Abstract
Abstract. The Baltic Sea is a seasonally ice-covered, marginal sea in central northern Europe. It is an essential waterway connecting highly industrialised countries. Because ship traffic is intermittently hindered by sea ice, the local weather services have been monitoring sea ice conditions for decades. In the present study we revisit a historical monitoring data set, covering the winters 1960/1961 to 1978/1979. This data set, dubbed Data Bank for Baltic Sea Ice and Sea Surface Temperatures (BASIS) ice, is based on hand-drawn maps that were collected and then digitised in 1981 in a joint project of the Finnish Institute of Marine Research (today the Finnish Meteorological Institute (FMI)) and the Swedish Meteorological and Hydrological Institute (SMHI). BASIS ice was designed for storage on punch cards and all ice information is encoded by five digits. This makes the data hard to access. Here we present a post-processed product based on the original five-digit code. Specifically, we convert to standard ice quantities (including information on ice types), which we distribute in the current and free Network Common Data Format (NetCDF). Our post-processed data set will help to assess numerical ice models and provide easy-to-access unique historical reference material for sea ice in the Baltic Sea. In addition we provide statistics showcasing the data quality. The website http://www.baltic-ocean.org hosts the post-processed data and the conversion code. The data are also archived at the Data Publisher for Earth & Environmental Science, PANGAEA (doi:10.1594/PANGAEA.832353).
Highlights
The Baltic Sea is a seasonally ice-covered marginal sea situated in a densely populated and highly industrialised area in northern Europe (Fig. 1)
Because ship traffic is intermittently hindered by sea ice, the local weather services have been monitoring sea ice conditions for decades
Baltic Sea Ice and Sea Surface Temperatures (BASIS) ice was designed for storage on punch cards and all ice information is encoded by five digits
Summary
The Baltic Sea is a seasonally ice-covered marginal sea situated in a densely populated and highly industrialised area in northern Europe (Fig. 1). One can expect that BASIS is the best source of information for historical sea ice conditions in the Baltic Sea. Both the original five-digit code and documentation are today available at the online portal “Environment Climate Data Sweden” at http://www.smhi.se/ecds.
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