Sea ice in the Baltic Sea – revisiting BASIS ice, a historical data set covering the period 1960/1961–1978/1979

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 Our post-processed data set will help to assess numerical ice models and provide easy-to-access unique historical reference material for sea ice in the Baltic Sea.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 www.baltic-ocean.org hosts the post-processed data and the conversion code.

Assessment of Extreme and Metocean Conditions in the Swedish Exclusive Economic Zone for Wave Energy

“…It is worth noting from Figure 4a that some areas could have ice more than 100 days per year on average, and some of these could have ice thicker than 0.5 m up to 40-50 days per year according to the climatology. This was largely consistent with the results presented in [39] discussing maximum extents of ice-periods up to even seven months in extreme cases. The spatial extent of these regions was however small, as will be further discussed later, and may be poor candidates for wave energy converter deployments unless the deployment were intended for testing the limits of survivability of new techniques and devices.…”

“…One of the issues of generating a homogenous dataset of sea-ice is the lack of continuous observations in space and time [39], and it is worth commenting that some variation existed over time in the number of files per ice-season with available data. Between the winters of 1979 to 2005, the underlying original data were available on average every fourth day and starting from autumn 2005 until spring 2015 about every second day.…”

“…Swedish seawater located roughly between latitude 55 and 66 • N includes a variety of sea-ice conditions that can be considered essentially ice-free in the south (at least far from coasts) to occurrences in the north that are several months long [39], typically starting with thin ice-cover some time in November/December and lasting in some regions on rare occasions all the way until March/April.…”

“…Other studies have focused on areas that are generally ice-free [36][37][38]. The seasonal ice-cover of the Baltic Sea [39,40] is, however, known to influence the wave climate, and Tuomi et al [41] suggested ways to calculate different types of statistics taking the ice-time into account. In practice, experience from both the WESA (Wave Energy for a Sustainable Archipelago) project [42][43][44] and several field tested deployment strategies [45,46] of wave energy equipment have increased the awareness of wave energy as an available potential renewable energy source in the region.…”

Sea-ice evaluation of NEMO-Nordic 1.0: a NEMO–LIM3.6-based ocean–sea-ice model setup for the North Sea and Baltic Sea

“…The original data were hard to access as BASIS ice was designed for storage on punchcards. Thus, Löptien and Dietze (2014) provided an easier-to-access version in the NetCDF free file format via www.baltic-ocean.org (or PANGEA https://doi.org/10.1594/PANGAEA.832353). BASIS ice thicknesses were originally indexed by numbers from 1 to 9.…”