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Niño Winters (nino + winter)
Selected AbstractsThe impact of El Niño,southern oscillation upon weather regimes over Europe and the North Atlantic during boreal winterINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2003Vincent Moron Abstract The influence of the warm and cold sea-surface temperatures in the eastern and central equatorial Pacific associated with El Niño,southern oscillation (ENSO) on the probability of occurrence of weather regimes (WRs) over the North Atlantic sector is investigated for the period November,March. Five WRs are identified from daily sea-level pressure anomalies (SLPAs) during 119 winters (1882,2000) over this sector by applying cluster analysis: the positive North Atlantic oscillation (NAO; called ZO for zonal) and negative NAO (called WBL for west blocking) patterns; GA (for Greenland anticyclone), with a positive SLPA shifted north of 60° N; EA (for European anticyclone) with a positive SLPA over Europe but enhanced north,south SLPA gradient over the western and central North Atlantic; and AR (for Atlantic Ridge) with a positive (negative) SLPA over the central North Atlantic (northern and central Europe). El Niño winters are associated with a significant increase (decrease) in the prevalence of ZO (WBL) in November,December and a significant increase (decrease) in the prevalence of GA and WBL (EA and ZO) in January,March. During La Niña winters, ZO (WBL and AR) occurs significantly less (more) frequently in November,December, and GA and WBL (EA and AR) are less (more) frequent in January,March. So, the anomalies of the WR frequencies are almost inverted between November,December and January,March. The response of the WR frequencies to ENSO extremes is most pronounced in February. On the inter- and multi-decadal time scales, the typical ENSO signals tend to be stronger during preferred phases of the basinwide westerlies, especially in January,March. The typical El Niño signal in January,March (e.g. more GA and WBL and less ZO and EA than normal) is strong when westerlies are slower than normal, around 1900, 1915 and mainly from 1930 to 1970. The generally reversed association during La Niña winters (e.g. more EA and AR and less GA and WBL than normal) in January,March is strong mainly when westerlies are faster than normal. Anomalies are weaker and quite different during ,slow westerlies,La Niña' and ,fast westerlies,El Niño' January,March winters. Such a modulation also appears in November,December with reversed association (i.e. stronger ENSO signal during ,slow westerlies,La Niña' and ,fast westerlies,El Niño' November,December winters), but the difference between the slow and fast westerlies phases is weaker than in January,March. Copyright © 2003 Royal Meteorological Society [source] Wintertime temperature anomalies in Alaska correlated with ENSO and PDOINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2001John M. Papineau Abstract Wintertime (November,March) surface air temperatures at 14 stations throughout the state of Alaska are correlated with the Southern Oscillation Index and the Pacific Decadal Oscillation index, for the years 1954,2000. On the seasonal and monthly timescales, the principal results are: (i) During El Niño winters, temperatures are near normal in western Alaska but significantly warmer than normal for the eastern two-thirds of the state. (ii) La Niña winters produce significant below normal temperatures statewide. (iii) Temperature patterns produced during El Niño, La Niña, and neutral winters are modified by the concurrent state of the North Pacific sea-surface temperature anomalies, as indicated by the Pacific Decadal Oscillation index. On the sub-monthly timescale, temperatures across Alaska are to the first order correlated with the alternating zonal to meridional Pacific/North American pattern. Analysis of daily winter temperatures at Fairbanks indicates that cold anomalies are more frequent and are longer in duration than warm anomalies, primarily due to radiational cooling of the boundary layer and the subsequent formation of deep temperature inversions. The development of strong inversions over the interior of Alaska limits the response of temperatures to changes in the synoptic-scale flow pattern. Warm anomalies in contrast to cold anomalies, are primarily a function of warm air advection, therefore temperatures during warm anomalies fluctuate in phase with changes in the synoptic-scale flow. Ultimately, air temperatures across Alaska are a function of: synoptic-scale forcings, radiative cooling of the boundary layer as well as local and regional effects such as downslope and drainage winds. Copyright © 2001 Royal Meteorological Society [source] Adjustment of the atmospheric circulation to tropical Pacific SST anomalies: Variability of transient eddy propagation in the Pacific,North America sector,THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 647 2010R. Seager Abstract El Niño,Southern Oscillation (ENSO) related precipitation anomalies in North America are related to changes in the paths of storm systems across the Pacific Ocean, with a more southern route into southwestern North America during El Niños and a more northern route into the Pacific Northwest during La Niñas. Daily reanalysis data are analyzed to confirm these changes. Seasonal mean upper tropospheric eddy statistics show, for El Niños (La Niñas), a pattern that is shifted southward (northward) compared with climatology. Paths of coherent phase propagation of transient eddies and of the propagation of wave packets are analyzed. A coherent path of propagation across the Pacific towards North America is identified that is more zonal during El Niño winters and, during La Niñas, has a dominant path heading northeastward to the Pacific Northwest. A second path heading southeastward from the central Pacific to the tropical east Pacific is more accentuated during La Niñas than El Niños. These changes in wave propagation are reproduced in an ensemble of seasonal integrations of a general circulation model forced by a tropical Pacific sea-surface temperature pattern, confirming that the changes are forced by changes in the mean atmospheric state arising from changes in tropical sea-surface temperature. A simplified model with a specified basic state is used to model the storm tracks for El Niño and La Niña winters. The results suggest that the changes in transient eddy propagation and the eddy statistics can be understood in terms of the refraction of transient eddies within different basic states. Copyright © 2010 Royal Meteorological Society [source] Effect of ENSO on the Hong Kong winter seasonATMOSPHERIC SCIENCE LETTERS, Issue 2 2009M. C. Wu Abstract The relationship between the ENSO condition and the winter condition in Hong Kong is investigated in this study. The winter monsoon over southern China tends to be weaker (stronger) during El Niño (La Niña) winters and Hong Kong tends to have higher (lower) mean winter temperatures against the background of the warming trend. On the other hand, there are more (fewer) surge events, which represents the southeastward advance of the Siberian cold air across the East Asian coast, affecting Hong Kong. Analyses showed that Hong Kong tends to be warmer with a shorter duration for the longest cold spell during the winter without blocking event over the Eurasian continent. Furthermore, blocking events are also less common during El Niño winters. Copyright © 2009 Royal Meteorological Society [source] | ||||||||||