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A sandstorm is a meteorological phenomenon that is manifested by strong winds causing deflation and the transport of sand particles into the atmosphere, by the saltation process, or even by suspension for fine sand. The dust storms are similar but the raised substrate is the dried soil.

These phenomena are common in the Great Plains of North America, in the Arabian Peninsula, in the Gobi Desert in Mongolia, in the Taklamakan Desert in western China, in the Sahara Desert in Africa, in the Thar Desert in India, as well as in other arid and semi-desert regions.

Weather causes

There are several phenomena that can lift sand or dust to give such storms. They can be classified into two categories:

• intense meteorological depressions and fronts that generate strong to violent winds over a diameter of several hundred kilometers;

• Mesoscale effects, such as thunderstorms, where the winds of the middle levels of the atmosphere are bent to the ground forming a more limited gust front that can sweep over a region.

Synoptic storms

In the first case, the action of the winds is exercised over vast territories and lasts up to a few days. They will lift the thin surface layer in a desert region and give visibility from reduced to zero depending on the variations of their speed. This is an effect similar to blowing snow, or high snow plow, in a snowstorm.

It is often a strong zone of winds when approaching a cold or near-stationary front during the summer period in the intertropical convergence zone. There is usually a strong wind parallel to the front in this situation which raises sand or dust. On the other hand, in winter, it is generally the winds behind and perpendicular to the front which are very strong because of the intrusion of cold air of the front which makes the air unstable.

One of the synoptic scale sandstorms occurs when a north wind, called "Shamal" or "Chammal", blows over the Arabian Peninsula. This situation occurs in summer behind a cold front; and in winter when there is heavy traffic between an anticyclone on the peninsula and a depression east of the Persian Gulf1. Other known winds from desert areas give sandstorms on the same scale as Harmattan, Simoun, Sirocco, etc.