Bias adjustments to Arctic precipitation: A comparison of daily versus monthly bias adjustments
David R Legates, University of Delaware, Newark, DE; and D. Yang, S. Quiring, K. Freeman, and T. Bogart
In the Arctic, gage-based measurements of precipitation contain significant systematic biases. These biases include wind-induced undercatch and, to a much lesser extent, wetting and evaporative losses. In addition, trace amounts of precipitation are not included in daily precipitation totals even though they can contribute significantly to precipitation totals in dry locations in the high latitudes. Therefore, gage-based measurements of precipitation in the Arctic substantially underestimate the actual (true) precipitation. Accurate Arctic precipitation data are required to realistically simulate runoff from Arctic watersheds and model the global water balance. This study addresses the need for accurate Arctic precipitation data by applying the bias corrections that have been developed from experimental studies (e.g., Larson and Peck, 1974; Goodison, 1978, 1981; Sevruk, 1982; Groisman et al., 1991) to gage-based measurements of precipitation. Bias adjustments were applied to nine years of daily data (1994–2002) from more than 2500 stations north of 50°N to: 1) determine the effect of applying bias adjustments on a daily versus monthly basis on totals of monthly and annual precipitation, and 2) examine the temporal variability of the bias adjustment factors.
Results indicate substantial inter– and intra-monthly variability in the magnitude of the bias adjustments. This is primarily driven by variations in wind speed, air temperature, and frequency of snowfall. The results also demonstrate that applying the bias corrections on a daily (as opposed to monthly) basis produces more realistic estimates of monthly and annual precipitation. Therefore, Arctic precipitation data that has been adjusted on a daily basis will be more accurate than data adjusted on a monthly basis (e.g., Legates and Willmott, 1990), or adjusted using mean monthly correction factors (e.g., Adam and Lettenmaier, 2003).
Extended Abstract (480K)
Session 5, The Polar Atmosphere - Precipitation
Tuesday, 11 January 2005, 2:15 PM-3:00 PM
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