Analysis of meteorological parameters in case studies of precipitation due to the Black Sea.
The Mediterranean region is the transition zone between the southern deserts of North Africa affected by high subtropical, and the central and northern Europe influenced by Western trends. Also, the Mediterranean region, influenced by some factors such as the South Asian summer monsoon, Siberian high pressure in winter, El Nino Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) . The Mediterranean Sea is a great sea enclosed between the 21 countries in Africa, Asia and Europe. This area is famous in Europe to the area of cyclone formation. Mountains around the Mediterranean Sea and the temperature contrast between land and sea surface, cause a complex structure and a spatial distribution of the cyclones and it is as a huge source of energy and moisture in the development of the cyclone . It has always been the case for climate scientists and meteorologists. The spatial distribution and the formation of surface cyclones in the northern hemisphere in 1956 were analyzed by Petterssen. The results showed that there are two important centers of cyclogenesis in the East and West of the Mediterranean region in the winter and there is an active center on Iberia in the summer. Gulf of Genoa is one of the important cyclogenesis areas from November to February. In the case of heavy precipitation in the Mediterranean region, Kasper and Muller  considered the role of anomaly of some quantities like positive vorticity advection of mid levels and meridional temperature gradient in the low levels. The occurrence of western Iran heavy rain is related to existence STJ in based on upper-level trough which is propagated to Western Iran located above surface cyclone with extending pressure trough to western Iran and North Arabia Saudi . Although the values of these anomalies in the central Europe are weaker than the Mediterranean region, it is caused the heavy precipitation in the Czech. The Aegean Sea and the Black Sea in winter are important cyclogenesis in the East Mediterranean region [2,9,1,11], but the mechanism of cyclogenesis in this area have been studied very few. The case studies about cyclogenesis over the Black Sea and the Middle East had been done between November and March [5,12,10]. The purpose of this study, is investigating some Meteorological parameters at a station where precipitation has occurred. Those parameters can be some indicators for predicting precipitation by the Black Sea.
Materials and Methods
In this study, we use a reanalysis dataset produced by the US National Centers for Environmental Prediction (NCEP) and the US National Centers for Atmospheric Research (NCAR) .
Several cases of heavy and light precipitation were selected in different months. To compare calculated parameters in the selected systems and recognize their differences, OROOMIEH Synoptic station with 37.32[degrees] N and 45.05[degrees] E are selected which is called the representative point. Some synoptical and dynamical quantities attain in this point, such as the mean sea level pressure and its anomaly, 500-hpa geopotential anomaly, relative vorticity advection and thermal vorticity advection and thickness advection. These parameters were investigated two days before and one day after precipitation with a twelve-hour interval in some graphs. In the graphs, horizontal axis shows 12 hours intervals and vertical axis shows the parameters. Relative Vorticity advection and thermal vorticity advection units are [10.sup.-10] [s.sup.-2] and thickness advection unit is [10.sup.-5] [ms.sup.-1] which they will not repeat in the text and only mentioned as a unit.
Figure 1 shows the mean sea level pressure in selected cases for the representative point. It is seen that this parameter has had decreasing trend else in February 1985 and after precipitation it has had increasing trend. In the case of February 1985 related to heavy precipitation, the amount of pressure has reduced 10mb during 12 hours. The case of November 2004 shows that after precipitation, the pressure has increased about 16mb during 24 hours due to fall of cold air. In the case of low precipitation in March 2005, maximum pressure reduction has occurred a day before precipitation. The decline has still continued until a day after precipitation which is due to establishment the low-pressure system. The case of July 2002, in the summer, it has a significant difference in contrast with others. It is the only case that the pressure has come down to the 1000mb.
[FIGURE 1 OMITTED]
Figure 2 shows the anomaly of mean sea level pressure in the selected cases for the representative point. The highest anomaly, respectively, is related to the case in November 2004 and February 1985, when the heavy precipitation of 53 mm is occurred, and the Pressure is 12mb and 9mb times less than the average. The lowest anomaly is related to summer case and light precipitation case which the pressure in precipitation day is 1mb time less than the average. Also this parameter changes in summer and during the study was close to the zero line.
