Recently, the growing frequency of tropical cyclones in Arabian Sea has surprised many climatologists and scholars. The origin of cyclones “Kyarr” and “Maha” within a week is signalling something abnormal that deserves greater attention. We have also saw furry of nature in the form of cyclone “Tautae” on Indian western coast. Likewise, in this blog, “Growing cyclones in Arabian sea” I am going to explain some of reasons responsible for the ongoing natural calamities.
Understanding tropical cyclone?
Among all types of cyclones, tropical cyclone is the most disastrous climatic phenomenon generally occurs around the low pressure in the tropical regions of the oceanic water. For this, temperature, humidity, and low pressure area are the most important conditions.
Tropical cyclone uses moist air as a fuel for the typical climatic engine.
As usually, such systems are being formed in the proximity of equator and coastal regions. In the world, these are known by different names as per the regional identities like, hurricane, tornado, and typhoon etc.
According to the intensity and severity of cyclones, cyclone rating agencies based on the parameters of WMD, classify all originating cyclones in the five categories.
Recent Kyarr and Maha are classified as 4th and 3rd categories. For the North Indian Ocean, Indian meteorological department uses seven categories to rate the cyclone in question.
Meaning and examples of tropical cyclones
Funnel shaped meteorological phenomenon accompanied by gusty rotating winds with dark cumulonimbus clouds and heavy thunderstorms is generally known as tropical cyclone. Geographically, they can only originate, as well as sustain in the tropical and subtropical oceanic regions. Here, I’m going to describe meaning and examples of tropical cyclone.
Meaning and explanation of tropical cyclone
Tropical cyclone is the finest manifestation of land sea interaction by the means of atmospheric elements such as winds, heat, water vapour etc.
As a meaning, “It is a meteorological system of rotating gusty winds around low pressure accompanied by huge cumulonimbus clouds and thunderstorms”.
“Explaining Major determinants of tropical cyclone”
In order to originate and develop a catastrophic cyclone, certain conditions are need to be fulfilled. These are,
- Tropical and subtropical oceanic regions, more than 26 degree surface water temperature,
- Vast oceanic regions,
- Adequate relative humidity,
- Atmospheric instability,and
- Sufficient Coriolis force.
1. Tropical and subtropical oceanic regions
These regions have sufficient temperature and humidity to intensify the process of cyclogenesis.
Second, easterly winds are predominant in these regions. And, equatorial regions are devoid of Coriolis force and mid-latitude regions have opposite factors.
Hence, only tropical and subtropical oceanic regions are conductive to form such phenomenon.
2. Coriolis force effect
As I stated earlier that tropical cyclone is funnel shaped meteorological system. So, spinning force is indispensable to form such rotating structure.
Coriolis force is absent in the equatorial region but enough in the tropical zones. As a result, it gives spinning momentum for high velocity winds entering in the low pressure area.
3. Large oceanic regions
Whenever such cyclones enter in the land, frictional force drastically reduces the force of winds. Consequently, the intensity of cyclones quickly decreases. For this reason, large oceanic regions are highly essential to maintain required intensity for rotating gusty winds.
4. Adequate humidity
High humidity plays an important role in the formation of convection currents and cumulonimbus clouds. Both act as a prerequisite conditions in the clouds formation and thunderstorms.
And, we know that high humidity is the product of high temperature of vast oceanic surface in the tropical zones.
Examples of tropical cyclone
Cyclones in the tropical and subtropical oceanic regions are,
- Hurricane Tropical Storms
- Tornadoes
- Typhoons,
- Willy-Willy, etc.
For better insight, mere meaning and examples of tropical cyclone is not enough. Therefore, proper understanding of determinants of tropical cyclone is equally important.
Causes of cyclogenesis in the North Indian Ocean
Humid and moist air is the driving force behind the cyclonic phenomenon. And, Inter-tropical converging belt that originates in the north of equator in the summer season, is highly instrumental in the onseting of monsoon over the Indian subcontinent.
What is ITCZ (Intercontinental tropical conversing zone)
ITCZ is a (Intertropical Converging Zone) low pressure belt which migrates seasonally in the north and south of the equator.
Logically, it crosses twice in a year – with the advancement of summer and with the beginning of retreat.
Therefore, the ideal conditions for the formation of cyclones in the North Indian Ocean get developed in the month of may/June and October/Nov.
In the Indian subcontinent, data suggests that the frequency of cyclones has been observed with the advancement and retreating phases of the monsoon.
Why is cyclogenesis absent during the monsoon period?Though the effects of tropical cyclone are beyond the managing capacity of human beings and sound so destructive, it requires wind free atmosphere at the higher level (or low wind shear) to develop and strengthen it properly.
Otherwise, in case of stronger wind at the higher level in the form or jet stream or monsoonal wind, it cannot sustain longer and gets easily disrupted. If the wind shear is strong, the dry air replaces moist, humid air which is highly essential for the cyclonic phenomenon.
Monsoon effect on formation of tropical cyclones
During monsoon, the strong wind prevents the formation of required conditions in the North Indian Ocean. Hence, the cyclogenesis in the North Indian Ocean during monsoon remains absent. This is the reason why the frequency of cyclones is mainly observed in the pre-monsoonal months, as well as during retreating phases.
In the absence of strong wind generated by monsoonal phenomenon, tranquillity returns favouring cyclogenesis in the May and October months.
Why the difference in cyclogenesis in the Bay of Bengal and Arabian Sea?In the Arabian Sea compare to Bay of Bengal, the wind shear phenomenon is stronger so it inhibit the formation of ideal conditions for cyclogenesis.
Apart from this, the dry air that blows from the western Thar Desert prevents the formation of cyclones as the moist, humid air act as fuel to develop, sustain and strengthen the tropical cyclones.
Impacts of global climate change on growth of tropical cyclones in Arabian sea
Moreover, the global climatic changes have also profound impacts on the formation. Whereas, in the Bay of Bengal the conditions are opposite of the Arabian Sea. These are some reasons that make the difference between Arabian Sea and Bay Of Bengals in terms of cyclogenesis.
Then, why the frequency of cyclones in the Arabian Sea? The concrete and concluding evidences are yet to be recognized about the recent growing cyclones in the Arabian Sea, but the common consensus is gaining momentum in favour of impacts of human induced climate change.
In the summer season, in the region of Marathwada, as well as other parts of the Maharashtra, Karnataka, and other western Indian states were reeling under unbearable drought and water scarcity problem and now these are the same region which are being washed away by the heavy rains and catastrophical unseasoned cyclones.
The abnormal extremity of droughts and devastating floods are the clear-cut manifestation of impacts of climate change and for that we need to prepare.
Undoubtedly, in the agriculturally predominant regions of the developing countries, such impacts of climate change have greater affecting capacity.
Recent incidents of tropical cyclones in Arabian sea
Recently, in the Maharashtra and other western states of India where kharif crops were on the verge of ripping, the Kyarr and Maha cyclones damaged the entire standing crops, is self-evident.
Here whom to blame? Nature, human ignorance, or procrastination…
But, in the coming days, one thing is going to be inevitable and that is unpredictability of climate, as well as nature. This is all about the rising tropical cyclone in Arabian sea.
Elements of weather and climate
Climate change causes and impacts
Understanding capital formation