Scholarly Works, Center for Space Science and Engineering Research (Space@VT)

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Research articles, presentations, and other scholarship

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Conjugate observations of electromagnetic ion cyclotron waves associated with traveling convection vortex events
Kim, Hyomin; Clauer, C. Robert; Gerrard, Andrew J.; Engebretson, Mark J.; Hartinger, Michael D.; Lessard, Marc R.; Matzka, Juergen; Sibeck, David G.; Singer, Howard J.; Stolle, Claudia; Weimer, Daniel R.; Xu, Zhonghua (2017-07)
We report on simultaneous observations of electromagnetic ion cyclotron (EMIC) waves associated with traveling convection vortex (TCV) events caused by transient solar wind dynamic pressure (P-d) impulse events. The Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft located near the magnetopause observed radial fluctuations of the magnetopause, and the GOES spacecraft measured sudden compressions of the magnetosphere in response to sudden increases in Pd. During the transient events, EMIC waves were observed by interhemispheric conjugate ground-based magnetometer arrays as well as the GOES spacecraft. The spectral structures of the waves appear to be well correlated with the fluctuating motion of the magnetopause, showing compression-associated wave generation. In addition, the wave features are remarkably similar in conjugate hemispheres in terms of bandwidth, quasiperiodic wave power modulation, and polarization. Proton precipitation was also observed by the DMSP spacecraft during the wave events, from which the wave source region is estimated to be 72 degrees-74 degrees in magnetic latitude, consistent with the TCV center. The confluence of space-borne and ground instruments including the interhemispheric, high-latitude, fluxgate/induction coil magnetometer array allows us to constrain the EMIC source region while also confirming the relationship between EMIC waves and the TCV current system.
Correlations Between the Thermosphere's Semiannual Density Variations and Infrared Emissions Measured With the SABER Instrument
Weimer, Daniel R.; Mlynczak, M. G.; Emmert, J. T.; Doornbos, E.; Sutton, E. K.; Hunt, L. A. (2018-10)
This paper presents measurements of the amplitudes and timings of the combined, annual, and semiannual variations of thermospheric neutral density, and a comparison of these density variations with measurements of the infrared emissions from carbon dioxide and nitric oxide in the thermosphere. The density values were obtained from measurements of the atmospheric drag experienced by the Challenging Minisatellite Payload, Gravity Recovery and Climate ExperimentA, Gravity field and Ocean Circulation Explorer, and three Swarm satellites, while the optical emissions were measured with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. These data span a time period of 16years. A database containing global average densities that were derived from the orbits of about 5,000 objects (Emmert, 2009, https://doi.org/10.1029/2009JA014102, 2015b, https://doi.org/10.1002/2015JA021047) was employed for calibrating these density data. A comparison with the NRLMSISE-00 model was used to derive measurements of how much the density changes over time due to these seasonal variations. It is found that the seasonal density oscillations have significant variations in amplitude and timing. In order to test the practicality of using optical emissions as a monitoring tool, the SABER data were fit to the measured variations. Even the most simple fit that used only filtered carbon dioxide emissions had good correlations with the measured oscillations. However, the density oscillations were also well predicted by a simple Fourier series, contrary to original expectations. Nevertheless, measurements of the optical emissions from the thermosphere are expected to have a role in future understanding and prediction of the semiannual variations. Plain Language Summary The uppermost atmosphere, known as the thermosphere, undergoes oscillations in the density of the neutral atoms and molecules, producing two peaks and valleys in the density in each year. The timing of of these "semiannual" variations or oscillations, as well as their amplitudes, tends to vary. Their unpredictability makes it harder to accurately model the amount of drag experienced by orbiting satellites. It had been noticed that the infrared light emitted by carbon dioxide molecules in the thermosphere has a tendency to follow the semiannual oscillations. Such emissions have been measured by an instrument on a NASA satellite for the past 16years. We have compared these emissions with the variations in the semiannual oscillations that were derived from measurements of the drag seen by six different satellites flown by both NASA and the European Space Agency during the same time period, though not at the same time. The results of the comparison show how well the infrared emissions match the density oscillations, due to changes in both the composition and temperature of the thermosphere that influence both. Results show that further study will be needed to be able to accurately predict the density oscillations.
