Terrestrial Thermosphere Research Articles

Proof of concept demonstration of a metastable helium fluorescence lidar for thermospheric wind and temperature measurements.

We report on the first, to the best of our knowledge, spectral measurements of terrestrial thermospheric metastable helium using ground-based lidar. By stimulating fluorescence of He(23S) at four closely spaced wavelengths within the He line around 1083 nm and measuring the lidar returns, we measured the He(23S) spectrum at 600 km, providing coarse constraints on the He(23S) temperature and vertical wind speed. This work serves as a proof of concept and precursor experiment for future, more powerful helium lidar systems capable of measuring vertical profiles of neutral wind and temperature in the upper terrestrial thermosphere.

On the variability of the atomic oxygen density in the upper atmosphere under different solar activity and geomagnetic conditions and its impacts on satellite drag

Atomic oxygen (AO) is the most abundant species in the terrestrial thermosphere at altitudes of 180 to 700 km and plays a crucial role in numerous upper atmospheric processes. The drag encountered by a spacecraft is directly influenced by the background atmospheric density, making AO a notable contributor in this regard. The objective of this study is to analyze the variability of the density of AO in the near-Earth space environment under different solar activity conditions, as well as during severe space weather events. The analysis is primarily focused on the altitude range of 300 to 500 km in the Earth’s thermosphere across the globe, which is a crucial operating region for a large number of Low Earth Orbiting satellites. AO exerts significant drag on the Low Earth Orbit (LEO) satellites and reacts with the materials of the satellite body and in situ probes mounted therein, causing considerable degradation to both. Additionally, AO interferes with measurements made by optical instruments through phenomena such as ‘shuttle glow’. Analysis based on NRLMSIS 2.0 model revealed that the concentration of AO displays significant seasonal variations primarily due to the asymmetry in solar insolation. The highest concentration of AO was observed during the spring equinoctial month of the solar maximum year, while the lowest concentration was noted during the winter solstitial month of the solar minimum year. The enhancement seen in AO density contours show an asymmetry in the zonal direction at approximately 50∘ N in June and 50∘ S in December. Similarly, during geomagnetically disturbed days, the AO density shows enhancements along various longitudes, as indicated by the elongated contours. During geomagnetic storms, the heightened Joule heating in the polar region modifies the meridional circulation, which in turn affects the global distribution of AO density. Similarly, an analysis of thermospheric neutral winds obtained from the HWM93 model reveals that the zonal winds exhibit a strong westward acceleration over the region where AO density is enhanced. Furthermore, such an increase in AO density during geomagnetic storms has been found to cause orbital degradation ranging from a few tens of meters to a few hundred meters, depending on the strength and geo-effectiveness of the storms. This study emphasizes the critical contribution of AO density to satellite drag force, necessitating in situ measurements for an accurate estimation of the altitude decay of the spacecraft.

Solar Rotation Effects in Earth's and Mars' Thermospheric Densities as Revealed by Concurrent MAVEN, Swarm‐C, and GOES Observations

AbstractThe responses of Earth's and Mars' thermospheric densities to quasi‐periodic (∼27‐day) solar rotation variations in flux were measured contemporaneously by the Mars Atmosphere and Volatile EvolutioN, Geostationary Operational Environmental Satellites, and Swarm‐C satellites. While large solar rotation variability is found in both planetary thermospheres, correlation analyses performed on over 6 years of observations reveal that, independently of extreme ultraviolet flux level, Earth's daytime density response is about 10%–50% larger than Mars' at a similar density level. Important altitude dependencies in the density sensitivity to the solar rotation in solar flux are found in the Martian thermosphere, while the terrestrial thermosphere is shown to exhibit only small (±5%) day/night and latitude variations in the response. Detailed analyses focused on correlative periods in 2015–2016 and 2020 indicate important solar cycle effects in the sensitivities of both planetary thermospheres, with increased slopes under low solar flux conditions. These results provide important new insights into processes relevant to the interpretation of the sources of short‐term density variability in Mars' and Earth's thermospheres associated with solar drivers and point to the need for targeted modeling efforts along with dedicated data analyses to help resolve current unknowns in thermal balance processes.

