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Synoptic Structure of Severe Zonda Downslope Windstorms in Argentina

Federico Otero , Diego Araneo, Maximiliano Viale

Abstract

The Zonda wind is a characteristic Argentinian downslope windstorm that occurs on the eastern slopes of the Andes Mountains, creating extremely windy, warm, and dry conditions with substantial socioeconomic impacts. This study aims to characterize and understand the synoptic-scale atmospheric dynamics, as well as the vertical structure of the atmosphere on both sides of the Andes, associated with severe and long-duration Zonda events compared to non-severe. 64.8% of occurrences of severe events are most frequent between August and October. These events exhibit an earlier onset and later cessation, resulting in more late-night and morning Zonda hours compared to non-severe events. The synoptic structure for severe and long Zonda events is associated with a more baroclinic structure, featuring a deep trough at both low and mid-levels and shifted west with altitude. Lower levels present higher anomalies and move faster than mid-level anomalies when it crosses the Andes. This is accompanied by a deep trough east of the Andes with a tilted axis and a slower eastward movement. The associated upper-level dynamic shows a stronger convergence and divergence pattern on the windward and lee sides of the Andes, respectively, along with a stronger, elongated and persistent jet-streak. The precipitation pattern is in agreement with the more intense winds impinging on the Andes, resulting in more intense rising motions and more precipitation on the windward slopes. The analysis of the vertical structure in severe events shows a more humid windward profile, especially at low and mid-levels, with stronger winds. The leeward side presents a more unstable temperature profile, warmer at low levels and colder at upper levels, and an extreme dryness between low and mid-levels indicating the Zonda presence at this altitude before the event starts. Given the limited studies on the Zonda downslope windstorms in South America, this research makes a major step in our understanding of the severe events and provides valuable insights for weather forecasters.

ES24030  Accepted 29 April 2025

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