4. Heavy snow storms and snow drifting

4.1. General description

4.2. Selection criteria

4.3. Annual duration and seasonal variation

4.4. Snowstorms in the western Arctic

4.5. Snow drifting

4.1. General description

Snowstorms are considered as threatening and dangerous atmospheric phenomena, sharply decreasing visibility, giving rise to snow drifts, and resulting in snow avalanches in the mountains. Snowstorms, especially when accompanied by high speed wind and intensive snow transport, cause difficulties for building projects and general outdoor operations, impede transportation and delivery of cargo, and accelerate corrosion of vehicles and other equipment.

Snowstorms always occur in association with cyclones in the regions with large atmospheric pressure gradients and strong winds. They are observed ahead of the warm front or after the cold front of a cyclone, and they move along with the cyclone. Heavy snowstorms occur less frequently after a cold cyclone than in front of a warm one because cold fronts pass more quickly. Thus, these snowstorms are short-lived and very often do not become "hazardous." Snowstorms ahead of a warm front are steadier. Cyclones passing from the Atlantic Ocean up to Novaya Zemlya and the Kara Sea meet an obstruction - the periphery of the Asian anticyclone. This gives rise to even stronger pressure gradients that slow the eastward motion of the cyclones or cause them to be slowly destroyed.

Arctic snowstorms are extremely powerful [6, 7, 9, 11, 14]. In addition, the dry fine grained snow that falls in the Arctic is easily transported over large areas by the wind. During snowstorms, the blowing snowflakes are broken up further and penetrate into the smallest holes clogging mechanical devices and instruments.

When the snow cover is loose and the wind begins to rise (about 6 meters per second measured with a wind vane at a height of 10 meters), a near surface layer of drifting snow appears first. When wind speed increases to 8 meters per second a snowstorm or blizzard begins. Snow particles rise from the snow surface into the air above the height of a person. At this point, horizontal visibility decreases and the snowstorm becomes dangerous.

Snowstorms can either be accompanied by snow falling from clouds (the usual type of snowstorm) or they can occur without snow falling (low level blowing snow). In addition, they may be classified visually by intensity (weak, medium and strong). Blizzards are observed in the Arctic especially during the polar night. In these cases, it is impossible to distinguish between blowing snow and the usual type of snowstorm, nor is it possible to determine whether or not the snow is falling.

Snowstorms are observed for the most part during prevailing wind conditions. Over most of the Russian Arctic this means that the winds are from the southwest, and in the Chukchi Sea storms occur primarily when the winds are from the northwest and north. In places with orographic distortions, snowstorms also occur during prevailing wind conditions for those particular areas.

Before we describe heavy snowstorms in the Eurasian Arctic, we will give a brief background description of the spatial and temporal distribution of snowstorm activity in the Arctic. For this purpose we use the main variables to define the climatic characteristics of snowstorms. These include the number of days and duration period of snowstorms per year and for selected months. The results have been derived based on observational data from the Soviet Arctic stations from 1936 to 1980. For some specific parameters this record continued to 1985 [44, 60]. Data have also been incorporated from the North Pole drifting stations and from the arctic stations of other countries [32, 33]. To produce contour plots of snowstorm parameters, an empirical formula relating the number of days with snowstorms to the duration period was used for interpolation in some areas. For the Eurasian Arctic, this formula is as follows:

t= 11.7 n - 128 ,

where t is the total duration of snowstorms per year in hours, and n is the number of days with snowstorms per year. The spatial distribution of the number days with snowstorms and the average snowstorm duration per year in the Arctic and adjacent regions are presented in Figures 13 and 14.

In the western area of the Eurasian Arctic, where cyclones, high speed winds and snowfall dominate the winter weather conditions, snowstorm frequency is high and snowstorm duration is long. On average, there are 80 to 100 days with snowstorms lasting 800 to 1000 hours or more per year. In the European Subarctic, the number of days with snow storms is 40 to 60 days and the average annual total duration is only 300 to 500 hours.

