\vsssub
\subsubsection{~$S_{bot}$: \js\ bottom friction} \label{sec:BT1}
\vsssub

\opthead{BT1}{\js\ experiment}{H. L. Tolman}

\noindent 
A simple parameterization of bottom friction is the empirical, linear \js\
parameterization \citep{art:JONSWAP}, as used in the \wam\ model
\citep{art:WAM88}. Using the notation of \cite{tol:JPO91b}, this source term
can be written as

%-------------------------%
% JONSWAP bottom friction %
%-------------------------%
% eq:JONSWAP_bot

\begin{equation}
\cS_{bot}(k,\theta) = 2 \Gamma \: \frac{n-0.5}{gd} \: N(k,\theta)
\: , \label{eq:JONSWAP_bot}
\end{equation}

\noindent
where $\Gamma$ is an empirical constant, which is estimated as $\Gamma =
-0.038\:\mbox m^2 \mbox s ^{-3}$ for swell \citep{art:JONSWAP}, and as $\Gamma
= -0.067\:\mbox m^2 \mbox s^{-3}$ for wind seas \citep{art:BK83}. $n$ is the
ratio of phase velocity to group velocity given by (\ref{eq:cg}). The default
value for $\Gamma = -0.067$ can be redefined by the user by changing the {\F SBT1} namelist parameter {\code GAMMA}.