Sensible Heat Flux Measurements Near a Cold Surface
YIN-CHAO YEN
I. GENERAL REVIEW OF PREVIOUS WORK
Eddy flux can be measured directly, but the method is expensive and complex and has generally
been used only for short periods of time. For these reasons, estimates of these fluxes are generally
obtained with the use of semi-empirical formulas involving simultaneous measurements of wind,
temperature and humidity at several levels.
Field measurements have been conducted by numerous investigators, but the results usually
differ from one another. In addition, most of the work was done over grass fields, crops, open water,
ice, and glaciers. Swinbank (1951) reported the measurement of vertical transfer of heat and water
vapor by eddies in the lower atmosphere. Thorpe et al. (1973) studied the eddy correlation mea-
surements of evaporation and sensible heat flux over Arctic sea ice and reported bulk transfer
coefficients of cn = 1.2 103 and cw = 0.55 103 with the Bowen ratio ranging from 1 to 15.
Andreas et al. (1979) reported the measurement of turbulent heat flux from Arctic leads and
suggested the sensible component of their turbulent heat flux can be predicted from bulk quantities.
They suggested the results can be either expressed in an exponential relation, i.e., Nu = 0.14
Rex0.72, or in a linear form as Nu = 1.6 103 Rex + 1400, where Nu is the Nusselt number and Rex
is the Reynolds number based on fetch across the leads. They stated, based on the similarity theory,
that these expressions applied to the latent heat transfer as well. Over leads in winter, they found the
sensible heat flux is two to four times greater than the latent heat flux. Wesley et al. (1970)
employed a three-dimensional pressure-sphere anemometer and fast thermometer system to mea-
sure the vertical heat flux density in the atmosphere surface layer at 14 m above alta fescue and
snap beans. They found the system is sufficiently small and has adequate high-frequency response
and accuracy for eddy correlation measurements within 1 m of the surface.
Verma et al. (1978) reported measurements of turbulent exchange coefficient for sensible heat
and water vapor over alfalfa and soybeans under conditions of advection. The exchange coefficient
for sensible heat Kh is found to be generally greater than the exchange coefficient for water vapor
Kw, which is in contradiction to the usual assumption of equality of Kh and Kw under nonadvective
(lapse or unstable) conditions (i.e., the net transfer of both sensible heat and water vapor are
directed away from the surface). On the other hand, under advective conditions heat and water
vapor can be transferred in opposite directions. These results were confirmed by conclusions
derived from a theoretical analysis by Warhaft (1976), who stated that the greatest departure of Kh/
Kw from unity will occur where temperature and humidity gradients are of opposite signs.
Miyake et al. (1970) reported the comparison of turbulent fluxes over water determined by
profile and eddy correlation techniques. The measurements were made with limited fetch and were
under near-neutral conditions. However, the agreements were found to be well within the experi-
mental error.
Hicks (1970) developed a general approach for the measurement of atmospheric fluxes near the
surface; a covariance computer capable of accepting analog signals representing any two atmo-
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