6.6. jules_surface.nml

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

6.6.1. JULES_SURFACE namelist members

JULES_SURFACE::all_tiles

Type:

integer

Permitted:

0,1

Default:

0

Perform calculations of tile properties on all tiles (except land ice) for all gridpoints even when the tile fraction is zero.

0. Off

1. On

JULES_SURFACE::cor_mo_iter

Type:

integer

Permitted:

1-4

Default:

1

Corrections to Monin-Obukhov surface exchange calculation. Please see also UMDP24 “The Parametrization of Boundary Layer Processes” (section 8.4.1).

1. Correct convective gustiness in low winds

2. Correct U* in dust scheme,

3. Limit Obukhov length in low winds

4. Improve the initialisation of the iteration

Note

Option 4 should be the preferred option.

JULES_SURFACE::beta_cnv_bl

Type:

real

Permitted:

>=0.0

Dimensionless coefficient scaling the boundary layer convective gustiness contribution to surface exchange. Historically this was set to 0.08 but is recommended to be reduced to 0.04 when gustiness from convective downdraughts is included, either from the convection parametrization or when convection is resolved (so resolutions ~1km or finer). Please see also UMDP24 “The Parametrization of Boundary Layer Processes” (section 8.1).

JULES_SURFACE::l_aggregate

Type:

logical

Default:

F

Switch controlling number of surface tiles for each gridbox.

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

TRUE

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

FALSE

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

JULES_SURFACE::i_aggregate_opt

Type:

integer

Permitted:

0-1

Default:

0

Option for aggregating surface properties to surface 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 surface 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 surface types. If l_urban2t then the anthropogenic heat will be distributed between the urban_canyon and urban_roof according to anthrop_heat_scale, otherwise it is added to urban only.

TRUE

Add anthropogenic effect.

FALSE

No effect.

JULES_SURFACE::iscrntdiag

Type:

integer

Permitted:

0-3 (standalone: 0 or 1 only)

Default:

0

Switch controlling method for diagnosing screen temperature.

0. Use surface similarity theory (no decoupling).

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

2. Diagnose the screen temperature including transient effects and radiative cooling.

3. Diagnose the screen temperature and humidity including transient effects and radiative cooling. The diagnosis of the screen temperature follows option 2. This is an experimental option and is undergoing development and additional testing.

Note

Option 0 should be the preferred option in standalone i.e. no decoupling until the decoupled options are fully tested in standalone scenarios.

JULES_SURFACE::l_elev_lw_down

Type:

logical

Default:

false

If surface 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 surface 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 surface tiles conserves the gridbox mean energy in the original forcing.

JULES_SURFACE::l_elev_land_ice

Type:

logical

Default:

false

Allows multiple ice surface 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 surface 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 surface tile.

JULES_SURFACE::l_flake_model

Type:

logical

Default:

false

Switch for using the freshwater lake model ‘FLake’ on the lake/inland-water surface tile. More information on the FLake model can be found on the FLake website. A description of how FLake is coupled to JULES can be found in Rooney and Jones 2010.

When using FLake, it is not necessary to use a canopy representation of lake properties so catch_nvg_io, ch_nvg_io and vf_nvg_io should all be set to zero for the lake tile.

JULES_SURFACE::l_urban2t

Type:

logical

Default:

false

Switch for using the two-tile urban schemes (including MORUSES). This allows two urban surface tiles (urban_canyon and urban_roof) to be used instead of one. Additional parameters must be supplied via JULES_NVEGPARM, with some able to be provided by MORUSES (see JULES_URBAN).

JULES_SURFACE::l_mo_buoyancy_calc

Type:

logical

Default:

false

Default JULES (l_mo_buoyancy_flux = false) uses the buoyancy from the previous timestep to calculate the surface transfer coefficients. In coupled simulations this can lead to unrealistic surface temperatures if the stability suddenly switches from stable to unstable, due to the low turbulence determined by the stable buoyancy flux.

With the interactive buoyancy flux option (l_mo_buoyancy_flux = true) the surface energy balance and buoyancy flux are calculated within the iterative calculation for the Monin-Obukhov similarity theory for the surface exchange coefficients. On occations when the stability is around neutral it is possible that the iterative calculation does not converge. In this case the larger of the last two calculated transfer coefficients is then used to prevent any unrealistic surface temperatures.

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, available from the Met Office Library.

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, available from the Met Office Library.

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.