Land-Ocean-Atmosphere
Interactions: Mechanisms
for the Seasonal Variations in Precipitation over Tropical Land
(01/2002 - 12/2004)
The principal objective
of the research under this grant has been the examination of the mechanisms
responsible for seasonal variations of precipitation over tropical land and
the determination of how these variations are affected by land-atmosphere
interaction. In particular, thermodynamic and land-ocean-atmosphere processes
responsible for initiation of the wet season in the Amazon and the North
American monsoon have been investigated through diagnostic analyses and
numerical simulation. The examination of these processes addresses the
relative roles of land versus ocean SST in determining the onset of the wet
seasons and the observed spatial patterns in these two regions. The components of this proposal of greatest interest to the
co-investigators has been accelerated by their success in later
receiving separate funding through the NOAA CLIVAR PACS program.
The problems we address
are difficult and must be solved through the contributing efforts of many.
Our group actively collaborates with many other scientists and institutions
in the US
and abroad. In particular, we have strongly participated in the development
and applications of the Community Climate System Model.
Our group studies how
land cover and its changes modify regional climates through their
interactions with radiative and hydrological
processes. How does soil moisture vary in time and how does
this in turn affect the atmosphere? What are the controls in various regions on the
seasonality of rainfall? Basic theoretical understanding of these issues is
supported through our NSF grant. Some aspects
especially need the development of higher resolution approaches for the land
modeling. Such is supported through our DOE SCIDAC grant. We also consider how aerosols modify the radiation reaching land
and how land processes in turn determine aerosols. Climate
over land is coupled to oceanic processes such as El Nino and we study how
clouds and aerosols over the ocean also interact with the climate system.
Our group has been
actively engaged with scientists at Boston
University, Maryland,
Arizona,
NCAR and other institutions to make better use of the latest NASA satellite
data to improve the representation of land in climate models. The satellite
data analyses are being done through our NASA IDS project. Part of this effort has been the
redesign of the land component of climate models to make better use of
observational information, and part to improve the usefulness of the NASA
observations for land models. Now is a very exciting time because of the
recent availability of high quality multiyear data from NASA EOS satellites,
and the new Community Land Model (CLM)
component (e.g. Dai et al, 2003) of the Community Climate System Model, also
supported by our NSF project. The previous
and current development has been spearheaded by our group (in collaboration
with many other scientists). Much of our current research involves bringing
together these two latest technologies to provide an improved climate model.
A current major thrust of
land modeling as part of climate is to better combine the modeling of
biophysics (i.e. the determinations of surface temperatures, water status,
and water and energy fluxes) with leaf metabolic processes and through this
the ties to dynamics of ecosystems and biogeochemical cycling. The key
concept is that leaves in transpiring water (the main means by which soil
moisture exerts climate controls) also assimilate carbon dioxide. This carbon
assimilation in turn depends on the presence in the leaves of other nutrients
such as nitrogen which are taken from the soil and recycled to the soil
through the death and decay of plants and the dynamics of soil microbiota. The carbon assimilation is also a chief
consideration in determining the major contributions that exchanges with land
make to the carbon dioxide content of the atmosphere and in the competitive
growth of individual plant elements. Much of our activity in this area
(sponsored through our current NSF project)
builds upon the Community Land Model (Dai et al, 2003) and interacts with the
Land Surface and Biogeochemical Working groups of the Community Climate
System Modeling activity.
The coupling between the
atmosphere and surface addressed in our other projects leads us to an overall
examination of the processes of climate variability. What are the underlying
causes of the most significant systems of long-term climate variability? How
can we define feedbacks to better recognize all the dimensions of coupling
between the atmosphere and surface? What aspects of the system are most
important for its predictability (i.e. theoretical limits to prediction)? Our
efforts to address such issues are supported by our NSF
grant.
Grunt Supported Publications
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. Oleson, C.A.
Schlosser, and Z.-L.Yang, 2003a: The Common Land
Model (CLM) Version 1.0, Bull. Amer. Meter. Soc. In press.
Dai, Y., R. E. Dickinson and Y. P. Wang, 2003b: A
two-big leaf Model for Canopy Temperature, Photosynthesis and Stomatal Conductance. Submitted to J. Climate.
Dickinson, R.E., J. A. Berry, G. B.Bonan, G. J. Collatz, C. B.
Field, I. Y. Fung, M. Goulden,
W. A. Hoffman,R.
B. Jackson, R. Myneni, P. J. Sellers and M. Shaikh, 2002a: Nitrogen Controls on
Climate Model Evapotranspiration. J. Clim., 15,
No. 3, 278-295.
Dickinson, Robert E., Stephen E. Zebiak, et al., 2002b: How Can We Advance Our Weather and
Climate Models as a Community? Bulletin. Amer.Meteor.
Soc. Vol. 83, No. 3, pp 431-434.
Liu, Q., and R. E. Dickinson, 2003: Use of a
two-mode soil pore size distribution to estimate soil water transport in a
land surface model, Geophys. Res. Lett., 30(6), 1331, doi:10.1029/2002GL016562.
Wu, W.,
M. A. Geller and Robert E. Dickinson, 2002a: The Response of Soil Moisture to
Long-Term Variability of Precipitation. J. Hydrometeorol.,
Vol. 3, No. 5, pp. 604-613.
Wu, W., M. A. Geller and R. E. Dickinson, 2002b: A
Case Study of Land Model Evaluation: Simulation of Soil Moisture Amplitude
Damping and Phase Shift. J. Geophys. Res.,Vol. 107, No. D24, 4793,
doi:10.1029/2001JD001405,2002.
Wu, W., and R. E. Dickinson, 2004: Time scales of layered
soil moisture memory in the context of land-atmosphere interaction, J. Climate, Vol.
17, No. 14, 2752-2764.
Yu. H., S. C. Liu, and R. E. Dickinson, 2002: Radiative Effects of Aerosols on the Evolution of the
Atmospheric Boundary Layer Journal of Geophysical Research,Vol. 107, (D12), 4142,
doi:10.1029/2001JD000754.
Yu, Hongbin, R.E.
Dickinson, M. Chin, Y.J. Kaufman, B.N. Holben, I.V.
Geogdzhayev, and M.I. Mishchenko,
2003: 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:
10.029/2002JD002717.
Zeng, X., M. Shaikh, Y. Dai, R. E. Dickinson and R. Myneni, 2002: Coupling of the Common Land Model to the
NCAR Community Climate Model. Journal of Climate, Vol. 15, pp. 1832-1854.
Zeng, X., R. E.
Dickinson, M. Barlage, Y. Dai, G. Wang and K. Oleson: Treatment of Under-Canopy Turbelence
in Land Models. Submitted to Journal of Climate, 2003.
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