Impact of Boundary Layer Physics on Tropical Cyclone Simulations in the Bay of Bengal Using the WRF Model
- PDF / 11,616,856 Bytes
- 28 Pages / 547.087 x 737.008 pts Page_size
- 41 Downloads / 206 Views
Pure and Applied Geophysics
Impact of Boundary Layer Physics on Tropical Cyclone Simulations in the Bay of Bengal Using the WRF Model J. R. RAJESWARI,1,2 C. V. SRINIVAS,1,2 P. RESHMI MOHAN,1,2 and B. VENKATRAMAN1,2 Abstract—In this work, the sensitivity of tropical cyclone (TC) simulations over the Bay of Bengal to planetary boundary layer (PBL) physics in the WRF model is investigated. Numerical simulations are performed with WRF-ARW model using NCEP GFS data for five very severe cyclonic storms (Vardha, Hudhud, Phailin, Lehar and Thane). Five conceptually different PBL schemes (YSU, MYJ, QNSE, MYNN and BouLac) are evaluated. Results of 25 sensitivity experiments showed that PBL physics mainly affected the intensity while producing small variations in track prediction. The QNSE, followed by MYJ and BouLac, produced highly intensified storms, and MYNN produced weakly intensified storms. The YSU scheme showed better comparisons with IMD best track estimates. From the analysis of five cyclones, it is found that the YSU produced minimum errors for central pressure (-5.4, -0.8, -2.6, -5.25 hPa), maximum wind (19, 7.6, -0.96, -0.77 m/s) and track (66, 146, 182, 217 km) at 24-, 48-, 72- and 96-h forecast intervals. Analysis of various thermodynamical and dynamical parameters clearly showed that the PBL physics impacts the predictions by variation of (1) surface energy fluxes, (2) convergence, (3) inflow/outflow, (4) tangential winds, (5) vertical motion and (6) strength of the warm core and associated storm structure. A detailed analysis conducted in the case of Hudhud indicated that the PBL schemes influenced the intensity predictions through a WISHE type of feedback by the variation of convergence, radial inflow, vertical motion, and surface fluxes. While the YSU and MYNN schemes produced moderate values of radial inflow, the QNSE, MYJ and BouLac schemes produced stronger inflow. The stronger inflow, spin-up and stronger wind-induced transport of energy fluxes in the QNSE, MYJ and BouLac schemes led to a stronger convection and a higher intensification of TCs in these simulations. Keywords: Tropical cyclone, WRF, simulation, PBL physics, intensity.
1 Health, Safety and Environment Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamilnadu 603102, India. E-mail: [email protected]; [email protected] 2 Homi Bhabha National Institute, Anushakti Nagar, Mumbai 400094, India.
1. Introduction Tropical cyclones (TC) are one of the most disastrous weather phenomena that form over warm tropical oceans. TCs are rotational wind systems in the tropics characterized by a large central pressure deficit and strong winds. They cause enormous damage to life and infrastructure during their landfall along the coastal areas due to heavy winds, storm surge and rainfall. TCs in the North Indian Ocean (NIO) are quite variable in their movement and intensity (Raghavan and Sen Sarma 2000). Though cyclones are largely steered by large-scale flows and the Coriolis force (Gray 1968), the actual movement is a result of complex
Data Loading...
