Department of Meteorology/Univ. of Maryland/College Park
Advanced EOS observations provide us an unique opportunity to detect and simulate urban induced climate changes. Using 5km EOS MODIS-observed skin temperature, land cover, albedo, emissivity, LAI, aerosol optical depth, and cloud properties, we examine the surface-atmosphere interactions and urban heat island effects from selected big cities (New York, Beijing, Phoenix, and Houston) to global coverage. These analyses address physical processes modified by urban constructions as well as the general features of urban climate. We find the largest urban impacts in terms of temperature are observed over 30-60N, where most cities are located. In addition, urban regions overall decrease surface albedo by 3-5% and decrease surface emissivity by 1-2%. Focusing on Houston, we develop an urban scheme and couple it into NCAR Community Land Model (CLM-urban) to simulate urban climate. CLM-urban can improve the simulation of water and energy cycles over Houston with the use of observed LAI, albedo and emissivity, as well as urban thermal properties.
Diurnal, seasonal, and interannual variations of urban aerosols were analyzed using 4-year National Aeronautics and Space Administration (NASA) Earth Observing System (EOS) Moderate Resolution Imaging Spectroradiometer (MODIS) observations, in situ AErosol RObock NETwork (AERONET) observations, and in situ EPA PM2.5 data for one mid-latitude city (New York) and one sub-tropical city (Houston). Seasonality is evident in aerosol optical depth measurements, with a minimum in January and a maximum in April to July. The diurnal variations of aerosols, however, are largely determined by local and regional weather conditions, such as surface and upper-level winds. On calm, clear days, aerosols peak during the two rush hours in the morning and evening. In addition, corresponding cloud properties observed from MODIS and rainfall measurements from NASA's Tropical Rainfall Measuring Mission (TRMM) demonstrate opposite phase to the seasonality of aerosols. These analyses suggest typical spatial and temporal variations that illustrate the linkages and feedbacks among the urban environment, water cycle processes, and climate.