The effect of a cyclonic storm on the energy fluxes at the urban interface — A preliminary experiment

Abstract

SummaryThe spatial and temporal variations of the energy and moisture budgets of a megalopolis (Los Angeles basin) were examined during a frontal passage February 23, 1969) and during an extremely clear day (March 4, 1969) in order to determine the existing continuum of possible extremes during that season. The distributional aspects of solar radiation (direct and diffuse), reflected solar radiation, net radiation, latent heat flux, sensible heat flux, and heat flux in or out of the urban interface were examined. Budgets of input and output of the storm study were contrasted with those of the clear day study. Also measured and compared were actual surface temperatures, terrain radiant temperatures, radiant sky temperatures, and dry and wet-bulb temperatures. Especially in the case of the clear day investigation, a series of empirical and physical-theoretical models were tested and proved to be rather realistic in comparison with actual observations in the field. Such models were less successful during the storm when the city surface received extremely low amounts of energy. Especially striking were the multitude of energy processes and their probable causes during the storm. The frontal passage caused a reduction of 92 ~ of the absorbed solar radiation as compared to the clear day. Infrared components of the budget were much less affected.

The structure of Heat Islands

“…Few urban energy balance measurements are available for comparison with the Myrup and Morgan study. Terjung [1969Terjung [ , 1971 during a cloudy, a rainy, and a clear day. However, owing to the paucity of fixed observation points, the traversing techniques used, and the need to compute the sensible heat flux as an energy balance residual, it is difficult to draw firm conclusions from these preliminary studies (W. H. Terjung, personal communication, 1973).…”

Urban heat storage derived as energy balance residuals

“…MEASUREMENT When investigating heat storage uptake and release from facets of the urban system such as roads, roofs, walls, and open land, it is appropriate to use standard heat flux plates (e.g., Nunez and Oke, 1977). One or more plates have also been used to represent heat storage in studies of the areally-averaged energy balance of a city (e.g., Terjung et al, 1971;Kerschgens and Hacker, 1985;Kerschgens and Drauschke, 1986). Unless a very wide variety of surface materials and orientations is sampled, the approach seems open to serious error.…”

Microclimatic Variations in a Downtown Urban Environment

“…Terjung et al (1971) have found a value of 35 % during the study of one clear day in Los Angeles. No water was present on the pavement during the days of this study so evaporation was not a factor in the energy budget.…”