Bulletin of the American Physical Society
Mid-Atlantic Section Meeting 2021
Volume 66, Number 18
Friday–Sunday, December 3–5, 2021; Rutgers University, New Brunswick, New Jersey
Session G02: Ionosphere-Thermosphere |
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Chair: Gareth Perry, New Jersey Institute of Technology Room: 201B |
Sunday, December 5, 2021 9:00AM - 9:36AM |
G02.00001: Improving the Performance of High-Power Radio Facilities for Plasma Wave Generation in Space Invited Speaker: Paul Bernhardt High power radio are used for ionospheric modification experiments from ground VLF and HF facilities with large antenna arrays and transmitters. VLF signals are generated by both Navy systems to communicate with submarines and by HF signal modulation of the currents in the E-region electrojet. The HF facilities at HAARP in Alaska and EISCAT Heating in Norway can produce electromagnetic wave beams with effective radiated powers in excess of one Gigawatt. New techniques are being developed to increase the effectiveness of these facilities for generation of field-aligned irregularities, artificial plasma clouds, and intense whistler modes waves that interact with the earth's radiation belt electrons. Techniques to increase the intensity of waves in space plasma from these facilities include EM wave beam focusing with artificial lenses and parametric amplification of whistler modes by extracting energy from an external lower-hybrid pump. For focusing, a large lens is formed in the lower ionosphere using the thermal pressure inside the heated plasma or a chemical release that rapidly attaches electrons, yielding a plasma hole in the bottom side of the ionosphere. Since the refractive index is larger inside the neutralized region of the electron hole, HF wave become focused by 20 dB. For amplification, a rocket burning in the ionosphere above a ground transmitter drives a ring beam distribution in the pickup ions yielding lower-hybrid waves that pumps a parametric amplification process. The parametric waves may also be produced by decay of an upper hybrid wave sustained by the HF EM wave into daughter UH and LW waves. When wave and wave-number matching conditions are met, the whistler traveling wave parametric amplifier (WTWPA) process yields 30 to 50 dB amplification of whistler waves generated by modulation of the earth's electrojet with fluctuating HF signals in the VLF frequency range. Amplifying whistlers is a new concept for influencing the energetic electron population in the radiation belts. Any existing whistler wave generator produces, at most, signals of 10 pT strength. The WTWPA can boost the artificial whistler amplitudes to greater than 300 pT. Several configurations for active amplification of VLF signals in space will be discussed. [Preview Abstract] |
Sunday, December 5, 2021 9:36AM - 10:12AM |
G02.00002: STEVE, a mysterious subauroral optical structure Invited Speaker: Bea Gallardo-Lacourt The recent discovery of the subauroral phenomenon called STEVE (Strong Thermal Emission Velocity Enhancement) has been an exciting development in auroral research. Discovered by citizen scientists, STEVE is an upper-atmosphere manifestation of an extremely thin yet long ribbon of vibrant purple and white hues across the night-sky. Scientific space and ground-based instruments combined with citizen scientists’ data provide a unique tool to analyze this new phenomenon. STEVE is a great visual example of the complex coupling between the solar wing, Earth’s magnetosphere, and its upper atmosphere. In this talk, we will review some of the current understanding that the scientific community has reached regarding STEVE, as well as some outstanding open questions. [Preview Abstract] |
Sunday, December 5, 2021 10:12AM - 10:48AM |
G02.00003: Resolving the spatial-scales and drivers of high-latitude ionospheric irregularities using innovative ground-based radar techniques Invited Speaker: Lindsay Goodwin The ionosphere contains a wide variety of plasma density structures, known as irregularities, whose properties impact the propagation of high-frequency radiation, such as radio waves. Resolving the spatial-scales of these irregularities (and thus their drivers) is challenging using Incoherent Scatter Radars (ISRs) either due to the long duration over which a scan of observations at a single altitude must be taken, or the large spatial separations that are associated with probing different locations at the same altitude simultaneously. Between 200 and 400 km altitude, plasma is magnetized, weakly-collisional, and participates in resonant charge exchange through collisions between O$+$ and O, leading to anisotropic ion temperatures at electric fields greater than 40 mV/m. At high-latitudes, geomagnetic field lines are nearly vertical, which, due to diffusion being the dominant transport mechanism parallel to the magnetic field and cross-field diffusion being slow at scales greater than 10 km, leads to changes in the vertical plasma density profile above 200 km altitude being predominately the result of scale height effects. Leveraging these points, this work employs a novel technique that uses volumetric plasma density measurements from phased array Advanced Modular Incoherent Scatter Radars (AMISRs) to resolve high-latitude ionospheric irregularity spectra at a higher spatial-temporal resolution than has been previously possible with ISRs. By applying this technique to high-latitude AMISRs, we can resolve the spatial-scales of irregularities in relation to different solar and geomagnetic parameters. This presentation will focus on spatial-scale variations between 20 and 110 km from November 28 to December 3 2016. Here, we distinguish variations that result from changes in geomagnetic activity from diurnal variations, such as an increase in the dominant spatial-scales at noon. This presentation will expand on this dataset and discuss the future goals of this work. [Preview Abstract] |
Sunday, December 5, 2021 10:48AM - 11:00AM |
G02.00004: Multi-hop propagation mode in Antarctica: Simulating HF radio wave propagation between the McMurdo and South Pole stations Binjie Liu, Gareth Perry, Alex Chartier High Frequency (HF) remote sensing techniques are sensitive to the plasma density variations in the ionosphere, which makes it an effective tool for understanding the behavior of the ionosphere. It is widely believed that multi-hop propagation modes (requiring ground scatter) cannot be supported in Antarctica because of the coverage of ice and snow, which are strong HF absorbers. We present HF ray-tracing simulation results in Antarctica and compare them with experimental data collected by a multi-frequency HF transmitter/receiver radio link between McMurdo (transmitter) and South Pole (receiver) stations. Simulation results include: the 5.1 MHz channel shows a clear E-region reflection mode and is highly absorbed under sunlit conditions (0-5 and 21-24 UT). A two-hop propagation mode exists in 4.1 MHz channel at around 9 UT. The highly absorbed signals in both the simulation and observations indicates that the receiver is sensitive enough to detect signals with significant ionospheric absorption. The presence of multi-hop propagation in the simulations and data suggests that this mode is attainable in Antarctica under certain conditions, although it appears to be sporadic in nature. [Preview Abstract] |
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