3. Wind
3.1. General description
3.2. High speed winds
3.3. Storms
3.5. Local scale hazardous wind conditions
Arctic wind speed and direction over completely open territory are defined primarily by the location of the barometric fields and associated horizontal pressure gradients. But in some regions, where there are glaciers, mountains, or straits, the wind field is often distorted by the local orographic conditions. Average barometric conditions that form as a result of the atmospheric circulation define winds of specific directions. These winds also have a significant frequency pattern both in direction and in speed. For example, the winter distribution of pressure fields in the Russian Arctic is dominated by the intense development of three climatic centers of atmospheric action, specifically the Icelandic and Aleutian Lows and the Siberian High. The activity in these areas defines the cyclone frequency from the Atlantic in the western part of the Arctic (the Barents and Kara seas). In the eastern region, cyclone frequency is significantly less. Some cyclones reach this region from the northern part of the Pacific ocean. Eastern Siberia is a source region for anticyclones because of the intense winter cooling that occurs there. Over almost the entire Arctic, these winter conditions are related to the most frequent wind directions, which are from the west and southwest (called monsoons). This does not include the Chukchi Sea, where winds are most often from the Northeast (Fig. 2).
In March the seasonal changes in the pressure gradients occur, and over the entire Arctic they decrease and level out. The eastern trough of the Icelandic Low shrinks and disappears completely in May. The Siberian High decays and a wide shallow low takes its place in May. In spring, the wind does not have a preferred direction.
In summer, weak cyclones are predominant, penetrating into the Arctic from Canada and Siberia. The frequency of anticyclones is often nearly negligible. This gives rise to a high frequency of north winds (Fig.2).
In September and October, the winter pressure field pattern forms. The eastern branch of the Icelandic Low develops on the western side of the Arctic. In the East beginning in October, the Aleutian Low decreases and spreads out. North winds are quite frequent during this time.
The air flow directions described above show distortions at most of the arctic stations, except those that are located on islands in the open sea [54, 69]. In regions where there are mountain ranges, river valleys, straits and gulfs, the wind is often modified by local orographic peculiarities. In these cases, the winds blow most often from the mountains and along the bays and coasts. These distortions occur in the Matochkin Shar, Karskoe Vorota, Vil'kitskiy, Dmitry Laptev, and Bering Straits. They also occur in the valleys of the Ob, Enisey, Kolyma and other rivers. In these regions, the main air flow caused by the large scale barometric field is redirected along the direction of the bay, strait or valley. The pattern of air flow that develops due to the influence of mountains depends on the configuration of a particular range. As a rule, winds blow perpendicular to the direction of the range. Cooler air subsiding from glaciers and ice caps moves in directions specified by synoptic conditions.
Figure 2. Frequency of wind direction (%) in winter (a), in spring (b), in summer (c), in autumn (d): I - Rudolf Island, II - Zhelaniya Cape, III - Maliye Karmakuly, IV - Dixon Island, V - Kotelniy Island, VI - Tiksi, VII - Chokurdakh, VIII - Pevek, IX - Cape Schmidt, and X - Wrangel Island; the numbers in the circles denote the frequency of dead calm.
Strong amplification of wind speed is observed on Novaya Zemlya. As a result, the highest wind speeds in the Arctic are observed at the Russkaya Gavan' station, which is adjacent to glaciers. The wind speeds decrease as the distance from glaciers and mountains increases.
Table 6Frequency of high winds at the stations on Novaya Zemlya in % | |||||
Station | Wind speed, m/s | Total | |||
25-28 | 29-30 | 35-40 | >40 | ||
Russkaya Gavan' | 1.3 | 1.0 | 0.4 | 0.05 | 2.75 |
Maliye Karmakuly | 1.2 | 0.7 | 0.3 | 0.01 | 2.21 |
Cape Zhelaniya | 0.6 | 0.3 | 0.1 | 1.00 | |
Cape Stolbovoy | 0.8 | 0.4 | 0.1 | 1.30 | |
Cape Vikhodnoy | 0.5 | 0.3 | 0.2 | 0.03 | 1.03 |
On Novaya Zemlya, the winds blow down from the glaciers and mountains both west to the Barents Sea and east to the Kara Sea. The frequency of high winds is higher, when the wind blows from mountains and glaciers. In Russkaya Gavan' these winds are from the South, at Maliye Karmakuly they are from the east and southeast, and at Cape Zelaniya they are from the southeast and south. On the eastern coast of Novaya Zemlya the strong winds are from the northwest and west. At Cape Vikhodnoy, the number of days with high wind speeds is more than 100 days per year (Table 7), and it is close to the values observed at the western coastal stations. This was also pointed out by Vize [13].
Strong local winds that are increased by relief do not extend far out to sea in the Arctic. Observations at 30-50 kilometers from the stations show that the wind speeds at these distances have already dropped to values normally observed over the seas.
Table 7Number of days per year with wind speed of 15 m/s and higher | |||
Station on the west side of Novaya Zemlya | # of days | Station on the east side of Novaya Zemlya | # of days |
Russkaya Gavan | 120 | Matochkin Shar | 113 |
Maliye Karmakuly | 122 | Cape Vikhodnoy | 101 |
Cape Stolbovoy | 93 | Cape Zhelaniya (northern tip of island) | 115 |
The wind direction, characteristic of open, low, and flat coastal regions, is also analogous for the peripheral seas out to 250 kilometers from the coast. Note that over seas far from the coast, the wind direction is essentially rotated to the left by about 22 to 45 degrees from the direction at the coasts [69].
Sometimes, local wind eddies are observed in several arctic regions mostly in the large bays. In these areas, small source regions of cyclones are formed with diameters of 100 to 400 kilometers. Anticyclones can also form there but occur less often. Wind eddies are caused by source regions of low air pressure, creating winds of different direction over the water areas of bays and gulfs. When the cyclones move, rapid changes in wind direction occur in the newly formed system. The authors have found eddies of this kind in daily synoptic charts of Baidaratskaya Bay, Chaunskaya Bay and other regions. They cause strong winds and wind direction changes.
Sometimes in the Arctic very steady winds that do not change for several days are observed. Winds that do not change direction within 4 to 6 days have been observed in every region in each month, but only infrequently - on average 1 to 4 times in 10 years. In regions where topography does not influence the wind, the direction of such steady wind coincides with the prevailing wind direction in only 55 percent of cases, while in the other cases completely different directions are often observed. In the regions where topography has the greatest influence, the direction of the most steady wind and the prevailing one coincides 75 percent of the time.
Average speeds were determined for the period from 1936 to 1985. These values were obtained using wind vanes and anemometers. The use of the anemometer (model M-63) began in 1970. Reduction of concurrent wind vane and anemometer data was carried out using the following formula [3]:
,
where Vvane is the average value of wind speed obtained by wind vane; Vanem is an average value of wind speed obtained by anemometer; and m, n are the number of years over which observations were measured by wind vane and anemometer respectively. The spatial distribution of annual averages of wind speed is presented in Figure 3.
Figure. 3. Annually averaged wind speed, meters per second.
The average speed across the Arctic ranges between 4 meters per second and 8 meters per second. The annual variations in mean monthly wind speeds in different regions do not follow the same pattern. In the western and eastern regions the highest monthly averages occur during the winter from November to February, and the lowest values occur in summer. But the general character of the average wind speed variations over the year is often perturbed by additional periodic effects. The amplitude of variation in the average monthly wind speed is small at the observation stations, from 1 to 3 meters per second. Only in places where there is local intensification in the winter does the amplitude reach 4 meters per second. Over the eastern Laptev Sea and the western East Siberian Sea, the opposite pattern is observed such that the amplitude is less in winter than that in summer. This is connected with the prevalence of anticyclonic circulation in these regions together with the weak intensities of the cyclones that reach these areas during the winter. In summer, though, cyclonic activity developing in the northern parts of Siberia has a significant effect.
