- Dona Paula, Goa, India.
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| Abstract Submission No. | ABS-2022-14-0277 |
| Title of Abstract | Dynamical and Synoptic characteristics of four extreme heavy rainfall events that occurred during the last four years (2018-2021) in the state of Kerala. |
| Authors | ARUN KUMAR VH*, DR.V.K.MINI, N.T.NIYAS, K.SANTHOSH, DR.S.BALACHANDRAN, KARTHIK P |
| Organisation | INDIA METEOROLOGICAL DEPARTMENT,THIRUVANANTHAPURAM |
| Address | METEOROLOGICAL CENTRE,INDIA METEOROLOGICAL DEPARTMENT,THIRUVANANTHAPURAM THIRUVANANTHAPURAM, KERALA, India Pincode: 695033 Mobile: 8554932213 E-mail: arunkumarvh@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | The state of Kerala witnessed several extremely heavy rainfall events during the last four years and this study is revisiting those events by analyzing the synoptic as well as dynamical aspects associated with those events. We had considered four extremely heavy rainfall events in this study 1) 14-16 August 2018 2) 08-10 August 2019 3) 04-08 August 2020 and 4) 16th October 2021. Case one and two is associated with large-scale flooding over Kerala whereas case three and four is associated with severe landslides. ERA 5 reanalysis data (0.25oX0.25o) is utilized in this study for estimating various dynamical parameters associated with severe weather events. The main factor for the first three cases is the stronger westerly/southwesterly winds over the Arabian Sea along and off the Kerala coast. Usually, the strength of this westerly/southwesterly winds increases in association with the formation of low-pressure areas over the northwest Bay of Bengal and their further intensification and westward movement. These systems led to the strengthening of westerly/southwesterly winds along and off Kerala coasts due to the increase of the cross-equatorial monsoon flow towards the region of the low-pressure system. The extremely heavy rainfall events in August 2018 can be attributed to the consecutive formation (within seven days) of the low-pressure systems on 6th and 13th August morning over Northwest Bay of Bengal. Further both these low-pressure systems intensified into Depression and moved west-northwestwards along the monsoon trough. The extremely heavy rainfall spell in August 2019 was attributed to the formation of a depression over NW BoB on 06th August 2019. This system further intensified and moved North Westwards during 07-09 August 2019. In August 2020, the formation of a low-pressure area over North Bay of Bengal on 4th Aug 2020, and its intensification and movement caused the strengthening of the strong south-westerlies in the lower-mid tropospheric levels over the peninsular region caused intense rain spell during 04-08 August 2020 over Kerala. In all these three cases, strong low level (925-850 hPa) wind convergence (~20-25 X 10-5 s-1) was observed during the extreme weather period with strong vertical velocities indicating updrafts (1-2 Pa/sec). On 15 August 2018, even the vorticity field was very high at 300 hPa (~10-20 X 10-5 s-1), especially over central Kerala. On 08 August 2019, strong upper level (200 hPa) divergence (~10-15 X 10-5 s-1) was observed over Kerala. On 06 August 2020, strong upper-level easterlies (~ 50 knots) were seen over south Kerala which may in turn increase upper-level divergence during the extremely heavy rainfall event. The extremely heavy rainfall event that occurred on 16th October 2021 was different from the previous three cases. A low-Pressure Area has formed over east-central & adjoining the southeast Arabian Sea off the Lakshadweep area on 14 October 2021 and it moved eastsoutheastwards and reached the Kerala coast on the morning hours of 16th October 2021 this, in turn, triggered the extremely heavy rainfall activity over south Kerala. It was observed that the vorticity, convergence, and vertical velocity had a steep increase during 03 UTC to 12 UTC of 16 October 2021 over south Kerala. The rainfall received from an automatic weather station at Peerumade of Idukki district was also indicated the peak rainfall activity during 03 to 06 UTC of 16 October 2021. Area-averaged (Centered around 9.5oN,76.5oE) vorticity, divergence, and vertical velocity at 850 hPa had shown a sharp increase from almost zero to ~ 40 X10-5 s-1, ~-20X10-5 s-1, and 3Pa/sec during this period. The vorticity field, as well as vertical velocity, was extending up to 300 hPa with a high value of upper-level divergence (~ 40 X10-5 s-1) over the same region which in turn increased the convection within the short period and created havoc over south Kerala. |