Geoscience Reference
In-Depth Information
Chapter 5
Turbulence Scales for the Ice/Ocean Boundary
Layer
Abstract: Understanding the scales of turbulence in the IOBL is the central issue
in developing reasonable models for transfer of properties between the ice cover
and the underlying ocean. This chapter presents several examples from field obser-
vations that shed light on the impact of both stress and buoyancy on turbulence in
the IOBL, and use them to develop a heuristic approach to specifying the mixing
length. A key in this development is the apparent connection between the inverse
wave number at the peak of the area-preserving
w
spectrum and the master length
scale for turbulence. As discussed in Section 3.6, the concept was first explored
for the IOBL using data from the 1972 AIDJEX Pilot Study (McPhee and Smith
1976). Figure 5.1, adapted from that work, shows our estimates of eddy viscos-
ity based on admittedly crude analysis of the spectra observed during an AIDJEX
storm, analyzed in the manner suggested by Busch and Panofsky (1968), and com-
pared with calculations from one of the first attempts at large eddy simulation for
the atmospheric boundary layer (Deardorff 1972). This was far from conclusive;
however, later measurements tended to confirm that basic approach.
5.1 Neutral OBL Scales
Several ice-station experiments have provided data on spectral characteristics of
turbulence at various levels in the IOBL. Here we concentrate on two experiments
that illustrate the connection between the inverse of the wave number at the peak
of the area preserving vertical velocity variance spectrum and
λ
, as introduced in
Section 3.6.
5.1.1 Ice Station Weddell
The hodograph of Reynolds stress traction vectors depicted in Fig. 4.4 was obtained
during a storm at Ice Station Weddell in 1992 (McPhee and Martinson 1994). For
