جستجوی مقالات مرتبط با کلیدواژه « cut » در نشریات گروه « جغرافیا »

In the most areas of our country, especiallyin heights, the most common kind of precipitation is assnow that can be considered a main source of waterfor streams, springs, underground watersheds and Qanats. The heights ofYazd province is one of the snowy regions in ourcountry because of geographical situation and topographic conditions. The purposeof this research was to understand, examine and analyze synoptically-dynamically snowfall in Yazd Province. For this purpose, 12 snowfallcourses during the statistical period 1999-2011 were selected following theaccess to the required data and the identification of thegeographical situation in the region. Daily snow and rain dataand synoptic maps of surface level and upper levels ofatmosphere, jetstream, omega, vorticity and moisture, NCEP/NCA base wereused in order to identify air mass movement and studysynoptic systems in the province and the related maps wereplotted in GrADS environment. Three synoptic patterns were extracted afterconducting climatic thermodynamic researches affecting Yazd province and studying dynamiccharacteristics in terms of strengthening and weakening pressure systems. Inthe first pattern, low-pressure combinatory systems of eastern Mediterraneanand Sudanese lead to snowfall especially in Yazd province heights. This is accompanied with the eastern Mediterranean troughs and entranceof cold air from high pressures of high altitudes. Inthe second pattern, the emergence of the blocking phenomenon causessnowfall and severe cold in Yazd province. This phenomenon occursalong with deep troughs of eastern Mediterranean and Red sealeading to cold air and snowfall for several days. Inthe final pattern , the availability of Caspian and Siberian highpressures lead to cut-off low in the central andnorthern regions of Iran which in turn causes snowfall inthe central regions including Yazd province.

Unusual periods of heavy rainfall in Iran with climatic variation in each part of the country are very important.The heavy rainfall always have been one of the hazards of climate That the destruction and irreparable damages life and property is involved. Therefore, understanding the factors and parameters that create the climate system precipitation in any place and at any time of the year, especially transitional period is necessary. Rainfall phenomenon is very complex and nonlinear that the great variability over time and space and a variety of conditions that have important role in the occurrence can be divided into two categories: Synoptic Patterns and local conditions.
Weather is largely controlled by the passage of Synoptic Patterns. On the other hand the occurrence of any weather's particular pattern is to a large extend determined by the distributions of land masses, sea surface temperature gradients,Characteristics and type of land cover (biosphere), topography and the orientation of baroclinic zones.
The objective in this paper is analysis of synoptic patterns and vertical profiles of air in local heavy rainfall in South East of Iran including Sistan and Baluchestan, Kerman, Hormozgan and South Khorasan provinces.
In the summer, synoptic patterns of seasonal rains in South East of Iran often Due of the spread of monsoon air mass. In winter, westerly winds extend towards lower latitudes including the study area; the seasonal rainfall pattern in the region brings.
In this study, the main question is that the synoptic patterns of rainfall during the transitional period (spring and summer) how do they arise? And what are the characteristics?
Data and The purpose of this research is analysis of synoptic patterns and vertical profiles of air in local heavy rainfall in South East of Iran. Meteorological stations studied in this article are located in four provinces including Sistan and Baluchestan province, Kerman province, Hormozgan province and South Khorasan province. Review of daily precipitation data of 31 meteorological stations during (1981-2013) showed that heavy rainfall occurred in October 1390 in South East of Iran, one of the heaviest rain falls during transitional period is local function and the amount of rainfall is greater in most of the stations to compared whit the normal monthly rainfall. To investigate the Characteristics of meteorological parameters in rainyday and the days before rainyday, initially thermodynamic diagrams were analyzed. To determine the synoptic pattern, Weather maps up to 250 hPa Geopotential were examined.
Thermodynamic diagrams in rainy days as compared to the days before rainy days showed that the temperature and air pressure has dropped; Relative humidity and dew point temperature has increased. Thermodynamic diagrams in rainy days as compared to the days before rainy days showed that the temperature and air pressure has dropped; Relative humidity and dew point temperature has increased.
The results of the plot Ski-T, height of FCL and LCL, altitude difference Cloud top relative to the FCL and the amount of Dynamic indices: KINX, SHOW, CAPE, was Show prepared for the unstable Weather conditions. Calculation of instability indices showed that the convection factor was a supporting role in the occurrence of such precipitation, because when convective precipitation is the main factor the Convection is enough intensity and provide the instability needed to create precipitation. Synoptic pattern analysis suggests the establishment of Cut off low. The cut-off low is a cold low (depression) in mid-latitudes (occasionally almost in subtropical latitudes) where air of polar origin is cut off from the main subpolar belt of low pressure and cold air, the normal track of depressions. Cyclonicity around the the core of Cut off low and South wind flow on the eastern edge of Cut off low, arrangements for air convection is unstable in South East of Iran. Cut off low activity from this point is very important, which complements the summer rainfall caused by the monsoon system and winter precipitation caused by western cyclones can play a significant role for autumn rains transitional period In South East of Iran. Calculation of instability indices showed that the convection factor was a supporting role in the occurrence of such precipitation, because when convective precipitation is the main factor the Convection is enough intensity and provide the instability needed to create precipitation. Synoptic pattern analysis suggests the establishment of Cut off low. The cut-off low is a cold low (depression) in mid-latitudes (occasionally almost in subtropical latitudes) where air of polar origin is cut off from the main subpolar belt of low pressure and cold air, the normal track of depressions. Cyclonicity around the the core of Cut off low and South wind flow on the eastern edge of Cut off low, arrangements for air convection is unstable in South East of Iran. Cut off low activity from this point is very important, which complements the summer rainfall caused by the monsoon system and winter precipitation caused by western cyclones can play a significant role for autumn rains transitional period In South East of Iran.

In this study, one of the heaviest rainfalls in southwest and central areas of Iran (09/11/87) over the last four years (1387 to 1390) because of the occurrence of the phenomenon cut-off low,. The purpose of this study is to explore the thermodynamic it will rain. First days of rain precipitation data were obtained from the meteorological precipitation zonation map was, charts Holf - Moller and relative vorticity for the days of the draw. The results showed that the index the instability of the heavy rainfall was considerably for on the map it was not an especially severe precipitation is not particularly high rates the anti-cyclone over the Arabian moisture settled on the Red Sea, Arabian Sea and Gulf of Aden to the south west and central areas of the injected The supply of humidity and precipitation has. Also suggests that a significant amount of relative vorticity the position of the trough axis over the Persian Gulf and southern Arabia and quantity relative vorticity values are consistent with each other