observed few changes in its structure. Finally, we use the LISAM index to monitor the monsoon during the year 2017. Results show the great benefit of having this tool to detect the breaking and intensification of the monsoon system as well as the start and end of it

Are We at Risk of Losing the Current Generation of Climate Researchers to Data Science?

Climate model output has progressively increased in size over the past decades and is expected to continue to rise in the future. Consequently, the research time expended by Early Career Researchers (ECRs) on data-intensive activities is displacing the time spent in fostering novel scientific ideas and expanding the frontiers of climate sciences. Here, we highlight an urgent need for a better balance between data-intensive and foundational climate science activities, more open-ended research opportunities that reinforce the scientific freedom of the ECRs, and strong coordinated action to provide infrastructure and resources to the ECRs working in under-resourced environments