HR: 1340h
AN: GC13B-1230    [Abstracts]
TI: Climatic Effects of Urbanization
AU: * Barzyk, T M
EM: barzykt@uchicago.edu
AF: The University of Chicago, Department of the Geophysical Sciences 5734 South Ellis Avenue, Chicago, IL 60637 United States
AU: Frederick, J E
EM: frederic@uchicago.edu
AF: The University of Chicago, Department of the Geophysical Sciences 5734 South Ellis Avenue, Chicago, IL 60637 United States
AB: Urban areas around the world have been increasing in size and population density in recent decades. The United Nations reports that in 1900, urbanites comprised 14% of the world's population. This value has increased to 47% in the year 2000, and is expected to grow to 60% by 2030. The goal of this study is to isolate the effects of urbanization on surface radiation balance components and meteorology. Data are recorded from urban and rural locations with a net radiometer and weather station. Instruments record incoming and outgoing solar and thermal radiation, and meteorological variables such as air temperature and pressure, relative humidity and wind speed. Data are incorporated into an energy balance model for urban and natural surfaces to compute heat fluxes due to solar and thermal infrared (longwave) radiation (Q_SOL and Q_LW); sensible heat transport (Q_SENS); evaporation (Q_EVAP); and conduction (Q_CONDUC). These fluxes comprise the heating and cooling elements for the different sites. After sunset, the urban surface to air temperature differential (T_S - T_A) is lower than that in the rural area, and wind speed is decreased due to increased surface roughness, so Q_SENS is lower. This value decreases even more in an urban canyon environment. Wind speeds in urban canyons are recorded to be up to 15 mph less than regional ones. Urban heat islands are generally assumed to be constant phenomena, existing as much during daytime as at night, but this is not always the case. Rural air temperatures can be greater than or equal to urban ones during the day, which is a reflection of the low specific heats of rural surfaces, but cooling rates are lower in urban areas after sunset, due to their surfaces' high heat capacities, causing these areas to be warmer at night, resulting in the formation of an urban heat island (UHI). UHIs in this respect are cyclical phenomena that occur diurnally. Results show that urban cooling rates can be half as much as rural ones, resulting in nighttime UHI intensities of over 8°C in early August in metropolitan Chicago. Incoming thermal radiation values are largely a function of atmospheric characteristics such as optical depth and cloudiness. They are also a function of the vertical build-up of urban areas. Incoming thermal radiation values in a low-rise urban environment are nearly the same as those in a rural one; however, a high-rise (urban canyon) site with a large aspect ratio (building height to street width) and low sky-view factor shows consistently higher incoming thermal values through time, being an average of ~25 Wm^-2 higher, and as much as 60 Wm^-2 during some periods, so downwelling Q_LW will increase with increased building height. This also decreases urban cooling rates.
DE: 0360 Radiation: transmission and scattering
DE: 3307 Boundary layer processes
DE: 3309 Climatology (1616, 1620, 3305, 4215, 8408)
DE: 3322 Land/atmosphere interactions (1218, 1631, 1843)
DE: 3359 Radiative processes
SC: Global Climate Change [GC]
MN: Fall Meeting 2005