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Thermal equilibrium in planetary atmospheres occurs at altitudes where the ion, electron, and neutral temperatures are equal. Thermal equilibrium is postulated to occur in the collision-dominated lower ionosphere. This postulated altitude is above the lower boundary of all empirical models of planetary ionospheres. Physics-based model predictions of the altitude can not be validated due to a lack of adequate simultaneous observations of temperature profiles. This study presents temperature profiles from simultaneous observations on Atmosphere Explorer–C below 140 km and quiet-time neutral observations from TIMED/GUVI over Millstone Hill. These are compared with profiles from physics-based models with a discussion of their respective limitations. We conclude that there does not yet exist a quantitative understanding of the ion, electron, and neutral thermalization processes in low-altitude planetary ionospheres. Progress on this topic requires an adequate database of simultaneous ion, electron, and temperature profiles in the 110 to 140 km altitude range.

In this paper we analyze temperature data from the Near-Infrared Spectrometer (NIRS) instrument on Remote Atmospheric and Ionospheric Detection System experiment on the International Space Station and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite during June and July 2010 to investigate structures of the migrating semidiurnal (12 h) and quaddiurnal (6 h) tides in the upper mesosphere and lower thermosphere. Temperature measurements from the NIRS and SABER instruments allow us to examine the tides from the stratosphere to the lower thermosphere. We find that the amplitude of the migrating 6 h tide grows from ~5 K near 100 km altitude to ~30 K near 130 km. The amplitudes of the tide at altitudes accessible by NIRS are much larger than those previously reported at lower altitudes from the Aura Microwave Limb Sounder and the SABER instruments. The amplitude of the 12 h tide in the NIRS data shows two peaks in the lower thermosphere (between 95 and 130 km) with a maximum around 60 K occurring in the winter hemisphere near 20° latitude and a second maximum around 40 K occurring in the summer hemisphere near 30° latitude. The structure of the migrating terdiurnal (8 h) tide is also investigated in the NIRS data and shows increasing amplitude with altitude over a broad range of latitudes, roughly between 50°N and 30°S. Altitudinal variations seen in the 6, 8, and 12 h tides suggest an evolving mix of various Hough modes.

Observations of molecular oxygen are difficult to make in the Earth's atmosphere between 140 and 200 km altitude. Perhaps the most accurate measurements to date have been obtained from satellite instruments that measure solar occultations of the limb. These do provide height-resolved O2 density measurements, but the nature of this technique is such that the temporal/spatial distribution of the measurements is uneven. Here a new space-based technique is described that utilizes two bright dayglow emissions, the (0,0) transition of the O2 atmospheric band and the O I (630 nm), to derive the height-resolved O2 density from 140 to 180 km. Data from the Remote Atmospheric and Ionospheric Detection System, which was placed on the International Space Station in late 2009, are used to illustrate this technique. The O2 density results for periods in May 2010 that were geomagnetically quiet and disturbed are compared to model predictions.

The Global Ultraviolet Imager (GUVI) onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite senses far ultraviolet emissions from O and N2 in the thermosphere. Transformation of far ultraviolet radiances measured on the Earth limb into O, N2, and O2 number densities and temperature quantifies these responses and demonstrates the value of simultaneous altitude and geographic information. Composition and temperature variations are available from 2002 to 2007. This paper documents the extraction of these data products from the limb emission rates. We present the characteristics of the GUVI limb observations, retrievals of thermospheric neutral composition and temperature from the forward model, and the dramatic changes of the thermosphere with the solar cycle and geomagnetic activity. We examine the solar extreme ultraviolet (EUV) irradiance magnitude and trends through comparison with simultaneous Solar Extreme EUV (SEE) measurements on TIMED and find the EUV irradiance inferred from GUVI averaged (2002–2007) 30% lower magnitude than SEE version 11 and varied less with solar activity. The smaller GUVI variability is not consistent with the view that lower solar EUV radiation during the past solar minimum is the cause of historically low thermospheric mass densities. Thermospheric O and N2 densities are lower than the NRLMSISE-00 model, but O2 is consistent. We list some lessons learned from the GUVI program along with several unresolved issues.

