Surface Circulation Associated with Frosts in the Wet Pampas.

MÜLLER GABRIELA V; COMPAGNUCCI, ROSA; NUÑEZ, MARIO; SALLES, ALEJANDRA.

INTERNATIONAL JOURNAL OF CLIMATOLOGY

JOHN WILEY & SONS LTD

Año: 2003 vol. 23 p. 943 - 961

0899-8418

The aim of this paper is to make a synoptic-climatic classification of atmospheric circulation in order to obtain synoptic frost-related patterns in the west Pampas.  Both partial (recorded in 25 to 75% of the meteorogical stations) and widespread (record in more than 75%) frost events that occurred during the winter ( June-July-August) of 1972-83 are included in this study. Frost days are grouped into Neutral (G1), El Niño (G2), and La Niña (G3) years. In addition, the complete dataset, called the data group, is analysed for reference purposes. Each group is analysed using the unrotated and Varimax rotated principal component analysis using the T-mode approach. Six synoptic situations accounted for 94% of the variance associated with frost in the air studied. In general, the principal component score patters given by the unrotated and rotated components are similar. The biggest difference between unrotated an rotated solutions was in variance redistribution. After rotation, only on of the two possible situations (direct-inverse) of each patterns represented a real synoptic type associated with frost in the west Pampas. Persistence and location cause temperature drops in the area studied. The most frequent patterns in rotated results those termed A, B, C* (in G2) and D (in G1 and G3). They are connected with cold anticyclones, which cause adjective and/or radiative frosts. The remaining patterns accounted for about 5% of the variance and represent real, though rare, situations, which are important because of their effect on the west Pampas. The results obtained for the different groups show that inter-winter variability of the equatorial Pacific signal produces changes in the frequency of the frost-connected patterns, rather than different patterns for cold events.