A Simulation Study on the Variation of Thermospheric O/N2 With Solar Activity

AbstractThe ratio of number density of atomic oxygen (O) to that of molecular nitrogen (N2) in the thermosphere (O/N2) on the constant pressure surface, which has complex temporal and spatial characteristics, is widely regarded as an important parameter connecting the terrestrial thermosphere and daytime ionosphere. Previous studies demonstrated that the thermospheric O/N2 increases with increasing solar activity, and the changes in O/N2 with solar activity show significant difference between winter and summer hemispheres. However, the root causes, which are responsible for the solar activity variation of O/N2, are not fully understood. In this study, the contributions of various physical and chemical processes on the response of O/N2 to the solar radiation change were quantitatively investigated through a series of controlled simulations from the Thermosphere Ionosphere Electrodynamics General Circulation Model. The simulation results suggested that the chemical processes lead to the increase of thermospheric O/N2 over the globe with increasing solar activity. The increase of O/N2 with solar activity is dominated by the enrichment of O abundance and the loss of N2 abundance in the lower and upper thermosphere, respectively. Moreover, the simulation results suggested that the stronger hemispheric asymmetry is attributed to the stronger thermospheric circulation, which changes the vertical advection of O/N2 through both direct and indirect effects.

N2(A) in the Terrestrial Thermosphere

AbstractRecent work has indicated the presence of a nitric oxide (NO) product channel in the reaction between the higher vibrational levels of the first electronically excited state of molecular nitrogen, N2(A ), and atomic oxygen. A steady‐state model for the N2(A) vibrational distribution in the terrestrial thermosphere is here described and validated by comparison with N2 A‐X, Vegard‐Kaplan dayglow spectra from the Ionospheric Spectroscopy and Atmospheric Chemistry spectrograph. A computationally cheaper method is needed for implementation of the N2(A) chemistry into time‐dependent thermospheric models. It is shown that by scaling the photoelectron impact production of ionized N2 by a Gaussian centered near 100 km, the level‐specific N2(A) production rates between 100 and 200 km can be reproduced to within an average of 5%. This scaling, and thus the N2 electron impact ionization/excitation ratio, is nearly independent of existing uncertainties in the 2–20 nm solar soft X‐ray irradiance. To investigate this independence, the N2 electron‐impact excitation cross sections in the GLOW photoelectron model are replaced with the results of Johnson et al. (2005, https://doi.org/10.1029/2005JA011295) and the multipart work of Malone et al. (2009 https://doi.org/10.1103/PhysRevA.79.032704) (Malone, Johnson, Young, et al., 2009, https://doi.org/10.1088/0953-4075/42/22/225202; Malone, Johnson, Kanik, et al., 2009, https://doi.org/10.1103/PhysRevA.79.032705; Malone et al., 2009, https://doi.org/10.1103/PhysRevA.79.032704), together denoted J05M09. Upon updating these cross sections it is found that (1) the total N2 triplet excitation rate remains nearly constant; (2) the steady state N2(A) vibrational distribution is shifted to higher levels; (3) the total N2 singlet excitation rate responsible for the Lyman‐Birge‐Hopfield emission is reduced by 33%. It is argued that adopting the J05M09 cross sections supports (1) the larger X‐ray fluxes measured by the Student Nitric Oxide Explorer (SNOE) and (2) a temperature‐independent N2(A)+O reaction rate coefficient.

Retrieval of Lower Thermospheric Temperatures from O2 A Band Emission: The MIGHTI Experiment on ICON.

The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) is a satellite experiment scheduled to launch on NASA's Ionospheric Connection Explorer (ICON) in 2017. MIGHTI is designed to measure horizontal neutral winds and neutral temperatures in the terrestrial thermosphere. Temperatures will be inferred by imaging the molecular oxygen Atmospheric band (A band) on the limb in the lower thermosphere. MIGHTI will measure the spectral shape of the A band using discrete wavelength channels to infer the ambient temperature from the rotational envelope of the band. Here we present simulated temperature retrievals based on the as-built characteristics of the instrument and the expected emission rate profile of the A band for typical daytime and nighttime conditions. We find that for a spherically symmetric atmosphere, the measurement precision is 1 K between 90-105 km during the daytime whereas during the nighttime it increases from 1 K at 90 km to 3 K at 105 km. We also find that the accuracy is 2 K to 11 K for the same altitudes. The expected MIGHTI temperature precision is within the measurement requirements for the ICON mission.