[1] Thermospheric temperatures derived from limb observations of the O2 A-Band (0,0) emission spectrum obtained from January–July 2010, with the Remote Atmospheric and Ionospheric Detection System (RAIDS) Near Infrared Spectrometer (NIRS) aboard the International Space Station, are compared to temperature results from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment. To account for a lack of simultaneous common volume observations, the observed temperatures were scaled by the NRLMSIS-00 model temperatures for comparison. It was found that on average SABER, temperatures are warmer than NIRS at all altitudes between 90 and 140 km. In the altitude range 90–100 km, the SABER temperatures were warmer than NIRS by ~10 K consistent with previous validation experiments and in agreement with Optical Spectrograph and Infrared Imaging System (OSIRIS) O2 A-band comparisons in the polar mesopause region. At higher altitudes, the differences between SABER and NIRS exceed 30 K on average. Thus, the NIRS observations reinforce the idea that the SABER temperatures are too warm below ~110 km; and above that altitude, they are increasingly in error consistent with expectations based on estimated inaccuracies in the retrieval algorithm. Large standard deviations of the SABER and NIRS ratios are reflective of substantial variability of the thermospheric temperatures throughout the region.

[1] Measurements of the Earth's low latitude thermosphere returned by the ionization gauge on the Streak mission are reported and discussed. The measurements are of the amount of gas rammed into the sensor by its passage through the thermospheric medium. They were obtained in the dusk sector in the altitude range 130–330 km and are shown to be strongly structured by the geomagnetic field. Similarities to the structure of the equatorial ionization anomaly are discussed. The structure is interpreted as being due to rapid (several hundred meters per second) meridional winds having an antisymmetric pattern with respect to the geomagnetic equator. The measurements are interpreted in light of results from other missions and are shown to fit well with ideas based on complementary measurements from the Dynamics Explorer 2 mission discussed as the Equatorial Temperature and Wind Anomaly. Several features of these winds are described and discussed, including their altitude dependence, how they form convection cells that extend to high latitude, and how the wind amplitudes vary with geographic longitude with an apparent wavenumber one variation. The latter characteristic is shown to be consistent with being the signature of tidal variations observed by others. Approximate calculations utilizing published values for the pertinent parameters are used to show that heating from the dissipation due to ion drag within the ionospheric F region is a dominant driver of the inferred winds.

In this paper, we examine the nighttime ionosphere climatology structure in the low latitude region and discrepancies between Global Ultraviolet Imager (GUVI) observations and the IRI model predictions using (1) the magnetic zonal mean of electron number density as a function of altitude and magnetic latitude, (2) vertical electron density profiles at various levels of F10.7 index, (3) nighttime descent and magnitude decrease of the ionosphere, (4) point-to-point comparisons of F-peak height (hmF2) and density (NmF2), and (5) the magnetic longitudinal variations of hmF2 and NmF2. The data collected from the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) mission since its launch in December 2001 have provided great opportunities for many scientific investigations of the ionosphere. In this analysis, we investigate the climatology of the nighttime low-latitude ionosphere under low geomagnetic activity (kp ⩽ 4) using the electron density profiles inferred from the airglow measurements obtained by the GUVI aboard the TIMED spacecraft and compared with the results obtained from IRI (International Reference Ionosphere) model-2001. The observed climatology is an essential tool for further understanding the electrodynamics in the low-latitude region and improving the model’s prediction capability. The time range of the GUVI data used in this study is from 2002 (day 053) to 2006 (day 304), and the IRI model predictions were produced at every GUVI location. The ionosphere observed is generally of greater density than what IRI predicts throughout the night for all four seasons for low and moderate solar activity while the model over-predicts the electron density near the F-region peak at high solar activity before midnight. Observations show that the height of the F-region peak has a steep descent from dusk to midnight and near midnight the height of layer is insensitive to solar conditions, significantly different than what is predicted by IRI. Longitudinal features shown in GUVI data are present in the low-latitude ionosphere after sunset and continue through to midnight after which the low-latitude ionosphere is largely zonally symmetric.

A portion of waves generated by deep convection have scales and amplitudes large enough to be detected by space borne instruments. We have analyzed temperature data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite for sub-tidal scale fluctuations. Filtering was applied both vertically and horizontally to extract wave variances. We have analyzed the altitude region between 70 and 130 km and focus on the variances at equatorial latitudes for the altitude region between 70 and 120 km as a function of season, local time intervals, geographical location and altitude. We find significant variances where convection is particularly prolific (Intertropical Convergence Zone) and at altitudes where wave trapping is known to be favored (e.g., the lower thermospheric duct). The locations of significant variances persist from year to year. Standard deviations of a few of tens of kelvins are found. We have also performed simulations of the response to deep tropical convection with a time dependent, high-resolution fully compressible dynamical model. Our simulations give wave amplitudes that agree reasonably well with the observed amplitudes and show layering that is consistent with the observations. Our main finding is that significant variations seen in TIMED/SABER temperature data have a convective wave source and are concentrated in layers where thermal ducts occur.

