Climatic conditions over the territory
of Russia.

The total number of winter and summer cases (days), when daily air temperatures or atmospheric precipitation sums were above extreme, was used as variability indices of abnormal phenomena on the Russian territory. In winter, the number of days with maximum temperatures which are above limiting values increases in most of European Russia (except for southern and south - eastern regions) and in West Siberia (Fig. 1). In the east of country, except for the Pacific coasts of Chukot Peninsula and Kamchatka, winter daily maximum air temperatures also exhibit the growing number of extremes.

Fig. 1. Linear trend coefficient (days/10 years) in the series of days with abnormally high air temperatures in winter (December-February), 1961-1998.

For the winter period 1961-1998, most of the stations under considerations exhibit a tendency for fewer minimum temperature extremes. Maximum (in absolute value) coefficients of the linear trend were obtained in the south of the country and in eastern Yakutia.

From the data for 1966-1998, the growing number of winter atmospheric precipitation extremes was found at the stations of European Russia north of 55° N and central Siberia. The growing number of days with extreme winter precipitation is also recorded at Chukot stations. When considering extremes in summer temperature conditions, it was found that the stations in the east of European Russia, in central Siberia, in Yakutia and in eastern Russia showed a growing number of days with maximum temperature above limiting value. At the same time, negative coefficients of the linear trend in the series containing lowest of the minimum temperatures were obtained for the most of the Russian stations. Only a few stations in the north-east of Russia showed a trend for stronger extremity associated with low air temperatures. A number of stations in the southern regions of the country showed the tendencies for reduced extremity associated both with maximum and minimum temperatures.

On the Russian territory, the increase in the number of the days with extreme summer precipitation prevails (Fig. 2). Only some of the stations in central Siberia, in the Magadan Region and in the Maritime Territory showed negative coefficients of the linear trend.

Fig. 2. Linear trend coefficient (days/110 years) in the series of days with abnormally high precipitation in summer (June-August), 1966-1998.

Winter (December 1999 - February 2000)

A few winter periods were identified on the Russian territory when the number of days with extremely low temperatures was above a long - term mean by more than standard deviation (Fig.3).

Fig. 3. Number of days with abnormally high (Nmax) and abnormally low (Nmin) air temperature in winter (December-February) over the Russian territory.
- N max > 10 days,        - N min > 10 days.

During the first ten days period in January, severe frosts persisted in West Siberia (-40...-45° C), Krasnoyarsk Territory (-54...-57° C, in the south, -30...-35° C), and Irkutsk Region (-50...-55° C, in the south, -30...-35° C). It was also very cold in the Magadan Region and in most of Kamchatka: mean monthly temperature in January proved to be 8-9° C below normal. The number of days with minimum air temperatures below the value corresponding to the boundary of the 5% interval exceeded the normal by more than standard deviation in the south of the Khabarovsk Territory, in the east of Chukot Peninsula (Chukotka)., and in the remaining region of West Siberia. Figure 3 shows monthly variation in minimum air temperature for individual meteorological stations located in these areas of extreme temperatures. The diagrams show limiting values of minimum air temperatures, Tmin_ 5% . At the station in West Siberia (Irkutsk and Boguchany), all the cases with extremely low air temperatures were recorded during the first ten days in January. In Khabarovsk, the lowest air temperatures were recorded in the second ten-day period. In eastern Chukotka, December was the most extremal month in terms of minimum winter temperatures. In Providence Bay, the minimum air temperature was below -26.7° C (boundary of the 5% interval) from 18 to the end of December.