First Observation of Ionospheric Convection From the Jiamusi HF Radar During a Strong Geomagnetic Storm
Zhang, J. J.; Wang, W.; Wang, C.; Lan, A. L.; Yan, J. Y.; Xiang, D.; Zhang, Q. H.; Ruohoniemi, J. Michael; Kunduri, B. S. R.; Nishitani, Nozomu; Shi, X.; Qiu, H. B. (2019-12-11)
The Super Dual Auroral Radar Network (SuperDARN) is an international low-power high-frequency (HF) radar network, which provides continuous observations of the motion of plasma in the ionosphere. Over the past 15 years, the network has expanded dramatically in the middle latitudes of the Northern Hemisphere to improve the observation capabilities of the network during periods of strong geomagnetic disturbance. However, a large coverage gap still exists in the middle latitudes. A newly deployed middle-latitude HF radar in China (the Jiamusi radar) is about to join the network. This paper presents the first observation of the ionospheric convection from the Jiamusi radar during the strong geomagnetic storm on 26 August 2018. The Jiamusi measurements are compared with the simultaneous measurements from the SuperDARN Hokkaido East radar. The features of the high-velocity westward flows including the equatorward expansion and variation tendency of the line-of-sight velocities observed by the two radars are consistent with each other. According to joint analysis with auroral images, we can confirm that the westward flows observed by the two radars are sunward return flows of the duskside convection cell in the auroral region. The impact the Jiamusi data had on the calculation of SuperDARN convection patterns is also examined. The results show that the inclusion of the Jiamusi data can increase the number of gridded line-of-sight velocity measurements by up to 24.42%, the cross-polar cap potential can be increased by up to 13.90% during the investigated period.
Ground-based instruments of the PWING project to investigate dynamics of the inner magnetosphere at subauroral latitudes as a part of the ERG-ground coordinated observation network
Shiokawa, Kazuo; Katoh, Yasuo; Hamaguchi, Yoshiyuki; Yamamoto, Yuka; Adachi, Takumi; Ozaki, Mitsunori; Oyama, Shin-Ichiro; Nosé, Masahito; Nagatsuma, Tsutomu; Tanaka, Yoshimasa; Otsuka, Yuichi; Miyoshi, Yoshizumi; Kataoka, Ryuho; Takagi, Yuki; Takeshita, Yuhei; Shinbori, Atsuki; Kurita, Satoshi; Hori, Tomoaki; Nishitani, Nozomu; Shinohara, Iku; Tsuchiya, Fuminori; Obana, Yuki; Suzuki, Shin; Takahashi, Naoko; Seki, Kanako; Kadokura, Akira; Hosokawa, Keisuke; Ogawa, Yasunobu; Connors, Martin; Ruohoniemi, J. Michael; Engebretson, Mark J.; Turunen, Esa; Ulich, Thomas; Manninen, Jyrki; Raita, Tero; Kero, Antti; Oksanen, Arto; Back, Marko; Kauristie, Kirsti; Mattanen, Jyrki; Baishev, Dmitry; Kurkin, Vladimir; Oinats, Alexey; Pashinin, Alexander; Vasilyev, Roman; Rakhmatulin, Ravil; Bristow, William A.; Karjala, Marty (2017-11-28)
The plasmas (electrons and ions) in the inner magnetosphere have wide energy ranges from electron volts to mega-electron volts (MeV). These plasmas rotate around the Earth longitudinally due to the gradient and curvature of the geomagnetic field and by the co-rotation motion with timescales from several tens of hours to less than 10 min. They interact with plasma waves at frequencies of mHz to kHz mainly in the equatorial plane of the magnetosphere, obtain energies up to MeV, and are lost into the ionosphere. In