Geoscience Reference
In-Depth Information
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Figure 9.17.
Modeled surface mass balance trend (1958-2007) in kg m
−2
based on a
simulation with RACMO2/GR. Thin dashed lines are 250 m elevation contours (from
Ettema et al,
2009
, by permission of AGU). (See plate section for color version.)
of NWP models as an optimal blend of observations and an AGCM or regional
atmospheric model.
In climate simulations, such as for hindcasts or for greenhouse-gas experiments,
specification of the initial boundary conditions (e.g., of SST, sea ice distribution,
land surface cover, greenhouse gas concentrations) is much more important than
the specification of the initial atmospheric state (i.e., the three-dimensional distri-
bution of temperature, winds, and humidity at the start of the model simulation).
However, because of the complex and chaotic nature of the atmosphere, predicting
the weather at a given time and place depends critically on specification of the initial
atmospheric state.
NWP starts with an initial atmospheric state to get a short term (e.g., typically
six hours) forecast of the future atmospheric state as well as of various surface