The number of days with extremely high air temperatures exceeded the normal by more than standard deviation in the north-west of European Russian, the north of the Volga-Vyatka region, the south of the Tyumen region, and the south of the Far East region (Fig. 3). In European Russia, February was the warmest winter month. At meteorological station Vytegra, the boundary value of the 95% interval in the arranged series of maximum February air temperatures is 1,8° C. Eight days with maximum temperatures above this value were recorded in February 2000. The same number of extremely warm days in February was also obtained for Vologda. Extreme air temperatures in the north-east of the Amur region are caused by high temperatures during the first ten days in January and on individual days at the end of the month. This is well seen from the data at meteorological station Bomnak. In the south of the Tyumen region, the largest number of abnormally warm days in winter was recorded in December. As for winter precipitation regime, the extreme pattern characterized by the number of days with high precipitation was recorded in different regions of Russia. The December of 1999 was most extremal in Middle Ural, central West Siberia, southern Yakutia and on the western coast of the Sea of Okhotsk (Fig.4). The relation of the monthly precipitation sum to the normal in Middle Ural and central West Siberia exceeded 200%. At meteorological station Ayan (western coast of the Sea of Okhotsk), December precipitation was 300% of monthly normal. Extreme values of daily precipitation sums were recorded in six cases out of 12 days with precipitation. In January, the number of days with precipitation above the boundary value of the 95% interval exceeded the normal by more than standard deviation in Kola Peninsula and eastern Chukotka. The extreme pattern in winter precipitation regime in the south of Komi Republic is caused by a large number of days with abnormal precipitation was recorded in the third ten-day period in February.

Fig. 4. Number of days with abnormally high precipitation (Nr) in winter (December-February) over the Russian territory.
- Nr > 8 days

Spring (March - May)

In spring, extreme patterns in precipitation regime were recorded in northern European Russia, Central Black Earth region, southern Ural, Krasnoyarsk Territory, Irkutsk region and the Far East. In Kola Peninsula, precipitation was above normal during all spring months. In Murmansk, 17 cases were recorded in spring when daily precipitation sum was above the boundary value of the 95% interval, with March being most abnormal (10 cases). Six days with abnormal precipitation were recorded in April. Central Black Earth regions also experienced the largest amount of abnormal precipitation in Marct and April. In Kursk, the days with high precipitation were distributed as follows: March - five days, April - four days, and May - three days. In Southern Ural, Krasnoyarsk Territory and Irkutsk region, the largest number of days with abnormal precipitation was recorded in March and May. At meteorological station Boguchany, five cases were recorded in March and seven out of 13 cases throughout the season, in May. In Ekaterinburg, March and May each exhibited four cases out of ten cases with abnormal precipitation. In the south of the Far East region, for all the spring months, the same number of days with high precipitation is typical for most of the stations.

The extreme pattern in spring temperature conditions associated with high air temperatures was recorded in European Russia, central West Siberia and north-eastern Kamchatka. At the meteorological stations of European Russia, the number of days with maximum air temperature above the boundary value of the 95% interval exceeded the spring normal by more than two standard deviations . April was most abnormal. Mean monthly temperature anomalies at the stations of European Russia were above 5° C. In Velikiye Luki, 15 days with abnormally high temperatures were recorded in spring, with ten cases falling on April; in Pskov there were 14 such days throughout the spring season, with 11 of then also falling on April; in Smolensk there were 15 days with abnormally high temperatures, with 12 of these falling on April. In central West Siberia, the days with abnormally high temperatures were recorded in all the spring months. At meteorological station Troitsko-Pechorskoye there were 11 cases throughout the season; in Alekksandrovskoe and Kolpashevo, 12 and 11 cases were respectively recorded.

Summer (June-August).

The number of days with abnormally high (Nmax) and abnormally low (Nmin) air temperatures in summer (June-August) for the Russian territory is analyzed in Fig. 5.

Fig. 5. Number of days with abnormally high (N max) and abnormally low (Nmin) air temperatures in summer (June-August) over the Russian territory
- N max > 10 days,        - N min > 10 days.

The summer season is largely characterized by extreme temperature conditions associated with high temperatures in the Archangelsk region, on Taimyr Peninsula, in the southern Far East, Koryak Autonomous Area and Magadan region. In the Arkhangelsk region, positive anomalies of mean monthly temperatures were observed in June and July. The greatest number of days with abnormally high temperatures falls on July. For example, at station Koinas (Fig. 5), of 14 abnormally warm summer days, eight days were recorded in July and six days, in June. It was particularly hot in the second ten-day period in July. July was the hottest summer month in the Magadan region, too. At station Seimchan, the maximum air temperature was above the limiting value for nine days in the second ten-day period in July. A total of twelve such cases was recorded in the season. In the Chita and Amur regions, the largest number of days with abnormally high temperatures was recorded in the first half of August. In this period, stations Mogocha and Arkhara each exhibited 11 cases with abnormally high air temperatures.

