Tropospheric wave response to decelerated stratosphere seen as downward propagation in northern annular mode

Coughlin, K.; Tung, K. K.

doi:10.1029/2004jd004661

Cited by 22 publications

(14 citation statements)

References 11 publications

(25 reference statements)

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“…However, as shown here and in the previous paper (Coughlin and Tung 2005), the EOF pattern also contains a wave 1 structure, which gives rise to a change in the tropospheric NAM index. Such examples may be more easily understood with a classical framework of the vertical propagation of planetary waves and wave mean-flow interaction.…”

Section: Discussionsupporting

confidence: 79%

“…2 in Coughlin and Tung (2005) reveals that prior to the change in the stratospheric NAM index, the NAM index in the troposphere changes due to the wave 1 component. However, during the winter, variability is large both in the stratosphere and troposphere so that it is difficult to see a causal relationship between them.…”

Section: Introductionmentioning

confidence: 99%

“…In fact, Coughlin and Tung (2005) showed that an apparent propagation of the NAM signal during the winter 1998/99 does not necessarily mean a propagation of the annular structure, but the tropospheric NAM signal is due to the projection of the wave 1 structure in the leading EOF. They showed that an apparent downward propagation of the NAM can appear due to a reflection of wave 1 in the stratosphere due to a stratospheric warming.…”

Section: Introductionmentioning

confidence: 99%

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Apparent Vertical Propagation of the NAM Index Due to an Embedded Wave Structure

Kodera¹,

Coughlin

2007

Journal of the Meteorological Society of Japan

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The leading empirical orthogonal function (EOF) of the geopotential height is called the Northern Annular Mode (NAM). Stratosphere-troposphere connections seen in the multilevel NAM signal are often considered as due to a propagation of the annular structure. However, the tropospheric leading EOF contains not just an annular structure, but also a wave structure. This indicates that the NAM index is sensitive to changes in wave activity.A previous study showed that an apparent downward propagation of the NAM index can appear as a result of a reflection of wave 1 due to a stratospheric sudden warming. If this result is correct, we may also expect to find a reverse case. Here we show a case when an amplification of a tropospheric wave 1 leads to a stratospheric warming, an apparent upward propagation of the ''Annular'' mode signal, i.e., change in the amplitude of the NAM index appears due to a projection on the wave component of the tropospheric NAM.

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Section: Discussionsupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Apparent Vertical Propagation of the NAM Index Due to an Embedded Wave Structure

Kodera¹,

Coughlin

2007

Journal of the Meteorological Society of Japan

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“…There had not been enough experimental evidences for such a connection till date. However, some of the recent studies discussing the dynamical changes in the lower atmosphere over the northern high latitude regions not only indicate the presence of a zero wind line but also discuss about significance in context of the propagation of PWs (Baldwin and Dunkerton, 1999;Walterscheid et al, 2000;Coughlin and Tung, 2005;Liu and Roble, 2005).…”

Section: Introductionmentioning

confidence: 99%

Tropical connection to the polar stratospheric sudden warming through quasi 16-day planetary wave

et al. 2010

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Abstract. The Planetary Waves (PWs) are believed to have significant role in generating the wintertime warming over the polar stratosphere, known as Stratospheric Sudden Warming (SSW). However, the origin, characteristics and evolution of these waves are still speculative. The possibility that the PWs over the polar stratosphere, which play an important role in the generation of SSW, could also have contribution from the tropics has been indicated through many numerical simulations in the past, but due to the paucity of global measurements it could not be established unequivocally. The earlier numerical studies also indicated the presence of a zero-wind line (more general the critical layer, where the zonal wind amplitude becomes zero) whose real counterparts were not observed in the atmosphere. The present study based on the NCEP/NCAR reanalysis of stratospheric wind and temperatures of recent years clearly shows that (i) the zero-wind line appears over the tropics ∼60 days prior to the major SSWs and progresses towards the Pole and (ii) an enhanced PW activity of quasi periodicity 16-days, which is also seen almost simultaneously with the zero-wind line, shows a propagation from equator to the Pole. This result is significant as it presents for the first time the connection between the tropics during the SSW events and the pole, through the quasi 16-day wave.

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“…In support with this, Coughlin and Tung (2005) have shown that the quasi-stationary planetary waves in the troposphere are also sensitive to the stratospheric conditions, so they can also respond to downward propagating stratospheric anomalies in zonal-mean zonal windū. Note here that the various mechanisms listed here and before are not exclusive with each other, with the "downward control" effect for instance, and the effect due to the planetary waves reinforcing each other in Song and Robinson (2004).…”

Section: Introductionmentioning

confidence: 71%

On the time-scales of the downward propagation and of the tropospheric planetary wave response to the stratospheric circulation

Nikulin

Lott

2010

Ann. Geophys.

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Abstract. Three datasets (the NCEP-NCAR reanalysis, the ERA-40 reanalysis and the LMDz-GCM), are used to analyze the relationships between large-scale dynamics of the stratosphere and the tropospheric planetary waves during the Northern Hemisphere (NH) winter. First, a crossspectral analysis clarifies the time scales at which downward propagation of stratospheric anomalies occurs in the lowfrequency band (that is at periods longer than 50 days). At these periods the strength of the polar vortex, measured by the 20-hPa Northern Annular Mode (NAM) index and the wave activity flux, measured by the vertical component of the Eliassen-Palm flux (EPz) from both the troposphere and the stratosphere, are significantly related with each other and in lead-lag quadrature. While, in the low-frequency band of the downward propagation, the EPz anomalies of the opposite sign around NAM extremes drive the onset and decay of NAM events, we found that the EPz anomalies in the troposphere, are significantly larger after stratospheric vortex anomalies than at any time before. This marked difference in the troposphere is related to planetary waves with zonal wavenumbers 1-3, showing that there is a tropospheric planetary wave response to the earlier state of the stratosphere at low frequencies. We also find that this effect is due to anomalies in the EPz issued from the northern midlatitudes and polar regions.

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Tropospheric wave response to decelerated stratosphere seen as downward propagation in northern annular mode

Cited by 22 publications

References 11 publications

Apparent Vertical Propagation of the NAM Index Due to an Embedded Wave Structure

Apparent Vertical Propagation of the NAM Index Due to an Embedded Wave Structure

Tropical connection to the polar stratospheric sudden warming through quasi 16-day planetary wave

On the time-scales of the downward propagation and of the tropospheric planetary wave response to the stratospheric circulation

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