Dynasonde approach to ionospheric radio sounding capitalizes on high precision of physical parameters and rich statistics of recognized echoes phase-based methods can provide. As has been recently demonstrated, the Dynasonde profiles of the electron density and of the horizontal gradients, complemented with profiles of the Doppler speed, carry comprehensive quantitative information about Atmospheric Gravity Waves, a ubiquitous feature of the space weather that has become an important objective of atmospheric modeling. Being combined into a time series, and without additional processing, the profiles allow visualization of the time fronts of the Traveling Ionospheric Disturbances (TIDs). They also provide high-resolution input data for calculating the complete set of parameters (both vertical and horizontal) of TID activity in the upper atmosphere between the base of the E layer and the maximum of the F layer. Application of the Lomb-Scargle periodogram technique to the tilt data provides unique insight into the dynamics of spectral composition of the TIDs. A similar technique applied to longer time series allows determining characteristics of thermospheric tides. Single sounding sessions allow observations of ionospheric manifestations of acoustic waves produced by ground-based sources. All the mentioned products of the Dynasonde data analysis require a common, standard ionogram mode of radar operation. Therefore, information about standard parameters of the ionospheric E, F regions, possibility to obtain vector velocities characterizing movement of plasma contours, and quantitative parameters of the km-scale irregularity spectrum are not lost and contribute into comprehensive description of wave activity in the thermosphere-ionosphere system.
Figure shows one of standard products of autonomous Dynasonde analysis: Temporal scans of the vertical cross-section of several ionospheric parameters as a function of Universal Time and the true altitude for one day over Wallops Island, VA. Two panels use a gray color scale to show the zonal (b) and meridional (c) tilt components; two other panels use a color scale to show the plasma frequency (a) and the vertical projection of the line-of-sight Doppler speed (d). The transition from night to day conditions happens at around 11 UT and from day to night conditions at around 23 UT.
The three panels of this animation show the dynamics of the normalized Lomb-Scargle periodograms in the period vs real altitude coordinates for the following observables:
- Arecibo ISR plasma frequency from plasma line
- Arecibo ISR vertical speed from ion line
- San Juan Dynasonde vertical projection of line-of-sight Doppler speed
The PSDs were calculated using 1.5-hour long sliding window independently for every altitude, with a 2 min step. Qualitative similarities between the spectra measured by the ISR and the Dynasonde, which are 67 km apart, are obvious, and leave no doubt that the two instruments observe the same phenomenon: thermospheric waves.
This link leads to a web interface to data storage and data analysis tools for Dynasondes participating in the University of Colorado projects.
Recent theoretical and experimental work indicates that in a wide range of altitudes and for
periods from a few minutes to several hours, a significant part of the wave activity observed
in the thermosphere is due to acoustic gravity waves radiated by infragravity waves in the
ocean. It is proposed to study this impressive connection between geospheres in Antarctica,
at the location where close proximity of the Ross Ice Shelf makes it very special. Infragravity
waves are able to excite the fundamental mode and low-order oscillations in the Ross Ice Shelf
at its resonance frequencies, with the latter creating standing wave structures throughout
the atmosphere. It is likely that this effect was recently detected using lidar observations
at McMurdo. This project will study implications of this phenomenon, as well as more general
aspects of wave activity in Antarctic geospheres, using data from a unique combination of
recently installed instruments: the Dynasonde at Korean Jang Bogo station, the NSF-sponsored
network of seismographs and microbarometers on the Ross Ice Shelf, and the IMS-affiliated
infrasound station near McMurdo.
Image credit: Ted Scambos, NSIDC
The goal of this research is to study atmospheric waves in the thermosphere in Antarctica
and to investigate the roles that the Ross Ice Shelf and the Southern Ocean play in generation
of the atmospheric waves. Anticipated results are of interest also for general aeronomy and
for glaciology. This project will verify the hypothesis that the persistent atmospheric waves
in mesosphere and lower thermosphere, which are observed with a lidar instrument at McMurdo,
are related to the low-frequency vibration resonances of the Ross Ice Shelf excited by infragravity
waves in the ocean. An accurate characterization will be achieved for low-frequency oscillations
of the Ross Ice Shelf and the quality factors of its resonances will be assessed. Investigation
of a consistency between observed and predicted vertical distributions of the wave intensity
is expected to provide insights into where the horizontal momentum carried by AGWs is transferred
to the mean motion, i.e., to the large-scale dynamics of the Antarctic thermosphere. A determination
of whether accurate measurements of the acoustic resonant frequencies and their variations
can provide useful constraints on the neutral temperature profile in the atmosphere will be
done. Extensive use of Jang Bogo Dynasonde data in all mentioned tasks will allow further
developing Dynasonde techniques.
Theory predicts strong coupling between waves in the atmosphere and the ocean at low frequencies where mechanical waves in both fluids should be treated as acoustic gravity waves (AGWs). It has been shown recently that at the frequency of the order of 1 mHz, a transition in behavior of oceanic infragravity waves occurs; at higher frequencies the infragravity waves penetrate into the atmosphere only up to heights of the order of their wavelength, but below the transition frequency, the energy and momentum of infragravity waves are radiated into the atmosphere and are expected to reach the upper atmosphere, including thermosphere and ionosphere. This effect may be called Wideband Transparency of the air-sea interface.
The project aims to confirm the effect of transparency and to investigate its global consequences with theoretical and experimental means. Innovative passive techniques of noise interferometry are applied to an unprecedented combination of ocean and ionosphere sensors. Data obtained with Deep-ocean Assessment and Reporting of Tsunami probes are analyzed together with the data of precision ionospheric radio sounding performed with Dynasonde systems. Correlation between the spectra of infragravity wave motions in the ocean and the spectra of AGWs measured over coastal regions at ionospheric altitudes reveal strong coupling between the geospheres caused by the effect of transparency mentioned above. This allows one to trace waves of oceanic origin and to quantify related transport of energy and momentum to thermospheric altitudes.
The left panel of the figure illustrates the experiment idea. The right panel shows measured significant linear spectral correlation between the infragravity waves in the ocean and the thermospheric waves.