NOTES AND CORRESPONDENCE Simple Modifications to Improve Fifth-Generation Pennsylvania State University- National Center for Atmospheric Research Mesoscale Model Performance for the Phoenix, Arizona, Metropolitan Area

The diurnal temperature cycle in the Phoenix, Arizona, metropolitan area, as represented in the fifth-generation Pennsylvania State University‐National Center for Atmospheric Research Mesoscale Model (MM5), is examined using a high-resolution 2-km grid spacing to simulate the dry portion of the summer. The model is run for a 48-h period with negligible synoptic forcing and a sufficiently dry atmosphere so that moist convection does not occur. The standard version of MM5 underestimates the magnitude of the diurnal maximum and also causes the maximum to occur too early. This behavior is due to an overestimate of the latent heat flux in the model, resulting from a poor specification of the land cover category and corresponding physical parameters. Adjusting the available moisture improves the modeled temperature maximum at both rural and urban sites, but the model temperatures are still cooler than those observed at the urban site at night because of a poorly represented urban heat island effect. It is the aim of this note to highlight deficiencies associated with running MM5 without any urban parameterization and without correcting the NCEP Eta Model analysis used as initial and boundary conditions.