عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Study and Analysis of Synoptic of Dust and Black Storms in Yazd Province
One of the natural hazards resulted in great damages in dry and wild regions of world and Iran annually is the occurrence of dusty and black storms. Due to Iran geographical situation in arid and semiarid zone of the world, this country is continually exposed to local and synoptic dust systems. Yazd province is also exposed to various dust systems and this destructive phenomenon because of climatic and geographical conditions and adjacency to deserts in neighbor countries. Therefore, the knowledge of this phenomenon can be an efficient step towards its destructive effects, in particular in stabilizing smooth sands within this region.
2-Data and Methods
In this research, using wind direction and speed data, horizontal view, pressure, temperature, humidity, could and dust phenomenon in synoptic stations, synoptic maps in the ground surface, 850 and 500 hpa levels, omega, wind vector, wind stream, humid blowing and cyclone and atmospheric data above Yazd station, dusty and black storms in low atmospheric levels were studied during 17 stages in selecting the sample in 1989-2009 years. The necessary maps were taken since two days before starting dust until its peak from NCEP/NCAR databases and drawn in GrADS software.
3-Result and Discussion
The results of the research show three dust storm patterns and strong winds during three autumn, winter and spring seasons.
The first is autumn pattern (storm October 2, 1997) in which there are pressure gradient between south and central areas of Iran and a hod with deep amplitude in 850 and 500 hecto-pascal levels in western Iran and Yzad province which it couldnât be fed well in terms of temperature and humidity. The passage of hod and releasing its energy and long term dryness in summer across this region resulted in blowing strong winds and dust storm in this province, especially in Yazd-Ardekan plain. The second is winter pattern (storm February 22, 2009) due to the presence of low-pressure center over the ground and along with deep hods in high levels as well as the passage of cold front through the province and the contact between cold air mass behind front and warm air mass dominant over region. After passing the cold front, sudden downfall of cold air can increase wind speed greatly in dry atmosphere and reduce horizontal view and the occurrence of dust storm in this region. The third is spring pattern (storm may 29, 2003) in which deployment of low pressure cell on the surface of the ground, tilting hod hinge in the upper levels of atmosphere across western Iran and its quick movement and sending short waves through central Iran and Yazd province along with the passage of cold dry and weak front from western north resulted in upward strong flows, high air instability and very serious dust and black storms in Yazd province and get to zero the horizontal view.
The results of the research show three dust storm patterns and strong winds during three autumn (storm October 2, 1997), winter (storm February 22, 2009) and spring (storm may 29, 2003) seasons.
The majority of such storms occur in afternoon hours and in may month and its strong winds mostly blow from west to western north.
Keywords: Dust, Storm, Synoptic Map, Trough , Yazd Province