Väriilmapiiri

Väriilmapiiri, literally “colour radar,” is a form of weather radar used primarily for climatological and forecasting purposes. Unlike conventional Doppler radars that provide continuous real‑time data on precipitation intensity and velocity, a väriilmapiiri system records microwave backscatter only for a short period, typically a few hours, and then stores the data for later statistical processing. The resulting images are displayed in colour maps that show the distribution of cloud–rain drops over a regional area.

The technique was developed in Finland during the late 1970s and early 1980s to overcome the computational limitations faced by early meteorological centres. By sampling only a limited volume of the atmosphere at set intervals, the system could operate with the modest electronics of the time and still deliver useful climatological information, such as mean rainfall amounts and the location of storm clusters. The data were then input into numerical weather‑prediction models to improve their initial conditions.

After the introduction of more powerful processors and full‑time Doppler radars, the technical advantage of the color‑radar approach diminished. Today, ävriilmapiiri is largely regarded as a historical technology, though its data archives continue to provide valuable long‑term comparisons of rainfall patterns and radar performance.

The term is used mainly in Finnish meteorology literature but has parallels in other countries under different names, such as “colour radar” in the United Kingdom and “spherical” radar in some Eastern European contexts.