| | | Environmental Conditions
Climatology
Esrange has a typical continental climate with cold winters and relatively warm summers. The precipitation and humidity are relatively low all year. Snow begins to fall by late September, and normally by mid-October the ground is covered and the lakes are frozen. The 24 hour average temperature falls below 0° C in early October and stays below until the beginning of May. During the coldest months, December, January and February, the average temperature is normally around -15°C. However, a low of - 48° C has been recorded. During winter the temperature at the radar hill is generally 10°C higher than in the valley.
By the end of May the snow and ice disappear. Summer temperatures are in the 10° to18° C range, rising occasionally to 30°C. Mosquitoes are prevalent throughout the summer and the use of repellents is advisable. From a medical point of view the arctic mosquitoes are harmless as they do not spread any diseases.
The number of clear days varies during the year. The probability of a clear sky or very few clouds is highest (about 50 %) in January through March and lowest in September through November (about 20 %). Fog can occur in the Vittangi valley before the river freezes in October - November, otherwise fog is rarely seen. More detailed weather statistics are available at Esrange.
Winter Clothing
As temperature drops well below zero during winter, you should be equipped with proper warm clothing if your visit falls within the period October to April.
The following recommendation should be used as a guideline packing list:
Long winter underwear
Sportshirt, long sleeves
Thick sweater
Warm socks
Heavy duty winter-boots
Thick overcoat or arctic parka
Warm gloves
Hat with flaps for ear protection
Please remember that you should always carry warm clothing as a prec aution in case of an emergency, for instance a car breakdown on the Esrange road. Some special arctic clothing is available in the Esrange store.
Winds
The launch areas for rockets and balloons are situated in a valley and are thus sheltered from the wind. Ground winds are generally low (below 5 m/s). However, areas of low pressure can occur during spring and autumn moving in from the west and causing 2-3 days of relatively strong winds. The dominant wind direction at ground level is southwest. The yearly variations of high altitude winds above 30 km are interesting, and can result in excellent conditions for the launching facility for scientific balloons. Wind statistics from a twelve-year period have been processed; the results follow below.
The winds above 30 km are generally westerly during the winter and easterly during summer. The turn-around from easterly to westerly winds starts 20-30 of August. During September the wind velocity slowly increases from near zero to about 50 km/h by the end of the month. Typical flight times at the ceiling over Scandinavian territory would be 3-7 hours during September. The wind velocity continues to increase during October-November-December and maximum wind velocities have been measured in January-February (max. 380 km/h, February 10, 1974). The turn-around from westerly to easterly generally occurs in April.
Typical balloon flight times at the ceiling in October are 3-5 hours and in November 1-4 hours. The wind velocity varies and even in December - January - February there are normally some days with winds permitting flight times of 1-2 hours at the ceiling over Scandinavian territory.
During the winter period the wind direction normally varies between 250° and 290°. There are, on average, one sudden stratospheric warming period every winter. The length of such a period can be more than one week and the high altitude wind then is very unpredictable. During these periods the wind direction can turn as much as 180° and wind velocities normally decrease. The high altitude winds start decreasing in early March and turn to an easterly direction by 20-30 to April. The turn-around time in spring is more difficult to predict than the turn-around in August. Furthermore, it seems that wind velocities are higher in April than in August and the wind direction is rather unstable before the turn-around.
About 5-10 hours flight time at the ceiling can be expected in April. After the turn-around the wind velocity increases to a maximum of 100 km/h 20-25 of June; after that the velocity rapidly decreases. The wind direction seems to be stable between 80°-100° during the summer period. By the end of July the wind velocity is normally 20 km/h at 30 km altitude and 30-40 km/h at 35 km. By placing the ceiling of the balloon on the right level long flight times can be achieved. The turn-around to westerly winds regularly occurs between 20 and 30 of August. The wind is low (5-20 km/h) during the whole of August and flight times of 20-60 hours' duration above Scandinavia can be expected if the right days are chosen. The result from the high altitude wind measurements at Esrange during the period 1972 to 1984 are presented as 12 average wind profiles.
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