Gravity wave momentum fluxes in the MLT—Part I: Seasonal variation at Collm (51.3°N, 13.0°E)

Placke, Manja; Stober, Gunter; Jacobi, Christoph

doi:10.1016/j.jastp.2010.07.012

Cited by 38 publications

(59 citation statements)

References 23 publications

(30 reference statements)

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“…The summer maximum is dominated by wind variances caused by short-period GWs as derived from meteor radar observations [Beldon and Mitchell, 2009;Placke et al, 2011]. The experimentally determined seasonal dependence of the GW activity on the zonal background winds was based on data from one particular year and agrees qualitatively with the zonal mean model results.…”

Section: Introductionsupporting

confidence: 64%

Trends of mesospheric gravity waves at northern middle latitudes during summer

Hoffmann¹,

Rapp²,

Singer³

et al. 2011

J. Geophys. Res.

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[1] Recent investigations of the seasonal variation of the activity of gravity waves in the mesosphere/lower thermosphere (MLT) at middle and high latitudes suggest a semiannual variation with maxima during winter and summer and minima during the equinoxes. It is generally assumed that this annual cycle is determined by filtering processes due to the background winds in the stratosphere and lower mesosphere. On the other side, long-term observations of mesospheric winds at Juliusruh (55°N, 13°E) since 1990 indicate a stable increase of westward directed winds below 80 km (negative trends) during summer, as, e.g., clearly evident in monthly means in July. Here, we are studying how these long-term changes of winds are related to trends of the activity of gravity waves (GW) with periods between 3-6 hours. Our results show that the observed zonal wind trend at about 75 km during July goes along with an enhancement of the GW activity at altitudes above 80 km. Indeed, also the year-to-year variation of maxima of the observed westward directed winds at altitudes near 75 km and the GW activity at about 80 km are significantly correlated. Our results stimulate the further study of long-term wind changes and corresponding gravity wave trends.

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Section: Introductionsupporting

confidence: 64%

Trends of mesospheric gravity waves at northern middle latitudes during summer

Hoffmann¹,

Rapp²,

Singer³

et al. 2011

J. Geophys. Res.

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“…Owing to the small horizontal phase speeds of GWs, which is of the order of the background mean flow, GWs are very sensitive to background wind filtering in the middle atmosphere (Placke et al 2011a). In general a GW can propagate only against the wind; otherwise it would have encountered a critical level in the mesosphere.…”

Section: Discussionmentioning

confidence: 99%

Multi-year observations of gravity wave momentum fluxes at low and middle latitudes inferred by all-sky meteor radar

et al. 2015

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• W) were used to estimate the GW momentum fluxes and variances in the MLT region. Our analysis can provide monthly mean altitude profiles of vertical fluxes of horizontal momentum for short-period (less than 2-3 h) GWs. The averages for each month throughout the entire data series have shown different behavior for the momentum fluxes depending on latitude and component. The meridional component has almost the same behavior at the three sites, being positive (northward), for most part of the year. On the other hand, the zonal component shows different behavior at each location: it is positive for almost half the year at Cariri and SM but predominantly negative over CP. Annual variation in the GW momentum fluxes is present at all sites in the zonal component and also in SM at 89 km in the meridional component. The seasonal analysis has also shown a 4-month oscillation at 92.5 km over SM in the zonal component and over CP at the same altitudes but for the meridional component.

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“…Based upon 2-hourly means, GW variances and fluxes are obtained according to Hocking (2005) by projecting the 2-hourly mean GW fluxes in a 3 km height gate to the radial direction of the respective meteor, and minimizing the difference between projected and measured meteor trail drift variances. Details can be found in Placke et al (2011). The data are averaged to obtain 3-monthly means for each height gate under consideration.…”

Section: Collm Meteor Radarmentioning

confidence: 99%

Some anomalies of mesosphere/lower thermosphere parameters during the recent solar minimum

et al. 2011

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Abstract. The recent solar minimum has been characterized by an anomalous strong decrease of thermospheric density since 2005. Here we analyze anomalies of mesosphere/lower thermosphere parameters possibly connected with this effect. In particular, nighttime mean LF reflection heights measured at Collm, Germany, show a very strong decrease after 2005, indicating a density decrease. This decrease is also visible in mean meteor heights measured with VHF meteor radar at Collm. This density decrease is accompanied by an increase of gravity wave (GW) amplitudes in the upper mesosphere and a decrease in the lower thermosphere. On the decadal scale, GWs are negatively correlated with the background zonal wind, but this correlation is modulated in the course of the solar cycle, indicating the combined effect of GW filtering and density decrease.

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Gravity wave momentum fluxes in the MLT—Part I: Seasonal variation at Collm (51.3°N, 13.0°E)

Cited by 38 publications

References 23 publications

Trends of mesospheric gravity waves at northern middle latitudes during summer

Trends of mesospheric gravity waves at northern middle latitudes during summer

Multi-year observations of gravity wave momentum fluxes at low and middle latitudes inferred by all-sky meteor radar

Some anomalies of mesosphere/lower thermosphere parameters during the recent solar minimum

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