Figure 3 shows the anomaly of 500hpa geopotential in selected cases for the representative point. The highest anomaly of this parameter is related to the November 2004 rate which height is 230 m less than average. The lowest fluctuations are related to the July 2002 case. In all cases, except in February 1985 which is decreasing steeply (24 hours after a precipitation, the height has decreased 100 m), an increasing trend is observed.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
Figure 4 shows the relative vorticity advection of 500-hpa geopotential in selected cases for the representative point. This parameter is positive a day before the precipitation occurs in all cases. In the case in November 2004 this parameter is reached to 20 units. Also after precipitation, in November 2004, this parameter decreases 11 units. The lowest volatility is related to the July 2002.
[FIGURE 4 OMITTED]
Figure 5 shows the thermal vorticity advection of 500 hpa geopotential in the selected cases for the representative point. The highest value of this parameter is in November 2004 when has happened in the day of precipitation with the amount of 7 units. In both of light precipitation case and summer case, the amount of this parameter will fluctuate around zero. The remarkable change is in February 1985, during 12 hours the amount of parameter has changed from -7 to 3.
[FIGURE 5 OMITTED]
Figure 6 shows the 500/1000 thickness advection by geostrophic wind of 1000 hpa level in the selected case studies to represent. The most amount of this parameter is related to the case in February 1985, the day of precipitation with the value of 100 units. Also in the case of March 2009 the amount of parameter in the day of precipitation is 80 units. For both March 2005 (light precipitation) case and July 2002 (summer) case, the amount of this parameter does not have much fluctuation. For both, November 2004 case and April 1995 case, the value of this parameter has reached to the least its amount in the precipitation day, the -110 and -80, respectively. But their relative vorticity advection and thermal vorticity advection are considerable. It can be explained as follows:
Absolute vorticity advection by geostrophic wind in 500 hpa level and 1000/500 thickness advection by geostrophic wind of 1000 hpa level can interpret development or decline of the system pressure. Positive absolute vorticity advection with the positive thick advection caused a negative trend in the pressure and development of the ground pressure trough. Development (deterioration) of mid level trough of the atmosphere convergence (divergence) of horizontal wind at lower levels and the upward vertical motion cause strengthening (weakening) of the surface pressure systems, so the relative or absolute vorticity advection of 500hpa level by its geostrophic wind, positive thermal vorticity advection of 500 hpa level by its thermal wind, positive thickness advection of 500/1000 by geostrophic wind of 1000 hpa level are considered as indicators of development in the mid-latitude pressure systems.
[FIGURE 6 OMITTED]
Comparison of the calculated parameters for the selected systems and recognizing their differences, OROOMIEH Synoptic station with 37.32[degrees] N and 45.05[degrees] E are introduced as a representative point. Some synoptic, thermodynamic and dynamic parameters are calculated in this point. These parameters are investigated two days prior to precipitation day and one day after that with a twelve-hour interval in the graphs. Comparing these parameters of items can show differences between cases. The overall results show that the meteorological parameters change during precipitation in North-West of Iran due to the Black Sea cyclogenesis. Thus, further studies and index determination can be used as a tool for prediction.
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(1) Parvin Ghafarian, (1) Amir H. Meshkatee, (2) Majid Azadi and (3) Majid M. Farahani
(1) Department of Meteorology, Science and Research Branch, Islamic Azad University, Tehran, Iran.
(2)Atmospheric Sciences and Meteorological Research Centre (ASMERC), Tehran, Iran
(3)Institute of Geophysics, University Of Tehran, Iran.
Parvin Ghafarian, Department of Meteorology, Science and Research Branch, Islamic Azad University, Tehran, Iran.
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|Title Annotation:||Original Article|
|Author:||Ghafarian, Parvin; Meshkatee, Amir H.; Azadi, Majid; Farahani, Majid M.|
|Publication:||Advances in Environmental Biology|
|Date:||Jan 1, 2012|
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