Geoscience Reference
In-Depth Information
Regional Climate Models : As the name implies, such models are applied to
regional domains. They are typically run at a horizontal resolution of 10-100 km
and with high vertical resolution. They couple an atmospheric model to LSMs, sea
ice, and (for some) ocean models. The atmospheric model is driven at the model
boundaries by output (e.g., of temperature, wind, and humidity at a series of atmo-
spheric levels) from numerical weather prediction models or GCMs.
Numerical Weather Prediction (NWP) Models : These are used for short- to
medium-range weather forecasting for which accurate specification of the initial
atmospheric state is of key importance. Global NWP models can be thought of
as AGCMs (including an LSM with prescribed boundary conditions such as SSTs
and sea ice concentration) that are constrained by data assimilation. One obtains
“analyses,” which represent an optimal blend of the atmospheric model output and
observations, and forecasts of variables such as precipitation and radiation fluxes.
While analyses are generally thought of as “truth,” biases can be present because of
problems in the atmospheric model, assimilation approaches, and the amount and
quality of assimilation data. Strong biases can be present in the surface fields. In an
operational setting, NWP models are undergoing continual improvement, the intent
being to improve forecast skill. These changes, however, complicate retrospective
analyses from archived fields. In recognition, atmospheric reanalyses have been
performed with fixed versions of both the atmospheric model and the data assimi-
lation system. This results in more temporally consistent outputs spanning multiple
decades. Wide use has been made of output from atmospheric reanalyses in previ-
ous chapters.
Ecosystem Models : An ecosystem represents a system of organisms and the
environment in which they interact. Ecosystem models are used to simulate func-
tional and structural dynamics of terrestrial ecosystems. Functional dynamics of
ecosystems includes the transfer of water, energy, carbon, and nitrogen between
the atmosphere, soil, and vegetation. Structural dynamics of ecosystems includes
changes that occur after disturbances (e.g., fire) or changes that occur in response
to climate change (e.g., the migration of trees into tundra regions). Functional and
structural changes of ecosystems can influence regional climate by affecting water
and energy exchange with the atmosphere and may influence global climate by
affecting the concentrations of radiatively active gases. Traditionally, LSMs repre-
sented a functionally and structurally static conceptualization of ecosystems (vege-
tation cover and type is specified and unchanged through the simulation), but have
subsequently incorporated concepts from ecosystem models to better represent how
interannual to century-scale variations in ecosystem structure and function influ-
ence climate. When vegetation can change, the term “dynamic vegetation model” is
often used. Components of ecosystem models are part of Earth System Models.
9.2
Single Column Models
Chapter 5 has already provided a few examples of the applications of single column
models. These include assessments of cloud radiative forcing over the sea ice cover
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