Half of the Earth — north or south of the equator, east or west of the Prime Meridian. All of India, Pakistan and Bangladesh sit in the northern and eastern halves.
ClimateWhat is a Hemisphere?
A hemisphere is half of the Earth. Two different cuts are in common use, and weather forecasting cares about both.
The equator splits the planet into the Northern and Southern Hemispheres. The Prime Meridian at zero degrees longitude, together with the 180th meridian on the far side, splits it into the Eastern and Western Hemispheres.
Every city on Mausam Online sits in the same two halves: northern and eastern. India’s mainland reaches down to Kanniyakumari at the southern tip of Tamil Nadu, and its southernmost territory lies in the Nicobar Islands, only a few degrees north of the equator. In the other direction, northern Pakistan and the Kashmir Himalaya reach well into the mid-latitudes. That span — near-equatorial islands at one end, glaciated mountains at the other, all on one side of the equator — is why a single country can run a heatwave bulletin and a snow advisory on the same morning.
The hemisphere is not trivia. It sets the sign of the Coriolis effect, the calendar of the seasons, and the direction from which the rain arrives.
Why the hemisphere decides how storms spin
The Earth rotates eastward. Because of that rotation, anything moving freely over the surface is deflected — to the right in the Northern Hemisphere, to the left in the Southern. This is the Coriolis effect, and it is the single most important hemispheric difference in meteorology.
Air flowing inward toward a low-pressure centre is bent sideways as it goes. North of the equator that bending produces anticlockwise rotation; south of the equator, clockwise. So a cyclone in the Bay of Bengal spins anticlockwise, while a cyclone off Western Australia — the same kind of storm, the same physics — spins the other way.
The Coriolis deflection weakens toward the equator and vanishes on it. This is why tropical cyclones rarely form in the narrow band straddling the equator: there is too little deflection to spin the converging air into a closed circulation. Storms that threaten Odisha, Andhra Pradesh, Bangladesh and Sindh form well north of that dead band, then curve as they move.
The same rule governs the winds you feel on an ordinary day. Around a high-pressure area — the winter anticyclone that settles over northern India, for example — the flow is clockwise in the Northern Hemisphere, the mirror image of a cyclone.
Hemispheres and the South Asian monsoon
The southwest monsoon is a cross-equatorial system, and that is what makes hemispheres matter more here than almost anywhere else.
In the northern summer, the Indo-Gangetic plain and the Tibetan Plateau heat intensely and low pressure builds over the land. The zone of converging trade winds, the Inter-Tropical Convergence Zone, migrates north of the equator. Air is drawn out of the Southern Hemisphere’s southeasterly trade winds, across the equator, and into the northern low.
The moment that air crosses the equator, the Coriolis deflection reverses sign. Southeasterly flow becomes southwesterly flow — the monsoon wind that strikes Kerala, climbs the Western Ghats, and eventually reaches Punjab and the Himalayan foothills. A concentrated low-level wind stream along the East African coast, usually called the Somali Jet, funnels much of this cross-equatorial air toward India.
So the rain that floods Mumbai in July is drawn from a hemisphere where it is midwinter. When the Northern Hemisphere cools in autumn the whole system reverses: the ITCZ slides back south, high pressure builds over the land, and the dry northeast monsoon takes over — bringing its own wet season to Tamil Nadu and Sri Lanka while the rest of the subcontinent dries out.
Seasons, daylight and time in the northern half
Because the Earth’s axis is tilted roughly 23.5 degrees, the two hemispheres lean toward the Sun at opposite times of year. Around the June solstice the Northern Hemisphere is tilted sunward: longest days, highest sun angle, and in South Asia the peak of pre-monsoon heat. Around the December solstice the position reverses, giving the region its short days and its cool, dry, often foggy north Indian winter.
This is why the seasons in Australia, southern Africa and South America run opposite to South Asia’s, and why someone leaving Delhi in December lands in a southern summer.
Being firmly in the Eastern Hemisphere sets the clocks, too. The region runs several hours ahead of Greenwich — Pakistan at UTC+5, India and Sri Lanka at UTC+5:30, Bangladesh at UTC+6. Forecast products issued in UTC, which most global weather model output is, therefore need converting before they line up with a local sunrise or a local afternoon thunderstorm.
Hemispheric patterns that reach South Asia
Several of the climate drivers that shape a South Asian year are themselves hemispheric or cross-hemispheric.
- The subtropical westerly jet is a Northern Hemisphere feature that shifts south over the Himalaya in winter, steering the western disturbances that bring rain to Punjab and snow to Kashmir, Gilgit-Baltistan and Himachal Pradesh.
- El Nino and La Nina develop in the Pacific and straddle the equator, and their influence on monsoon rainfall is one of the most studied links in meteorology.
- The Indian Ocean Dipole works across the tropical Indian Ocean, with one pole near Indonesia in the southern tropics and the other off East Africa.
None of these respect national borders, and several of them only make sense if you treat the two hemispheres as one connected machine.
Frequently asked questions
Which hemisphere is India in? India lies entirely in the Northern Hemisphere and entirely in the Eastern Hemisphere. So do Pakistan, Bangladesh, Nepal and Sri Lanka. Within South Asia, only the southernmost atolls of the Maldives lie south of the equator.
Why do cyclones spin anticlockwise in the Bay of Bengal? Because of the Coriolis effect. In the Northern Hemisphere, air moving toward a low-pressure centre is deflected to its right, which sets up an anticlockwise circulation. South of the equator the deflection is to the left, and the same storm would spin clockwise.
Does the hemisphere affect the monsoon? Directly. The summer monsoon draws air across the equator out of the Southern Hemisphere. When that air crosses into the north, the Coriolis deflection flips and turns a southeasterly trade wind into the southwesterly monsoon flow that reaches the Indian coast.
Is it true that water drains the other way in the Southern Hemisphere? No. The Coriolis effect is far too weak to control something the size of a sink or a bucket; basin shape and how the water entered decide the direction. Coriolis matters for systems hundreds of kilometres across, such as cyclones and jet streams.
Where can I see how this plays out in my city? Northern Hemisphere seasonality shows up clearly in the forecasts — compare a near-tropical coastal station with a Himalayan one on the same day. Try Chennai, Thiruvananthapuram, Delhi, Srinagar, Skardu and Dhaka.