This paper discusses the connection between changes in Earth's thermosphere and ionosphere induced by changes in the Earth's local space environment (or “space weather”) and the phenomena observed in far ultraviolet images of the Earth. Two new experiments, the Global Ultraviolet Imager (GUVI) and the Special Sensor Ultraviolet Imager (SSUSI), will provide a new capability for monitoring changes in thermospheric composition and ionospheric density as they change in response to space weather. These sensors provide a ten-fold improvement in spatial and temporal resolution and a greater than ten-fold improvement in sensitivity over that provided by sensors on the POLAR and IMAGE satellites. These sensors are expected to provide new insights into the mesoscale coupling between the ionosphere and thermosphere, as well as allowing us to develop a better specification of the high latitude convection electric field pattern.

To obtain information regarding the spatial scales involved in lower thermospheric composition changes in the auroral zone, simultaneous observations were carried out using photometers at Kangerlussuaq and Narsarsuaq, Greenland, two sites separated by ∼750 km in distance. At night, Kangerlussuaq, located at 67°N geographic is most often at the northern edge of the auroral oval, while Narsarsuaq, at the southern tip of Greenland, is more often in or at the southern edge of the auroral oval. On January 29–30, 1998, moderate auroral activity was recorded from both sites. Besides the photometer systems, observations were obtained during part or all of this period from Polar satellite instruments, from the Greenland magnetometer chain, from the CANOPUS chain of magnetometers and photometers, from DMSP, and from the Sondrestrom incoherent scatter radar. The analysis of these data show the necessity of considering both nonlocal and local sources in modeling aurorally induced changes in lower thermospheric composition.

An analysis is reported of near zenith viewing brightness observations of O I 844.6 nm, N2+ ING 391.4 nm, N2 2PG 337.1 nm, O I 555.7 nm, and O I 630.0 nm recorded by photometers onboard the ARIA II rocket launched from Poker Flat, Alaska, on February 12, 1994. The rocket passed through diffuse aurora mixed with intermittent soft precipitation on the upleg followed by much more structured precipitation on the downleg. The most meaningful analysis of the data comes from the upleg portion of the flight and is reported here. The primary objective of the investigation was to quantify possible departures of the density profiles of N2 and O from their representations within the MSIS model. To do so requires knowledge of the electron precipitation responsible for the observed emissions. This was obtained by fitting electron transport results to altitude profiles of in situ electron spectrometer data and 391.4 nm photometer data. Good agreement with profile shapes was achieved with precipitation characterized by a Maxwellian distribution having a characteristic energy E0 of 1.75 keV. The strength of the precipitation was determined by the brightness of the 391.4 nm profile which yielded an energy flux Q of 3.08 ergs cm−2 s−1. Simultaneous good fits to the low-altitude 391.4 nm and O I 844.6 nm data required a scaling of the MSIS-based O density profile by a factor of 0.45. This factor amounts to a significant reduction in O and is close to that obtained from an analysis of coincident ground-based optical data [Christensen et al., 1997]. Perhaps more significant is a clear sign of an abrupt composition change as the rocket approached apogee based on the observed brightness ratios of 844.6/391.4 and 557.7/391.4. Both exhibit the same gross structure as well as fine structure arising from intermittent soft precipitation. Their ratios are observed to drop by more than a factor of 2 along a portion of the trajectory as the rocket passed above 218 km. Upon achieving such heights, a close relationship exists between these ratios and the ratio of O to N2 column densities (O/N2). Full consideration of the relationships between the observed brightnesses of O I 844.6 nm, O I 557.7 nm, and 391.4 nm leads to the conclusion that the rocket entered a region of enhanced N2 density with continued depletion of the O density similar to what was observed prior to entering this region. Relative to MSIS, the N2 densities are at least a factor of 2 higher while the O densities are at least a factor of 2 smaller leading to a reduction in MSIS-based O/N2 of more than a factor of 4.