Spatial variations of changes in wind speeds are also defined by the atmospheric circulation patterns. In winter the highest wind speeds are observed over the western seas. In the Barents Sea, monthly averaged wind speeds exceed 8 meters per second at certain times of the year. These values decrease in the continental area near the coast. In the Kara Sea the average monthly wind speed decreases to 7 meters per second in the western part and to 6 meters per second value on the eastern side.
Average monthly wind speed decreases noticeably as one moves eastward from the Kara Sea. In the western part of the East Siberian Sea the values reach the minimum for the entire Arctic Basin, approximately 5 meters per second. In the southern area over the coast, the mean wind speed decreases to 4 meters per second. In the northern part of Eastern Siberia, where anticyclonic circulation predominates, it decreases to 3 meters per second in protected mountain valleys. In April the winter wind speed patterns still remain. The highest speeds (more than 7 meters per second) are observed over the Barents Sea, and the lowest ones (about 5 meters per second) are observed over the East Siberian Sea. The weakest winds are predominantly located over the northern areas of the East Siberia. In May, the wind speeds decrease in the western and eastern seas. Strong winds become less frequent and moderate winds (6-10 meters per second) become more frequent.
In summer, average monthly wind speeds are nearly the same over all the seas, essentially 5 to 6 meters per second. They decrease to the south over the northern continent edge, but less intense than in winter, and there is a very weak decrease to the north over the central part of the Arctic basin.
As in winter, an increase in the wind speed is mostly observed over the capes, straits and gulfs. The increases in speed in the northern parts of the continent are related to the development of cyclonic activity. As a result, increasing wind is observed during the summer in the following locations: over the western Barents Sea, near Cape Kanin Nos and the southern coast of the Barents Sea, over the northernmost extremes of Novaya Zemlya, in Baidaratskaya Bay, in Vil'kitskiy, Laptev, Sannikov, and Bering straits, and over the Gydansky, Yenisey and Khatanga Gulfs.
In September the circulation patterns begin to change. There is a corresponding change in the spatial distribution of mean wind speed and the frequency distribution of various speeds. In October the wind speed regime is very similar to that of winter, but the gradients are still less than in winter.
All winds are initially formed under cyclonic conditions, mostly by extremely deep cyclones, and come in from the North Atlantic Ocean in the west and from the Pacific Ocean in the east. Wind amplification in cyclones does not always happen. It occurs if a blocking crest exists in the form of a moving cyclone or anticyclone. The pressure gradient increases sharply and the wind speed increases accordingly. The high-speed winds occur principally at the forefront of the cyclone ahead of the warm front. For example, the Atlantic cyclone of 23-25 January, 1975 caused strong winds over the southern Kara Sea. Its center was located over the south-western Barents Sea where the pressure was 970 millibars. The anticyclone over the Taimyr Peninsula obstructed the eastward motion of the adjacent cyclone resulting in an increase in the pressure gradient. The warm front moved from south to north in the western Kara Sea. On 26 January, the cyclone moved into the eastern Kara sea, its pressure rose, and the strong winds died out. Other cases of high speed winds also occurred at other stations under similar conditions, but the spatial locations of the centers of the cyclones bringing the storms were different.
As has been pointed out, strong winds more often are related to synoptic conditions and surface relief. For example, on 3 January 1972 the high winds at Maliye Karmakuly were caused by a cyclone from the North Atlantic, whose center was located over the southwestern Barents Sea. A warm front crossed Kolguev Island and the southwestern part of Novaya Zemlya and proceeded further to the northwest. South winds, propagating along the isobars, allowed cold air to flow down from mountains to the Barents Sea. East and southeast wind was observed at Maliye Karmakuly. The average speed of all winds from these directions was equal to 11.7 meters per second. Equally strong winds were recorded at Russkaya Gavan' station. When the wind direction is from the southeast and south, cooled air from above the glacier flows down toward the sea, and the average wind speed is equal to 12.1 meters per second. To produce hazardous wind conditions, synoptic situations of the site described above associated with cyclonic activity are required at any location, but vigorous cyclonic activity is typical throughout the entire winter.
During the cold half of the year cyclones from the North Atlantic as well as from the southwestern parts of the continent occasionally penetrate to the Laptev Sea producing high winds. Such winds are observed especially frequently at Tiksi in the central sector of the Russian Arctic. They are caused by the mountains nearby. For example, from 21 to 25 February 1981 a cyclone, whose center was located over the eastern part of the Taimyr Peninsula, caused maximum wind speeds of 51 meters per second. At Tiksi, the average speed of the west and southwesterly winds at times when hazardous wind conditions arise is equal to about 8 meters per second. At other stations in this region, the dangerous winds occur significantly less often.
In the eastern Arctic the high speed winds arise from the penetration of strong cyclones penetrating from the Bering Sea and the Sea of Okhotsk and even from the Atlantic ocean toward the East Siberian Sea. High speed winds are principally observed in this region if the wind direction is north and northwest (except for Pevek).
The extreme northeastern part of Asia is mountainous. The Chukchi mountains are 1500-1800 meters in elevation and restrict the motion of the air masses in the area. Deep cyclones tend to cross the range through the lower areas. As a result, the southern cyclones enter the Chukchi Sea most often through the Bering Strait and Kolyuchinskiy Bay and the East Siberian Sea through Kolyma lowland from the Sea of Okhotsk. Southern cyclones that reach Alaska and produce northern air flow have a very strong influence on formation of high speed winds. These cyclones have little effect on longitudes beyond Cape Billings, however. Cyclones from the Sea of Okhotsk affect the Chukchi Peninsula to varying degrees. Those cyclones that enter the Chukchi Sea cause the formation of high speed winds from the southwest, while those reaching the East Siberian Sea cause high winds from the southeast.
The highest frequency of storm winds in the eastern Arctic area is observed at Pevek. The formation of hurricane force winds is almost exclusively connected with the cyclones leaving the Sea of Okhotsk.
In the middle of winter, synoptic events are encountered in the Bering sea are encountered approximately 20 percent of the time. These cyclones travel from the Bering sea to Kolyma. At those times, an anticyclone is located over the Chukchi Sea.
Natural wind speed in the Arctic was measured using two devices: wind vanes with rigid boards (from 1966 to 1973) and M-63 anemometers (from 1974 to 1985). Wind vane measurements were recorded as two-minute averages, as opposed to 10-minute averages with the anemometers. There appears to be a difference between the results of the measurements, performed by these devices [3]. This difference increases with wind speed. It is 0 meters per second when wind speed is between 5 and 8 meters per second and increases to 8 meters per second when the speed indicated by the wind vane is 40 meters per second (Table 8).
We believe that the reason for the difference in speeds is not only the difference in averaging interval but also in differences in the design of the devices and in the measurement specifications. While averaging of wind speed measured by M-63 is performed automatically, an observer using the wind vane tends to weight the extreme excursions of the wind vane more heavily in determining an average.
Table 8Comparison of wind speed measured by wind vane and M-63 anemometer, m/s | |||||||||
Wind vane | 8 | 10 | 12 | 14-20 | 22-28 | 30 | 32 | 34 | 36-40 |
M-63 Anemometer | 8 | 9 | 10 | 11-17 | 18-24 | 25 | 26 | 27 | 28-32 |
Difference | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
Therefore, the number of days with dangerous speed winds depends to some extent on the method of wind speed measurement. The number of such days was calculated from observations over the time intervals indicated in the TM-1 tables. The maximum speeds were recorded for both steady wind and gusts. Comparison of maximum steady wind speed and the speed of gusts determined by wind vane showed that the differences between them depends on the magnitude of the wind speed. For higher values of the actual wind speed, the difference is greater (Table 9). On average, the difference is about 5 meters per second.
