O.V. Marchukova, E.N. Voskresenskaya
Institute of Natural and Technical Systems, Russian Federation, Sevastopol, Lenin St., 28
Using sea surface temperature fields from global HadISST data sets (1° на 1° space resolution) the analyses of La-Nina (LN) features in different phases of Pacific Decadal Oscillation (PDO) in 1900 – 2014 were done taking into account two LN type: Central Pacific (CP) and Eastern Pacific (EP). Their differences in frequency, duration and intensity of events were found. The manifestations of different LN types associated with negative and positive PDO is demonstrated for example in global fields monthly of anomalies of 500 mb geopotential heights and air surface temperature from 20th Century Reanalysis V2c data sets in the same period. The following results were found.
The negative PDO phase is accompanied by 30% raising of LN number and about 3 times growth of intensity in comparison with positive PDO phase.
The study of LN types characteristics associated with PDO phases reveals some their features.
During negative PDO phase mid duration of CP and EP types is 15 и 16 months. The typical time of their existing is 2 years having 2 autumn-winter maxima.
The positive PDO phase is accompanied by 1 year duration LN events having one maximum in the mutual autumn-beginning of winter. The proportion between CP and EP LN number of events and their intensity at the beginning and at the end of XX century has the significant differences: the frequency became higher, the intensity became twice more. However the LN intensity in positive PDO is much less in comparison with LN in negative PDO phase.
The revealed LN features typical for different PDO phases are accompanied by associated manifestations in the atmospheric fields.
Positive PDO phase in general is characterized by large-scale negative anomaly of 500 mb geopotential heights at the South Hemisphere and by positive anomaly at the North Hemisphere in winter. This positive anomaly shifts to the South-East and leads to Azor high and North Atlantic (NAO) intensification.
In negative phase LN manifest in the opposite way: negative anomaly of 500 mb geopotential heights in the the North Hemisphere is arise in winter, it leads to Azor high and NAO weakening.
The manifestation of LN types during two PDO phases is the following.
During the positive PDO phase the CT LN in winter are characterized by negative is accompanied by negative anomaly of 500 mb geopotential heights in the Southern Hemisphere and positive one in the North Hemisphere, which are more pronounced in comparison with EP events. In this case NAO is intensified and leads to the shift of cyclones from North Atlantic to the North Europe. Air temperature due to such scheme become higher in January and February. That is why there are mild winters there.
During negative PDO phase CP LN are characterized by more pronounced positive anomaly of 500 mb geopotential heights in South Hemisphere in comparison with EP LN and by negative one in the Northern Hemisphere. That manifests in the NAO weakening and leads to the severe winter at the North-West Europe.
Keywords: Pacific Decadal Oscillation, La Niña, El Niño, Equatorial Pacific, global manifestations, North Atlantic Oscillation.
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