Unlike the shortwave radiation, no corrections are made for sloped surfaces.
4.1.3 Sensible Heat
The sensible heat flux incorporates the transfer of energy between the surface and the
atmosphere due to molecular conduction and turbulent mixing. It depends on the
temperature gradient between the two media. It is given as (Jordan 1991)
H = ( e0 + ρac p,aCDW ) (Ta - T )
h
(4.5)
with e0 the windless exchange coefficient for sensible heat (2.0 W/m2) (Jordan 1996), ρa
the air density (kg/m3), cp,a the specific heat of dry air at constant pressure (1005.6
J/kgK), CD the dimensionless drag coefficient (discussed below), W the wind speed (m/s)
at a height of 2.0 m, and Ta the air temperature (K) at a height of 2.0 m. Based on the
work of Balick et al. (1981), ρa = 0.00348( Pa / Ta ) where 0.00348 (kgK/m3Pa) is the
molecular weight of air divided by the universal gas constant and Pa is the air pressure
(Pa).
h
The parameterization of the drag coefficient, CD , is dependent on the snow depth. If the
snow depth is greater than measuring height, Za (m) of the air temperature, wind speed
and relative humidity, then CD = 0.002 + 0.006(Z / 5000) , where Z is the site elevation
h
(m). Otherwise (Koenig 1994),
CD = ΓhChgn0
h
(4.6)
where
⎧
1.0
Rib < 0.0
⎪
(1.0 - 16.0Rib )
0.5
⎪
⎪
Γh = ⎨
Rib = 0.0
1.0
⎪
1.0
.
(4.7)
⎪
⎪ 1.0 - 5.0Rib 0.0 < Rib < 0.2
⎩
(
)
2
⎡k ln Za z0 ⎤
2 gZa (Ta - T )
g
=⎣
⎦
Rib =
Chgn0
(Ta + T )W 2
rch
Γh is the sensible heat exchange stability correction factor, Chgn0 is the bulk transfer
coefficient near the ground, Rib is the bulk Richardson number, g is the gravitational
g
length (0.0006 m for snow/ice, 0.0001 m for pavements, 0.001 m for all soils), and rch is
the turbulent Schmidt number (0.63).
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