Empirical orthogonal functions and related techniques in atmospheric science: A review

Hannachi, Abdel; Jolliffe, Ian T.; Stephenson, David B.

doi:10.1002/joc.1499

Cited by 894 publications

(651 citation statements)

References 142 publications

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“…In search for possible latitudinal patterns in the A h indices we use the principal component analysis (PCA) method (for a review, see, e.g., Hannachi et al, [2007]). In simple terms, PCA is a method which can be used to present a large number of partly correlated variables in terms of a smaller number of uncorrelated variables, called the principal components.…”

Section: Principal Component Analysis Methodsmentioning

confidence: 99%

Annual fractions of high‐speed streams from principal component analysis of local geomagnetic activity

et al. 2014

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We study the latitudinal distribution of geomagnetic activity in 1966–2009 with local geomagnetic activity indices at 26 magnetic observatories. Using the principal component analysis method we find that more than 97% of the variance in annually averaged geomagnetic activity can be described by the two first principal components. The first component describes the evolution of the global geomagnetic activity, and has excellent correlation with, e.g., the Kp/Ap index. The second component describes the leading pattern by which the latitudinal distribution of geomagnetic activity deviates from the global average. We show that the second component is highly correlated with the relative (annual) fraction of high‐speed streams (HSS) in solar wind. The latitudinal distribution of the second mode has a high maximum at auroral latitudes, a local minimum at subauroral latitudes and a low maximum at midlatitudes. We show that this distribution is related to the difference in the average location and intensity between substorms related to coronal mass ejections (CMEs) and HSSs. This paper demonstrates a new way to extract useful, quantitative information about the solar wind from local indices of geomagnetic activity over a latitudinally extensive network.

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Section: Principal Component Analysis Methodsmentioning

confidence: 99%

Annual fractions of high‐speed streams from principal component analysis of local geomagnetic activity

et al. 2014

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“…We compared the NAO derived by using two approaches, the first one was based on an EOF analysis of the SLP (Hannachi et al, 2007) and the second one consisted of regressing the SLP of model outputs onto a reference NAO pattern. Previously, SLP anomalies were weighted as a function of the cosine of latitude (Wu and Straus, 2004).…”

Section: Methodsmentioning

confidence: 99%

Trends of precipitation over the Iberian Peninsula and the North Atlantic Oscillation under climate change conditions

Rodríguez-Puebla

Isidro

2009

Intl Journal of Climatology

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The trends of precipitation over the Iberian Peninsula (IP) and the North Atlantic Oscillation (NAO) index from December to March are compared using observations and model simulations from the Coupled Model Intercomparison Project phase 3 (CMIP3). The evaluation is performed in two multi-models as derived by averaging simulations corresponding to two experiments: one represents climate in the 20th century (20C3M) and the other the scenario with medium forcing IPCC SRES A1B in the 21st century. The NAO index shows a trend to more positive phases and precipitation tends to decrease in the case of observations, with greater significance in the NAO than in precipitation. The simulations in the 20th century underestimate the trend both in the NAO and in precipitation compared to observations. The multi-model in the 21st century indicates a change in the NAO regimes to being more positive; this leads to a reduction of precipitation over the IP. To explain the precipitation trend changes we consider the response of precipitation to the NAO, the regression between sea level pressure (SLP) over the Euro-Atlantic area onto precipitation averaged over the IP and the composite of precipitation for years with greater and lower NAO.

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“…Preisendorfer 1988;Hannachi et al 2007) both for the winter season (DJF) and the summer season (JJA). On this basis, the daily AO indices were obtained by projecting the daily mean sea-level pressure anomalies poleward of 20°N onto the winter and summer AO patterns, respectively.…”

Section: Atmospheric Circulation Changesmentioning

confidence: 99%

Arctic warming, moisture increase and circulation changes observed in the Ny-Ålesund homogenized radiosonde record

Maturilli

Kayser

2016

Theor Appl Climatol

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Radiosonde measurements obtained at the Arctic site Ny-Ålesund (78.9°N, 11.9°E), Svalbard, from 1993 to 2014 have been homogenized accounting for instrumentation discontinuities by correcting known errors in the manufacturer provided profiles. The resulting homogenized radiosonde record is provided as supplementary material at http://doi. pangaea.de/10.1594/PANGAEA.845373. From the homogenized data record, the first Ny-Ålesund upper-air climatology of wind, temperature and humidity is presented, forming the background for the analysis of changes during the 22-year period. Particularly during the winter season, a strong increase in atmospheric temperature and humidity is observed, with a significant warming of the free troposphere in January and February up to 3 K per decade. This winter warming is even more pronounced in the boundary layer below 1 km, presumably amplified by mesoscale processes including e.g. orographic effects or the boundary layer capping inversion. Though the largest contribution to the increasing atmospheric water vapour column in winter originates from the lowermost 2 km, no increase in the contribution by specific humidity inversions is detected. Instead, we find an increase in the humidity content of the large-scale background humidity profiles. At the same time, the tropospheric flow in winter is found to occur less frequent from northerly directions and to the same amount more frequent from the South. We conclude that changes in the atmospheric circulation lead to an enhanced advection of warm and moist air from lower latitudes to the Svalbard region in the winter season, causing the warming and moistening of the atmospheric column above Ny-Ålesund, and link the observations to changes in the Arctic Oscillation.

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Empirical orthogonal functions and related techniques in atmospheric science: A review

Cited by 894 publications

References 142 publications

Annual fractions of high‐speed streams from principal component analysis of local geomagnetic activity

Annual fractions of high‐speed streams from principal component analysis of local geomagnetic activity

Trends of precipitation over the Iberian Peninsula and the North Atlantic Oscillation under climate change conditions

Arctic warming, moisture increase and circulation changes observed in the Ny-Ålesund homogenized radiosonde record

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