Geoscience Reference
In-Depth Information
the short-duration impacts and marked damages, dust storms create a regular
constituent of the global ecodynamics which can manifest itself in decades and even
centuries.
Thunderstorms play a special role in the environmental change. Lightning dis-
charges occurring practically in all latitudes, affect the photochemical reactions in
the atmosphere and are a factor of
fire risk. From available estimates, 1800 thun-
derstorms, on the average, occur at any moment on Earth, each being followed by
200 lightning
fl
ashes per hour (or 3.3
fl
flashes per minute). From satellite observa-
tions,
the global frequency of lightning
fl
ashes averages 22
65
fl
ashes per s.
-
Observations from Microlab-1 satellite gave 44
±
5
fl
flashes per s, which corresponds
to 1.4 billion
flashes per year. The use of Microlab-1 data has made it possible to
draw global maps of the frequency of lightning discharges in different seasons. An
analysis of these maps has shown that lightning discharges occur mainly over land,
and the ratio between their number over land and ocean averages approximately
10:1. About 78 % of lightning discharges fall on the latitudinal band 30
fl
S.
The all-the-year-round regime of lightning discharges is most intensive in the river
Congo basin where the average frequency of
°
N
−
70
°
ashes
per km
2
per year, which corresponds to conditions in the Central Florida State
(USA). The all-the-year-round intensive regime of lightning
fl
flashes reaches (in Rwanda) 80
fl
fl
flashes is characteristic
of the northern sector of the Paci
uence of cold air
advection over the warm ocean surface the atmosphere becomes unstable. In the
eastern sector of the tropical Paci
c Ocean where under the in
fl
c and in the Indian Ocean, where the atmosphere
is warmer, the lightning discharges are not that frequent. Maximum frequency of
lightning occurrence in the Northern Hemisphere falls on summer, whereas in the
tropics, lightning discharges are characterized by a semi-annual cycle.
In the northern regions, an important constituent of the controlling mechanism of
evolution are strong frosts, whose impact on vegetation cover depends on plants
'
hardiness. J
nsson et al. (2004), with the Norwegian spruce Picea abies as an
example have studied the response of boreal forests to temperature changes. It has
been shown that sudden temperature variations cause changes in wood compact-
ness, and that an expected climate change can change the vegetation cover.
During the last years, in connection with discussions of the causes of potential
climate change, of key importance have been estimates of uncertainties of values
which serve the basis for conclusions about climate change and measures to prevent
it. Particularly important is the problem of assessing the levels of GHGs emissions
to the atmosphere connected,
ö
first of all, with solution of the problem of global
carbon cycle. It is evident that without a reliable veri
cation of available estimates
of emissions all discussions concerning the ecological bene
t of various measured
and respective expenditure are abstract (Nilsson et al. 2002). For instance, how can
the
fines for not meeting recommendations on GHGs emissions reduction be sub-
stantiated if it is impossible to prove that emissions in 2012 will differ from those in
1990? So far, in the course of discussions on the Kyoto Protocol problem, quan-
titative estimates of uncertainties of the levels of GHGs sinks have been ignored
(especially it concerns the biosphere). Uncertainties of the estimates of total CO
2
fl
fluxes are, however, very substantial (exceeding 100 % in Russia). Calculations of
Search WWH ::
Custom Search