Interannual variability of mesopause zonal winds over Ascension Island: Coupling to the stratospheric QBO

Wit, R. J. de; Hibbins, R. E.; Espy, P. J.; Mitchell, N. J.

doi:10.1002/2013jd020203

Cited by 25 publications

(27 citation statements)

References 48 publications

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“…Usually the QBO winds are asymmetric with a strong westward wind phase (as strong as about −40 m s −1 ) and much weaker eastward winds (only about 20 m s −1 at maximum). The SAO has a period of 6 months, and both eastward and westward winds can be quite strong: about −60 to −20 m s −1 for westward wind, and about 20 to 40 m s −1 for eastward wind (e.g., Hirota, 1980;Delisi and Dunkerton, 1988;Dee et al, 2011, and references therein). More details about QBO and SAO can be found in Baldwin et al (2001) and references therein.…”

Section: Introductionmentioning

confidence: 99%

“…This filtering of waves is relevant for the formation of circulation patterns at higher altitudes. For example, the pre-filtered wave spectrum is likely responsible for the formation of a QBO and an SAO in the tropical mesopause region (see also Dunkerton, 1982;Burrage et al, 1996;Baldwin et al, 2001;Richter and Garcia, 2006;Peña-Ortiz et al, 2010;de Wit et al, 2013;Kishore Kumar et al, 2014, and references therein). It has also been found that the QBO and the SAO interact with each other.…”

Section: Introductionmentioning

confidence: 99%

“…Different from this, the wind reversal from SAO eastward to westward wind is assumed to be mainly driven by horizontal advection and meridional momentum transport of extratropical planetary waves (e.g., Reed, 1966;Hirota, 1980;Delisi and Dunkerton, 1988;Hamilton and Mahlmann, 1988). Therefore the descent of the SAO westward wind phase with time is usually much steeper than the descent of the SAO eastward wind phase, which is mainly driven by vertically propagating waves.…”

Section: Introductionmentioning

confidence: 99%

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Driving of the SAO by gravity waves as observed from satellite

Ern¹,

Preusse²,

Riese³

2015

Ann. Geophys.

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Abstract. It is known that atmospheric dynamics in the tropical stratosphere have an influence on higher altitudes and latitudes as well as on surface weather and climate. In the tropics, the dynamics are governed by an interplay of the quasi-biennial oscillation (QBO) and semiannual oscillation (SAO) of the zonal wind. The QBO is dominant in the lower and middle stratosphere, and the SAO in the upper stratosphere/lower mesosphere. For both QBO and SAO the driving by atmospheric waves plays an important role. In particular, the role of gravity waves is still not well understood.In our study we use observations of the High Resolution Dynamics Limb Sounder (HIRDLS) satellite instrument to derive gravity wave momentum fluxes and gravity wave drag in order to investigate the interaction of gravity waves with the SAO. These observations are compared with the ERA-Interim reanalysis. Usually, QBO westward winds are much stronger than QBO eastward winds. Therefore, mainly gravity waves with westward-directed phase speeds are filtered out through critical-level filtering already below the stratopause region. Accordingly, HIRDLS observations show that gravity waves contribute to the SAO momentum budget mainly during eastward wind shear, and not much during westward wind shear. These findings confirm theoretical expectations and are qualitatively in good agreement with ERA-Interim and other modeling studies. In ERAInterim most of the westward SAO driving is due to planetary waves, likely of extratropical origin. Still, we find in both observations and ERA-Interim that sometimes westwardpropagating gravity waves may contribute to the westward driving of the SAO. Four characteristic cases of atmospheric background conditions are identified. The forcings of the SAO in these cases are discussed in detail, supported by gravity wave spectra observed by HIRDLS. In particular, we find that the gravity wave forcing of the SAO cannot be explained by critical-level filtering alone; gravity wave saturation without critical levels being reached is also important.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Driving of the SAO by gravity waves as observed from satellite

Ern¹,

Preusse²,

Riese³

2015

Ann. Geophys.

