doc/phys_pkgs/darwin_light.rst

a4f2018aab Oliv*0001 .. include:: ../defs.hrst
                0002
                0003 .. _Light:
                0004
                0005 Non-spectral Light
                0006 ^^^^^^^^^^^^^^^^^^
                0007
                0008 To have non-spectral light, disable the radtrans package.
                0009
                0010 There are three alternatives for incoming PAR at the surface: if
                0011 :varlink:`PARfile` is set, it is read in from files (it can also be set to a
                0012 constant, :varlink:`PARconst`); if :varlink:`darwin_useQsw`\ =T, it is computed
                0013 from model shortwave radiation,
                0014
                0015 .. math::
                0016
                0017    I(0) = -f_{\op{PAR}} c_{\op{PAR}} Q_{SW}
                0018    \;;
                0019
                0020 otherwise, it is computed as a function of latitude using solar declination,
                0021 see :filelink:`~pkg/darwin/darwin_insol.F`.  Note that this only works for
                0022 lat-lon grids.
                0023
                0024 Incoming PAR is reduced by the fraction of the ocean surface covered
                0025 by ice, unless model shortwave radiation, which has seaice already taken into
                0026 account, is used,
                0027
                0028 .. math::
                0029
                0030    I(0) = (1 - f_{\op{ice}}) I_{\op{in}}
                0031    \;.
                0032
                0033 The ice cover fraction, :math:`f_{\op{ice}}`, is taken from the seaice
                0034 package if compiled, and read in from :varlink:`icefile` otherwise.
                0035
                0036 PAR is attenuated by water and chlorophyll,
                0037
                0038 .. math::
                0039
                0040    I(r) = I(0) \op{e}^{-\int_0^r k_{\op{w}} + k_{\op{Chl}} \op{Chl} \,\mathrm{d}r}
                0041
                0042 If :varlink:`DARWIN_AVPAR` is defined, the resulting function is averaged
                0043 over the thickness of a grid layer.  When no chlorophyll tracer is used (#undef
                0044 :varlink:`DARWIN_ALLOW_CHLQUOTA`), it is computed from total phytoplankton
                0045 carbon biomass.  With :varlink:`DARWIN_ALLOW_GEIDER`, it is taken from the
                0046 computation at the previous time step, without, a fixed Chlorophyll-to-C ratio,
                0047 :varlink:`R_ChlC`, is used.
                0048
                0049 .. csv-table:: Non-spectral light parameters
                0050    :delim: &
faa67d1773 Oliv*0051    :widths: 18,12,14,16,40
a4f2018aab Oliv*0052    :header: Param, Symbol, Default, Units, Description
                0053
                0054    :varlink:`parfrac`    & :math:`f_{\op{PAR}}` & 0.4      &                    & fraction of Qsw that is PAR
                0055    :varlink:`parconv`    & :math:`c_{\op{PAR}}` & 1/0.2174 & µEin/s/W           & conversion from W/m2 to uEin/m2/s
                0056    :varlink:`katten_w`   & :math:`k_{\op{w}}`   & 0.04     & 1/m                & attenuation coefficient of water
                0057    :varlink:`katten_Chl` & :math:`k_{\op{Chl}}` & 0.04     & m\ :sup:`2`/mg Chl & attenuation coefficient of chlorophyll
faa67d1773 Oliv*0058    :varlink:`aphy_chl_ave` &                    & 0.02     & m\ :sup:`2`/mg Chl & Chl-specific absorption coefficient for photosynthesis