In winter, the weather in the central Arctic is strongly influenced by the Siberian High. The number of days with snowstorms is 60 to 80 on the coast of the Laptev Sea and 15 to 40 days in the continental area. On the islands the annual duration of snowstorms is 500 to 700 hours and in the coastal areas 300 to 400 hours. Further inland toward the continental interior where the influence of the anticyclones is much weaker, snowstorm activity decreases to almost zero. In Verkhoyansk, for example, snowstorm activity has been recorded on average for only a single day per year [44].

A local increase in the number of days with snowstorms (10 to 12 days per month) is observed in Tiksi Bay, where there is orographic amplification of the wind. This is also the case in the Kolyma Gulf. This is partly related to the displacement of cyclones to the north along the river valleys, but it is primarily due to regeneration of these cyclones as well as local cyclogenesis in the bays.

In the eastern area of the Eurasian Arctic, cyclonic activity is less intense than that in the western area. Rather sharp differentiation between snowstorms is observed in the east, not only in the north-south direction (between the sea and the continent) but along the coast as well. For example, on Ayon Island in the East Siberian Sea, there were 44 days per year with snowstorms. On Wrangel Island and Cape Schmidt in the Chukchi Sea, more than 80 snowstorm days per year were observed. The corresponding annual duration was 450 hours in the first case and more than 1000 hours in the second.

Average daily snowstorm duration varied over the ranges (a) from 7 to 9 hours along the continental coastlines of the Eurasian Arctic; (b) from 9 to 10 hours in the Arctic Basin; and (c) from 10 to 11 hours along the coasts of the islands, seas and capes. Cases have been recorded at Dixon, Tiksi and Cape Schmidt when the continuous duration period of snowstorm lasted 6 to 7 days. Total number of hours per month taken up by snowstorms varies significantly. The maximum occurs in December and January: 180 to 190 hours per month in the southern Kara Sea; 130 hours in the northern Kara Sea; 60 to 90 hours on average in the central seas; and 130 to 150 hours in the eastern seas.

Figure 13

Figure 13. Contour plot of the number of days per year with snowstorms.

Figure 14

Figure 14. Contour plot of the average values of annual total duration of snowstorms (hours).

Table 22
Intra-annual distribution of the # of days with snowstorms in the Eurasian Arctic (%)
Sea Month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Barents 18 17 17 8 4 0     <1 6 12 17
Kara 14 13 13 10 8 2 0 <1 3 10 12 14
Laptev 13 12 13 12 8 1 0 <1 2 12 13 13
East Siberian and Chukchi 15 13 12 9 5 0.5 0 0.5 3 11 16 15

In some years the number of days with snowstorms exceeds the average value by 1.3 to 1.8 times and can reach 150 days in the western part of the Arctic, and 130 days in the eastern part. The maximum number of days was recorded on Novaya Zemlya, near the Cape Zhelaniya Cape (192 days). A slightly smaller number (185 days) was observed in the subarctic at Yukspor station in the Khibinski Mountains and at Ra-Iz station in the Polar Urals, with a similar result (182 days) at Beringovskaya station on the coast of the Bering Sea.

Figure 15

Figure 15. Interannual variations in the number of days with snowstorms from 1948 through 1990 at 1 - Dixon Island, 2 - Wrangel Island, and 3 - Chokurdakh.

To evaluate the maximum number of days when snowstorms occurred in various regions of the Arctic and Subarctic we can use the following empirically derived formula:

nmax = 1.4 n + 13,

where n and nmax are the average and maximum number of days per year with snowstorms respectively.

Snowstorms can be observed all year round in the Arctic especially in the central Arctic Basin. The intra-annual distribution of number of days with snowstorms by months is presented in Table 22. According to this table, during the winter months the study parameter is rather uniform, with no clear maximum. There is a clear minimum in the summer.

In the central region, an average of 76 percent of the days with snowstorms are observed from October though March, compared with about 87 percent in the western region. In August snowstorms are observed very rarely and not over the total area. There are almost no snowstorms in July over most areas.

