SURFACE FLUXES
233
Numerical Weather Prediction (NWP), but important physics is lost. In
general, a fraction, f i , of the ocean surface may be covered by sea-ice,
leaving a fraction, f o = 1 − f i , exposed to the atmosphere above. The
ocean surface fluxes are, therefore, given by
Q = f i Q io + f o Q as
F = f i F io + f o F as + R
τ = f i τ io + f o τ as ,
(4)
where the subscripts ”as” and ”io” denote air-sea and ice-ocean fluxes,
respectively. In (4), R is the continental runoff. The number of required
fields has already expanded from 4 to 10, and there are further increases
as the air-sea, ice-ocean and air-ice fluxes are explored individually below.
2.1
Air-sea fluxes
The air-sea heat flux has radiative (shortwave and longwave), turbulent (sensible and latent) and particle components, which are all defined
here as positive when they act to heat the ocean. Similarly, water fluxes
(precipitation, evaporation and runoff) are positive when they add water
to the ocean. The wind stress is a turbulent flux aligned to the vector
difference between
U (d) and the ocean surface current,
U 0 . A major
complication for GODAE is that air-sea heat and freshwater fluxes need
to be broken down into estimates of their components, namely;
Q as = Q S + Q L + Q E + Q H + Q P
F as = P + E,
(5)
because the penetration of solar radiation, Q S into the upper ocean is an
important process governing the evolution of SST (Denman and Miyake,
1973) and evaporation, E, from the ocean surface is accompanied by a
latent heat flux, Q E = −ΛE, where Λ = 2.5 × 10 6 j/kg is the latent
heat of vaporization. Delivery of near real time estimates of all these
components to a GODAE system is a daunting challenge. Instead, at
least some degraded products will need to be used, but then the difficulty
will be to specify the appropriate uncertainty. The growth of air-sea flux
fields from 4 to as many as 14 is shown in Table 1.
Solar radiation includes wavelengths between 0.3 and 3µ and is always
positive. It passes through the atmosphere where it is attenuated, mainly
by clouds, before reaching the surface as solar insolation, Q I , and the
surface albedo (α) is the fraction that is reflected back to the atmosphere.
About 40% of this insolation is diffuse, with an albedo α df = 0.06 (Payne,
233
Numerical Weather Prediction (NWP), but important physics is lost. In
general, a fraction, f i , of the ocean surface may be covered by sea-ice,
leaving a fraction, f o = 1 − f i , exposed to the atmosphere above. The
ocean surface fluxes are, therefore, given by
Q = f i Q io + f o Q as
F = f i F io + f o F as + R
τ = f i τ io + f o τ as ,
(4)
where the subscripts ”as” and ”io” denote air-sea and ice-ocean fluxes,
respectively. In (4), R is the continental runoff. The number of required
fields has already expanded from 4 to 10, and there are further increases
as the air-sea, ice-ocean and air-ice fluxes are explored individually below.
2.1
Air-sea fluxes
The air-sea heat flux has radiative (shortwave and longwave), turbulent (sensible and latent) and particle components, which are all defined
here as positive when they act to heat the ocean. Similarly, water fluxes
(precipitation, evaporation and runoff) are positive when they add water
to the ocean. The wind stress is a turbulent flux aligned to the vector
difference between
U (d) and the ocean surface current,
U 0 . A major
complication for GODAE is that air-sea heat and freshwater fluxes need
to be broken down into estimates of their components, namely;
Q as = Q S + Q L + Q E + Q H + Q P
F as = P + E,
(5)
because the penetration of solar radiation, Q S into the upper ocean is an
important process governing the evolution of SST (Denman and Miyake,
1973) and evaporation, E, from the ocean surface is accompanied by a
latent heat flux, Q E = −ΛE, where Λ = 2.5 × 10 6 j/kg is the latent
heat of vaporization. Delivery of near real time estimates of all these
components to a GODAE system is a daunting challenge. Instead, at
least some degraded products will need to be used, but then the difficulty
will be to specify the appropriate uncertainty. The growth of air-sea flux
fields from 4 to as many as 14 is shown in Table 1.
Solar radiation includes wavelengths between 0.3 and 3µ and is always
positive. It passes through the atmosphere where it is attenuated, mainly
by clouds, before reaching the surface as solar insolation, Q I , and the
surface albedo (α) is the fraction that is reflected back to the atmosphere.
About 40% of this insolation is diffuse, with an albedo α df = 0.06 (Payne,