Table 9Differences between maximum wind speed and wind gusts in m/s from wind vane observations | |||||||
Maximum steady speed | 8-10 | 11-15 | 16-19 | 20-24 | 25-30 | 31-34 | 35-40 |
Gusts | 12-14 | 15-20 | 21-23 | 24-30 | 31-35 | 36-40 | >40 |
Difference | 4 | 4-5 | 4-5 | 5-6 | 5-6 | 5-6 | 6-7 |
The differences between maximum wind speed and gust speeds measured by anemometer are significantly larger than those obtained from wind vanes (Table 10). On average, the difference is equal to 9 meters per second, 4 meters per second greater than the results from the wind vanes. This is due to the fact that a wind vane has more inertia than an anemometer sensor.
Table 10Differences between maximum wind speed and wind gusts in m/s from anemometer observations | |||||||
Maximum steady speed | 8-10 | 11-15 | 16-19 | 20-24 | 25-30 | 31-34 | 35-40 |
Gusts | 14-17 | 18-23 | 24-27 | 28-33 | 34-40 | 41-45 | 46-51 |
Difference | 6.5 | 7.5 | 8.0 | 8.5 | 9.5 | 10.5 | 11.0 |
In connection with this, we now consider a methodology to define the number of days with dangerous wind speeds. Our analysis has shown that a wind vane speed of 25 meters per second corresponds to a value of 21 meters per second measured by anemometer. As a result, a non-uniformity in the number of days with wind speeds of 25 meters per second and 30 meters per second has appeared in the data set. According to the results of 150 records comparing wind vane and anemometer results, there are differences of 2 to 4 days. When wind speed is 15 meters per second and above the difference of number of days with hazardous speeds is equal to 2. For 25 meters per second and above, the difference is 3 days; and for 30 meters per second and higher it increases to 4 days. Based on these data, a reduction of number of days with hazardous winds measured by wind vane has been carried out to make the results consistent with the anemometer records. As a result, the records for frequency of occurrence of wind speeds of 15, 25 and 30 meters per second are much more uniform.
We thus have several criteria for strong winds. In the present work, wind speed equal to 15 meters per second and above is considered as strong, and the frequency of occurrence of strong winds in the Arctic is considerable. These high speed winds are classified by the following criteria: high speed wind (15-24 meters per second); storms (25-29 meters per second); and hurricane force wind (30 meters per second and higher). Using observational data from more than 200 stations from 1936 up to 1980-1985 we have constructed a chart showing contours of the number of days per year with strong winds over the entire Arctic, including both the Russian and non-Russian sectors (Fig. 4).
Figure 4. Number of days per year with wind speeds of 15 meters per second and above.
The highest frequency is observed for the mountainous and coastal regions (75-100 days). These areas include the zone from Novaya Zemlya to the open part of the Barents Sea, the southeastern coast of the Kara Sea, the mouth of Lena river, and the coast of the Chukchi Peninsula. The minimum frequency is observed in the central arctic basin and the arctic portion of Yakutia (5-10 days).
Winds with 15 meters per second speed are observed more often in winter than in other seasons. On average, there are 6 to 8 such days per month in the open area of the Barents Sea, 4 to 6 days in the Kara Sea, 3 to 4 days in the Laptev Sea, and 2 to 3 days in the East Siberian Sea.
Such winds are observed much more frequently in the coastal regions of the islands and the continent. For example, on average 10-12 days per month with wind speeds of 15 meters per second or above are observed on the coast of the Kola Peninsula, in the vicinity of Amderma and Dixon, on Franz Josef Land, and particularly on the Taimyr Peninsula coast. In the coastal zones of Novaya Zemlya, wind speeds of 15 meters per second or higher are recorded on almost half of the days every winter month. In the eastern Arctic, high winds are observed on average on 6 to 10 days (Table 11).
Table 11Average number of days with wind speed 15 m/s and higher | |||||||||||||
Station | # per Month | Annual Total | |||||||||||
Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | ||
Rudolph Island | 11 | 10 | 10 | 8 | 5 | 3 | 2 | 3 | 5 | 9 | 8 | 9 | 83 |
Maliye Karmakuly | 16 | 13 | 14 | 11 | 8 | 7 | 5 | 6 | 8 | 10 | 12 | 14 | 124 |
Amderma | 13 | 10 | 10 | 8 | 5 | 3 | 2 | 3 | 5 | 9 | 12 | 12 | 92 |
Dixon Island | 11 | 9 | 10 | 8 | 6 | 5 | 2 | 3 | 6 | 9 | 9 | 11 | 89 |
Golomyanniy Island | 3 | 2 | 4 | 3 | 4 | 2 | 1 | 1 | 2 | 3 | 3 | 3 | 31 |
Cape Chelyuskin | 7 | 7 | 6 | 5 | 4 | 4 | 4 | 3 | 5 | 7 | 5 | 8 | 65 |
Khatanga | 2 | 2 | 1 | 2 | 2 | 1 | 1 | 1 | 1 | 1 | 1 | 2 | 17 |
Kotel'niy Island | 3 | 3 | 4 | 4 | 3 | 3 | 3 | 4 | 4 | 3 | 2 | 4 | 40 |
Muostakh | 5 | 4 | 4 | 3 | 2 | 1 | 1 | 3 | 4 | 7 | 5 | 5 | 44 |
Chokurdakh | 1 | 1 | 1 | 2 | 2 | 1 | 2 | 1 | 1 | 2 | 2 | 1 | 17 |
Chetiryokhstolbovoy Island | 6 | 4 | 4 | 3 | 2 | 2 | 2 | 2 | 2 | 4 | 5 | 4 | 40 |
Ayon Island | 3 | 2 | 2 | 1 | 1 | 1 | 1 | 1 | 1 | 3 | 3 | 3 | 22 |
Wrangel Island | 10 | 8 | 9 | 7 | 5 | 2 | 3 | 4 | 6 | 9 | 12 | 11 | 86 |
Cape Schmidt | 7 | 6 | 6 | 4 | 2 | 1 | 2 | 2 | 4 | 8 | 9 | 7 | 58 |
Uelen | 8 | 4 | 4 | 4 | 3 | 4 | 9 | 6 | 7 | 11 | 11 | 6 | 77 |
In spring, winds of 15 meters per second and higher speed are observed infrequently: in the Barents Sea on 4 to 7 days per month, on average and 3 to 5 days in the Kara Sea. In the Laptev and East Siberian seas, this number decreases to 2 or 3 days. In the Chukchi Sea the number rises slightly to 4 days. In some places along the coasts and over the continent, wind speed increases up to 15 meters per second and above significantly more often. For example, an average of 6-8 days per month are observed in the Amderma and Dixon regions, on Franz Josef Land, and particularly along the coast of the Taimyr Peninsula. On the coast of Novaya Zemlya, the average number is 10 days and above. An increase in the number of such days compared with the results from the open sea areas, of up to 4 days per month on average, is observed in Vil'kitsky Strait, at the mouth of the Lena river, in Kolymsky Bay, at Pevek, and along the coast of Chukchi Peninsula. With the exception of the Barents Sea, winds of 15 meters per second and higher are seldom observed on the open sea, where the winds are generally weaker. In the central arctic basin, the same lower values (5 to 10 days per year) are observed.
In summer, high wind speeds are much less frequent. On the coast of the open seas, 1-2 days per month are observed on average, increasing to 3 days in certain places. Sometimes, however, this can increase to as much as 10 to 12 days per month. Over the sea far from the coasts and also in the continental regions, high wind speeds are rarely observed in summer - not even every year (approximately 5 to 8 times in 10 years). The largest summer values of all (up to 5 to 7 days per month) are observed on the coast of Novaya Zemlya, at Pevek, and particularly along the Chukchi Peninsula coast.
