Center for Space Science and Engineering Research (Space@VT)

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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.
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.
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.
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.
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.
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.
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.
Improving Neutral Density Predictions Using Exospheric Temperatures Calculated on a Geodesic, Polyhedral Grid
Weimer, Daniel R.; Mehta, P. M.; Tobiska, W. K.; Doornbos, E.; Mlynczak, M. G.; Drob, Douglas P.; Emmert, J. T. (2019-12-10)
A new model of exospheric temperatures has been developed, with the objective of predicting global values with greater spatial and temporal accuracy. From these temperatures, the neutral densities in the thermosphere can be calculated, through use of the Naval Research Laboratory Mass Spectrometer and Incoherent Scatter radar Extended (NRLMSISE-00) model. The exospheric temperature model is derived from measurements of the neutral densities on several satellites. These data were sorted into triangular cells on a geodesic grid, based on location. Prediction equations are derived for each grid cell using least error fits. Several versions of the model equations have been tested, using parameters such as the date, time, solar radiation, and nitric oxide emissions, as measured with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. Accuracy is improved with the addition of the total Poynting flux flowing into the polar regions, from an empirical model that uses the solar wind velocity and interplanetary magnetic field. Given such inputs, the model can produce global maps of the exospheric temperature. These maps show variations in the polar regions that are strongly modulated by the time of day, due to the daily rotation of the magnetic poles. For convenience the new model is referred to with the acronym EXTEMPLAR (EXospheric TEMperatures on a PoLyhedrAl gRid). Neutral densities computed from the EXTEMPLAR-NRLMSISE-00 models combined are found to produce very good results when compared with measured values.
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.
Testing the electrodynamic method to derive height-integrated ionospheric conductances
Weimer, Daniel R.; Edwards, Thom (2021-01-14)
We have used empirical models for electric potentials and the magnetic fields both in space and on the ground to obtain maps of the height-integrated Pedersen and Hall ionospheric conductivities at high latitudes. This calculation required use of both "curl-free" and "divergencefree" components of the ionospheric currents, with the former obtained from magnetic fields that are used in a model of the field-aligned currents. The second component is from the equivalent current, usually associated with Hall currents, derived from the ground-level magnetic field. Conductances were calculated for varying combinations of the interplanetary magnetic field (IMF) magnitude and orientation angle, as well as the dipole tilt angle. The results show that reversing the sign of the Y component of the IMF produces substantially different conductivity patterns. The Hall conductivities are largest on the dawn side in the upward, Region 2 field-aligned currents. Low electric field strengths in the Harang discontinuity lead to inconclusive results near midnight. Calculations of the Joule heating, obtained from the electric field and both components of the ionospheric current, are compared with the Poynting flux in space. The maps show some differences, while their integrated totals match to within 1 %. Some of the Poynting flux that enters the polar cap is dissipated as Joule heating within the auroral ovals, where the conductivity is greater.
Effect of polyoxymethylene (POM-H Delrin) off-gassing within the Pandora head sensor on direct-sun and multi-axis formaldehyde column measurements in 2016-2019
Spinei, Elena; Tiefengraber, Martin; Mueller, Moritz; Gebetsberger, Manuel; Cede, Alexander; Valin, Luke; Szykman, James; Whitehill, Andrew; Kotsakis, Alexander; Santos, Fernando; Abbuhasan, Nader; Zhao, Xiaoyi; Fioletov, Vitali; Lee, Sum Chi; Swap, Robert (2021-01-28)
Analysis of formaldehyde measurements by the Pandora spectrometer systems between 2016 and 2019 suggested that there was a temperature-dependent process inside the Pandora head sensor that emitted formaldehyde. Some parts in the head sensor were manufactured from the thermal plastic polyoxymethylene homopolymer (E.I. Du Pont de Nemour & Co., USA; POM-H Delrin (R)) and were responsible for formaldehyde production. Laboratory analysis of the four Pandora head sensors showed that internal formaldehyde production had exponential temperature dependence with a damping coefficient of 0.0911 +/- 0.0024 degrees C-1 and the exponential function amplitude ranging from 0.0041 to 0.049 DU. No apparent dependency on the head sensor age and heating and cooling rates was detected. The total amount of formaldehyde internally generated by the POM-H Delrin components and contributing to the direct-sun measurements were estimated based on the head sensor temperature and solar zenith angle of the measurements. Measurements in winter, during colder (< 10 degrees C) days in general, and at high solar zenith angles (> 75 degrees) were minimally impacted. Measurements during hot days (> 28 degrees C) and small solar zenith angles had up to 1 DU (2.69 x 10(16 )molec. cm(-2)) contribution from POM-H Delrin parts. Multi-axis differential slant column densities were minimally impacted (< 0.01 DU) due to the reference spectrum being collected within a short time period with a small difference in head sensor temperature. Three new POM-H Delrin free Pandora head sensors (manufactured in summer 2019) were evaluated for temperature-dependent attenuation across the entire spectral range (300 to 530 nm). No formaldehyde absorption or any other absorption above the instrumental noise was observed across the entire spectral range.
