Convection and precipitation in the Southern Amazon region: Comparison between a normal and dry year

We examine the diurnal cycles of deep convection and precipitation in the Southern Amazon region, using mainly the Advanced Microwave Sounding Unit, contrasting a year of drought (2004-2005) with a “normal” year (2005-2006). MODIS 550nm aerosol optical thickness data and TRMM 3B42 precipitation products were also used to investigate whether a significant relationship between these two parameters can be identified. We use a simple, tractable method to identify convective areas based on humidity channels of AMSU. We found through comparisons with independent ground precipitation data that the diurnal cycle of convection in regional scale can be realistically described by this method. We observe that deep convective areas have a slow build-up early in the rainy season of the dry year, and rapid in the normal year, and in both cases, convection starts around midday. As the rainy season advances, the peak hour of maximum convective activity shifts towards mid-afternoon, and eventually spreads towards the night. During the peak of rainy season (December through February) convective activity was up to 12% larger in the “normal” year. Convective overshooting was found to be 50% less frequent in the drought year compared to the following year. A simple spatial correlation analysis of MODIS 550nm and TRMM 3B42 monthly mean data show d that by the end of dry season, aerosol loading and precipitation amounts have a positive (albeit low) significant correlation

Two case studies of severe storms in the Mediterranean using AMSU

International audienceMediterranean storms and their associated upper level features are diagnosed here using Advanced Microwave Sounding Unit (AMSU) observations. AMSU-A channel 8 is used to identify upper-level intrusions of stratospheric air, which are often present upstream of heavy precipitating areas, while a combination of AMSU-B channels 3 and 5 is chosen to discriminate moderate to heavily precipitating areas. This precipitation detection method provides results that are in good agreement with TRMM rainfall product and independent ground-based precipitation data. These tools allow us to follow the concomitant evolution of two severe rainfall events in the Mediterranean region and associated upper-level features

The role of convective overshooting clouds in tropical stratosphere-troposphere dynamical coupling

International audienceThis paper investigates the role of deep convection and overshooting convective clouds in stratosphere–troposphere dynamical coupling in the tropics during two large major stratospheric sudden warming events in January 2009 and January 2010. During both events, convective activity and precipitation increased in the equatorial Southern Hemisphere as a result of a strengthening of the Brewer–Dobson circulation induced by enhanced stratospheric planetary wave activity. Correlation coefficients between variables related to the convective activity and the vertical velocity were calculated to identify the processes connecting stratospheric variability to the troposphere. Convective overshooting clouds showed a direct relationship to lower stratospheric upwelling at around 70–50 hPa. As the tropospheric circulation change lags behind that of the stratosphere, outgoing longwave radiation shows almost no simultaneous correlation with the stratospheric upwelling. This result suggests that the stratospheric circulation change first penetrates into the troposphere through the modulation of deep convective activity

Temperature climatology with Rayleigh lidar above Observatory of Haute-provence : dynamical feedback

International audienceRayleigh lidar in synergy with satellite observations (SSU and AMSU) allow insuring an efficient monitoring and showing that cooling has continued. New approach for trend detection has been developed allowing a better estimate of changes due to radiative forcing. Stratospheric Warmings and gravity waves contribute to insure a dynamical feedback of the long-term changes

Precipitación extrema en la Puna del Desierto de Atacama: ¿Cómo gestionar la incertidumbre actual y futura?

Chile is one of the Latin American countries most affected by Climate Change. There is a high level of uncertainty regarding the variability of precipitation and its projections in many regions of this country. This poses challenges for climate characterization and for defining strategies to reduce its risks. The study area is the Puna of Atacama Desert, Andean highlands located to the eastern side of the extreme arid lands, a region that concentrates the main copper and lithium mining at word scale, and where meteorological observations are scarce, with missing data and unreliable projections. Considering this data limitations, a daily precipitation database of 35 weather stations was constructed in order to evaluate some extreme precipitation indices that allow establishing changes between 1981-2017, in addition to spatial interpolations based on topography. It is concluded that most of the meteorological stations do not present significant trends of change, e.g. Extremely wet days (R99p), Wet days (RR) and Consecutive wet days (CWD). The index with the highest number of stations with a trend is CDD, which shows an increase in consecutive dry days. One of the main contributions of this research was to expand the number of observations and to generate maps of the spatial distribution of the indices of extremes. We are facing open questions regarding living with uncertainty, and meeting the challenges of maintaining records to increase the levels of certainty of climatic changes.Chile es uno de los países de América Latina más afectados por el cambio climático. Existe un elevado nivel de incertidumbre respecto a la variabilidad de las precipitaciones y sus proyecciones en muchas de sus regiones. Ello plantea desafíos para su caracterización climática y para definir estrategias para reducir los riesgos asociados. Se estudia la Puna del Desierto de Atacama, paisaje andino de altura que bordea las tierras áridas por el lado este, y que concentran las principales minas de cobre y litio a escala mundial, y donde existen escasas observaciones meteorológicas, con datos perdidos y proyecciones de poca fiabilidad. Es por ello que se construyó una base diaria de precipitación de 35 estaciones con el fin de evaluar algunos índices extremos que permitan establecer cambios entre 1981-2017, además de interpolaciones espaciales basadas en la topografía. Se concluye que la mayoría de las estaciones meteorológicas no presenta tendencias significativas de cambio, destacando días extremadamente húmedos (R99p), días húmedos (RR) y días húmedos consecutivos (CWD). El índice con mayor cantidad de estaciones con tendencia es CDD, que muestra un incremento de los días consecutivos secos. Uno de los principales aportes de esta investigación fue ampliar el número de observaciones y generar mapas de la distribución espacial de los índices de extremos. Nos quedan preguntas abiertas respecto a convivir con la incertidumbre, y alcanzar desafíos de mantener los registros para aumentar los niveles de certeza de los cambios climáticos.The authors acknowledge support by the Program CLIMAT AmSud Project PRELASA (21-CLIMAT-12)