Observations of the neutral wind profiles in the post-midnight sector of the auroral oval show the development of a narrow jet near 110–120 km altitude during disturbed conditions. The shears on the bottom side of the jet are highly unstable with Richardson numbers near or below the critical value of 0.25. The unstable shears imply that turbulence and, consequently, the eddy diffusivity will be enhanced in that part of the atmosphere.

The ARIA II experiment carried out on February 12, 1994, provided the neutral wind and electron density measurements needed to calculate the neutral-driven field-aligned current densities. In situ rocket measurements were made approximately 60 min after the onset of an auroral substorm in a moderately disturbed (Kp=5−) postmidnight auroral oval over Alaska. Two chemical release rockets deployed four widely separated TMA trails, and E region neutral wind profiles were obtained from the motion of those trails. An instrumented rocket launched near-simultaneously measured the electric fields, electron densities, and neutral composition. The divergence and the vertical component of the vorticity in the neutral flow were obtained from the neutral wind profiles, and those values, together with the measured electron densities, were used to calculate the neutral-driven field-aligned current densities. Our best estimate is that the current density below 114 km was effectively zero. Above 114 km the field-aligned current was downward with a peak value 0.23 μA m−2. Our results indicate that, although the wind-driven current was a significant contributor to the total field-aligned current in the recovery phase of the substorm, the dominant sources of the field-aligned current were due to conductivity gradients and the divergence in the ionospheric electric field. The measurements also show that the current density profile has vertical structure with a scale of ∼ 10 km due to height variations in the vorticity, divergence, and conductivity profiles.

A study is presented that discusses the information content of a zenith viewing brightness ratio for optically thin O and N 2 emissions arising from auroral electron impact excitation. The discussion focuses on the altitude dependence of the ratio and distinguishes between a topside portion and the rest which lies below. The topside is defined as the region in which the auroral electron flux is essentially constant with altitude. The lower boundary to the topside is a function of the average energy of the precipitating electrons. The profile of the brightness ratio is a function of and the ratio of O to N 2 column densities (designated as O/N 2 ). On the topside, the dependence disappears leaving a unique relationship between the brightness ratio and O/N 2 . Thus profiles of both quantities have identical shapes on the topside. The shape depends on the exospheric temperature T exo . Thus a model-based brightness ratio being used to compare with measurements on the topside must take this into account. The temperature can be quantified from measurements having good counting statistics or in their absence from an atmospheric model such as the mass spectrometer/incoherent scatter (MSIS) model. Without knowledge of , data/model comparisons must be restricted to the topside in order to uniquely specify O/N 2 . With such knowledge, however, data/model comparisons may be extended into the region below the topside. The chief advantages are better counting statistics and the decreasing dependence of the brightness ratio on T exo with decreasing altitude. Derived values of O/N 2 may be related to O density profiles throughout the lower thermosphere with the use of a model atmosphere. MSIS-83 is used in this work following the preference of J. H. Hecht and colleagues in analyzing ground-based optical data. The findings discussed above are used to analyze zenith viewing OI 844.6/N 2 + 391.4 ratio data from the Atmospheric Response in Aurora (ARIA) flights I and IV. The ARIA I data support an O concentration that is a factor of ∼1.1 above MSIS-83 (similar to the findings of Hecht et al. [1995]), while the ARIA IV data lead to a factor of ∼0.75 referenced to the ARIA IV MSIS atmosphere. Both atmospheres possess similar O/N 2 values below 120 km. Within relative calibration errors between the experiments, one may conclude that the ARIA IV O concentrations throughout the lower thermosphere (120 km - 200 km) were less than ARIA I by a factor of ∼0.7.

We test the utility of the OII 83.4 nm emission feature as a measure of ionospheric parameters. Observed with the Remote Atmospheric and Ionospheric Detection System (RAIDS) Extreme Ultraviolet Spectrograph on the International Space Station (ISS), limb profiles of 83.4 nm emissions are compared to predicted dayglow emission profiles from a theoretical model incorporating ground-based electron density profiles measured by the Millstone Hill radar and parameterized by a best-fit Chapman-{\alpha} function. Observations and models are compared for periods of conjunction between Millstone Hill and the RAIDS fields-of-view. These RAIDS observations show distinct differences in topside morphology between two days, 15 January and 10 March 2010, closely matching the forward model morphology and demonstrating that 83.4 nm emission is sensitive to changes in the ionospheric density profile from the 340 km altitude of the ISS during solar minimum. We find no significant difference between 83.4 nm emission profiles modeled assuming a constant scale height Chapman-{\alpha} best-fit to the ISR measurements and those assuming varying scale height.

