Raschke, E., Meywerk, J. & Rockel, B. 2002. Has the project BALTEX so far met its original objectives? Boreal Env. Res. 7: 175–182.

After more than six years of build-up and basic research, the Baltic Sea Experiment (BALTEX) undergoes a transition into its second phase, where major attention is paid to provide a long-term data set, covering at least two complete seasonal cycles. This new phase called BRIDGE, is part of a world-wide effort to study energy and water cycles and also related fluxes of carbon and other constituents over continental-scale regions. Some of the major findings obtained during the first phase of BALTEX are summarized in this paper.

Döscher, R., Willén, U., Jones, C., Rutgersson, A., Meier, H.E.M., Hansson, U. & Graham, L.P. 2002. The development of the regional coupled ocean-atmosphere model RCAO. Boreal Env. Res. 7: 183–192.

A regional coupled ocean-atmosphere-ice general circulation model for northern Europe is introduced for climate study purposes. The Baltic Sea is interactively coupled. The coupled model is validated in a 5-year hind-cast experiment with a focus on surface quantities and atmosphere-ocean heat fluxes. The coupled sea surface temperature matches observations well. The system is free of drift, does not need flux corrections and is suitable for multi-year climate runs. With flux forcing from the atmospheric model the regional ocean model gives sea surface temperatures statistically equivalent to the uncoupled ocean model forced by observations. Other oceanic surface quantities do not reach this quality in combination with the current atmosphere model. A strong dependence of sea ice extent on details of the atmospheric radiation scheme is found. Our standard scheme leads to an overestimation of ice, most likely due to a negative bias of long-wave radiation. There is indication that a latent heat flux bias in fall contributes to the ice problem. Other atmosphere-ocean heat fluxes are generally realistic in the long term mean.

Fortelius, C., Andræ, U. & Forsblom, M. 2002. The BALTEX regional reanalysis project. Boreal Env. Res. 7: 193–201.

The BALTEX regional reassimilation project uses meteorological data assimilation for quantifying the climatic energy and water cycles over the catchment basin of the Baltic Sea during the course of one annual cycle, Sep. 1999–Oct. 2000. This report presents the data assimilation system used, the available products, and a sample of preliminary results. The latter demonstrate that the system is capable of simulating the essential features of the energy and water cycles of the Baltic drainage basin. We find this encouraging, because the model has not been tuned to reproduce these cycles, but mainly to predict the atmospheric state.

Lorant, V., McFarlane, N. & Laprise, R. 2002. A numerical study using the Canadian Regional Climate Model for the PIDCAP period. Boreal Env. Res. 7: 203–210.

Simulations of summertime conditions over the BALTEX region using the Canadian Regional Climate Model (CRCM) are compared with observations for the PIDCAP period. A systematic cold bias of the surface temperature was found in a reference simulation made with a version of the CRCM which uses the physical processes package of the third generation global climate model of the Canadian Centre for Climate Modeling and Analysis. This cold bias is found to be due to excessive cloud near the surface. Revision of the cloud scheme, which was originally designed for use in conjunction with relatively coarse resolution of the AGCM, results in a reduction of the cloud cover, improved net radiative flux at the surface and substantial reduction of the cold bias. An associated result is that the lower atmosphere becomes more conditionally unstable which increases the number of convective events. Nevertheless the incidence of convective precipitation events remains unrealistically low.

Pirazzini, R., Vihma, T., Launiainen, J. & Tisler, P. 2002. Validation of HIRLAM boundary-layer structures over the Baltic Sea. Boreal Env. Res. 7: 211–218.

The boundary-layer structures of the operational atmospheric model HIRLAM were validated over the Baltic Sea on the basis of rawinsonde soundings and surface-layer observations during r/v Aranda expeditions. The validation was made for two regions in 1999: a coastal sea ice zone in March and the Baltic Proper in October. In March, HIRLAM wind analyses and six-hour forecasts were very good. The main discrepancies were related to the surface and 2-m temperatures: in cold nights the inversions were too weak and delayed in HIRLAM. Experiments applying a two-dimensional mesoscale model suggested that HIRLAM results could be improved by updating the values of surface albedo and the parameters of the force-restore surface temperature scheme on the basis of the snow age and temperature. In October, the temperature profiles were accurate within 0.5 K, on average, but the boundary layer was too moist in HIRLAM. The wind speed in the analyses and six-hour forecasts was accurate within 1 m s^–1, and errors in the sea surface temperature had a strong effect on the turbulent surface fluxes.

