6.3. jules_surface.nml

This file sets the surface options. It contains one namelist called JULES_SURFACE.

6.3.1. JULES_SURFACE namelist members

JULES_SURFACE::l_aggregate

Type:logical Default:F

Switch controlling number of tiles for each gridbox.

This is used to set the number of surface energy balances that are solved for each gridbox (ntiles).

TRUE

Aggregate parameter values are used to solve a single energy balance per gridbox. This option sets ntiles = 1.

FALSE

A separate energy balance is calculated for each surface type. This option sets ntiles = ntype.

JULES_SURFACE::i_aggregate_opt

Type:integer Permitted:0-1 Default:0

Option for aggregating surface propeties to tiles:

0. Aggregate momentum roughness lengths and set the thermal roughness length as a given fraction of this (in practice the ratio of roughness lengths for the first surafce type).
1. Aggregate the thermal roughness lengths separately from the momentum roughness lengths using an analogous algorithm.

Note

This option is ignored unless l_aggregate is true.

JULES_SURFACE::l_epot_corr

Type:logical Default:F

TRUE

Use correction to the calculation of potential evaporation.

FALSE

No effect.

JULES_SURFACE::l_point_data

Type:logical Default:F

Flag indicating if driving data are point or area-average values. This affects the treatment of precipitation input and how snow affects the albedo.

TRUE

Driving data are point data. Precipitation is not distributed in space (see FALSE below) and is all assumed to be large-scale in origin. The albedo formulation is suitable for a point.

FALSE

Driving data are area averages. The precipitation inputs are assumed to be exponentially distributed in space, as in UMDP25, and can include convective and large-scale components. The albedo formulation is suitable for a gridbox.

JULES_SURFACE::l_land_ice_imp

Type:logical Default:F

Switch to control the use of implicit numerics to update land ice temperatures.

TRUE

Use implicit numerics to update land ice temperatures.

FALSE

Use explicit numerics to update land ice temperatures.

JULES_SURFACE::l_anthrop_heat_src

Type:logical Default:F

Switch for inclusion of anthropogenic contribution to the surface heat flux from urban tiles.

TRUE

Add anthropogenic effect.

FALSE

No effect.

JULES_SURFACE::iscrntdiag

Type:integer Permitted:0 or 1 Default:0

Switch controlling method for diagnosing screen temperature.

0. Use surface similarity theory.
1. Use surface similarity theory but allow decoupling in very stable conditions based on the quasi-equilibrium radiative solution.

JULES_SURFACE::l_elev_lw_down

Type:logical Default:false

If tiles are set to be at an elevation offset from the gridbox mean altitude (see JULES_SURF_HGT) this switch controls whether downwelling longwave radiation is adjusted along with surface air temperature and relative humidity.

If true, the downwelling longwave for each tile not at the gridbox mean height is adjusted by an amount proportional to the fourth power of the adjustment that has been made to the surface air temperature. The adjustments are then scaled such that the sum over all tiles conserves the gridbox mean energy in the original forcing.

JULES_SURFACE::l_elev_land_ice

Type:logical Default:false

Allows multiple ice tiles to exist in an ice gridbox, usually with each representing a different elevation (JULES_SURF_HGT) band on in icesheet areas so that a sub-gridscale surface mass balance term (a strong function of altitude) can be derived for forcing icesheet/glacier models. When enabled, ice tiles in a gridbox do not use the usual (gridbox mean) JULES soil/ice subsurface model, but each tile has an independent single layer bedrock-type solid ice boundary condition under the snowpack.

In addition, when selected, dense snowpacks on elevated ice gridboxes are parameterised to behave more like firn in two ways: 1) The meltwater-holding capacity of snow layers reduces as a linear function of their density, becoming zero above the pore-closure density of 850 kg/m^2 so as to restrict retention of melt within the snowpack. 2) Where the top few centimetres of the pack has a density appropriate to firn/bare ice and the grain-size physics otherwise used for snow albedo become less appropriate, surface albedo becomes a function of density, tending towards that of bare ice as density increases (see rho_firn_albedo, amax, aicemax).

If this scheme is enabled, a depth for the bedrock layer must be provided (dzsoil_elev) and the new tile numbers must be specified (JULES_SURFACE_TYPES) as either type elev_ice (for fully glaciated areas) or elev_rock (for non-glaciated areas where the bedrock may become exposed under a thin snow layer). The total number of non-vegetated tiles, and their surface properties (JULES_NVEGPARM, usually set to be the same as the normal ice tile) must be set accordingly, as with any tile.

Surface parameters

JULES_SURFACE::hleaf

Type:real Default:5.7e4

Specific heat capacity of leaves (J K^-1 per kg carbon).

See Hadley Centre Technical Note 30 p6.

JULES_SURFACE::hwood

Type:real Default:1.1e4

Specific heat capacity of wood (J K^-1 per kg carbon).

See Hadley Centre Technical Note 30 p6.

JULES_SURFACE::beta1

Type:real Default:0.83

Coupling coefficient for co-limitation in photosynthesis model.

See Cox et al. (1999), Eq.61.

JULES_SURFACE::beta2

Type:real Default:0.93

Coupling coefficient for co-limitation in photosynthesis model.

See Cox et al. (1999), Eq.61.

JULES_SURFACE::fwe_c3

Type:real Default:0.5

Constant in expression for limitation of photosynthesis by transport of products, for C3 plants.

See Cox et al. (1999) Eq.60.

JULES_SURFACE::fwe_c4

Type:real Default:20000.0

Constant in expression for limitation of photosynthesis by transport of products, for C4 plants.

See Cox et al. (1999) Eq.60.