Showing papers by "Sharon L. Vadas published in 2022"

Multi‐Step Vertical Coupling During the January 2017 Sudden Stratospheric Warming

Abstract: This study analyzes a simulation of the Arctic winter 2016–2017 with focus on multi‐step vertical coupling (MSVC) by primary, secondary, and higher‐order gravity waves (GWs). We employ the HIgh Altitude Mechanistic general Circulation Model with nudging of the large scales to MERRA‐2 reanalysis. Simulation results confirm the well‐known effects from primary GWs in the winter middle atmosphere regarding strong westward GW drag and a warm winter polar stratopause during the strong‐vortex period in late December 2016, as well as weak eastward GW drag and mesospheric cooling during the sudden stratospheric warming (SSW) in late January and early February 2017. Since the amplitudes of the primary GWs that dissipate in the middle atmosphere are weaker for a reversed or weakened polar vortex, the theory for secondary GW generation predicts reduced MSVC in this case. This is confirmed by strongly reduced secondary and higher‐order GW amplitudes during the SSW and the weak‐vortex period in February. The wintertime higher‐order GWs show partial concentric ring structures above their sources in the lower thermosphere. We find that mostly those higher‐order GWs propagate to higher altitudes that have horizontal propagation directions against the tidal winds. The simulated GWs at 300 km height and observed perturbations of total electron content over Europe and North America during selected days of low geomagnetic activity show very good agreement regarding (a) the wave characteristics and (b) the reduction of amplitudes during the SSW and early February as compared to late December.

3D Numerical Simulation of Secondary Wave Generation From Mountain Wave Breaking Over Europe

Abstract: In this paper, we simulate an observed mountain wave event over central Europe and investigate the subsequent generation, propagation, phase speeds and spatial scales, and momentum deposition of secondary waves under three different tidal wind conditions. We find the mountain wave breaks just below the lowest critical level in the mesosphere. As the mountain wave breaks, it extends outwards along the phases and fluid associated with the breaking flows downstream of its original location by 500–1,000 km. The breaking generates a broad range of secondary waves with horizontal scales ranging from the mountain wave instability scales (20–300 km), to multiples of the mountain wave packet scale (420 km+) and phase speeds from 40 to 150 m/s in the lower thermosphere. The secondary wave morphology consists of semi‐concentric patterns with wave propagation generally opposing the local tidal winds in the mesosphere. Shears in the tidal winds cause breaking of the secondary waves and local wave forcing which generates even more secondary waves. The tidal winds also influence the dominant wavelengths and phase speeds of secondary waves that reach the thermosphere. The secondary waves that reach the thermosphere deposit their energy and momentum over a broad area of the thermosphere, mostly eastward of the source and concentrated between 110 and 130 km altitude. The secondary wave forcing is significant and will likely be very important for the dynamics of the thermosphere. A large portion of this forcing comes from nonlinearly generated secondary waves at relatively small‐scales which arise from the wave breaking processes.

Simulation Study of the 15 January 2022 Tonga Event: Development of Super Equatorial Plasma Bubbles

Abstract: We present high‐resolution simulation results of the response of the ionosphere/plasmasphere system to the 15 January 2022 Tonga volcanic eruption. We use the coupled Sami3 is Also a Model of the Ionosphere ionosphere/plasmasphere model and the HIgh Altitude Mechanistic general Circulation Model whole atmosphere model with primary atmospheric gravity wave effects from the Model for gravity wavE SOurces, Ray trAcing and reConstruction model. We find that the Tonga eruption produced a “super” equatorial plasma bubble (EPB) extending ∼30° in longitude and up to 500 km in altitude with a density depletion of 3 orders of magnitude. We also found a “train” of EPBs developed and extended over the longitude range 150°–200° and that two EPBs reached altitudes over 4,000 km. The primary cause of this behavior is the significant modification of the zonal neutral wind caused by the atmospheric disturbance associated with the eruption, and the subsequent modification of the dynamo electric field.

Systematic Detection of Anomalous Ionospheric Perturbations Above LEOs From GNSS POD Data Including Possible Tsunami Signatures

Abstract: In this article, we show the capability of a global navigation satellite system (GNSS) precise orbit determination (POD) low Earth orbit (LEO) data to detect anomalous ionospheric disturbances in the spectral range of the signals associated with earthquakes and tsunamis, applied to two of these events in Papua New Guinea (PNG) and the Solomon Islands during 2016. This is achieved thanks to the new PIES approach (POD-GNSS LEO Detrended Ionospheric Electron Content Significant Deviations). The significance of such ionospheric signals above the swarm LEOs is confirmed with different types of independent data: in situ electron density measurements provided by the Langmuir Probe (LP) onboard swarm LEOs, DORIS, and ground-based GNSS colocated measurements, as it is described in this article. In this way, we conclude the possible detection of the tsunami-related ionospheric gravity wave in PNG 2016 event, consistent with the most-recent theory, which shows that a tsunami (which is localized in space and time) excites a spectrum of gravity waves, some of which have faster horizontal phase speeds than the tsunami. We believe that this work shows as well the feasibility of a future potential monitoring system of ionospheric disturbances, to be made possible by hundreds of CubeSats with POD GNSS receivers among other appropriate sensors, and supported for real-time or near real-time confirmation and characterization by thousands of worldwide existing ground GNSS receivers.