From d9cf6ebf3f6db98fdd030be97c5d308429fc1041 Mon Sep 17 00:00:00 2001 From: Maggie Hendry Date: Tue, 30 Jan 2024 13:29:17 +0000 Subject: [PATCH] jules_snow consistent with metadata changes jules:#1482 including general tidying --- .../doc/source/namelists/jules_snow.nml.rst | 276 ++++++++++++------ 1 file changed, 185 insertions(+), 91 deletions(-) diff --git a/user_guide/doc/source/namelists/jules_snow.nml.rst b/user_guide/doc/source/namelists/jules_snow.nml.rst index f14128a1..9c3d9144 100644 --- a/user_guide/doc/source/namelists/jules_snow.nml.rst +++ b/user_guide/doc/source/namelists/jules_snow.nml.rst @@ -39,16 +39,16 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office FALSE No effect. - - + + .. nml:member:: frac_snow_subl_melt :type: integer :permitted: 0 or 1 :default: 0 - + Switch for use of snow-cover fraction in the calculation of sublimation and melting. - + 0. Off 1. On @@ -56,24 +56,24 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office .. nml:member:: graupel_options :type: integer - :permitted: 0 or 1 or 2 + :permitted: 0, 1 or 2 :default: 0 - + Switch for treatment of graupel in the snow scheme - + 0. Include graupel as snowfall 1. Ignore graupel in the surface snowfall 2. Treat graupel separately - Always "Include graupel as snowfall" (option 0) in standalone JULES because + Always "Include graupel as snowfall" (option 0) in standalone JULES because separate snow and graupel driving data are not available. - If graupel is included in the UM surface snowfall diagnostic - then JULES can either include this graupel as snow in the surface scheme (option 0), + If graupel is included in the UM surface snowfall diagnostic + then JULES can either include this graupel as snow in the surface scheme (option 0), ignore this graupel completely, thereby breaking conservation - of water and energy in the coupled land-atmosphere model (option 1) or - treat graupel seperately (currently this only means allowing graupel to + of water and energy in the coupled land-atmosphere model (option 1) or + treat graupel separately (currently this only means allowing graupel to fall straight through the canopy) - + .. nml:member:: dzsnow @@ -104,7 +104,7 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Only used if :nml:mem:`JULES_VEGETATION::can_model` = 4. - The model of snow under the canopy is currently only suitable for coniferous trees. + The model of snow under the canopy is currently only suitable for trees. TRUE Snow can be held under the canopy. @@ -122,7 +122,7 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Grain size for fresh snow (\ |mu|\ m). - Only used if :nml:mem:`JULES_RADIATION::l_snow_albedo` = TRUE. See HCTN30 Eq.15. + Only used if :nml:mem:`JULES_RADIATION::l_snow_albedo` = TRUE or :nml:mem:`JULES_RADIATION::l_embedded_snow` = TRUE. .. nml:member:: rmax @@ -132,7 +132,7 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Maximum snow grain size (\ |mu|\ m). - Only used if :nml:mem:`JULES_RADIATION::l_snow_albedo` = TRUE. See HCTN30 p4. + Only used if :nml:mem:`JULES_RADIATION::l_snow_albedo` = TRUE or :nml:mem:`JULES_RADIATION::l_embedded_snow` = TRUE. .. nml:member:: snow_ggr @@ -142,9 +142,24 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Snow grain area growth rates (\ |mu|\ m\ :sup:`2` s\ :sup:`-1`). - Only used if :nml:mem:`JULES_RADIATION::l_snow_albedo` = TRUE. See HCTN30 Eq.16. + Only used if :nml:mem:`JULES_RADIATION::l_snow_albedo` = TRUE or + :nml:mem:`JULES_RADIATION::l_embedded_snow` = TRUE, and requires + a snow grain size to calculate the albedo. + + The three values are for melting snow, cold fresh snow and cold + aged snow respectively, the use of which depends on the setting + :nml:mem:`i_grain_growth_opt` as follows: - The 3 values are for melting snow, cold fresh snow and cold aged snow respectively. + ============================= ========================= ================================================================= + :nml:mem:`i_grain_growth_opt` Growth rates used Notes + ============================= ========================= ================================================================= + 0 :nml:mem:`snow_ggr` (1:3) Uses all values; melting snow, cold fresh snow and cold aged snow + 1 :nml:mem:`snow_ggr` (1) Uses values for melting snow only. + + For cold snow a separate scheme is used following + :ref:`Taillandier et al. (2007)`, where the + parameters are currently hard-wired. + ============================= ========================= ================================================================= .. nml:member:: amax @@ -154,11 +169,27 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Maximum albedo for fresh snow. - Only used if :nml:mem:`JULES_RADIATION::l_snow_albedo` or :nml:mem:`JULES_SURFACE::l_elev_land_ice` - are true + Only used if :nml:mem:`JULES_RADIATION::l_snow_albedo` or + :nml:mem:`JULES_SURFACE::l_elev_land_ice` is TRUE. Values 1 and 2 are for VIS and NIR wavebands respectively. + When: + + :nml:mem:`JULES_RADIATION::l_snow_albedo` = TRUE + These parameters are used as limits at all snow-covered + grid points. + + :nml:mem:`JULES_RADIATION::l_embedded_snow` = TRUE + These parameters are not used. + + :nml:mem:`JULES_SURFACE::l_elev_land_ice` = TRUE + Irrespective of whether either of the two previous options + are selected, these parameters are used to adjust the albedo + of dense snow to a value more appropriate for firn. See + also :nml:mem:`aicemax`. + + .. nml:member:: aicemax :type: real(2) @@ -166,7 +197,8 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Maximum albedo for bare ice - Only used if :nml:mem:`JULES_SURFACE::l_elev_land_ice` = TRUE. See also `rho_firn_albedo` + Only used if :nml:mem:`JULES_SURFACE::l_elev_land_ice` = + TRUE. See also :nml:mem:`rho_firn_albedo`. Values 1 and 2 are for VIS and NIR wavebands respectively. @@ -176,7 +208,15 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office :type: real :default: 50.0 - Used in exponent of equation weighting snow-covered and snow-free albedo. + Used in the calculation of the weighting factor for snow in the + setting of the overall surface albedo, the surface resistance + and surface melting. It represents the inverse of the e-folding + depth for masking by snow. A higher value indicates that masking + by snow is more effective. + + N.B. This was originally used to multiply the snow mass (with a + standard value of 0.2), but is now used to multiply the snow + depth. .. nml:member:: dtland @@ -186,7 +226,12 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Degrees Celsius below zero at which snow albedo equals cold deep snow albedo. - Only used if :nml:mem:`JULES_RADIATION::l_snow_albedo` = FALSE. This is 2.0 in HCTN30 Eq4. + This is used only if the diagnostic snow albedo scheme is + selected, i.e. if :nml:mem:`JULES_RADIATION::l_snow_albedo` = + FALSE and :nml:mem:`JULES_RADIATION::l_embedded_snow` = + FALSE. This is 2.0 in HCTN30 Eq4. + + Must not be zero. .. nml:member:: kland_numerator @@ -196,11 +241,13 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Used in snow-ageing effect on albedo. - Only used if :nml:mem:`JULES_RADIATION::l_snow_albedo` = FALSE. - - Must not be zero. + This is used only if the diagnostic snow albedo scheme is + selected, i.e. if :nml:mem:`JULES_RADIATION::l_snow_albedo` = + FALSE and :nml:mem:`JULES_RADIATION::l_embedded_snow` = + FALSE. This is 2.0 in HCTN30 Eq4. - ``kland`` is computed by dividing this value by :nml:mem:`dtland` - see HCTN30 Eq4. + ``kland`` is computed by dividing this value by + :nml:mem:`dtland` - see HCTN30 Eq4. .. nml:member:: can_clump @@ -210,13 +257,18 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Clumping parameter for snow on the canopy in calculation of albedo. - Only used if :nml:mem:`JULES_VEGETATION::can_model` = 4, :nml:mem:`JULES_SNOW::cansnowpft` = TRUE on that surface tile and :nml:mem:`JULES_RADIATION::l_embedded_snow` = TRUE. + Only used if :nml:mem:`JULES_VEGETATION::can_model` = 4, + :nml:mem:`JULES_RADIATION::l_embedded_snow` = TRUE and + :nml:mem:`cansnowpft` = TRUE on that surface tile. The model of snow under the canopy is currently only suitable - for coniferous trees. + for trees. The inverse of this parameter specifies the fraction of the - canopy over which snow is distributed when calculating the albedo. + canopy over which snow is distributed when calculating the + albedo. It should not be less than 1 and higher values indicate + that snow on a canopy is more clumped, leaving more of the bare + canopy exposed. .. nml:member:: n_lai_exposed @@ -228,8 +280,8 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office A power-law distribution of leaf area density is assumed within the canopy for calculating masking of snow by vegetation using - the embedded scheme. Larger