Model ECHAM1+LSG: Elaborations
Note: The ECHAM1 + LSG model was jointly sponsored by the Max Planck
Institut für Meteorologie (MPI) and the Deutsches
Model ECHAM1+LSG is an entry in the CMIP1 intercomparison only.
The procedure for spinup/initialization to the simulation starting
of the MPI (ECHAM1+LSG) coupled model is as follows (references:
et al. 1992,
von Storch et al. 1997,
personal communication U. Cubasch):
- The atmospheric model was integrated with prescribed
and sea ice extents derived from the AMIP data until quasi-equilibrium
- The ocean model was integrated first with prescribed Hellerman
and Rosenstein (1983) wind stresses, and was relaxed toward surface
salinity data of Levitus (1982),
a feedback to effective monthly mean surface air temperatures
from the COADS data set (cf. Woodruff
al. 1987). In a second stage, the diagnosed freshwater fluxes from
this run, together with the same surface wind stresses and surface air
temperatures then were used as external forcing (along with a mild
to AMIP SSTs). In a third stage, the ocean model was integrated further
with the forcings of the second stage, except for the additional
of monthly mean values of the daily forcing anomalies. The total length
of the three stages was ~7,000 years.
- The atmospheric model then was integrated again to
20-year run), with SSTs and sea ice extents derived from the third
of the ocean-only run. Monthly mean flux corrections for heat,
momentum (surface wind stresses) were computed following the method of Sausen
et al. 1988. The SSTs were also flux-corrected to adjust for the
bias between the AMIP and COADS climatologies.
- The atmospheric and oceanic models then were coupled and
the application of these fixed monthly mean flux corrections.
Land Surface Processes
- Soil temperature is determined after Warrilow
et al. (1986) from the heat conduction in 5 layers (proceeding
layer thicknesses are 0.065, 0.254, 0.913, 2.902, and 5.70 m), with net
surface heat fluxes as the upper boundary condition and zero heat flux
as the lower boundary condition at 10 m depth.
- Snow pack temperature is also computed from the soil heat
heat diffusivity/capacity for ice in regions of permanent continental
and for bare soil where water-equivalent snow depth is <0.025 m. For
snow of greater depth, the temperature of the middle of the snow pack
solved from an auxiliary heat conduction equation (cf. Bauer
et al. 1985). The temperature at the upper surface is determined by
extrapolation, but it is constrained not to exceed the snowmelt
of 0 degrees C.
- There are separate prognostic moisture budgets for snow,
and soil reservoirs. Snow cover is augmented by snowfall and is
by sublimation and melting. Snow melts (augmenting soil moisture) if
temperatures of the snow pack and of the uppermost soil layer exceed 0
degrees C. The canopy intercepts precipitation and snow (proportional
the vegetated fraction of a grid box), which is then subject to
evaporation or melting.
- Soil moisture is represented as a single-layer "bucket" model
1969) with field capacity 0.20 m that is modified to account for
and orographic effects. Direct evaporation of soil moisture from bare
and from the wet vegetation canopy, as well as evapotranspiration via
uptake, are modeled. Surface runoff includes effects of subgrid-scale
of field capacity related to the orographic variance; in addition,
the soil is frozen, moisture contributes to surface runoff instead of
moisture. Deep runoff due to drainage processes also occurs
of infiltration if the soil moisture is between 5 and 9 percent of
capacity (slow drainage), or is larger than 90 percent of field
(fast drainage). When the model atmosphere is coupled to a dynamical
this source of freshwater is discharged at coastal points by means of a
river transport model that uses local runoff as input. Cf. Dümenil
and Todini (1992) and Sausen et
for further details.