order to provide the global distribution and quantitative evaluation of the dynamical variation of these plasmas and waves in the inner magnetosphere, the PWING project (study of dynamical variation of particles and waves in the inner magnetosphere using ground-based network observations, (http://www.isee.nagoya-u.ac.jp/dimr/PWING/) has been carried out since April 2016. This paper describes the stations and instrumentation of the PWING project. We operate all-sky airglow/aurora imagers, 64-Hz sampling induction magnetometers, 40-kHz sampling loop antennas, and 64-Hz sampling riometers at eight stations at subauroral latitudes (~ 60° geomagnetic latitude) in the northern hemisphere, as well as 100-Hz sampling EMCCD cameras at three stations. These stations are distributed longitudinally in Canada, Iceland, Finland, Russia, and Alaska to obtain the longitudinal distribution of plasmas and waves in the inner magnetosphere. This PWING longitudinal network has been developed as a part of the ERG (Arase)-ground coordinated observation network. The ERG (Arase) satellite was launched on December 20, 2016, and has been in full operation since March 2017. We will combine these ground network observations with the ERG (Arase) satellite and global modeling studies. These comprehensive datasets will contribute to the investigation of dynamical variation of particles and waves in the inner magnetosphere, which is one of the most important research topics in recent space physics, and the outcome of our research will improve safe and secure use of geospace around the Earth.
High correlations between temperature and nitric oxide in the thermosphere
Weimer, Daniel R.; Mlynczak, M. G.; Hunt, L. A.; Tobiska, W. K. (American Geophysical Union, 2015-07-01)
Obtaining accurate predictions of the neutral density in the thermosphere has been a long-standing problem. During geomagnetic storms the auroral heating in the polar ionospheres quickly raises the temperature of the thermosphere, resulting in higher neutral densities that exert a greater drag force on objects in low Earth orbit. Rapid increases and decreases in the temperature and density may occur within a couple days. A key parameter in the thermosphere is the total amount of nitric oxide (NO). The production of NO is accelerated by the auroral heating, and since NO is an efficient radiator of thermal energy, higher concentrations of this molecule accelerate the rate at which the thermosphere cools. This paper describes an improved technique that calculates changes in the global temperature of the thermosphere. Starting from an empirical model of the Poynting flux into the ionosphere, a set of differential equations derives the minimum, global value of the exospheric temperature, which can be used in a neutral density model to calculate the global values. The relative variations in NO content are used to obtain more accurate cooling rates. Comparisons with the global rate of NO emissions that are measured with the Sounding of the Atmosphere using Broadband Emission Radiometry instrument show that there is very good agreement with the predicted values. The NO emissions correlate highly with the total auroral heating that has been integrated over time. We also show that the NO emissions are highly correlated with thermospheric temperature, as well as indices of solar extreme ultraviolet radiation.