Kücken, M., Gerstengarbe, F.-W. & Werner, P.C. 2002. Cluster analysis results of regional climate model simulations in the PIDCAP period. Boreal Env. Res. 7: 219–223.

On the basis of an extended cluster analysis algorithm, a new validation method is presented for the quality control of climate model simulation results. To test the method, a comparison of four climate model simulation runs was carried out, comprising on the one hand results of the non-hydrostatic model (LM) of the German Weather Service (DWD) and on the other hand results of a hydrostatic model (REMO) of the Max-Planck-Institute for Meteorology, Hamburg (MPI). The results of the cluster analysis show that the method is suitable to describe the differences between reference and simulation data in space and time.

Etling, D., Harbusch, G. & Brümmer, B. 2002. Large-Eddy-Simulation of an off-ice airflow during BASIS. Boreal Env. Res. 7: 225–228.

The boundary layer modification for the case of an off-ice airflow during the BALTEX-BASIS field experiment is simulated by means of a Large Eddy Simulation (LES) model. Model results are compared with aircraft observations for turbulent fluxes of momentum, heat and moisture.

Gryning, S.-E. & Batchvarova, E. 2002. Marine boundary-layer height estimated from the HIRLAM model. Boreal Env. Res. 7: 229–233.

Two-weeks of measurements of the boundary-layer height over a small island (Christiansø) in the Baltic Sea is discussed. The meteorological conditions were characterised by positive heat flux over the sea. The boundary-layer heights derived from radiosonde measurements were compared to Richardson-number estimates based on output from the operational numerical weather prediction model HIRLAM (a version of SMHI with a grid resolution of 22.5 km x 22.5 km). For southwesterly winds it was found that a relatively large island (Bornholm) lying 20 km upwind of the measuring site influences the boundary-layer height. In this situation Richardson-number based methods with the HIRLAM data fail most likely because the island of Bornholm and the water fetch to the measuring site are about the size of the grid resolution of the HIRLAM model and therefore poorly resolved. For northerly winds the water fetch to the measuring site is about 100 km and the Richardson methods reproduce the height of the marine boundary layer. This suggests that the HIRLAM model adequately resolves a water fetch of 100 km with respect to predictions of the height of the marine boundary layer.

Crewell, S., Drusch, M., van Meijgaard, E. & van Lammeren, A. 2002. Cloud observations and modeling within the European BALTEX Cloud Liquid Water Network. Boreal Env. Res. 7: 235–245.

A prototype of a European cloud observation network was established as part of the EU-project CLIWA-NET during three campaigns. The first CLIWA-NET network campaign (CNN I) took place in August/September 2000 and first results are presented in this work. Cloud properties, with a focus on liquid water path (LWP), were derived at 11 stations within the BALTEX modeling area from passive microwave radiometer, lidar ceilometer and infrared radiometer measurements. In an indirect evaluation of LWP accuracy performed during cloud free scenes, clear-sky biases in LWP ranging between –15 and +6 g m^–2 were identified, which are well within the theoretical accuracy of the retrievals. For the Lindenberg station the retrievals were compared with forecasts from four atmospheric models. After restricting the model predictions to non-precipitating cases, which are the only cases for which retrieved LWPs are accurate, reasonable agreement was found between the observations and three of the models.

Hollmann, R. & Gratzki, A. 2002. The satellite derived surface radiation budget for BALTEX. Boreal Env. Res. 7: 247–251.

The Satellite Application Facility for Climate Monitoring (CM-SAF) will derive operationally consistent cloud and radiation parameters in high spatial resolution for an area that covers Europe and part of the north Atlantic Ocean in an off-line mode. The availability of the 12-channel instrument SEVIRI and the GERB onboard the MSG satellite, together with the five-channel AVHRR instrument onboard the NOAA and METOP satellites provides a unique opportunity to derive consistent cloud and radiation parameters. The cloud and surface radiation products will be based on data from the polar orbiting satellites NOAA and METOP for the northern latitudes, and on data from the MSG satellite for the mid-latitudes. To reduce inhomogeneities in the transition from the mid-latitudes to the northern latitudes as much as possible, the same algorithms will be used for both areas. Here a brief description of the planned surface radiation budget products and the selected algorithms is given.

Koistinen, J. & Michelson, D.B. 2002. BALTEX weather radar-based precipitation products and their accuracies. Boreal Env. Res. 7: 253–263.

