On the Formation of Continental Polar Air

Abstract

This research investigates the transformation of maritime polar air into continental polar air in the Arctic during winter. The evolution of the vertical profiles of temperature and humidity is simulated using a one-dimensional model. The following physical processes are examined 1) surface enthalpy flux; 2) infrared radiative cooling due to emission by CO2, water vapor, water droplets, and ice crystals; 3) gravitational setting of the condensed water, 4) turbulent mixing, and 5) subsidence. The modeled formation of continental polar air is dominated by the radiative cooling due to emission by ice crystals and water droplets. The model reproduces the formation of low-level clouds that are frequently observed in these cold air masses, and also the phenomenon of ?cloudless? ice crystal precipitation. The model requires two weeks for the formation of fully-developed continental polar air, although after only four days of cooling the air has acquired most of the air mass properties. The rate of cooling is shown to be very sensitive to the amount of condensed water in the atmosphere. Condensate is produced in the model primarily by radiative cooling, and is depleted from the atmosphere primarily by gravitational settling. Gravitational settling of the condensate significantly increase the amount of radiative cooling by decreasing the opacity of the condensate. Subsidence modifies the formation of continental polar air by reducing the supply of moisture for condensation, thus influencing the radiative cooling.