A CUT-OFF LOW IN SOUTHERN SOUTH AMERICA: DYNAMIC AND THERMODYNAMIC PROCESSES

ALEJANDRO ANIBAL GODOY; NORMA E. POSSIA; CLAUDIA M. CAMPETELLA; YANINA GARCÍA SKABAR

REVISTA BRASILEIRA DE METEOROLOGIA

Sociedade Brasileira de Meteorologia

Año: 2011 vol. 26 p. 287 - 294

0102-7786

The dynamic and thermodynamic processes involved in the life cycle of a cutoff low occurred in March 2007 are studied. These processes are analyzed using the vorticity and thermodynamic equations and a set of analyses generated with the BRAMS model. The main processes that explain the segregation of the subtropical part of the trough are the horizontal advection of cyclonic vorticity at high levels and warm horizontal advection at middle levels, both over the Pacific Ocean extending south to the Patagonia region, building the ridge located upstream of the trough. Increased intensity of the upper level low pressure system is mainly explained by intensification of the ridges down and upstream. The divergence effect is opposed to the horizontal advection of vorticity which explains the stagnation of the cut-off low windward of the Andes. The decay stage is dominated by warm vertical advection. Assuming the conservation of potential vorticity the analysis of parcel trajectories, allowed detecting the entrance of stratospheric air to middle levels of the lower troposphere around the cut-off low.