LARGE SCALE ANALYSIS OF METEOROLOGICAL PHENOMENA FOR THE PERIOD OF THE 'FIRST HIMALAYAN SOARING EXPEDITION'

Abstract

The wind and temperature distribution at lower levels  between northern India and the Tibetan plateau indicates a modification of the up- and down-valley circulations in comparison to alpine regions. This is attributed to the different  geometrical relationships between high level plateau and slope area.  The adiabatic heating of subsiding down-valley current originating over the vast plateau areas cannot be compensated by the radiational colloing along the slopes at night. This prevents airmasses from the plateau to reach the plains of southern Nepal and northern India by means of direct thermal circulations.  These air masses were therefore found at heights above 3000 m m.s.l. The investigation reveals a close coupling between the weather phenomena experienced at lower levels and the position  of the jet streams which appeared to be separated into three different cores.  The cores were showing wave-like lateral shifts wlth no apparent modification when crossing from the plains into the Himalayan ranges. Changes of wind and temperature connected with these shifts were mainly limited to levels at and above 400 hPa while lthe lower troposphere remained amazingly conservative. Tracks of surface depressions seemed to avoid the highest ranges or plateaus. The development of a lee-depression was observed over Pakistan. Its track over the plains along the southern side of the Himalayas could be followed as far as Burma. Though the depression appeared to be too weak initially for comparison with the behaviour of high latitude waves, the temperature changes at 850 hPa, the cloudiness and the jet stream patterns are showing simiiar phenomena. The large scale circulations at jet stream levels and at the surface reveal a significant change during the expedition. Findings during the first days can therefore not stiictly be compared with those at the end of the period.