Seasonal dynamics of the near-surface alongshore flow off central Chile

The seasonal cycle of the near-surface circulation off central Chile was analyzed using satellite altimetry and an oceanic model. To evaluate the role of the wind stress curl on the circulation we performed two identical simulations except for the wind-forcing: the "control run" used long-term monthly mean wind stress and the "no-curl run" used a similar wind stress field, but without curl. The observed and modeled (control run) surface currents showed a strong seasonal cycle and a well-defined equatorward flow with a jet like-structure. This jet develops during spring and summer, consistent with the presence of a low-level wind jet. South of Punta Lavapie cape (similar to 37 degrees S), the equatorward surface current remains close to the coast. After the flow-passes this cape, however, it separates to become an offshore jet. In contrast, in the no-curl simulation the separation at Punta Lavapie is not observed and the offshore jet farther north is not present, demonstrating the importance of the wind stress curl on the dynamics of this flow. Although the offshore integrated Sverdrup transport was similar to the model transport, the offshore jet was not located where the wind stress curl was maximum. Instead, the position of the jet followed approximately the zero wind stress curl, which corresponds to the climatological location of the low-level wind jet axis. These results illustrate the importance of the offshore upwelling/downwelling associated with curl-driven Ekman pumping, which tilts isopycnals upward (downward) toward the east (west) of the wind jet, forcing a northward flow through thermal wind balance.Keywords: Low level jet, Circulation, west coast, Coastal Upwelling jet, California current system, Separation, Transition zone, Subtropical South America, Wind stress curl, Variabilit

The CAMELS-CL dataset: catchment attributes and meteorology for large sample studies – Chile dataset

We introduce the first catchment dataset for large sample studies in Chile. This dataset includes 516 catchments; it covers particularly wide latitude (17.8 to 55.0∘ S) and elevation (0 to 6993 m a.s.l.) ranges, and it relies on multiple data sources (including ground data, remote-sensed products and reanalyses) to characterise the hydroclimatic conditions and landscape of a region where in situ measurements are scarce. For each catchment, the dataset provides boundaries, daily streamflow records and basin-averaged daily time series of precipitation (from one national and three global datasets), maximum, minimum and mean temperatures, potential evapotranspiration (PET; from two datasets), and snow water equivalent. We calculated hydro-climatological indices using these time series, and leveraged diverse data sources to extract topographic, geological and land cover features. Relying on publicly available reservoirs and water rights data for the country, we estimated the degree of anthropic intervention within the catchments. To facilitate the use of this dataset and promote common standards in large sample studies, we computed most catchment attributes introduced by Addor et al. (2017) in their Catchment Attributes and MEteorology for Large-sample Studies (CAMELS) dataset, and added several others. We used the dataset presented here (named CAMELS-CL) to characterise regional variations in hydroclimatic conditions over Chile and to explore how basin behaviour is influenced by catchment attributes and water extractions. Further, CAMELS-CL enabled us to analyse biases and uncertainties in basin-wide precipitation and PET. The characterisation of catchment water balances revealed large discrepancies between precipitation products in arid regions and a systematic precipitation underestimation in headwater mountain catchments (high elevations and steep slopes) over humid regions. We evaluated PET products based on ground data and found a fairly good performance of both products in humid regions (r>0.91) and lower correlation (r<0.76) in hyper-arid regions. Further, the satellite-based PET showed a consistent overestimation of observation-based PET. Finally, we explored local anomalies in catchment response by analysing the relationship between hydrological signatures and an attribute characterising the level of anthropic interventions. We showed that larger anthropic interventions are correlated with lower than normal annual flows, runoff ratios, elasticity of runoff with respect to precipitation, and flashiness of runoff, especially in arid catchments. CAMELS-CL provides unprecedented information on catchments in a region largely underrepresented in large sample studies. This effort is part of an international initiative to create multi-national large sample datasets freely available for the community. CAMELS-CL can be visualised from http://camels.cr2.cl and downloaded from https://doi.pangaea.de/10.1594/PANGAEA.894885

2018 International Atmospheric Rivers Conference: Multi‐disciplinary studies and high‐impact applications of atmospheric rivers

