Study of mesoscale convective systems for curving cyclone madi and non-curving cyclone phailin using WRF model

Abstract

The formation and intensity of tropical cyclone (TC) over the Ocean not only depends on proper synoptic-scale atmosphere but also on active Mesoscale Convective Systems (MCSs). In this study, cyclone Phailin and Madi are considered to simulate and analyze the characteristics of convective cells and their MCSs properties using Weather Research and Forcasting (WRF) model. Cyclone Phailin formed over the Bay of Bengal (BoB) in October 2013 was an extremely severe cyclonic storm with maximum wind speed of 140 knots (72 ms-1) and during its lifetime its direction is almost straight. Cyclone Madi also formed over the BoB in December 2013 was a very severe cyclonic storm with maximum wind speed of 85 knots (43.72 ms-1) and during lifetime it has changed its direction to the angle of almost 140 degrees from its original track. The WRF model has been run for 4 days from 0000 UTC 10 Oct to 0000 UTC 14 Oct in 2013 to simulate cyclone Phailin and 0000 UTC 09 Dec to 0000 UTC 13 Dec 2013 for cyclone Madi with two way nested domains of 12 km and 4 km resolutions. Joint Typhoon Warning Center (JTWC) and NCEP-CFSR reanalysis data have been used to verify the simulated result. The average root mean square error of position for Madi is found 60 km whereas it is 50 km for Phailin track. On the other hand, maximum wind speed in JTWC and simulation are 43.72 ms-1 and 36 ms-1, respectively in Madi and 72 ms-1 and 70 ms-1 in case of Phailin respectively. The moderate convective available potential energy (CAPE) and high shear with unidirectional wind suggests about the possibility of supercell formation in the rainband of cyclone Madi whereas the moderate CAPE and small shear are favorable for ordinary convective cells development in Phailin. At the mature stage, the average cells length is found approximately 31 km for cyclone Madi whereas 30 km for Phailin and cells are moving along with the TC movement with average speed of almost 9 ms-1. The average lifetime of the cells of cyclone Madi (Phailin) has been found 3.5 (4.6) hours. The vortex pair within the cells in both TCs indicates the existence of mesovortices. However, the vortex pair is more intense in the cyclone Madi than that in Phailin. Significant convective systems are found in the northern side of cyclone Madi and southwest side for Phailin. MCS length (height) before 1 hr of recurving of Madi is approximately 220 (9.8) km, which is shorten to ~180 (5.7) km during curving time even though cyclone has highest wind speed at that time. On the other hand, the MCS length (height) is found 275 (8.5) km for Phailin during the similar wind speed of the curving time of cyclone Madi and remains almost same before and after of this time. The difference in low level moisture flux may cause the variation of the structure of MCS. The maximum reflectivity within the MCS of both TCs are found more than 50 dBZ, which indicates heavy rainfall in the cyclone area.