Geoscience Reference
In-Depth Information
investigated the phenomenon with artificially imposed patterns of surface heating
and demonstrated modeled mesoscale circulation linked to precipitation, see
Fig. 25.10. Later studies (e.g., Weaver and Avissar, 2001) sought validation of such
circulations and their consequences with reference to observations, see Fig. 25.10.
Some attempts have been made to parameterize the effect of land surface hetero-
geneity on ABL turbulence (e.g., Liu
et al.
, 1999) but, at this writing, this is rarely
if ever done in GCMs, perhaps because other surface features such as topography
and soil moisture heterogeneity can also give rise to mesoscale circulations.
Given the plausibility that mesoscale circulations will arise in response to land
surface heterogeneity circulations, and that these can be simulated in mesoscale
meteorological models and associated boundary layer cloud patterns have some-
times been observed, this mechanism is considered 'extremely likely' in Table 25.1.
Assessing the level of understanding and modeling of this influential mechanism
is complicated by the fact that the phenomenon is readily represented in mes-
oscale meteorological models suggesting an assessment of 'good, but they are not
yet represented in GCMs suggesting an assessment of 'poor. As a compromise, in
Table 25.1 the assessment given is 'medium.
Important points in this chapter
Land surfaces do matter
: because a continental influence is evident in
global-scale atmospheric general circulation, see Chapter 9.
●
Review
: a critical review of the available literature in three general areas,
i.e.,(a) the influence of existing land-atmosphere interactions; (b) the
influence of transient changes in land surfaces; and (c) the influence of
imposed persistent changes in land cover indicates the following conclusions
which are summarized in Table 25.1:
●
— The credibility of all the land surface influences on the atmosphere
considered is assessed as being 'extremely likely' or 'very likely, except
in one case when it is considered 'likely.
— Present ability to quantify the magnitude and model all these
influences is assessed as 'medium, except in one case it is assessed as
'high' and in one case as 'poor.
— The influence of soil moisture, vegetation cover, and frozen
precipitation cannot be separately modeled. Future improvements will
most effectively be made by studies in which sustained observations
are made over several seasons and include measurements associated
with all three of these influential mechanisms simultaneously.
Recommendations
: areas that priorities in future research are as follows:
●
— Quantification and modeling of the effect of topography on weather
and climate at short time scales is assessed as being poor and there is a
clear need for more research in this area.
