\begin{table}%T1
\caption{Definitions of atmospheric time constants.}
\label{tab:def}
%\medskip
%\centering
\small
\begin{tabular}{lll}
\hline\hline
\noalign{\smallskip}
Quantity of interest & Formula & Time constant\\ 
\noalign{\smallskip}
\hline
\noalign{\smallskip}
Phase SF & $D_\varphi(t) = (t/\tau_0)^{5/3}$ & 
$\tau_0 = 0.314\; r_0/\overline{V}_{5/3}$  \smallskip \\
Piston SF, $t<  d/V$ & $D_\phi(t) = (t/t_1)^{2}$ & 
$t_1 = 0.273\; (r_0/\overline{V}_{2})(d/r_0)^{1/6}$  \smallskip \\
Piston SF,  $t> d/V$ & $D_\phi(t) = (t/t_0)^{5/3}$ & 
$t_0 = 0.66 \; \tau_0  $  \smallskip \\ 
Piston variance during an exposure $t> d/V$ & $\sigma^2_\phi (t)=
(t/T_0)^{5/3}$ & 
$ T_0 = 2.58\; \tau_0  $ \smallskip \\
Phase tracker error, $\nu_{\rm c}> 0.3 \; d/V$ & $\sigma_{\rm c}^2 (\nu_{\rm c})= (2 \pi \nu_{\rm c} t_1)^{-2}$
& $t_1$  \smallskip \\
\hline
\end{tabular}
\end{table}