Systematic correction of precipitation gauge observations using analyzed meteorological variables

Precipitation gauge measurements suffer from several sources of error, the most significant of which is the wind error caused by the flow distortion about the gauge orifice. An existing statistical Dynamic Correction Model (DCM) has been implemented with the intent to perform a systematic correction of precipitation measurements from gauges found in and near the Baltic Seaʹs drainage basin. The DCM implementation makes use of hourly gridded meteorological variables from an operational mesoscale analysis system. Twelve-hour precipitation amounts are disaggregated into hourly components, corrected, and then summed back to yield corrected 12-hour accumulations. Sensitivity studies for shielded H & H-90, Tretyakov, SMHI, and unshielded Hellmann gauge types demonstrate the behaviour of the DCM; the H & H-90 gauge requires the least amount of correction whereas the unshielded Hellmann gauge requires by far the most. This DCM implementation has been evaluated using two years of independent gauge data from the so-called Double Fence Intercomparison Reference (DFIR) gauge, along with independent H & H-90 observations, at Jokioinen, Finland. The results show that the H & H-90 gauge underestimates precipitation by around 8% on average and that the implementation appears to yield results which are fully consistent with previous findings and experience at this site. A second evaluation was performed with one year of measurements from Kiel, Germany, using data from a ship rain gauge (SRG) as a reference and data from two Hellmann gauges, one co-located with the SRG and the other 5.6 km distant. The results from this evaluation are more ambiguous but reveal both an overcorrection and an increased variability in the derived relation compared with uncorrected observations, one explanation being a well shielded site which the method, by its general nature, does not take into account. Although uncertainties remain in the treatment of measurements from some gauge types, systematic correction using this DCM should lead to more accurate measurements for use in hydrometeorological applications.