COLA Report 9
Meeting on Problems in Initializing Soil Wetness: Review
P. A. Dirmeyer
January 1995
Preface
It has been well recognized that the memory required for dynamical prediction of seasonal
climate anomalies resides primarily in the slowly varying boundary conditions at the earth's
surface. The role of tropical sea surface temperature anomalies has been investigated through
a large number of observational and modeling experiments. About twenty years ago, atmospheric
general circulation models were forced by hypothetical (quite unrealistic) sea surface temperature
anomalies. However, during the past ten years only realistic (observed) sea surface temperature
anomalies are used to force atmospheric models. Similarly, about ten years ago, hypothetical
(quite unrealistic) land surface anomalies were used to force general circulation models. With
the advent of more realistic models of the land-surface processes, a few GCM experiments have
begun to show that large-scale realistic anomalous soil wetness, which may persist for a season
or longer, can influence seasonal mean land surface temperature and rainfall.
Recognizing the need for accurate specification of soil wetness to initialize GCMs for
weather and climate prediction, the Center for Ocean-Land-Atmosphere Studies, with the
encouragement and support of E. Kalnay, convened an informal meeting on 19 August 1994 to
discuss the problems faced by atmospheric modelers in initializing soil wetness for forecasts and
climate studies. The participants were principally scientists involved in the numerical simulation
or prediction of the atmosphere, and land-atmosphere interactions, although hydrologists and
program officials were also in attendance. Current problems include the lack of reliable data over
much of the world, spin-up and climate drift of soil moisture in the numerical models,
inconsistent representation of soil moisture between different models, and the scientific merit of
statistical methods for initializing soil wetness. Several speakers gave presentations, and a
subsequent discussion session allowed the attendees to deliberate on the more pressing issues.
This meeting served in part as a prelude to the GEWEX workshop on global soil moisture held
in Longmont, Colorado during 4-6 October 1994.
Complete copies of this report are available from:
Center for Ocean-Land-Atmosphere Studies
4041 Powder Mill Road, Suite 302
Calverton, MD 20705-3106
(301) 595-7000
(301) 595-9793 Fax
last update: 17 February 1995
comments to: www@grads.iges.org