ATLAS Self-Siphoning Rain Gauge Error Estimates*

Abstract

This report describes sampling and error characteristics of self-siphoning rain gauges used on moored buoys designed and assembled at NOAA's Pacific Marine Environmental Laboratory (PMEL) for deployment in the tropical Pacific and Atlantic Oceans in support of climate studies. Self-siphoning rain gauges were chosen for use on these buoys because they can be calibrated at PMEL before and after deployment. The rainfall data are recorded at 1-min intervals, from which daily mean rate, standard deviation, and percent time raining are calculated and telemetered to PMEL in real time. At the end of the deployment, the 1-min, internally recorded data are recovered and processed to produce 10-min rain rates. Field data from a subset of these rain gauges are analyzed to determine data quality and noise levels. In addition, laboratory experiments are performed to assess gauge performance. The field data indicate that the noise level during periods of no rain is 0.3 mm h Ϫ1 for 1-min data, and 0.1 mm h Ϫ1 for 10-min data. The estimated error in the derived rain rates, based on the laboratory data, is 1.3 mm h Ϫ1 for 1-min data, and 0.4 mm h Ϫ1 for 10-min data. The error in the real-time daily rain rates is estimated to be at most 0.03 mm h Ϫ1. These error estimates do not take into account underestimates in accumulations due to effects of wind speed on catchment efficiency, which, though substantial, may be correctable. Estimated errors due to evaporation and sea spray, on the other hand, are found to be insignificant.

Estimating diffusivity from the mixed layer heat and salt balances in the North Pacific

“…Evaporation is estimated from latent heat flux and surface temperature. Precipitation was based on the measured raingauge rain rate corrected for the wind distortion using the Serra et al [2001] correction. The reduction in measured rain due to wind can be quite substantial.…”

Analysis of MJO Wind-Flux Feedbacks in the Indian Ocean Using RAMA Buoy Observations

“…Both moorings measure air temperature (T), relative humidity (RH), wind velocity, downwelling shortwave (SW) radiation and rain between 3 and 4 m above mean sea level, and sea surface temperature (SST) at 1 m below the sea surface (McPhaden et al 2009). Rainfall is measured with a self-siphoning rain gauge (Serra et al 2001). The 80.5°E mooring additionally records downwelling longwave (LW) radiation and barometric pressure (McPhaden et al 2009).…”

Site-specific precipitation estimate from TRMM data using bilinear weighted interpolation technique: An example from Kuwait

“…This is extremely good considering that rain gauges are believed to underestimate precipitation of the order of 10-20% due to the wind speed, precipitation rates, and sometimes the apparatus itself (Bell and Kundu, 2003;Habib et al, 1999;Krajewski et al, 2000;Nespor and Sevruk, 1999;Serra et al, 2001). …”