The usual irregularities characteristic of meteorological time-series data sets can be found in long-term changes in the number of days with snowstorms. These involve quasi periodicities on time scales of 2 to 3, 4 to 5, and 7 to 9 years (Fig. 15). Superimposed on these, however, is a decreasing trend in snowstorm activity from 1950 through 1990. This appears to varying degrees at the regional stations.

4.2. Selection criteria

According to the 1986 specifications, snowstorms are considered to be heavy when the prevailing wind speed is equal to 15 meters per second or more for a full day or night, however, for the coastal areas of the arctic and the far-eastern seas the threshold is 25 meters per second and above. It is clear that this definition is convenient for general operations. It would be expedient to add some refinements and corrections for the purpose of climatic investigations, the goal of which is the subsequent specification of land use for practical design of various structures. As a rule, during a snowstorm in the Arctic, the wind speed does not reach the maximum values. Even for a heavy snowstorm, the wind speed may be less than 15 meters per second for some time, and in many cases it does not reach 25 meters per second at all even at the coastal stations. For climatic data processing purposes, the two criteria used in the classification of snowstorms as "heavy" are wind speed and the duration period of the storm [51], however, these parameters do not depend on station location and they are differentiated on the basis of wind speed. Snowstorms are considered to be "heavy" if they are accompanied by winds that satisfy at least one of the following criteria:

This more precise determination has made it possible to avoid the uncertainties arising from stations classified as being located on the arctic coast (wind speed 25 meters per second and higher) or on the continent (wind speed 15 meters per second and higher). It also introduces numerical criteria to quantify the concept of "in the course of a day or a night" used in the 1986 specifications [51], which because of the phenomena of polar day and polar night were not well defined for the specific conditions in the Arctic.

Extraction of heavy snowstorm data was performed at the arctic branches of AARI located in Amderma, Dixon, Tiksi, and Pevek using the TM-1 meteorological observation tables. As a result, a data catalog developed including results from 74 stations in the Arctic and Subarctic for every year over the 20-year period from 1966 to 1985. Information about 7000 heavy snowstorms has been included in the catalog, which is divided into two parts. The first part includes all cases and dates when the snowstorms were accompanied by an increase in wind speed up to 15 meters per second or more, and the second part includes all cases when snowstorms were observed with wind speeds of 25 meters per second or more. The second part also lists storms occurring in conjunction with hurricane force winds (³ 30 meters per second). Data in this catalog served as the basis for further study of heavy snowstorms in the Eurasian Arctic.

Calculation of the duration period of a heavy snowstorm is explained below. Figure 16 shows the distribution of wind speed from beginning to end for a representative snow storm recorded at Marresalya hydrometeorological station.

Figure 16

Figure 16. Schematic illustrating the determination of heavy snowstorm duration with a specific wind speed distribution.

Total duration of the snowstorm ts is defined as the time from beginning to end of the snowfall. Then:

t s = t 15 + t 1

where t 15 and t 1 are the sums of the intervals when the wind speed is 15 meters per second or more, and lower than 15 meters per second respectively, and

t 1 = S t 1i and t 15 = S t 15i.

The index i represents each of the individual intervals as shown in Fig 16. The value of t 15 represents the actual dangerous portion snowstorm. This includes the duration, if any, of the most dangerous part of the storm with wind speeds of 25 meters per second or more. During the storm, the wind speed may be exceed 15 meters per second or 25 meters per second many times. Thus the following sum is also recorded:

t 25 = S t 25i


4.3. Annual duration and seasonal variation

The number of days with heavy snowstorms, including the most dangerous part where wind speeds are 15 meters per second or more, varies from 1-2 days up to 20 days and more per year along the Eurasian coastal zone. The corresponding total duration of heavy snowstorms ranges from 20 to 300 hours and more. Moving inland from the coastal regions, as the distance increases toward the continental interior, heavy snowstorms are observed less frequently, and their total duration decreases to a few hours per year (in Yar-Sale the average duration is 15 hours, in Tyumeti 2 hours, and in Kyusyur 11 hours). The distribution of number of days per year with heavy snowstorms is presented in Fig. 17. Just as for ordinary snow storms, heavy snowstorms are observed more often in the western and eastern parts of the Eurasian Arctic. They are observed least often (on average less than 1 day per year) in the continental part of the central region.

