Tropical cyclones are among the most destructive weather systems. High-speed winds, torrential rainfall and storm surges devastate coastal regions.
Destruction left behind by cyclone Fani. Image: courtesy Sanghmitra
But their influence does not end at the surface. They extend high into the atmosphere. The enormous energy released contained in these storms can, when released, set the atmosphere in motion, generating intense turbulence and vertical air currents that reach several kilometres upward. Under normal conditions, the tropopause acts as a boundary, between the troposphere and the stratosphere, the two lowest layers of the atmosphere. Cyclones can breach this boundary between troposphere and stratosphere. But research has not yet been able to generalise the stratosphere troposphere exchange.
How do atmospheric dynamics change due to the intensity of the cyclone?
Cyclone Fani, one of the most intense cyclones to strike the Odisha coast in 2019, provided scientists with a rare opportunity to observe this process in action. Researchers from the Space Physics Laboratory, the Vikram Sarabhai Space Centre, ISRO, Thiruvananthapuram, and the National Atmospheric Research Laboratory, Gadanki tracked and measured Fani’s impact on the upper troposphere.
From April 29 to May 3, 2019. the researchers tracked the Fani’s atmospheric effects as it moved through the Bay of Bengal towards their observation facility. The researchers used the newly upgraded Advanced Indian Mesosphere-Stratosphere-Troposphere Radar, a 53 MegaHertz pulse Doppler radar operating in active aperture mode at Gadanki, as the core instrument of their study.
The researchers programmed the radar to scan continuously in a 360° sweep. They operated the system simultaneously in two distinct modes: one profiled the winds, and the other scanned the volume of air mass.
To obtain vertical profiles of physical and chemical parameters in the upper atmosphere, they launched GPS-based radiosondes and other instruments on balloons. Every day from 22 April to 14 May, 2019 they launched balloons to investigate the dynamics constituents of the troposphere and stratosphere.
On the key days of the storm’s transit, 30 April 30 and 1 May, 2019, the researchers integrated two ozonesondes with the radiosondes to measure high-resolution profiles of the ozone mixing ratio. To contextualize the vertical profiles, they gathered surface meteorological data and surface ozone concentrations.
They also used outgoing longwave radiation and cloud imagery at 30-minute intervals from the geostationary INSAT-3DR satellite to verify the presence of deep convective clouds directly over the radar. From the Indian Monsoon Data Assimilation and Analysis high-resolution reanalysis dataset, they extracted regional, low-level background wind profiles. The raw measurements were processed, standardized and synthesised to draw inferences. After analysing the processed datasets to locate key atmospheric boundaries and features, the researchers extracted the final observational results.
They found that, on April 30, 2019, when Cyclone Fani was closest to the observation site, the amount of ozone in the middle troposphere increased sharply. Ozone levels were higher by about 50–60 parts per billion by volume than they were on May 1, 2019. The ground-level surface ozone increased by 20–30 parts per billion by volume. Between April 30 and May 4, the cyclone disrupted the typical diurnal ozone pattern causing anomalous surface ozone spikes of 20–30 parts per billion by volume at night.
These changes in ozone levels occurred despite the absence of sunlight-driven photochemical production, suggesting that ozone was transported downward from the upper atmosphere by the cyclonic disturbances, suggesting the weakening or breaking of the tropopause.
When the cyclone was at its strongest, the Advanced Indian MST Radar detected some unusual patterns in the atmosphere near the tropopause, the boundary between the troposphere and stratosphere. The ozone intrusion was confirmed by a wedge of extremely dry air and by the warming of the mid-troposphere due to adiabatic compression.
These findings throw light on how ozone is redistributed during extreme events. The insights are vital for accurate local air quality forecasting and managing public health alerts. Such observations can also directly help improve the accuracy of long-term global climate models. Continued research in this area will lead to better meteorological tools, eventually translating to superior weather tracking and more precise forecasting models that could protect lives and property during extreme cyclonic events.
Current Science, 131 (2): 160-171 (2026)
DOI: 10.18520/cs/v131/i2/160-171
Reported by Sanghamitra Deobhanj
Freelance science writer, Cuttack
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