In winter, the maximum continuous duration of certain winds of 15 meters per second and higher in the western and eastern regions is 10 to 12 hours. At specific stations where the frequency of such winds is higher (Maliye Karmakuly, Ambchik, and Pevek) the maximum continuous duration is 15 hours. More often, their duration varies, mainly from 1 to 3 hours and from 3 to 6 hours. Longer intervals with winds of 15 meters per second and above winds are seldom observed. This is a result of the close proximity of mountains combined with the synoptic and orographic conditions.
In summer, the duration of winds in particular areas of more than 15 meters per second speed is significantly less. Over the open seas it is typically 5 to 8 hours; on the coasts of the continent and the islands it increases to 9 to 11 hours; but to the south far from the coasts the duration of winds of this sort decreases to 3 to 6 hours. Their maximum duration in the summer is generally from 30 to 50 hours, but at selected points it can reach as much as 90 hours. The mean duration of wind speeds of 15 meters per second and above per month equals 40 to 60 hours, but in areas with local amplification durations of 100 to 150 hours are reached (e.g. Novaya Zemlya, Amderma, Dickson Island, and Wrangel Island).
Direction of winds with speeds of 15 meters per second and higher varies considerably. At Maliye Karmakuly the wind is always from the east and southeast, and at Amderma it is from the southwest. In the northeastern part of the Kara Sea in spring wind directions vary, but most often they are from the south. In the central part of the Eurasian Arctic spring winds are from the west and northwest. In the eastern part of the Arctic, high speed winds in spring blow in a southerly direction.
Before proceeding with the graphical presentation of the spatial distribution of hazardous winds, we point out that the display needs to be modified slightly to avoid crowding. Dangerous wind speeds are observed mainly at distinct points purely as a local strengthening of the wind. As mentioned above, these winds do not extend out very far over the sea or land so that in certain areas the isopleths can become very crowded. In order to alleviate this problem, the density of lines has been thinned. In figure 5, the observed isopleths in a given region corresponding to maximum wind speed have been replaced by isopleths for a restricted range of speeds (15 to 24 meters per second) that is close to the synoptic estimate of the number of days. From figures 4 and 5 it is apparent that compared with the distribution of number of days with wind speeds of 15 meters per second and above, the number of days with strong winds in the range 15 to 24 meters per second is on average 10 to 15 days less.
Thus it is evident that in the Arctic, the principal contribution to the frequency of wind speeds of 15 meters per second and above comes from the winds in the range 15-24 meters per second, and the winds greater than 25 meters per second occur only about 20 percent of the time [11, 22, 30].
Figure 5. Number of days per year with high wind speeds in the range 15-24 meters per second.
Storm winds are often observed in the Arctic. According to the Beaufort scale these winds have speeds of 25 meters per second and higher [38]. Storm winds most often form on the boundaries of pressure fronts, especially during cold fronts. In this connection, the direction of such winds is defined by the location of low pressure areas in specific circumstances. The frequency of storm wind speeds as a function of direction is presented in Table 12. Calculations were performed according to the specifications of the Russian Hydrometeorological Office [44, 60].
Table 12Frequency (in %) of storm wind speeds (of 25 m/s and higher) in the Western and Eastern Arctic versus direction | ||||||||||||||
Direction | Month | Annual Total | ||||||||||||
Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |||
Western Arctic | ||||||||||||||
N | 0.4 | 0.3 | 0.4 | 0.1 | 0.1 | 0.2 | 0.3 | 0.3 | 0.4 | 0.6 | 3.1 | |||
NE | 0.4 | 0.3 | 0.4 | 0.4 | 0.1 | 0.1 | 0.3 | 0.8 | 1.1 | 3.9 | ||||
E | 3.4 | 5.1 | 4.3 | 2.1 | 1.3 | 0.8 | 1.0 | 0.5 | 0.5 | 1.1 | 0.6 | 5.0 | 25.7 | |
SE | 1.3 | 2.7 | 2.8 | 1.8 | 0.5 | 0.2 | 0.2 | 0.3 | 0.4 | 0.5 | 2.7 | 1.7 | 15.1 | |
S | 5.1 | 2.8 | 1.8 | 0.5 | 0.2 | 0.2 | 0.7 | 2.8 | 3.0 | 17.1 | ||||
SW | 5.3 | 3.1 | 2.9 | 0.9 | 0.0 | 0.2 | 0.0 | 0.4 | 1.7 | 2.6 | 2.0 | 19.1 | ||
W | 2.1 | 1.7 | 1.2 | 1.3 | 0.4 | 0.5 | 0.5 | 0.4 | 0.4 | 0.6 | 0.9 | 1.3 | 11.3 | |
NW | 0.9 | 0.4 | 0.7 | 0.7 | 0.0 | 0.0 | 0.0 | 0.1 | 0.4 | 0.4 | 0.3 | 0.8 | 4.7 | |
Total | 18.9 | 16.4 | 14.5 | 7.8 | 2.4 | 2.1 | 1.7 | 1.7 | 2.3 | 5.6 | 11.1 | 15.5 | 100 | |
Eastern Arctic | ||||||||||||||
N | 4.0 | 5.5 | 4.1 | 1.0 | 0.0 | 0.0 | 0.6 | 4.4 | 8.6 | 8.1 | 36.3 | |||
NE | 0.5 | 3.0 | 1.1 | 0.4 | 0.0 | 0.1 | 0.5 | 2.0 | 2.0 | 9.6 | ||||
E | 1.2 | 2.5 | 1.6 | 0.3 | 0.2 | 0.0 | 0.0 | 5.8 | ||||||
SE | 3.5 | 1.0 | 0.8 | 0.0 | 0.3 | 0.7 | 0.4 | 6.7 | ||||||
S | 2.0 | 1.0 | 1.0 | 1.9 | 0.2 | 0.3 | 3.9 | 1.1 | 11.4 | |||||
SW | 3.2 | 1.4 | 0.7 | 0.3 | 0.2 | 0.2 | 0.2 | 1.9 | 0.2 | 8.3 | ||||
W | 1.0 | 0.4 | 0.7 | 1.6 | 1.4 | 0.9 | 6.0 | |||||||
NW | 3.5 | 0.7 | 1.6 | 0.7 | 0.7 | 2.0 | 4.8 | 1 9 | 15.9 | |||||
Total | 18.9 | 15.5 | 11.6 | 4.6 | 0.2 | 0.0 | 1.8 | 9.5 | 23.3 | 14.6 | 100 |
In the western Arctic, the storm winds most frequently come from the south (specifically from the east to the southwest) as a result of cyclones from the Atlantic. This occurs 77 percent of the time. In the eastern Arctic, the maximum frequency of storm winds (52 percent) is observed for a different set of wind directions - specifically north to northwest. These wind directions are caused by deep cyclones coming in from the Bering Sea. In addition, an increase in the frequency of the southerly winds is observed there as a result of cyclones from the Sea of Okhotsk. The frequency of wind directions described above is observed principally during the winter both in the western and eastern Arctic. In other months, especially from June to August, the frequency of storm winds is quite small. (less than 2 percent per season). These calculations are based on data from reference books on climate studies of the Soviet Union [44, 60].
Including all of the Eurasian Arctic, storm winds from the north, east and south have the highest frequency [Table 12]. The frequency of the storm winds (regardless of the direction) in the Arctic vary considerably depending on the season. Their maximum frequency is observed in the winter months (from November to March). On average, 80 percent of all storms occur then distributed roughly evenly at 16 percent per month. The remaining 20 percent are distributed over the other three seasons, of which only 1 percent occur during the summer months (July-August).
The number of days with storm winds with speeds of 25 meters per second and above includes all cases when the criterion was met during the course of one of the observation intervals (3 hours). The number of days with wind speeds of this magnitude in the Arctic in the majority of cases, is defined by the geographic location (Table 13).