values imply greater densities - toward the base of the canopy. + the embedded scheme. Higher values indicate that snow is more + effective in covering vegetation. Only used if :nml:mem:`JULES_RADIATION::l_embedded_snow` = TRUE. @@ -241,14 +293,16 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Minimum LAI in calculation of albedo in the presence of snow. - A minimum albedo is imposed when calculating the albedo of - plant canopies (historically 0.5). This parameter allows it - to be set for each PFT in the presence of snow. A separate variable, - :nml:mem:`JULES_PFTPARM::lai_alb_lim_io` is used in the absence of snow. + A minimum albedo is imposed when calculating the albedo of plant + canopies (historically 0.5). This parameter allows it to be set + for each PFT in the presence of snow. Crudely, it represents the + stem area of vegetation remaining when the true LAI is 0. A + separate variable, :nml:mem:`JULES_PFTPARM::lai_alb_lim_io` is + used in the absence of snow. .. nml:group:: Other snow parameters - + .. nml:member:: rho_snow_const :type: real @@ -256,10 +310,12 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Constant density of lying snow (kg m\ :sup:`-3`). - This value is used if :nml:mem:`nsmax` = 0, in which case all - snow is modelled as a single layer of constant density. If - :nml:mem:`nsmax` > 0, snow density is prognostic. + If :nml:mem:`nsmax` = 0, snow is modelled as a single layer of + constant density using this value. + If :nml:mem:`nsmax` > 0, snow density is prognostic, except for + snow on the canopy when :nml:mem:`cansnowpft` is TRUE, and for + thin layers of snow when :nml:mem:`nsmax` > 0. .. nml:member:: rho_snow_fresh @@ -269,17 +325,22 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Density of fresh snow (kg m\ :sup:`-3`). - This value is only used if :nml:mem:`nsmax` > 0. + Only used if :nml:mem:`nsmax` > 0. .. nml:member:: rho_firn_albedo :type: real :default: 550.0 - If :nml:mem:`JULES_SURFACE::l_elev_land_ice` = TRUE, this is the threshold density (as measured over the ~top 10cm, depending - on how the dzsnow layers are specified) at which the grain-size calculation of prognostic snow albedo will switch to one - dependent on the surface density of the snowpack. Albedo is linearly scaled between `amax` for `rho_snow_const` and `aicemax` - for rho_ice=917 kg/m^3. + Only used if :nml:mem:`JULES_SURFACE::l_elev_land_ice` = TRUE. + + This is the threshold density (as measured over the ~top 10 cm, + depending on how the :nml:mem:`dzsnow` layers are specified) at + which the grain-size calculation of prognostic snow albedo will + switch to one dependent on the surface density of the + snowpack. Albedo is linearly scaled between :nml:mem:`amax` for + :nml:mem:`rho_snow_const` and :nml:mem:`aicemax` for density the + of ice (917 kg m\ :sup:`-3`). .. nml:member:: snow_hcon @@ -287,9 +348,12 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office :type: real :default: 0.265 - Thermal conductivity of lying snow (W m\ :sup:`-1` K\ :sup:`-1`). + Thermal conductivity of lying snow (W m\ :sup:`-1` K\ + :sup:`-1`). - See HCTN30 Eq.42. + This value is used for all snow if :nml:mem:`nsmax` = 0, but only + for thin snow if :nml:mem:`nsmax` > 0. See HCTN30 Eq.42. for its + application. .. nml:member:: snow_hcap @@ -345,9 +409,12 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office :type: real(npft) :default: MDI - Constant term in the background unloading rate for snow on the canopy. + Constant term in the background unloading rate for snow on the + canopy. Snow is unloaded from the canopy as a background process + or because it is melting. - Only used if :nml:mem:`JULES_VEGETATION::can_model` = 4 and :nml:mem:`JULES_SNOW::cansnowpft` = TRUE on that surface tile. + Only used if :nml:mem:`JULES_VEGETATION::can_model` = 4 and + :nml:mem:`cansnowpft` = TRUE on that surface tile. .. nml:member:: unload_rate_u @@ -355,9 +422,11 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office :type: real(npft) :default: MDI - Term proportional to wind speed in unloading rate for snow on the canopy. + Term proportional to wind speed in the background unloading rate + for snow on the canopy. - Only used if :nml:mem:`JULES_VEGETATION::can_model` = 4 and :nml:mem:`JULES_SNOW::cansnowpft` = TRUE on that surface tile. + Only used if :nml:mem:`JULES_VEGETATION::can_model` = 4 and + :nml:mem:`cansnowpft` = TRUE on that surface tile. .. nml:member:: i_snow_cond_parm @@ -368,16 +437,14 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Scheme used to calculate the conductivity of snow + Only used if :nml:mem:`nsmax` > 0. + Two parametrizations of snow conductivity are available taken from the papers of :ref:`Yen (1981)` and :ref:`Calonne et al. (2011)`. - Only used if :nml:mem:`JULES_SNOW::nsmax` > 0. - - = ===================== - 0 Yen (1981) - 1 Calonne et al. (2011) - = ===================== + 0. :ref:`Yen (1981)` + 1. :ref:`Calonne et al. (2011)` .. nml:member:: l_et_metamorph @@ -385,22 +452,28 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office :type: logical :default: F + This parametrization follows the form used by e.g. :ref:`Dutra + et al. (2010)`. + + Only used if :nml:mem:`nsmax` > 0. + TRUE Include the effect of thermal metamorphism on the snow density. FALSE No effect. - This parametrization follows the form used by eg. Dutra et al. (2010) - .. nml:member:: l_snow_infilt :type: logical :default: F + Only used if :nml:mem:`nsmax` > 0. + TRUE - Pass rainfall and melting from the canopy to the snowpack as infiltration. + Pass rainfall and melting from the canopy to the snowpack as + infiltration. FALSE No effect. @@ -411,11 +484,13 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office :type: logical :default: F + Only used if :nml:mem:`nsmax` > 0. + TRUE Do not include the canopy heat capacity in the surface energy balance at the top of the snow pack on surface tiles without a canopy snow model. FALSE - The canopy heat capacity is include in the surface energy balance at the top of the snow pack. + The canopy heat capacity is included in the surface energy balance at the top of the snow pack. .. nml:member:: a_snow_et @@ -425,7 +500,7 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Constant in parametrization of thermal metamorphism. - Only used if :nml:mem:`JULES_SNOW::l_et_metamorph` = TRUE. + Only used if :nml:mem:`l_et_metamorph` = TRUE. .. nml:member:: b_snow_et @@ -434,7 +509,7 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Constant in parametrization of thermal metamorphism. - Only used if :nml:mem:`JULES_SNOW::l_et_metamorph` = TRUE. + Only used if :nml:mem:`l_et_metamorph` = TRUE. .. nml:member:: c_snow_et @@ -443,7 +518,7 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Constant in parametrization of thermal metamorphism. - Only used if :nml:mem:`JULES_SNOW::l_et_metamorph` = TRUE. + Only used if :nml:mem:`l_et_metamorph` = TRUE. .. nml:member:: rho_snow_et_crit @@ -452,7 +527,7 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Critical density in parametrization of thermal metamorphism. - Only used if :nml:mem:`JULES_SNOW::l_et_metamorph` = TRUE. + Only used if :nml:mem:`l_et_metamorph` = TRUE. .. nml:member:: i_grain_growth_opt @@ -463,13 +538,14 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Scheme used to calculate the rate of growth of snow grains. - Setting this to 0 invokes the original scheme based on Marshall (1989), - with no dependence of the rate of growth of small grains on the - temperature. + 0. Invokes the original scheme based on :ref:`Marshall + (1989)`, with no dependence of the rate of + growth of small grains on the temperature. - Setting it to 1 invokes the scheme for growth of snow grains proposed - by Taillandier et al. (2007) for equitemperature metamorphism. This - is significantly slower than the default scheme at low temperatures. + 1. Invokes the scheme for growth of snow grains proposed by + :ref:`Taillandier et al. (2007)` for + equitemperature metamorphism. Growth is significantly + slower than the default scheme at low temperatures. .. nml:member:: i_relayer_opt @@ -478,14 +554,17 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office :permitted: 0 or 1 :default: 0 - Scheme used to relayer the snowpack. Setting the option to 0 invokes - the original scheme with relayering of the grain size involving the - grain size itself, while setting it to 1 causes the relayering to be - done using the inverse of the grain size. This is more consistent - with conserving the SSA, though full conservation would require - mass weighting to be invoked during regridding. + Scheme used to relayer the snowpack. + + Only used if :nml:mem:`nsmax` > 0. + + 0. Invokes the original scheme with relayering of the grain size + involving