THE ADVANCING MONSOON / SOUTH WEST MONSOON JUNE TO SEPTEMBER

TEMPERATURE CONDITIONS TEMPERATURE ALL OVER THE COUNTRY BEGINS TO FALL AS THE MONSOON RAINFALL INTENSIFIES. THE NORTH – WESTERN PARTS AND DESERT AREAS OF RAJASTHAN HAVE TEMPERATURES REACHING 40 DEGREE CELSIUS.

PRESSURE AND WINDS TEMPERATURES IN NORTH WESTERN PLAINS ARE STILL VERY HIGH AND THEREFORE LOW PRESSURE CONDITIONS ARE POWERFUL ENOUGH TO ATTRACT THE TRADE WINDS OF SOUTHERN HEMISPHERE. THESE SOUTH EAST TRADE WINDS ARE OF OCEANIC ORIGIN. COMING FORM THE INDIAN OCEAN THEY CROSS THE EQUATOR AND ENTER THE BAY OF BENGAL AND THE ARABIAN SEA. AFTER CROSSING THE EQUATOR THEY FOLLOW A SOUTH WESTERLY DIRECTION. THIS IS WHY THEY ARE KNOWN AS SOUTH – WEST MONSOONS.

DIRECTION OF THE SOUTH WEST MONSOON WINDS IT IS INTERESTING TO NOTE THAT THE SOUTH WEST MONSOON WINDS FOLLOW A SOUTH ESTERLY DIRECTION THROUGHOUT THE PENINSULAR PART OF INDIA, BUT THEIR DIRECTION UNDERGOES A CHANGE IN THE INDO-GANGETIC PLAIN WHERE THEY MOVE FROM EAST TO WEST. THE CHANGE IN THE DIRECTION IS DUE TO RELIEF FEATURESAND THERMAL PRESSURE OVER NORTH- WEST INDIA.

RAINFALL IN THE SOUTH WEST MONSOON SEASON THREE-FOURTHS OF THE TOTAL ANNUAL RAINFALL OF INDIA IS RECEIVED DURING THIS SEASON. THE PROGRESS OF THE MONSOON WINDS BEYOND SOUTH KERALA IS IN THE FROM OF TWO BRANCHES – 1. THE ARABIAN SEA BRANCH 2. THE BAY OF BENGAL BRANCH

THE ARABIAN SEA BRANCH THE ARABIAN SEA BRANCH OF THE SOUTH WEST MONSOON STRIKES THE WESTERN COAST OF INDIA IN KERALA ON 1st JUNE. THE WINDWARD SIDE OF THE SAHYADRIS RECEIVES VERY HEAVY RAINS. CROSSING THE WESTERN GHATS, THE WINDS RUN OVER THE DECCAN PLATEAU AND MADHYA PRADESH, CAUSING FAIR AMOUNT OF RAINFALL. THEREAFTER THE WINDS ENTER THE GANGA PLAINS AND MINGLE WITH THE BAY OF BENGAL BRANCH. ANOTHER PART OF THE ARABIAN SEA STRIKES THE SAURASHTRA PENINSULA AND THE KUCCH. IT THEN PASSED OVER WEST RAJASTHAN AND ALONG THE ARAVALLIS, CAUSING ONLY SCANTY RAINFALL. IN PUNJAB AND HARYANA, IT JOINS THE BAY OF BENGAL BRANCH. THESE TWO BRANCHES, REINFORCED BY EACH OTHER, CAUSE RAIN IN THE WESTERN HIMALAYAS.

THE MONSOON BURST THE RAIN BEARING WINDS ARE STRONG. THEY BLOW AT AN AVERAGE SPEED OF MORE THAN 30 KILOMETRES PER HOUR. THE SUDDEN ONSET OF MOISTURE LADEN WINDS IS ASSOCIATED WITH VIOLENT THUNDER, LIGHTNING AND HEAVY DOWNPOUR. THIS SUDDEN ONSET OF RAIN IS TERMED AS MONSOON BURST.

