عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The climate is such that large system interaction between the four large-scale climatic: hydrosphere, cry sphere, lithosphere and Biosphere. If a change occurs in one of these systems, other systems quickly or slowly make their coordinators. The consequence of this arrangement, the skirt has been instrumental in changing the initiator includes an endless chain links, the device will tie together. Because this is the most important link between climates scientists in the fields of concern in recent years as climate change. Why the climate change caused by global warming and subsequently climate of the planet for future decades, the rapidly growing world system has been disturbed.
In this study, were used the data of mid-level atmospheric pressure, geopotential height pressure from the center's database based on National Centers for Environmental Prediction / National Center for Atmospheric Research(NCEP/NCAR). This data are available for 6 hours GMT time and period 1948 to 2007 on the website Climate Diagnostics Center. National Oceanographic & Atmospheric Administration Government (www.esrl.noaa.gov). The spatial resolution of the data is 2/5 degrees of arc and the area from 0 - 90 degrees north and 0 - 360 degrees meridian and contains 5184 pixels. For comparison, the t - test was used for paired samples and to achieve this goal, the 30-year period was divided into two periods. Diagnosis and detection of positive or negative trend (increase or decrease) during the period of the subtropical high pressure system in the area used the f Kendall's tau trend test and a significance level SPSS software 0/05 and 0/01.
Results of Kendall's tau trend test calculation showed, increases in all months of the area insubtropical high pressure system at significance level of 0/01. August has highest and April has lowest area rate. The system is based on semi-warm and generally higher latitude and has the lowest area. With the passing of spring, and the system is still moving higher latitude, until in July to reach its highest latitude. But with the start of the transition period and beginning of cold period of the year, this contour is pulled toward the low latitudes and most of the area is covered and In February to reach its lowest latitude.
The results showed that all the months of the study period, with an increasing trend (positive) area are subtropical high pressure system. August has the highest and April has the lowest area rate. The northern limit of the system (contour of 5840 geopotential) in the semi-warm temperate latitudes generally is based as parts of the North, Central Mediterranean, central Europe and North America and is area lowest in July. But with the onset of cold periods, the contour is pulled down latitude and occupies the most area in February.