Characterization of multi-scale ionospheric irregularities using ground-based and space-based GNSS observations
Peng, YuXiang; Scales, Wayne A.; Hartinger, Michael D.; Xu, Zhonghua; Coyle, Shane (2021-07-12)
Ionospheric irregularities can adversely affect the performance of Global Navigation Satellite System (GNSS). However, this opens the possibility of using GNSS as an effective ionospheric remote sensing tool. Despite ionospheric monitoring has been undertaken for decades, these irregularities in multiple spatial and temporal scales are still not fully understood. This paper reviews Virginia Tech’s recent studies on multi-scale ionospheric irregularities using ground-based and space-based GNSS observations. First, the relevant background of ionospheric irregularities and their impact on GNSS signals is reviewed. Next, three topics of ground-based observations of ionospheric irregularities for which GNSS and other ground-based techniques are used simultaneously are reviewed. Both passive and active measurements in high-latitude regions are covered. Modelling and observations in mid-latitude regions are considered as well. Emphasis is placed on the increased capability of assessing the multi-scale nature of ionospheric irregularities using other traditional techniques (e.g., radar, magnetometer, high frequency receivers) as well as GNSS observations (e.g., Total-Electron-Content or TEC, scintillation). Besides ground-based observations, recent advances in GNSS space-based ionospheric measurements are briefly reviewed. Finally, a new space-based ionospheric observation technique using GNSS-based spacecraft formation flying and a differential TEC method is demonstrated using the newly developed Virginia Tech Formation Flying Testbed (VTFFTB). Based on multi-constellation multi-band GNSS, the VTFFTB has been developed into a hardware-in-the-loop simulation testbed with external high-fidelity global ionospheric model(s) for 3-satellite formation flying, which can potentially be used for new multi-scale ionospheric measurement mission design.
Trends in the polar summer mesosphere temperature and pressure altitude from satellite observations
Bailey, Scott M.; Thurairajah, Brentha; Hervig, Mark E.; Siskind, David E.; Russell, James M. III; Gordley, Larry L. (2021-09-01)
Time series of mesospheric temperature and pressure altitude are produced through combining observations by the Halogen Occultation Experiment (HALOE), Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER), and Solar Occultation for Ice Experiment (SOFIE) instruments. Time series of both temperature and pressure altitude are produced through the combination of HALOE/SABER providing 29 years in length and HALOE/SOFIE providing 22 years in length. The different sampling of the three instruments constrains the time series to June in the northern hemisphere and December in the southern hemisphere and 6470 degrees in both hemispheres. We interpret the time series by fitting them to simple descriptions of the variations including solar, intra-hemispheric, inter-hemispheric, and linear trend terms. The inferred intra- and inter-hemispheric terms show that dynamical influences rival solar variability in the mesosphere. We find a robust result that the mesosphere is in general cooling at most altitudes at approximately 1-2 K per decade in response to greenhouse gas increases. That cooling leads to a shrinking of the atmosphere on the order of 100-200 m per decade. The shrinking leads to a reduction in cooling and eventually a warming near 0.005 hPa due to hydrostatic contraction.
Ionospheric Remote Sensing with GNSS
Peng, YuXiang; Scales, Wayne A. (MDPI, 2021-11-22)
The Global Navigation Satellite System (GNSS) plays a pivotal role in our modern positioning, navigation and timing (PNT) technologies. GNSS satellites fly at altitudes of approximately 20,000 km or higher. This altitude is above an ionized layer of the Earth’s upper atmosphere, the so called “ionosphere”. Before reaching a typical GNSS receiver on the ground, GNSS satellite signals penetrate through the Earth’s ionosphere. The ionosphere is a plasma medium consisting of free charged particles that can slow down, attenuate, refract, or scatter the GNSS signals. Ionospheric density structures (also known as irregularities) can cause GNSS signal scintillations (phase and intensity fluctuations). These ionospheric impacts on GNSS signals can be utilized to observe and study physical processes in the ionosphere and is referred to ionospheric remote sensing. This entry introduces some fundamentals of ionospheric remote sensing using GNSS.