Atmospheric Drag, Occultation ‘N’ Ionospheric Scintillation (ADONIS) mission proposal

The Atmospheric Drag, Occultation 'N' Ionospheric Scintillation mission (ADONIS) studies the dynamics of the terrestrial thermosphere and ionosphere in dependency of solar events over a full solar cycle in Low Earth Orbit (LEO). The objectives are to investigate satellite drag with in-situ measurements and the ionospheric electron density profiles with radio occultation and scintillation measurements. A constellation of two satellites provides the possibility to gain near real-time data (NRT) about ionospheric conditions over the Arctic region where current coverage is insufficient. The mission shall also provide global high-resolution data to improve assimilative ionospheric models. The low-cost constellation can be launched using a single Vega rocket and most of the instruments are already space-proven allowing for rapid development and good reliability. From July 16 to 25, 2013, the Alpbach Summer School 2013 was organised by the Austrian Research Promotion Agency (FFG), the European Space Agency (ESA), the International Space Science Institute (ISSI) and the association of Austrian space industries Austrospace in Alpbach, Austria. During the workshop, four teams of 15 students each independently developed four different space mission proposals on the topic of "Space Weather: Science, Missions and Systems", supported by a team of tutors. The present work is based on the mission proposal that resulted from one of these teams' efforts.

Lyman α airglow emission: Implications for atomic hydrogen geocorona variability with solar cycle

Satellite‐based measurements of geocoronal Lyman α (Lyα) emission at 121.6 nm, created through multiple scattering of solar Lyα photons by atomic hydrogen, offer a valuable means of inferring the hydrogen abundance, [H], in the terrestrial thermosphere and exosphere on a global, long‐term basis. We present initial results from an analysis of Lyα radiance measurements acquired across the Earth's limb from 2002 to 2007 by the Global UltraViolet Imager (GUVI) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) spacecraft. This data spans nearly half of a solar cycle, and both the absolute Lyα radiance as well as its relative variation across the limb are shown to exhibit a significant dependence on solar activity. We describe sensitivities of a forward radiative transport (RT) model to key parameters governing the [H] distribution in order to assess implications for [H] estimation from the GUVI limb scan data throughout the solar cycle. Based on data‐model comparisons, we conclude that the observed solar cycle variability is indicative of a decrease in dayside H density at the exobase with increasing solar activity. These results, along with additional forward RT modeling based on NRLMSISE‐00 model specification of [H], are also used to assess contemporary semiempirical model accuracy.

Evaluation of isotopic fractionation of oxygen ions escaping from terrestrial thermosphere

Oxygen isotopic ratios in contemporary lunar soils indicate a highly mass-independent fractionation (MIF) of Δ17O≈25 per mil. This fraction is comparable to the ratio for stratospheric ozone and is thus supposed to have originated from the terrestrial upper atmosphere through transport of oxygen ions by the intense Earth wind. In this paper, we develop a one-dimensional chemical model that can solve for the ionic and neutral compositions of oxygen isotopes by including the isotopic effects in dynamical, photolytic, and chemical processes. We first confirm that the isotopic ratios of O+, O2+, O, and O2 are nearly mass dependent, Δ17O≈0 per mil, when the isotopic effects of multiple (eddy, molecular, and ambipolar) diffusion processes are taken into account. We examine which photolytic and chemical processes can produce a strong MIF for oxygen species and select four candidates: photo-dissociative ionization of O2, photo-dissociation of O2 by Lyman-α solar emissions, charge exchange between O+ and O2+, and atomic exchanges between O and O2. We estimated the oxygen isotopic ratio to be Δ17O≈1–4 per mil at the height of 100–400km on the basis of a statistical treatment of atom mechanics. These values are smaller than those in the lunar case, and we conclude that a more rigorous quantum mechanical treatment of photo-dissociation processes will be necessary before we can make an evaluation of the role of Earth-escaping oxygen isotopes.

