A good example of the viento blanco and viento zonda carrying large amounts of dust across Bolivia and Argentina, is given in the Meteosat-9 RGB composite image below.
05 May 2023
21 July 2009
By Jochen Kerkmann (EUMETSAT)
According to Wikipedia, the zonda wind (in Spanish, viento zonda) is a regional term for the foehn wind that often occurs on the eastern slopes of the Andes, in Argentina. The Zonda is a dry wind (often carrying dust) which comes from the polar maritime air, warmed by descent from the crest of the Andes, which is some 6000m above sea level. While this type of foehn wind may occur over most central parts of western Argentina, its effects are more impressive in La Rioja, San Juan, and northern Mendoza provinces, because the mountain barrier is higher, while to the north the Puna plateau dissipates these winds.
The Zonda wind is basically produced by the northeastward movement of polar fronts, and although it is hot and dry over the low-lands, it is the main mechanism for snow precipitation at higher altitudes, where it is called viento blanco, reaching speeds sometimes over 200km/h. Thus, instead of being a snow-eater, this wind is particularly important for this arid region, as it results in the build-up of the winter snow cover and accumulation over the scarce local glaciers.
According to studies (conducted over the period 1967–1976), the Zonda wind most commonly starts during the afternoon (between 12 and 6pm), and tends to last between one and 12 hours, though it may present itself intermittently for as long as two or three days. It is usually brought to an end by the entrance of cold air masses moving northwestward (viento sur). In 90% of the cases, the phenomenon takes place between May and November.
In this case, the polar front is visible over Bolivia, Paraguay and Southern Brazil while the centre of the cyclone (at 700hPa) is located in the Uruguay-Argentina border region (see 700hPa absolute topography, ECMWF analysis).
A close inspection of the animation shows that the origin of the dust is located in the high altitude Andes in northern Argentina and southern Bolivia, e.g. in the area of the Salar de Uyuni. This area in Bolivia is actually one of the so-called dust hotspots , as identified in the paper from Engelstaedter and Washington (2007).