Iranian authorities called a public holiday in the city of Tehran on Tuesdayand Wednesday as thick clouds of dust spread over much of the nation. Theimmediate concern was for the health risks owing to exposure to the dust, whichwas reported to be at its worst level in 30 years. Low visibility, down tohundreds of yards in many areas, also led to the grounding or delaying offlights. Businesses were shuttered.The origin of the shroud of dust actually lay beyond the Iranian border inneighboring Iraq. Here, much of the nation suffered severe dust and sandstorms, storms said to be the worst in memory, in early July. The dust waswhipped up by the prevailing `shamal,` the regional northwesterly wind, thenwafted eastward to Iran on westerly winds higher in the atmosphere.
The land surface of Iraq is inherently prone to becoming loose dust easilyraised by the wind once the wind speed reaches 15-20 mph. Disturbance of theland surface by the activities of war and construction may have made thisprocess even more effective, thereby worsening sandstorms when they do happen.
Story by AccuWeather.com Senior Meteorologist Jim Andrews.