To produce charts of annual total duration of heavy snowstorms over the water area of the Kara Sea, the following set of empirical equations was used which had been obtained from station data in the areas of the Kara and Laptev seas, primarily Amderma and Tiksi.

t M = 14.3 nS

t 15 = 10 n15

n15 = 0.7 nS where nS is the total number of days per year with snowstorms, and n15 is the number of days with heavy snowstorms with wind speeds of 15 meters per second and higher.

To draw isolines in the water areas of the East Siberian and Chukchi seas, an additional empirical relationship was obtained from data collected mainly at Pevek. Specifically:

nM = 2.3 x,

where x is the number of heavy snowstorms recorded. This equation gives good results for most of the stations in this region (with the exception of Ambarchik, Cape Schmidt and Vankarem).

Figure 18 gives the spatial distribution of t 15. It shows features which are similar to those in Figure 17.

To estimate the distribution of the duration of observed snowstorms, t M , and its hazardous part, t 15, data were used from 1966 through 1989 from the coastal meteorological stations on the Yamal Peninsula including Novyi Port (133 storms), Marresalya (144 storms), and Cape Kamennyi (169 storms). The corresponding empiric distributions in differential and integral form are presented for Novyi Port station in Figure 19. They are also representative of the main features of snowstorm distributions at the other two stations. The most frequent value of t M equals 20 to 30 hours while the most frequently observed value of t 15 is 10 to 20 hours. The significant interval for t 15 is 0 to 10 hours. The distribution for dangerous snowstorms is more asymmetric than the total distribution and approaches a c 2 distribution with n » 3.

Figure 17

Figure 17. The number of days per year with heavy snowstorms.

Figure 18

Figure 18. Total duration per year (in hours) of heavy snowstorms with wind speed 15 meters per second and above.

Figure 19

Figure 19. Differential (a) and cumulative (b) distributions of the duration period of individual snowstorms observed at the Novyi Port station. The dashed lines denote the distributions for t15.

Very heavy snowstorms with wind speeds of 25 meters per second and higher, observed during 2 or more sampling intervals, are observed every year only in the eastern and western regions. Specific locations include the vicinity of Amderma; the island stations of the Rudolph Islands, Novaya Zemlya, Vaigach, and Severnaya Zemlya; the Yamal and Taimyr Peninsulas; and Pevek, Uelen, and Cape Chaplin. The spatial distribution of t25, the portion of very heavy snowstorms is presented in Fig. 20. In the extensive circumpolar region, the heavy snowstorms with wind speeds of 25 meters per second and higher do not last for 2 or more observation periods according to data from the NP drifting stations.

The most dangerous heavy snowstorms for people are those whose duration is several days in a row. As a example, a case observed in December 1974 in the region of current intensive development in the Yamal Peninsula is presented on Fig. 21. A heavy snowstorm lasting from 21 to 28 December was observed at several hydrometeorological stations. During almost the entire extent of the snowstorm, the wind speed at Marresalya station was more than 15 meters per second, and on 25 and 26 December it reached 25 meters per second with gusts up to 30-35 meters per second. Similar wind speeds were also observed at Tambey station. At other nearby stations (Tadibeyakha, Se-Yakha, and Cape Kamennyi), gust speeds also reached 25-26 meters per second. Such a snowstorm is a rather rare event for the Yamal Peninsula, both with respect to its duration and wind speed, and its spatial extent. It can indeed be classified as hazardous phenomenon. Information on extreme duration periods of individual snowstorms in other parts of the Arctic are presented in Table 23.

Figure 20

Figure 20. Number of days per year with heavy snowstorms accompanied by wind speeds of 25 meters per second and above.

Figure 21

Figure 21. Temporal dependence of wind speed during the heavy and extremely protracted snowstorm on the Yamal Peninsula (data are given for 21-27 December, 1974). For each station, the first number (or numbers) denote the dates in December, and the second indicate the gust speeds.

