Joint Seminar: Regional atmospheric mechanism controlling austral summer precipitation over the southern tropical Andes

In this study, we revisited the regional atmospheric mechanisms controlling the austral summer precipitation variability over the southern tropical Andes (STA), a region marked by a strong seasonality with a wet season during the December-February season. Indeed, the interannual precipitation variability in this Andean region was believed to be only related to the Bolivian High, an anticyclonic system located at the upper-troposphere over the Bolivian Andes and originating from the liberation of latent heat due to central Amazon convection. Using in-situ and satellite precipitation products and reanalysis data sets, we found that western Amazon convection also plays an important role, especially after 2002, when this mechanism became the principal factor in explaining the precipitation variability in the STA. Moreover, we related the change in the controlling mechanism to the recent intensification of the regional Hadley cell over South America.

By using the Weather Research and Forecasting Model on a global simulation and with a zoom over western tropical South America, we found that the association between the western Amazon and the southern tropical Andes is related to the atmospheric stability between the mid-and the upper-troposphere over western tropical South America. Furthermore, in an experiment in which deep convection over the western Amazon was suppressed, we noticed a weakening of the regional Hadley cell. However, small changes were observed in the Bolivian High, suggesting that these two mechanisms, the Bolivian High and western Amazon convection, are independent.

Date

29.06.2021

Time

15:15 h

Place

Virtual Seminar
Hamburg

Speaker

Hans Segura

Organizers

Diego Jiménez-de-la-Cuesta Otero

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