In the

natural sciences Natural science is one of the branches of science concerned with the description, understanding and prediction of natural phenomena, based on empirical evidence from observation and experimentation. Mechanisms such as peer review and repeatab ...

, especially in

atmospheric An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

and Earth sciences involving

applied statistics Statistics (from German language, German: ''wikt:Statistik#German, Statistik'', "description of a State (polity), state, a country") is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of ...

, an ''anomaly'' is a persisting deviation in a

physical quantity A physical quantity is a physical property of a material or system that can be quantified by measurement. A physical quantity can be expressed as a ''value'', which is the algebraic multiplication of a ' Numerical value ' and a ' Unit '. For examp ...

from its expected value, e.g., the

systematic Systematic may refer to: Science * Short for systematic error * Systematic fault * Systematic bias, errors that are not determined by chance but are introduced by an inaccuracy (involving either the observation or measurement process) inheren ...

difference between a measurement and a trend or a model prediction.Wilks, D.S. (1995) ''Statistical Methods in the Atmospheric science'', Academic Press. (page 42) Similarly, a standardized anomaly equals an anomaly divided by a

standard deviation In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the set, while ...

. A group of anomalies can be analyzed spatially, as a map, or temporally, as a

time series In mathematics, a time series is a series of data points indexed (or listed or graphed) in time order. Most commonly, a time series is a sequence taken at successive equally spaced points in time. Thus it is a sequence of discrete-time data. Exa ...

. It should not be confused for an isolated

outlier In statistics, an outlier is a data point that differs significantly from other observations. An outlier may be due to a variability in the measurement, an indication of novel data, or it may be the result of experimental error; the latter are ...

. There are examples in atmospheric sciences and in geophysics.

Calculation

The location and scale measures used in forming an anomaly time-series may either be constant or may themselves be a time series or a map. For example, if the original time series consisted of daily mean temperatures, the effect of seasonal cycles might be removed using a

deseasonalization Seasonal adjustment or deseasonalization is a statistical method for removing the seasonal component of a time series. It is usually done when wanting to analyse the trend, and cyclical deviations from trend, of a time series independently of the ...

filter.

Robust statistics Robust statistics are statistics with good performance for data drawn from a wide range of probability distributions, especially for distributions that are not normal. Robust statistical methods have been developed for many common problems, suc ...

, resistant to the effects of

s, are sometimes used as the basis of the

transformation Transformation may refer to: Science and mathematics In biology and medicine * Metamorphosis, the biological process of changing physical form after birth or hatching * Malignant transformation, the process of cells becoming cancerous * Trans ...

Examples

Atmospheric sciences

In the atmospheric sciences, the climatological

annual cycle An annual cycle refers to a set of changes or events that uniformly, or consistently, take place at the same time of year. In biology, the annual cycle for plants and animals details behavioral and chemical changes that take place as the seasons ...

is often used as the expected value. Famous atmospheric anomalies are for instance the Southern Oscillation index (SOI) and the

North Atlantic oscillation The North Atlantic Oscillation (NAO) is a weather phenomenon over the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level (SLP) between the Icelandic Low and the Azores High. Through fluctuations in the ...

index. SOI is the atmospheric component of El Niño, while NAO plays an important role for

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...

by modification of the exit of the Atlantic storm track. A climate normal can also be used to derive a climate anomaly.{{Cite book, url=https://books.google.com/books?id=ypcMBwAAQBAJ&dq=climate+anomaly&pg=PA53, title=Dictionary of Global Climate Change, date=August 15, 2008, publisher=Springer Science & Business Media, isbn=9780585295732, via=Google Books

Geophysics

Gravity anomaly The gravity anomaly at a location on the Earth's surface is the difference between the observed value of gravity and the value predicted by a theoretical model. If the Earth were an ideal oblate spheroid of uniform density, then the gravity meas ...

, difference between the observed gravity and a value predicted from a model ** Bouguer anomaly, anomaly in gravimetry ** Free-air anomaly, gravity anomaly that has been computed for latitude and corrected for elevation of the station *

Iridium anomaly The term iridium anomaly commonly refers to an unusual abundance of the chemical element iridium in a layer of rock strata at the Cretaceous–Paleogene (K–Pg) boundary. The unusually high concentration of a rare metal like iridium is often take ...

, an unusual abundance of what is normally a very rare element in the Earth's crust *

Magnetic anomaly In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying ...

, local variation in the Earth's magnetic field **

Bangui magnetic anomaly The Bangui magnetic anomaly is a local variation in the Earth's magnetic field centered at Bangui, the capital of Central African Republic. The magnetic anomaly is roughly elliptical, about , and covers most of the country, making it one of the "l ...

, in central Africa ** Kursk Magnetic Anomaly, territory rich in iron ores located within Kursk Oblast, Belgorod Oblast, and Oryol Oblast **

Temagami Magnetic Anomaly The Temagami Magnetic Anomaly, also called the Temagami Anomaly or the Wanapitei Anomaly, is a magnetic anomaly resulting from a large buried geologic structure in the Canadian Shield near Temagami, Ontario, Canada. It stretches from Lake Wanapit ...

, large buried geologic structure in the Temagami region of Ontario, Canada

References

Time series Climate and weather statistics Geophysics

Calculation

Examples

Atmospheric sciences

Geophysics

See also

References