Precipitation Estimates over the Baltic Sea: Present State of the Art

Abstract

Precipitation is one of the main components in the water balance, and probably the component determined with the greatest uncertainties. In the present paper we focus on precipitation (mainly rain) over the Baltic Sea as a part of the BALTEX project to examine the present state of the art concerning different precipitation estimates over that area. Several methods are used, with the focus on 1) interpolation of available synoptic stations; 2) a mesoscale analysis system including synoptic, automatic, and climate stations, as well as weather radar and an atmospheric model; and 3) measurements performed on ships. The investigated time scales are monthly and yearly and also some long-term considerations are discussed. The comparison shows that the differences between most of the estimates, when averaged over an extended period and a larger area, are in the order of 10-20%, which is in the same range as the correction of the synoptic gauge measurements due to wind and evaporation losses. In all data sets using gauge data it is important to include corrections for high winds. To improve the structure of precipitation over sea more focus is to be put on the use of radar data and combinations of radar data and other data. Interpolation methods that do not consider orographic effects must treat areas with large horizontal precipitation gradients with care. Due to the large variability in precipitation in time and space, it is important to use long time periods for climate estimates of precipitation Ship measurements are a valuable contribution to precipitation information over sea, especially for seasonal and annual time scales.

Present-day and future precipitation in the Baltic Sea region as simulated in a suite of regional climate models

“…It can be seen that in the land areas HadAM3H tends to overestimate the precipitation during the winter half of the year. The land-based uncorrected rain-gauge data used by CRU have a problem with undercatch especially during the winter half of the year (Rubel and Rudolf 2001;Rutgersson et al 2001). In the corrected and time-adjusted GPCPV2 data set this problem is reduced, and compared to this dataset the simulated precipitation is much closer to the observations.…”

“…The models are able to simulate, for instance, the main features of the seasonal cycle of precipitation. In addition to process studies, the models complement existing observational networks, in particular over the Baltic Sea where stations are few (e.g., Rutgersson et al 2001). Precipitation in the Baltic Sea runoff area determines, together with the other components of the water budget, the river runoff to the Baltic Sea with implications for salinity and water quality.…”

Detailed assessment of climate variability in the Baltic Sea area for the period 1958 to 2009

“…A detailed comparison of SMHI meteorological data with observations has been performed by Rudolph & Lehmann (2006). Rutgersson et al (2001) compared SMHI precipitation data with estimates based on NOAA's Comprehensive Ocean Atmosphere Data Set (COADS) and showed that both data sets agree very well. However, the SMHI data may underestimate precipitation, because of the neglect of the rain gauges flow distortion and evaporation error correction.…”

Modelling sensible and latent heat fluxes over sea during unstable, very close to neutral conditions

“…For the period 2002-2004 data from the SMHI(1 × 1) • database is used. The SMHI(1 × 1) • database is developed at SMHI (Swedish Meteorological and Hydrological Institute) and covers the Baltic Sea drainage basin in (1 × 1) • grid squares and uses all available synoptic weather stations in the area (Rutgersson et al 2001c). The two gridded databases have been analysed and compared for the purposes of Baltic Sea research by Omstedt et al (2005).…”