Table 13Average number of days with wind speed of 25 m/s and above | |||||||||||||
Station | # of days per Month | Annual Total | |||||||||||
Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | ||
Rudolph Island |
2.6 | 2.9 | 1.3 | 1.0 | 0.6 | 0.2 | 0.2 | 0.4 | 0.5 | 1.4 | 2.6 | 2.8 | 16.5 |
Russkaya Gavan |
7.8 | 6.3 | 6.2 | 3.8 | 2.2 | 1.5 | 1.0 | 0.9 | 2.8 | 3.6 | 5.4 | 6.0 | 47.5 |
Maliye Karmakuly |
3.9 | 3.3 | 2.9 | 2.2 | 1.9 | 1.8 | 1.4 | 0.5 | 1.5 | 1.5 | 2.8 | 2.9 | 26.7 |
Amderma |
2.6 | 2.2 | 1.2 | 0.6 | 0.3 | 0.1 | 0.1 | 0.3 | 0.6 | 1.0 | 2.0 | 11.0 | |
Golomyanny Island |
0.2 | 0.3 | 0.1 | 0.3 | 0.2 | 0.2 | 1.3 | ||||||
Dixon Island |
2.0 | 1.3 | 0.6 | 1.0 | 0.7 | 0.4 | 0.2 | 0.8 | 0.8 | 1.0 | 2.7 | 11.5 | |
Cape Chelyuskin |
1.0 | 0.9 | 0.2 | 0.5 | 0.4 | 0.2 | 0.1 | 0.2 | 0.4 | 0.5 | 0.6 | 5.0 | |
Khatanga |
0.2 | 0.2 | 0.3 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.3 | 2.3 |
Tiksi |
4.5 | 3.1 | 1.4 | 1.0 | 0.6 | 0.2 | 0.2 | 0.2 | 2.0 | 2.8 | 4.6 | 20.0 | |
Muostakh |
1.4 | 1.1 | 0.4 | 0.4 | 0.5 | 0.1 | 0.2 | 0.7 | 0.8 | 1.5 | 7.1 | ||
Kotel'ny Island |
0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 2.9 |
Chokurdakh |
0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.7 | |||||
Chetyryokhstolbovoy Is. |
0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.3 | 0.9 | |||||
Ayon Island |
0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.3 | 1.4 | |||
Pevek |
2.4 | 2.6 | 2.2 | 1.4 | 2.7 | 3.0 | 1.3 | 1.4 | 1.7 | 2.2 | 2.4 | 2.6 | 25.9 |
Cape Schmidt |
0.9 | 0.9 | 0.8 | 0.2 | 0.1 | 0.1 | 0.1 | 0.8 | 2.0 | 1.1 | 7.0 | ||
Wrangel Island |
3.0 | 2.6 | 2.1 | 1.5 | 0.6 | 0.2 | 0.1 | 0.2 | 0.4 | 2.0 | 2.7 | 2.4 | 17.8 |
Uelen |
2.0 | 0.5 | 0.5 | 0.2 | 0.2 | 0.2 | 0.4 | 0.3 | 0.8 | 1.6 | 2.6 | 2.1 | 11.4 |
Provideniya Bay |
2.5 | 1.2 | 1.0 | 0.4 | 0.2 | 0.1 | 0.1 | 0.5 | 1.6 | 2.2 | 9.8 |
At stations that show the clear influence of orographic effects, a significant increase is observed in the mean annual number of days with storm winds. For example: Russkaya Gavan' - 48 days, Pevek - 26 days, Maliye Karmakuly - 22 days, Cape Zhelaniya, Tiksi - 20 days, and Wrangel Island - 18 days. In these locations, orography always increases the wind speed. The main reason for the increase is the cyclone activity which tends to generate air flow from the mountains. At Dixon, Rudolph Island and Uelen stations, the frequency of storm winds is caused only by significant cyclone activity and acceleration along the coastlines. In other locations and regions with weaker cyclone activity the mean annual number of days with such winds does not exceed 2 days, but in regions with anticyclonic winter weather conditions the value is about 0.5 days per year (Chokurdakh, Kyusyur).
The spatial distribution of the number of days per year with storm winds is quite inhomogeneous. On the islands of the Franz Josef Land archipelago values range from 5 to 15 days. Such winds are observed most often on Novaya Zemlya, from 15 to 48 days, blowing down from the glaciers. At other locations, the number of days is as follows: on the coast of the Kara Sea from Yamal to Cape Chelyuskin 5-11 days; near Tiksi and Muostakh 5-20 days; at the mouth of Kolyma river 5 days; in Pevek 26 days; on Wrangel Island 18 days; in the Bering Sea (Uelen, Provideniya) 5-12 days (Fig. 6).
Figure 6. Number of days per year with wind speed 25 meters per second and higher.
Analysis of monthly averages of the number of days with wind speed 25 meters per second and higher shows the presence of a yearly cycle that is primarily defined by the seasonal progression of atmospheric circulation conditions. Maximum values are observed during autumn and winter from 2 to 5 days per month at stations that have high winds. At the majority of stations, mean monthly storm frequencies are characteristically much less, with high winds occurring between 0.1 and 1 day per month. The minimum number of stormy days is observed during the summer and is less than 1 day everywhere even at those stations where the frequency of high speed wind is significant at other times. For example, in July and August there are many stations where not a single case of high wind has been recorded (see Table 13). When averaged over 44 stations throughout the entire Russian Arctic, the number of days with wind speeds of 25 meters per second and above is equal to 7.7 per year. There are 4 stations that stand out in particular as being the locations with the highest frequency of storm winds - Russkaya Gavan', Maliye Karmakuly, Tiksi, and Pevek. If the results from these stations is not included, the average drops to 5.2 storms per year.
Calculation of the distribution of numbers of stations reporting winds of 25 meters per second and above shows that of the 44 stations, more than half (26) report a very small number of stormy days - from 1 to 5 per year, 7 stations have storms on 5 to 10 days per year, 6 stations on 10 to 20 days, and only 5 stations have 20 or more stormy days. The maximum frequency of storm winds (up to 47 days) is observed on Novaya Zemlya at Russkaya Gavan', Maliye Karmakuly.
The annual average value is lowest for the central part of the Eurasian Arctic, where only 0.2 to 3.1 stormy days are recorded, with the exception of Tiksi where the number of storm days reaches 20 due to the particular orographic conditions in this area. On Muostakh Island, located near Tiksi, the number of days with high winds is also rather high, 7 per year, also due to the influence of the orographic conditions near Tiksi. At Ambchik station where the average is 5 days per year, there is a small increase in comparison with the general conditions in the region due to the effects of the Anyuisky Mountain Range and the valley winds in the mouth of Kolyma River. As one proceeds southward from the coast, the average annual number of days with wind speeds of 25 meters per second and higher steeply decreases, reaching values of 0.2 to 0.3 days. This is due to the influence of the Siberian anticyclone which typically has very weak winds. Proceeding northward from the coast to the Laptev and East Siberian seas, the number of days with storm winds also decreases because the orographic effects are no longer felt and/or cyclone activity is small. In this region, the number of days with stormy wind changes little throughout the year. The only exceptions are in the vicinity of Tiksi and Muostakh stations where the annual cycle is analogous to that in other regions with maximum activity in winter, and minimum in the summer.
In the eastern parts of the Arctic, high wind speeds are the result of a combination of cyclonic activity and local orographic conditions, particularly at Pevek, Provideniya, and Wrangel Island.
The average continuous duration of stormy conditions in the Arctic during the cold part of the year is 3 days, decreasing to 1.5 days in the warm season. There have, however, been cases when the storm duration have significantly exceeded the average value. For example, wind speeds higher than 25 meters per second with a continuous duration of 12 days (from 11 November to 22 November) were observed at Russkaya Gavan' station in the winter of 1982. In the summer, however, the maximum duration was never more than 4 days (Table 14). At most stations the total duration of storms was 1 to 2 days per month.
