1. CLIMATE OF INDIA # FACTORS AFFECTING THE CLIMATE OF INDIA # THE FOUR DISTINCT SEASONS IN INDIA AND THEIR CHARACTERISTICS #MAJOR FEATURES OF THE INDIAN MONSOON #COMPARISION OF THE NORTH EAST AND SOUTH WEST MONSOONS # COMPARISION OF THE ARABIAN SEA BRANCH AND THE BAY OF BENGAL BRANCH OF MONSOON WINDS # THE LOCAL WINDS # DISTRIBUTION OF RAINFALL IN INDIA # DIFFERENCE BETWEEN THE TROPICAL CYCLONES AND THE TEMPERATE CYCLONES

2. PART I - FACTORS AFFECTING THE CLIMATE OF INDIA & WINTER SEASON

3. FACTORS AFFECTING THE CLIMATE – 1.LATITUDE 2. HIMALAYAN MOUNTAINS 3.DISTANCE FROM SEA 4. ALTITUDE 5. CONDITIONS IN SURROUNDING REGIONS 6. JET STREAMS 7.VARIED RELIEF

4. LATITUDINAL EXTENT OF INDIA 8 degree N to 37 degree N. Southern part in tropical zone and northern part in sub-tropical zone. Temp high in summer all over except in high altitudes. Temp below freezing point in Himalayan belt / low temp in northern plains in winter. Overall hot tropical climate.

5. T he Himalayan mountains protect India from the cold Siberian winds from the north, thus responsible for the tropical climate of India. The Himalayas also obstruct the south westerly monsoons thereby causing heavy rainfall in the Northern plains of India.

6. SOUTH WESTERLY WINDS AND THE HIMALAYAS The southwest summer monsoon is attracted to India by a low pressure area that's caused by the extreme heat of the Thar Desert and adjoining areas, during summer. Moisture-laden winds from the Indian Ocean come to fill up the void, but because they can't pass through the Himalaya region, they're forced to rise.Thar Desert The gain in altitude of the clouds results in a drop in temperature, bringing about rain. When the southwest monsoon reaches India, it splits into two parts around the mountainous region of the Western Ghats in south-central India. One part moves northwards over the Arabian Sea and up the coastal side of the Western Ghats. The other flows over the Bay of Bengal, up through Assam, and hits the Eastern Himalaya range.

7. DISTANCE FROM THE SEA : The peninsular character of southern India has its climatic influence. With a long coastline, we have a large coastal area enjoying equable influence of the sea. However, a large area in the northern part of India lies too far away from the sea. Here the climate is continental. Places located away from the coast have a far larger daily and seasonal range of temperature.

8. ALTITUDE : Higher altitude is responsible for lower temperatures in northern mountainous regions as well as the peninsular plateau region. Hill stations of the Peninsular plateau region, such as Ootacamund or Ooty, though quite close to the Equator, have a cool climate. However, the temperatures in the Himalayan region are still lower due to both a greater distance from the Equator and a higher altitude. That is why the hill stations are numerous in the Himalayas.

9. JET STREAMS THEY HAVE AN IMPACT ON THE ARRIVAL OR DEPARTURE OF THE MONSOON. What is the Jet Stream? The jet stream is a band of wind that blows horizontally through the upper layers of the troposphere, generally from west to east, at an altitude of 20,000 - 50,000 feet (6,100 - 9,144 meters), or about 7 miles (11 kilometers) up. A jet stream develops where air masses of differing temperatures meet. For this reason, surface temperatures determine where the jet stream will form. The greater the difference in temperature, the faster the wind velocity inside the jet stream. Jet streams can flow up to 200 mph (322 km/h), are 1000's of miles long, 100's of miles wide.

10. HOW ARE JET STREAMS FORMED? Air warmed in the tropics around the equator fuels the jet stream as it rises. Hitting the tropopause it is drawn toward the colder air at the north and south poles. JET STREAMS HAVE AN IMPACT ON THE ARRIVAL AND DEPARTURE OF THE MONSOONS IN INDIA. DETAILS OF HOW THE JET STREAMS AFFECT THE MONSOONS NOT TO BE ASSESSED. HOWEVER THE INFORMATION IS PROVIDED IN THE FOLLOWING SLIDE IN DETAIL.

11. JET STREAMS IN INDIA There are different jet streams and in respect of the climate and monsoons of India it is the Subtropical Jet Stream (STJ) and the countering easterly jet that are most important. As the summertime approaches there is increased solar heating of the Indian subcontinent, this has a tendency to form a cyclonic monsoon cell situated between the Indian Ocean and southern Asia. This cell is blocked by the STJ. As long as the STJ is in this position the development of summer monsoons is inhibited. During the summer months the STJ deflects northwards and crosses over the Himalayan Range. With the STJ out of the way the subcontinental monsoon cell develops very quickly indeed, often in a matter of a few days. Warmth and moisture are fed into the cell by a lower level tropical jet stream which brings with it air masses laden with moisture from the Indian Ocean. As these air masses are forced upward by north India’s mountainous terrain the air is cooled and compressed, it easily reaches it’s saturation vapour point and the excess moisture is dissipated out in the form of monsoon rains. The end of the monsoon season is brought about when the atmosphere over the Tibetan Plateau begins to cool, this enables the STJ to transition back across the Himalayas. This leads to the formation of a cyclonic winter monsoon cell typified by sinking air masses over India and relatively moisture free winds that blow seaward. This gives rise to relatively settled and dry weather over India during the winter months.

