a) Pressure Gradient — It is the rate of change of atmospheric pressure between two points on the earth’s surface. (b) Winds — Horizontal movements of the air from high pressure to low pressure areas are called winds. (c) Coriolis force — This force is created by the rotation of the earth as the winds in different belts deflect towards right in Northern hemisphere and to the left in Southern hemisphere. (d) Altitude — The pressure also decrease with increasing altitude at the rate of 100 millibars in every 1000 metres of height gained. (e) Monsoons — are the periodic seasonal winds blowing in the regions of South East Asia and Northern Australia. The word monsoon is derived from the Arabic word ‘Mausim’ meaning ‘Season’, on ACCOUNT of deeply affecting the seasons of the particular region. Question 2. Name the four main pressure belts of the earth. ANSWER: Equatorial low pressure belt Sub-tropical high pressure belt Circum-polar low pressure belt Polar high pressure areas. Question 3. What is Circum-polar Low Pressure Belt ? Answer: It is the belt of low pressure belt between 60°N – 70°N and 60° S – 70° S. Question 4. How does Coriolis Force vary latitudinally ? Answer: In the northern hemisphere the winds deflect towards right and in Southern hemisphere deflect towards left due to the effect of the rotation of the earth, e.g. the trade winds take the Southwest DIRECTION in place of southern direction in northern tropical belt and in southern tropical belt these winds take northwest direction in place of northern direction.  Question 5. Name the three chief types of wind. Answer: Three chief types of winds are Trade winds, Westerlies, and Polar winds. Question 6. What are periodic winds ? Answer: Periodic winds blow at regular intervals or in regular cycles. They are winds that result from localised differences in pressure and temperature. For example, land and sea breezes and the seasonal winds. Question 7. What are local winds ? Name any two local winds. Answer: The local winds blow in certain places and these are warm and cold according to the area from which they blow, e.g. Foehn winds blow descending on the slopes of the Alps and makes the temperature ideal for grapes due to its warm effect. In the same way Chinook winds blowing and coming down from the Rockies mountains in North AMERICA helps to increase the temperature and are beneficial to keep grasslands ice free and warms the ranches, so good for animal rearing.  Question 8. Name two types of variable winds ? Why are they so called ? Answer: Variable winds change their direction and force from place to place due to changing the pressure system. These blow for a short time or for a few days. These are cyclones and anticyclones. These are the circular winds with low pressure and high pressure in the centre respectively. Question 9. Why are cyclones frequent in summer in the tropical region ? Answer: In summer in the tropical region due to die shifting of Doldrums, the low pressure region is strongly originate between 8° and 20° N and S. They mainly originate in China sea and surrounding area. In Bangla Desh, these are known as ‘KalBaisakhi’ rneaning ‘Time of Death’ and cause heavy calamities and destruction. These are known as ‘hurricanes’ in North America, ‘Typhoons’ in China,‘willywillies’ in Australia.  Question 10. Mention any two differences between Tropical Cyclones and Temperature Cyclones. Answer: Tropical Cyclones : .