scholarly journals The Role of Tropospheric Rossby Wave Breaking in the Pacific Decadal Oscillation

2009 ◽  
Vol 22 (7) ◽  
pp. 1819-1833 ◽  
Author(s):  
Courtenay Strong ◽  
Gudrun Magnusdottir
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Rossby Wave ◽  
Pacific Decadal Oscillation ◽  
Wave Breaking ◽  
El Nino ◽  
Sea Surface ◽  
Rossby Wave Breaking ◽  
The Pacific ◽  
Circulation Patterns

Abstract The leading pattern of extratropical Pacific sea surface temperature variability [the Pacific decadal oscillation (PDO)] is shown to depend on observed variability in the spatiotemporal distribution of tropospheric Rossby wave breaking (RWB), where RWB is the irreversible overturning of potential vorticity on isentropic surfaces. Composite analyses based on hundreds of RWB cases show that anticyclonic (cyclonic) RWB is associated with a warm, moist (cool, dry) column that extends down to a surface anticyclonic (cyclonic) circulation, and that the moisture and temperature advection associated with the surface circulation patterns force turbulent heat flux anomalies that project onto the spatial pattern of the PDO. The RWB patterns that are relevant to the PDO are closely tied to El Niño–Southern Oscillation, the Pacific–North American pattern, and the northern annular mode. These results explain the free troposphere-to-surface segment of the atmospheric bridge concept wherein El Niño anomalies emerge in summer and modify circulation patterns that act over several months to force sea surface temperature anomalies in the extratropical Pacific during late winter or early spring. Leading patterns of RWB account for a significant fraction of PDO interannual variability for any month of the year. A multilinear model is developed in which the January mean PDO index for 1958–2006 is regressed upon the leading principal components of cyclonic and anticyclonic RWB from the immediately preceding winter and summer months (four indexes in all), accounting for more than two-thirds of the variance.

The Forcing of the Pacific Decadal Oscillation*

2005 ◽  
Vol 18 (21) ◽  
pp. 4355-4373 ◽  
Author(s):  
Niklas Schneider ◽  
Bruce D. Cornuelle
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Pacific Decadal Oscillation ◽  
North Pacific ◽  
Sea Surface ◽  
Aleutian Low ◽  
The Pacific ◽  
Sea Surface Temperature Anomalies ◽  
Zonal Advection ◽  
The Kuroshio

Abstract The Pacific decadal oscillation (PDO), defined as the leading empirical orthogonal function of North Pacific sea surface temperature anomalies, is a widely used index for decadal variability. It is shown that the PDO can be recovered from a reconstruction of North Pacific sea surface temperature anomalies based on a first-order autoregressive model and forcing by variability of the Aleutian low, El Niño–Southern Oscillation (ENSO), and oceanic zonal advection anomalies in the Kuroshio–Oyashio Extension. The latter results from oceanic Rossby waves that are forced by North Pacific Ekman pumping. The SST response patterns to these processes are not orthogonal, and they determine the spatial characteristics of the PDO. The importance of the different forcing processes is frequency dependent. At interannual time scales, forcing from ENSO and the Aleutian low determines the response in equal parts. At decadal time scales, zonal advection in the Kuroshio–Oyashio Extension, ENSO, and anomalies of the Aleutian low each account for similar amounts of the PDO variance. These results support the hypothesis that the PDO is not a dynamical mode, but arises from the superposition of sea surface temperature fluctuations with different dynamical origins.

scholarly journals Modelled Rainfall Response to Strong El Niño Sea Surface Temperature Anomalies in the Tropical Pacific

2015 ◽  
Vol 28 (8) ◽  
pp. 3133-3151 ◽  
Author(s):  
Christine T. Y. Chung ◽  
Scott B. Power
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
Sea Surface ◽  
Precipitation Pattern ◽  
Convergence Zone ◽  
The Pacific ◽  
Sea Surface Temperature Anomalies

Abstract El Niño–Southern Oscillation strongly influences the interannual variability of rainfall over the Pacific, shifting the position and orientation of the South Pacific convergence zone (SPCZ) and intertropical convergence zone (ITCZ). In 1982/83 and 1997/98, very strong El Niño events occurred, during which time the SPCZ and ITCZ merged into a single zonal convergence zone (szCZ) extending across the Pacific at approximately 5°S. The sea surface temperature anomalies (SSTAs) reached very large values and peaked farther east compared to other El Niño events. Previous work shows that tropical Pacific precipitation responds nonlinearly to changing the amplitude of the El Niño SSTA even if the structure of the SSTA remains unchanged, but large canonical El Niño SSTAs cannot reproduce the szCZ precipitation pattern. This study conducts idealized, SST-forced experiments, starting with a large-amplitude canonical El Niño SSTA and gradually adding a residual pattern until the full (1982/83) and (1997/98) mean SST is reproduced. Differences between the canonical and strong El Niño SSTA patterns are crucial in generating an szCZ event. Three elements influence the precipitation pattern: (i) the local meridional SST maxima influences the ITCZ position and western Pacific precipitation, (ii) the total zonal SST maximum influences the SPCZ position, and (iii) the equatorial Pacific SST influences the total amount of precipitation. In these experiments, the meridional SST gradient increases as the SSTAs approach szCZ conditions. Additionally, the precipitation changes evident in szCZ years are primarily driven by changes in the atmospheric circulation, rather than thermodynamic changes. The addition of a global warming SST pattern increases the precipitation along the equator and shifts the ITCZ farther equatorward.