The impact of tropical tropopause cooling on Sahelian extreme deep convection

Previous studies have suggested that the recent increase in tropical extreme deep convection, in particular over Asia and Africa during the boreal summer, has occurred in association with cooling in the tropical lower stratosphere. The present study is focused on the Sahel region of West Africa, where an increased occurrence of extreme precipitation events has been reported over recent decades. The results indicate that the changes over West Africa since the 1980s involve a cooling trend in the tropical lower stratosphere and tropopause layer, combined with warming in the troposphere. This feature is similar to that which might result from increased greenhouse-gas levels but is distinct from the interannual variation of precipitation associated with the transport of water vapor from the Atlantic Ocean. It is suggested that the decrease in the vertical temperature gradient in the tropical tropopause region enhances extreme deep convection over the Sahel, where penetrating convection is frequent, whereas tropospheric warming suppresses the shallower convection over the Guinea Coast. Therefore, the essential feature of the recent changes over West Africa is the depth of convection rather than the total amount of surface precipitation

VARIABILITE SPATIO-TEMPORELLE DU CYCLE DIURNE DE LA CONVECTION EN AMAZONIE.

International audienceWe examine the diurnal cycle of precipitation and convection in the Amazon region, particularly in the state of Mato Grosso, Brasil, where changes in land use and forest cover have been dynamical in the last decades. We consider the years 2004 to 2006, which encompass a period of severe drought (2005) that affected several parts of Amazon, and had a significant socio-economical impact. We use mainly satellite data from the Advanced Microwave Sounding Unit (AMSU) and the Tropical Rainfall Measuring Mission (TRMM) to detect and characterize convective activity. This study aims at a better representation of the variability of convective activity in the Amazon basin, and may also contribute to e.g. validation of regional climate models.Cet article présente la variabilité spatio-temporelle des précipitations convectives d'une portion de la région sud de l'Amazonie (Etat du Mato Grosso) en utilisant des données satellitaires et en les comparant pendant et après la sécheresse prolongée de 2005. Il s'agit d'examiner la différence du cycle diurne et l'extension spatiale de la convection et des précipitations convectives entre une année "normale" et la situation de sécheresse extrême de 2005. On utilise les données satellitaires « Advanced Microwave Sounding Unit » (AMSU) et « Tropical Rainfall Measuring Mission » (TRMM) pour détecter et caractériser l'activité convective et les précipitations. Cette étude vise une meilleure représentation de la variabilité de l'activité convective dans le bassin amazonien, et elle peut contribuer aussi par exemple à la validation des modèles climatiques

Perceptions of climate and climate change by Amazonian communities

International audienceThe Amazon region has been undergoing profound transformations since the late 15 '70s through forest degradation, land use changes and effects of global climate change. The 16 perception of such changes by local communities is important for risk analysis and 17 for subsequent societal decision making. In this study, we compare and contrast observations 18 and perceptions of climate change by selected Amazonian communities particularly vulnerable 19 to alterations in precipitation regimes. Two main points were analysed: (i) the notion of 20 changes in the annual climate cycle and (ii) the notion of changes in rainfall patterns. About 21 72% of the sampled population reports perceptions of climate changes, and there is a robust 22 signal of increased perception with age. Other possible predictive parameters such as gender, 23 fishing frequency and changes in/planning of economic activities do not appear overall as 24 contributing to perceptions. The communities' perceptions of the changes in 2013-2014 were 25 then compared to earlier results (2007-2008), providing an unprecedented cohort study of the 26 same sites. Results show that climate change perceptions and measured rainfall variations 27 differ across the basin. It was only in the southern part of the Amazon that both measured and 28 perceived changes in rainfall patterns were consistent with decreased precipitation. However, 29 the perception of a changing climate became more widespread and frequently mentioned, 30 signalling an increase in awareness of climate risk. 31 3

Observation of Mediterranean precipitating systems using AMSU

9-11 Jan 200