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Lidar and radar observations of persistent atmospheric wave activity in the Antarctic atmosphere motivate investigation of generation of acoustic‐gravity waves (AGWs) by vibrations of ice shelves and exploiting their possible ionospheric manifestations as a source of information about the ice shelves' conditions and stability. A mathematical model of the waves radiated by vibrations of a finite area of the lower boundary of the atmosphere is developed in this paper by extending to AGWs an efficient, numerically exact approach that was originally developed in seismology and underwater acoustics. The model represents three‐dimensional wave fields as Fourier integrals of numerical or analytical solutions of a one‐dimensional wave equation and accounts for the source directionality, AGW refraction and diffraction, and the wind‐induced anisotropy of wave dissipation. Application of the model to the generation of atmospheric waves in Antarctica by free vibrations of the Ross Ice Shelf reveals a complex three‐dimensional structure of the AGW field and elucidates the impact of various environmental factors on the wave field. The intricate variation of the wave amplitude with altitude and in the horizontal plane is shaped by the spatial spectrum of the ice surface vibrations and the temperature and wind velocity stratification from the troposphere to the mesosphere. It is found that the waves due to the low‐order modes of the free oscillations of the Ross Ice Shelf, which have periods of the order of several hours, can transport energy to the middle and upper atmosphere in a wide range of directions from near‐horizontal to near‐vertical.

 

The main subject of this study is the low‐frequency (with the periods longer than 2 hr) wave processes in the coupled regional system of the Ross Ice Shelf (RIS), the Ross Sea and the atmosphere above them. We investigate possible causal relationships between the wave activity in the three media using a unique set of geophysical instruments: a hydrophone measuring pressure variations on the seafloor, a network of seismometers measuring vertical displacements of the RIS surface, and a Dynasonde system measuring wave characteristics at the ionospheric altitudes. We present an extension of the previously introduced theoretical model of the coupled resonance vibrations of the RIS that quantifies the connection between the ocean tide and the resonance vibrations of the RIS. The ocean tide is confirmed as the most significant source of excitation of the resonances. Analysis of average power spectra in year‐long data sets reveals multiple harmonics of the tide (eight) detected by the RIS seismometers while only three are detected by the seafloor sensor. This may represent a confirmation of the effect of resonance‐related broadband amplification predicted by the model. Several peaks in the spectrum of RIS vibrations have periods different from the periods of nearby tidal constituents and may be associated with broad‐scale resonance RIS vibrations. Resonances may play a role in maintaining the coupled atmosphere‐ocean wave activity. Our results reveal a statistically significant correlation between the spectra of the vertical displacements of the RIS and the spectra of the atmospheric waves.

 

We describe observations of a trend between the level of km‐scale irregularity activity and the amplitudes of medium‐scale traveling ionospheric disturbances (MSTIDs) at mid‐latitudes using data from December 2019 through June 2021. These include measurements of both heigh‐specific and vertically integrated quantities. Region‐specific, bottom‐side measurements were made with the dynasonde system near Wallops Island (WI) and included phase structure function parameters related to km‐scale irregularities as well as height‐specific tilts/density gradients, which are especially sensitive to MSTIDs. A complementary data set was derived from the nearby Deployable Low‐band Ionosphere and Transient Experiment (DLITE) array in southern Maryland. The DLITE array was used to measure the vertically integrated irregularity index,C_kL, via scintillometry of bright cosmic radio sources at 35 MHz. Transverse gradients in the line‐of‐sight total electron content (TEC) were also measured with DLITE using apparent shifts in the sources' sky positions. Relatively simple layer‐based models for the vertical distribution of km‐scale irregularities applied to dynasonde‐measured properties yielded results that correlated well with DLITE measurements ofC_kL. Similarly, spectral analysis showed that fluctuation amplitudes of vertically integrated bottom‐side density gradients derived from dynasonde data were well correlated with DLITE TEC gradient measurements. A significant trend was found betweenC_kLand TEC gradient MSTID amplitudes among DLITE‐based data as well as among the extrapolated dynasonde measurements. Additionally, within the bottom‐side F‐region, irregularity levels were found to be well correlated with fluctuation amplitudes for the tilt as measured with the WI dynasonde.

 

The impact of regional-scale neutral atmospheric waves has been demonstrated to have profound effects on the ionosphere, but the circumstances under which they generate ionospheric disturbances and seed plasma instabilities are not well understood. Neutral atmospheric waves vary from infrasonic waves of <20 Hz to gravity waves with periods on the order of 10 min, for simplicity, hereafter they are combined under the common term Acoustic and Gravity Waves (AGWs). There are other longer period waves like planetary waves from the lower and middle atmosphere, whose effects are important globally, but they are not considered here. The most ubiquitous and frequently observed impact of AGWs on the ionosphere are Traveling Ionospheric Disturbances (TIDs), but AGWs also affect the global ionosphere/thermosphere circulation and can trigger ionospheric instabilities (e.g., Perkins, Equatorial Spread F). The purpose of this white paper is to outline additional studies and observations that are required in the coming decade to improve our understanding of the impact of AGWs on the ionosphere. 