Atmospheric rivers (ARs) play a vital role in shaping the hydroclimate of many regions globally, and can substantially impact water resource management, emergency response planning, and other socioeconomic entities. The second International Atmospheric Rivers Conference took place at the Scripps Institution of Oceanography, University of California, San Diego, during 25–28 June, 2018, in La Jolla, California, USA. It was sponsored by the Center for Western Weather and Water Extremes (CW3E). A total of 120 people attended the Conference with 94 abstracts submitted and 30 participating students. In addition to the conference, the Student Forecasting Workshop was organised in the same week. During this workshop, students were exposed to AR forecasting tools, and learned examples of how these tools could be used to make decisions for various applications. The main goals of this conference were to bring together experts from across the fields of hydrology, atmospheric, oceanic, and polar sciences, as well as water management, civil engineering, and ecology to advance the state of AR science and to explore the future directions for the field. The conference was organised into traditional oral and poster presentations, along with panel discussions and Breakout Groups. This format allowed enhanced interaction between participants, driving progress within the scientific community and the enhanced communication of societal needs by various stakeholders. Several emerging topics of research were highlighted, including subseasonal‐to‐seasonal (S2S) prediction of ARs and an overview of the AR Reconnaissance campaign. In addition to providing a forum to disseminate and debate new results from scientific talks and posters, the conference was equally effective and useful in linking scientists to users and decision‐makers that require improved knowledge on ARs to manage resources and prepare for hazards.The third International Atmospheric Rivers Conference will be held in Chile in 2020, and hosted by the University of Chile, Santiago.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151348/1/asl2935.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151348/2/asl2935_am.pd

The 2019 Southern Hemisphere stratospheric polar vortex weakening and its impacts

This study offers an overview of the low-frequency (i.e., monthly to seasonal) evolution, dynamics, predictability, and surface impacts of a rare Southern Hemisphere (SH) stratospheric warming that occurred in austral spring 2019. Between late August to mid-September 2019, the stratospheric circumpolar westerly jet weakened rapidly, and Antarctic stratospheric temperatures rose dramatically. The deceleration of the vortex at 10 hPa was as drastic as that of the first ever observed major sudden stratospheric warming in the SH during 2002, while the mean Antarctic warming over the course of spring 2019 broke the previous record of 2002 by ~50% in the mid-stratosphere. This event was preceded by a poleward shift of the SH polar night jet in the uppermost stratosphere in early winter, which was then followed by record-strong planetary wave-one activity propagating upward from the troposphere in August that acted to dramatically weaken the polar vortex throughout the depth of the stratosphere. The weakened vortex winds and elevated temperatures moved downward to the surface from mid-October to December, promoting a record strong swing of the Southern Annular Mode (SAM) to its negative phase. This record-negative SAM appeared to be a primary driver of the extreme hot and dry conditions over subtropical eastern Australia that accompanied the severe wildfires that occurred in late spring 2019. State-of-the-art dynamical seasonal forecast systems skilfully predicted the significant vortex weakening of spring 2019 and subsequent development of negative SAM from as early as late July

Pronostico de la convencion en el altiplano sudamericano:empleo del Modelo Regional ETA/CPTEC

En este trabajo se evalúa el desempeno deI modelo regional Eta/CPTEC para pronosticar Ia precipitación estival sobre el Altiplano, con énfasis en su carácter convectivo y episódico. Para ello fueron comparadas Ias salidas operativas deI modelo correspondientes aI período diciembre 1999 a febrero 2000 con algunas observaciones disponibles y, fundamentalmente, con los campos de radiación de onda larga emergente. La precipitación pronosticada por el modelo logra capturar rasgos de Ia organización espacial y de Ia variabilidad temporal de Ia convección sobre el Altiplano. Los pronósticos a 24 horas tienen un mayor acierto en Ia distribución espacial, mientras que a 48 horas reproducen con mayor precisión su carácter episódico. Sin embargo, Ia mejor metodología de pronóstico se logra en forma, indirecta, a través de Ia relación de mezcla en el nível de 550 hPa promediada sobre el Altiplano. Este resultado estadístico se baga en Ia fuerte relación simultánea entre Ia convección y el contenido de vapor de agua, y en el buen grado de acierto deI pronóstico de esta variable. Este hecho indica que el modelo prevé correctamente el transporte regional de aire húmedo desde Ias tierras hajas bacia el Altiplano.Pages: 25-3

Assessment of satellite precipitation estimates over the slopes of the subtropical Andes