13. VARIED RELIEF INFLUENCING THE CLIMATE OF INDIA The Western Ghats rise abruptly like a wall from the Western Coastal Plains more or less parallel to the coastline. This wall like mountain range forces the moisture laden South west monsoons from the Arabian Sea to ascent the slope thereby giving heavy rainfall in the West Coastal Plain and still heavier rainfall on the western slopes of the Western Ghats., i.e., the windward side of the mountain range.

14. The winds have to descend the slope of the Western Ghats after crossing the crest of the Ghats. In this process their temperature rises and their humidity decreases. Therefore, they cause little rainfall and the area east of the Ghats is called the leeward side or the rain shadow region. Thus while Mumbai on the west coast records heavy rain, Pune [ central Maharashtra] on the leeward side receives only 50 cm of rainfall during the monsoon season.

15. CYCLE OF SEASONS THE FOUR SEASONS OF INDIA – 1. THE COLD WEATHER SEASON [ NOVEMBER TO MARCH ] 2. THE HOT WEATHER SEASON [ MARCH TO MAY ] 3. THE RAINY SEASON / SOUTH-WEST MONSOON / ADVANCING MONSOON [ JUNE TO SEPTEMBER ] 4. THE RETREATING MONSOON SEASON [ OCTOBER AND NOVEMBER ]

16. THE COLD WEATHER SEASON MAJOR CHARACTERISTICS – CLEAR SKY PLEASANT WEATHER LOW TEMPERATURE LOW HUMIDITY COOL AND SLOW NORTHERN WINDS

17. TEMPERATURE VARIATION IN NORTH AND SOUTH THE ISOTHERM OF 20 DEGREE C RUNS NEARLY PARALLEL TO THE TROPIC OF CANCER. IT DIVIDES INDIA INTO NORTHERN AND SOUTHERN PARTS CLIMATICALLY. TO THE SOUTH OF THE ISOTHERM TEMPERATURE ALWAYS REMAINS ABOVE 21 DEGREE CELSIUS. TO THE EXTREME SOUTH TEMPERATURE IS ABOVE 25 DEGREE CELSIUS. TO THE NORTH, THE MEAN TEMPERATURE IS BELOW 21 DEGREE CELSIUS. GANGA PLAINS HAVE TEMPERATURE GOING LOW FROM 12.5 TO 17.5 DEGREE CELSIUS. [ JANUARY – COLDEST MONTH]

18. PRESSURE CONDITIONS IN COLD WEATHER SEASON/ WINTER NORTHERN PLAINS HAVE LOW TEMPERATURES THEREFORE THEY HAVE HIGH PRESSURE. WINDS BLOW FROM HIGH PRESSURE AREA OF NORTH WEST TO LOW PRESSURE AREA OF SOUTH EAST. NORTH EAST TRADE WINDS PREVAIL OVER THE COUNTRY, BLOWING FROM LAND TO SEA OVER MOST PART OF THE COUNTRY. AS THESE WINDS BLOW FROM LAND TO SEA, THEY DO NOT CAUSE MUCH RAINFALL.

19. QUESTION – WHY DON’T THE NORTH EAST TRADE WINDS CAUSE MUCH RAINFALL ? [ ANSWER ON THE PREVIOUS SLIDE]

20. WESTERN DISTURBANCES CYCLONIC DEPRESSIONS CALLED AS THE WESTERN DISTURBANCES ORIGINATE OVER THE MEDITERRANEAN SEA. THEY TRAVEL EASTWARDS ACROSS WEST ASIA, IRAN, AFGHANISTAN AND PAKISTAN, BEFORE THEY REACH THE NORTH WESTERN PARTS OF INDIA. ON THEIR WAY, THEIR MOISTURE CONTENT INCREASES WHEN THEY BLOW OVER THE CASPIAN SEA IN THE NORTH AND THE PERSIAN GULF IN THE SOUTH. THE WESTERN DISTURBANCES CAUSE LIGHT RAINFALL IN INDIA, WHICH IS BENEFICIAL TO WHEAT, RABI CROP. THEY CAUSE HEAVY SNOWFALL IN THE HIMALAYAS AND THIS SNOW SUSTAINS THE FLOW OF WATER IN THE HIMALAYAN RIVERS DURING SUMMER.

21. QUESTION – WHAT ARE THE WESTERN DISTURBANCES? HOW ARE THEY BENEFICIAL TO INDIA?

22. PRECIPITATION IN WINTER MONTHS IN WINTER, THE WINDS BLOW FROM LAND TO SEA AND THEREFORE DO NOT CAUSE MUCH RAINFALL. THESE WINDS PICK UP SOME MOISTURE WHILE CROSSING THE BAY OF BENGAL AND CAUSE RAINFALL IN TAMILNADU, SOUTH ANDHRA PRADESH, SOUTH-EAST KARNATAKA AND SOUTH- WEST KERALA. NORTH EASTERN PARTS OF INDIA ALSO RECEIVE RAINFALL IN THE WINTER MONTHS.