This paper briefly reviews the measurement of precipitation by radar, discusses factors affecting the accuracy of such measurements, and outlines how such factors may be dealt with to improve the quality of precipitation measurements by radar for the purposes of the Baltic Sea Experiment (BALTEX). Precipitation products from the BALTEX Radar Network (BALTRAD) are then briefly presented, along with descriptions of how their qualities are improved, as are some new results on their accuracies. Intelligent compositing of data from a heterogeneous network, combined with innovative quality control, is shown to give high quality high resolution information for monitoring relative precipitation variability simultaneously over land and sea in both time and space. Gauge adjustment of radar-derived accumulated precipitation is shown to efficiently minimize the radar data's bias with increasing distance, thus yielding quantitatively useful datasets for application by the BALTEX community.

Feijt, A.J., Jolivet, D. & van Meijgaard, E. 2002. Retrieval of the spatial distribution of liquid water path from combined ground-based and satellite observations for atmospheric model evaluation. Boreal Env. Res. 7: 265–271.

In the framework of CLIWA-Net, observations and model values of cloud properties are compared. The observations are obtained from a network of ground-based radiometers and polar orbiting meteorological satellites. The project includes a number of novel aspects among which the retrieval of the horizontal distribution of cloud liquid water from a combination of AVHRR and ground-based measurements. This new approach results in a spatial distribution of LWP of optimum accuracy. A case study is presented, that demonstrates the added value of this approach for atmospheric model evaluation.

Sepp, M. & Jaagus, J. 2002. Frequency of circulation patterns and air temperature variations in Europe. Boreal Env. Res. 7: 273–279.

The relationship between the frequency of circulation patterns and air temperature fields in Europe are analysed. The circulation forms W, E and C according to the classification elaborated by Vangengeim and Girs, and the zonal, meridional and half-meridional circulation groups by Hess and Brezowsky are used in this study, and the correlation maps between circulation patterns and sea level pressure are composed. The highest correlation was observed in winter. In northern and central Europe zonal circulation causes a higher temperature in winter and a lower temperature in summer. The meridional circulation has an opposite relationship with the temperature. The northern circulation has the maximum negative correlation in spring and autumn.

Post, P., Truija, V. & Tuulik, J. 2002. Circulation weather types and their influence on temperature and precipitation in Estonia. Boreal Env. Res. 7: 281–289.

An existing objective classification scheme of the atmospheric circulation, where daily circulation is determined through the strength, direction and vorticity of the geostrophic flow has been applied over the Baltic Sea region for the time period of 1968–1997. The results at sea level and the higher isobaric levels of 500 hPa, 700 hPa and 850 hPa are presented here. The analysis revealed that the most common circulation types are anticyclonic and cyclonic. The mean-square-error skill scores are used to investigate classification's suitability for describing the variability of the local (Pärnu) daily weather elements. The skill scores of the objective classification are essentially higher than those for the German Weather Service's "Grosswetterlagen" scheme, but the scores are still low due to the high variability of daily temperature and precipitation within the weather types. Temperature is best described by the classifications at higher levels of pressure (500 hPa and 700 hPa), but precipitation is best described by those at the lower levels (sea level and 850 hPa). Developing one good classification for both variables is non-trivial.

Okulov, O., Ohvril, H. & Kivi, R. 2002. Atmospheric precipitable water in Estonia, 1990–2001. Boreal Env. Res. 7: 291–300.

Knowledge on atmospheric precipitable water is necessary as input to hydrological, energetic and radiation models. Short historical review of parameterization of precipitable water is given. For Tallinn (Estonia), simple formulas are proposed to calculate precipitable water from observations of surface water vapor pressure. Seasonal changes of precipitable water in Tallinn are expressed by time series for 1990–2001 as well as by tabulation of monthly averages for this period. Parameterization of precipitable water, decadal time series, and tabulation of monthly averages are also given for three neighboring stations — St. Petersburg (Russia), Jokioinen and Sodankylä (Finland).

Oesterle, H. 2002. Selection of representative stations by means of a cluster analysis for the BAMAR region in the PIDCAP period. Boreal Env. Res. 7: 301–304.

A cluster analysis procedure is presented that allows to select stations that are typical for different meteorological conditions. The estimations of mean daily minimum and maximum air temperatures, and also mean daily precipitation were used as parameters of the classification procedure. The means are calculated using verified synoptic data which are collected in the course of interval from August to October 1995 at 950 synoptic sites allocated on the Baltex Model Area (BAMAR) region. As a result 83 representative stations are selected, and used for validation of the LM-model at PIK.