A principal characteristic of storm winds is their spatial extent. Storm winds in the Arctic are rarely observed simultaneously at several stations. Their occurrence is related principally to orographic effects which extends to not more than several tens of kilometers while the stations are typically separated from one another by distances of several hundred kilometers. The areal extent of storm winds is influenced by the diameter of the cyclones and the length of atmospheric fronts. Storm winds can occur both ahead of and behind these fronts. An event of particular note occurred in 1967, when stormy winds were observed at 5 Arctic stations simultaneously. Most often, however, such winds have been observed only at individual stations. Stormy winds have been observed simultaneously at 2 or more stations most often in January (32 percent of the time - see Table 14). The minimum frequency occurs during the summer (1 to 2 percent).
Data on the total number of days per year with wind speeds of 25 meters per second and above have been collected from 74 stations over a 20 year period (1966 to 1985), but at some stations such speeds are not observed every year and occur very rarely. To describe the variability in the number of days with storm winds, data from 19 stations were used, for which yearly values have been compiled and for which the average number of days per year is equal to 5 or more (Table 15). In addition to these 19 stations we have also considered 28 others for which the above criteria for wind speeds of 25 meters per second and above have been met in 75 percent of the observation years (from 15 to 19 years).
Table 14Maximum number of days with wind speeds of 25 meters per second and above plus the frequency of storm wind (percent per year) observed simultaneously at 2 and more stations | ||||||||||||
Station | Month | |||||||||||
Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
# of days |
||||||||||||
Rudolph Island | 4 | 11 | 4 | 3 | 2 | 1 | 2 | 2 | 5 | 8 | 5 | |
Russkaya Gavan | 7 | 7 | 5 | 9 | 3 | 2 | 2 | 2 | 5 | 9 | 12 | 9 |
Maliye Karmakuly | 6 | 6 | 10 | 4 | 5 | 4 | 4 | 3 | 4 | 4 | 7 | 9 |
Amderma | 3 | 5 | 4 | 3 | 2 | 1 | 1 | 1 | 4 | 2 | 3 | |
Uedineniya Island | 2 | 2 | 2 | 1 | 1 | 2 | 2 | 2 | 3 | |||
Dixon Island | 3 | 2 | 2 | 3 | 2 | 2 | 1 | 1 | 4 | 2 | 2 | 7 |
Lake Taimyr | 3 | 4 | 2 | 3 | 2 | 2 | 2 | 2 | 2 | 6 | 5 | 2 |
Cape Chelyuskin | 3 | 4 | 1 | 4 | 2 | 2 | 4 | 2 | 3 | 1 | 2 | |
Khatanga | 1 | 2 | 1 | 2 | 3 | 1 | 1 | 1 | 1 | 2 | 2 | 2 |
Tiksi | 9 | 6 | 3 | 8 | 2 | 2 | 1 | 2 | 3 | 6 | 4 | |
Kotel'ny Island | 2 | 1 | 2 | 2 | 4 | 1 | 2 | 1 | 2 | 2 | 1 | 1 |
Chokurdakh | 1 | 1 | 1 | 1 | 1 | 1 | 1 | |||||
Pevek | 3 | 3 | 4 | 4 | 4 | 3 | 3 | 3 | 4 | 4 | 4 | 5 |
Cape Schmidt | 3 | 3 | 3 | 1 | 1 | 1 | 1 | 2 | 4 | 4 | 3 | |
Wrangel Island | 5 | 4 | 3 | 6 | 2 | 2 | 1 | 1 | 2 | 4 | 4 | 5 |
Uelen | 5 | 2 | 1 | 2 | 1 | 2 | 2 | 2 | 3 | 4 | 5 | |
Provideniya Bay | 4 | 2 | 3 | 2 | 2 | 2 | 1 | 3 | 4 | 2 | ||
Frequency, % | ||||||||||||
32 | 14 | 7 | 6 | 4 | 3 | 1 | 2 | 5 | 6 | 9 | 11 |
Up to this point we have been describing storm winds with speeds of 25 meters per second and higher, and hurricane force winds (30 meters per second and higher) are included in these results. The number of days with storm winds below the hurricane force level (25-29 meters per second) is presented in Fig. 7. At stations where the frequency of storm and hurricane force winds is large, the mean number of non-hurricane storm days is equal to 8.8 per year, but at stations where storms are encountered less frequently, the mean number is only 1.8 (Table 16). As shown in Table 16, at the low-wind stations the number of hurricane force winds occur 4.5 times less often than the storm winds, but at stations with higher frequencies of strong winds, hurricanes occur only 1.6 times less often than 25-29 meters per second winds.
As a result of many years of measurements of days with storm winds at the 19 stations listed in Table 15, where such winds are recorded every year, various trends have been observed. The majority have indicated a decrease in the winds, however, a distinct decreasing trend has appeared only in the western part of the Arctic (Fig. 8).
During the years 1966 to 1985, the frequency of zonal patterns of atmospheric circulation decreased. This in turn decreased the number of cyclones which could produce strong winds.
The decreasing tendency was rather weak in the eastern part of the Kara Sea. In this region a slight increase of 5-8 days was recorded from 1966 to the middle of the 1970s, and after that a decrease followed by an almost constant level. A decreasing trend in the number of days with wind speed ³ 25 meters per second was observed in the central Arctic from the Taimyr Peninsula to Pevek and Val'karkay. In the eastern Arctic on the Chukchi Peninsula there was essentially no trend, and the curve is essentially flat. Only at the two stations of Russkaya Gavan (Novaya Zemlya) and Provideniya (southern part of the Chukchi Peninsula) has an increasing trend been observed in the number of days with wind speed ³ 25 meters per second.
Table 15Number of days with wind speed 25 m/s and above, and maximum wind speed | ||||||
Station | Number of days | Speed | ||||
Annual Average | Maximum | Maximum | Date | |||
# of days | Year | |||||
Nagurskaya | 6.4 | 21 | 1973 | 44 | 28 Mar.,1973 | |
Rudolph Island | 16.5 | 30 | 1966 | 40 | 06 Nov.,1971 | |
Cape Zhelaniya | 21.1 | 45 | 1973 | 42 | 22 Dec.,1979 | |
Russkaya Gavan' | 47.5 | 62 | 1983 | 50 | 29 Jan.,1979 | |
Maliye Karmakuly | 26.7 | 59 | 1966 | 45 | 02 Mar.,1981 | |
Amderma | 11.0 | 37 | 1971 | 40 | 01 Feb.,1967 | |
Dixon Island | 11.5 | 28 | 1972 | 42 | 22 Oct.,1970 | |
Cape Sterlegova | 9 9 | 22 | 1975 | 42 | 09 Sep.,1975 | |
Lake Taimyr | 11.0 | 38 | 1975 | 44 | 19 Feb.,1975 | |
Tiksi | 20.0 | 51 | 1967 | 47 | 26 Dec.,1975 | |
Muostakh | 7.1 | 20 | 1967 | 40 | 02 Oct.,1971 | |
Cape Valkarkai | 5.0 | 13 | 1966 | 44 | 07 Jan.,1982 | |
Pevek | 25.9 | 45 | 1966 | 47 | 17 Mar.,1978 | |
Cape Schmidt | 7.0 | 13 | 1966 | 40 | 23 Oct.,1971 | |
Wrangel Island | 17.8 | 33 | 1970 | 43 | 01 Nov.,1972 | |
Netten | 5.0 | 12 | 1967 | 40 | 21 Jan.,1967 | |
Uelen | 11.4 | 20 | 1967 | 42 | 15 Dec.,1984 | |
Cape Chaplin | 10.0 | 23 | 1976 | 40 | 21 Nov.,1972 | |
Provideniya Bay | 9.9 | 18 | 1984 | 40 | 31 Jan.,1966 |
Figure 7. Number of days per year with storm winds with speeds of 25-29 meters per second.
