A remarkable correlation between short period gravity waves and semiannual oscillation of the zonal wind in the equatorial mesopause region

Rao, N. V. S.; Tsuda, Toshitaka; Kawatani, Yoshio

doi:10.5194/angeo-30-703-2012

Cited by 11 publications

(11 citation statements)

References 26 publications

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“…Possibly the westward waves may deposit their momentum at the lower height region, and this leads to a reduction in westward momentum transfer to the MLT. Recent observations by Venkateswara Rao et al [] showed less gravity wave variances at MLT heights during 2004 and 2006 compared to 2008.…”

Section: Resultsmentioning

confidence: 98%

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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Section: Resultsmentioning

confidence: 98%

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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“…The MSAO structure of the zonal winds (with westward winds at the equinoxes and eastward winds at the solstices) in the equatorial and low‐latitude MLT region is a well‐established feature and has been studied by both satellite and ground based observations [e.g., Burrage et al , 1996; Garcia et al , 1997; Sridharan et al , 2007; Venkateswara Rao et al , 2012]. Burrage et al [1996] from satellite observations showed that the SAO is the dominant mode of oscillation in the MLT region with a maximum over the equator and extending symmetrically to 20–30° in both hemispheres.…”

Section: Discussionmentioning

confidence: 99%

“…proposed that the selective absorption and subsequent filtering of small‐scale gravity waves by the SSAO is responsible for the existence of the MSAO and can explain the anti‐phase relation between the two oscillations. Recent experimental studies also show a good correlation between the MSAO and short period gravity waves [e.g., Venkateswara Rao et al , 2012].…”

Section: Introductionmentioning

confidence: 99%

“…To a large extent, the characteristics of the MSAO have been studied through satellite and ground based observations [ Burrage et al , 1996; Garcia et al , 1997; Venkateswara Rao et al , 2012]. In satellite observations of High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS), the MSAO is seen to extend to latitudes of 20–30° in both hemispheres without any obvious asymmetry about the equator [ Burrage et al , 1996].…”

Section: Introductionmentioning

confidence: 99%

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Long‐term variability of mean winds in the mesosphere and lower thermosphere at low latitudes

et al. 2012

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[1] Long-term variations of monthly mean zonal and meridional winds in the Mesosphere and Lower Thermosphere (MLT) at low-latitudes are analyzed using four medium frequency (MF) radars and three meteor radars located in the Asia-Oceania region. Radar data taken at close-by latitudes are appended to construct long-term data sets. With this, we have long-term data from five distinct latitudes within AE22 (viz., 22 N, $9 N, 0-2 N, 6-7 S and 21 S). The data length varies at different latitudes and spans a maximum of two decades during 1990-2010. The zonal winds show semiannual oscillation (SAO) at all locations with westward (eastward) winds during equinoxes (solstices). The month height pattern of SAO is similar within AE9and is different at AE22 . The westward winds in the March equinox were enhanced every two or three years during 1990-2002. We define this phenomenon as Mesospheric Quasi-Biennial Enhancement (MQBE). Such signature is not clear after 2002. The meridional winds show annual oscillation (AO), with northward and southward winds during the December and June solstices, respectively. However, the timing at which the wind direction changes does not coincide at all latitudes. The amplitude of the AO is enhanced after 2004 and 2008 at $9 N and $7 S, respectively. Orthogonal components of SAO and AO are detected with persistent phase relation, which suggests that the zonal and meridional winds are coupled. The meridional winds show long-term trends at latitudes of $9 N and $6-7 S, but not at other latitudes . The zonal winds do not show significant long-term trends.Citation: Venkateswara Rao, N., T. Tsuda, D. M. Riggin, S. Gurubaran, I. M. Reid, and R. A. Vincent (2012), Long-term variability of mean winds in the mesosphere and lower thermosphere at low latitudes,

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“…Semiannual and annual variations in various background parameters reported here are consistent with the semiannual and annual oscillations reported earlier from various low‐latitude stations [e.g., Takahashi et al ., ; Garcia et al ., ; Siva kumar et al ., ; Taylor et al ., ; Guharay et al ., ]. The seasonal variations in the tidal and gravity wave activities are also consistent with those reported earlier [e.g., Reddi and Ramkumar , ; Sridharan and Sathishkumar , ; Venkateswara Rao et al ., , ]. However, it is important to mention that the gravity wave periods considered by Sridharan and Sathishkumar [] were 2–6 h and the gravity wave variances reported by them peaked in the equinoxes.…”

Section: Summary and Discussionmentioning

confidence: 99%

On the governing dynamics of the VHF radar echoes from the mesosphere and collision‐dominated lower E region over Gadanki (13.5°N, 79.2°E)

et al. 2017

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In the present communication, the role of neutral dynamical processes in governing the morphology and seasonal variations of daytime VHF radar echoes from the mesosphere and the collision‐dominated lower E region is discussed. While the seasonal variations of mesospheric echo occurrence show semiannual variation with their maxima in the equinoxes, the occurrence of E region echoes shows strong annual variation peaking in the summer with two secondary maxima identical to semiannual variation of the mesospheric echoes. The occurrence rates of the E region echoes, however, display year‐to‐year variability. Semiannual variations in the occurrence of low‐latitude mesospheric echoes are closely linked with similar variations in the occurrences of temperature inversion, large wind shear, tides, and gravity wave activities in the same height region. In the case of E region echoes, the summer maximum and equinoctial secondary maxima are found to be linked with similar variations in wind and wind shear, Es activity, tidal, and gravity wave activities. Further, the summer maximum is found to be strongly correlated with that of meteor flux and nonmigrating diurnal tide. This finding is significant given the fact that such wind field in the presence of metallic ions could form both Es and field‐aligned irregularities. The present results show that tides and gravity waves are the most important dynamical factors governing the morphology and seasonal variations of the mesospheric as well as lower E region echoes observed over Gadanki. These results are discussed in the light of current understanding on the dynamical coupling of the mesosphere and lower E region through tides and gravity waves.

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A remarkable correlation between short period gravity waves and semiannual oscillation of the zonal wind in the equatorial mesopause region

Abstract: Abstract. The variability of zonal winds and the horizontal wind velocity variance of short period (20-120 min) gravity waves (GWs) in the equatorial mesopause region are studied using medium frequency (MF) radar observations from Pameungpeuk

Cited by 11 publications

References 26 publications

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

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

Long‐term variability of mean winds in the mesosphere and lower thermosphere at low latitudes

On the governing dynamics of the VHF radar echoes from the mesosphere and collision‐dominated lower E region over Gadanki (13.5°N, 79.2°E)

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