An exceptionally strong stationary planetary wave with Zonal Wavenumber 1 led to a sudden stratospheric warming (SSW) in the Southern Hemisphere in September 2019. Ionospheric data from European Space Agency's Swarm satellite constellation mission show prominent 6‐day variations in the dayside low‐latitude region at this time, which can be attributed to forcing from the middle atmosphere by the Rossby normal mode “quasi‐6‐day wave” (Q6DW). Geopotential height measurements by the Microwave Limb Sounder aboard National Aeronautics and Space Administration's Aura satellite reveal a burst of global Q6DW activity in the mesosphere and lower thermosphere during the SSW, which is one of the strongest in the record. The Q6DW is apparently generated in the polar stratosphere at 30–40 km, where the atmosphere is unstable due to strong vertical wind shear connected with planetary wave breaking. These results suggest that an Antarctic SSW can lead to ionospheric variability through wave forcing from the middle atmosphere.
The advanced E-Region Wind Interferometer (ERWIN II) combines the imaging capabilities of a CCD detector with the wide field associated with field-widened Michelson interferometry. This instrument is capable of simultaneous multi-directional wind observations for three different airglow emissions (oxygen green line (O(1S)) at a height of ~97 km, the PQ(7) and P(7) emission lines in the O2(0–1) atmospheric band at ~93 km and P1(3) emission line in the (6, 2) hydroxyl Meinel band at ~87 km) on a three minute cadence. In each direction, for 45 s measurements for typical airglow volume emission rates, the instrument is capable of line-of-sight wind precisions of ~1 m s−1 for hydroxyl and O(1S) and ~4 m s−1 for O2. This precision is achieved using a new data analysis algorithm which takes advantage of the imaging capabilities of the CCD detector along with knowledge of the instrument phase variation as a function of pixel location across the detector. This instrument is currently located in Eureka, Nunavut as part of the Polar Environment Atmospheric Research Laboratory (PEARL) (80°N, 86° W). The details of the physical configuration, the data analysis algorithm, the measurement calibration and validation of the observations from December 2008 and January 2009 are described. Field measurements which demonstrate the capabilities of this instrument are presented. To our knowledge, the wind determinations with this instrument are the most accurate and have the highest observational cadence for airglow wind observations of this region of the atmosphere and match the capabilities of other wind-measuring techniques
For the first time, a generalized bin-by-bin analysis approach developed to characterize the visibility, phase, and brightness from Doppler Michelson interferometry (DMI) fringe images is presented. This approach allows for significant advances to the spatial/temporal resolution and sensitivity of DMI utilized for measuring upper atmospheric motions. Expressions for the sensitivity that depend only on the instrument parameters are derived. A unique calibration approach, developed to take full advantage of the DMI imaging capability, is described. The usefulness and validity of this approach is demonstrated using observations from two field-widened interferometers implemented in the field (E-Region Wind Interferometer (ERWIN-II) and the Michelson Interferometer for Airglow Dynamics Imaging (MIADI)). Incorporating the imaging capability into the DMI approach enhances the spatial/temporal information that can be extracted from geophysical observations.
We investigate the high‐latitude mesospheric and lower thermospheric winds during the 2013 sudden stratospheric warming event using ground‐based optical Doppler remote sensing observations of the OH and O (557.7 nm) emission from Eureka (80°N, 86°W) and Thermosphere Ionosphere Mesosphere Electrodynamics‐General Circulation Model (TIME‐GCM) simulations. Simulations with and without lunar tidal forcing of the TIME‐GCM were performed. It has been found that the additional lunar tidal forcing only impacts slightly the semidiurnal tidal amplitude and phase at Eureka. The TIME‐GCM simulations still have noticeable discrepancies in the mean winds and the semidiurnal tidal amplitude and phase compared to the observations. The semidiurnal tidal phase shift during the stratospheric warming event may be associated with the sudden stratospheric warming related zonal mean wind reversal, which is similar to the seasonal change in the zonal mean wind from winter to summer. Accordingly, during the reversal, more modes of the semidiurnal tide propagate to the mesosphere, changing the phase of the semidiurnal tide.
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