IMD: Aug was India’s warmest since 1901

Sub: Geo

Sec: Climatology

Context:

The average minimum temperature across India in August was 24.29°C, the highest since records began in 1901. The normal average is 23.68°C.
Persistent cloudy conditions contributed to this temperature increase.

Details:

Multiple favourable weather factors at local, regional, and global levels kept the southwest monsoon active, resulting in a 15.3% surplus rainfall for August.
August experienced six low-pressure systems, one of which developed into a rare cyclone named Asna in the Arabian Sea.
Central and southern peninsular India also recorded their warmest August since 1901, with minimum temperatures exceeding the long-term average.
Southern India had a 6.6% surplus in rainfall, and central India had a 165% surplus.

Contributing Factors to Heavy Rainfall:

The low-pressure systems were responsible for extremely heavy rainfall, especially in Tripura, Rajasthan, and Gujarat in the latter half of the month.
The Madden Julian Oscillation (MJO) also contributed to continuous rainfall, preventing the usual ‘monsoon break’ phase in August.

Overall Monsoon Season Performance:

By the end of August, the country recorded 749 mm of rain for the southwest monsoon season, a 7% surplus.
A comparison of August rainfall from 2019 to 2024 shows a concerning trend of high rainfall deficits in the northeast and northwest regions.

Cyclone Asna:

As per the India Meteorological Department (IMD) Cyclone Asna has formed over the Kutch coast in Gujarat and adjoining areas of Pakistan.
This is the first cyclonic storm in the Arabian Sea in August since 1976.
The name Asna, which means “the one to be acknowledged or praised”, has been given by Pakistan.
Between 1891 and 2023,only three cyclonic storms formed in the Arabian Sea in August (in 1976, 1964, and 1944).

Madden-Julian Oscillation (MJO):

The MJO can be defined as an eastward moving ‘pulse’ of clouds, rainfall, winds and pressure near the equator that typically recurs every 30 to 60 days.
It’s a traversing phenomenon and is most prominent over the Indian and Pacific Oceans.

Phases of Madden-Julian Oscillation:

The MJO consists of two phases: Strong MJO activity often dissects the planet into halves. One half within the enhanced convective phase and the other half in the suppressed convective phase.
- Enhanced rainfall (or convective) phase: winds at the surface converge, and the air is pushed up throughout the atmosphere. At the top of the atmosphere, the winds reverse (i.e., diverge). Such rising air motion in the atmosphere tends to increase condensation and rainfall.
- Suppressed rainfall phase: winds converge at the top of the atmosphere, forcing air to sink and, later, to diverge at the surface. As air sinks from high altitudes, it warms and dries, which suppresses rainfall.
It is this entire dipole structure, that moves west to east with time in the Tropics, causing more cloudiness, rainfall, and even storminess in the enhanced convective phase, and more sunshine and dryness in the suppressed convective phase.

How Does MJO Affect the Indian Monsoon?

The journey of MJO goes through eight phases.
When it is over the Indian Ocean during the Monsoon season, it brings good rainfall over the Indian subcontinent.
On the other hand, when it witnesses a longer cycle and stays over the Pacific Ocean, MJO brings bad news for the Indian Monsoon.
It is linked with enhanced and suppressed rainfall activity in the tropics and is very important for the Indian monsoonal rainfall.

Periodicity of MJO:

If it is nearly 30 days then it brings good rainfall during the Monsoon season.
If it is above 40 days then MJO doesn’t give good showers and could even lead to a dry Monsoon.
Shorter the cycle of MJO, the better the Indian Monsoon. Simply because it then visits the Indian Ocean more often during the four-month-long period.
The presence of MJO over the Pacific Ocean along with an El Nino is detrimental for Monsoon rains.

Source: IE