Table 16Average number of days with storm winds, hurricane force winds and their ratio | |||
Stations with monthly mean wind speed (V) from Oct. to Apr., m/s | # of days per year | Ratio | |
Storm winds, 25 to 29 m/s | Hurricane ³30 m/s | ||
V£6 m/s (22 stations) | 1.8 | 0.4 | 4.5 |
V³7 m/s (20 stations) | 8.8 | 5.4 | 1.6 |
All stations (42) | 10.6 | 5.8 | 1.8 |
Figure 8. Multiyear temporal dependence of the number of days with wind speed of 25 meters per second and above in the (1) south-western Kara Sea (solid line); (2) north-eastern Kara Sea (dotted line); (3) Laptev and East Siberian seas (dashed line); and (4) Chukchi Sea (dash-dot line).
The long-term variability in the number of days with wind speeds ³ 25 meters per second and ³ 30 meters per second observed at Pevek station is presented in Fig. 9. Both curves show a decreasing trend over a 20 year period. For 25 meters per second and above, the number of days decreases from near 40 per year to 27 per year. For 30 meters per second and above, the decrease goes from about 25 down to 10 days per year.
Figure 9. Multiyear temporal dependence of the number of days with wind speeds of (1) 25 meters per second and higher, and (2) 30 meters per second and higher at Pevek.
In Pevek, high wind speeds are observed when the winds are steady and southerly. This is called the "yuzhak." A. A. Dmitryev [26], in his study of the "yuzhak", discovered a decrease in the duration of the wind during the winter as well as for the entire year. He explained it in terms of a gradual change that occurred in the macro-scale circulation over the entire northern hemisphere, and he noted a tendency towards an increase in the zonal airflow and a decrease in the meridional flow. He correctly determined that the "yuzhak" arises mainly under conditions of meridional flow. Long-term changes in the number of days per year with meridional circulation patterns (called M1 and M2) in the Pacific ocean sector show a decreasing trend over the 20 year period 1966 to 1985 (Fig. 10) and an increase in the zonal circulation of type Z.
This explanation also applies to the strong winds over the entire eastern sector of the Arctic. In this area, all synoptic cases during which strong winds are observed occur during conditions of meridional circulation.
The decreasing trend in the frequency of high winds in the western and central regions occurs at the expense of a decrease in the number of days with meridian circulation in the Atlantic-European sector and an increase in the number of days with westerly zonal circulation (form W). During cyclonic circulation conditions, half of the cases with strong winds are southerly (form S) and a quarter of the cases have forms W or E.
In the central region, during cyclonic situations, the cases with strong winds are distributed evenly among each of the three circulation forms W, E, and S. This is true for all of the central Arctic region, where atmospheric circulation forms are not as distinct.
According to the Beaufort scale, a hurricane force wind is one that has a wind speed of 33 meters per second or more. In the present work, winds are considered to have hurricane force if they have speeds of 30 meters per second and above, so that severe storms are also partly included in this category. In this way, accommodation is made for both the precise definition as well as the more severe general climatic conditions (low air temperatures and snow storms), which accompany hurricane force winds in the Arctic. Hurricane winds cause widespread destruction including a great deal of property damage. For example, in November 1983 in Provideniya Bay a wind speed of 30 meters per second destroyed several structures. In Uelen in December 1984, wind speeds reached 42 meters per second blowing away the roofs of some houses and completely destroying other structures [28, 38].
Particularly high speed winds are observed at Pevek, where the local "yuzhak" wind has an average speed 15 to 18 meters per second and reaches maximum speeds of 60 meters per second. In the city of Pevek, the houses are built to withstand the winds. Once, however, a sea launch was moved several tens of meters along the ground by high speed wind gusts. Another time during the winter, a metal radio mast 15 centimeters in diameter and 20 meters tall was twisted into the shape of the letter S in about 10 minutes.
Hurricane winds caused serious flooding along the coast of the Laptev Sea. For example, at Tiksi Bay on the 26th of September, 1988, the ebb level was followed by a strong surge, and on the 27th of September the water level reached 175 centimeters above normal. In the course of 20 hours the water level rose 3 meters.
Among 74 arctic stations, hurricane force winds have been observed each year only at 7 stations over the 20-year observation period from 1966 to 1985. These include Rudolph Island, Russkaya Gavan', Maliye Karmakuly, Tiksi, Pevek, Wrangel Island, and Uelen. Winds of this strength were also observed over 15 of the 20 years at 7 additional stations including Cape Zhelaniya, Dixon Island, Lake Taimyr, Capes Sterligov, Val'karkay and Schmidt, and Provideniya Bay. At the remaining 60 arctic stations on average the frequency of observation of hurricane wind speeds was no more than twice a year, and over a period of 14 years the observed annual average was even less. At some of these stations, wind speeds of 30 meters per second and higher were not observed at all throughout the entire period from 1966 to 1985. The maximum average number of days with hurricane force wind was recorded at Russkaya Gavan and Maliye Karmakuly [20]. Data for selected arctic stations is presented in Table 17. This table shows the mean number of days per year as well as the maximum number and the year when the maximum occurred.
There is a great deal of interest in the spatial distribution of maximum wind speeds in the Arctic (Fig. 11). As a rule, the maximum observed wind speeds are between 25 meters per second and 45 meters per second (excluding wind gusts). "Spots" of maxima are observed at various stations or over the whole region, but they are essentially all observed along the arctic seas coasts or in the mountains. The highest wind speed or 62 meters per second was recorded at Russkaya Gavan' station.
The analysis showed that spatial distribution of the number of days with wind speeds of 30 meters per second and above is extremely diverse and depends on local conditions as well as the frequency of cyclones (Fig. 12). The maximum frequency is observed at the coast, decreasing both to the south and to the north. There are four arctic stations, where due to orography the frequency of winds with speeds of 30 meters per second and higher is significant: Russkaya Gavan', Maliye Karmakuly (on Novaya Zemlya), Tiksi (at the mouth of Lena river), and Pevek (on Chaunskaya Bay).
The present study shows that frequency of stormy and hurricane force winds in the Arctic is not as high as was previously supposed. The frequency of high speed winds in the range 15 to 25 meters per second is consistent with prior estimates, since winds of this type occur often enough in the Arctic for a good statistical sample even with a shorter record. Besides that, stormy and hurricane force winds are observed principally at particular locations where there is a strong influence of orography in combination with the atmospheric circulation processes as described earlier in this chapter. A few of these winds have their own names and are described below.
Table 17Annual average of the number of days with wind speed of 30 m/s and above | |||
Station | # of days per year | ||
Average | Maximum Number | Year when Max. Occurred. | |
Nagurskaya | 1.6 | 10 | 1973 |
Rudolph Island | 6.0 | 17 | 1966 |
Cape Zelaniya | 5.0 | 23 | 1973 |
Russkaya Gavan | 22.0 | 33 | 1983 |
Maliye Karmakuly | 19.2 | 39 | 1968 |
Amderma | 1.9 | 31 | 1968 |
Dixon Island | 3.6 | 13 | 1971 |
Cape Sterlegov | 2.4 | 8 | 1971 |
Lake Taimyr | 2.4 | 17 | 1974 |
Tiksi | 9.0 | 28 | 1967 |
Muostakh | 2.6 | 7 | 1963 |
Kotel'ny Island | 0.2 | 2 | 1967 |
Cape Valkarkai | 1.8 | 8 | 1966 |
Pevek | 14.7 | 27 | 1966 |
Cape Schmidt | 2.4 | 6 | 1979 |
Wrangel Island | 3.7 | 8 | 1972 |
Uelen | 4.1 | 12 | 1967 |
Cape Chaplin | 1.9 | 11 | 1970 |
Provideniya Bay | 1.9 | 5 | 1984 |
Figure 10. Long-term (or multiyear) variation in the number of days with meridional circulation patterns in the Pacific Ocean Sector.
