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Rae-Seol Park
,
Jung-Hyo Chae
, and
Song-You Hong
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Rae-Seol Park
,
Jung-Hyo Chae
, and
Song-You Hong

Abstract

In this study, a revised prognostic cloud fraction scheme for atmospheric models is proposed and its performance is evaluated with a diagnostic cloud fraction scheme. A revision is proposed through a direct linkage between hydrometeors in the cumulus parameterization scheme and the amount of predicted cloud fractions. Cloud fractions that are determined via the prognostic cloud fraction scheme appear to be more realistic than those determined via a diagnostic cloud fraction scheme when both are compared with satellite data. In a medium-range forecast test bed, the biases of large-scale features such as temperature, geopotential height, and mean sea level pressure are moderately reduced when the prognostic cloud fraction scheme is used.

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Jong-Jin Baik
,
Rae-Seol Park
,
Hye-Yeong Chun
, and
Jae-Jin Kim

Abstract

A circulating water channel is constructed to examine urban street-canyon flow. In the cases of an even-notch street canyon in which model buildings on both sides of the street have equal heights, one vortex is observed in model canyons with aspect ratios of 1 and 1.5, and two counterrotating vortices are observed in canyons with aspect ratios of 2, 2.4, and 3. In all of the even-notch cases, the center of the vortex (or the upper vortex) is located slightly downstream of the canyon center, and the downward motion downstream is stronger than the upward motion upstream. The magnitudes of the maximum updraft and downdraft are almost independent of the aspect ratio. In the case of a stepup notch, one vortex is observed in the canyon. In the case of a stepdown notch, two counterrotating vortices are observed. The upper vortex resembles to some extent an isolated roughness flow, and the lower vortex is characterized by a skimming flow. It is shown that the results of the water-channel experiments are generally in good agreement with those simulated using a numerical model with a turbulent kinetic energy–dissipation (k–ε) turbulence closure scheme, although there is a noticeable difference in the relative strengths of the upper and lower vortices in the two-vortex regime. This study demonstrates that the circulating water channel is useful for the study of street-canyon flow.

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