Mean annual air temperatures and precipitation on the Greenland Ice Sheet, as estimated from snow profile studies and long-term meteorological records at coastal stations, have been used to prepare mean annual air temperature and mean annual precipitation charts for the Greenland Ice Sheet. It is shown that melting of surface snow may occur at elevations of about 1,300 m. in north Greenland and up to 2,700 m. in south Greenland. The warming trend in the Arctic, as indicated by increases in mean annual air temperature, may have occurred to a lesser extent on the ice sheet than at sea-level coastal stations. Annual accumulation of precipitation is two or three times as great at 2,700 m. on the west side of the ice sheet as at the crest. South of lat. 66° N., precipitation may be about twice as great on the east side of the crest as on the west side.
The mean temperature profile of the atmosphere indicates the probable existence of two horizontally distributed sound waveguides in the atmosphere. The lower one usually occurs between the surface and 50 km, and the upper between 50 and 110 km. Wind data above 30 km, which have become available recently through the use of meteorological rockets, have resulted in revised concepts of atmospheric circulation patterns for the northern hemisphere. Wind data obtained from these patterns have been combined with mean atmospheric temperature data to determine seasonal sonic patterns of the atmospheric waveguide that can exist between the surface and an altitude of about 50 km. These patterns indicate the general existence of a waveguide for sound having an eastward propagation component in winter and a westward propagation component in summer. For other combinations of propagation directions and seasons, a waveguide does not usually exist between the surface and 50 km. The refraction of sound from upper altitudes to the surface will generally occur only in winter at sites located to the east of the source and in summer at sites located to the west of the source.
The record of annual precipitation as obtained from stratigraphic studies on snow profiles in the interior of northern Greenland made in 1954 by SIPRE personnel shows a decreasing precipitation trend since 1920 with the largest decrease occurring since 1932. A residual mass curve analysis of the data indicates that, in spite of large fluctuations in the accumulated precipitation, the decreasing trend may be considered valid over a period of several years.
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