8.2      Summer and wintertime variations of the surface and near-surface UHI in a semiarid environment.

Salamanca, Francisco, and Alex Mahalov, Arizona State University

This paper examines summer and wintertime variations of the surface and near-surface UHI for Phoenix metropolitan area using MODIS, near-surface meteorological observations, and the WRF model during a 31-day summer and a 31-day wintertime periods. The surface UHI is found to be higher at night and during the warm season. On the other hand, the morning surface UHI is low and frequently exhibits an urban cool island that increases during the summertime period. Similarly, the near-surface UHI is higher at night and during summertime. On the other hand, the daytime near-surface UHI is low but rarely exhibits and urban cool island. To evaluate the WRF model's ability to reproduce the diurnal cycle of near-surface meteorology and surface skin temperature, two WRF model experiments (one using the Bougeault and Lacarrere turbulent scheme and one with the MYJ turbulent parameterization) at high spatial resolution are conducted for each 31-day period. Modeled results show that WRF model (coupled to Noah-MP land surface model) tends to underestimate to some extent surface skin temperature during daytime but overestimate nighttime values during the wintertime period. In the same way, WRF model tends to accurately reproduce the diurnal cycle of near-surface air temperature and wind speed during summertime, but notably overestimate nighttime near-surface air temperature during wintertime.