No. IV-18.4 - (IMD), Pune

15
moist layer is confined to 900 mb, above which, air becomes quite dry and the
layer between 900 mb and 700 mb is more stable than even November or December.
The cooling and the decrease of the moisture are associated with the extension
of the dry continental air from the north progressively into more southerly
latitudes in the winter. Similar characteristics are noted over Vizag and
Bangalore also.
10.4 Further south, over Trivandrum, the decrease in moisture content is
appreciable only by January. The cooling of the lower troposphere and the formation
of a stable layer noticed further north (Madras) is not seen over
Trivandrum.
10.5 The mean tephigrams of Madras for days of strong to vigorous and
weak monsoon conditions are given in Fig. 10.2. It is seen that:
i) during strong to vigorous monsoon days the air has a lapse rate which is
nearly saturated adiabatic. A high degree of saturation extends upto
450 mb, and
ii) there is no difference between the dry bulb curves on strong and weak
monsoon days. But, on weak monsoon days the air is much drier; the dryness
is more above 750 mb.
10.6 A typical day's Tephigram of Madras for active and weak monsoon is
given in Fig. 10.3,
11. Typical synoptic situations affecting weather over South Peninsula
during the Northeast Monsoon period
11.1 The typical synoptic situations affecting weather over south Peninsula
during the northeast monsoon season are:—
i) Storms and depressions which form over the sea areas and move towards the
coast
ii) Low pressure areas (surface and/or upper air) and low pressure waves
iii) "East-west oriented trough line across the Peninsula, seasonal trough over
Bay well-marked or a trough of low pressure off Kerala coast