A description of the total annual duration of heavy snowstorms for stations in the Eurasian Arctic is presented in Table 24. The maximum values often exceed the average values by more than a factor of two, which can cause the difficult working conditions during those particular winters. The maximum number of days with heavy snowstorms accompanied by wind speeds of 25 meters per second and above (20 days or more) was observed in the western region of the Eurasian Arctic (Maliye Karmakuly, Tambey, Morzhovaya). The maximum annual duration was observed on Novaya Zemlya (more than 200 hours), the Yamal Peninsula and the coast of the Chukchi Peninsula (30-50 hours). But at most stations in the Eurasian Arctic, the maximum number of days with heavy snowstorms and wind speeds of 25 meters per second and higher does not exceed 5 days. Indeed at about half of the stations snowstorms of this intensity were not observed at all.

Heavy snowstorm can occur in any month of the cold part of the year, primarily from November through April. In some years, heavy snowstorms have been observed in September, May, June, and late August. Specific dates for the earliest and latest heavy snowstorms at several stations in the Eurasian Arctic are presented in Table 25.

In the central arctic basin, heavy snowstorms are observed very rarely. Dates for the heavy snowstorms with wind speeds 15 meters per second and higher recorded at the North Pole drifting stations for the period 1954 through 1990 are presented in Table 26.

Heavy snowstorms in the arctic basin are observed from September to February. According to Table 26, the maximum number of days with heavy snowstorms is recorded in November (5 days) and December (4 days) over the 37-year period. The mean annual number of days with heavy snowstorms, averaged over all North Pole station data, is 0.54. Heavy snowstorms in the arctic basin may last for two days or more.

Table 23
Description of the total duration of specific heavy snowstorms
Station Duration, hours Maximum wind speed, m/s
Maximum Minimum
Viktoriya Island 102 9 28
Nagurskaya 119 9 27
Rudolph Island 200 4 34
Heisa Island 102 10 28
Maliye Karmakuly 103 - 37 (50)
Russkaya Gavan 139 7 43
Cape Zhelaniya 225 3 36
Amderma 82 12 27 (34)
Ushakova Island 156 9 29
Vize Island 86 9 28
Belyi Nos 80 9 19 (24)
Cape Menshikova 69 10 22 (29)
Bolvanski Nos 102 7 26 (34)

Note: The speed of gusts is given in parentheses.

Table 24
Maximum annual duration period of snowstorms
Station Number of days Duration, hours
Total V ³ 15 m/s V ³ 25 m/s Total V ³ 15 m/s V ³ 25 m/s
Amderma 23/1988 16/1988 7/1988 307/1988 175/1988 9/1990
Belyi Island 23/1989 15/1989 4/ 1986 292/1989 150/1989 Gusts
Tambei 71/1975 51/1975 25/1975 954/1975 573/1975 39/1974
Khatanga 6/1975 5/1975 1/1975 89/1975 57/1975 3/1975
Dunai Island 44/1981 35/1981 1 729/1981 378/1981 Gusts
Zemlya Bunge 13/1985 11/1985 0 251/1985 123/1985 0
Chokurdakh 7/1982 3/1982 0 90/1985 39/1982 0
Chetiryokhstolbovoy Is. - - - 414/1982 204/1982 Gusts
Cape Billings - - - 226/1984 126/1984 6/1981
Cape Netten - - - 139/1984 77/1984 9/1975
Cape Chaplin - - - 466/1976 304/1976 57/1975

Note: The year is given in the denominator.

