Revisiting the Quasi-Biennial Oscillation as Seen in ERA5. Part I: Description and Momentum Budget

Pahlavan, Hamid A.; Fu, Qiang; Wallace, John M.; Kiladis, George N.

doi:10.1175/jas-d-20-0248.1

Cited by 37 publications

(36 citation statements)

References 83 publications

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“…Increased downwelling leads to higher ozone mixing ratios. Hence there is a large component of QBO variability in ozone (Pahlavan et al., 2021). We find that although a large part of the ozone variability is indeed related to the QBO, a large non‐QBO component is also present.…”

Section: Introductionmentioning

confidence: 99%

What Contributes to the Inter‐Annual Variability in Tropical Lower Stratospheric Temperatures?

Ming

Hitchcock

2021

JGR Atmospheres

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The inter-annual variability of temperatures in the tropical lower stratosphere is of interest since temperature in this region controls the entry of water vapor into the stratosphere which can then modify the surface radiative balance (Fueglistaler et al., 2014). The chemical composition of the stratosphere is strongly impacted by the balance reached between the circulation, radiation and chemistry in this region. A number of trace species including ozone, water vapor, and stratospheric aerosols in this region have significant climate impacts. Temperatures in the tropical lower stratosphere are closely coupled to these trace species and thus to their influence on the energy balance of the climate system. Despite their importance, temperatures in this region exhibit more uncertainty in reanalysis datasets than in any other region in the atmosphere below 10 hPa (see Hersbach et al., 2020, their Figure 11). A detailed understanding of the processes that determine temperatures in this region is thus desirable.The inter-annual variability in dynamical heating arising from changes in upwelling in the Brewer-Dobson circulation has been identified as a main contributor to this temperature variability (Fueglistaler et al., 2014). An increase in upwelling decreases temperature below radiative equilibrium by adiabatic cooling. It also changes the transport of ozone, water vapor and aerosol-all radiatively active trace species. These species induce local and

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Section: Introductionmentioning

confidence: 99%

What Contributes to the Inter‐Annual Variability in Tropical Lower Stratospheric Temperatures?

Ming

Hitchcock

2021

JGR Atmospheres

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“…For example, at 28 km (22 km), the GW drag in the narrow longitude band of

[λ_{0} badbreak- 20 °, λ_{0} badbreak+ 20 °]

contributes by 92% (31%) to the zonal‐mean GW drag of 0.28 m s −1

d^{- 1}

(−0.23 m s −1 d −1 ) during

t =

11–18 days, where

λ_{0}

moves eastward with the speed of 15 m s −1 from

normal120 °

E at

t =

11 days. Note that at 28 km, this magnitude of drag is sufficiently large for a significant impact on the mean‐wind evolution, given that the total wave forcing driving this early phase of the 20‐hPa E–W transition is estimated to be about 0.33–0.5 m s −1 d −1 in reanalyses (e.g., Kim & Chun, 2015, Figure 12b; Pahlavan et al., 2020, Figure 9b).…”

Section: Resultsmentioning

confidence: 97%

Interaction Between Stratospheric Kelvin Waves and Gravity Waves in the Easterly QBO Phase

