Rossby Wave Propagation into the Northern Hemisphere Stratosphere: The Role of Zonal Phase Speed

Domeisen, Daniela I. V.; Martius, Olivia; Jiménez‐Esteve, Bernat

doi:10.1002/2017gl076886

Cited by 39 publications

(50 citation statements)

References 47 publications

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“…Accordingly, the stratospheric background atmosphere is dominated by planetary waves with zonal wavenumbers smaller than 4 (e.g. Domeisen et al, 2018;Barnett and Labitzke, 1990;Pawson and Kubitz, 1996), consistent with the findings in this paper. In order to investigate altitudes below 20 km from LEO infrared sounders, higher wavenumbers than wavenumber 6 have to be taken into account.…”

supporting

confidence: 91%

Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods

Strube¹,

Ern²,

Preusse³

et al. 2020

Preprint

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Abstract. Gravity waves are important drivers of dynamic processes in particular in the middle atmosphere. To analyse atmospheric data for gravity wave signals it is essential to separate gravity wave perturbations from atmospheric variability due to other dynamic processes. Common methods to separate small-scale gravity wave signals from a large-scale background are separation methods depending on filters in either the horizontal or vertical wavelength domain. However, gravity waves are not the only process that could lead to small-scale perturbations in the atmosphere. Recently, concerns have been raised that vertical wavelengths filtering can lead to misinterpretation of other wave-like perturbations, such as inertial instability effects, as gravity wave perturbations. In this paper we assess the ability of different spectral background removal approaches to separate gravity waves and inertial instabilities using artificial inertial instability perturbations, global model data and satellite observations. We investigate a horizontal background removal, which applies a zonal wavenumber filter with additional smoothing of the spectral components in meridional and vertical direction, a sophisticated filter based on 2D time-longitude spectral analysis (see Ern et al. (2011)) and a vertical wavelength Butterworth filter. Critical thresholds for the vertical wavelength and zonal wavenumber are analysed, respectively. Vertical filtering has to cut deep into the gravity wave spectrum in order to remove inertial instability remnants from the perturbations (down to 6 km cutoff wavelength). Horizontal filtering, however, removes inertial instability remnants in global model data at wavenumbers far lower than the typical gravity wave scales for the case we investigated. Specifically, a cutoff zonal wavenumber of 6 in the stratosphere is sufficient to eliminate inertial instability structures. Furthermore, we show that for infrared limb-sounding satellite profiles, it is possible as well to effectively separate perturbations of inertial instabilities from those of gravity waves using a cutoff zonal wavenumber of 6. We generalize the findings of our case study by examining a one-year time series of SABER data.

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supporting

confidence: 91%

Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods

Strube¹,

Ern²,

Preusse³

et al. 2020

Preprint

View full text Add to dashboard Cite

show abstract

“…Stationary waves, that is, waves that do not move in the zonal direction, can only propagate vertically into the stratosphere when the zonal winds are westerly and below some critical threshold (Charney & Drazin, ), which is why they are inhibited in their propagation during summer, when easterly winds prevail in the extratropical stratosphere (Plumb, ). This propagation window is shifted for zonal phase speeds different from zero, which can lead to enhanced wave propagation ahead of SSW events (Domeisen, Martius, et al, ). Wave breaking in addition contributes to the driving of the Brewer‐Dobson circulation, which is associated with downwelling over the polar cap (Butchart, ).…”

