%0 Journal Article
%T Changes in the Austral Winter Hadley Circulation and the Impact on Stationary Rossby Waves Propagation
%A Ana Carolina Vasques Freitas
%A T¨¦rcio Ambrizzi
%J Advances in Meteorology
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/980816
%X The present study investigates how changes in the Hadley Cell (HC) intensity impact the stationary Rossby waves energy propagation in the Southern Hemisphere (SH) extratropics. Composites for weak and strong HC Intensity Index (HCI) were used in this analysis. The results for weak HC cases showed a wave train emanating from the subtropical central-west Indian Ocean in an arc-like route, with zonal wavenumber three in the polar jet waveguide, and reaching the north of South America. For strong HC cases, the wave train is also trapped inside the polar jet waveguide with zonal wavenumber four, emanating from subtropical central-east Indian Ocean and reaching the subtropical west coast of Africa. A weaker zonally oriented wave train with zonal wavenumber five has been found in the subtropical region with opposite polarity for weak and strong HC cases. Over the South America, the results show that an HC weakening can lead to a very cold and rainy winter in the southwest of the continent and a mild warm and dry winter on Brazilian states of Minas Gerais and Bahia. A pattern almost opposite was observed when the CH strengthens. 1. Introduction The Hadley Cell (HC) plays a key role in the climate system. Generally defined as the zonal mean meridional mass circulation in the atmosphere bounded roughly by 30¡ãS and 30¡ãN, with warmer air rising in the tropics and colder air sinking in the subtropics, this circulation transports momentum flux to the subtropics and heat from the tropics to the subtropics and to high latitudes through extratropical eddies. Both heat and momentum transports have important influences on subtropical jet streams, which consequently impact on waves and atmospheric circulations at middle and high latitudes [1]. In particular, upper level jet streams play an important role acting as waveguides for the Rossby waves [2]. Moreover, the deep convection in the rising branch of the HC and the associated divergence at high levels results in a meridional displacement of the air parcels, which causes a disturbance in the vorticity field and then, by absolute vorticity conservation a Rossby wave is generated. Thus, tropical variability affects the extratropical atmospheric circulation due to the generation of Rossby waves that propagate from the tropics into the extratropics in a westerly background flow [2¨C4]. Marengo et al. [5] found that stationary Rossby waves emanating from the western tropical Pacific during wintertime can lead to cooling and occurrence of freezes in south-eastern South America. M¨¹ller and Ambrizzi [6] found, in the austral
%U http://www.hindawi.com/journals/amete/2012/980816/