Figure 11. Contours of the annual average of the maximum wind speed (meters per second).
Figure 12. Contours of the annual average of the maximum number of days with hurricane force wind (30 meters per second and higher).
3.5. Local scale hazardous wind conditions
The highest speed winds in the Arctic form due to presence of mountains or glaciers. In winter they are often called drainage or katabatic winds. In Greenland, for example, the speed of the drainage wind from the ice cap can reach nearly 85 meters per second. The Greenlanders call this the "piterak." V.E. Vozgrin wrote in his book Greenland and Greenlanders, (Moscow, Mysl, 1984, p.158) that in February 1970 at Angmagssalik station this wind blew away many homes and public buildings in a single night. The force of the wind driven snow was so intense that it sand blasted the paint off the cars. By the morning they become "silvery."
In the Russian Arctic, the best known local winds are the bora on Novaya Zemelya, the yuzhak at Pevek, and the winds blowing from the mountains in the vicinity of Russkaya Gavan and Tiksi stations. These are gusty winds which reach hurricane force speeds of 40 meters per second with gusts above 60 meters per second. The bora causes dangerous waves and superstructure icing on ships near the western coast of Novaya Zemlya and produces tornados in the atmosphere.
Vize [12] was the first to describe the bora using data from ground-based observations from 1882 to 1883, 1897, 1899 to 1890, and 1902 to 1909. He analyzed temporal changes in the cloud cover, atmospheric pressure, air temperature, and relative humidity during bora events. Vize included all cases when the wind speed was 16 meters per second and higher and the wind direction was from the coastal plateau toward the Barents Sea.
The data sets for 1967 to 1978 were analyzed at the Murmansk branch of the Arctic and Antarctic Research Institute (AARI) [20]. 162 cases of the bora (consisting of easterly winds) were identified for the southern part of Novaya Zemlya. The average frequency of occurrence for the bora together with the number of days per month are presented in Table 18. The bora occurs on average 33.5 days per year. Its maximum is observed in winter (4.4 days in December and January), and its minimum is observed in summer (1.2 days in July).
Table 18Averages of the number of cases and days per month of the occurrence of the bora on Novaya Zemlya | ||
(Maliye Karmakuly, 1967 to 1978) | ||
Month | # of cases per month | # of days per month |
January | 1.6 | 4.4 |
February | 1.3 | 3.5 |
March | 1.4 | 3.5 |
April | 1.2 | 3.3 |
May | 0.9 | 3.2 |
June | 0.8 | 1.3 |
July | 0.7 | 1.2 |
August | 0.8 | 1.5 |
September | 0.8 | 1.8 |
October | 0.8 | 1.8 |
November | 1.5 | 3.6 |
December | 1.7 | 4.4 |
Total | 13.5 | 32.5 |
The bora forms when air mass flows round or crosses over the mountains. Increased wind is observed in layers from 0 to 200 meter or 0 to 300/400 meter elevation and also in a layer from 200 to 500 meters, in which air passing down from the hillsides is adiabatically heated and causes a bora or foehn depending on how low the temperature was at the level from which the air descended.
On average, in the case of a bora event (strong easterly winds), the speed of the surface wind exceeds the wind speed at the 850 millibar level by a factor of about 1.6. Comparison of the speeds of the actual wind and the barometrically determined gradient wind in the surface layer showed that the actual wind during the bora typically exceeds the gradient wind by more than 8 meters per second.
High speed local wind, called the "yuzhak", is observed in Pevek on Chukchi Peninsula [25, 26, 28]. It occurs as a result of specific synoptic conditions, principally, when a cyclone over Kolyma and an anticyclone over Chukchi Sea interact with one another. In this case, conditions arise such that the wind blows across the Pevek range. Zimich [28] has defined various different characteristic types. The most frequently encountered types occur about 47 percent of the time and are observed during the warm months (May-September). In these cases, cyclones move west and southwest into the East Siberian Sea. As a rule, the "yuzhak" precedes a warm front at a distance of 300 to 400 kilometers then becomes weaker in the warm sector of the cyclone and dies out before passing the associated cold front of the cyclone.
In winter, the "yuzhak" occurs when cyclones move from the Sea of Okhotsk across the mountains to the Kolyma lowland. At that time, a high pressure ridge is located over the Bering Sea and eastern termination of the Chukchi Peninsula. The onset of the "Yuzhak" is very sudden, usually when a warm front from south passes through Pevek. There are on average 78 days of "yuzhak" winds per year in Pevek consisting of 44 separate events when the wind speed is higher than 15 meters per second. Statistics for the observation period 1951 to 1987 are presented in Table 19.
Table 19Mean annual number of cases and days with "yuzhak" winds (15 m/s and higher) in Pevek over the period 1951 to 1987 | ||
Month | # of cases per yr. | # of days per yr. |
January | 4.1 | 7.1 |
February | 3.0 | 4.9 |
March | 3.5 | 6.4 |
April | 3.6 | 6.0 |
May | 4.8 | 8.3 |
June | 4.6 | 8.6 |
July | 3.5 | 6.6 |
August | 3.0 | 5.8 |
September | 3.7 | 6.5 |
October | 3.5 | 6.0 |
November | 3.1 | 5.5 |
December | 3.6 | 6.3 |
Annual Total | 44.0 | 78.0 |
"Yuzhak" winds have been observed on average 6.4 days per month, but a weak maximum of 8.5 to 9 days is occurs in May and June, and a minimum of 5 days is observed in February. In the summer, "yuzhak" winds have a shorter duration period and there are no snow storms. The wind speeds are also less than those in winter. The predominant duration period of the "yuzhak" is about 12 to 24 hours, but the average duration for an individual case is 27 hours. The maximum recorded duration of 252 hours was observed from 24 May through 4 June 1951.
Table 20Mean annual number of cases and days with "yuzhak" winds which reach hurricane force speeds (30 m/s and higher) in Pevek from 1951 to 1987 | ||
Month | # of cases | # of days |
January | 1.6 | 2.1 |
February | 1.1 | 1.6 |
March | 1.2 | 1.8 |
April | 0.9 | 1.1 |
May | 1.3 | 1.4 |
June | 0.7 | 0.7 |
July | 0.3 | 0.4 |
August | 0.2 | 0.5 |
September | 0.5 | 0.6 |
October | 1.0 | 1.2 |
November | 1.1 | 1.5 |
December | 1.4 | 1.8 |
Year | 11.3 | 14.7 |
The mean annual number of days and frequency with hurricane force wind speed of 30 meters per second and above for the "yuzhak" in Pevek has been compiled in Table 20. Every year these winds are observed for 1 to 2 days per month during the cold part of the year, but during the warm months they occur less than one day per month. "Yuzhak" Winds with speeds of 30 meters per second and above occur 15 days per year on average.
Average duration period of all "yuzhak" wind events is 64 days per year. The number of days and duration decrease sharply with increasing wind speed. Hurricane force winds with speeds of more than 40 meters per second were only observed on 5 days (Table 21). The duration period of high speed wind, however, decreases only slightly with increasing wind speed - from 14 hours per day for weak "yuzhak" winds to 11 hours per day for hurricane force winds.
Table 21Mean annual number of days with high speed winds and their durations per year and per day for "yuzhak" winds in Pevek | |||
Wind speed | # of days | Duration | |
Hours per year | Hours per day | ||
³15 m/s | 64 | 880 | 14 |
³25 m/s | 26 | 326 | 12 |
³30 m/s | 13 | 145 | 11 |
³40 m/s | 5 | 38 | 8 |