** Brian Arbic**

University of Texas, Austin

### Global energy dissipation rate of oceanic low-frequency flows by quadratic bottom drag: Results from observations and 1/32 degree models

The energy budget of the deep ocean is a subject of great current
interest, because of the potential implications for the strength of
the overturning circulation. An important energy source is the
1 TW wind power input into geostrophic (low-frequency) flows.
How these flows dissipate is largely unknown.

Here we discuss one potential dissipation mechanism, namely bottom boundary layer drag.
First, we show that eddy kinetic energy in idealized geostrophic
turbulence models has realistic length scales, vertical structure, and
amplitudes only if the nondimensional bottom friction strength is of
order one. This is true for both linear and quadratic bottom drag
(Arbic and Scott, in press). Next, we estimate the global energy
dissipation rate of oceanic low-frequency flows by quadratic bottom
drag (Sen et al., in review). We use data from 290 moored near-bottom
current meters. We also utilize satellite altimetry data, 1) to
estimate the bias in the global integral due to the poor sampling of
the ocean by current meters, and 2) to estimate global maps of bottom
velocity, given relationships computed at the mooring locations
between surface and bottom flows. Finally, the dissipation rate is
estimated from the output of a global ocean model run at
1/32 degree resolution (Arbic et al., in review). The model is
validated by comparison to the current meter dataset. Our estimates
of the dissipation rate range from 0.14 to 0.83 TW, with both the low
and high ends likely being unrealistic. While uncertainty remains, we
can say that bottom boundary layers very likely dissipate a
substantial fraction of the 1 TW wind-power input into
geostrophic flows.