Cloud Layer Detection by WSR-57 Radar

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  • 1 U. S. Weather Bureau, Washington, D. C.
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Abstract

The ability of the WSR-57 radar to detect “cloud” layers of various types is studied from data collected during the period from late winter through mid-summer of 1960. Results indicate the best correlation between the radar echo layers and those visually observed is among the middle cloud types. Detection of the low cloud types was impeded, to some extent, by the presence of falling precipitation combined with radar beam width distortion, while only the more dense high clouds could be detected. Considering this denser group of high clouds, along with only the broken or overcast middle and low layers, 50 per cent of those observed visually were detected by the radar.

The rather close agreement between the WSR-57 and a 1.25 cm “cloud” radar in the middle cloud group comparison, suggests the presence of precipitation-size particles in many so-called “clouds.” In addition, the greater incidence of detection of clouds in colder months indicates the influence of ice crystal content upon detectability. The effect of change in temperature-moisture structure in the atmosphere has been demonstrated, also, in the variation of radar base presentation in altocumulus layers. Closely related to this is the pronounced effect of seasonality upon radar layer base heights, with a tendency for better agreement with the observed during the warmer months.

Abstract

The ability of the WSR-57 radar to detect “cloud” layers of various types is studied from data collected during the period from late winter through mid-summer of 1960. Results indicate the best correlation between the radar echo layers and those visually observed is among the middle cloud types. Detection of the low cloud types was impeded, to some extent, by the presence of falling precipitation combined with radar beam width distortion, while only the more dense high clouds could be detected. Considering this denser group of high clouds, along with only the broken or overcast middle and low layers, 50 per cent of those observed visually were detected by the radar.

The rather close agreement between the WSR-57 and a 1.25 cm “cloud” radar in the middle cloud group comparison, suggests the presence of precipitation-size particles in many so-called “clouds.” In addition, the greater incidence of detection of clouds in colder months indicates the influence of ice crystal content upon detectability. The effect of change in temperature-moisture structure in the atmosphere has been demonstrated, also, in the variation of radar base presentation in altocumulus layers. Closely related to this is the pronounced effect of seasonality upon radar layer base heights, with a tendency for better agreement with the observed during the warmer months.

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