Improved Neutral Density Predictions Through Machine Learning Enabled Exospheric Temperature Model
Licata, Richard J.; Mehta, Piyush M.; Weimer, Daniel R.; Tobiska, W. Kent (American Geophysical Union, 2021-12)
The community has leveraged satellite accelerometer data sets in previous years to estimate neutral mass density and exospheric temperatures. We utilize derived temperature data and optimize a nonlinear machine-learned (ML) regression model to improve upon the performance of the linear EXospheric TEMPeratures on a PoLyhedrAl gRid (EXTEMPLAR) model. The newly developed EXTEMPLAR-ML model allows for exospheric temperature predictions at any location with one model and provides performance improvements over its predecessor. We achieve reductions in mean absolute error of 2 K on an independent test set while providing similar error standard deviation values. Comparing the performance of both EXTEMPLAR models and the Naval Research Laboratory Mass Spectrometer and Incoherent Scatter radar Extended model (NRLMSISE-00) across different solar and geomagnetic activity levels shows that EXTEMPLAR-ML has the lowest mean absolute error across 80% of conditions tested. A study for spatial errors demonstrated that at all grid locations, EXTEMPLAR-ML has the lowest mean absolute error for over 60% of the polyhedral grid cells on the test set. Like EXTEMPLAR, our model's outputs can be utilized by NRLMSISE-00 (exclusively) to more closely match satellite accelerometer-derived densities. We conducted 10 case studies where we compare the accelerometer-derived temperature and density estimates from four satellites to NRLMSISE-00, EXTEMPLAR, and EXTEMPALR-ML during major storm periods. These comparisons show that EXTEMPLAR-ML generally has the best performance of the three models during storms. We use principal component analysis on EXTEMPLAR-ML outputs to verify the physical response of the model to its drivers.
Comparison of a Neutral Density Model With the SET HASDM Density Database
Weimer, Daniel R.; Tobiska, W. Kent; Mehta, Piyush M.; Licata, R. J.; Drob, Douglas P.; Yoshii, Jean (American Geophysical Union, 2021-12)
The EXospheric TEMperatures on a PoLyhedrAl gRid (EXTEMPLAR) method predicts the neutral densities in the thermosphere. The performance of this model has been evaluated through a comparison with the Air Force High Accuracy Satellite Drag Model (HASDM). The Space Environment Technologies (SET) HASDM database that was used for this test spans the 20 years 2000 through 2019, containing densities at 3 hr time intervals at 25 km altitude steps, and a spatial resolution of 10 degrees latitude by 15 degrees longitude. The upgraded EXTEMPLAR that was tested uses the newer Naval Research Laboratory MSIS 2.0 model to convert global exospheric temperature values to neutral density as a function of altitude. The revision also incorporated time delays that varied as a function of location, between the total Poynting flux in the polar regions and the exospheric temperature response. The density values from both models were integrated on spherical shells at altitudes ranging from 200 to 800 km. These sums were compared as a function of time. The results show an excellent agreement at temporal scales ranging from hours to years. The EXTEMPLAR model performs best at altitudes of 400 km and above, where geomagnetic storms produce the largest relative changes in neutral density. In addition to providing an effective method to compare models that have very different spatial resolutions, the use of density totals at various altitudes presents a useful illustration of how the thermosphere behaves at different altitudes, on time scales ranging from hours to complete solar cycles.
Impact Angle Control of Local Intense dB/dt Variations During Shock-Induced Substorms
Oliveira, Denny M.; Weygand, James M.; Zesta, Eftyhia; Ngwira, Chigomezyo M.; Hartinger, Michael D.; Xu, Zhonghua; Giles, Barbara L.; Gershman, Daniel J.; Silveira, Marcos V. D.; Souza, Vítor M. (American Geophysical Union, 2021-12-01)
The impact of interplanetary shocks on the magnetosphere can trigger magnetic substorms that intensify auroral electrojet currents. These currents enhance ground magnetic field perturbations (dB/dt), which in turn generate geomagnetically induced currents (GICs) that can be detrimental to power transmission infrastructure. We perform a comparative study of dB/dt variations in response to two similarly strong shocks, but with one being nearly frontal and the other highly inclined. Multi-instrument analyses by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Los Alamos National Laboratory spacecraft show that nightside substorm-time energetic particle injections are more intense and occur faster in the case of the nearly head-on impact. The same trend is observed in dB/dt variations recorded by THEMIS ground magnetometers. THEMIS all-sky imager data show a fast and clear poleward auroral expansion in the first case, which does not clearly occur in the second case. Strong field-aligned currents computed with the spherical elementary current system (SECS) technique occur in both cases, but the current variations resulting from the inclined shock impact are weaker and slower compared to the nearly frontal case. SECS analyses also reveal that geographic areas with dB/dt surpassing the thresholds 1.5 and 5 nT/s, usually linked to high-risk GICs, are larger and occur earlier due to the symmetric compression caused by the nearly head-on impact. These results, with profound space weather implications, suggest that shock impact angles affect the geospace driving conditions and the location and intensity of the subsequent dB/dt variations during substorm activity.
Can Column Formaldehyde Observations Inform Air Quality Monitoring Strategies for Ozone and Related Photochemical Oxidants?
