This annual climate assessment is
the tenth in an ongoing series produced by the Climate Prediction Center. It is designed
to provide a timely summary of the global climate system during 1999. Specific components
of the assessment include a documentation of global climate variations, an examination of
oceanic and atmospheric anomalies in the global Tropics and extratropics, and an analysis
of selected significant regional climate highlights.
Issues related to global temperatures are addressed in section 2. In
section 3 an analysis is presented of the Pacific cold episode (La Niņa) which persisted
throughout the year. The La Niņa impacts on global precipitation and atmospheric
circulation patterns are also examined. Regional climate highlights and summaries of the
major monsoon systems are discussed in section 4. Topics include heavy wintertime
precipitation in the Pacific Northwest United States, an active North Atlantic hurricane
season, above-average monsoon rains over the southwestern United States, severe drought in
the northeastern and south-central United States, above-average rains in southern Africa,
the African Sahel, and northern/ northwestern Australia, dryness in southeastern
Australia, near-average monsoon rains in India, above-average rains in central China,
excessive JanuaryFebruary snowfall in the Alps, and December wind storms in Europe.
In section 5, an assessment of various trace gas concentrations and
their potential impacts on climate is presented. This analysis includes a description of
the near-record Antarctic ozone hole during 1999, along with trends in such gases as
carbon dioxide, carbon monoxide, methane, and several chlorofluorocarbon species. In
section 6, seasonal maps of temperature anomalies, precipitation percentiles, and 500-hPa
heights and anomalies are presented. These maps are included for reference, and to
continue the analyses that have appeared in previous annual climate assessments. While
each section is essentially self-contained, there is liberal cross-referencing between
sections to aid navigation through the document.
A variety of data sources were used in the compilation of this assessment, including 1)
gridded analyses from the National Centers for Environmental Prediction/National Center
for Atmospheric Research (NCEP/ NCAR) Climate Data Assimilation System/Reanalysis Project
(Kalnay et al. 1996), 2) surface data obtained from the operational Global
Telecommunications System (GTS), 3) satellites, 4) radiosondes, and 5) ship reports.
Selected analyses were also obtained from international climate data centers. It should be
noted that due to the variety of different data sources used in this assessment, it is not
possible to maintain a consistent base period among all anomaly fields.