Section: A Brief Overview Of the Stratospheric Circulationmentioning

confidence: 99%

The Teleconnection of El Niño Southern Oscillation to the Stratosphere

Domeisen

Garfinkel²,

Butler

2019

Reviews of Geophysics

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302

284

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El Niño and La Niña events in the tropical Pacific have significant and disrupting impacts on the global atmospheric and oceanic circulation. El Niño Southern Oscillation (ENSO) impacts also extend above the troposphere, affecting the strength and variability of the stratospheric polar vortex in the high latitudes of both hemispheres, as well as the composition and circulation of the tropical stratosphere. El Niño events are associated with a warming and weakening of the polar vortex in the polar stratosphere of both hemispheres, while a cooling can be observed in the tropical lower stratosphere. These impacts are linked by a strengthened Brewer-Dobson circulation. Anomalous upward wave propagation is observed in the extratropics of both hemispheres. For La Niña, these anomalies are often opposite. The stratosphere in turn affects surface weather and climate over large areas of the globe. Since these surface impacts are long-lived, the changes in the stratosphere can lead to improved surface predictions on time scales of weeks to months. Over the past decade, our understanding of the mechanisms through which ENSO can drive impacts remote from the tropical Pacific has improved. This study reviews the possible mechanisms connecting ENSO to the stratosphere in the tropics and the extratropics of both hemispheres while also considering open questions, including nonlinearities in the teleconnections, the role of ENSO diversity, and the impacts of climate change and variability.Plain Language Summary El Niño and La Niña events, the irregular warming and cooling of the tropical Pacific that occurs every couple of years, have disrupting impacts spanning the entire world. These remote impacts, so-called "teleconnections", also reach the stratosphere, the layer of the atmosphere starting at around 10 km above the Earth's surface. El Niño leads to a warming of the stratosphere in both hemispheres, while the lower tropical stratosphere cools. These signatures are linked by a strengthened stratospheric circulation from the tropics to the polar regions. El Niño also leads to more frequent breakdowns of the stratospheric polar vortex, a band of strong eastward winds in the polar stratosphere. For La Niña, these effects tend to be opposite, though they are not always robust, suggesting nonlinear or nonstationary effects, long-term variability, and trends in the teleconnections. The observational data record is not yet long enough to make conclusions with certainty, and models that try to reproduce the teleconnections indicate that teleconnections might be more linear than the limited number of observations indicate. Further research will be needed to separate the El Niño and La Niña teleconnections from other effects and to determine to what extent nonlinearity and nonstationarity are indeed present.

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“…Inertial instabilities in a rotating stratified fluid, like the earth's atmosphere, arise from an imbalance between the pressure gradient and the centrifugal forces when the absolute angular momentum decreases with the radius (Dunkerton, 1981). To stabilize the imbalance, horizontal circulation generates transport of angular momentum in the meridional direction.…”

Section: Introductionmentioning

confidence: 99%

Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods

et al. 2020

View full text Add to dashboard Cite

Abstract. Gravity waves are important drivers of dynamic processes in particular in the middle atmosphere. To analyse atmospheric data for gravity wave signals, it is essential to separate gravity wave perturbations from atmospheric variability due to other dynamic processes. Common methods to separate small-scale gravity wave signals from a large-scale background are separation methods depending on filters in either the horizontal or vertical wavelength domain. However, gravity waves are not the only process that could lead to small-scale perturbations in the atmosphere. Recently, concerns have been raised that vertical wavelength filtering can lead to misinterpretation of other wave-like perturbations, such as inertial instability effects, as gravity wave perturbations. In this paper we assess the ability of different spectral background removal approaches to separate gravity waves and inertial instabilities using artificial inertial instability perturbations, global model data and satellite observations. We investigate a horizontal background removal (which applies a zonal wavenumber filter with additional smoothing of the spectral components in meridional and vertical direction), a sophisticated filter based on 2D time–longitude spectral analysis (see Ern et al., 2011) and a vertical wavelength Butterworth filter. Critical thresholds for the vertical wavelength and zonal wavenumber are analysed. Vertical filtering has to cut deep into the gravity wave spectrum in order to remove inertial instability remnants from the perturbations (down to 6 km cutoff wavelength). Horizontal filtering, however, removes inertial instability remnants in global model data at wavenumbers far lower than the typical gravity wave scales for the case we investigated. Specifically, a cutoff zonal wavenumber of 6 in the stratosphere is sufficient to eliminate inertial instability structures. Furthermore, we show that for infrared limb-sounding satellite profiles it is possible as well to effectively separate perturbations of inertial instabilities from those of gravity waves using a cutoff zonal wavenumber of 6. We generalize the findings of our case study by examining a 1-year time series of SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) data.

show abstract

Rossby Wave Propagation into the Northern Hemisphere Stratosphere: The Role of Zonal Phase Speed

Cited by 39 publications

References 47 publications

Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods

Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods

The Teleconnection of El Niño Southern Oscillation to the Stratosphere

Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods

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