- 1Leibniz Institute of Atmospheric Physics at the University of Rostock, Kühlungsborn, Germany (cstolle@iap-kborn.de)
- 2Department of Physics, Indian Institute of Technology Roorkee, India
- 3High Altitude Observatory, NSF National Center for Atmospheric Research, Boulder, CO, USA
- 4Robert Koch Institute, Climate and Societal Analytics, Center for Artificial Intelligence in Public Health Research, Berlin, Germany
The coupling between the stratosphere and the mesosphere-lower thermosphere (MLT) has been known for several years. Its investigation was further pushed during the deep minimum of solar cycle 24 when the upper atmosphere was less affected by solar and geomagnetic forcing and by variability due to atmospheric forcing from below became more significant in observations. Another aspect supporting the understanding of the vertical atmosphere coupling has been the increased availability of globally distributed observations and of sophisticated general circulation models reaching up to the thermosphere.
A negative correlation between the strength of the northern stratospheric polar winter vortex and solar-migrating semidiurnal tides (SW2) in winds at around 100 km altitude has been derived recently by Pedatella and Harvey (2022) based on 38 years of SD-WACCM-X model data. Observational evidence of this correlation was provided shortly afterwards by Kumar et al. (2023) using 26 years of geomagnetic observations of the equatorial electrojet, the latter being largely driven by thermospheric winds.
In this study, we have used a 60-year free-run simulation by the upper atmospheric extension of the ICOsahedral Non-hydrostatic (UA-ICON) general circulation model to explore the influence of northern hemisphere (NH) and southern hemisphere (SH) stratospheric polar vortex variability on the MLT. This study also elucidates the response of SW2 in MLT winds to variations in the strength of polar vortices. A weak NH polar vortex is associated with an increase in SW2, while a strong NH vortex results in a decrease in SW2. The response of SW2 to changes in the strengths of the SH polar vortex is similar, although considerably weaker. The NH polar vortex variability can explain around 40 − 50% of the variability in the SW2 during NH winter. The SH polar vortex, however, accounts for only a small fraction of the variability (up to ∼ 5%) in SW2, highlighting hemispheric differences in the response to stratospheric polar vortex variability.
References:
Kumar, S., Siddiqui, T. A., Stolle, C. and Pallamraju, D., Impact of strong and weak stratospheric polar vortices on geomagnetic semidiurnal solar and lunar tides. Earth Planets Space, 75, 52, https://doi.org/10.1186/s40623-023-01810-x, 2023.
Pedatella, N.M. and Harvey, V. L., Impact of strong and weak stratospheric polar vortices on the mesosphere and lower thermosphere. Geophys. Res. Lett. 49, e2022GL098877. https://doi.org/10.1029/2022GL098877, 2022.
How to cite: Stolle, C., Kumar, A., Yamazaki, Y., Pedatella, N. M., Kunze, M., Stephan, C. C., Siddiqui, T. A., and Krishna, M. V. S.: Impact of Weak and Strong Polar Vortices in the Northern and Southern Hemispheres on Solar-Migrating Semidiurnal Tides in the lower thermosphere using UA-ICON model simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3334, https://doi.org/10.5194/egusphere-egu25-3334, 2025.
