عنوان مقاله [English]
Moisture flux convergence (MFC) is some moisture in atmosphere that moves from side to another side. It combines from advection humidity and moisture convergence terms. The function is calculated on the basis special humidity and wind vectors and it is used to forecast the thunderstorms and heavy precipitations. It is a term in the conservation of water vapor equation and was first calculated in the 1950s and 1960s as a vertically integrated quantity to predict rainfall associated with synoptic-scale systems. MFC was eventually suggested for use in forecasting convective initiation in the midlatitudes in 1970, but practical MFC usage quickly evolved to include only surface data, owing to the higher spatial and temporal resolution of surface observations. Since then, surface MFC has been widely applied as a short-term (0â3 h) prognostic quantity for forecasting convective initiation, with an emphasis on determining the favorable spatial locations for such development. This research investigates moisture flux convergence in convective, non-convective, super-heavy and heavy precipitation events in the southern coasts of Caspian Sea. It study role of each humidity resources to occur precipitation in different regions in the north of Iran.
2- Methodology: On the basis of daily precipitations in seven stations during 1961 to 2008, with regard to 25 and 50 percent probability, precipitation events are divided into heavy and super heavy precipitations. The events are also grouped into convective and non-convective precipitations based on the clouds synoptic codes. The moisture sources are distinguished using moisture flux convergence and humidity advection in different level pressures from 1000 to 500 hpa over the past 2 days. Moisture sources are distinguished for precipitations in the north of Iran.
Figure1 shows that there is the most frequency of moisture flux convergence in the west area in compare with the east and mountainous regions. There are the maximum functions at 06:00 GMT for different precipitation regions. Figure 2 indicates that the functions are in the convective group more than non-convective group and super-heavy than heavy precipitation events. There are the maximum functions at 06:00 GMT for different precipitation groups.
Fig.1. Moisture flux convergence mean in different precipitation regions in 1000hpa level(gr/kgs)
18 12 06 00 Observational times
10 12 16 12 west region, super heavy group
5 8 12 9 West region, heavy group
8 10 14 11 Mountainous region, super heavy group
4 8 12 6 Mountainous region, heavy group
6 8 8 6 East region, super heavy group
4 8 8 6 East region, heavy group
Fig.2. Moisture flux convergence mean in different precipitation groups in 1000hpa level(gr/kgs)
18 12 06 00 Observational times
6 15 18 12 Convective and super heavy precipitation
6 9 12 8 Nonconvective and super heavy precipitation
4 8 12 7 Convective and heavy precipitation
2 6 11 5 Nonconvective superheavy precipitation
The difference between heavy and super-heavy precipitation in terms of moisture flux convergence is more in convective than non-convective events. The frequency of moisture sources are more in super-heavy precipitation than heavy precipitation. However, the Caspian Sea is the first supplier moisture sources for the precipitation in the north of Iran, the Black Sea and Mediterranean Sea are the second supplier sources respectively in super-heavy and heavy precipitation.