By Bidisha Saha, Dipti Yadav, Kumar Kunal: After rousing the Arabian Sea for over a week, Cyclone Biparjoy made landfall on the coastline of northwestern India and southern Pakistan on June 15. The cyclonic storm spent eight days in the sea, moving north at a slow speed until it took an eastern turn on June 14.
Mrutyunjay Mahapatra, the Director General of the India Meteorological Department (IMD), told India Today, "Several factors impact the intensity of a cyclone that includes heat content, rotational power and humidity. Normally, the eastern part of the Arabian Sea is hotter and hence the cyclone is sustained long, due to enough heat and humidity feeding it continuously."
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Mahapatra attributed the longevity of Cyclone Biparjoy to the larger sea surface area of the Arabian Sea. He said, “The Arabian Sea has a larger area in comparison to the Bay of Bengal and hence the cyclones are longer. Even in 2019, there was a super cyclone called Kyarr in the Arabian Sea which lasted nine days and 15 hours. Biparjoy has a duration of almost 11 days but it is not unusual.” He added that Biparjoy’s speed was really slow and hence it lasted longer.
ALSO READ | Cyclone Biparjoy weakens as it closes in on Gujarat, over 74,000 evacuated, Navy on standby
UNUSUALLY WARM WATERS
Climate scientist Roxy Mathew Koll at the Indian Institute of Tropical Meteorology noted that the sea surface temperature in the Arabian Sea ranged from 31 to 32 degrees Celsius over the past week, that’s two to four degrees Celsius above the average. A rule of thumb in climatological science is that ocean temperatures should be above 27 degrees Celsius for the tropical cyclone to persist. This increase in temperature aided in maintaining a low-pressure area in the sea, which further intensified Cyclone Biparjoy, according to a report published by NASA’s Earth Observatory.
“Biparjoy is an example of how climate change — especially warming in the upper ocean — is contributing to cyclones moving slower and lasting longer,” Raghu Murtugudde, a visiting professor at the of IIT-Bombay, as quoted in the report.
Between June 6 and 7, the sustained wind speed of Cyclone Biparjoy increased from 55 km/h to 139 km/h, and between June 9 and 10, its wind speed increased from 120 km/h to 196 km/h. This made it a category 3 storm.
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SLOW MOVEMENT
Another salient cause behind the long life of this cyclonic storm was its sluggish pace — an average of five km/h initially for the first two days and then remaining “practically stationary” for the next five days over the Arabian Sea, as per IMD. In its latter stage, the cyclonic storm made a turn and moved at a speed of eight km/h.
India Today’s OSINT team spoke to weather researcher Dr Vineet Kumar Singh to understand the unhurried nature of this cyclone. As per his analysis, the low-pressure area of the cyclonic storm was centered between two typical high-pressure zones acting as anticyclones. One of the high-pressure areas was lying in central India to the east of the cyclone with winds moving in the clockwise direction. This acted as an indicator to move the cyclone from the south to the north direction.
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The other high-pressure zone was persistent to the west of the cyclone over the Arabian peninsula, including Pakistan and the other adjoining areas of the Middle East. Lying near the western periphery of the high-pressure zone, the winds were moving from north to south. These were the two compensating forces that restricted the movement of the cyclone, as per the climate expert.
The movement of the cyclones is regulated by the winds that lie on the upper zones in the atmosphere, i.e. five to 10 km above the land surface (mid to upper level). With an Accumulated Cyclone Energy (ACE) of 24.8, Cyclone Biparjoy tops the list of cyclones in the North Indian Ocean history.
A 2021 study, conducted by climatologists at the Indian Institute of Tropical Meteorology, highlighted a significant trend of increasing intensity, frequency, and duration of cyclonic storms over the Arabian Sea region.
“The increase in the duration of tropical cyclones in the Arabian Sea is associated with an increase in mid-level relative humidity and column-averaged moist static energy, which is significantly correlated to an increase in sea surface temperatures and tropical cyclone heat potential in the basin,” the study noted.
Another factor contributing to the longer duration of tropical cyclones is the origin of the cyclones in lower latitudes.
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ANALYSING 10-DAY TRAJECTORY OF BIPARJOY
June 5 - IMD detected the genesis of the cyclonic circulation over the Southeast Arabian Sea which extended up to 5.8 km above mean sea level.
June 6 - In the next 24 hours, a Low Pressure Area (LPA) developed about 920 km west southwest of Goa, and 1,120 km south southwest of Mumbai over the southeast Arabian Sea. By 11:30 IST, the LPA intensified into a Deep Depression forecasted to move northwards and intensify into a cyclonic storm.
Over the next 6 hours (5:30 IST), the cyclonic storm Biparjoy over the east-central Arabian Sea was formed, likely to move northwards and intensify into a severe cyclonic storm.
June 7 - Biparjoy now hauled over the east-central and adjoining southeast Arabian Sea and developed into a severe cyclonic storm. The same day, it developed into a very severe cyclonic storm that moved north-northeast with a speed of 5 km/h with sustained wind speed of 118 km/h and gusts up to 166 km/h.
June 8 - IMD forecasted that in the next 3 days, Biparjoy could further intensify. The government made preparations to conduct evacuation operations at a massive scale from the Karnataka-Goa-Maharashtra coast as the cyclone is due to barrel through parts of India's Gujarat state and Sindh province in Pakistan.
June 9 - IMD detected a Well Marked Low (WML) Pressure Area persisting over the north-east Bay of Bengal off the Myanmar Coast.
June 10 - While lying only 600 km west-southwest from Mumbai, Cyclone Biparjoy was forecasted to reach near the city of Karachi in Pakistan coastline by June 15 with wind speed of approximately 90 km/h.
June 11 - At 23:30 IST, IMD forecasted that storm would intensify even further and move across the adjoining Saurashtra and Kutch coast. At 08:30 IST Cyclone Biparjoy developed into an extremely severe cyclonic storm moving north-eastwards with an average speed of 8 kilometre per hour, and sustained wind speed of 125-135 km/h, gusting to 150 km/h.
June 12 - Biparjoy was predicted to cross Mandvi in Gujarat and Karachi in Pakistan by noon on June 15. Later on the same day, it was predicted that this extremely severe cyclonic storm would fall near Jakhau Port in Gujarat.
June 13 - An Orange message was circulated by IMD as Biparjoy weakened into a very severe cyclonic storm, likely to cross Saurashtra and Kutch near Jakhau Port.
June 14 - Storm surge warning was circulated with astronomical tide along the low-lying areas of Kachchh, Devbhumi Dwarka, Porbandar, Jamnagar and Morbi districts. Tide levels are forecast to be six to 10 feet above normal in areas near and just south of the cyclone’s center.
A flood hazard map of IMD predicted 0.50 to 1 metre flood (Moderate) would occur over Narela, Alipur, Dwarka, Loni Dehat, Ghaziabad, Hansi, Meham, Sonipat, Rohtak, Sahranpur, and Kharkhoda.
June 15 - Landfall process commenced with cyclonic weather and heavy rainfall over Nalia, Bhuj and Jakhau port in Gujarat.
After the storm moves inland it is expected to quickly weaken as it accelerates into northern India.
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