No. IV-18.4 - (IMD), Pune

14
Coastal Andhra Pradesh.
9.4 In all the synoptic systems approaching the coast, it is usually
observed that the lower tropospheric northeasterlies in the northwest quadrant
are much stronger than the winds in the other quadrants.
9.5 The upper tropospheric easterlies which are only weak to moderate during
the season, sometimes temporarily (for 1 or 2 days) strengthen to 50-60 kts in
association with the formation and movement of intense systems like depressions/
cyclonic storms. This feature is more likely in the earlier part of the season.
9.6 The location of the anticyclonic cell in the middle and upper troposphere
appears to have an influence over the rainfall activity in south Peninsula.
A southeasterly/southerly flow over the south Peninsula corresponding to the
western end of the sub—tropical anticyclonic cell over the south Bay of Bengal
has been noticed to be more favourable for rainfall over south Peninsula, than a
northwesterly/northerly at these levels, corresponding to the location of the
eastern end of the Arabian Sea anticyclonic cell.
10. Upper Air Temperatures and Humidity
10.1 The mean monthly tephigrams of Madras from September to December are
given in Fig. 10.1. Between September and October there is hardly any difference
either in the temperatures or humidities. Thus the heralding of the
northeast monsoon does not bring about any change in the thermodynamic structure
of the atmosphere over Madras.
10.2 Significant changes take place from October to November. They are:-
i) a cooling in the lower troposphere (below 700 mb)
ii) decrease of moisture at all levels, the decrease being more above 850 mb
iii) a tendency to build a stable lapse rate between 850 mb and 700 mb levels.
10.3 These features progressively become more marked till January when the
northeast monsoon is completely established over the whole Bay. In January, the