Cyclone Asna

Cyclone Asna and the deep depression in western India were recently observed due to a rare phenomena and unusual conditions leading to their formation.

About Cyclone Asna and the Deep Depression:

Formation and Development:

• The deep depression, which has been affecting Gujarat with heavy rainfall, would intensify into Cyclone Asna over the Arabian Sea.
• It started as a deep depression over land and will transition into a cyclone over the sea, and such  cyclones usually form over the ocean rather than over land.
• This cyclone is the first to form in August in the North Indian Ocean (NIO) region since 1981 and the first in the Arabian Sea since 1976.
• Historically, there have been only 32 cyclones in the NIO in August and four in the Arabian Sea from 1891 to 2023.
• The configuration of large-scale winds and presence of strong easterly winds over southern India have been crucial in the development of this system.
• The interaction between these winds and convective storms has contributed to the intensification of the deep depression.

Impact:

• Gujarat has seen 48% excess rainfall for the season, which represents a significant increase from 17% excess rainfall.
• The state, particularly the dry regions of Saurashtra and Kutch, has experienced severe flooding due to the sudden and intense rainfall.

Meteorological Analysis:

• Typically, cyclones form over warm ocean waters where there is ample moisture and vorticity. However, this deep depression began over land, which is atypical.
• The unusual behavior of the monsoon winds and a strong monsoonal event known as the Boreal Summer Intra-seasonal Oscillation (BSISO) have played a crucial role in this phenomenon.
• The BSISO involves heat transfer from the Indian Ocean to the Western Pacific, impacting weather patterns.

Low Pressure System & BSISO:

• The relationships between Low Pressure Systems (LPS) and the BSISO involve interactions between large-scale atmospheric patterns and localized weather phenomena.

Low Pressure Systems (LPS):

• An LPS is a region where the atmospheric pressure is lower than that of the surrounding areas, which results in converging winds and often developing clouds and precipitation.
• LPSs are crucial for various weather phenomena, including cyclones, monsoon depressions, and heavy rainfall events.
• They form due to factors like temperature gradients, humidity, and atmospheric instability.
• In the context of monsoon systems, LPSs can be influenced by the convergence of moist air masses and can intensify into more organized systems like tropical cyclones.

Boreal Summer Intra-seasonal Oscillation (BSISO):

• The BSISO is a periodic pattern of atmospheric circulation that occurs in the tropics during the boreal summer.
• It involves the transfer of heat and moisture between the Indian Ocean and the Western Pacific Ocean and affects weather patterns on a timescale of 30-60 days.
• This influences the distribution of rainfall and large-scale wind patterns.
• It can lead to variations in the strength and position of the monsoon trough, which is a region of low pressure associated with the monsoon.

Interaction between LPS and BSISO:

• Active BSISO phases enhance convection and moisture convergence between the Indian Ocean and the Western Pacific, making the atmosphere more favorable for LPS formation.
• The BSISO can shift or strengthen the monsoon trough, which is crucial for LPS formation, creating conditions that support the development of these systems.
• Increased atmospheric instability and moisture lead to intensified convection, causing LPSs to develop more rapidly.
• Its influence can lead to cyclogenesis, where an LPS evolves into a stronger cyclonic system due to the added moisture and heat.

Ref: Source

UPSC IAS Preparation Resources
Current Affairs Analysis	Topperspedia
GS Shots	Simply Explained
Daily Flash Cards	Daily Quiz

Frequently Asked Question: