;
;jeff snider, univeristy of wyoming, march 2006
;
;diffusivity and conductivity are temperature-dependent see chapter 13 of P&K (1997 edition)
;
function dif_h2o, p_parcel, tk_parcel
;
common  constants, gascon, rho_h2o, mw_nh42so4, rho_nh42so4, sigma_0,      $
        sigma_t, dsigmadmolality_nh42so4, dsigmadmolality_nacl, mw_h2o,    $
        mw_nacl, rho_nacl, tkmelt, c_nh42so4, a_nh42so4, c_nacl, a_nacl,   $
        cp_air_o, cp_h2o_o, mw_air, gravity, p0, alpha, beta_local,        $
        gascon_h2o, cw_h2o_o, tk_o, lv_o, ew_o, tk_aerosol, salt_type,     $
        epsilon, c_twomey, k_twomey, aerosol_type, right_tail,             $
        gascon_air, tc_base, tk_base, p_base, h_start, hmax,               $
        r0, dt, rmin, rmax, coef, epsilon_aerosol, specific_volume_meas,   $
        nchan, mw_salt, rho_salt, a_salt, c_salt, specific_volume_base,    $
        dsigmadmolality_salt, rho_insoluble, volume_insoluble_to_soluble,  $
        mixrat_tot_1,r_1,geo_sigma_1,mixrat_tot_2,r_2,geo_sigma_2,         $
        tk_start,p_start,sratio_start,mixrat_tot_3,r_3,geo_sigma_3
;
return, 0.211d-4*(p0/p_parcel)*(tk_parcel/tkmelt)^1.94d
;
end