the grain size itself. + 1. Relayering is done using the inverse of the grain size. This + is more consistent with conserving the specific surface area + of snow, though full conservation would require mass + weighting to be invoked during regridding. - Only used if :nml:mem:`JULES_SNOW::nsmax` > 0. .. nml:member:: i_basal_melting_opt @@ -493,17 +572,19 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office :permitted: 0 or 1 :default: 0 - Option to treat basal melting of the snow pack. When snow falls - on warm ground, it will melt from the base of the snowpack, - where the temperature of the snow will rise to the melting point. - The 0-layer snow scheme, which is used for thin snow even when the - multilayer scheme is selected, did not represent this process and - included only melting at the surface. This option allows - basal melting to be omitted if it is set to the defaut value of 0, - but offers an alternative setting of 1, which results in basal - melting taking place instantaneously if the temperature of the - first soil layer is above freezing, until the snow is removed or - the temperature of soil layer is reduced to freezing. + Option to treat basal melting of the snow pack. + + When snow falls on warm ground, it will melt from the base of + the snowpack, where the temperature of the snow will rise to the + melting point. The 0-layer snow scheme, which is used for thin + snow even when the multilayer scheme is selected, did not + represent this process and included only melting at the surface. + + 0. Default: Basal melting is omitted. + 1. Basal melting takes place instantaneously if the temperature + of the first soil layer is above freezing, until the snow is + removed or the temperature of soil layer is reduced to + freezing. @@ -512,7 +593,7 @@ HCTN30 refers to Hadley Centre technical note 30, available from `the Met Office Example of the evolution of snow layer thickness ------------------------------------------------ -The table below gives an example of how the number and thickness of snow layers varies with total snow depth for the case of :nml:mem:`JULES_SNOW::nsmax` = 3 and ``dzsnow = (0.1, 0.15, 0.2)``. Note that if the values given by the user for :nml:mem:`JULES_SNOW::dzsnow` are a decreasing series with ``dzsnow(i) <= 2 * dzsnow(i - 1)``, the algorithm will result in layers ``i`` and ``i + 1`` being added at the same time. Don't panic - this should not be a problem for the simulation. +The table below gives an example of how the number and thickness of snow layers varies with total snow depth for the case of :nml:mem:`nsmax` = 3 and ``dzsnow = (0.1, 0.15, 0.2)``. Note that if the values given by the user for :nml:mem:`dzsnow` are a decreasing series with ``dzsnow(i) <= 2 * dzsnow(i - 1)``, the algorithm will result in layers ``i`` and ``i + 1`` being added at the same time. Don't panic - this should not be a problem for the simulation. .. tabularcolumns:: |p{3cm}|p{1.5cm}|p{3cm}|p{7cm}| @@ -545,10 +626,23 @@ The table below gives an example of how the number and thickness of snow layers ------------------------------- * Calonne, N., Flin, F., Morin, S., Lesaffre, B., du - Roscoat, S. Rolland, and Geindreau, C. (2011), Numerical and + Roscoat, S. Rolland, and Geindreau, C. (2011). Numerical and experimental investigations of the effective thermal conductivity of snow, Geophys. Res. Lett., 38, L23501, https://doi.org/10.1029/2011GL049234. +* Dutra, E., Balsamo, G., Viterbo, P., Miranda, P. M., Beljaars, A., + Schar, C., and Elder, K. (2010). An improved snow scheme for the ECMWF land + surface model: Description and offline validation, J. Hydrometeorol., + 11, 899–916, https://doi.org/10.1175/2010JHM1249.1. +* Marshall, S.E. (1989). A physical parameterization of snow albedo for + use in climate models. NCAR Cooperative Thesis 123. Boulder, CO : + National Center for Atmospheric + Research. https://atmos.washington.edu/~sgw/PAPERS/1989_Marshall.pdf +* Taillandier, A.-S., F. Domine, W. R. Simpson, M. Sturm, + and T. A. Douglas (2007). Rate of decrease of the specific surface + area of dry snow: Isothermal and temperature gradient + conditions, J. Geophys. Res., 112, F03003, + https://doi.org/10.1029/2006JF000514. * Yen, Y.-C. (1981). Review of thermal properties of snow, ice and sea ice. Cold Regions Research and Engineering Laboratory (CRREL) Report 81-10. https://hdl.handle.net/11681/9469