Long-term trends in the mesopause wind field obtained from LF D1 wind measurements at Collm, Germany

Jacobi, Ch.; Schminder, R.; Kürschner, D.; Bremer, J.; Greisiger, K. M.; Hoffmann, Peter; Singer, W.

doi:10.1016/s0273-1177(97)00599-1

Cited by 33 publications

(27 citation statements)

References 8 publications

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“…Note that these mean drift velocities are not necessarily equal to the prevailing winds at Collm published previously (e.g. Jacobi et al, 1997b), because we did not make an extraction of tides here. But calculated in the manner used here, the mean velocities better reflect the true background conditions corresponding to the drift velocity measurements.…”

Section: Background Atmospherementioning

confidence: 89%

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A study of seasonal variations of gravity wave intensity in thelower thermosphere using LF D1 wind observations and a numerical model

Гаврилов

Jacobi

2004

Ann. Geophys.

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Abstract. The data of the regular low-frequency D1 E-region observations at Collm, Germany (52 • N, 15 • E) in 1983-1999 are used for estimations of the intensity of short-period perturbations of the horizontal drift velocity at 85-110 km altitude. A simple half-hourly-difference numerical filter is used to extract perturbations with time scales of 0.7-3 h.The average monthly standard deviations of short-period perturbations of the zonal velocity near altitude 83 km have a main maximum in summer, a smaller maximum in winter, and minimum values at the equinoxes. At higher altitudes the summer maximum is shifted towards the spring months, and a second maximum of perturbation amplitudes appears in autumn at altitudes near and above 100 km. The seasonal changes in the standard deviations of meridional velocity show the maxima in spring and summer. A numerical model describing the propagation of a set of harmonics modeling a spectrum of internal gravity waves in the atmosphere is used for the interpretation of observed seasonal variations of wind perturbation intensity. Numerical modeling reveals that the observed altitude changes in the seasonal variations of the drift velocity standard deviations may be explained by a superposition of IGWs generated at different levels in the troposphere and middle atmosphere. IGWs generated in the stratospheric and mesospheric jet stream may have substantial amplitudes at altitudes near and above 100 km, where they may modify the seasonal variations, which are typical for IGWs propagating from the troposphere.

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Section: Background Atmospherementioning

confidence: 89%

“…However, we use relations between h and z (e.g. Jacobi et al, 1997b) that are based on full wave field calculations performed by Singer (1975), using the mean electron density profiles. The relations give z values 1-2 km smaller than h at an altitude of 100 km, with the difference decreasing at lower altitudes.…”

Section: Measurements Of Igw Intensity At Collmmentioning

confidence: 99%

A study of seasonal variations of gravity wave intensity in thelower thermosphere using LF D1 wind observations and a numerical model

Гаврилов

Jacobi

2004

Ann. Geophys.

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“…Using observations at different stations, Bremer et al (1997) derived weakly negative correlations of the zonal wind, as well as the semidiurnal tidal amplitude with the solar activity, whereas for the meridional component and the diurnal tidal amplitude the correlations are nearly zero. Many further investigations have been carried out (Fraser, 1990;Namboothiri et al, 1993Namboothiri et al, , 1994Jacobi et al, 1997;Jacobi, 1998;Middleton et al, 2002;Baumgaertner et al, 2005). The detected solar impact on the wind field in the MLT region agrees only partly in that, only the tidal components correlate at most observations negatively with the solar activity.…”

Section: Introductionmentioning

confidence: 92%

“…The meridional wind component, however, shows only a small, nonsignificant positive trend. Jacobi et al (1997) reported about long-term oscillations mainly in the summer zonal winds and in the amplitudes of the semidiurnal tidal component. Similar results were derived by D 'Yachenko et al (1986) for the semidiurnal tide.…”

Section: Introductionmentioning

confidence: 99%

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

Keuer¹,

Hoffmann²,

Singer³

et al. 2007

Ann. Geophys.

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Abstract. Continuous MF radar observations at the station Juliusruh (54.6 • N; 13.4 • E) have been analysed for the time interval between 1990 and 2005, to obtain information about solar activity-induced variations, as well as long-term trends in the mesospheric wind field. Using monthly median values of the zonal and the meridional prevailing wind components, as well as of the amplitude of the semidiurnal tide, regression analyses have been carried out with a dependence on solar activity and time. The solar activity causes a significant amplification of the zonal winds during summer (increasing easterly winds) and winter (increasing westerly winds). The meridional wind component is positively correlated with the solar activity during summer but during winter the correlation is very small and non significant. Also, the solar influence upon the amplitude of the semidiurnal tidal component is relatively small (in dependence on height partly positive and partly negative) and mostly non-significant.The derived trends in the zonal wind component during summer are below an altitude of about 83 km negative and above this height positive. During the winter months the trends are nearly opposite compared with the trends in summer (transition height near 86 km). The trends in the meridional wind components are below about 85 km positive in summer (significant) and near zero (nonsignificant) in winter; above this height during both seasons negative trends have been detected. The trends in the semidiurnal tidal amplitude are at all heights positive, but only partly significant.The detected trends and solar cycle dependencies are compared with other experimental results and model calculations. There is no full agreement between the different results, probably caused by different measuring techniques and evaluation methods used. Also, different heights and observation periods investigated may contribute to the detected differences.

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“…Results using radar measurements are still inconclusive, generally showing a decrease in tidal amplitudes since the 1960s (Bremer et al, 1997) at mid and high latitudes, which is in accordance with modelling (Ross and Walterscheid, 1991), but the studies have relied on partly inhomogeneous datasets. Additionally, closer inspection of the semidiurnal tide time series shows that the negative trend seems to cease after the mid 1980s (Jacobi et al, 1997;Portnyagin et al, 2006), or may even reverse. Observations at Scott Base, Antarctica reveal a positive trend since the late 1980s (Baumgaertner et al, 2005).…”

Section: Non-stationary Trends Discrepancies and Missing Informationmentioning

confidence: 99%

Emerging pattern of global change in the upper atmosphere and ionosphere

et al. 2008

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Abstract. In the upper atmosphere, greenhouse gases produce a cooling effect, instead of a warming effect. Increases in greenhouse gas concentrations are expected to induce substantial changes in the mesosphere, thermosphere, and ionosphere, including a thermal contraction of these layers. In this article we construct for the first time a pattern of the observed long-term global change in the upper atmosphere, based on trend studies of various parameters. The picture we obtain is qualitative, and contains several gaps and a few discrepancies, but the overall pattern of observed long-term changes throughout the upper atmosphere is consistent with model predictions of the effect of greenhouse gas increases. Together with the large body of lower atmospheric trend research, our synthesis indicates that anthropogenic emissions of greenhouse gases are affecting the atmosphere at nearly all altitudes between ground and space.

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Long-term trends in the mesopause wind field obtained from LF D1 wind measurements at Collm, Germany

Cited by 33 publications

References 8 publications

A study of seasonal variations of gravity wave intensity in thelower thermosphere using LF D1 wind observations and a numerical model

A study of seasonal variations of gravity wave intensity in thelower thermosphere using LF D1 wind observations and a numerical model

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

Emerging pattern of global change in the upper atmosphere and ionosphere

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