consideration. Although the estimates may differ from the observed radiation for
both the clear-sky and overcast-sky cases, each of the five parameterization schemes
does predict temporal behavior that coincides with that in the experimental data.
Though we here confirm KL&A's longwave parameterization, eq 12, with only
Antarctic data, remember that KL&A formulated that relation on the basis of both
Arctic and Antarctic data. Consequently, we have no reason to suspect that it is
inappropriate to use it in our Arctic sensitivity studies in the next section.
MODEL SENSITIVITY TO THE DESCRIPTION
OF LONGWAVE RADIATION
An equation for the heat budget of the upper surface is a necessary component
of prognostic and climatic sea ice models regardless of their complexity (Maykut
and Untersteiner 1971, Parkinson and Washington 1979, Makshtas et al. 1988, Ebert
and Curry 1993). In contrast with Maykut and Untersteiner's (1971) nonstationary,
one-dimensional sea ice model, in which the characteristics of the energy exchange
between the atmosphere and the ocean were prescribed, in subsequent models the
turbulent surface fluxes of sensible (Hs) and latent heat (HL), the longwave radia-
tion balance (B), and the shortwave radiation balance are internal parameters of
the model. That is, these are simulated conditions of the sea ice cover and, as such,
are prescribed by the parameters of the atmospheric surface layer.
Above we showed that, using the same input data, calculations of the longwave
radiation at a sea ice surface differ depending on which of several popular
parameterizations we use. It is, thus, interesting to consider how applying these
parameterizations in a sea ice model might affect the computed equilibrium thick-
ness of the sea ice. For this purpose, we perform several numerical experiments
using the one-dimensional sea ice model described by Makshtas (1991b).
As the external parameters in the model, we used the 3-hour standard meteo-
rological observations from October 1982 to October 1983 on drifting station North
Pole 25, which was above 85N during that period. For the daily averaged value
of incoming shortwave radiation, we averaged continuous measurements of the
global solar radiation. The heat flux from the ocean to the bottom of the sea ice
was assigned the usual value, 2 W/m2 (e.g., Parkinson and Washington 1979).
For calculating the turbulent surface heat fluxes, we use the bulk-aerodynamic
method (e.g., Andreas 1996):
Hs = ρ cp CHr Ur (Ts - Tr ) ,
(13a)
HL = ρ Lv CEr Ur (Qs - Qr ) ,
(13b)
where ρ = the air density
cp = the specific heat of air at constant pressure
Lv = the latent heat of vaporization or sublimation
Ur = the wind speed at reference height r
Ts and Qs = the temperature and specific humidity of the air at the surface
Tr and Qr = the temperature and humidity at height r.
The crux of the bulk-aerodynamic method is defining the bulk transfer coefficients
appropriate at height r, CHr and CEr. These are (e.g., Andreas and Murphy 1986)
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