Akio Wake

Heat storage of pavement and its effect on the lower atmosphere

Abstract Heat flux at the air/ground interface was observed and analyzed for various pavement materials on summer days. The surface temperature, heat storage and its subsequent emission to the atmosphere were significantly greater for asphalt than for concrete or bare soil. At the maximum, asphalt pavement emitted an additional 150 W m−2 in infrared radiation and 200 W m−2 in sensible transport compared to a bare soil surface. Analyses based on a parallel layers model of the atmosphere indicated that most of the infrared radiation from the ground was absorbed within 200 m of the lower atmosphere, affecting air temperature near the ground. With large difference between air and ground surface temperature at noon, the rate of infrared absorption by the lower atmosphere over asphalt pavement was greater by 60 W m−2 than that over the soil surfaces: or concrete pavement, a figure comparable to the absorption by turbulent transport.

NATURAL CONVECTION OF WATER NEAR THE DENSITY EXTREMUM FOR A WIDE RANGE OF RAYLEIGH NUMBERS

A time-dependent penalty finite element model was used to investigate natural convection of pure water in a rectangular enclosure with vertical end walls differentially heated near the temperature of maximum density. Attention was focused on the main features of the flow at high Rayleigh numbers not considered previously (Ra = 105−108). Water in a rectangular enclosure for the aspect ratio of 1.25 was initially kept at 4°C. The enclosure was then suddenly heated and cooled on the opposing vertical walls, i.e., 8°C and 0°C. The Rayleigh number was varied by the size of the enclosure. In the Rayleigh number range considered here, steady state was reached within a time of the order of 2tf, where tf is the time to steady state suggested by Patterson and Imberger [1]. The steady state flow field and temperature structure were symmetric at about the enclosures midpoint, and a stable sinking jet was formed in the interior of the enclosure as a result of density inversion. The velocity profile near the vertical ...