Climatology or climate science is the study of climate, scientifically defined
as weather conditions averaged over a period of time. This modern field of
study is regarded as a branch of the atmospheric sciences and a subfield of
physical geography, which is one of the Earth sciences. Climatology now includes
aspects of oceanography and biogeochemistry. Basic knowledge of
climate can be used within shorter term weather forecasting using analog
techniques such as the El Niño – Southern Oscillation, the Madden-Julian
Oscillation, the North Atlantic Oscillation, the Northern Annualar Mode
which is also known as the Arctic oscillation, the Northern Pacific Index,
the Pacific Decadal Oscillation, and the Interdecadal Pacific Oscillation.
Climate models are used for a variety of purposes from study of the dynamics of
the weather and climate system to projections of future climate.
History Chinese scientist Shen Kuo inferred that
climates naturally shifted over an enormous span of time, after observing
petrified bamboos found underground near Yanzhou, a dry-climate area unsuitable
for the growth of bamboo. Early climate researchers include Edmund
Halley, who published a map of the trade winds in 1686 after a voyage to the
southern hemisphere. Benjamin Franklin first mapped the course of the Gulf
Stream for use in sending mail from the United States to Europe. Francis Galton
invented the term anticyclone. Helmut Landsberg fostered the use of
statistical analysis in climatology, which led to its evolution into a
physical science. Different approaches
Climatology is approached in a variety of ways. Paleoclimatology seeks to
reconstruct past climates by examining records such as ice cores and tree
rings. Paleotempestology uses these same records to help determine hurricane
frequency over millennia. The study of contemporary climates incorporates
meteorological data accumulated over many years, such as records of rainfall,
temperature and atmospheric composition. Knowledge of the atmosphere and its
dynamics is also embodied in models, either statistical or mathematical,
which help by integrating different observations and testing how they fit
together. Modeling is used for understanding past, present and
potential future climates. Historical climatology is the study of climate as
related to human history and thus focuses only on the last few thousand
years. Climate research is made difficult by
the large scale, long time periods, and complex processes which govern climate.
Climate is governed by physical laws which can be expressed as differential
equations. These equations are coupled and nonlinear, so that approximate
solutions are obtained by using numerical methods to create global
climate models. Climate is sometimes modeled as a stochastic process but this
is generally accepted as an approximation to processes that are
otherwise too complicated to analyze. Indices
Scientists use climate indices based on several climate patterns in their
attempt to characterize and understand the various climate mechanisms that
culminate in our daily weather. Much in the way the Dow Jones Industrial
Average, which is based on the stock prices of 30 companies, is used to
represent the fluctuations in the stock market as a whole, climate indices are
used to represent the essential elements of climate. Climate indices are
generally devised with the twin objectives of simplicity and
completeness, and each index typically represents the status and timing of the
climate factor it represents. By their very nature, indices are simple, and
combine many details into a generalized, overall description of the atmosphere or
ocean which can be used to characterize the factors which impact the global
climate system. = El Niño – Southern Oscillation=
El Niño-Southern Oscillation is a global coupled ocean-atmosphere phenomenon. The
Pacific ocean signatures, El Niño and La Niña are important temperature
fluctuations in surface waters of the tropical Eastern Pacific Ocean. The name
El Niño, from the Spanish for "the little boy", refers to the Christ child,
because the phenomenon is usually noticed around Christmas time in the
Pacific Ocean off the west coast of South America. La Niña means "the little
girl". Their effect on climate in the subtropics and the tropics are profound.
The atmospheric signature, the Southern Oscillation reflects the monthly or
seasonal fluctuations in the air pressure difference between Tahiti and
Darwin. The most recent occurrence of El Niño started in September 2006 and
lasted until early 2007. ENSO is a set of interacting parts of a
single global system of coupled ocean-atmosphere climate fluctuations
that come about as a consequence of oceanic and atmospheric circulation.
ENSO is the most prominent known source of inter-annual variability in weather
and climate around the world. The cycle occurs every two to seven years, with El
Niño lasting nine months to two years within the longer term cycle, though not
all areas globally are affected. ENSO has signatures in the Pacific, Atlantic
and Indian Oceans. In the Pacific, during major warm
events, El Niño warming extends over much of the tropical Pacific and becomes
clearly linked to the SO intensity. While ENSO events are basically in phase
between the Pacific and Indian Oceans, ENSO events in the Atlantic Ocean lag
behind those in the Pacific by 12–18 months. Many of the countries most
affected by ENSO events are developing countries within tropical sections of
continents with economies that are largely dependent upon their
agricultural and fishery sectors as a major source of food supply, employment,
and foreign exchange. New capabilities to predict the onset of ENSO events in
the three oceans can have global socio-economic impacts. While ENSO is a
global and natural part of the Earth's climate, whether its intensity or
frequency may change as a result of global warming is an important concern.
Low-frequency variability has been evidenced: the quasi-decadal
oscillation. Inter-decadal modulation of ENSO might exist. This could explain the
so-called protracted ENSO of the early 1990s.
= Madden–Julian Oscillation= The Madden–Julian Oscillation is an
equatorial traveling pattern of anomalous rainfall that is planetary in
scale. It is characterized by an eastward progression of large regions of
both enhanced and suppressed tropical rainfall, observed mainly over the
Indian and Pacific Oceans. The anomalous rainfall is usually first evident over
the western Indian Ocean, and remains evident as it propagates over the very
warm ocean waters of the western and central tropical Pacific. This pattern
of tropical rainfall then generally becomes very nondescript as it moves
over the cooler ocean waters of the eastern Pacific but reappears over the
tropical Atlantic and Indian Oceans. The wet phase of enhanced convection and
precipitation is followed by a dry phase where convection is suppressed. Each
cycle lasts approximately 30–60 days. The MJO is also known as the 30–60 day
oscillation, 30–60 day wave, or the intraseasonal oscillation.