Table 25
The dates of seasonal extremes for heavy snowstorms (V³15 m/s)
Station Date
Autumn Spring
Russkaya Gavan 03 Oct 12 Jun
Amderma 17 Oct 24 May
Belyi Island 10 Oct 15 Jun
Pravdy Island 21 Sep 14 Jun
Khatanga 30 Oct 29 May
Tiksi 03 Oct 29 May
Zemlya Bunge 22 Aug 18 Jun
Chokurdakh 30 Sep 01 Jun
Cape Billings 28 Sep 28 May
Cape Vankarem 27 Sep 28 May
NP Drifting Stations (Arctic basin) 18 Sep 5 Feb
Table 26
Chronology of heavy snowstorms in the Arctic Basin
Year Date Number of days per year Drifting stations Station coordinates, degrees
N lat. E long.
1962 September 18
November 1
2 NP-11 81.5
82.2
201.2
210.3
1963 February 5
November 28
November 29
3 NP-10 80.1
84.5
84.6
160.1
147.1
148.5
1965 November 15
November 21
2 NP-13 80.3
80.3
170.8
142.5
1966 November 17 1 NP-15 82.4 161.9
1978 November 27
December,29
2 NP-22 73.2
73.9
201.1
196.7
1987 September 30
October 7
December 31
3 NP-29
NP-28
NP-30
81.1
84.4
74.1
111.3
160.3
178.0
1988 January 1
January 2
September 27
October 9
October 10
December 9
December 10
7 NP-30
 
NP-28
74.1
74.1
75.3
86.5
86.6
84.1

83.6
177.1
177.0
166.2
356.3
353.5
350.4
352.2

4.4. Snowstorms in the western Arctic

Heavy snowstorms are observed during the winter in the European Arctic, mostly as Atlantic cyclones which advect a great amount of moisture. An example of a synoptic situation accompanying a heavy winter snowstorm is shown in Figure 22. Heavy snowstorms are also observed in summer in the areas of the Arctic where the air temperatures are negative, creating conditions which are favorable to their development. An example of a synoptic situation accompanying such a summer snowstorm on Franz Josef Land is presented in Figure 23. In this case, the heavy snowstorm was caused by the arrival of a deepening cyclone from the continent. In many cases, heavy snowstorms occur simultaneously at several stations located in the cyclone's zone of influence.

Figure 22

Figure 22. Synoptic conditions giving rise to the snowstorm of 3 January 1972.

Figure 23

Figure 23. Synoptical conditions giving rise to the snowstorm of 11 June 1978.

In addition to the investigation of heavy snowstorms at individual stations, there is considerable interest in the study of severe storms which occur simultaneously at several stations in a particular region. When heavy snowstorms are observed over extended areas, the phenomenon can be classified as "hazardous."

To develop a statistical picture of the amount of time that heavy snowstorms occurred simultaneously at two or more stations, the two most heavily studied regions were chosen: (1) the northern part of the Barents and Kara seas; (2) the vicinity of Vaygach Island in the southern Barents and Kara seas. There are eight stations in the first region, which includes Viktoriya, Vize, Ushakov, and Novaya Zemlya Islands, and Franz Josef Land archipelago; and there are four stations in the second region, which includes the Kara Strait and Yugorsky Shar. The dates of heavy snowstorms observed at the stations within each region were compared, and corresponding periods with heavy snowstorms were catalogued. During the period 1975 to 1990, a total of 276 cases of coincident heavy snowstorms were identified at 2 or more stations in the northern area. In the southern area, 90 cases were found (Table 27).

Table 27
Number of days with heavy snowstorms in two regions concurrently
Year The Northern Barents and Kara seas Vicinity of Vaigach Island - The southern Barents and Kara seas
1975 49 13
1976 59 11
1977 38 3
1978 36 10
1979 35 7
1980 40 13
1981 51 3
1982 59 7
1983 62 12
1984 37 17
1985 40 7
1986 38 10
1987 48 8
1988 30 20
1989 61 18
Average 43 11

On average, the period of heavy snowstorms is 12 percent per year in the northern part of the Barents and Kara seas, with an interannual variation from 8 percent (1988) to 17 percent (1983). For the southern area around Vaygach Island, the duration of severe snowstorms is several times less frequent - corresponding to a period of about 3 percent per year (varying from 1 percent to 5 percent). In the first region, this is related primarily to physical and geographical and climatic conditions, in particular, the bora phenomenon on Novaya Zemlya.

The relatively large number of samples makes it possible to analyze the frequency distribution of the number of heavy snowstorms that occur concurrently at two or more stations in each region together with the frequency of snowstorm duration in each case. Shown in Figure 24a shows the distribution of the number of heavy snowstorms occurring concurrently versus the number of stations involved for the northern Barents and Kara seas. Data are presented in both cumulative and differential form.

