Forecasters Guide - (IMD), Pune

2.4 ANALYSIS OF UPPER AIR CHARTS.
Forecasting Circular 1970/1/ Dated 7 August 1970
In supersession of instructions contained in Forecasting Circular 1969/2 and
Forecasting Circular 1969/7, the follow ing practices are to be follow ed by all D.M.Os and
Storm Warning Centres in respect of plotting and analysis of constant pressure charts with
effect from 16 th August 1970.
Plotting :
Constant pressure data (contour height, dry bulb and dew point temperatures) w ill be
plotted on the usual upper w ind charts along w ith the w inds for the entire area of the chart as
show n below :
i. DMOs : 850, 700 and 500 hPa levels.
ii.
Analysis :
Weather Sections at Alipore, Colaba and Madras:
850, 700, 500 and 300 hPa levels.
i. Contour analysis is to be done at all the levels as indicated above.
ii.
iii.
iv.
Isopleths of contour heights should be at intervals of 20/ 40/ 80 meters
depending on the gradient and w ill be draw n in ordinary black pencil. Interval
may be chosen to delineate significant features.
Isotherms w ill be draw n at intervals of 2/5 O C in red pencil, depending on the
gradient. Interval may be chosen to delineate significant features.
Streamline analysis is to be done for all the other levels.
v. Streamline analysis may be meshed w ith the contour analysis to bring out
vi.
small scale/ feeble systems.
The above instructions are only in the nature of general guidance laying dow n
the minimum number of levels for w hich constant pressure analysis is to be
done in order to introduce certain uniform practices at all the Forecasting
Offices. There is no restriction on the additional levels for w hich constant
pressure data are to be plotted and for w hich contour analysis is to be done.
Sd/
( M. S. V. Rao)
Director
Performing current duties of DDGF
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