Observations of Reduced Turbulence and Wave Activity in the Arctic Middle Atmosphere Following the January 2015 Sudden Stratospheric Warming
Triplett, Colin C.; Li, Jintai; Collins, Richard L.; Lehmacher, Gerald A.; Barjatya, Aroh; Fritts, David C.; Strelnikov, Boris; Luebken, Franz-Josef; Thurairajah, Brentha; Harvey, V. Lynn; Hampton, Donald L.; Varney, Roger H. (2018-12-16)
Measurements of turbulence and waves were made as part of the Mesosphere-Lower Thermosphere Turbulence Experiment (MTeX) on the night of 25-26 January 2015 at Poker Flat Research Range, Chatanika, Alaska (65 degrees N, 147 degrees W). Rocket-borne ionization gauge measurements revealed turbulence in the 70- to 88-km altitude region with energy dissipation rates between 0.1 and 24mW/kg with an average value of 2.6mW/kg. The eddy diffusion coefficient varied between 0.3 and 134m(2)/s with an average value of 10m(2)/s. Turbulence was detected around mesospheric inversion layers (MILs) in both the topside and bottomside of the MILs. These low levels of turbulence were measured after a minor sudden stratospheric warming when the circulation continued to be disturbed by planetary waves and winds remained weak in the stratosphere and mesosphere. Ground-based lidar measurements characterized the ensemble of inertia-gravity waves and monochromatic gravity waves. The ensemble of inertia-gravity waves had a specific potential energy of 0.8J/kg over the 40- to 50-km altitude region, one of the lowest values recorded at Chatanika. The turbulence measurements coincided with the overturning of a 2.5-hr monochromatic gravity wave in a depth of 3 km at 85km. The energy dissipation rates were estimated to be 3mW/kg for the ensemble of waves and 18mW/kg for the monochromatic wave. The MTeX observations reveal low levels of turbulence associated with low levels of gravity wave activity. In the light of other Arctic observations and model studies, these observations suggest that there may be reduced turbulence during disturbed winters. Plain Language Summary Turbulence remains an outstanding challenge in understanding coupling, energetics, and dynamics of the atmosphere. However, turbulence is recognized as a critical component in our models of terrestrial and space weather. Obtaining routine and accurate measurements of turbulence continues to be a major challenge. We present new rocket-borne measurements of turbulence in January 2015 at Poker Flat Research Range, Alaska. These rocket-borne measurements were coordinated with a suite of ground-based instruments. The rocket-borne instruments captured the small-scale structure of the turbulence. The ground-based measurements documented the meteorological and space weather conditions. We find low levels of turbulence coinciding with a disturbed atmosphere where wave activity is reduced. These finding suggest that there may be systematically low levels of turbulence in the Arctic middle atmosphere, as the Arctic middle atmosphere is routinely disturbed in winter.
Seasonal and Solar Cycle Variations of Thermally Excited 630.0 nm Emissions in the Polar Ionosphere
Kwagala, Norah Kaggwa; Oksavik, Kjellmar; Lorentzen, Dag A.; Johnsen, Magnar G.; Laundal, Karl M. (2018-08)
Solar cycle and seasonal variations have been found in the occurrence of strong thermally excited 630.0 nm emissions in the polar ionosphere. Measurements from the European Incoherent Scatter Svalbard Radar have been used to derive the thermal emission intensity. Thermally excited emissions have been found to maximize at solar maximum with peak occurrence rate of similar to 40% compared to similar to 2% at solar minimum. These emissions also have the highest occurrence in equinox and the lowest occurrence rate in summer and winter. There is an equinoctial asymmetry in the occurrence rate which reverses with the solar cycle. This equinoctial asymmetry is attributed to variations of the solar wind-magnetosphere coupling arising from the Russell-McPherron effect. The occurrence rate of thermal excitation emission on the dayside, at Svalbard, has been found to be higher in autumn than spring at solar maximum and the reverse at solar minimum. Enhanced electron temperatures characterize the strong thermal component for solar minimum and winter, whereas enhanced electron densities characterize the thermal component for solar maximum. The results point to solar wind-magnetosphere-ionosphere coupling as the dominant controlling process.
Storm time meridional wind perturbations in the equatorial upper thermosphere
Haaser, R. A.; Davidson, R.; Heelis, R. A.; Earle, Gregory D.; Venkatraman, S.; Klenzing, J. (American Geophysical Union, 2013-05-01)
We present observations from the Coupled Ion Neutral Dynamics Investigation (CINDI) of storm time meridional winds in the neutral atmosphere near the magnetic equator at 400km altitude. Observations near the magnetic equator in the southern geographic hemisphere are dominated by energy inputs from the southern Polar Regions that produce south to north (equatorward) wind perturbations to accompany perturbations in the neutral density and temperature. In one exceptional case, when observations are made near midnight and the north magnetic pole rotates through the midnight sector, north to south (poleward) meridional wind perturbations are observed just south of the magnetic equator. Accompanying perturbations in the neutral density on the dayside and the nightside are consistent with observed increases in the ion temperature and inferred increases in the neutral temperature in accord with hydrostatic equilibrium.

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