Figure 24

Figure 24. Graph (a) shows the differential (dots) and cumulative (solid line) distributions of the number of cases of concurrent heavy snowstorms versus the number of stations. Graph (b) shows the corresponding distributions of snowstorm duration in days. Data are combined from several stations in the northern Barents and Kara seas.

The frequency is plotted along the Y-axis, and the number of stations together with the percent of the area over which the phenomenon was observed are plotted along the X-axis. In this example, 100 percent denotes concurrent heavy snowstorm conditions at all 8 stations, and 25 percent denotes concurrent storms at 2 stations. It was found that about 75 percent of the concurrent cases occur at 2 to 4 stations (over 25-50 percent of the area). The Cape Zhelaniya and Russkaya Gavan' stations on Novaya Zemlya were almost always included among these stations. Figure 24 b shows the distribution function for duration (in days) of heavy snowstorms at several stations in the northern Barents and Kara seas. The frequency is plotted along the Y-axis, and the number of days with heavy snowstorms which are simultaneously observed at 2 and more stations, is plotted along the X-axis. The frequency maximum of the duration interval was 2 days. A similar conclusion may be reached for the southern area in the vicinity of Vaygach Island, however, the duration period of concurrent heavy snowstorms at several stations never exceeded 5 days in that area.

We suggest as a conditional criterion that a snowstorm becomes most dangerous in cases when it extends over more than 75 percent of a specified region. For the cases considered in this study, this condition corresponds to simultaneous occurrence at 6 or more stations in the northern Barents and Kara seas and at 3 or more stations in the vicinity of Vaygach Island. Table 28 presents a chronology of the heavy snowstorms which correspond to the criteria noted above. Over an observational period of 16 years, heavy snowstorms extended over more than ¾ of the study area in the northern part of the seas for 11 of those years and in the southern part (Vaygach Island) for 5 years. The mean annual number of days with these conditions is 3.7 for the northern area and 2.5 for the southern area.

In the territories of the European Arctic, heavy snow storms can occupy very large areas which are comparable in size to the cyclones themselves, however, such cases are observed relatively infrequently (see Table 28). Over the 16-year period, heavy snowstorms were observed concurrently over both of the specified regions only once, in February 1990.

In conclusion, Table 29 shows the empirical probability distribution of the number of days, n15, during which the dangerous part of a heavy snowstorm was observed on the Yamal Peninsula. These data make it possible to estimate the number of days per year with heavy snowstorms n. For example, once in 100 years at Novyi Port station we can expect 29 days with heavy snowstorms. More frequently, for example, once in 10 years, we can expect 19 days with heavy snowstorms.

Table 28
Chronology of dangerous snowstorms in certain parts of the Western Arctic
Event # Date Number of Days Number of stations with heavy snowstorms and V³ 15 m/s Maximum wind speed, m/s
Northern Barents and Kara seas
1 22-26 Jan 1975 5 7 29
2 4- 7 Apr 1975 4 8 29
3 5- 7 Mar 1976 3 7 25
4 5- 8 Jan 1977 4 7 34
5 21,22 Dec 1979 2 7 35
6 18-24 Feb 1981 7 8 28
7 25-28 Dec 1984 4 7 34
8 4- 6 Feb 1986 3 8 32
9 11-14 Mar 1986 4 7 27
10 9-11 Jan 1987 3 8 24
11 19-22 Jan 1987 4 7 28
12 21-24 Mar 1988 4 7 22
13 16-19 Feb 1989 4 7 23
14 8-11 Feb 1990 4 7 42
Southern Barents and Kara seas in the vicinity of Vaygach Island
1 12-14 Dec 1975 3 4 -
2 10,11 Feb 1979 2 4 -
3 27,28 Feb 1979 2 4 -
4 28 Jan 1984 1 4 -
5 1- 3 Dec 1989 3 4 27
6 7-10 Feb 1990 4 4 27
The Central Arctic Basin
1 7 Oct 1987 1 2 -
Table 29
Calculated number of days per year with heavy snowstorms, n15, on the Yamal Peninsula
Station Probable number of snowstorm days with V>15 m/s once every q years
q = 100 q = 20 q = 10 q = 5 q = 1
Yar-Sale 5 4 3 2 1
Novyi Port 29 23 19 15 6
Kharasavei 17 14 12 10 6