Vertical incidence pulsed ionospheric radar (VIPIR) has been operated to observe the polar ionosphere with Dynasonde analysis software at Jang Bogo Station (JBS), Antarctica, since 2017. The JBS-VIPIR-Dynasonde (JVD) provides ionospheric parameters such as the height profile of electron density with NmF2 and hmF2, the ion drift, and the ionospheric tilt in the bottomside ionosphere. The JBS (74.6°S, 164.2°E) is located in the polar cap, cusp, or auroral region depending on the geomagnetic activity and local time. In the present study, an initial assessment of JVD ionospheric densities is attempted by the comparison with GPS TEC measurements which are simultaneously obtained from the GPS receiver at JBS during the solar minimum period from 2017 to 2019. It is found that the JVD NmF2 and bottomside TEC (bTEC) show a generally good correlation with GPS TEC for geomagnetically quiet conditions. However, the bTEC seems to be less correlated with the GPS TEC with slightly larger spreads especially during the daytime and in summer, which seems to be associated with the characteristics of the polar ionosphere such as energetic particle precipitations and large density irregularities. It is also found that the Dynasonde analysis seems to show some limitations to handle these characteristics of the polar ionosphere and needs to be improved to produce more accurate ionospheric density profiles especially during disturbed conditions. 

Korea Polar Research Institute (KOPRI) installed an ionospheric sounding radar system called Vertical Incidence Pulsed Ionospheric Radar (VIPIR) at Jang Bogo Station (JBS) in 2015 in order to routinely monitor the state of the ionosphere in the auroral oval and polar cap regions. Since 2017, after two-year test operation, it has been continuously operated to produce various ionospheric parameters. In this article, we will introduce the characteristics of the JBS-VIPIR observations and possible applications of the data for the study on the polar ionosphere. The JBS-VIPIR utilizes a log periodic transmit antenna that transmits 0.5–25 MHz radio waves, and a receiving array of 8 dipole antennas. It is operated in the Dynasonde B-mode pulse scheme and utilizes the 3-D inversion program, called NeXtYZ, for the data acquisition and processing, instead of the conventional 1-D inversion procedure as used in the most of digisonde observations. The JBS-VIPIR outputs include the height profiles of the electron density, ionospheric tilts, and ion drifts with a 2-minute temporal resolution in the bottomside ionosphere. With these observations, possible research applications will be briefly described in combination with other observations for the aurora, the neutral atmosphere and the magnetosphere simultaneously conducted at JBS. 

A part of the Southern Ocean, the Ross Sea, together with the Ross Ice Shelf and the atmosphere over the region represent a coupled system with respect to the low-frequency (with the periods longer than 1 hour) wave processes observed in the three media. We study interconnections between them using a unique combination of geophysical sensors: hydrophones measuring pressure variations on the bottom of the open ocean, seismographs measuring vertical displacements of the surface of the Ross Ice Shelf, and the Jang Bogo Dynasonde system measuring wave parameters at the altitudes of the lower thermosphere. Analysis of a year-long data sets from Ross Ice Shelf-based instruments reveals presence in their average power spectra of the peaks in the 2-11 hours period range that may be associated with the low-order resonance vibrations of the system. More harmonics of the 24 hour tide (seven) are detected by the RIS seismographs compared to the sea floor sensor (where only two are clearly visible). This may be a consequence of the RIS resonance-related broadband amplification effect predicted by our model. There are several peaks in the RIS vibration spectrum (T = 8.37, 8.23, 6.3 and 6.12 hours) that are not detected by the hydrophone and may be directly related to RIS resonances. The prominent T = 25.81 hour peak is a likely candidate for the sub-inertial RIS resonance. The periods of lower RIS resonance modes predicted by our simple model and the observed spectral peaks are in the same general band. This is the first direct observation of the resonance effects in vibrations of the Ross Ice Shelf. Our results demonstrate the key role of the resonances of the Ross Ice Shelf in maintaining the wave activity in the entire coupled system. We suggest that the ocean tide is a major source of excitation of the Ross Ice Shelf’s resonances. The ice shelf vibrations may also be supported by the energy transfer from wind, swell, and infragravity wave energy that couples with the ice shelf. Overlapping 6-month-long data sets reveal a significant linear correlation between the spectra of the vertical shifts of the Ross Ice Shelf and of the thermospheric waves with the periods of about 2.1, 3.7, and 11.1 hours. This result corroborates earlier lidar observations of persistent atmospheric wave activity over McMurdo. We propose a theory that quantifies the nexus between the ocean tide and the resonance vibrations of the Ross Ice Shelf. It complements the theoretical model of the process of generating the atmospheric waves by the resonance vibrations of the Ross Ice Shelf published by us earlier.