- Upper-Level Cut-Off Lows in Southern South America.

CAMPETELLA, CLAUDIA M.; NORMA E. POSSIA.

METEOROLOGY AND ATMOSPHERIC PHYSICS

Springer

Año: 2006

0177-7971

Abstract This paper presents a statistical study of the spatial and geographical distribution and duration of cutoff low systems over the southern South American region based on the NCEP-NCAR reanalysis data for the period 1979-1986. The cutoff lows were first objectively determined as a minimum in the 250 hPa geopotential height and then subjectively imposing a cutoff circulation and a cold core. A total of 171 cutoff low events were detected, being more frequent in austral autumn followed by winter, spring and summer. However, considering the events with no baroclinic development autumn maintained as the more frequent season but now followed by spring, summer and winter. There is preferred region of occurrence in spring and autumn located between 68º-80ºW and 30º-45ºS. The Pacific area showed the greatest frequency of occurrence followed by the Atlantic area and the continental area. Most of the cutoff lows latest 2 or 3 days (around 90% of the cases) though there is a tendency of the continental events to be longer. The cutoff low event developed upwind the Andes on 22-28 September 1986 was selected as case study. The low level cold air advection was the main responsible of the deepening of the upper level low system.