Dust and Sand Storm Formation
Dust and sand storms are a persistent problem in Iraq, Saudi Arabia and Upper African Countries and other areas in the Middle East, but they are most prevalent in the spring and summer months due to the strong (northwesterly shamal) winds that characterize the weather during the winter-spring seasonal transition. Specifically, dust and sand storms occur when the strong (mostly dry) storms — that often accompany well-defined cold fronts — stir up these particles. Dust and sand lift both ahead of and (even more so) behind cold fronts (since winds tend to be stronger behind the front than ahead of it). This seasonal trend can best be characterized as a combination of two separate weather systems: the sub-tropical jet stream pushing up from south of the Arabian Peninsula and a polar front jet stream pushing down from the European continent. When these two systems come into close proximity, they create much more dynamic weather than is usually found in this region, especially the strong northwesterly “shamal” winds (shamal winds at several Southwest Asia international airports have been recorded as high as 43 knots or 49 mph).
The larger the particles, the stronger the wind required to lift them into the air. But for there to be any long-range transport, there also needs to be considerable vertical motion. The vertical speed determines how much the particulate matter is lifted into the air. Another factor that influences the impact of the shamal is the dampness of the sand. Even a very small amount of precipitation can keep a tremendous amount of sand from entering the air (although the very dry conditions that predominate in Iraq mean that there is a high probability that strong sandstorms can arise — as recent events have shown).
The unique topography and human intervention within the region also contribute to the frequency and intensity of dust and sand storms in this area. The natural funneling of large air masses by the high mountains in Turkey and Iran, combined with the high plateaus in Saudi Arabia, help to funnel air across the Mediterranean into the Persian Gulf. Furthermore, many Iraqi wetlands have been drained for agriculture or seriously deprived of water by reservoirs upstream. This exacerbates dust as wind lifts dry silt from exposed lake and marsh beds.
