In the annual oscillation, the highest pressure occurs in December, and the pressure of January is also nearly as high, while the lowest takes place in June and July. In November and December, the winter ante-monsoon south of the Satpuras blows from the east, and is followed by an interval of three or four months in which the prevalent winds are from west and north-west. In the spring months, the temperature and pressure of the dry winds of Rajputana and Central India are very high, forming an exception to the rule that the seat of the greatest temperature is also that of the lowest pressure. From this tract of country, hot dry winds blow with considerable force towards the Central Provinces south of the Satpura’s. The land winds of April and May set in at 9 or 10 a.m., about the hour of maximum diurnal pressure, and begin to decline at 4 or 5 p.m., thus indicating that to some extent they are related to the diurnal oscillation of pressure. When the summer monsoon sets in, there is a rapid substitution of a saturated west wind for an exceedingly dry north-west wind, and the fall of pressure and of temperature is considerable, the former amounting to nearly 0.1 inch, and the latter to 14° or 15°.
The general direction of the winds for each month of the year is as follows:—
In January the winds are from the east, and in February from the north-east. In March they are from north-east, east-north-east, and south-south-west; while in April they are north-west and north-east. In May the winds blow from west-north-west and north. In June they are generally west, and in July south-west and west-southwest. In August they are west-south-west and west-north-west; in September west; and in October west, north-west, and north. In November the winds are west, west-north-west, and north-east; and in December east-north-east and east. The winds however, do not blow in a direct course, but very obliquely; and the tendency is to veer from left to right, a north-west wind often changing to easterly, and a wind from the south inclining to south-west, west and even north-west. Thus a certain scheme of pressure distribution, which determines the course of the winds, is peculiar to each season. But there are variations in different years, and these are no doubt closely connected with those variations of rainfall and temperature which characterise the seasons of different years.
