Geoscience Reference
In-Depth Information
9
Global Scale
Influences on
Hydrometeorology
Introduction
The purpose of this chapter is to give general insight into why hydrological
catchments located in different regions of the world have characteristically
different hydrometeorological context. Although there is always very substantial
variability in the atmosphere, the air in the troposphere undergoes large-scale
circulation which is on average organized at the global scale. The global patterns
created lead to distinguishable regional differences in hydroclimate. Such
organization happens because there are large-scale influences on atmospheric
behavior that have a discernable consequence.
As mentioned in the previous chapter, the process of four-dimensional data
assimilation, by means of which available weather observations are merged into
GCMs, has allowed synthesis of time series of model-calculated fields of atmos-
pheric variables that are available globally. The availability of these fields facilitates
a fusion of existing and more recent understanding of large-scale atmospheric cir-
culation. Much of the description of atmospheric behavior given in this chapter
draws on knowledge provided by this useful byproduct of the regular and repeated
initiation of the GCM at numerical weather prediction centers.
Global scale influences on atmospheric circulation
Differential heating by the Sun is the primary cause of the general circulation of the
atmosphere. The spatial pattern of atmospheric heating is greatly influenced by the
relative geometry of the Sun and the Earth and how this changes with time, but it is
also influenced by regional differences in the terrestrial controls involved in
transferring solar energy into the atmosphere. Cartoons in Fig. 9.1 illustrate the