[1] Observations of airglow emission using the RAIDS (Remote Atmospheric and Ionospheric Detection System) instruments on the International Space Station Kibo module are reported and compared to a photochemical model of the emission process. Launched in Sept. 2009, RAIDS performed routine observations of the O2(b1Σ → X3Σ) Atmospheric band (O2 A-band) transition during solar minimum conditions from October 2009 to December 2010. Limb brightness of the (0,0), (0,1) and (1,1) vibration band emissions were measured in the altitude range 80 to 180 km with the Near Infrared Spectrometer (NIRS) instrument, one of eight limb viewing instruments in the RAIDS experiment. Comparison of observed brightness profiles with the model shows very good agreement for the (0,0) and (0,1) bands. The model underestimates the (1,1) brightness profiles throughout the region, especially near the peak. Reasonable variations of composition and selected rate constants do not account for the underestimation of (1,1) band brightness. A contributing factor could be in the assumption of detailed balance and the accepted energy transfer pathways that redistribute energy between the v = 0 and v = 1 states.

[1] We present the first published measurement of an altitude profile of the O II 61.7 nm emission, a dayglow feature that can be used to monitor photoionization of O in the lower thermosphere. This photoionization process also results in the O II 83.4 nm emission that, unlike 61.7 nm, is resonantly scattered by ionospheric O+. Although ionospheric characteristics can be inferred from the shape and intensity of 83.4 nm altitude profiles, the interpretation can result in nonunique ion density profiles if the intensity of this source of photons that illuminates the ionosphere from below is unknown. The 61.7 nm emission provides a means to test the accuracy of current models used to calculate the intensity of that source. The data presented here were collected by the Remote Atmospheric and Ionospheric Detection System from the International Space Station on 29 October 2009. The measured 61.7 nm profiles show a steeper drop in intensity below 260 km, where the emission peaks, compared to our model calculations. While the current analysis cannot resolve if the discrepancy is caused by inaccuracies in our model thermospheric composition, photoabsorption cross sections, or both, a 15%–20% increase in the effective O2 photoabsorption at 61.7 nm produces the best qualitative match to the measured profile. Ostensibly, 61.7 nm measurements could replace these model calculations as a more direct measure of the intensity of the 83.4 nm photon source region. In either case, accurate specification of local thermospheric neutral species remains an important component of daytime ionospheric remote sensing.

[1] During the space shuttle main engine burn, some 350 t of water vapor are deposited at between 100 and 115 km. Subsequent photodissociation of water produces large plumes of atomic hydrogen that can expand rapidly and extend for thousands of kilometers. From 2002 to 2007, the Global Ultraviolet Imager (GUVI) on NASA's Thermosphere Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite imaged many of these hydrogen plumes at Lyman α (121.567 nm) while viewing in the nadir. The images reveal rapid plume expansion and occasional very fast transport to both north and south polar regions. Some plumes persist for up to 6 d. Near-simultaneous direct detections of water vapor were made with the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) instrument, also on TIMED. We compare the spreading of the hydrogen plume with a two-dimensional model that includes photodissociation as well as both vertical and horizontal diffusion. Molecular diffusion appears to be sufficient to account for the horizontal expansion, although wind shears and turbulent mixing may also contribute. We compare the bulk motion of the observed plumes with wind climatologies derived from satellite observations. The plumes can move much faster than predictions of wind climatologies. But dynamical processes not contained in wind climatologies, such as the quasi-two-day wave, can account for at least some of the high speed observations. The plume phenomena raise a number of important questions about lower thermospheric and mesospheric processes, ranging from dynamics and chemistry to polar mesospheric cloud formation and climatology.

