Net precipitation over the Baltic Sea for one year using models and data-based methods

Abstract

Precipitation and evaporation over the Baltic Sea are calculated for a one-year period from September1998 to August 1999 by four different tools, the two atmospheric regional models HIRLAM andREMO, the oceanographic model PROBE-Baltic in combination with the SMHI (1 × 1)° database andInterpolated Fields, based essentially on ship measurements. The investigated period is slightly warmerand wetter than the climatological mean. Correlation coefficients of the differently calculated latentheat fluxes vary between 0.81 (HIRLAM and REMO) and 0.56 (SMHI/PROBE-Baltic and InterpolatedFields), while the correlation coefficients between model fluxes and measured fluxes range from 0.61and 0.78. Deviations of simulated and interpolated monthly precipitation over the Baltic Sea are lessthan ±5 mm in the southern Baltic and up to 20 mm near the Finnish coast for the one-year period. Themethods simulate the annual cycle of precipitation and evaporation of the Baltic Proper in a similarmanner with a broad maximum of net precipitation in spring and early summer and a minimum in latesummer. The annual averages of net precipitation of the Baltic Proper range from 57 mm (REMO) to262mm(HIRLAM) and for the Baltic Sea from 96mm(SMHI/PROBE-Baltic) to 209mm(HIRLAM).This range is considered to give the uncertainty of present-day determination of the net precipitationover the Baltic Sea.