CLIMATE

1. Planetary winds

Planetary winds are within the pattern of permanent pressure groups around the globe. Winds tend to blow from the high-pressure area to low-pressure areas as the planetary winds. Instead of blowing directly from one pressure belt to another, however, the effect of the rotation of the earth (Coriolis force) tends to deflect the direction of the winds. In the northern hemisphere, winds are deflected to their right, and in the southern hemisphere to their left. This is known as Ferrel’s law of deflection.

The Coriolis force is absent along the equator but increases progressively towards the poles. The trade winds are the most regular of planetary winds. They gather more moisture and bring more rainfall to the east coast of the continents within the tropics. From the subtropical high-pressure belts, winds flow towards the temperature low-pressure belts as a variable are called westerlies.  The warming effect and the other local pressure differences in very variable climates in the temperature zones. The weather is damp and cloudy and the seas are violent and stormy due to heavy precipitation. California, Iberia, central Chile, southern Africa and South Western Australia receive Westerlies in the winter season due to the shifting of the wind belts.

The Mediterranean parts of the southern continent receive rainfall in June due to the influence of the westerlies. The ‘Mediterranean’ parts of Europe and California then come under the influence of the westerlies and receive rainfall in December. The polar Easterlies are formed which blow out from the polar high-pressure belts towards the temperature low-pressure belts. These are more regular in the south than in the north.

2. Land, sea breezes and monsoons

Land and sea breezes are in fact, monsoon on a smaller scale. Both are caused by the differential heating of the land and sea, the former in a diurnal rhythm and the seasonal rhythm. The land gets heated up much faster than the sea and warm air rises and forms a region of local low pressure.

The sea remains comparatively cool with higher pressure so a sea breeze blows in from sea to land.  Its speed or strength is between 5-20 m.p.h.  It is generally stronger in tropical than temperate regions. Its influence does not normally exceed 15 miles from the coast. It is most deeply felt when one stands facing the sea in a coastal resort.

As land cools down much faster than the sea, the cold and heavy air produces a region of local high pressure. The sea covers its heat and remains quite warm and its pressure is comparatively low. The land breeze flows out from sea to land, in the same way, monsoons are formed. The rapid heat in the summer attracts the low pressure over the land and blows in bringing territorial rain into the sub-continent.

Similarly, in winter when the land is cool, the surrounding seas remain comparatively warm. High pressure is created over Indo-Pakistan and the North-East Monsoon blows out from the continent into the Indian Ocean and the Bay of Bengal.

Fohn Wind or Chinook Wind: Both the Fohn and Chinook winds are dry winds experienced on the leeward side of mountains when descending air becomes compressed with increased pressure.  The Fohn wind is experienced in the valleys of the northern Alps, particularly in Switzerland in spring. Chinook winds are experienced on the eastern slopes of the Rockies in the U.S.A. and Canada in winter. Condensation takes place when the air is saturated. Rain and even snowfall on the higher slopes. The air is compressed and warmed. It melts and causes avalanches.

3. Cyclonic activity

Tropical cyclones, typhoons, hurricanes and tornadoes: All these are different kinds of tropical cyclones. They are well-developed low-pressure systems into which violent winds blow. The storms, depending on where they occur, may be called hurricanes, typhoons or cyclones.

1. Typhoons occur mainly at 6° and 20° north and south of the equator and are most frequent from July to October. These are smaller than temperate cyclones and have a diameter of only 50-200 miles. Violent winds with a velocity of 100 mph are common. Typhoons occur in the China Sea:  
2. Hurricanes are claimed, rainless centres, dark clouds gather and violent stormy weather lasts for hours. Hurricanes in the West Indian islands in the Caribbean;
3. Tornadoes are small but very violent with a tremendous speed of 500 mph. It appears in a dark funnel cloud of 250 -1400 feet in diameter. Tornadoes in the Guinea lands of West Africa, and the southern U.S.A. in which the local name of Whirl-wind is often applied, and willy-willies occur in north Western Australia.

4. World climate types