In summer, abnormally low air temperatures were recorded most frequently at individual stations in Yakutia, north-eastern Kamchatka region and Transcaucasia. In summer, meteorological station Zhigansk (Yakutia) experienced 11 cases of abnormally low air temperatures, with seven eases falling on the period 15-25 August (Fig. 5). In Transcaucasia, mean monthly summer temperatures were below normal only in June. However, in Makhachkala, July and August air temperatures dropped below limiting value (five cases in the both months). In June, this minimum temperature was recorded for eight days. In the north-east of the Kamchatka region, June and August air temperatures were close to normal, with July showed positive temperature anomalies. Six cases of abnormally low air temperatures were recorded in June and August at meteorological station Korf.

Western European Russia received much above normal precipitation in summer. Very rainy June was recorded in Tula, Ryazan, Nizhny Novgorod, Tambov, Lipetsk, Penza, Perm, Orenburg and Saratov regions, as well in Bashkortostan and Mordovia. These receive in places more than three monthly precipitation normals; heavy showers were often accompanied by thunderstorms, wind strengthening (to 20- 22 m/s) and hail. In the west of the Central region and in the North-Western region, was also rainy in July. These receive in places more than two monthly precipitation normals. There are two areas in European Russia where the number of days with abnormally high precipitation exceeded the normal by more than standard deviation (Fig. 6). Both in Kkursk and Pskov, the largest number of days with abnormal precipitation falls on July.

In central Yakutia and throughout Sakhalin, it was very rainy in June: in places there were more than three monthly precipitation normals. Seven cases with abnormal precipitation was recorded in June at meteorological station zhigansk, the total of these being twelve for the whole summer period. In Transbaikalia, July rains soil drought. Monthly precipitation sum was 160-250% of monthly normal. Rains caused rainfall floods on the rivers Vitim and Chitinka in the Chita region. In Chara, the largest number of days with high summer precipitation was recorded in July. Heavy rains, which were recorded in the Maritime Territory in the third ten-day period in July, produced The water level rise to 1m for most of the rivers in the Territory. In Vladivostok the monthly precipitation sum in July was 268% of normal. All the cases of abnormal precipitation in Vladivostok were recorded in the third ten- day period in July (Fig..6).

Fig. 6. Number of days with abnormally high precipitation (Nr) in winter (December-February) over the Russian territory.
- Nr > 8 days

Autumn (September-October)

In autumn, the number of cases with maximum air temperature above the boundary value of the 95% Interval exceeded the normal by more than standard deviation in northern and western European Russia, Northern Ural and in most of the Far East region. The largest number of days with abnormally high temperatures was recorded at the following stations: Murmanskk (15 days), Kkandalakksha (14 days), Onega (13 days), St-Petersburg (14 days), Vologda (11 days), Petrozavodskk (11 days), and Naryan-Mar (11 days). In Kola Peninsula, the largest number of days with extreme temperatures was recorded in October; at the remaining stations, abnormally high temperatures were also recorded in November.

From analyzing the extreme pattern in temperature conditions associated with low minimum temperatures, the vast areas were identified where the number of cases with abnormally low temperatures was above normal. Among these are Volga-Vyatka and Volga regions, Southern Ural, the South of West and East Siberia, Central and Southern Yakutia, and Kamchatka. However, the cases with normals exceeded by more than standard deviation were only recorded at the individual stations in Siberia, Yakutia and Kamchatka (in Barnaul, Kirensk, Zhigansk, Ust-Mai, and Klyuchi). At the rest of the stations, minimum temperatures below the limiting value were more often recorded in October.

In autumn, abnormally high precipitation was recorded in the north of European Russia (Naryan-Mar: 14 cases, Khoseda-Khard:10 cases). Small areas of the extreme pattern in precipitation regime were recorded in the northern Sverdlovsk region (Ivdel: 10 days), south-western and south-eastern Yakutia (Vitim: 9 days, Suntar: 9 days, Oimyakon: 11 days), Transbaikalia (Mogocha: 11 days), Northern Caucasia (Armavir: 8 days, Machachkala: 9 days). In European Russia and Ural, the largest number of days with abnormally high precipitation falls on September, while in Yakutia, October was most abnormal.