Tag: Meteorology and Earth Sciences

In this article, we will discuss The Hot Weather Season in India. So, let’s get started.

The Hot Weather Season in India

The north Indian region experiences a well defined hot weather season from mid-March to mid-June. With the northward march of the sun towards the Tropic of Cancer after the vernal Equinox, the temperature begins to rise. Thermal heating over north-western India gradually establishes a thermal “low’ at the surface but, while the jet stream remains south of the Himalayas, it maintains its dynamic anticyclone aloft over Afghanistan and the borderland of Pakistan. This “lid” of subsiding warming dry air prevents the surface thermal “low” from having sufficient effect as a lifting agent to carry air aloft and so to bring about precipitation.
At the advent of March, the temperature starts rising abruptly. By April, the Peninsular regions
south of the Vindhyan Range heat up with mean maximum temperature of 40℃. In May, the mean maximum temperature reaches 42°C in Rajasthan, Delhi, west Uttar Pradesh, south Punjab, Jammu and Haryana.

Temperature exreeding 54℃ was recorded at Sri Ganganagar in 1967. At some places, particularly in north-western India, day temperature may be as high as 45℃ or 47℃. The mean minimum daily temperature in May also remains quite high being about 26°C at Delhi and Jaipur. The temperature in the eastern states of India and in the hilly regions in the month of May is generally cool and invigorating the minimum average in Shillong being 15°C and 17°C in Kohima.

In the month of April the 30°C isotherm of average temperature encloses a vast area of the
country between 10°N and 26°N latitudes (except the west coast and the hilly states of north-east India). The diurnal range of temperature ranges between 5℃ and 6℃ in coastal areas, but reaches 15°-20°C in the interior parts of the country and in the north-west Satluj Ganga Plains.
Being a transitional season between the north-east and the south-west monsoon (rainy season), it is characterised by unstable air pressure and wind circulation. With the northward movement of the sun, the low pressure area also moves from south-east to north-west. It finally settles over north-western India in the end of May or early part of June. the pressure generally increases towards south in the neighbouring sea. The general direction of winds is from north-west and west in north-western India; from south-west in the Arabian Sea and the adjoining coasts. The tornado-like dust storms of Punjab, Haryana, and western Uttar Pradesh, the hot winds (Loo) in western India, the Norwesters (Kalbaisakhis) of West Bengal are the characteristics of summer season.

During summer season, the sun is scorching and the relative humidity is generally below
30%, occasionally reaching below 10%. The total rainfall of the season is below 2 cm in Rajasthan, Gujarat, Madhya Pradesh; between 5 and 15 cm in the sub-montane region of Uttarakhand, Himachal Pradesh, Punjab, Uttar Pradesh, Bihar and Odisha; and between 15 and 25 cm in the Malabar coast and over 50 cm in Assam, Meghalaya, Mizoram, and Nagaland. The rains caused by thunderstorms in Karnataka are called as “Cherry Blossoms” (where these are beneficial for coffee plantation) and elsewhere in south India as “mango showers”.

In this article, we will discuss Winter Season in India. So, let’s get started.

Winter Season in India

The cold weather season in the greater parts of India begins in the later part of November in the north, and by the beginning of December in the rest of the country. The cold weather season is characterised by out-flowing winds, dry and stable air, and clear skies. There develops a high pressure (anti-cyclone) area over north India, and a north-westerly flow prevails down the Indus and Ganges Valleys. During this season the southern branch of the subtropical jet stream is positioned over northern India. The middle latiude westerlies reach down to the surface north of about 25°N. South of this latitude the general movement of air is from the north-east. This north-easterly wind is called the winter monsoon. In Peninsular India, the general direction of wind is from east to west. Because of its trajectory over the Bay of Bengal, the easterlies are full of moisture and yield some precipitation along south-east coastal regions.
During winter season there is a general decrease in temperature from south to north. The
isotherms run almost parallel to the latitudes. The 18° C isotherm for the month of January runs in a east-west direction through the middle of the country, connecting the Tapi estuary in the west and the Mahanadi delta in the east .
In the month of January, the north-western parts of the Great Plains of India (Punjab, Haryana,
western Uttar Pradesh, and Rajasthan) experience less than 15°C mean monthly temperature. The night temperature in the plains of Punjab, Haryana, and Rajasthan (Amritsar, Hissar, and Jodhpur) Occasionally reads below the freezing point, producing ground frost condition. Often, there is a decrease of more than 6°C in the mean temperature, resulting into cold wave in the northern plains of India. In south India, the isotherms tend to bend to the south and run almost parallel to the coast. The western coast is warmer than that of the eastern coast by about 2℃. The diurnal range of temperature is about 15℃ in the Great Plains and only abut 5℃ in the coastal areas of the Peninsula. January is the coldest month in india, especially in northern India. Peninsular India, however, does not have a well defined cold weather season. The mean maximum temperature for the month of January at Thiruvananthapuram and Chenni reads 31℃ and 30℃, respectively.

A characteristic feature of the cold weather season is the inflow of western disturbances originating from the Mediterranean Sea. The frequency of these disturbances is 4 to 6 per month between December, January and February. In north-western region of the subcontinent, winter precipitation is caused by the depressions that are associated with the westerly disturbances moving out from the Mediterranean Sea. The cold weather precipitation, though small, is highly beneficial to Rabi crops. Besides, snowfall from the western disturbances feed the glaciers of the Western Himalayas. The north-eastern parts of India also get some rainfall during the winter season. Arunachal pradesh, Nagaland, and Assam may get about 50 cm of rainfall during these months.