The Zonda event in Argentina. State of Climate in 2006, A. Arguez, Ed. Special Supplement to the Bulletin of American Meteorological Society

NORTE, F. A.; ULKE, A. G.; SIMONELLI, S. C.; VIALE, M.

BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY

American Meteorological Society (AMS)

Lugar: Boston, MA. ; Año: 2007 p. 94 - 94

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The Zonda event in Argentina—F. Norte, G. Ulke, S. Simonelli, and M. Viale The Zonda is a strong, warm, and very dry wind associated with adiabatic compression upon descending the eastern slopes of the Andes, preferentially in winter and spring. It is the Argentine version of katabatic winds, which are also called mistral, chinook, Santa Ana, and foehn winds in different parts of the world. Although this phenomenon occurs across the entire length of the extratropical Andes, it is most frequently detected near the cities of Mendoza (33°S) and San Juan (31.5°S), which are the most populated cities in western Argentina (1.5 million inhabitants). Four categories define the strength of the Zonda. The top two categories, “severe” (Z3) and “extremely severe” (Z4), respectively, account for less than 8% of Zonda events (Norte 1988). The event of 11 July reached categories Z3 and Z4 in the surrounding area of Mendoza and San Juan, where wind speeds reached over 120 km hˉ¹ during a 2–3-hour period without interruption. The synoptic surface and upper-air conditions were the typical ones associated with a severe Zonda wind occurrence: 1) a surface cold front approaching the central coast of Chile driven by a 500-hPa-level trough, 2) a deep low pressure surface system appoximately over 55°S and 65°W, and 3) a strong upper-level jet stream. The main feature of the event is the sharp polar air advection from the south and an intense meridional 500–1000-hPa thickness gradient. The occurrence of the Zonda episode was characterized by a marked increase in temperature and a decrease in humidity. Thus, in Mendoza, the temperature reached 28.2°C while the dewpoint dropped to –6°C. At San Juan, the air temperature rose to 33.0°C, and the dewpoint fell to –15.0°C (Fig. 6.24). The Zonda caused severe impacts in the region, including fires, power outages, fallen trees, and destroyed buildings.