## Experimental Design |

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The Aqua-Planet Experiment suite is specified in a similar manner to AMIP II, using a set of experimental requirements and recommendations.

Requirements

Surface Boundary Conditions:

Prescribed SST distributions for the control and sensitivity experiments are specified here, and in the appendix of Neale and Hoskins (2000a).

There is no sea ice (minimum SST is 0^{o}C).

Radiative forcing and orbital parameters:

Fixed equinoctial insolation, symmetric about the equator, but including the diurnal cycle, in all experiments.

Solar constant 1365 W m^{-2}.

To obtain perpetual symmetric forcing with the prescribed solar irradiance, we recommend modifying the Earth orbit parameters, setting eccentricity and obliquity to zero, to give a circular equinoctial orbit. The distribution of solar irradiance will then be independent of the calendar.

Well-mixed radiatively active gases:

[CO_{2}]: 348 ppmv, as in AMIP II.

Ozone:

A zonally symmetric latitude-height distribution of ozone is specified, symmetrized about the equator, corresponding to the annual mean climatology used in AMIP II. The data are available here.

Simulation period:

3.5 years for each experiment, omitting the first 0.5 years as spin-up.

Model spin-up:

Start each experiment from a model-simulated state, obtained from either a real-Earth or previous aqua-planet integration. Omit the first 6 months as spin-up, but check for equilibration during this period.

Recommendations

Geophysical constants and parameters:

Earth rotation rate w = 7.292115 x 10 ^{-5}s^{-1}[1] Mean Earth radius a = 6371.0 km [2] Mean surface gravity g = 9.79764 m s ^{-2}[2] Gas constant for dry air Rd = 287.04 J kg ^{-1}K^{-1}[3] Specific heat capacity for dry air Cpd = 1004.64 J kg ^{-1}K^{-1}=7Rd/2 Consistent kappa=Rd/Cpd Water vapour gas constant Rv = 461.50 J kg ^{-1}K^{-1}[3] Water vapour specific heat capacity Cpv = 1846.0 J kg ^{-1}K^{-1}=4Rv Latent heat of vaporization at 0 ^{o}CLv0 = 2.501 x 10 ^{6}J kg^{-1}[3] Latent heat of fusion at 0 ^{o}CLv0 = 3.337 x 10 ^{5}J kg^{-1}[3] Latent heat of sublimation at 0 ^{o}CLv0 = 2.834 x 10 ^{6}J kg^{-1}[3]

References:

[1] Dickey, J.O. (1995) Earth rotation. In Ahrens (ed)Global Earth Physics: A Handbook of physical constants. AGU, Washington, 356-368.

Online-references: link

[2] Rounding of surface gravity averaged over the Earth ellipsoid 9.797644656 m s^{-2},in

Moritz, H. (1992) Geodetic reference system 1980. Bulletin Geodesique (The Geodesist's Handbook), 66(2), 187-192.

Online-references: link1 link2 link3

[3] Emanuel, K.A. (1994)Atmospheric Convection. OUP, 580pp.

which references:

List, R.J. (1951)Smithsonian Meteorological tables, 6th Edn., Smithsonian Institution Press, Washington, 527pp.;

Iribarne, J.V. & Godson, W.L. (1973)Atmospheric Thermodynamics. D. Reidel, 222pp.

Quoted values for the temperature dependent specific heat capacities and their ratios with the gas constants vary in the literature, and List (1951) quoted them only to limited accuracy. Hence the theoretical recommendations quoted above.

Well-mixed radiatively active gases:

Follow AMIP II recommendations:

[CH_{4}]: 1650 ppbv; [N_{2}O]: 306 ppbv. Halocarbon concentrations should yield ~0.24 W m^{-2}radiative forcing.

Use of an "equivalent" [CO_{2}] is not recommended.

Aerosols:

No radiatively active aerosol.

Any aerosol specification for cloud condensation should use an oceanic distribution which is fixed in time, zonally symmetric and symmetric about the equator.

Atmospheric Mass:

Specify the initial dry mass to be equivalent to a global mean surface pressure (101325 minus 245) Pa. This corresponds to a global moisture content of 25.006 kg m^{-2}using the recommended value for surface gravity.

Dry mass should be conserved throughout the integration.

There is no topography.

Calendar:

A 365 or 360 day year, with variable- or fixed-length months respectively. The 3.5 year integration length means that a realistic calendar can be used if integrations are started in March of a leap year. Insolation does not follow the calendar.

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