"MoNsOoN TiMeS-SouTh InDiaN WeAtHeR"
Analysis by: Sai praneeth, Sai krishna.
Monsoon onset conditions:
After the month january, the hot sun starts its journey from tropic of Capricorn due to the tilt of earth. The temperature of south Asia starts to raise and becomes hot by april first week. The intertropical convergence zone starts moving from the southern hemisphere. When it touches the equator, the conditions will be such that the heat will be equally distributed on either hemispheres. Then after northern hemisphere undergoes adiabatic expansion under constant volume and varying pressure. The thermodynamic instability froms over the south asia. This will continue for nearly 30-40 days. As the normal MJO sets a constructive OLR in the indian ocean, a system forms. This system is called Low latitude cyclonic circulation. Which develops its vorticity and normally moves towards North-North east direction and touch burma coast or the arab countries when in arabian sea. The MJO will also does a favour in pulling up the ITCZ from the southern hemisphere. The heat instability setup earlier creates a thermal low at the most heated up desert area. The parts of western rajasthan forms a low of 999mb, which pulls the wind from over 4000kms, I.e from south madagascar. The proper orientation of mascarene high is needed. Suppose any system near the high pressure belt will make a delay in onset. Once the monsoon sets ovet the andaman by may 15th. The LLCC comes to picture. The silent seas will launch a tropical system, which affects the coast of india/ pakistan/ Oman/ bangladesh. If the LLCC moves to oman/pakistan, there will be a small delay in onset of monsoon. Once the monsoonal South east winds crosses equator, the cross-equatorial currents makes a 90°-120° bend and turns the wind to South west. The wind splits into two:
One--The bay of bengal Branch
Two--The arabian sea branch.
These two will meet near the thermal low, provided the anti-Cyclone over the Tibet is strong, to make the winds to turn east over north india. The break period occurs, if there is no supporting parameters like MJO, the inflow of moisture, the increase in pressure at thermal low, the dissipation of anti-Cyclone over Tibet etc.
All the above occurs at the same time and thus results in break period, where most of the precipitation is concentrated near the foot hills of himalayas.
The monsoon takes a specified time to cover entire india. It reaches the thermal low by July 15-19 or sometimes august.
Once the ITCZ moves down, the monsoon retreats, finally there will be the onset of North-east monsoon by october 20-25 over Tamilnadu
