Climate indicators - geostrophic wind

Direct wind measurements have been made at some stations since the 1800s. During the 1950s anemometers became common at airports and coastal stations. But it wasn’t until 1996 that a network of 130 automatic stations was established with comparable wind measurement equipment. The anemometers have changed a lot technically over time, and surrounding vegetation and buildings significantly affect the wind speed.

This means that there are no long homogenous time series for measured wind speed. Instead of direct wind measurements, the climate indicator uses geostrophic wind – an idealised average wind speed calculated from air pressure observations.

How has the wind varied in Sweden?
Have there been any changes?
Are there any trends?

Geostrophic wind has been calculated for nine triangles over Sweden, as shown in the figure.

Click on the map you will be linked to a site in Swedish

The following link shows diagrams and data for the geostrophic wind in Sweden for the different triangles for each year since 1901 or 1951.

Geostrofisk vind - se och ladda ner (only in Swedish).

Difficult to estimate the wind climate from wind measurements

In the more distant past, the observer estimated the wind strength by watching the way the wind affected the surroundings. The estimates tell us a lot about the wind climate but are naturally subjective giving an uncertainty over time.

Even if coastal stations in particular have carried out wind monitoring since the 1800s it has been technically difficult to obtain good quality wind speed measurements. It wasn’t until the 1950s that the measurements became good enough to compare over time.

As well as the technical difficulties of comparing measurements there are also other reasons why older wind observation are not always homogeneous over time. For example the equipment has been placed at a non-standard height (10 m) for practical reasons and the wind has often been noticeably affected by nearby buildings, hills and vegetation. The measurement instruments have been moved or changed. All these factors contribute to the fact that wind measurements are rarely comparable over time.

Geostrophic wind based on air pressure observations

One way to get an idea of how the wind can have varied over a longer time period is to consider the air pressure observations. Differences in air pressure are one of the causes of wind and these measurements have been very stable over a long period of time.

The geostrophic wind is a type of idealised average wind speed between observation points. Air pressure measurements have been taken at least three times a day since 1879 and therefore provide a data series for geostrophic winds starting in 1879.

Data for the years 1879-1950 have not received the same quality control as data after 1950 and include inaccuracies. Data prior to 1901 is not shown at all since the quality is dubious.