Jh. Trowbridge et Sj. Lentz, DYNAMICS OF THE BOTTOM BOUNDARY-LAYER ON THE NORTHERN CALIFORNIA SHELF, Journal of physical oceanography, 28(10), 1998, pp. 2075-2093
Time-series measurements of velocity, temperature, and conductivity on
the northern California shelf during two winter seasons permit an obs
ervational test, in vertically integrated form, of a simple set of sub
inertial momentum and heat balances for the bottom boundary layer, whi
ch have resulted from recent theoretical work. These are 1) an along-i
sobath momentum equation that reduces to a classic Ekman balance; 2) a
cross-isobath momentum equation in which the Ekman balance is modifie
d by a buoyancy force caused by distortion of the isopycnal surfaces w
ithin the boundary layer; and 3) a heat balance in which variability o
f temperature is produced by cross-isobath advection. The measurements
confirm the importance of buoyancy in the cross-isobath momentum equa
tion, and, as has recently been predicted theoretically, they indicate
that buoyancy is a dominant effect when the boundary layer is thick,
which typically occurs during downwelling-favorable flows. An Ekman ba
lance describes subinertial fluctuations in the along-isobath momentum
equation with only moderate success. In contrast to idealizations mad
e in most theoretical work, a buoyancy force caused by an along-isobat
h temperature gradient is as important as bottom stress in the mean al
ong-isobath momentum equation, and along-isobath advection is as impor
tant as cross-isobath advection in the heat balance.