Shifting of pressure belts
Topic: Atmospheric Pressure, Winds and General Circulation · NCERT: Class 11, Ch 9 "Atmospheric Circulation and Weather Systems"
Meaning
The world's pressure belts and wind belts do not stay in one place. They follow the overhead Sun. They move about 5–10° north in the northern summer and back south in the northern winter. As the belts move, a place can fall under a different belt in each season. This gives some regions their special seasonal climates. The Mediterranean lands get winter rain and summer drought, and the monsoon lands get winds that reverse with the season.
Example
In July the ITCZ (Inter-Tropical Convergence Zone, the belt where the trade winds meet) swings far north over South Asia and forms the monsoon trough over north India. The south-east trades cross the equator and turn into India's south-west monsoon. In winter the belts move back south and the winds over India reverse.
Don't confuse with
- Local winds (land and sea breezes): these also change direction, but every day and night over a small area. The belts shift with the seasons over the whole planet.