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“…9a of PO10. It is also interesting to note that de Wit et al (2013) found similar structures in correlations between the mesospheric and stratospheric monthly-mean winds. In particular, they found a positive correlation of the 90 km wind with the 70 hPa wind, while the correlation was negative for 20 hPa.…”

Section: Resultsmentioning

confidence: 54%

“…In addition, they modulate the semi-annual oscillation (SAO) in the stratopause region and contribute to the wind variations in the mesosphere (Andrews et al 1987;Baldwin et al 2001;Plumb 2002;Fritts and Alexander 2003;Haynes 2005;Shepherd 2007). Observations of inter-annual (year-to-year) variations of winds in the equatorial upper mesosphere (80-100 km) are available for the last decades (Garcia et al 1997;Day and Mitchell 2013;de Wit et al 2013;Kishore Kumar et al 2014). Strong easterly wind anomalies during early spring (so-called Mesospheric Spring Equinox Enhancements, MSEE) are usually observed during the westerly phase of the QBO (hereafter: QBO-West) (Garcia et al 1997), but not in all years.…”

Section: Introductionmentioning

confidence: 99%

Relation between Equatorial Mesospheric Wind Anomalies during Spring and Middle Atmosphere Variability Modes

Zülicke

Becker

2017

SOLA

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Strong easterly wind anomalies in the equatorial upper mesosphere were observed during northern hemispheric spring equinox. While the anomalies are mainly related to the semi-annual oscillation (SAO) in the stratopause region and to the quasi-biennial oscillation (QBO) in the stratosphere, an additional influence of sudden stratospheric warmings (SSWs) was recently suggested. In order to analyze this relation, we use an 18-year simulation of the Kühlungsborn Mechanistic Circulation Model (KMCM) that includes these middle atmosphere variability modes. We compute composites for the different phases of the QBO and intensities of SSWs. The results support the notion that easterly equatorial mesospheric wind anomalies occur during spring equinox if the QBO is in its westerly phase. In addition we show that this relation does not hold when the preceding winter is characterized by strong SSWs. We interpret this phenomenon as a result of a persistent strengthening of the residual circulation in the equatorial stratopause region.(Citation: Zülicke, C., and E. Becker, 2017: Relation between equatorial mesospheric wind anomalies during spring and middle atmosphere variability modes. SOLA, 13A, 31−35,

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Mesosphere and lower thermosphere zonal wind variations over low latitudes: Relation to local stratospheric zonal winds and global circulation anomalies

Kumar

Singer

et al. 2014

JGR Atmospheres

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Long-term observations from medium-frequency and meteor radars (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) and rocket soundings (1979-1990 and 2002-2007) are used to study mesosphere and lower thermosphere (MLT) zonal wind variations in relation to the stratospheric winds over northern low latitudes. The combined data set provides a complete height profile of amplitude of semiannual oscillation (SAO) up to 100 km, with an exception around 75-80 km. The SAO signal has maxima around 50 km and 82 km and a minimum around 65 km. The MLT zonal winds show remarkable interannual variability during northern hemispheric spring equinox and much less during fall equinox. Zonal wind mesospheric spring equinox enhancements (MSEE) appear with a periodicity of 2-3 years, suggesting a modulation by the quasi-biennial oscillation, which we identified with the strength of stratospheric westward winds. Out of 20 years of observations, the stratospheric westward winds are strong during 11 years (non-MSEE) and weak during 9 years. Six of these 9 years show large MLT winds (MSEE), and 3 years (1999, 2004, and 2006) show small MLT winds (missing MSEE). These unexpected small winds occur in years with global circulation anomalies associated with strong sudden stratospheric warmings and an early spring transition of zonal winds. With the proposed three MSEE classes, we take into account local and global forcing factors.

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Interannual variability of mesopause zonal winds over Ascension Island: Coupling to the stratospheric QBO

Cited by 25 publications

References 48 publications

Driving of the SAO by gravity waves as observed from satellite

Driving of the SAO by gravity waves as observed from satellite

Relation between Equatorial Mesospheric Wind Anomalies during Spring and Middle Atmosphere Variability Modes

Mesosphere and lower thermosphere zonal wind variations over low latitudes: Relation to local stratospheric zonal winds and global circulation anomalies

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