\begin{table}%t1
%\centering
\par
\caption{Time-averaged $b_1$ and $b_2$ values.}
%\centering
\par
\begin{tabular}{c c c c c c c}
\hline\hline
Model  & \multicolumn{2}{c}{Model~1} & \multicolumn{2}{c}{Model~2} &
\multicolumn{2}{c}{Model~3} \\
\hline
Height & $b_1$ & $b_2$ & $b_1$ & $b_2$ & $b_1$ & $b_2$ \\
(km)   & ...   & ...   & ...   & ...   & ...   & ...   \\
\hline
  500 & 4.43E-01 & 3.12E-01 & 3.82E-02 & 8.99E-03 & 4.21E-02 & 6.63E-02 \\
 1000 & 5.27E+00 & 1.73E+00 & 6.73E+00 & 1.50E+00 & 1.01E+02 & 1.34E+01 \\
 1500 & 1.05E+01 & 1.89E+00 & 4.18E+01 & 3.71E+00 & 4.61E+03 & 7.38E+01 \\
 2000 & 8.02E+02 & 1.27E+01 & 8.31E+03 & 3.75E+01 & 1.25E+08 & 1.35E+04 \\
 2400 & 5.44E+03 & 1.69E+01 & 4.37E+04 & 4.66E+01 & 6.13E+12 & 1.26E+07 \\
\hline
\end{tabular}
\end{table}