Abstract

High resolution regional climate simulations of Iceland for 1991-2000 have been performed using Polar MM5 with three nested domains and short duration integrations. The simulated results are compared with the monthly mean surface observations for 1991-2000 to demonstrate the high level of model performance. The simulation results are used to analyze the near-surface wind, temperature, dew point and precipitation climate over Iceland. The simulated near-surface winds in winter are primarily katabatic. The land-sea breeze pattern is clearly evident in summer. The land is colder than the ocean during winter, with a strong (weak) temperature gradient along the southern (northern) coast. This temperature pattern forces the katabatic wind. The diurnal cycle of near-surface air temperature is large in summer over the land areas, which drives the land-sea breeze. The near-surface climate for extremes of the North Atlantic Oscillation (NAO) index is discussed.

The time-averaged mesoscale precipitation distribution over Iceland is reasonably well simulated by Polar MM5. The winter amounts are much larger than those during the summer. In positive NAO years precipitation over Iceland is above average, whereas in negative NAO years precipitation is reduced. The simulated interannual precipitation variations during winter for 1991-2000 agree with those observed from accumulation measurements on Vatnajökull ice cap. The winter precipitation decrease for 1991-2000 dominates the annual signal for all of Iceland except the northeastern and eastern parts where the precipitation increases. The large precipitation trends are caused by the eastward shift and weakening of the Icelandic low during the 1990s.