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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers | Copyright
https://doi.org/10.5194/angeo-2018-51
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 20 Jun 2018

Regular paper | 20 Jun 2018

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Annales Geophysicae (ANGEO).

Connection between the length of day and wind measurements in the mesosphere and lower thermosphere at mid and high latitudes

Sven Wilhelm1, Gunter Stober1, Vivien Matthias2, Christoph Jacobi3, and Damian J. Murphy4 Sven Wilhelm et al.
  • 1Leibniz Institute of Atmospheric Physics at the University of Rostock, Kühlungsborn, Germany
  • 2Potsdam Institute for Climate Impact Research, Potsdam, Germany
  • 3Universität Leipzig, Institute for Meteorology, Germany
  • 4Australian Antarctic Division, Kingston, Tasmania, Australia

Abstract. This work presents a connection between the density variation within the mesosphere and lower thermosphere (MLT) and changes in the intensity of the solar radiation. On a seasonal time scale, these changes take place due to the revolution of the Earth around the Sun. While the Earth, during the northern hemispheric winter, is closer to the Sun, the upper mesosphere expands due to an increased radiation intensity, which results in changes in density at these heights. Theses density variations, i.e. a vertical redistribution of atmospheric mass, have an effect on the rotation rate of Earth's upper atmosphere owing to angular momentum conservation. In order to test this effect we applied a theoretical model, which shows a decrease of the atmospheric rotation speed of about ~4m/s in the case of a density change of 1% between 70 and 100km. To support this statement, we compare the wind variability obtained from meteor radar (MR) and MLS satellite observations with fluctuations in the length of a day (LOD). The LOD is defined as the difference between the astronomical determined time the Earth needs for a full turnaround and a standard day length of 86.400 seconds. Changes in the LOD on time scales of a year and less are primarily driven by tropospheric large scale geophysical processes. A global increase of eastward directed winds leads, due to friction with the Earth's surface, to an acceleration of the Earth's rotation by up to a few milliseconds per rotation. The LOD shows an increase during northern winter and decrease during summer, which corresponds to changes in the MLT density due to the Earth – Sun movement. Further, we show that, even after removing the seasonal and solar cycle variations, the wind and the LOD are connected, by analyzing trends for the years 2005–2016.

Sven Wilhelm et al.
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Sven Wilhelm et al.
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This work presents a connection between density varitations within the upper atmosphere and changes in the intensity of solar radiation. On seasonal time scales, changes takes place due to the revolution of the Earth around the Sun, which results in density changes in these heights. We developed a model to show that these variations have an effect on the rotation rate of the Earths uppers atmosphere and to support this, we compare the wind obtained by meteor radar with day lengths fluctuations.
This work presents a connection between density varitations within the upper atmosphere and...
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