The Atlantic Region

In the cold half-year, the most striking feature of this region is its extreme high temperatures (relative to other parts of the Arctic) related to strong and vigorous cyclonic activity and the warm ocean currents which are branches of the Gulf Stream (see Figure 4.4). For example, the mean monthly air temperatures in Spitsbergen are about 20°C higher than in the Canadian Arctic at the same latitude. The anomalies get smaller to the north, northeast, and east because the influence of cyclonic activity and warm oceanic currents is reduced. On the other hand, the cold East Greenland and East Spitsbergen currents significantly cool the areas where they occur. The intense cyclonic activity also brings exceptionally great cloudiness and heavy precipitation to the Atlantic region. The wind speeds occurring here are the highest in the entire Arctic. Also the variability of some meteorological elements (in particular the air temperature) is greatest here (see Figure 4.7). The Atlantic region is characterised by the lowest degree of climate continentality (see Figure 4.2). The ocean between Jan Mayen and Bjômôya has almost a 'pure oceanic' type of climate. For example, the mean monthly temperatures (1951-1980) at Jan Mayen range between -6.1°C (February) and 4.9°C (August) with absolute maximum and minimum temperatures reaching only 18.1°C and -28.4°C (1922-1980), respectively (Steffensen 1982). Prik (Atlas Arktiki 1985), taking into account the spatial differentiation of the climatic conditions in this region, delimited four sub-regions: southern, western, northern, and eastern.

The southern sub-region is the largest one (see Figure 1.2) and can be characterised in brief as the warmest, cloudiest, and rainiest area in the entire Arctic. The average air temperatures of the winter months in the southern parts of this sub-region oscillate between -1°C and 0°C and in the northern part between -8°C and -10°C. Storms and heavy precipitation, often occurring in the form of wet snow and sometimes as rain, are frequent here. The highest variability of temperature in the entire Arctic (see Figure 4.7) is in the border areas of the southern and northern sub-regions, where there is the greatest changeability of thermally contrasted air masses inflowing from northern and southern sectors.

The western sub-region is significantly smaller than the southern one, but has an area similar to the two others (the northern and eastern regions). Prik (1971) has distinguished this sub-region for three reasons: 1) maximum horizontal temperature gradients, 2) significant variability in the average monthly and diurnal temperatures, and 3) clear predominance of severe northern winds. In comparison with the previous sub-region, lower temperature, cloudiness and precipitation characterize the western sub-region. On the other hand, the greatest variability of precipitation is observed here (see Figures 7.8 and 7.9).

The northern sub-region includes the eastern half of Spitsbergen, other Svalbard islands, Zemlya Frantsa Josifa, the northern parts of the Barents and Kara seas, and the part of the Arctic Ocean adjoining them. The climatic conditions are more severe here than in the southern sub-region because the influence of both atmospheric and oceanic circulation is significantly weaker and, in the case of the latter factor, it is even absent. On the other hand, cyclones reaching this sub-region have an occluded stage. This, according to Prik (1971), creates considerable fluctuations in temperature, an increase in cloudiness, and an intensification of winds. Air temperatures are lower than in the other two sub-regions and rapidly decrease from -10°C and -12°C in the south-western part to -25°C in the north-eastern part. The winds blow mainly from south-easterly and easterly directions and their speed is lower than in other sub-regions. Cloudiness is quite extensive (60-65%). The interesting feature of this sub-region is the fact that in winter it is characterised by the greatest temperature variability, while in summer the temperature variability is the lowest in the entire Arctic.

The eastern (or Kara) sub-region includes the eastern half of Novaya Zemlya, the Kara Sea up to the Taymyr Peninsula, and the part of continent that is washed by it. Climatic conditions are most severe in this sub-region because Novaya Zemlya acts as a climatic barrier. It significantly reduces the entering of warm water from the Barents Sea and also, to a lesser degree, the movement of travelling cyclones along the Iceland-Kara Sea trough. Cyclones, which reach this sub-region passing Novaya Zemlya island from its northern and southern sides, together with the cyclones developing in the south-east of this sub-region, cause quite large diurnal variation in temperature, severe winds (mainly south-westerly or southerly), an insignificant occurrence of cloudy days, and frequent, although not heavy, precipitation. Correlation analysis reveals that the temperature relationship of this sub-region is greater with the Siberian region than with the Atlantic region (Przybylak 1997b). Therefore, it is proposed that this sub-region be included within the Siberian region.

The above characterisation of the climate of the Atlantic region and its sub-regions is based mainly on winter conditions, which occur throughout most of the year. In addition, under these conditions the spatial differentiation of the climate is significantly the greatest. For this reason, the summer climate is presented only for the Atlantic region as a whole. In summer, because of the decrease in the meridional gradient of temperature between moderate and high latitudes, the cyclonic activity is less intense. On the other hand, the frequency of cyclones is only slightly lower than in winter due to the drop in air pressure in the Arctic. The influence of warm currents is also limited in summer. This is true both of their magnitude and their spatial occurrence. The most important factor differentiating the climate is the incoming solar radiation (the polar day). As a consequence, a zonal distribution of meteorological elements is observed (see Figure 4.4). For example, the temperatures decrease to the north from 8-10°C (southern part) to about -1°C and 0°C (northern part). The cold East Greenland and East Spitsbergen currents considerably reduce the air temperature. In summer, the winds blow from the opposite directions than in winter, i.e., from the north and east. Cloudiness over the ocean and seas is very high (75-85%), while on land (both in coastal and inland areas) it rapidly decreases to about 60-65%.

9.2 The Siberian Region

This region is located far from the Atlantic and Pacific oceans. Therefore, this area is characterised by one of the most extreme continental climates on earth. The winter climate is dominated by the Siberian high, which undoubtedly mostly determines the climatic regime of the region. Cyclones are a rather rare phenomenon and, if they occur, they travel mainly along the Lena and Kolyma rivers. The influence of the Siberian high is seen in the directions of winds, which are here mostly from the southern sector and have moderate speeds (about 5 m/s in the maritime areas and below 3 m/s in the continental areas). In comparison with the Atlantic region, the annual cycle of wind speed in this region is the opposite: lower winds occur in winter and higher ones in summer. Air temperatures are among the lowest in the Arctic and drop below -30°C. On the continent, they rapidly decline in direction to the centre of the Siberian high, where near Oimekon and Verkhoyansk the lowest temperatures in the Northern Hemisphere occur. However, this area lies outside the Arctic. The variability of air temperature and pressure is lower here than in neighbouring regions. As a result of the domination of anticy-clonic circulation, low cloudiness (35—45%) and precipitation (< 10 mm/month) is observable.

In summer, anticyclones still prevail but cyclones also occur very often (see Figure 2.3b, d), mainly in the southern part of the Siberian region. The highest occurrence of anticyclones is noted over the Laptev and East Siberian seas; they rarely enter the continental part. Such a synoptic situation determines the prevalence of winds from the northern and eastern sectors. Thus, on the continental part, a monsoon-like change of wind directions between winter and summer is observed. The synoptic situation, which is less stable than in winter, also results in wind speeds being slightly higher in these areas, ranging from 5 to 6 m/s. Air temperatures in the maritime parts are rather low (0 - 2°C), but rapidly increase on land, reaching 10-12°C near the southern boundary of the Arctic. There is considerably more precipitation than in winter: from 20-25 mm/month over the seas to about 3040 mm/month over the continent. Fogs are very frequent over the water areas (up to 30% in the North), while over the continent they are a rather rare phenomenon (5%).

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