How Bay of Bengal and Arabian Sea twin vortices will drench India till July end
There is a kind of photograph that never shows a face. It is taken from far above the Earth by a satellite that reads the
There is a kind of photograph that never shows a face. It is taken from far above the Earth by a satellite that reads the world not in ordinary light but in temperature. Set two of them side by side, one looking west over the Arabian Sea and one east over the Bay of Bengal, both caught in the same afternoon light of July 26, and you can watch the Indian monsoon work as a single machine: a storm gathering its strength in one sea while the other quietly hands it the fuel. Read Full Story On the ground, that machine already has a number. In the 24 hours to the morning of July 26, Jagatsinghpur in Odisha collected 33 centimetres of rain, roughly a third of a metre of water falling out of the sky in a single day. Both images come from the Indian Space Research Organisation (Isro)'s INSAT-3DR, India's weather sentinel in space, reading the sky in one narrowband of infrared light at 10.8 micrometres. This is thermal infrared, a wavelength no eye can register, but the satellite feels as heat. What it truly measures is how cold the top of each cloud is. And in the atmosphere, cold means tall. The colder a cloud top, the higher it has climbed, and the harder it is raining beneath. Deep blue is warm and quiet. White is the coldest of all, storm towers that have punched to the roof of the sky, some 14 to 16 kilometres up, where the air sinks below minus 70 degrees Celsius. Read that way, the two seas tell one connected story. THE VIEW EAST: A DEPRESSION FINDS ITS CENTRE Turn first to the Bay of Bengal. Here, the cloud has collapsed into a single dense mass of brilliant white, the coldest tops in either frame, sprawled across the northwest and west-central Bay of Bengal off the Odisha and West Bengal coasts. Those palest patches mark cloud tops below minus 70 degrees, the fingerprint of cumulonimbus towers reaching the very top of the atmosphere.
This is a monsoon depression, centred in the morning of July 26 near 20.6 degrees north and 88.4 degrees east, about 130 kilometres off West Bengal’s Sagar Island. The pale central dense overcast over the northwest Bay marks the deepest convection, where storm towers reach the roof of the troposphere. (Photo: IMD/ISRO) The IMD expects it to deepen into a deep depression and cross the north Odisha and West Bengal coasts, between Paradip and Sagar Island, around the forenoon of July 27. That white heart is what forecasters call a central dense overcast, the pale, near-solid shield of storm cloud that crowns a mature system, and around it, the bands have begun to curl inward, the signature of air spiralling toward a low centre and rising. A long convective arm reaches southwest from the core, dragging moisture deep inland over Chhattisgarh, Jharkhand and eastern Madhya Pradesh. The rain shield has arrived over land before the centre has, which is how a depression announces itself. THE VIEW WEST: THE SEA THAT FEEDS THE STORM Now, the Arabian Sea. There is no rival whirlpool here, no closed white spiral over open water. What the western frame shows instead is the machinery of supply. Long cloud streets run from the Somali coast across the sea toward India, the signature of a vigorous southwesterly monsoon flow. A broad plume of moisture pushes into Gujarat and Saurashtra. Heavy convection stacks up along the Konkan, Goa, coastal Karnataka and Kerala, where the moist wind slams into the Western Ghats and is forced upward. Far to the south, a band of cold clouds flares along the equator, the cross-equatorial surge that recharges the whole system. A long convective arm sweeps southwest from the depression over the Bay of Bengal, carrying moisture deep into Chhattisgarh, Jharkhand and Madhya Pradesh. (Photo: IMD/ISRO) This is the Arabian Sea doing its real job: not storming, but breathing moisture inland. That moisture feeds the season's second system, a low over west Rajasthan and its neighbourhood, whose circulation leans out toward the northeast Arabian Sea to draw the humid air in over Gujarat.
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