Why Cyclones Rarely Form in August in India ? cylclone asna in news

Cyclone Asna is rare for a number of reasons, including: 

1) Land-born origin

Cyclone Asna originated over land in Rajasthan, which is unusual for cyclones that typically originate in the ocean. 

2) August formation

Cyclone Asna formed in August, which is rare for the Arabian Sea, where cyclones are less common during this month. 

3) Monsoon season

Cyclones rarely intensify into cyclones during the June-September monsoon season due to strong monsoon currents and other ocean factors. 

4) Number of cyclones in the Arabian Sea

Cyclone Asna is only the fourth cyclone to develop in the Arabian Sea in August since 1944.

Cyclone formation in the Arabian Sea is rare in August due to a combination of factors related to atmospheric and oceanic conditions. Here's why:

1. Monsoon Season Influence

Southwest Monsoon Dominance: August falls in the middle of the Southwest Monsoon season (June to September) in the Indian subcontinent. During this period, the strong monsoon winds and associated weather systems dominate the Arabian Sea, which discourages the development of cyclones. The monsoon trough (a low-pressure area extending across the region) stabilizes the atmosphere, reducing the chances of cyclone formation.

2. High Wind Shear

Strong Vertical Wind Shear: Wind shear refers to the change in wind speed and direction with height. During the monsoon season, the Arabian Sea experiences high vertical wind shear, which disrupts the vertical structure of a developing cyclone. Cyclones require low wind shear to organize and intensify, but the strong monsoon winds create conditions unfavorable for cyclogenesis (cyclone formation).

3. Sea Surface Temperatures (SST)

Cooling Due to Monsoon Winds: The strong monsoon winds cause upwelling (the rise of cooler water from the deep sea) and mixing of the sea surface, which leads to lower sea surface temperatures (SSTs). Cyclones need warm SSTs (typically above 26.5°C) to gain energy. The cooler SSTs during August reduce the potential for cyclogenesis.

4. Moisture Availability

High Moisture Content but Misaligned: While the monsoon brings a lot of moisture to the region, it is often not concentrated in a way that supports cyclone development. The widespread rainfall and cloud cover associated with the monsoon spread the moisture over a large area, which dilutes the potential energy needed for cyclone formation.

5. Position of the Intertropical Convergence Zone (ITCZ)

ITCZ Shift: The Intertropical Convergence Zone (ITCZ), a key factor in tropical cyclone formation, shifts northwards during the monsoon season. This shift means that the conditions necessary for cyclone formation are not usually present over the Arabian Sea during August.

Due to these factors, cyclones are more likely to form in the Arabian Sea during the pre-monsoon (May-June) and post-monsoon (October-November) periods when the atmospheric and oceanic conditions are more favorable.