Assessing sea breeze and heat island interactions using coastal-urban mesoscale ensembles
Teddy R. Holt, NRL, Monterey, CA; and J. Pullen
A high-resolution (less than 2-km horizontal grid increment) ensemble transform (ET)-based mesoscale modeling system utilizing urbanization and sea surface temperature (SST) perturbations is used to examine characteristics of sea breeze/heat island interactions and atmospheric transport and dispersion for the high population density cities of Tokyo and Manila. For the urban perturbations, two different urban canopy models embedded within the Coupled Ocean Atmosphere Mesoscale Prediction System* (COAMPS®) are used: the WRF Urban Canopy Model and the Los Alamos National Laboratory urban model. The parameters perturbed are urban canopy height, anthropogenic heating, urban classification, urban fraction, roof fraction, and sky view factor. SST perturbations are derived from time-lagged hourly forecast fields produced by the ocean model within the coupled system (Navy Coastal Ocean Model).
Results from Tokyo simulations using the ensemble system indicate a positive spread-skill relationship, with the addition of urban perturbations enabling the ensemble variance to distinguish a larger range of forecast error variances. For a pre-frontal period (stronger synoptic flow), there is less variability among ensemble members in the strength of the urban heat island and its interaction with the sea breeze front. During the post-frontal time period the sea breeze frontal position is very sensitive to the details of the urban representation, with large horizontal frontal variability relative to the width of the urban center, and displaying significant impacts on the development and strength of the heat island. Moreover, the dosage values of a tracer released at offshore and urban sites have considerable variability among ensemble members in response to small-scale features such as coastally upwelled water, enhanced anthropogenic heating, and variations in building heights. Realistic variations in SST produce subtle sea breeze alterations that dramatically impact tracer distributions.
*COAMPS® is a registered trademark of the Naval Research Laboratory.
Joint Session 5, Geographic Effects on Urban Weather and Climate
Wednesday, 14 January 2009, 4:00 PM-5:30 PM, Room 126A
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