Abstract ID- MA19-Th3-P002 North Cyclones of 2019 and Associated Upper Ocean Thermal Structure A. A. Deo and D. W. Ganer Indian Institute of Tropical Meteorology, Pune, India [email protected]

Introduction Methodology and Study Area Discussion and Conclusion

Tropical cyclone (TC) interact not only with the Several studies have shown that the cooling in surface but also with the deeper oceans, the sea surface is 2–3ºC in Indian Ocean during the depth depending upon the strength of the wind passage of depending upon its mixing.TC induced ocean vertical mixing can intensity. Few studies are there depicting the alter the upper-ocean temperature structure, change in the subsurface of the ocean.The heat Fani(ESCS) Vayu(VSCS) Maha(ESCS) Bulbul(VSCS) influencing ocean heat content. The upper ocean 115 80 100 75 (kts) content of ocean plays important role in response is typically characterized by sea Figure -2 intensification (Sharma et al 2014) and movement surface cooling and subsurface warming which is OMT is average temperature of an ocean layer. of the TC induced by a combination of physical processes OMT data of different layers, surface to 50, Figure-5 including enthalpy flux exchange, Ekman pumping, 100, 150, 200, 300, 500, 700 meters and that up Change in OMT during Vayu and Bulbul geostrophic advection and ocean vertical mixing. to 26ºC isotherm depth, have been derived using In exploring the ocean’s role in cyclone’s sea surface height anomaly, estimated from intensification, it is necessary to consider not altimeter observations, and SST obtained from only SST, but the thermal structure of the radiometers. These daily data available at upper-ocean column because cyclones interact not NRSC Bhuvan site at a resolution of 0.25ºx only just with the surface, but also with the 0.25º have been used. Weekly data of temperature subsurface ocean. However, it has been difficult from the Copernicus Marine Environment to explore the upper ocean thermal structure Monitoring Service (CMEMS)at the same resolution related issues because of the lack of subsurface along with daily NOAA/OISST data is also used. observations, over the vast oceans. With the Track data has been archived from National advancement in remote sensing and in situ ocean Environmental Satellite, Data, and Information measurements it is now possible to study this Service (NESDIS ). subject with more reliable new observations. From Fig 3. In cases of ESCS : Fani, the reduction in Results temperature at 50m is ~ 4º C , at 100m ~ 1.2º C and at 150 m it is 0.4º C. From 200 m warming starts in the deeper layer. Where as for Maha , the reduction in temperature at 50m is ~ 3.2º C •Fani (26 April - 2 May) was the first s Extremely 2019 Cyclone Season and at 100m it is ~ 1º C. The minor cooling of 0.1 ºC and Severe Cyclonic Storm in BoB and also the strongest Warminng up to 1.5º C is seen near the track at 150 and 200 m. tropical cyclone to hit Odisha since 1999. From Fig 4, in cases of VSCS: Vayu, the reduction in Total number of cyclones in the North Indian •Vayu was the second Very Severe Cyclone Storm formed temperature at 50m is ~ 4º C and at 100m it is ~ 2º C. Where Ocean region in the year 2019 reached eight in the from 10 – 17 June. Vayu reached its as for Bulbul , the reduction in temperature up to 100 m is ~ (Figure 1), which is the highest number of peak intensity as a high-end Very Severe Cyclonic Storm 1.5º C. The change at 150 m and 200 m is very small ~0.5º C. cyclones in a single year since 1976, when nine on 12June, with sustained winds of 145 kmph. cyclonic storms had formed in the region. Six •Maha (30 Oct- 7 Nov) formed in the Arabian Sea,. It Figure-6 (TCHP Change) of the cyclones this year were of the 'Severe' became VSCS on Nov 3 and ESCS in Nov 4. category. While in October •Bulbul developed as remnants of severe tropical storm Matmo in west Pacific traversed into the Bay of Bengal reached super cyclone intensity with wind and formed as Cyclonic Storm from 6 -11 Nov. speeds in excess of 250 kilometres per hour (km/hr), in April-May and Cyclone Figure-3 Change in SST during the cyclone passage Maha in October were of the 'Extremely Severe' From this category, with wind speeds greater than 200 figure it km/hr. , and Cyclone is seen Bulbul were of the 'Very Severe' category. that SST is reduced by Figure-1 Cyclone tracks in 2019 ~ 3ºC for all cases except Maha cyclone, where reduction is ~ 2ºC due to Fig 6. depicts reduction in TCHP which is up to 80 kJ/cm2 in vertical cases of Fani and Vayu cyclones from daily data. Weekly data 2 mixing shows reduction of 40 and 70 kJ/cm for Maha and Bulbul. induced by ------Major Findings ------Figure-4 upwelling. .In all cases SST is reduced by ~ 3ºC except Change in OMT during Fani and Maha Maha cyclone (decrease of ~ 2ºC) due to vertical Objectives mixing induced by upwelling. .Cooling of subsurface up to 100 m is seen in all the cases, during cyclone passage. In the present study we have studied upper ocean .In cases of Fani and Vayu cyclones reduction in response to storms of the year 2019. The ocean TCHP up to 80 kJ/cm2 occurs during cyclone’s pass parameters like SST, subsurface temperatures, TCHP are analysed using remote sensing data. Two Acknowledgements- Authors are thankful to Director IITM Extremely Severe Cyclonic Storms: Fani and Maha and Data portals of NOAA, NRSC Bhuvan, NESDIS, & CMEMS References- N. Sharma, M. M. Ali., Oceanography, 2014, 2 : 124. and two Very Severe Cyclonic Storms: Vayu and doi : 10.4172/2332-2632.1000124 BulBul, which impacted our continent are Annual Monsoon E Workshop(AMW 2019 - 2020)& National E considered. The tracks of these cyclones are Symposium on “Cloud and Precipitation Processes” shown in the next figure (figure 2). January 18-20, 2021, Pune, , INDIA