Long-term variations of the mesospheric wind field at mid-latitudes

Keuer, D.; Hoffmann, Peter; Singer, W.; Bremer, J.

doi:10.5194/angeo-25-1779-2007

Cited by 49 publications

(92 citation statements)

References 27 publications

(75 reference statements)

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“…In future studies, the momentum balance should also be estimated and discussed for similar radar instruments at other latitudes, like the MF radar at the midlatitude site Juliusruh (see, e.g., Keuer et al, 2007). This would allow the definition of the time and height range where the mainly GW-determined momentum balance is fulfilled for different latitudes.…”

Section: Discussionmentioning

confidence: 99%

First experimental verification of summertime mesospheric momentum balance based on radar wind measurements at 69° N

2015

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Abstract. Gravity waves (GWs) greatly influence the background state of the middle atmosphere by imposing their momentum on the mean flow upon breaking and by thus driving, e.g., the upper mesospheric summer zonal wind reversal. In this situation momentum is conserved by a balance between the vertical divergence of GW momentum flux (the so-called GW drag) and the Coriolis acceleration of the mean meridional wind. In this study, we present first quantitative mean annual cycles of these two balancing quantities from the medium frequency Doppler radar at the polar site Saura (SMF radar, 69 • N, 16 • E). Three-year means for 2009 through 2011 clearly show that the observed zonal momentum balance between 70 and 100 km with contributions from GWs only is fulfilled during summer when GW activity is strongest and more stable than in winter. During winter, the balance between GW drag and Coriolis acceleration of the mean meridional wind is not existent, which is likely due to the additional contribution from planetary waves, which are not considered by the present investigation. The differences in the momentum balance between summer and winter conditions are additionally clarified by 3-month mean vertical profiles for summer

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Section: Discussionmentioning

confidence: 99%

First experimental verification of summertime mesospheric momentum balance based on radar wind measurements at 69° N

2015

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“…Unfortunately, with the measurements available today, it is not possible to determine definitively to what extent observed changes in gravity waves are due to filtering by middle atmosphere winds and to what extent changing sources or other changes in local conditions contribute. Jacobi et al (2012) and Keuer et al (2007) also reported on NH midlatitude MLT wind trends. Jacobi et al (2012) noted the differences in the trends between North America and Europe, suggesting that changes in planetary waves contributed to the trends.…”

Section: Long-term Trendsmentioning

confidence: 99%

Global Dynamics of the MLT

2012

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The transition between the middle atmosphere and the thermosphere is known as the MLT region (for mesosphere and lower thermosphere). This area has some characteristics that set it apart from other regions of the atmosphere. Most notably, it is the altitude region with the lowest overall temperature and has the unique characteristic that the temperature is much lower in summer than in winter. The summer-to-winter-temperature gradient is the result of adiabatic cooling and warming associated with a vigorous circulation driven primarily by gravity waves. Tides and planetary waves also contribute to the circulation and to the large dynamical variability in the MLT. The past decade has seen much progress in describing and understanding the dynamics of the MLT and the interactions of dynamics with chemistry and radiation. This review describes recent observations and numerical modeling as they relate to understanding the dynamical processes that control the MLT and its variability. Results from the Whole Atmosphere Community Climate Model (WACCM), which is a comprehensive high-top general circulation model with interactive chemistry, are used to illustrate the dynamical processes. Selected observations from the Sounding the Atmosphere with Broadband Emission Radiometry (SABER) instrument are shown for comparison. WACCM simulations of MLT dynamics have some differences with observations. These differences and other questions and discrepancies described in recent papers point to a number of ongoing uncertainties about the MLT dynamical system.

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“…Figure 2 indeed shows such a connection for solar maximum. During solar maximum, mesospheric eastward winds are stronger, leading to a negative correlation between solar flux and mean wind there (e.g., Keuer et al, 2007). However, stronger winds and consequently larger GW amplitudes lead to a stronger GW drag, stronger wind shear, and therefore a decreasing solar cycle effect on the mean wind with height, which reverses at some altitude.…”

Section: Discussionmentioning

confidence: 99%

“…In particular, search for an effect of the 11-year solar Schwabe cycle has been undertaken, for example, to explain part of the observed variability of mesosphere and lower thermosphere (MLT), which can be studied by radars. Indeed, indication for a solar effect has been found in MLT radar wind time series over Central Europe Keuer et al, 2007). This effect is more pronounced in summer than in winter owing to the more disturbed middle atmosphere during winter, and essentially consists in a stronger mesospheric jet during solar maximum.…”

Section: Introductionmentioning

confidence: 93%

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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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Long-term variations of the mesospheric wind field at mid-latitudes

Cited by 49 publications

References 27 publications

First experimental verification of summertime mesospheric momentum balance based on radar wind measurements at 69° N

First experimental verification of summertime mesospheric momentum balance based on radar wind measurements at 69° N

Global Dynamics of the MLT

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

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