Measurements of light rain, drizzle and heavy fog
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Measurements of light rain, drizzle and heavy fog
Ismail Gultepe Cloud Physics and Severe Weather Research Section Meteorological Research Division, Toronto, Environment Canada, Ontario M3H 5T4, Canada
Table of contents 3.1 3.2
Introduction .................................................................................. 59 FRAM field projects and observations ......................................... 62 3.2.1 FD12P measurements ........................................................ 63 3.2.2 VRG101 measurements..................................................... 64 3.2.3 POSS measurements.......................................................... 65 3.2.4 Total Precipitation Sensor (TPS) measurements ............... 67 3.2.5 FMD and CIP measurements............................................. 68 3.3 Analysis........................................................................................ 68 3.4 Results .......................................................................................... 69 3.4.1 Case studies ....................................................................... 69 3.4.2 Overall comparisons .......................................................... 70 3.5 Discussion .................................................................................... 73 3.5.1 Light precipitation and drizzle measurements................... 75 3.5.2 Visibility calculations ........................................................ 75 3.5.3 Uncertainties...................................................................... 78 3.6 Conclusions .................................................................................. 79 References ............................................................................................. 80
3.1
Introduction
Measurements of light rain, drizzle and settling out (or collision collection at the surfaces) of heavy fog can be important to estimate daily, monthly and annually averaged precipitation amounts. For an
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example, in northern climates (Stewart et al. 2004), there are no accepted standards for the short-term measurements (on the minute time scale) due to low precipitation rates. This chapter explores the potential of various instruments to measure light precipitation and settling rate under heavy fog conditions. The World Meteorological Organization (WMO) Guide to Instruments and Methods of Observation (WMO 1983) suggested that precipitation rate should be measured from 0.02 up to 2000 mm h–1 and time average should be 1 min. In the guide, required uncertainties were 0.1 mm h–1 between 0.2 and 2 mm h–1 and 5% above 2 mm h–1 (also in WMO 1983). There are several manual instruments that collect precipitation amounts based on various techniques but most of them do not satisfy the criteria stated by WMO (Sevruk and Hamon 1984; Goodison et al. 1998). Nystuen et al. (1996) provided an extensive work on quality of automatic precipitation measurements. Automatic rain gauges usually provide both accumulated precipitation amount (PA) and precipitati
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