The atmospheric portion of the hydrological cycle in polar regions plays a role of special importance, in that

• the balance of polar ice masses is inseparably linked to precipitation,
• the clouds modify the radiation transfer,
• the release of latent heat modifies the temperature of the air, hence circulations.
  
  

Observation of precipitation and cloud properties is a challenging task. In polar regions, reliable measurements are available sporadically, but not polar-wide. Therefore, polar clouds and precipitation can presently be quantified only by modelling their formation and geografic distribution.

Despite the undisputed success of such models, the way that clouds and precipitation are handled in weather forecast and climate models is still a significant source of simulation error, as explicitly stated in e.g. the latest IPCC Report 2007. Urgent tasks to be performed are therefore, among others, to identify the mechanisms of precipitation formation under polar meteorological conditions and to improve the treatment of clouds and precipitation.