- Only the thermodyamics of sea ice are represented. Ice forms when
heat loss from the ocean would cause the SST to fall below the freezing
point. Existing ice thickens/melts in relation to the available
of fusion when the net heat flux is upward/downward. The heat flux is
from a surface energy balance which includes a conductive heat flux
the ocean and sea ice, based on the assumption of a linear temperature
profile. The surface albedo of the ice is assumed to remain
solar penetration, brine pockets, or other internal heat capacities are
- Snow cover is not represented and a modification of the heat flux
or partial ice cover is not accounted for. Salinity changes are
with changes of the volume of the sea ice on the asumption of constant
Chief Differences from Closest AMIP Model
Aside from its use of coarser horizontal resolution,
atmospheric component of the MPI (ECHAM1 + LSG) coupled model differs
AMIP model MPI
ECHAM3 (T42 L19) 1992 chiefly in the following respects (cf. Roeckner
et al. 1992 for further details):
Gravity-wave drag does not include the Miller et
modifications to the Palmer et al. (1986) parameterization, as in the AMIP
Instead of the Tiedtke (1989) mass-flux representation of deep
in the AMIP
model, a Kuo (1974) scheme is used.
convection is assumed to occur only in the presence of conditionally
layers in the vertical and large-scale net moisture convergence. In a
column, this total available moisture is divided between a fraction b
that moistens the environment and the remainder (1-b) that
to the latent heating (rainfall) rate. Shallow
is parameterized in the same way as in the AMIP
In contrast to the AMIP
model, the Roeckner et al. (1991) modifications of the the
cloud-formation scheme are not included.
Enhanced (envelope) orography is used
the mean orography of the AMIP
A low-wind correction to the surface fluxes
of a minimum wind speed rather than the Miller et al. (1992) approach
in the AMIP
model. The bulk Richardson number also does not include the effects
of clouds on buoyancy.
Bauer, H., E. Heise, J. Pfaendtner, and
V. Renner, 1985: Development of an economical soil model for climate
In Current Issues in Climate Research (Proceedings of the EC
Programme Symposium, held 2-5 Oct. 1984, in Sophia Antipolis, France),
A. Ghazi and R. Fantechi (eds.), D. Reidel, Dordrecht, 219-226.
Cubasch, U., K. Hasselmann, H.
E. Maier-Reimer, U. Mikolajewicz, B.D. Santer, and R. Sausen,
Time-dependent greenhouse warming computations with a coupled
model. Climate Dynamics, 10, 55-69.
Dümenil, L., and E.
1992: A rainfall-runoff scheme for use in the Hamburg climate model. In
in Theoretical Hydrology: A Tribute to James Dooge, J.P. O'Kane
European Geophysical Society Series on Hydrological Sciences, Vol. 1,
Press, Amsterdam, 129-157.
Hellerman, S., and M.
1983: Normal monthly wind stress over the world ocean with error
Phys. Oceanogr., 13, 1093-1104.
Kuo, H.L., 1974: Further studies of the
of the influence of cumulus convection on large-scale flow. J.
Sci., 31, 1232-1240.
Levitus, S., 1982: Climatological atlas
the world's oceans. NOAA Professional Paper 13, 173 pp.
Manabe, S., 1969: Climate and ocean
1. The atmospheric circulation and the hydrology of the Earth's
Wea. Rev., 97, 739-774.
Roeckner, E., K. Arpe, L.
S. Brinkop, L. Dümenil, M. Esch, E. Kirk, F. Lunkeit, M. Ponater,
B. Rockel, R. Sausen, U. Schlese, S. Schubert, and M. Windelband, 1992:
Simulation of present-day climate with the ECHAM model: Impact of model
physics and resolution. MPI Report No. 93, ISSN 0937-1060,
für Meteorologie, Hamburg, Germany, 171 pp.
Sausen, R., K. Barthels, and K.
1988: Coupled ocean-atmosphere models with flux correction. Climate
Dyn., 2, 154-163.
Sausen, R., S. Schubert, and L.
1994: A model of the river runoff for use in coupled atmosphere-ocean
Hydrology, 155, 337-352.
von Storch, J-S., V.V. Kharin,
U. Cubasch, G.C. Hegerl, D. Schriever, H. von Storch, and E. Zorita,
A description of a 1260-year control integration with the coupled
general circulation model. J. Climate, 10, 1525-1543.
Warrilow, D.A., A.B. Sangster,
A. Slingo, 1986: Modelling of land surface processes and their
on European climate. DCTN 38, Dynamical Climatology Branch, United
Meteorological Office, Bracknell, Berkshire RG12 2SZ, UK.
Woodruff, S., R.J. Slutz, R.L.
and P. Steurer, 1987: A comprehensive ocean-atmosphere dataset. Bull.
Amer. Meteor. Soc., 68, 1239-1250.
CMIP Documentation Directory
Last update 15 May, 2002. This page is maintained by Tom