PARAMETER ( MASCON =
     &    .0001 * 1.16898 / ( 6.09715E+03 + 4.60178E-04 ))
!     .0001 converts the numbers in the DATA statement to optical depth.
!     1.16898 converts .55 micron optical depth to the Slingo (1989)
!     band-1 optical depth (from the HadCM2 mod) & then we divide by
!     the total k (scattering+absorption) from spec3a_sw_3_tknlaero
!     for the same band (or very nearly so). spec3a_sw_3_tknlaero is
!     a file which defines the spectral properties of aerosols for 
!     HadAM3.