Parameters

The following parameters are varied in the climateprediction.net experiment:

vf1 Ice fall speed through clouds – important for the development of clouds and determining type (rain, sleet, hail, snow) and amount of precipitation

ct This relates how quickly cloud droplets convert to rain.

rhcrit ‘critical relative humidity’ relates the grid box scale atmospheric humidity to the amount of cloud in that grid box

cw_land, cw_sea This relates how much water there is in a cloud to when it starts raining, which is dependent on the condensation nuclei concentration – the more condensation nuclei there are (bits of dust, salt etc. in the atmosphere on which raindrops can form) the smaller the raindrops.

entcoef This parameter determines how rapidly a convective cloud (imagine a plume rising over a power station, or a bit thunder cloud) mixes in clear air from around it.

eacf Empirically adjusted cloud fraction This calculates how much cloud cover there will be when the air is saturated.

dtheta This has to do with the initial state of the atmosphere – what it looks like when the model starts in 1810.

ice_size This gives an effective radius for ice crystals in clouds – i.e. what radius would they have if they were perfectly spherical. It is important in the radiation scheme, to calculate how much incoming or outgoing radiation is reflected etc.

i_st_ice_sw, i_cnv_ice_sw, i_st_ice_lw, i_cnv_ice_lw These parameters all allow for non-spherical ice particles in the radiation scheme.

asym_lambda This has to do with how rapidly air mixes by turbulence in the boundary layer (the layer of the atmosphere closest to the Earth).

G₀ This has to do with the fact that the ability of turbulence to mix air varies with how stable the air is – the more stable the air, the less turbulent mixing you get.

z0fsea This parameter governs the transfer of momentum and energy between tropical oceans and the air (wind) above them.

charnock This parameter governs the transfer of momentum and energy between seas and the air (wind) above them.

r_layers This is related to the number and size of plant roots in the soil – and, consequently, to how water is taken up from the soil and into the atmosphere by plant transpiration.

eddydiff This parameter governs the diffusion of heat from the slab ocean to ice, where there is sea-ice present in the model.

start_level_gwdrag Gravity waves are waves in the atmosphere for which gravity is the restoring force – think of air passing over a mountain, it is forced upwards over the mountain, and then gravity will pull it back down, resulting in an oscillation (you often see clouds form downstream of mountains as a result). The air particles oscillating in these waves tend to lose energy because of friction (drag), and this energy manifests itself as heat. This parameter determines the lowest model level on which gravity wave drag is applied

kay_gwave kay_lee_gwdrag These parameters govern the way that gravity waves are formed as air interacts with surface features, such as mountains.

Alpham, dtice These have to do with the fact that the albedo (reflectivity) of sea ice varies with temperature.

diff_coeff, diff_exp Diffusion coefficients and exponents govern how quickly something spreads through the material it is in – so, for example, if you put a drop of oil dyed purple into a beaker of un-dyed oil, how rapidly the dyed oil mixes with the oil around it until all the beaker has the same colour. Diffusion refers to mixing due to the random motion of particles, rather than turbulent mixing which happens when there are actual vortexes mixing things (which would happen if you stirred the beaker with a spoon). In the case of the atmosphere, the horizontal diffusion coefficient and exponent determines the rate of diffusion of heat from a warm air mass to a cold one.

diff_coeff_q, diff_exp_q These diffusion parameters determine the rate at which water vapour diffuses from a very humid air mass to a relatively dry one.

anthsca The scaling factor given to the anthropogenic sulphur dioxide emissions to allow for the range of uncertainty in emissions.

isopyc Models the effects of mixing of water along surfaces of constant density in the oceans.

mllam, mld Mixes the top ~100m of the ocean.

vdiff Coefficient of vertical diffusion of temperature and salinity in the oceans.

vvisc Parameterises the friction between the different vertical layers in the oceans.

More information on experimental parameters can be found on the data portal.