Approach:
- Introduction – explain shifting of pressure belts and its cause.
- Give diagram.
- Link various climatic phenomena with associated regions which are influenced by shift of the belts.
- Discuss socio-economic significance through their impact on livelihood.
Pressure belts on earth’s surface appear to move along with the Sun. This is because of inclination of earth to its axis. With the apparent shift of the Sun between the tropics, both the thermally formed pressure belt (EQLP) and the dynamically formed pressure belt (STHP – North and South) move along. For example, in summers, when Sun is directly above tropics, rather than at equator, the entire belt system (EQLP and STHP) shifts northwards. As such, the High Pressure belt which is generally found at 25-30 degrees latitude also shifts northwards to up to 30-35 degrees. Similarly the Equatorial low also shifts upwards, varying considerably over the landmass and the ocean. On the Indian landmass, it can reach up to 20-22 degrees North because of immense heating of North Indian landmass and the consequent low pressure. On Oceans, the belts are fairly stable because the variances in temperature are not much pronounced.
Impact on formation of climates:
- Most significant impact is in form of inhibition of cloud formation under the HP Belt. As HPBs move over an area, it experiences lesser rainfall.
- STHP lies over Mediterranean region in summers, leading to aridity. When it moves south along with the apparent shift of the Sun, the region receives rainfall. During winters, Westerlies prevail and cause rain, where as in summers, the dry trade winds blow offshore.
- On Monsoon: Only on the northward shifting of the EQLP in the form of ITCZ (Inter-tropical Convergence Zone) do the south-east trade winds cross the equator and reach as monsoon winds.
- Besides convergence, convectional uplifting which causes rainfall in the northern plains also occurs in the shifted EQLP i.e. ITCZ.
- Sahara desert remains almost entirely in the region where STHP is found. The edges of Sahara experience some rainfall and therefore a transitional climatic zone has developed there.
Socio-economic significance:
- Mediterranean climate is conducive for growing citrus fruits and therefore it has developed as major supplier of fruits as well as wine worldwide.
- Similar climate in Natal (South Africa), Southern Australia and California has given to similar social setup there based on vineyards and fruit production.
- Monsoon determines the socio-economic setup of India via its agricultural economy.