Climatology of atmospheric and oceanic forcing data: Essential information for understanding sea-ice formation processes

07 February 2020

The atmosphere is an important component in the climate system and is crucial to sea-ice formation. The air temperature, humidity, pressure and wind fields determine the circulation, and with it, the inflow of warm air masses from the temperate latitudes. In addition, the ocean temperature is the most important factor in determining whether sea ice grows or melts. Climatological data on the atmosphere and ocean represent essential parameters for interpreting and assessing current sea-ice conditions. Accordingly, now also offers information on the most important climatological aspects, which is presented in map form and available for download here.

In the new “Climatological data” section under the "derived product menu" of the data portal, users will find the monthly mean figures for:

•    sea surface temperature anomaly (SST),
•    temperature anomaly at 925 hPa
•    sea level pressure anomaly (SLP),
•    precipitable water content anomaly (PWC), as well as
•    wind vectors on the air pressure anomaly field

in map form, as well as downloadable data in NetCDF format here. Anomalies are consistently calculated in terms of the reference period 1971 – 2000 (WMO reference period); only the SST employs the period 1982 – 2000 instead. The new maps reflect data reaching back to January 2002 and are calculated for the previous month at the beginning of every month (once they are available from the NCEP / NCAR).

Here’s what the new products (the examples reflect data on November 2019) look like:

Base data for climatological assessments

The new data product at is based on daily reanalysis data prepared by the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR). The NCEP / NCAR reanalysis data stem from a continually updated, globally gridded dataset that depicts the current state of the Earth’s atmosphere and includes observations and the outcomes of a numerical weather prediction (NWP) model from 1948 to the present. A large percentage of the data is available from the Physical Science Division of the NOAA Earth System Research Lab, both in its original format (calculated 4 times/day) and as a daily average. The resolution of the global reanalysis model is T62 (209 km) with 28 vertical sigma levels; the results are available at six-hour intervals. There are more than 80 variables (including the geopotential height, temperature, relative humidity, U and V wind components, etc.) in various coordinate systems, vertical height levels in Carthesian Coordinate, km height (so called z-levels) on 192 x 94 Gaussian grids and 11 isentropic levels on 2.5 x 2.5-degree grids (vertical layers of equal entropy or equal potential temperature).

At this data is presented in map form, using the monthly mean, not the 6-hour resolution. Dr Monica Ionita-Scholz, a climatologist whose work at the Alfred Wegener Institute chiefly focuses on statistical analyses of climate data, underscores the importance of this data for interpreting current sea-ice conditions: “The growth, melting and drifting of sea ice are to a considerable extent determined by atmospheric conditions. Whereas the current weather and here especially the air pressure distribution are what influence sea-ice dynamics, thermal conditions like the air temperature, latent heat from the precipitable water content, and the sea surface temperature are what dictate the ice’s thermodynamic growth / melting, not to mention snowfall.” In terms of analysing the long-term development, the mean distribution patterns for the climatological parameters offer insights into large-scale trends, which help us to evaluate sea-ice distribution. On a synoptic, daily basis the variability is too high for reliably identifying trends. “These new map products at are an important resource for sea-ice research, but also provide valuable information for other academic and societal actors (e.g. those in the fishing industry, shipping, etc.) with an interest (ecological or economic) in climatic developments in the polar regions,” adds Dr Renate Treffeisen, who spearheaded the products’ development for