Do Stationary Waves Drive the Zonal-Mean Jet Anomalies of the Northern Winter?

DeWeaver, Eric; Nigam, Sumant

doi:10.1175/1520-0442(2000)013<2160:dswdtz>2.0.co;2

Cited by 78 publications

(69 citation statements)

References 47 publications

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“…As the NH land-sea contrast topography is included, the zonal wind anomaly will be strongly dependent upon the phase of the NAO event in that climatological station- ary waves in the Northern Hemisphere can be excited by the land-sea contrast topography (not shown). As found by DeWeaver and Nigam (2000), the interaction between transient eddies (low frequency) and climatological stationary waves plays a large role in the ZI life cycle associated with the NAO. Thus, it is necessary that the NAO model presented here be extended to include land-sea contrast topography in order to simulate exactly the life cycle of the ZI.…”

Section: Relationship Between the Nao And The Zonal Indexmentioning

confidence: 68%

“…It can be anticipated from (10b) that there is a high correlation between the amplitude of ZI and the NAO index time series (DeWeaver and Nigam 2000). This also explains why there are many similarities between the dynamics of the ZI and NAO (Feldstein 2003).…”

Section: Relationship Between the Nao And The Zonal Indexmentioning

confidence: 92%

“…In addition, it is inferred that the zonal mean flow anomalies are indirectly driven by synopticscale eddies through the self-interaction of the excited NAO anomaly in that the NAO dipole anomaly is directly driven by the synoptic-scale eddies. In the NH, climatological stationary waves forced by land-sea contrast topography and heating play a certain role in a change in a zonal mean flow (DeWeaver and Nigam 2000), but the issue is beyond the scope of this work.…”

Section: B Derivation Of Eddy-driven Nao Anomaly Evolution Equationmentioning

confidence: 99%

See 2 more Smart Citations

Dynamics of Eddy-Driven Low-Frequency Dipole Modes. Part I: A Simple Model of North Atlantic Oscillations

Luo

Lupo

Han

2007

Journal of the Atmospheric Sciences

110

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A simple theoretical model is proposed to clarify how synoptic-scale waves drive the life cycle of the North Atlantic Oscillation (NAO) with a period of nearly two weeks. This model is able to elucidate what determines the phase of the NAO and an analytical solution is presented to indicate a high similarity between the dynamical processes of the NAO and zonal index, which is not derived analytically in previous theoretical studies. It is suggested theoretically that the NAO is indeed a nonlinear initial-value problem, which is forced by both preexisting planetary-scale and synoptic-scale waves. The eddy forcing arising from the preexisting synoptic-scale waves is shown to be crucial for the growth and decay of the NAO, but the preexisting low-over-high (high-over-low) dipole planetary-scale wave must be required to match the preexisting positive-over-negative (negative-over-positive) dipole eddy forcing so as to excite a positive (negative) phase NAO event. The positive and negative feedbacks of the preexisting dipole eddy forcing depending upon the background westerly wind seem to dominate the life cycle of the NAO and its life period.An important finding in the theoretical model is that negative-phase NAO events could be excited repeatedly after the first event has decayed, but for the positive phase downstream isolated dipole blocks could be produced after the first event has decayed. This is supported by observed cases of the NAO events presented in this paper. In addition, a statistical study of the relationship between the phase of the NAO and blocking activity over Europe in terms of the seasonal mean NAO index shows that blocking events over Europe are more frequent and long-lived for strong positive-phase NAO years, indicating that the positivephase NAO favors the occurrence of European blocking events.

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Section: Relationship Between the Nao And The Zonal Indexmentioning

confidence: 68%

Section: Relationship Between the Nao And The Zonal Indexmentioning

confidence: 92%

Section: B Derivation Of Eddy-driven Nao Anomaly Evolution Equationmentioning

confidence: 99%

See 1 more Smart Citation

Dynamics of Eddy-Driven Low-Frequency Dipole Modes. Part I: A Simple Model of North Atlantic Oscillations

Luo

Lupo

Han

2007

Journal of the Atmospheric Sciences

110

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“…Several recent papers have shown that on intraseasonal time-scales the NAO is closely linked to the dominant pattern of zonal mean ow variability. For example, DeWeaver and Nigam (2000a) nd a linear correlation of 0.80 between the principal component time series of the NAO and that of the rst empirical orthogonal function of the zonal mean zonal wind (this zonal mean pattern is usually referred to as the zonal index (ZI)).…”

