Geoscience Reference
In-Depth Information
Answer 4
(a) Shuttleworth is speaking about the annual average evaporation from the
oceanic surfaces of the globe which is about 1.2 m per year. Around 90% of
this water falls back to the ocean while 10% moves and falls over land. When
averaged over all continental surfaces, about 65% of the precipitation falling
over land re-evaporates back to the atmosphere but in semi-arid areas the
proportion is higher. In Arizona, for instance, around 95% re-evaporates.
(b) Shuttleworth is talking about General Circulation models (GCMs). The
two components of these models he is referring to are the
dynamics
and the
physics
. The dynamics applies conservation laws to calculate the fields of
atmospheric variables such as temperature, humidity and wind speed using
prescribed values for the divergence terms in these laws, see Chapters 16
and 17. The physics re-calculates the values of the divergence terms using
the (now modified) fields of atmospheric variables. Some of the processes
represented in the physics include radiation absorption, convection, and
precipitation processes in the atmosphere, and boundary layer and surface
exchange processes
(c) If all the Earth's continents were clustered at the equator the seasonality of
the global average surface reflection coefficient for solar radiation, i.e. the
global average albedo, might well be less because, being on average warmer
than at present, they would presumably experience less snowfall. The
change in albedo associated with seasonal variations in snow and ice cover
is large because the albedo of fresh snow is around 80% while that for most
natural surfaces is around 20%. Alternative reasons for reduced seasonality
in global albedo include the possibility of reduced seasonal changes in the
vigor of the vegetation covering the continents.
(d) Shuttleworth is referring to the fact that the processes giving rise to
precipitation above, but comparatively close to the Earth's surface, release
water vapor from the atmosphere and return it to the ground as precipitation,
which at the same time releases latent heat in the atmosphere. On average,
they therefore have the dual effect of reducing the lapse rate in the atmospheric
boundary layer so it is less than the adiabatic lapse rate while simultaneously
ensuring that atmospheric water vapor largely remains fairly near the surface.
(e) Presumably Shuttleworth is talking about GCMs again, because GCMs
have three main applications, namely (i) weather forecasting, (ii) climate
forecasting, and (iii) the synthesis of model-calculated fields of atmos-
pheric and surface variables across the entire globe as a by-product of
application (i). Weather forecasting seeks to predict actual weather a few
days ahead from well-defined initial conditions that may become the data
product (iii). In the case of (ii), initiation is less important because in this
application it is not actual weather but rather the statistics of weather (i.e.,
climate) that is the objective.
(f ) Shuttleworth is respectively referring to the specific heat and density of
water relative to that of air. This difference means that the water in oceans
