Middle-latitude climates - The Global Climate System: Patterns, Processes, and Teleconnections - page 99

beginning of the Second World War in 1939 was shown in Climate and Man
(US Department of Agriculture 1941 ); the 1940s and 1950s were the ''upper
balloon period''; the 1960s and 1970s were the ''modern rawinsonde'' period
and the 1980s heralded the ''satellite'' period.
Until the advent of satellites most of the reporting stations were unevenly
based on the continents and there was a sparsity of data for the ocean areas,
which constitute about 71% of the Earth's surface. In the second half of the
twentieth century more data were collected over the ocean areas as well as
over some of the more inhospitable land areas, more sophisticated measuring
instruments (including rawinsondes and satellites) were developed, but also
there was a realization that perhaps not all these data were comparable.
Various international efforts were made to make this diverse amount of
data internally compatible. It became apparent in the last quarter of the
century that the data could not be used objectively in some climatological
analyses, especially over the question of climate variability. Problems
included urbanization, comparatively sparse amounts of data over the poles
and oceans, changes in meteorological practices, and changes in station sites.
The development of computers and computer models required that data be
evenly distributed both horizontally and vertically rather than in the uneven
manner that typified the observing station network. Two strategies were
developed to overcome these problems and both relied on producing ''gridded''
data. The first strategy was the development of ''standardization'' or ''homo-
genization'' of climate data. An early example of this was the careful way in
which Manley ( 1953 ) constructed his first time series (1698-1952) of monthly
mean temperatures for Central England (CET). He used overlapping sequences
of observations from documented and carefully located stations. Although
Manley never produced daily values of CET, this was done in the British
Meteorological Office in the 1970s and early 1980s. But as Jones ( 1987 )points
out, there were by then three different monthly series and five different daily
series; which should be considered the definitive one? Parker et al.( 1992 )
published their CET daily series 1772-1991 and Jones ( 1994 ) a NH land
temperature anomaly series for 1851-1993. Each of these papers briefly
describes the methodology for producing a homogeneous temperature series
that makes allowances for site changes whether locational or environmental. A
detailed account of the methodology can be found in the three-part paper on
Swedish temperature homogenization by Alexandersson and Moberg ( 1997 ),
Moberg and Alexandersson ( 1997 ) and Moberg and Bergstr¨m ( 1997 ). For
other examples of this strategy see the works of Trenberth and Paolino ( 1980 ),
Easterling and Peterson ( 1995 ), and Jones and Bradley ( 1995 ). The homogen-
ization of rawinsonde data is described in Lanzante et al.( 2003 ).
At the same time, the second half of the twentieth century saw the rapid
development of synoptic climatology (Barry and Perry 1973 ). This discipline