A53U-3044 Understanding the Evolution and the Impact of Mesoscale and Severe Local Convective Storms

JUAN JOSE RUIZ; PAOLA SALIO; BECHIS, HERNÁN

San Francisco

Conferencia; 100 AGU Fall Meeting; 2019

American Geophisical Union

Drylines are low-level moisture boundaries that frequently occur in the summer season in Argentina. These features are commonly associated with the initiation of deep moist convection that, under favourable conditions, may lead to severe weather events. While some previous works and the experience of local forecasters acknowledge the existence of drylines in the region, little is known about how these boundaries form.On this work, ERA-Interim data is used to analyze 74 drylines of similar characteristics that were detected in Argentina. A composite analysis is performed to study the synoptic setting associated with them, and the processes described by the moisture conservation and thermodynamic equations are evaluated in order to determine the mechanisms responsible for their formation.It was found that these drylines form in the confluence between a warm and moist air mass driven by northerly and nortwesterly anticyclonic flow, and drier air flowing east over northern Patagonia. The dry air south of the dryline has its origin on top of the Pacific maritime boundary layer and experiences lee subsidence after crossing the Andes range. An area of dry and warm air aloft is created by this subsidence, and the westerly synoptic-scale flow contributes to its advection towards the east, while strong boundary layer turbulence transport it downwards. When this dry air encounters the moist air to the north in the confluent region the dryline form. At the same time, strong surface heating over the Plateau leads to substantial warming of the dry air behind the dryline, thus reversing the horizontal temperature gradient across the boundary.