A validation of four satellite daily precipitation estimates at a spatial resolution of 0.25° is performed over the subtropical Andes, an area of highly complex topography: The Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA, 3B42 V7 and RT), the Climate Prediction Center Morphing technique (CMORPH) and the Hydro-Estimator (HYDRO). Remote mountainous regions represent a major challenge for these satellite data products and for studies examining their quality with surface data. For the assessment of the satellite products, a period of seven years from January 1st 2004 to December 31st 2010 was considered. Different statistics were analyzed considering their variability in the study area and identifying their main differences between the warm and cold seasons. The results indicate a decrease in winter errors which coincides with the wet season over the windward side of the Andes. Also, a significant underestimation of precipitation is observed for all estimates throughout the period analyzed. The analysis with respect to terrain height shows a greater dependence of errors with topography for all the algorithms that combine infrared and passive microwave data, HYDRO providing the most stable result. The main limitations of the estimates associated with the type of precipitating event and their location relative to the orography are assessed. Finally, the analysis of two intense precipitation events is presented and allows the assessment of the latest advances in satellite derived estimates with the launch of the Global Precipitation Measurement.Fil: Hobouchian, María Paula. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; ArgentinaFil: Salio, Paola Veronica. 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; ArgentinaFil: Garcia Skabar, Yanina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Franco Argentino sobre Estudios del Clima y sus Impactos; Argentina. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; ArgentinaFil: Vila, Daniel. División de Satélites y Sistemas Ambientales; BrasilFil: Garreaud, Rene. Universidad de Chile; Chil

Climatological features of cutoff low systems in the Southern Hemisphere

Cutoff lows (COLs) pressure systems climatology for the Southern Hemisphere (SH), between 10 degrees S and 50 degrees S, using the National Center for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) and the ERA-40 European Centre for Medium Range Weather Forecast (ECMWF) reanalyses are analyzed for the period 1979-1999. COLs were identified at three pressure levels (200, 300, and 500 hPa) using an objective method that considers the main physical characteristics of the conceptual model of COLs. Independently of the pressure level analyzed, the climatology from the ERA-40 reanalysis has more COLs systems than the NCEP-NCAR. However, both reanalyses present a large frequency of COLs at 300 hPa, followed by 500 and 200 hPa. The seasonality of COLs differs at each pressure level, but it is similar between the reanalyses. COLs are more frequent during summer, autumn, and winter at 200, 300, and 500 hPa, respectively. At these levels, they tend to occur around the continents, preferentially from southeastern Australia to New Zealand, the south of South America, and the south of Africa. To study the COLs at 200 and 300 hPa from a regional perspective, the SH was divided in three regions: Australia-New Zealand (60 E-130 W), South America (130 degrees W-20 degrees W), and southern Africa (20 degrees W-60 degrees E). The common COLs features in these sectors for both reanalyses are a short lifetime (similar to 80.0% and similar to 70.0% of COLs at 200 and 300 hPa, respectively, persisting for up to 3 days), mobility (similar to 70.0% and similar to 50% of COLs at 200 and 300 hPa, respectively, traveling distances of up to 1200 km), and an eastward propagation.Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior do Brasil (CAPES)[BEX 0626/08-2]Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico do Brasil (CNPq-INCT de Mudancas Climaticas)Spanish Ministry of Education[PCI2006-A7-0544

Connection between Antarctic Ozone and Climate: Interannual Precipitation Changes in the Southern Hemisphere

In this study, we explored the connection between anomalies in springtime Antarctic ozone and all-year precipitation in the Southern Hemisphere by using observations from 1960&ndash;2018 and coupled simulations for 1960&ndash;2050. The observations showed that this correlation was enhanced during the last several decades, when a simultaneously increased coupling between ozone and Southern Annular Mode (SAM) anomalies became broader, covering most of the following summer and part of the previous winter. For eastern Australia, the ozone&ndash;precipitation connection shows a greater persistence toward the following summer than for other regions. On the other hand, for South America, the ozone&ndash;precipitation correlation seems more robust, especially in the early summer. There, the correlation also covers part of the previous winter, suggesting that winter planetary waves could affect both parameters. Further, we estimated the sensitivity of precipitation to changes in Antarctic ozone. In both observations and simulations, we found comparable sensitivity values during the spring&ndash;summer period. Overall, our results indicate that ozone anomalies can be understood as a tracer of stratospheric circulation. However, simulations indicate that stratospheric ozone chemistry still contributes to strengthening the interannual relationship between ozone and surface climate. Because simulations reproduced most of the observed connections, we suggest that including ozone variability in seasonal forecasting systems can potentially improve predictions