Improving the Processes of Land-Atmosphere Interaction in CCSM 2.0 at High ResolutionProgress (07/2002-06/2003) Our Project has focused on the physical and computational issues of including heterogeneities in the climate treatment of land atmosphere coupling. Such heterogeneities come from either atmospheric or surface details. We consider 3 approaches to such heterogeneity: a) run the full atmosphere+land climate model components at higher resolution; use either a regional or global model; b) integrate the land elements at higher resolution; c) parameterize the most significant heterogeneities. Our research has largely focused on use of the Community Land MODEL (CLM) as described by Co-I Dai et al. (2003), see also http://climate.eas.gatech.edu/dai/, and the version made available at NCAR, see http://www.cgd.ucar.edu/tss/clm/ Successful completion of
the research elements in our initial proposal requires a satisfactorily
functioning model base, and adequate computational facilities. The initial
simulations of the CCLM 2 model frozen at NCAR (Bonan
et al, 2003) revealed several deficiencies that have needed fixing before
lengthy integrations were warranted. Thus our investigations over the last
year have used earlier model versions. Hahmann at
the University of Arizona continues to use a CCM3/BATS framework for her
development of a fine submesh over land,
emphasizing precipitation and topographic effects (http://www.atmo.arizona.edu/personalpages/hahmann/ccpp/ccpp.html), and
various colleagues at Georgia Tech have continued to analyze simulations from
CCM3/CLM0, as documented by Zeng et al (2002). Steiner,
PhD student of Chamedies has incorporated CLM into
the RegCM2 and integrated for a year over The list of most glaring land model physics issues and their current status are summarized as follows: a) under canopy conductance - preliminary fix available and paper with colleagues on this submitted; b) excessive canopy evaporation - shown to reduced either by the Hahmann fine mesh approach to precipitation, or various approaches to subgrid canopy physics, but final resolution of the latter approach require more work, and a complete solution requires consideration also of correlation of incident solar radiation with occurrence of precipitation; c) model boundary conditions related to leaf area and albedo - advances have been made in this area through our NASA sponsored project, but further work is needed before improvements can be incorporated into CLM integrations. Other related model physics topics that have been addressed over the last year by Co-Is of this project have been the: a) variability of soil moisture in CLM on climate time scales. Wu have developed monthly soil moisture output by layers over a 50 year integration and has analyzed the results with regards climate variability. b) The forcing of land processes by aerosols: addressing this question has been data limited. In the past, the only information on the distribution of continental aerosols has been model generated. With the new data from the NASA MODIS, aerosols are observed over land but not uniformly or everywhere. Yu (http://climate.eas.gatech.edu/yu/) has developed global data sets for continental aerosol optical depth and single scattering albedo by combining MODIS with modeled information from the GSFC GOCART system. Publications over the past year primarily or entirely sponsored by this grant are listed below. In her paper, Hahmann has clearly demonstrated that inclusion of a fractional precipitation has major implications for climate simulations in the tropics; overall rainfall is reduced, temperatures are increased, and the surface air is drier. Wu has shown in her paper that the layered soil time statistics look quite different than the conventional wisdom provided by past bucket model analyses. In particular, it appears to indicate that the presence of large climate memory in the moist tropics. Yu as mentioned above has developed the data sets needed to study how aerosols modify land climate. Steiner and Chamedies have demonstrated that properties of the overlying aerosols are important for determining transpiration, carbon assimilation, and isoprene emissions through their impacts on leaf temperature. Dai has developed a modification of CLM that includes separate temperature calculations for sunlight and shaded (only irradiated by diffuse light) leaves and shows that this distinction can also significantly alter significantly respiration and carbon fluxes. Because of the need for developments as reported above, the planned very high resolution integrations have not yet been initiated. However, considerable effort by Co-I Shaikh has gone into development of the computational framework at Gatech needed to do such. We have also had conversations with ORNL colleagues as to possibly carrying out the integrations on their machines. Use of the enhanced facilities at NCAR is another possibility. References Hahmann, A.N., Representing spatial sub-grid scale precipitation
variability in a GCM, J.
Hydrometeorology, in press, 2003. Dai, Y., X. Zeng, R.E. Dickinson, I. Baker, G.B. Bonan,
M.G. Bosilovich, A.S. Denning, P.A. Dirmeyer, P.R. Houser, G.-Y. Niu,
K.W. Dai, Y. and R.E.
Dickinson, A two-big-leaf model for canopy temperature, photosynthesis and stomatal conductance, submitted to Journal of Climate, 2003. Wu, W., M. A. Geller,
and R. E. Dickinson, A case study for land model evaluation: Simulation of
soil moisture amplitude damping and phase shift, Journal of Geophysical Research, 107(D24), 4793,
doi:10.1029/2001JD001405, 2002. Wu, W., and R. E.
Dickinson, The persistence of soil moisture profiles in a multilayer soil
model coupled to a climate model, Journal
of Climate, submitted, May 2003. Yu, Hongbin,
R.E. Dickinson, M. Chin, Y.J. Kaufman, B.N. Holben,
I.V. Geogdzhayev, and M.I. Mishchenko:
Annual cycle of global distributions of aerosol optical depth from
integration of MODIS retrievals and GOCART model simulations, Journal of Geophysical Research, 108
(D3), 4128, doi:10.1029/2002JD002717, 2003. Yu, Hongbin,
R.E. Dickinson, M. Chin, M. Zhou, Y.J. Kaufman, L. Zhou, Y. Tian, O. Dubovik, and B.N. Holben: The direct radiative
effect of aerosols as determined from a combination of MODIS retrievals and
GOCART model simulations. To be submitted to Journal of Geophysical Research, 2003. |
Atmospheric Dynamics and Climate
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