Quarterdiurnal tide in the middle atmosphere (QuarTA)
Final Report Abstract
During QuarTA, the quarterdiurnal tide (QDT) has been studied using numerical modeling, radar observations, and satellite observations of sporadic E (ES ) occurrence rates (OR). Numerical model analyses have peen performed to study the forcing mechanisms of the migrating QDT through separately removing and/or including different forcing mechanisms in a mechanistic circulation model. The QDT component has been identified as the wavenumber 4 component in the model, while all other other non-zonal effects have been removed. The local forcing regions of the secondary mechanisms have been identied. Solar heating contributes to QDT forcing mainly in the troposphere and stratosphere due to water vapor and ozone, nonlinear interactions of tides contribute in the mesosphere, while GW-tide interactions contribute to the QDT in the mesosphere/lower thermosphere (MLT) region. The contribution of the different forcing terms to the total QDT amplitude was determined by removing and enhancing the different QDT forcing mechanisms. These studied showed that direct solar forcing is the most important forcing for the QDT. We also showed that heating through ozone absorption a more important source than water vapor forcing. The secondary mechanisms, namely nonlinear tidal interactions and gravity wave-tidal interactions, have a non-negligible impact on the QDT forcing in the middle and upper atmosphere, but contribute much less than solar forcing. It was observed that removing one of the secondary mechanisms may enhance the QDT rather than reduce it, which is owing to destructive interference between the tidal components of different origin. Analyses of MLT radar observations at midlatitudes showed a seasonal cycle similar than the modeled one, with larger/smaller amplitudes in winter/summer. Long-term analyses revealed an overall increase during winter, qualitatively in agreement with modeling results. Comparison of QDT MLT wind shear phases with phases of the QDT component ES OR showed a clear correspondence, highlighting the wind shear mechanism also acting at the 6-hour time scale. The global distribution of the QDT in both modeled wind shear and ES OR showed a clear correspondence as well. Future analyses will include the non-migrating tidal components. Since local MLT radar observations cannot distinguish between different zonal wavenumbers, this requires including more radar observations into the analysis.
Publications
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(2017). Radar observations of the quarterdiurnal tide at midlatitudes: Seasonal and long-term variations. J. Atmos. Sol. - Terr. Phys., 163, 70 -77
Jacobi, C., A. Krug, and E. Merzlyakov
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(2018). Forcing mechanisms of the 6 h tide in the mesosphere/lower thermosphere. Adv. Radio Sci., 16, 141-147
Jacobi, C., C. Geiÿler, F. Lilienthal, and A. Krug
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(2019). Quarterdiurnal signature in sporadic E occurrence rates and comparison with neutral wind shear. Ann. Geophys., 37 (3), 273-288
Jacobi, C., C. Arras, C. Geiÿler, and F. Lilienthal
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(2019). Tidal wind shear observed by meteor radar and comparison with sporadic E occurrence rates based on GPS radio occultation observations. Adv. Radio Sci., 17, 213-224
Jacobi, C. and C. Arras
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Trend analyses of solar tides in the middle atmosphere. Rep. Inst. Meteorol. Univ. Leipzig, 57, 71-83
Löffelmann, J., F. Lilienthal, and C. Jacobi
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(2020). Forcing mechanisms of the migrating quarterdiurnal tide. Ann. Geophys., 38 (2), 527-544
Geiÿler, C., C. Jacobi, and F. Lilienthal
