Role of Surface Roughness Length on Simulation of Cyclone Aila - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 250

Role of Surface Roughness Length
on Simulation of Cyclone Aila
Krishna K. Osuri*, U.C. Mohanty and A. Routray 1
C.A.S., Indian Institute of Technology Delhi, Hauz Khas
New Delhi - 110016, India
1 NCMRWF, Sector 62, Noida, Uttar Pradesh, India
*e-mail: [e-mail]
1. Introduction
The genesis of tropical cyclones over the Bay of Bengal (BoB) is highly
seasonal. The post-monsoon season, i.e. during the months of October to mid
December, contributes maximum number of TCs and the pre-monsoon season
(April to May) has secondary maxima. Detailed climatology of the TCs over
BoB is available in Storm Atlas of India Meteorological Department (IMD),
2008 and Mohanty et al. (2011). Mohanty et al. (2011) depict that out of a total
of 606 TCs [which include deep depression (DD), cyclonic storm (CS), and
severe cyclonic storm (SCS)] during 1891-2010 formed over the BoB, about
54% have crossed Indian coast. When the system comes close to land, the
track, intensity and structure is influenced by the land surface characteristics
of the coastal region such as terrain height, soil type, land use/land cover,
vegetation type etc.
Land surface processes strongly influence the atmospheric predictions in
regional to global and short to climate scales (Pielke Sr. et al., 2011). The
changes in terrain, land use/land cover, vegetation and soil type etc. significantly
change the hydrological cycle and surface energy budgets (Baldocchi et al.,
2001; Ek et al., 2003; Holt et al., 2006). These changes alter the surface drag
and roughness lengths which consequently modifies the exchange coefficients
for momentum, sensible and latent heat fluxes within the planetary boundary
layer. The surface frictional stress acts as a primary sink for atmospheric
momentum (Newton, 1971). Therefore, accurate parameterizations of surface
roughness improve model performance. Like many other subgrid-scale
processes, the roughness length is typically averaged over a grid box (Kalnay,
2003).