Kim

Achatz

2021

Geophysical Research Letters

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In the tropics, various types of atmospheric waves are generated from convection, which have a broad spectrum from mesoscales to planetary scales (Bergman & Salby, 1994;Lane & Moncrieff, 2008;Ortland et al., 2011). Not only do they contribute to the atmospheric variability on their own spatio-temporal scales but they also play a crucial role in the mean circulation via wave-mean-flow interactions (e.g., Booker & Bretherton, 1967). The latter is manifested by the quasi-biennial oscillation (QBO) in the tropical stratosphere (Baldwin et al., 2001). The QBO represents a large variation in the mean zonal wind, of up to ∼50 m s −1 depending on the altitude, which is driven by the momentum carried from the lower atmosphere by large-scale equatorial waves and mesoscale gravity waves (GWs) (Dunkerton, 1997;Holt et al., 2016).Theoretical studies of QBO dynamics have considered interactions of the zonally symmetric flow with tropical wave modes. For instance, in one-dimensional models (in the vertical) of the tropical stratospheric mean flow (e.g., Holton & Lindzen, 1972;Lindzen & Holton, 1968;Plumb, 1977), which have contributed essentially to the current understanding of the QBO dynamics, the forcing of the flow due to each wave mode is formulated as a function of mean wind and characteristics of the wave, being independent of other wave modes. In the real atmosphere, however, different modes such as equatorial waves and mesoscale GWs can encounter each other in the stratosphere, because the convective sources of these waves are ubiquitous in the tropics and equatorial waves have planetary scales. Among the equatorial wave modes, Kelvin waves especially are observed to have large amplitudes (∼10 m s −1 in the zonal wind; Wallace & Kousky, 1968), which suggests potential for these waves to affect the propagation and dissipation of GWs they encounter. Therefore it will be of great interest to observe such a wave-wave interaction across different scales in the tropics and to examine its impact on the QBO dynamics. However, to the authors' knowledge, this interaction has not been studied in the literature.

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“…The basic features of the QBO in ERA5 have been investigated by Pahlavan et al. (2021a, 2021b). Since monthly data are analyzed, any zonal eddy components are reasonably considered as “quasi‐stationary” eddies, although the validity of this assumption will be discussed later by using hourly data for two particular cases (cf., see Figure 6).…”

Section: Methodsmentioning

confidence: 99%

“…During 2000-2006.1 data are used for analysis since it gives a slightly better representation of the stratosphere (Simmons et al, 2020; hereafter, the combined data set of ERA5 and ERA5.1 is simply referred to ERA5). The basic features of the QBO in ERA5 have been investigated by Pahlavan et al (2021aPahlavan et al ( , 2021b. Since monthly data are analyzed, any zonal eddy components are reasonably considered as "quasi-stationary" eddies, although the validity of this assumption will be discussed later by using hourly data for two particular cases (cf., see Figure 6).…”

Section: Datamentioning

confidence: 99%

Discovery of Quasi‐Stationary Equatorial Waves Trapped in Stratospheric QBO Westerly and Easterly Jets

Sakazaki

Hamilton²

2021

JGR Atmospheres

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The monthly-mean atmospheric circulation in most atmospheric regions includes significant monsoonal flows and other quasi-stationary eddies ultimately caused by the geographic irregularities at the atmosphere's lower boundary. The equatorial stratosphere has been regarded as exceptional in this regard since the prevailing wind is zonally-symmetric, at least to first order. Indeed the stratospheric Quasi-Biennial Oscillation (QBO) has sometimes been treated approximately as a zonally-symmetric phenomenon (see Baldwin et al., 2001 for a review). The significant isolation of the equatorial middle stratosphere (e.g., 10 hPa level, which is the focus of this study) from the lower boundary effects is understandable, since at least in a linear theory, stationary equatorial waves forced in the tropical troposphere should not propagate upward far into the stratosphere as they will generally encounter a critical surface (or a layer of weak mean winds) near the tropopause and then a critical surface in a QBO transition shear layer (e.g., Andrews & McIntyre, 1976;Booker & Bretherton, 1967;Lindzen, 1970). In addition, the Walker circulations that are a prominent feature of the equatorial troposphere are found to decay rapidly in the lowermost equatorial stratosphere.

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Revisiting the Quasi-Biennial Oscillation as Seen in ERA5. Part I: Description and Momentum Budget

Cited by 37 publications

References 83 publications

What Contributes to the Inter‐Annual Variability in Tropical Lower Stratospheric Temperatures?

What Contributes to the Inter‐Annual Variability in Tropical Lower Stratospheric Temperatures?

Interaction Between Stratospheric Kelvin Waves and Gravity Waves in the Easterly QBO Phase

Discovery of Quasi‐Stationary Equatorial Waves Trapped in Stratospheric QBO Westerly and Easterly Jets

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