Accounting for Clouds in Sea Ice Models

Figure 2. Annual cycle in amounts of low-level, mid-level, and total clouds and in ice crystal precipitation in the lower troposphere

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Accounting for Clouds in Sea Ice Models

ALEKSANDR P. MAKSHTAS, EDGAR L ANDREAS,

PAVEL N. SVYASHCHENNIKOV, AND VALERY F. TIMACHEV

INTRODUCTION

Clouds play a dominant role in determining shortwave and longwave radia-

tion transfer in the atmosphere. Cloud area, height, thickness, and water content,

among other properties, all influence the radiative fluxes (Curry and Ebert 1990).

For sea ice modeling in polar regions, having an adequate description of the cloud

cover is especially important for estimating the radiative fluxes at the snow or sea

ice surface, because surface melting and ice growth are quite sensitive to short-

wave and longwave radiation (Maykut and Untersteiner 1971, Curry and Ebert

1990). In turn, the phase changes and heat storage in the snow or ice cover set the

intensity of the surface turbulent and radiative fluxes and the conductive flux into

the ice (Makshtas 1991a). As a result, there is a strong climatic feedback between

the sea ice and the albedo in polar regions (Barry 1984).

Despite the intensive development of methods for remotely sensing the atmo-

sphere, the main source of data on the climatic characteristics of Arctic cloudiness

is still in-situ visual observations. Though polar-orbiting satellites frequently cross

the Arctic, the small image contrast between the ice cover and the clouds in the

visible in summer and in the infrared in winter makes using satellite information

difficult for estimating cloudiness in polar regions, as Raschke (1987) explains.

Figure 1 illustrates this problem. It shows cloud amounts deduced from satellite

Figure 1. Annual variation in

monthly averaged total cloud

amount over the Arctic Ocean

on the basis of satellite data,

v i s u a l observations on the

North Pole drifting stations,

and the cloud climatology pub-

lished by Warren et al. (1988).

The satellite and Warren et al.

North Pole Stations

Warren et al. (1988)

traces derive only from grid

Satellites

points north of 80N. (Adapted

Jan

Mar

May

Jul

Sep

Nov

from Moritz et al. 1993.)

Feb

Apr

Jun

Aug

Oct

Dec

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