= North Atlantic Oscillation= Indices of the NAO are based on the
difference of normalized sea level pressure between Ponta Delgada, Azores
and Stykkisholmur/Reykjavik, Iceland. The SLP anomalies at each station were
normalized by division of each seasonal mean pressure by the long-term mean
standard deviation. Normalization is done to avoid the series of being
dominated by the greater variability of the northern of the two stations.
Positive values of the index indicate stronger-than-average westerlies over
the middle latitudes. = Northern Annular Mode or Arctic
Oscillation= The NAM, or AO, is defined as the first
EOF of northern hemisphere winter SLP data from the tropics and subtropics. It
explains 23% of the average winter variance, and it is dominated by the NAO
structure in the Atlantic. Although there are some subtle differences from
the regional pattern over the Atlantic and Arctic, the main difference is
larger amplitude anomalies over the North Pacific of the same sign as those
over the Atlantic. This feature gives the NAM a more annular structure.
= Northern Pacific Index= The NP Index is the area-weighted sea
level pressure over the region 30N–65N, 160E–140W.
= Pacific Decadal Oscillation= The PDO is a pattern of Pacific climate
variability that shifts phases on at least inter-decadal time scale, usually
about 20 to 30 years. The PDO is detected as warm or cool surface waters
in the Pacific Ocean, north of 20° N. During a "warm", or "positive", phase,
the west Pacific becomes cool and part of the eastern ocean warms; during a
"cool" or "negative" phase, the opposite pattern occurs. The mechanism by which
the pattern lasts over several years has not been identified; one suggestion is
that a thin layer of warm water during summer may shield deeper cold waters. A
PDO signal has been reconstructed to 1661 through tree-ring chronologies in
the Baja California area. = Interdecadal Pacific Oscillation=
The Interdecadal Pacific Oscillation display similar sea surface temperature
and sea level pressure patterns to the PDO, with a cycle of 15–30 years, but
affects both the north and south Pacific. In the tropical Pacific,
maximum SST anomalies are found away from the equator. This is quite
different from the quasi-decadal oscillation with a period of 8–12 years
and maximum SST anomalies straddling the equator, thus resembling ENSO.
Models Climate models use quantitative methods
to simulate the interactions of the atmosphere, oceans, land surface, and
ice. They are used for a variety of purposes from study of the dynamics of
the weather and climate system to projections of future climate. All
climate models balance, or very nearly balance, incoming energy as short wave
electromagnetic radiation to the earth with outgoing energy as long wave
electromagnetic radiation from the earth. Any unbalance results in a change
in the average temperature of the earth. The most talked-about models of recent
years have been those relating temperature to emissions of carbon
dioxide. These models predict an upward trend in the surface temperature record,
as well as a more rapid increase in temperature at higher latitudes.
Models can range from relatively simple to quite complex:
A simple radiant heat transfer model that treats the earth as a single point
and averages outgoing energy this can be expanded vertically, or
horizontally finally, atmosphere–ocean–sea ice global
climate models discretise and solve the full equations for mass and energy
transfer and radiant exchange. Differences with meteorology
In contrast to meteorology, which focuses on short term weather systems
lasting up to a few weeks, climatology studies the frequency and trends of
those systems. It studies the periodicity of weather events over years
to millennia, as well as changes in long-term average weather patterns, in
relation to atmospheric conditions. Climatologists study both the nature of
climates – local, regional or global – and the natural or human-induced factors
that cause climates to change. Climatology considers the past and can
help predict future climate change. Phenomena of climatological interest
include the atmospheric boundary layer, circulation patterns, heat transfer,
interactions between the atmosphere and the oceans and land surface, and the
chemical and physical composition of the atmosphere.
Use in weather forecasting A more complicated way of making a
forecast, the analog technique requires remembering a previous weather event
which is expected to be mimicked by an upcoming event. What makes it a
difficult technique to use is that there is rarely a perfect analog for an event
in the future. Some call this type of forecasting pattern recognition, which
remains a useful method of observing rainfall over data voids such as oceans
with knowledge of how satellite imagery relates to precipitation rates over
land, as well as the forecasting of precipitation amounts and distribution
in the future. A variation on this theme is used in Medium Range forecasting,
which is known as teleconnections, when you use systems in other locations to
help pin down the location of another system within the surrounding regime.
One method of using teleconnections are by using climate indices such as
ENSO-related phenomena. See also
Biogeochemistry Climate engineering
Climate Prediction Center Earth's rotational axial tilt
Geophysics Helmut Landsberg
List of climate scientists Meteorology
National Climatic Data Center Climate as complex networks
Paleoclimatology Paleotempestology
Pangaea Expedition Tornado climatology
Tropical cyclone rainfall climatology Urban climatology
References External links
The Earth's climate – Centre national de la recherche scientifique
Climatology News Daily publication with news in all areas of climatology plus
free news feeds for webmasters. Climate Prediction Center
KNMI Climate Explorer The Royal Netherlands Meteorological Institute's
Climate Explorer graphs climatological relationships of spatial and temporal
data. Climatology as a Profession Amer. Inst.
of Physics account of the history of the discipline of climatology in the 20th
century Sunpreview annual and global weather
project NOAA Weather Service