Sea level pressure is a fundamental weather and climate element and the very basis of everyday weather maps. Daily sea level pressure distributions provide information on the influence of high and low pressure systems, air flow, weather activity, and, hence, synoptic conditions.
Using sea level pressure distributions from the NCEP/NCAR Reanalysis 1 (Kalnay et al., 1996) and a simplified variant of the weather-typing scheme by Jenkinson and Collison (1977) atmospheric circulation over the Baltic Sea has been classified as to pattern and intensity on a daily basis starting in 1948. A full account of the original weather-typing scheme for the North Sea can be found in Loewe et al. (2005), while the variant scheme has been detailed in Loewe et al. (2006). The analysis has been carried out on the moved 16-point grid. Though formally valid at its central point (60°N, 20°E), results are representative of the Baltic Sea region between 55°N-65°N and 15°E-25°E.
The modified scheme allows for six weather types, namely four directional (NE=Northeast, SE, SW, NW) and two rotational types (C=cyclonic and A=anticyclonic). The strength of the atmospheric circulation is classified by way of a peak-over-threshold technique, employing re-calibrated thresholds for the gale index G* of 29.9, 38.7, and 47.2 hPa for gale (G), severe gale (SG), and very severe gale (VSG), respectively. Technically, the set of weather-typing and gale-classification rules is implemented as a lean FORTRAN code (lwtbssim.f), internally known as "Simple Lamb weather-typing scheme for the Baltic Sea v1". The processing run was done on a Linux server under Debian 10 (Buster).
Both, weather types and gale days, form a catalogue of more than 70 annual calendars since 1948 that is presented and continuously updated to the present day at https://www.bsh.de/EN/DATA/Climate-and-Sea/Weather-and-Gales/weather-and-gales_node.html. This catalogue concisely documents synoptic conditions in the Baltic Sea region. Possible benefits are manifold. Special events and episodes in regional-scale atmospheric circulation are easily looked up and traced. Beyond that, the dataset is well suited for frequency, trend, persistence, transition, and extreme-value statistics.
The quality of the NCEP/NCAR reanalyses input data is described in detail in Kalnay et al. (1996); see reference.
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Description
The quality of the NCEP/NCAR reanalyses input data is described in detail in Kalnay et al. (1996); see reference.
An evaluation of the weather type classification based on NCEP/NCAR reanalyses is given by Loewe et al. (2013); see references.
For a comparative evaluation of different weather type classification methods, please refer to Tveito et al. (2016),COST Action 733: harmonization and application of weather type classifications for European Regions; final scientific report. University of Augsburg, Germany. https://opus.bibliothek.uni-augsburg.de/opus4/3768.