A cut-off low in southern South America: dynamic and thermodynamic processes

Alejandro Anibal Godoy,Yanina García Skabar,Norma Edit Possia,Claudia Marcela Campetella

doi:10.1590/s0102-77862011000400001

Alejandro Anibal Godoy, Yanina García Skabar + Show 2 more

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https://doi.org/10.1590/s0102-77862011000400001

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Abstract

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.

Highlights

Cut-off lows (COLs) are synoptic scale phenomena that affect southern South America and are able of producing significant weather phenomena both in the Cordillera region and in the plains
Godoy et al (2011) presented a detailed description of the COL lifecycle that occurred from 24 March to 2 April 2007 over the coast of Chile and its links with significant weather events in southern South America
Given that BRAMS40 analyses provide a good simulation of the COL lifecycle, those analyses were used to study the processes driving the system’s lifecycle

Summary

Introduction

Cut-off lows (COLs) are synoptic scale phenomena that affect southern South America and are able of producing significant weather phenomena both in the Cordillera region (snowfall, blizzard) and in the plains (heavy rainfall, strong winds). Quispe and Avalos (2006) analyzed a COL event that caused heavy snowfall in the south of Peru, where huge losses of crops, livestock and homes were recorded. Pizarro and Montecinos (2000) found that COLs located close to the coast of Chile contributed by 5% to 10% to annual rainfall over Chile between 26o and 36oS. Funatsu et al (2004) showed that COLs could be precursors of cyclogenesis over southeastern South America. Godoy et al (2011) presented a detailed description of the COL lifecycle that occurred from 24 March to 2 April 2007 over the coast of Chile and its links with significant weather events in southern South America

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