Mechanism of Monsoon
Onset & Withdrawal · The Trough · Jet Streams
MICRO-REALM 01
The Onset (Burst)
- SUDDEN INCREASE IN RAINFALL
- AROUND JUNE 1ST
- HITS KERALA COAST FIRST
MICRO-REALM 02
The Advance
- SPLITS INTO TWO BRANCHES
- ARABIAN SEA & BAY OF BENGAL
- COVERS INDIA BY MID-JULY
MICRO-REALM 03
Arabian Sea Branch
- HITS WESTERN GHATS PERPENDICULAR
- HEAVY OROGRAPHIC RAINFALL
- PASSES OVER SAURASHTRA/KACHCHH
MICRO-REALM 04
Bay of Bengal Branch
- DEFLECTED BY ARAKAN YOMA
- ENTERS WEST BENGAL & ASSAM
- FUNNELED INTO MEGHALAYA (MAWSYNRAM)
MICRO-REALM 05
The Merger
- BOTH BRANCHES MEET
- OVER PUNJAB & HARYANA PLAINS
- BRINGS RAIN TO NW INDIA
MICRO-REALM 06
Monsoon Break
- DRY SPELLS OF A FEW DAYS/WEEKS
- JULY AND AUGUST
- CAUSED BY TROUGH SHIFTING TO HIMALAYAS
MICRO-REALM 07
The Withdrawal
- GRADUAL RETREAT PROCESS
- BEGINS SEPTEMBER IN NW INDIA
- CLEARS SOUTHERN TIP BY DECEMBER
MICRO-REALM 08
Monsoon Trough
- AXIS OF LOW PRESSURE
- OSCILLATES NORTH AND SOUTH
- DICTATES SPATIAL DISTRIBUTION OF RAIN
MICRO-REALM 09
STWJ Withdrawal
- SUB-TROPICAL WESTERLY JET
- MIGRATES NORTH OF HIMALAYAS IN SUMMER
- ITS DEPARTURE ALLOWS MONSOON ONSET
MICRO-REALM 10
Tropical Easterly Jet
- EAST TO WEST UPPER AIR FLOW
- STEERS MONSOON DEPRESSIONS
- 14°N LATITUDE IN PENINSULA
MICRO-REALM 11
Somali Jet
- LOW-LEVEL CROSS-EQUATORIAL WINDS
- ACCELERATES OVER ARABIAN SEA
- PUSHES MOISTURE VIGOROUSLY TO INDIA
MICRO-REALM 12
Monsoon Depressions
- LOW PRESSURE VORTICES
- FORM IN HEAD OF BAY OF BENGAL
- TRAVEL INLAND ALONG THE TROUGH