The structure of Heat Islands

Authors:
  • MGM. Garstang
    M. Garstang
  • PTP. D. Tyson
    P. D. Tyson
  • GEG. D. Emmitt
    G. D. Emmitt
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Abstract
Cities as well as ocean islands create mesoscale circulations in the atmosphere on a horizontal scale closely related to the size of the city or island. Contrast in albedo, heat capacity, and hence heating and cooling rates, heat generation, and surface roughness between the ‘island’ and its more uniform surroundings results in the generation of localized weather processes. Ocean islands, which may be simple in relief, free of pollution, and embedded in a uniform surface ocean temperature field, provide an excellent contrast to cities, which may be situated in complex topography and generate heat and pollution. The juxtaposition of the ocean and city islands is used to compare and contrast the induced atmospheric fields and the observed behavior of the atmosphere. The observed fields are then presented in terms of various numerical models. The simpler conditions prevailing over an ocean heat island lead to a more nearly complete three‐dimensional delineation of the thermodynamic and kinematic fields. These data for the ocean islands demonstrate significant deficiencies in the counterpart descriptions that exist for the atmosphere over the city. Complexities of modeling increase over both ocean and city heat islands as velocity fields change from zero to flow with strong vertical shear of the horizontal wind. Steady state models fare poorly under these conditions, whereas models that have attempted to account for the vertical redistribution of the horizontal momentum field show promise.

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