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Advances in Radio Science An open-access journal of the U.R.S.I. Landesausschuss in der Bundesrepublik Deutschland e.V.
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Volume 15
Adv. Radio Sci., 15, 199-206, 2017
https://doi.org/10.5194/ars-15-199-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Adv. Radio Sci., 15, 199-206, 2017
https://doi.org/10.5194/ars-15-199-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

  21 Sep 2017

21 Sep 2017

El Niño influence on the mesosphere/lower thermosphere circulation at midlatitudes as seen by a VHF meteor radar at Collm (51.3 ° N, 13 ° E)

Christoph Jacobi1, Tatiana Ermakova2, Daniel Mewes1, and Alexander I. Pogoreltsev2 Christoph Jacobi et al.
  • 1Leipzig Institute for Meteorology, Universität Leipzig, Stephanstr. 3, 04103 Leipzig, Germany
  • 2Russian State Hydrometeorological University, St. Petersburg, Russia

Abstract. Mesosphere/lower thermosphere (MLT) zonal winds continuously measured by a VHF meteor radar at Collm, Germany (51.3°N, 13.0°E) in the height range 82 – 97km from 2004 to date are analyzed with respect to the signature of El Niño. The comparison of Niño3 equatorial SST index and MLT wind time series shows that in January and especially in February zonal winds are positively correlated with the Niño3 index. We note a delay of about one month of the MLT zonal wind effect with respect to equatorial sea surface temperature variability. The signal is strong for the upper altitudes (above 90km) accessible to the radar observations, but weakens with decreasing height. This reflects the fact that during El Niño years the westerly winter middle atmosphere wind jet is weaker, and this is also the case with the easterly lower thermospheric jet. Owing to the reversal of the absolute El Niño signal from negative to positive with altitude, at the height of the maximum meteor flux, which is around 90km, the El Niño signal is weak. The experimental results can be qualitatively reproduced by numerical experiments using a mechanistic global circulation model with prescribed tropospheric temperatures and latent heat release for El Niño and La Niña conditions.

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There is continuous interest in coupling processes between the lower and middle atmosphere. Here we analyse midlatitude winds measured by radar at 82–97 km and find that especially in February they are positively correlated with El Niño. The signal is strong for the upper altitudes accessible to the radar, but weakens below. The observations can be qualitatively reproduced by numerical experiments using a mechanistic global circulation model.
There is continuous interest in coupling processes between the lower and middle atmosphere. Here...
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