Anomalously low solar extreme‐ultraviolet irradiance and thermospheric density during solar minimum

Solar activity during 2007–2009 was very low, and during this protracted solar minimum period, the terrestrial thermosphere was cooler and lower in density than expected. Measurements from instruments on the SOHO and TIMED spacecraft, and by suborbital rocket flights, indicate that solar extreme‐ultraviolet irradiance levels were lower than they were during the previous solar minimum. Analysis of atmospheric drag on satellite orbits indicate that the thermosphere was lower in density, and therefore cooler, and than at any time since the beginning of the space age. However, secular change due to increasing levels of carbon dioxide and other greenhouse gases, which cool the upper atmosphere, also plays a role in thermospheric climate. Simulations by the NCAR Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model are compared to thermospheric density measurements, yielding evidence that the primary cause of the low thermospheric density was the unusually low level of solar extreme‐ultraviolet irradiance.

Metrics for solar wind prediction models: Comparison of empirical, hybrid, and physics‐based schemes with 8 years of L1 observations

Space weather effects on technological systems originate with energy carried from the Sun to the terrestrial environment by the solar wind. In this study, we present results of modeling of solar corona‐heliosphere processes to predict solar wind conditions at the L1 Lagrangian point upstream of Earth. In particular we calculate performance metrics for (1) empirical, (2) hybrid empirical/physics‐based, and (3) full physics‐based coupled corona‐heliosphere models over an 8‐year period (1995–2002). L1 measurements of the radial solar wind speed are the primary basis for validation of the coronal and heliosphere models studied, though other solar wind parameters are also considered. The models are from the Center for Integrated Space‐Weather Modeling (CISM) which has developed a coupled model of the whole Sun‐to‐Earth system, from the solar photosphere to the terrestrial thermosphere. Simple point‐by‐point analysis techniques, such as mean‐square‐error and correlation coefficients, indicate that the empirical coronal‐heliosphere model currently gives the best forecast of solar wind speed at 1 AU. A more detailed analysis shows that errors in the physics‐based models are predominately the result of small timing offsets to solar wind structures and that the large‐scale features of the solar wind are actually well modeled. We suggest that additional “tuning” of the coupling between the coronal and heliosphere models could lead to a significant improvement of their accuracy. Furthermore, we note that the physics‐based models accurately capture dynamic effects at solar wind stream interaction regions, such as magnetic field compression, flow deflection, and density buildup, which the empirical scheme cannot.

A first-principles model of spectrally resolved 5.3 μm nitric oxide emission from aurorally dosed nighttime high-altitude terrestrial thermosphere

[1] The spectrally resolved nighttime 5.3 μm emission from NO observed by the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS-1A) experiment aboard space shuttle Discovery at 195 km tangent altitude during a strong auroral event is modeled using a first-principles kinetics model. An appropriate SHARC (Strategic High Altitude Radiance Code) Atmospheric Generator (SAG) is dosed with an IBC class III aurora. The spectrally resolved fundamental vibration-rotation band emissions from NO around 5.3 μm resulting from impacts of ambient NO with O as well as reactions of N atoms with O2 are calculated under steady state conditions. The calculated results, using a local translational temperature derived from the observed spectrum, are in excellent agreement with the CIRRIS-1A observations, validating our model. The importance of the accurate nascent vibrational and rotational distribution of chemically produced NO as well as the collisonally induced rotation-to-vibration relaxation of rotationally hot NO is pointed out.

On the rate coefficient of the N(2D)+O2→NO+O reaction in the terrestrial thermosphere

The temperature dependence of the rate coefficient of the N(2D)+O2→NO+O reaction has been determined using ab initio potential energy surfaces (PES) and classical dynamics. The calculation agrees with the recommended rate coefficient at 300 K (∼110 km altitude). The rate coefficient is given by the expression k(T) = 6.2 × 10−12(T/300) cm3/s/molec. In contrast to the nearly temperature‐independent value of this rate coefficient previously recommended, the value given here increases by almost a factor of about four as the altitude increases from 110 to 200 km. It is also shown that even though N(2D) atoms in the thermosphere are produced with large translational energies, using the value of the rate coefficient at the local temperature introduces negligible error in the amount of NO produced. The new value of this rate coefficient will significantly increase the amount of NO computed in the aeronomic models causing a re‐evaluation of the heat budget and temperature and density structure of the thermosphere. In particular, implications of the larger rate coefficient for the recent observations of dramatically enhanced 5.3 μm emission from NO in the thermosphere due to solar storms are discussed.

