The land, biosphere, atmosphere and ocean systems together form a
higher-order system that possesses a wide range of time and space scales. As
a result, a fairly simple periodic forcing (solar radiation at the top of
the atmosphere) is translated to variabilities covering scales ranging from
the planetary and interdecadal down to turbulence dissipation scales
(centimeters and seconds). The presence of water substance in all three
phases is an additional source of complexity for the earth
s
climate; water vapor in the troposphere, ice on the surface and liquid water
in the land-biosphere system all have major influence on the transformation
and transfer of the energy input to the atmosphere.
Depending on the level of space-time averaging, weather and climate may be defined to delineate and isolate the most influential physical and dynamical processes. Since variabilities in the land-atmosphere-ocean system occur over a broad range of scales whose interaction are often part of a cascade, the definitions of climatic variability and weather-synoptic features often blend into one-another. Furthermore, the detection of global change in the observational record and its analysis based on model predictions are affected by the presence of such broad range of scales of variability.
Variabilities in the climatic system may be partially re-constructed by integrating processes that work at synoptic and smaller time and space scales. For example, numerical models of the global land-atmosphere-ocean system are built on this premise; in these models, climatic variability is obtained by solving the relevant equations and relations governing the physical system. Without any added random fluctuations, the numerical model produces rich spectra for variabilities in a number of relevant environmental variables simply due to the disparate time-scales associated with various reservoirs in the land-atmosphere-ocean system.
In mathematical terms, the partial differential equations and parameterizations that are numerically solved in these models form a ``stiff system'' in that the characteristic time and space scales for various components of the differential system cover a wide range. This is precisely how a simple periodic input-forcing is translated to a virtually random response output. The system may additionally have a dynamical response that amplifies an initially small perturbation.
Land-atmosphere interaction investigations are directed to identify and isolate those features and interactions in the land-atmosphere-ocean system that result in the distinct modes of variabilities observed for continental climates. It is recognized that ``[land surface] processes are essential in maintaining climate and controlling its temporal variations [ Chahine, 1992].''
Local and regional investigations focus on stores and transfers of water and energy in the land-biosphere-ocean-atmosphere system that take simple periodic or noisy input and yield those spatial and temporal variabilities that are unique characteristics of continental climates. The importance of the large-scale and spatial distribution ultimately necessitate the use of numerical models, remote sensing and four-dimensional assimilation tools. The collection of papers in the edited volume by Wood [1991] reflect the increasing utilization of these tools and techniques for the investigation of land-atmosphere interaction and the parameterization of exchange processes.