scholarly journals Variability of multi-site decadal running means arising from year-to-year fluctuations

2020 ◽  
pp. 1-41
Author(s):  
Xiaogu Zheng ◽  
Carsten S. Frederiksen
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Pacific Decadal Oscillation ◽  
Geopotential Height ◽  
Radiative Forcing ◽  
Decadal Variability ◽  
Sea Surface ◽  
Annular Mode ◽  
Northern Annular Mode ◽  
The Pacific

AbstractDecadal mean variables are frequently used to characterise decadal climate variabilities. Decadal means are often calculated using yearly data which can represent variability at time scales from annual to centennial. Residuals from interannual fluctuations may contribute to the variability in decadal time series. Such variability is more difficult to be predicted at the long range. Removing it from the decadal variability means that the remaining variability is more likely to arise from slowly varying multi-decadal or longer time scale external forcing and internal climate dynamics which are more likely to be predicted.Here, a new approach is proposed to understand the uncertainty, potential predictability and drivers of decadal mean variables. The covariance matrix of multivariate decadal running means is decomposed into unpredictable fast decadal variability and the potentially predictable slow decadal variability. EOF analysis is then applied to the decomposed matrices to find the dominant modes which may be related to the drivers of the two types of variabilities in the multivariate decadal means.The methodology has been applied to 140 year datasets of North Pacific sea surface temperature and the Northern Hemisphere 1000hPa geopotential height. For sea surface temperature, the Pacific Decadal Oscillation is the major driver of the fast decadal variability, while the radiative forcing and the Atlantic Multi-decadal Oscillation are major drivers of the slow decadal variability. For the 1000hPa geopotential height, fast decadal variability is associated with the Northern Annular Mode, the East Atlantic Mode and the Pacific Decadal Oscillation. Slow decadal variability is associated with the Northern Annular Mode and the Atlantic Multi-decadal Oscillation.

scholarly journals Análise da Variabilidade Climática dos Oceanos Atlântico e Pacífico

2021 ◽  
Vol 14 (4) ◽  
pp. 1861-1879
Author(s):  
Pedro Fernandes de Souza Neto ◽  
Djane Fonseca Da Silva ◽  
Henrique Ravi Rocha de Carvalho Almeida
Keyword(s):  
Wavelet Analysis ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Pacific Decadal Oscillation ◽  
Temperature Anomaly ◽  
Sea Surface ◽  
Sea Surface Temperature Anomaly ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Northern Sector

The sea surface temperature is one of the main variables for analyzing the global climate, and with that, it is essential to know its behavior. Thus, the objective of this study is to understand the best temperature variability of the sea surface of the Atlantic and Pacific oceans, through information on the causes of its variability using Wavelet analysis, and also using the climatic trends of the TSM of the oceans. Sea surface temperature anomaly data obtained through the National Oceanic and Atmospheric Administration with period of 1955-2018, for the Atlantic and Pacific Oceans, divided into sectors and some statistical analyzes were used. Using the wavelet analysis method, it was possible to observe the phenomena El Niño South Oscillation, Atlantic Dipole, sunspots and Pacific Decadal Oscillation, acting on the studied time series; however, the Pacific Decadal Oscillation, which occurs in the Pacific Ocean, proved to be a phenomenon of dominant time scale in the Atlantic and Pacific Oceans. The Mann-Kendall trend test showed a linear increase in the sea surface temperature anomaly for the two studied Oceans, and in both, the South sector has a greater increase than the North sector. Climate trends indicate that the Pacific Ocean is warming more than the Atlantic Ocean. It is also possible to conclude that the Southern sector of the two Oceans is heating up more than the Northern sector. The signs of the limit ranges for the averages of the southern sectors demonstrate greater variability of the anomalies at the South Atlantic and South Pacific. The Northern sector was more similar to the general basin, both in the Atlantic and the Pacific, proving the importance of continental areas for warming the oceans. These results were strengthened with those found by box plots and frequency distribution. The warming of the Pacific was also reinforced in all statistics mad.

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