Nitric oxide production in collisions of hot O(3P) atoms with N2

Energetic oxygen atoms play a central role in the heat and energy balance of the terrestrial thermosphere. The reaction between hot O(3P) atoms and N2 has been suggested as a source of shuttle glow in low‐Earth orbits due to the formation of nitric oxide. We report cross sections and rate coefficients for the production of nitric oxide in the reaction between hot O(3P) atoms and N2 and show that vibrational excitation of N2 significantly enhances the reaction rate coefficients. Results are found to be in agreement with shock‐tube experiments as well as with crossed molecular beam data.

EFFECTS ON THE IONOSPHERE DUE TO PHENOMENA OCCURRING BELOW IT

The terrestrial thermosphere and ionosphere form the most variable part of theEarth's atmosphere. Because our society depends on technological systems thatcan be affected by thermospheric and ionospheric phenomena, understanding,monitoring and ultimately forecasting the changes of the thermosphere–ionosphere system are of crucial importance to communications, navigation and the exploration of near-Earth space. The reason for the extreme variability of the thermosphere–ionosphere system isits rapid response to external forcing from various sources, i.e., thesolar ionizing flux, energetic charged particles and electric fields imposed via the interaction between the solar wind, magnetosphere and ionosphere, as well as coupling from below (“meteorological influences”) by the upward propagating, broad spectrum,internal atmospheric waves (planetary waves, tides, gravity waves) generated in thestratosphere and troposphere. Thunderstorms, typhoons, hurricanes, tornadoes andeven seismological events may also have observable consequences in the ionosphere.The release of trace gases due to human activity have the potential to cause changes inthe lower and the upper atmosphere.A brief overview is presented concerning the discoveries and experimentalresults that have confirmed that the ionosphere is subject to meteorologicalcontrol (especially for geomagnetic quiet conditions and for middle latitudes).D-region aeronomy, the winter anomaly of radiowave absorption, wave-liketravelling ionospheric disturbances, the non-zonality and regional peculiaritiesof lower thermospheric winds, sporadic-E occurrence and structure, spread-Fevents, the variability of ionospheric electron density profiles and Total ElectronContent, the variability of foF2, etc., should all be considered in connection withtropospheric and stratospheric processes. “Ionospheric weather”, as a part of spaceweather, (i.e., hour-to-hour and day-to-day variability of the ionospheric parameters)awaits explanation and prediction within the framework of the climatological, seasonal,and solar-cycle variations.

Cooling mechanisms of the planetary thermospheres: the key role of O atom vibrational excitation of CO2 and NO.

Cooling due to infrared emissions from O atom excited CO2 and NO is a critically important process in the thermal budget of the terrestrial thermosphere. Increasing CO2 density due to human activity makes the role of its emission particularly worthy of quantitative evaluation. Furthermore, the O atom excited 15 microns CO2 emission has a unique role in the lower thermosphere of Venus where it is the only significant cooling mechanism; it is also an important process in the Martian thermosphere. The experimental and theoretical status of these rate coefficients is reviewed and the unsatisfactory current state of knowledge is pointed out.