Section: Introductionmentioning

confidence: 99%

“…This picture describes the ZI both for the winter and summer seasons of the southern hemisphere and for the northern hemisphere summer. However, for the ZI during the northern hemisphere winter, this picture is complicated by the large role played by the interaction between the transient eddies † and the climatological stationary eddies (Feldstein and Lee 1998;DeWeaver andNigam 2000a, 2000b).…”

Section: Introductionmentioning

confidence: 99%

The dynamics of NAO teleconnection pattern growth and decay

Feldstein

2003

Quart J Royal Meteoro Soc

254

214

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SUMMARYThis investigation performs both diagnostic analyses with NCEP/NCAR re-analysis data and forced, barotropic model calculations to examine the dynamical mechanisms associated with the growth and decay of the North Atlantic Oscillation (NAO) teleconnection pattern. The diagnostic calculations include projection and composite analyses of each term in the stream-function-tendency equation.The results of the analyses reveal a complete life cycle of growth and decay within approximately two weeks. The positive NAO phase is found to develop after anomalous wavetrain propagation across the North Paci c to the east coast of North America. This contrasts with the negative NAO phase which appeared to develop in situ.Both high-frequency (period < 10 days) and low-frequency (period > 10 days) transient eddy uxes drive the NAO growth. After the NAO anomaly attains its maximum amplitude, the high-frequency transient eddy uxes continue to drive the NAO anomaly in a manner that is consistent with a positive feedback process. The decay of the NAO occurs through both the divergence term and the low-frequency transient eddy uxes. The temporal and spatial properties of the divergence term are found to be consistent with Ekman pumping. These results illustrate many important differences between the NAO and Paci c/North American (PNA) teleconnection patterns, perhaps most striking being that the NAO life cycle is dominated by nonlinear processes, whereas the PNA evolution is primarily linear, In addition, the relation between the NAO and the zonal index is discussed.

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Vertical Structure of Zonal‐Mean Circulation Anomalies in the Southern Hemisphere in Austral Summer and Its Relationship with AAO and ENSO

Ying-Ying

Guan

Zhang³

2009

Chinese J of Geophysics

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The anomalous vertical structure of the austral summer (December∼February) zonal mean circulation [u] in association with Antarctic Oscillation (AAO) and ENSO has been investigated by means of 1979∼2004 NCEP/NCAR monthly reanalysis data. The Empirical Orthogonal Function (EOF) analysis has been performed for the zonal mean zonal wind anomalies in the present article. It is found that the EOF1 dominates the anomalous distribution of [u] in vertical with a positive-negative-positive sign pattern in the polar region, 70 • S∼50 • S and regions from 50 • S to the equator, respectively. The EOF1 exhibits the AAO signature and a close linkage with ENSO. The AAO is found to be statistically correlated with Nino3 index. To further clarify the effects of AAO and ENSO upon [u] variability in conjunction with the resulting structures, a one-variable regression scheme is utilized through Nino3 index to filter out the ENSO impact, and the remaining portion is decomposed with EOF analysis, obtaining AEOF1 for the [u] without the ENSO effect involved. It is displayed that AEOF1 represents the anomalous pattern of AAO-associated [u]. The residual of [u] after removing AAO-associated AEOF1 is analyzed by means of EOF, leading to a mode SEOF1, which is correlated with Nino3 index with a correlation coefficient of 0.9, thereby resulting in modes of [u] unrelated and related to ENSO. Besides the interdecadal and 3∼7-year interannual variations, the zonal mean zonal flow [u] shows weakening westerlies in the polar region, enhanced westerlies in the sub-polar zone, enfeebling subtropical westerlies and intensifying tropical easterlies as the long-term trends during the past 30 years.

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Do Stationary Waves Drive the Zonal-Mean Jet Anomalies of the Northern Winter?

Cited by 78 publications

References 47 publications

Dynamics of Eddy-Driven Low-Frequency Dipole Modes. Part I: A Simple Model of North Atlantic Oscillations

Dynamics of Eddy-Driven Low-Frequency Dipole Modes. Part I: A Simple Model of North Atlantic Oscillations

The dynamics of NAO teleconnection pattern growth and decay

Vertical Structure of Zonal‐Mean Circulation Anomalies in the Southern Hemisphere in Austral Summer and Its Relationship with AAO and ENSO

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