4.5. Snow drifting

The depth of the snow cover is usually small in the Russian Arctic. At the end of winter, with only a few exceptions, it does not exceed 40 to 50 centimeters, and at most stations it stays in the range of 20 to 30 centimeters [7, 10, 54]. However, snow transport during snowstorms and drifting events causes snow cover redistribution throughout the area and results in the formation of snowdrifts which tend to impede surface traffic.

Snow transport in the Arctic begins in late August or early September on the arctic archipelagoes and in late September or mid-October on the continent coast and continues until late June or mid-July [6, 7, 22, 42, 54].

The amount of snow transport is not routinely measured in the Arctic, however, field measurements carried out by the authors with specialized instrumentation have made it possible to develop a method for the quantitative determination of snow transport. Analysis of 400 sets of snow transport measurements from the snow surface to a height (h) of 6 meters have shown that snow transport intensity depends principally on wind speed but also on the structure of the surface of the snow pack. The amount of transported snow is at a maximum in a layer near the surface and sharply decreases with increasing height above the surface. This general pattern is observed over a wide range of wind speeds. During snowstorms, the intensity of snow transport near the surface (h = 1 centimeter) is 25 to 30 times larger than at a height of 10 centimeters and 100 times larger than at 1 meter (Table 30).

Table 30
Average intensity of snow transport at various heights, h, versus wind speed at 10m
Wind speed (m/s)
at h = 10 m
Snow transport intensity (g cm-2 hour-1) at various heights (cm)
h = 1 cm h = 10 h = 100 h = 200 h = 500 Total from
0 to 500 cm
6-8 86 (42) 10 (3)       96
9-10 150 (59) 17 (6) 1 (1)     168
11-13 325 (162) 22 (10) 2 (1) 1 (1)   350
14-16 520 (205) 34 (15) 4 (3) 2 (1) 1 (1) 561
17-20 900 (390) 45 (20) 8 (4) 5 (2) 2 (1) 960
21-25 1880 (953) 62 (38) 17 (8) 12 (7) 3 (2) 1974
26-30 2900 (1540) 72 (51) 26 (14) 17 (8) 9 (5) 3024

Note: the standard deviation is in brackets.

The snow transport volume increases with wind speed. The height dependence obtained was logarithmic, and a general formula for the entire air column from the surface to the top of the blowing snow layer was calculated using the formula:

equation2.gif,

where Q is the total snow transport intensity for the entire air column, q is snow transport intensity at each different level, and H is the height in the snowstorm corresponding to a transport intensity of 0.01 g cm-2 h-1. The following formula is then derived from the observational data:

equation3.gif gm × cm-2×h-1, where v is wind speed, meters per second, and C1 = 0.24.

If the density of the snowstorm snow is assumed to be 0.17 g/cm3, the calculated formula for the volume of snow transported horizontally per meter by the snowstorm is the following:

equation4.gif m3/m, where t is the duration of the snowstorm, and C2 = 1.4 × 10 -4. The relative error in calculating snow transport volume is approximately 16 %.

According to the present calculations, snow transport ranges in general from 250 to 500 meters cubed per meter per year in the arctic basin and in the East Siberian Sea up to 1500 meters cubed × m-1× yr-1 along the coast of the Kara and Barents seas (Fig. 25). In a few areas, however, the average volume of snow transport is equal to more than 2500 meters cubed×m-1× yr-1 [50, 70, 72].

Figure 25

Figure 25. Volume of snow transport (m3/m) for a year. During heavy snowstorms with maximum wind speeds and duration periods, the snow transport is on average 0.15-0.35 m3 × m-1×hr-1. As result, the snow transport volume for a single snowstorm may range from 6 to 8 m3/m at Khatanga and Chokurdakh stations up to as much as 40 to 50 m3/m for Cape Zhelaniya and Russkaya Gavan stations.