A preliminary semiempirical thermosphere model of Mars: DTM‐Mars

A semiempirical thermosphere model of Mars has been constructed based on the DTM algorithm that was developed for the terrestrial thermosphere. DTM‐Mars reproduces the observed densities with a 1‐σ model uncertainty of approximately 35% outside dust season. During dust storms the uncertainty increases by approximately a factor two. The data used in this study have been derived from the Mars Global Surveyor accelerometer observations as well as from analysis of precise orbit determination results. The temperature modeling is based on the Mars‐GRAM 2000 [Justus and James, 2000] and the MTGCM [Bougher et al., 2000] models, while the CO2, O, and He constituent modeling has been achieved through the adjustment of model coefficients to density data. DTM‐Mars is preliminary because the geographical and solar activity coverage of the assimilated density data currently available is not representative of all atmospheric conditions. For example, the effect of dust storms on the thermospheric density is only represented by a temperature increase on a planetary scale, because the data did not allow the determination of a semidiurnal variation caused by local effects in the lower atmosphere. The model accuracy will be improved in the future by assimilating density data taken under different atmospheric conditions, for example, from the Mars Odyssey mission, once these become available.

A model of odd nitrogen in the aurorally dosed nighttime terrestrial thermosphere

A model of the production and loss of odd nitrogen species (mainly, N(4S), N(2D), NO, and NO+) and the enhanced vibration‐rotation band emission from NO in the infrared from the aurorally dosed terrestrial nighttime thermosphere is described. This model is assessed by analyzing the observations of the fundamental (Δv = −1, ∼5.3 μm) and overtone (Δv = −2, ∼2.7 μm) NO vibration‐rotation band limb emissions made by a Michelson interferometer and radiometer, respectively, aboard the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS‐1A) experiment on the space shuttle Discovery during an auroral event. The auroral dosing along the line of sight is inferred from the 2.7‐μm radiance profiles using a self‐consistent procedure. The dosing obtained is then used in the model to predict the spectrally resolved emission in the 5.3‐μm region. The calculated overtone radiance profiles agree with the measured ones at lower tangent altitudes, where the signal‐to‐noise ratio is large. The calculation, however, underpredicts the observed radiance, both fundamental and overtone, at higher tangent altitudes by a factor of ∼3 and gives a colder rotational temperature for the rotationally hot component of the spectrally resolved emission from nascent NO. The causes of this discrepancy and its impact on the densities of the odd N species are discussed.

Impact of the new rate coefficients for the O atom vibrational deactivation and photodissociation of NO on the temperature and density structure of the terrestrial atmosphere

Recent laboratory work has arrived at a value of the rate coefficient for the room temperature O atom vibrational relaxation of NO(v=1) which is nearly one third the previously accepted value [Fernando and Smith, 1979]. Laboratory measurements have also established a new value for the rate coefficient for the photodissociation of NO which is ∼1.6 times the previously accepted value. Since the NO(v=1→v=0) emission, around 5.3 μm, is a very important cooling process in the lower terrestrial thermosphere, the new values of the two rate coefficients lead to a decrease in the amount of NO as well as the rate at which it cools. Using the global mean model [Roble, 1995] of the mesosphere, thermosphere, and ionosphere, we find that the new rate coefficients introduce large changes in the thermal and density structure of the atmosphere. The resulting model atmosphere appears unrealistic. We find that these large changes are moderated and the resulting neutral temperatures agree better with the Mass Spectrometer Incoherent Scatter (MSIS) model when the value of the CO2+O rate coefficient for excitation of the bending vibration is increased two fold to the value arrived at by modeling the 15 μm emission from CO2 from the lower terrestrial thermosphere. Finally, we describe the results of a number of runs with the thermosphere/ionosphere/mesosphere electrodynamics general circulation model (TIME‐GCM) to examine the global temperature, composition, and circulation changes that result from using the new rates for both NO and CO2.

Observation of highly rotationally excited NO + emissions in the thermosphere

Ro-vibrational band head emissions from highly rotationally-excited NO +( v, J) ( J⩾90) have been observed for quiescent and aurorally disturbed conditions at tangent altitudes between approximately 100 and 215 km in the terrestrial thermosphere. The formation of these band heads in NO + requires very high rotational excitation with rotational energy of at least 1.9 eV. The data were obtained between 28 and 30 April 1991 with the CIRRIS-1A cryogenic interferometer from on board the space shuttle. These are the first observations of non-thermal rotational emissions from NO + in the airglow. Several possible sources of these non-thermal emissions are discussed. This is the third in a series of recent discoveries (all from the CIRRIS-1A data base) of significant non-thermal rotational effects in an important atmospheric species.