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Subject: temporal variation Ă— WGL Institute: IAP Ă—

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    Long-term wintertime trend of zonally asymmetric ozone in boreal extratropics during 1979-2016
    (Basel : MDPI AG, 2018) Schneidereit, A.; Peters, D.H.W.
    Strong zonally asymmetric ozone (ZAO) changes are observed in the boreal extratropics for winter. During the TOMS (Total Ozone Mapping Spectrometer) period (1979-1992) the decrease of zonally asymmetric total ozone (ZATO) was twice as large as the observed zonal mean total ozone trend over Europe in January mainly caused by ultra-long wave transport. Recent studies have demonstrated that the ozone evolution reveals three different quasi-bidecadal trend stages: (i) Decline, (ii) leveling, and (ii) healing. This study focuses on the ZAO structure in boreal extratropics and on ozone transport changes by ultra-long waves during winter months. ERA-Interim data together with a linearized transport model are used. During the healing stage ZATO increases significantly over the North Atlantic/European region for January. The ZATO increase (healing stage) and ZATO decrease (decline stage) are caused by different monthly mean ozone transport characteristics of ultra-long planetary waves over the North Atlantic/European region. Furthermore, the vertical advection (ageostrophic transport) of ozone versus its horizontal component dominates in the lower and middle stratosphere during the healing stage. It is hypothesized that these ageostrophic wind changes are mainly caused by a wave train directed northeastwards which seems to be directly linked to the Arctic warming. © 2018 by the authors.
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    A modified index for the description of the ionospheric short- and long-term activity
    (Göttingen : Copernicus, 2010) Mielich, J.; Bremer, J.
    A modified ionospheric activity index AI has been developed on the basis of ionospheric foF2 observations. Such index can be helpful for an interested user to get information about the current state of the ionosphere. Using ionosonde data of the station Juliusruh (54.6° N; 13.4°E) this index has been tested for the time interval from January 1996 until December 2008. This index has no diurnal and seasonal variations, only a small positive dependence on the solar activity could be found. The variability of this index has, however, a marked seasonal variability with maxima during the equinoxes, a clear minimum in summer, and enhanced values in winter. The observed variability of AI is strongly correlated with the geomagnetic activity, most markedly during the equinoxes, whereas the influence of the solar activity is markedly smaller and mostly insignificant. Strong geomagnetic disturbances cause in middle latitudes in general negative disturbances in AI, mostly pronounced during equinoxes and summer and only partly during winter, thus in agreement with the current physical knowledge about ionospheric storms. © 2010 Author(s).