"كتيّب بلاد الرافدين. المجلد I. ١٩١٨" [‎٤‎١] (٥٦٨/٥٠)

CLIMATE
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41
The average range of temperature in a single day is naturally much
less ? and is given below for the same places :
Average Daily Range of Temperature
Month.
Mosul.
Baghdad.
Babylon.
Basra.
Bushire.
o f .
0 F.
0 F.
0 F.
0 F.
January
18-0
21.3
20-3
16-2
13-0
February .
17.7
22.8
24.6
16-4
12-6
March
18-9
23-3
26.7
17.3
13-4
April ....
22-5
24.7
26-8
18.8
14*1
May ....
27-0
25.4
29-0
19-6
135
June ....
28.9
28-4
33-6
18-9
11-2
July .
30-6
29.8
35-1
21-5
11-0
August
31.5
30.8
36.2
23.5
13-0
September .
31.1
30.8
36-4
24-6
14-8
October
28-4
29.3
31.7
22.7
16-3
November ,
22-5
24.6
27-9
18-3
15-6
December .
18-0
20.5
23.0
13-7
13-3
Winds. —The prevalent winds are shown in Table XI, p. 52, for
the different stations at which observations have been made. The
north-westerly and northerly winds blow with great steadiness,
especially in summer, when there is a steep pressure gradient from
the north of Mesopotamia to the Persian Gulf. In consequence
of heating, the lower layers of air which are in contact with the
ground rise, and in this way a mixing of the lower and upper air
takes place as the day advances. The result is that the more
rapid motion of the upper layers is imparted to the lower layers
with which they are being mixed, and increased velocity of the
surface Avind in the midday and afternoon hours is thus brought
about.
Observations of atmospheric pressure have been made at few
places in Mesopotamia, but from these and others in the Persian
Gulf, in Syria, Egypt, Arabia, and India the general trend of
the isobars can be deduced for the summer months, May to October,
when there is a well-defined pressure gradient towards the Persian
Gulf. In the winter months the gradient is slight, and the data are
insufficient for reliable deductions to be made of the velocity of the
upper air-currents. An approximate value can, however, be obtained
for the summer months, and the estimated velocity of the winds
at from 1,500 to 4,000 feet (gradient wind) is given in the following
table: