In this section the Caspian climate is described. Substantial differences occur between the northern and the southern section of the sea. The maps are shown here as illustration. For the original maps you can search the maps catalogue to find the owner.
The average annual airtemperature above the Caspian Sea changes from 10oC in the north to 17°C in the south. (Fig.1.3). The monthly average airtemperature in January is -5 - 10°C in the north and near the east coast of the Middle Caspian, and is -1 - 5°C in Makhachkala area. The coldest month above the southwestern and central areas of the sea is February. The approach of the strongest colds in February is one of the most typical features of climate. Increase of temperature from March to July occurs uniformly. Since the middle of March the temperature of air over eastern and western parts of the sea gets lower than over land; in the central deep-water areas of the sea and in the southwest this happens in April.
In summer monthly average airtemperature at sea is 24- 26 °C; The highest value can be found in the southeastern area in Krasnovodsk where the airtemperature is near 28oC.
The largest range of monthly average airtemperatures in deep-water areas of the Middle Caspian is 20,5 - 22°C, of the South Caspian it is 18 - 20°C. Above the remaining part of the South Caspian this range also does not exceed 20°C and increases up to 22°C only in the Apsheron area and around Cheleken peninsulas. The largest difference of monthly average airtemperatures is a little bit higher at the South Caspian shoreline (22° - 24°C), near the west coast it equals 21° - 24 °C (at shoreline 22 - 25 °C), near the northeastern coast it equals 24 - 25°C (increases at the shoreline up to 28°C). The greatest annual range of monthly average airtemperature is observed in the northwestern areas (25 - 27°C) and northeastern areas of the sea. This is significantly depending on increase of continental temperatures.
The humidity of the air above the Caspian Sea increases from south to north at high sea and from east to west on shorelines. It also increases towards the high sea. The average annual distribution of humidity is shown in Figure 3.2.
The humidity of air does not change much in the cold period of year, making 80-87% on western coast and 75-80% on eastern coast. In the high sea it decreases from 90% at the central parts of Middle Caspian to 85% at center of South Caspian.
The highest humidity of air on western coast is marked in northern part of Azerbaijan coast (87%), the lowest - in Apsheron (75-77%). In the summer the driest site of western coast is an area of Apsheron up to the mouth of Kura River (55-66%). This period the humidity changes within 55-60% limits. On the Iranian coast the humidity is more than 70%. In the high sea it reaches value of 80%.
The amount of precipitation on the Caspian coast depends on interaction of originally different air masses with relief of the coast. Distribution of precipitation above water area is extremely uneven. It oscillates from 210 (Neft Dashlari) to 1250mm(Lenkoran zone) of precipitation per year on western coast of southern part of the sea. To the north of Absheron peninsula the amount of precipitation makes 400-430 mm. Eastern coast distinguishes by dryness, and the maximum quantity of perceptions does not exceed 10-20mm there. On the Iranian coast it falls out about 1000-1200 mm of precipitation per year because of humid climate.
The cloudiness above Caspian Sea is more in the winter than in other seasons of year and its value changes form 5,5 ball on the southeast to 8 balls on the northwest. Generally, the cloudiness on western coast of Middle Caspian is the greatest in all seasons that is connected with cyclonic activity in this area (Fig. 3.3).
The spring range of cloudiness variation compounds from 3,2 to 6,8 balls, moreover it increases from the southeast to the northwest. Distribution of average cloudiness is more uniform in the summer. It changes within 2,4-3,9 balls limits over the most part of water area and over shoreline. The autumn distribution of cloudiness, which closes to the spring, is 3,6-6,7 balls.
The clear weather with cloudiness about 0-2 degrees prevails above the sea and the coast during a warm period of year; the cloudy weather with cloudiness about 8-10 balls has the largest repeatability during a cold period.
The disposition of Caspian Sea in rather low latitudes causes intensive influx of solar radiation. The positive size of annual radiation balance which equals difference between solar heat absorbed by the sea surface and the heat lost by the way of effective radiation testifies it. The radiation balance for all water area of the sea is positive and averages out 60 k.kal/sm2.
Within Northern Caspian it comes down to 50k.kal/sm2, within Middle and South Caspian it reaches 65 k.kal/sm2. Surplus of radiation heat predetermines intensive evaporation on what is spent 54 k.kal/sm2 of heat, and intensive connective heat exchange with an atmosphere.
The radiation balance is positive since March till October for all water area of the sea and has maximal values in June and July (11-12 k.kal/sm2 per month). The negative balance is only in December: form 2 k.kal/sm2 on the north of the sea to 1 k.kal/sm2 on the south (Fig. 3.4).
Direction and strength of wind blowing over Caspian are determined by three factors: distinctive general circulation of an atmosphere, field of temperature that is created by the sea itself and a relief of its coasts. (Figure 3.5)
Despite significant physiographic dissimilarity the water area of Caspian and its shoreline may be divided into regions with relatively stable regime of a wind direction. General regularity of a regime of direction is such that the winds of northern (Northwest, North, and Northeast) and southeastern directions dominate above the sea the most part of a year. The probability of setting up wind fields of the northern rhumbs makes up on average 41% for one year; moreover their probability in the summer is more (48,7%) than in other seasons of the year. All eastern winds make up on average 35,9% per a year. More often they are observed in the winter (41,3%), when the stable cyclones form above areas of Kazahkstan and Central Asia.
The average speed within the water area of the sea is 5,7 m/sec. The greatest average speeds are observed in the middle part of the sea and are on average 6-7 m/sec per a year. Their values are 8-9m/sek in the area of Absheron peninsula. The wind speed sometimes reaches 40 m/sec there. In the cold part of a year (December-February), when the intensity of an atmosphere circulation above Middle and South Caspian increases, the average wind speeds reaches 7-7,5 m/sec.
The annual average wind speeds are 5,0-6,3 m/sec from northern and eastern coast of Caspian to Gara-Bogaz-Gol Gulf and increase up 7 m/sec around Mangishlag peninsula and capes.
The average wind speeds are sizably lower in South Caspian: in central areas - 4-5 m/sec, on eastern coast - 3,5-4 m/sec, on the outside southeast -2,5-3 m/sec. Low speeds (2,2-3 m/sec) is observed on south-western coast, in Iranian waters and on southern coast of Caspian.
Although the average wind speeds increases form the south to the north in warm period of a year as well as in cold period, the distinction between areas of the high sea and the coast is the least in this period: above the sea the average wind speeds change from 3 to 5 m/sec, above the coast - from 2 to 5 m/sec.