Middle-latitude climates - The Global Climate System: Patterns, Processes, and Teleconnections - page 105

many that exist. The following examples show how reanalysis can be used for
different time intervals, in relation to other data sources, and for various climatic
elements.
A study using NCEP/NCAR reanalysis data for varying time intervals was
provided by Gulev et al.( 2001 ). They used 6-hourly NCEP/NCAR reanalysis
data for the period from 1958 to 1999 together with software providing improved
accuracy in cyclone identification to study the climatology of NHwinter cyclone
activity. The findings of this work showed that: (1) there are secular and decadal-
scale changes in cyclone frequency, intensity, lifetime, and deepening rates;
(2) in the Arctic and in the western Pacific there is an increase in the number of
cyclones, while over the Gulf Stream/North Atlantic Drift and in the subpolar
Pacific Ocean there is a decreasing trend; (3) both Atlantic and Pacific cyclone
activity is positively correlated to the NAO and PNA. The NAO relationship also
reflects the 1970s shift associated with European storm tracks. The PNA is
largely linked to the eastern Pacific cyclone frequencies, and, especially over
the last 20 years, cyclone activity over the Gulf of Mexico region and the eastern
North American coast.
The NCEP/NCAR reanalysis is also frequently used in conjunction with other
data sources to examine many aspects of the surface-atmosphere interaction.
A study by Washington et al.( 2003 ) used reanalysis together with both ground
station data and that derived from satellite, in this case the Total Ozone
Monitoring Spectrometer (TOMS). The objective of the study was to better
understand terrestrial sources and the transport mechanisms responsible for the
production and distribution of atmospheric dust, detailed knowledge of which is
important in reducing uncertainties in the modeling of past and future climates.
The study showed the Sahara to be the primary key source region while other key
regions were the Middle East, Taklamakan, southwest Asia, central Australia,
the Etosha and Mkgadikgadi basins of Southern Africa, the Salar de Uyuni
(Bolivia), and the Great Basin (United States). The study also outlined some
discrepancies that occurred between surface and satellite observations.
Reanalysis can be used in a number of ways for various climatic elements.
Using the Climate Prediction Center (CPC) Merged Analysis of Precipitation
(CMAP) product together with the Goddard Earth Observing System (GEOS)
reanalysis and the National Center for Environmental Prediction (NCEP) sea
surface temperature (SST) data Zhou and Lau ( 2002 ) examined the principal
modes of summer rainfall over South America for the period 1979-95. The
leading modes of rainfall variation identified annual, decadal, and long-term
variability. The first mode is highly correlated with El Ni˜o-Southern
Oscillation (ENSO), showing a regional rainfall anomaly pattern largely
consistent with previous results. This mode captures the summer season inter-
annual variability in northeast Brazil and its connection with excessive rainfall
over southern Brazil and Ecuador. The modes associated with long-term vari-
ability show that since 1980 there has been a decrease of rainfall from the