Grant AGS-1656912 entails collaborative research between Dr. Herbert C. Carlson (Utah State University, USU) and Dr. Frank T. Djuth (Geospace

There are three major goals of this project.  The first goal is to determine the physical properties and atmospheric response to the filamentation of the ionospheric plasma by a high-power HF wave. The problem that we plan to solve is how artificial field aligned irregularities, FAIs (a.k.a. electron density ducts), can be formed and reinforced in the

A large amount of filamentation takes place in the plasma [e.g., Djuth and DuBois, 2015].  In the current project a variety of HF pulsing sequences are used to support measurements of cross-field diffusion of a broad k spectrum of electron density ne irregularities in the HF-induced filamentary structure. We note that similar processes occur in the auroral oval, but in the auroral case an electron-beam plasma interaction is involved, whereas in our case a wave-plasma interaction drives the filamentation. Nevertheless the filamentation physics is similar and may be scalable. 

The second goal is to use the previously established HF-induced flux of upgoing suprathermal electrons [Carlson et al., 2017] to probe the plasmasphere/inner magnetosphere. With the new Arecibo HF facility it is feasible to probe the plasmasphere/inner magnetosphere with a large flux of HF excited suprathermal electrons (SE) directed up geomagnetic field lines.  However, what comes down may not be what went up. More specifically this is a unique, exploratory way of probing ionosphere–plasmasphere coupling.  The HF-excited SE beam provide new insight into the fraction of SEs lost in the plasmasphere, the fraction returned from the plasmasphere due to scattering into the loss cone, and the fraction that reaches the conjugate hemisphere and is scattered back to AO. The Langmuir waves are detected with the AO radar as “plasma lines” located by +/- the

local plasma frequency from which the electron energy that excited the Langmuir waves can be deduced. The origin of the nighttime plasma lines is nether locally produced photoelectrons nor photoelectrons originating from the conjugate hemisphere.  They are observed at a solar depression angle between 12 and 18 degrees.   The origin of the nighttime plasma line is currently unknown, but there are several theories that may apply.

Our third goal was to revisit our technique for determining arrival direction of the AO acoustic gravity waves (GWs).  The downward moving phase velocities of the GWs are observed as imprints on the background electron density profile throughout the altitude interval from 114 km to greater than 650 km  These waves are constantly present at AO day and night.  Typically the radar line feed is fixed in the vertical direction and the Gregorian feed is positioned at ~11°–15° in zenith angle.   The Gregorian feed is alternately aligned relative to the line feed in the geomagnetic meridian plane and the zonal plane, and the phase change of GW induced electron density perturbation in the two directions are used to determine GW arrival direction.  However, this technique is less than perfect because the GWs are broadband in wavenumber space and has not yielded decisive results on the propagation direction of the GWs.   Our goal is to implement a new technique that entails 2-D cross correlations of the GW packet radar image observed by the two beams.  This has successfully been tested on a limited data set.   A comparison of the results obtained with the above two techniques will be performed as part of this project.  In addition we monitored nighttime GWs in January to help resolve questions related to the prolific numbers of nighttime descending Tidal Ion Layers (TILs) present at Arecibo during this period [e.g., Morton et al., 1993].  The TILs have an average downward phase velocity of 14.7 m/s whereas the neutral layers descend at 0.69 m/s.  This indicates that lower thermosphere atomic metal layers are not necessarily associated with TILs.    However, the lower thermosphere atomic metal layers may be associated with and interact with the continuum of background GWs [e.g., Djuth et al., 2010].

References

Carlson, H. C., F. T. Djuth, P. Perillat, M. Sulzer (2015), Low Latitude 10s eV electrons: Night Time Plasma Line as a new Research Capability, Geophys. Res. Lett., 42, 7255-

7263, doi:10.1002/2015GL065172.

Carlson, H. C., F. T. Djuth, and L. D. Zhang (2017). Creating space plasma from the ground. Journal of Geophysical Research. 122 978. DOI: 10.1002/2016JA023380.

Djuth, F. T., L. D. Zhang, D. J. Livneh, I. Seker, S. M. Smith, M. P. Sulzer, J. D. Mathews, and R. L. Walterscheid (2010), Arecibo’s thermospheric gravity waves and the case for an ocean source, J. Geophys. Res., 115, A08305, doi:10.1029/2009JA014799.

Djuth, F. T., and D. F. DuBois (2015), Temporal Development of HF-Excited Langmuir and Ion Turbulence at Arecibo. Earth Moon and Planets , 116, 19-53, doi:10.1007/s11038-015-9458-x.

Last Modified: 06/26/2019
Modified by: Herbert C Carlson