THE BAY OF BENGAL BRANCH OF SOUTH WEST MONSOON THIS BRANCH IS ORIGINALLY DIRECTED TOWARDS THE COAST OF MYANMAR AND PART OF SOUTH-EAST BANGLADESH. BUT THE ARAKAN YOMA RANGE ALONG THE COAST OF MYANMAR IS GOOD ENOUGH TO DEFLECT A BIG CHUNK OF THIS BRANCH, ENABLING IT TO ENTER THE INDIAN SUBCONTINENT. THE MONSOON, THEREFORE ENTERS WEST BENGAL AND BANGLADESH FROM SOUTH AND SOUTH-EAST INSTEAD OF SOUTH WESTERLY DIRECTION. THERAFTER THIS BRANCH SPLITS INTO TWO UNDER THE INFLUENCE OF THE MIGHTY HIMALAYAS AND THE THERMAL LOW [ LOW TEMPERATURE] IN NORTH WEST INDIA.

THE SPLIT IN THE BAY OF BENGALBRANCH ONE BRANCH MOVES WESTWARD ALONG THE GANGA PLAINS REACHINF AS FAR AS PUNJAB PLAINS. THE OTHER BRANCH MOVES UP THE BRAHMAPUTRA VALLEY IN THE NORTH AND NORTH-EAST CAUSING WIDESOREAD RAINS IN THE NORTH-EASTERN INDIA. ITS SUB-BRANCH STRIKES THE GARO AND KHASI HILLS OF MEGHALAYA. MAWSYNRAM, LOCATED ON THE CREST OF THE SOUTHERN RANGE OF KHASI HILLS, RECEIVES THE HIGHEST AVERAGE ANNUAL RAINFALL IN INDIA. CHERRAPUNJI, LOCATED 16 KILOMETRES EAST OF MAWSYNRAM HOLDS THE HIGHEST RAINFALL RECORDS.

MAJOR FEATURES OF THE INDIAN MONSOON MOST OF THE COUNTRY GETS RAINFALL FROM SOUTH- WEST MONSOONS. RAINFALL FROM THE MONSOON WINDS IS VARIABLE AND UNDEPENDABLE. MUSH OF THE RAINFALL IS RECEIVED IN 3 – 4 MONTHS. DISTRIBUTION OF THE RAINFALL IS HIGHLY UNEVEN. INDIAN RAINFALL IS CONTROLLED BY OROGRAPHY, THAT IS MOST OF THE RAINFALL IS CAUSED DUE TO THE OBSTRUCTION OF MOISTURE BEARING WINDS.

TEMPERATE AND TROPICAL CYCLONES TEMPERATE CYCLONES ORIGINATE AND INFLUNCE THE TEMPERATE ZONE. LOW WIND VELOCITY MORE ACTIVE IN WINTER SEASON EXAMPLES ARE THE WESTERN DISTURBANCES THAT CAUSE RAINFALL IN PUNJAB, HARYANA. TROPICAL CYCLONES ORIGINATE AND INFLUENCE THE TROPICAL ZONE HIGH WIND VELOCITY MORE ACTIVE IN SUMMER SEASON EXAMPLES ARE THE CYCLONES THAT ORIGINATE IN BAY OF BENGAL AFFECTING ORISSA, ANDHRA PRADESH DURING JUNE- JULY.

SUMMER AND WINER MONSOONS SUMMER MONSOONS WINTER MONSOON ARE CALLED SOUTH-WEST MONSOONS OR ADVANCING MONSOONS BLOW FROM JUNE TO SEPTEMBER BLOW FROM HIGH PRESSURE OVER SEA TO LOW PRESSURE OVER LAND. BRING RAIN TO GREATER PART OF INDIA. BLO IN TWO BRANCHES – ARABIAN SEA & BAY OF BENGAL BRANCH. CHARACTERISED BY OPPRESSIVE HEAT & HUMIDITY KNOWN AS OCTOBER HEAT. ARE CALLED NORTH-EAST MONSOONS OR RETREATING MONSOONS BLOW FROM DECEMBER TO FEBRUARY. BLOW FROM HIGH PRESSURE OVER LAND TO LOW PRESSURE OVER SEA. BRING LITTLE RAIN ONLY TO TAMIL NADU COAST. HAVE ONLY ONE BRANCH CHARACTERISED BY PLEASANT SEASON WITH LOW TEMPERATURE, LOW HUMIDITY AND CLEAR SKIES.