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

FEDERICO A NORTE; ANA GRACIELA ULKE; SILVIA SIMONELL; MAXIMILIANO VIALE

BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY

American Meteorological Society

Año: 2007 vol. 88 p. 94 - 94

0003-0007

The  severe Zonda wind event of july 11 th. 2006 east of the Andes Cordillera (Argentine) by F. Norte*;G.Ulke**;S. Simonelli* and M.Viale* The zonda is a strong , warm and very dry wind associated to adiabatic compression upon  descending the eastern slopes of the Andes  in winter and spring time preferently.This wind exhibit the so called “foehn effect.”Although this phenomenom occurs on the entire length of the extratropical Andes it is most frequently detected near the cities of Mendoza   and  San Juan which represent the most important urban regions of western Argentina.(one million and a half inhabitans) There are defined  four categories , based on the maximum zonda  wind gust( The annual frequency distribution of  severe and extreme severe zonda  events is lower than  eight percent of the annual total cases .. The Zonda wind event of july 11 th. 2006   reached categories Z3 and Z4 in the surrounding area of Mendoza and  San Juan cities  where wind speed were over 120 Km/h during  two or three hours without interruption. The synoptic surface and upper air conditions were the typical associated with a severe zonda wind occurrence in the region: a surface cold front approaching to the central coast of Chile driven by a 500 hPa level trough, a deep low pressure surface system approximately over 55°S and 65°W, and a strong upper air jet stream. The   main feature of the event is the sharp polar air advection from the south and a remarkable 500/1000 hPa thickness gradient. In Mendoza airport meteorological station(32º50’S;  69ª 47’W , 704 masl a persistent northern wind clearly showed the zonda since 18 UTC 11 July to 03 UTC 12 July and a marked wind speed increase occurred from 18 UTC 11 July reaching a maximum of 60  km/h at 22 UTC , with an extreme wind gust of 80 km/h at 22:25 UTC In San Juan airport meteorological station  (31º 34’S; 68º 25’W, 598 masl),  wind speed became more intense between 12 UTC and 18 UTC 11 July reaching a maximum of 45 km/h  with an even stronger maximum (52 km/h) at 06 UTC 12 July. A distinguished increase  in temperature  and dryng   was observed  reaching 28.2 ºC, whereas the dewpoint temperature dropped to -6 ºC in Mendoza  and 33 ºC and -15 ºC at  San Juan The   July 11th  2006 zonda event caused  a great impact over the  communiy.The Mendoza newspapers informed that  hundred of   residences  were affected, many families  must leave  their homes, 159 country  and 23  buldings fires were reported , a hospital was partially destroyed,  25 school buildings were  affected, hundred of trees falling down, 50000 inhabitants without electric power and  1500 without telephonic service. Similar information appeared on San Juan newspapers *Programa Regional de Meteorología. Instituto Argentino de Nivología ,Glaciología y Ciencias Ambientales(IANIGLA) Consejo Nacional de Ciencia y Tecnologia(CONICET) **Departamento de Ciencias de la Atmósfera y los Océanos, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina