Geoscience Reference
In-Depth Information
These generalizations allowed, in the later decades
of the century, attempts to classify climates
regionally. In the 1870s Wladimir Koeppen, a St
Petersburg-trained biologist, began producing
maps of climate based on plant geography, as did
de Candolle (1875) and Drude (1887). In 1883
Hann's massive, three-volume
Handbook of
Climatology
appeared, which remained a standard
until 1930-1940 when the five-volume work of the
same title by Koeppen and Geiger replaced it. At
the end of World War I Koeppen (1918) produced
the first detailed classification of world climates
based on terrestrial vegetation cover. This was
followed by Thornthwaite's (1931-1933) classifi-
cation of climates employing evaporation and
precipitation amounts, which he made more
widely applicable in 1948 by the use of the theo-
retical concept of potential evapo-transpiration.
The Inter-War period was particularly notable for
the appearance of a number of climatic ideas
which were not brought to fruition until the
1950s. These included the use of frequencies
of various weather types (Federov 1921), the
concepts of variability of temperature and rain-
fall (Gorczynski 1942 and 1945) and micro-
climatology, the study of the fine climate structure
near the surface (Geiger 1927).
Despite the problems of obtaining detailed
measurements over the large ocean areas, the later
nineteenth century saw much climatic research
which was concerned with pressure and wind
distributions. In 1868 Buchan produced the first
world maps of monthly mean pressure; eight years
later Coffin composed the first world wind charts
for land and sea areas, and in 1883 L. Teisserenc
de Bort produced the first mean global pressure
maps showing the cyclonic and anticyclonic
'centers of action' on which the general circulation
is based. In 1887 de Bort began producing maps
of upper-air pressure distributions and in 1889 his
world map of January mean pressures in the
lowest 4km of the atmosphere was particularly
effective in depicting the great belt of the westerlies
between 30° and 50° north latitudes.
E MID-LATITUDE
DISTURBANCES
Theoretical ideas about the atmosphere and its
weather systems evolved in part through the needs
of nineteenth-century mariners for information
about winds and storms, especially predictions of
future behavior. At low levels in the westerly belt
(approximately 40
latitude) there is a
complex pattern of moving high and low pressure
systems, while between 6000m and 20,000m
there is a coherent westerly airflow. Dove (1827
and 1828) and Fitz Roy (1863) supported the
'opposing current' theory of cyclone (i.e.,
depression) formation, where the energy for the
systems was produced by converging airflow. Espy
(1841) set out more clearly a convection theory of
energy production in cyclones with the release of
latent heat (condensation of water vapor) as the
main source. In 1861 Jinman held that storms
develop where opposing air currents form lines of
confluence (later termed 'fronts'). Ley (1878) gave
a three-dimensial picture of a low pressure system
with a cold air wedge behind a sharp temperature
discontinuity cutting into warmer air, and
Abercromby (1883) described storm systems in
terms of a pattern of closed isobars (lines of equal
pressure) with typical associated weather types. By
this time, although the energetics were far from
clear, a picture, correct in is basics, was emerging
of mid-latitude storms being generated by the
mixing of warm tropical and cool polar air as a
fundamental result of the latitudinal temperature
gradients created by the patterns of incoming solar
radiation and of outgoing terrestrial radiation.
Towards the end of the nineteenth century two
important European research groups were dealing
with storm formation: the Vienna Group under
Margules, including Exner and Schmidt; and the
Swedish Group led by Vilhelm Bjerknes. The
former workers were concerned with the origins
of cyclone kinetic energy (energy of motion)
which was thought to be due to differences in
the potential energy of opposing air masses of
different temperature. Potential energy is energy
°
to 70
°