Travis, K. R.; Judd, L. M.; Crawford, J. H.; Chen, Gao; Szykman, James; Whitehill, Andrew; Valin, Lukas C.; Spinei, Elena; Janz, Scott; Nowlan, Caroline R.; Kwon, Hyeong-Ahn; Fried, Alan; Walega, James (American Geophysical Union, 2022-07-16)
Formaldehyde column density (omega HCHO) showed a potentially useful correlation with surface ozone during the LISTOS campaign on Long Island Sound and the KORUS-AQ campaign in Seoul, South Korea. This builds on previous work that identified this relationship from in situ aircraft observations with similar findings for ground-based and airborne remote sensing of omega HCHO. In the Long Island Sound region, omega HCHO and surface ozone exhibited strong temporal (r(2) = 0.66) and spatial (r(2) = 0.73) correlation. The temporal variability in omega HCHO (similar to 1 Dobson units [DU]) was larger than the range in the spatial average (similar to 0.1 DU). The spatial average is most useful for informing ozone monitoring strategies, demonstrating the challenge in using omega HCHO satellite data sets for this purpose. In Seoul, high levels of NO2 resulted in O-x better correlating with omega HCHO than surface ozone due to titration effects. The omega HCHO-O-x relationship may therefore reflect the sum of surface ozone and related photochemical oxidants, relevant to air quality standards set to regulate this quantity such as the U.S. EPA National Ambient Air Quality Standard (NAAQS). The relationship of omega HCHO to O-x shifted in Seoul during the campaign demonstrating the need to evaluate this relationship over longer time periods. With sufficient precision in future satellite retrievals, omega HCHO observations could be useful for evaluating the adequacy of surface air quality monitoring strategies.
Surface-to-space atmospheric waves from Hunga Tonga-Hunga Ha'apai eruption
Wright, Corwin J.; Hindley, Neil P.; Alexander, M. Joan; Barlow, Mathew; Hoffmann, Lars; Mitchell, Cathryn N.; Prata, Fred; Bouillon, Marie; Carstens, Justin; Clerbaux, Cathy; Osprey, Scott M.; Powell, Nick; Randall, Cora E.; Yue, Jia (Nature Portfolio, 2022-09-22)
The January 2022 Hunga Tonga-Hunga Ha'apai eruption was one of the most explosive volcanic events of the modern era(1,2), producing a vertical plume that peaked more than 50 km above the Earth(3). The initial explosion and subsequent plume triggered atmospheric waves that propagated around the world multiple times(4). A global-scale wave response of this magnitude from a single source has not previously been observed. Here we show the details of this response, using a comprehensive set of satellite and ground-based observations to quantify it from surface to ionosphere. A broad spectrum of waves was triggered by the initial explosion, including Lamb waves(5,6) propagating at phase speeds of 318.2 +/- 6 m s(-1) at surface level and between 308 +/- 5 to 319 +/- 4 m s(-1) in the stratosphere, and gravity waves(7) propagating at 238 +/- 3 to 269 +/- 3 m s(-1) in the stratosphere. Gravity waves at sub-ionospheric heights have not previously been observed propagating at this speed or over the whole Earth from a single source(8,9). Latent heat release from the plume remained the most significant individual gravity wave source worldwide for more than 12 h, producing circular wavefronts visible across the Pacific basin in satellite observations. A single source dominating such a large region is also unique in the observational record. The Hunga Tonga eruption represents a key natural experiment in how the atmosphere responds to a sudden point-source-driven state change, which will be of use for improving weather and climate models.
NRLMSIS 2.1: An Empirical Model of Nitric Oxide Incorporated Into MSIS
Emmert, J. T.; Jones, M.; Siskind, D. E.; Drob, D. P.; Picone, J. M.; Stevens, M. H.; Bailey, Scott M.; Bender, S.; Bernath, P. F.; Funke, B.; Hervig, M. E.; Perot, K. (American Geophysical Union, 2022-10)
We have developed an empirical model of nitric oxide (NO) number density at altitudes from similar to 73 km to the exobase, as a function of altitude, latitude, day of year, solar zenith angle, solar activity, and geomagnetic activity. The model is part of the NRLMSIS (R) 2.1 empirical model of atmospheric temperature and species densities; this upgrade to NRLMSIS 2.0 consists solely of the addition of NO. MSIS 2.1 assimilates observations from six space-based instruments: UARS/HALOE, SNOE, Envisat/MIPAS, ACE/FTS, Odin/SMR, and AIM/SOFIE. We additionally evaluated the new model against independent extant NO data sets. In this paper, we describe the formulation and fitting of the model, examine biases between the data sets and model and among the data sets, compare with another empirical NO model (NOEM), and discuss scientific aspects of our analysis.

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