Connection between the length of day and wind measurements in the mesosphere and lower thermosphere at mid- and high latitudes
<p>This work presents a connection between the density variation within the mesosphere and lower thermosphere (MLT) and changes in the intensity of solar radiation. On a seasonal timescale, these changes take place due to the revolution of the Earth around the Sun. While the Earth, during the...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-01-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/37/1/2019/angeo-37-1-2019.pdf |
| _version_ | 1819038355409600512 |
|---|---|
| author | S. Wilhelm G. Stober V. Matthias C. Jacobi D. J. Murphy |
| author_facet | S. Wilhelm G. Stober V. Matthias C. Jacobi D. J. Murphy |
| author_sort | S. Wilhelm |
| collection | DOAJ |
| description | <p>This work presents a connection between the density variation
within the mesosphere and lower thermosphere (MLT) and changes in the
intensity of solar radiation. On a seasonal timescale, these changes take
place due to the revolution of the Earth around the Sun. While the Earth,
during the northern-hemispheric (NH) 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. These 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 in the atmospheric rotation speed of about
<span class="inline-formula">∼4</span> m s<span class="inline-formula"><sup>−1</sup></span> at a latitude of 45<span class="inline-formula"><sup>∘</sup></span>
in the case of a density change of 1 % between 70 and 100 km. To support
this statement, we compare the wind variability obtained from meteor radar
(MR) and Microwave Limb Sounder (MLS) satellite observations with fluctuations in the length of a day
(LOD). Changes in the LOD on timescales of a year and less are primarily
driven by tropospheric large-scale geophysical processes and their impact on
the Earth's rotation. A global increase in lower-atmospheric
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 decreases
during summer, which corresponds to changes in the MLT density due to the
Earth–Sun movement. Within the MLT the mean zonal wind shows similar
fluctuations to the LOD on annual scales as well as longer time series, which
are connected to the seasonal wind regime as well as to density changes
excited by variations in the solar radiation. A direct correlation between
the local measured winds and the LOD on shorter timescales cannot clearly be
identified, due to stronger influences of other natural oscillations on the
wind. Further, we show that, even after removing the seasonal and 11-year
solar cycle variations, the mean zonal wind and the LOD are connected by
analyzing long-term tendencies for the years 2005–2016.</p> |
| first_indexed | 2024-12-21T08:36:00Z |
| format | Article |
| id | doaj.art-1c8d78e01188419d88292a3bae75186a |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-12-21T08:36:00Z |
| publishDate | 2019-01-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-1c8d78e01188419d88292a3bae75186a2022-12-21T19:10:03ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762019-01-013711410.5194/angeo-37-1-2019Connection between the length of day and wind measurements in the mesosphere and lower thermosphere at mid- and high latitudesS. Wilhelm0G. Stober1V. Matthias2C. Jacobi3D. J. Murphy4Leibniz Institute of Atmospheric Physics, University of Rostock, Kühlungsborn, GermanyLeibniz Institute of Atmospheric Physics, University of Rostock, Kühlungsborn, GermanyEarth System Analysis – Research Domain 1, Potsdam Institute for Climate Impact Research, Potsdam, GermanyInstitute for Meteorology, Universität Leipzig, Leipzig, GermanyAustralian Antarctic Division, Kingston, Tasmania, Australia<p>This work presents a connection between the density variation within the mesosphere and lower thermosphere (MLT) and changes in the intensity of solar radiation. On a seasonal timescale, these changes take place due to the revolution of the Earth around the Sun. While the Earth, during the northern-hemispheric (NH) 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. These 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 in the atmospheric rotation speed of about <span class="inline-formula">∼4</span> m s<span class="inline-formula"><sup>−1</sup></span> at a latitude of 45<span class="inline-formula"><sup>∘</sup></span> in the case of a density change of 1 % between 70 and 100 km. To support this statement, we compare the wind variability obtained from meteor radar (MR) and Microwave Limb Sounder (MLS) satellite observations with fluctuations in the length of a day (LOD). Changes in the LOD on timescales of a year and less are primarily driven by tropospheric large-scale geophysical processes and their impact on the Earth's rotation. A global increase in lower-atmospheric 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 decreases during summer, which corresponds to changes in the MLT density due to the Earth–Sun movement. Within the MLT the mean zonal wind shows similar fluctuations to the LOD on annual scales as well as longer time series, which are connected to the seasonal wind regime as well as to density changes excited by variations in the solar radiation. A direct correlation between the local measured winds and the LOD on shorter timescales cannot clearly be identified, due to stronger influences of other natural oscillations on the wind. Further, we show that, even after removing the seasonal and 11-year solar cycle variations, the mean zonal wind and the LOD are connected by analyzing long-term tendencies for the years 2005–2016.</p>https://www.ann-geophys.net/37/1/2019/angeo-37-1-2019.pdf |
| spellingShingle | S. Wilhelm G. Stober V. Matthias C. Jacobi D. J. Murphy Connection between the length of day and wind measurements in the mesosphere and lower thermosphere at mid- and high latitudes Annales Geophysicae |
| title | Connection between the length of day and wind measurements in the mesosphere and lower thermosphere at mid- and high latitudes |
| title_full | Connection between the length of day and wind measurements in the mesosphere and lower thermosphere at mid- and high latitudes |
| title_fullStr | Connection between the length of day and wind measurements in the mesosphere and lower thermosphere at mid- and high latitudes |
| title_full_unstemmed | Connection between the length of day and wind measurements in the mesosphere and lower thermosphere at mid- and high latitudes |
| title_short | Connection between the length of day and wind measurements in the mesosphere and lower thermosphere at mid- and high latitudes |
| title_sort | connection between the length of day and wind measurements in the mesosphere and lower thermosphere at mid and high latitudes |
| url | https://www.ann-geophys.net/37/1/2019/angeo-37-1-2019.pdf |
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