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Convection; sea breeze; urban heat island.

Doppler radar derived wind speed and direction profiles showed a well developed sea breeze circulation over the Chennai, India region on 28 June, 2003. Rainfall totals in excess of 100 mm resulted from convection along the sea breeze front. Inland propagation of the sea breeze front was observed in radar reflectivity imagery. High-resolution MM5 simulations were used to investigate the influence of Chennai urban land use on sea breeze initiated convection and precipitation. A comparison of observed and simulated 10 m wind speed and direction over Chennai showed that the model was able to simulate the timing and strength of the sea breeze. Urban effects are shown to increase the near surface air temperature over Chennai by 3.0 K during the early morning hours. The larger surface temperature gradient along the coast due to urban effects increased onshore flow by 4.0m s⁻¹. Model sensitivity study revealed that precipitation totals were enhanced by 25 mm over a large region 150 km west of Chennai due to urban effects. Deficiency in model physics related to night-time forecasts are addressed.

Matthew Simpson¹ Sethu Raman¹ R Suresh² U C Mohanty³

1. Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695-8208, USA.
2. India Meteorological Department, Chennai.
3. Indian Institute of Technology, New Delhi.

Published

December 2008

Manuscript received

18 December 2007

Manuscript revised

24 July 2008

Accepted

25 July 2008