The Remote Atmospheric and Ionospheric Detection System (RAIDS) is new NASA experiment studying the Earth's thermosphere and ionosphere from a vantage point on the International Space Station (ISS). RAIDS along with a companion hyperspectral imaging experiment were launched in September 2009 to operate as the first US payload on the Japanese Experiment Module-Exposed Facility. The scientific objectives of the RAIDS experiment are to study the temperature of the lower thermosphere (100-200 km), to measure composition and chemistry of the lower thermosphere and ionosphere, and to measure the initial source of O+ 83.4 nm emission. The RAIDS sensor complement includes three photometers, three spectrometers, and two spectrographs which span the wavelength range 50-874 nm and scan or image the atmospheric limb 90-300 km. After installation aboard the ISS, RAIDS underwent a 30-day checkout period before entering science operations. RAIDS is serving as a pathfinder for atmospheric remote sensing from the ISS, and the experiment team gained valuable operational insights using this space platform throughout the first year of the mission. This paper describes key aspects of experiment performance relevant to interpreting RAIDS science data and designing future atmospheric remote sensing experiments for the ISS.

The transmission variability is reported for two filters in the EUV, where the filters were supported on an 80% transmission nickel mesh and fabricated by means of a vacuum deposition technique. The first film consisted of 2500 A-thick indium, deposited on 500 A-thick tin, and had its primary bandpass in the 740-960 A range. The second consisted of 1800 A-thick tin and 2000 A-thick carbon, with a bandpass of 500-750 A. At the end of 10 months, the transmission of both filters was measured to check variations. It is demonstrated that the EUV transmission of such filters can change over the typical lifetime of satellite missions, and that such variation depends on the storage environment. The use of vacuum, rather than dry nitrogen storage is recommended.

[1] The satellite-borne Global Ultraviolet Imager (GUVI) has produced more than 20 images of NASA Space Shuttle main engine plumes in the lower thermosphere. These reveal atomic hydrogen and, by inference, water vapor transport over hemispherical-scale distances with speeds much faster than expected from models of thermospheric wind motions. Furthermore, the hydrogen plumes expand rapidly. We find rates that exceed the horizontal diffusion speed at nominal plume altitudes of 104-112 km. Kelley et al. (2009) have proposed a 2-D turbulence mechanism to explain the observed spreading rates (and rapid advection) of the plumes. But upon further investigation, we conclude that H atom diffusion can indeed account for the observed expansion rates by recognizing that vertical diffusion quickly conveys atoms to higher altitudes where horizontal diffusion is much more rapid. We also find evidence for H atom production directly during the Shuttle's main engine burn.

Limb images of the low latitude UV O2 Herzberg I emission were obtained from a low Earth orbit spacecraft in early 1988. The layer displays patchy, sometimes horizontally periodic, spatial variability on scales of tens of km with amplitude up to 20%. We interpret periodic wavelike features in terms of perturbations associated with gravity wave propagation through the layer. The putative waves are shown to have horizontal wavelength about 15 km, similar vertical wavelength, and temperature oscillation roughly equal to or exceeding the observed emission perturbation.

The Remote Atmospheric and Ionospheric Detection System (RAIDS) is a suite of three photometers, three spectrometers, and two spectrographs which span the wavelength range 50-874 nm and remotely sense the thermosphere and ionosphere by scanning and imaging the limb. RAIDS was originally designed, built, delivered, and integrated onto a NOAA TIROS satellite in 1992. After a series of unfruitful flight opportunities, RAIDS is now certified for flight on the Kibo Japanese Experiment Module-Exposed Facility (JEM-EF) aboard the International Space Station (ISS) in September 2009. The RAIDS mission objectives have been refocused since its original flight opportunity to accommodate the lower ISS orbit and to account for recent scientific progress. RAIDS underwent a fast-paced hardware modification program to prepare for the ISS mission. The scientific objectives of the new RAIDS experiment are to study the temperature of the lower thermosphere (100-200 km), to measure composition and chemistry of the lower thermosphere and ionosphere, and to measure the initial source of OII 83.4 nm emission. RAIDS will provide valuable data useful for exploring tidal effects in the thermosphere and ionosphere system, validating dayside ionospheric remote sensing methods, and studying local time variations in important chemical and thermal processes.

The Remote Atmospheric and Ionospheric Detection System (RAIDS) is a suite of eight sensors covering wavelengths from 55 to 874 nm that has been developed for comprehensive remote sensing of the upper atmosphere. Initially designed to orbit on a higher-altitude TIROS satellite, the RAIDS experiment has been refurbished for a new mission on the International Space Station Japanese Experiment Module Exposed Facility (JEM-EF). RAIDS measures the altitude profiles of dayglow and nightglow emissions for specification of key ionospheric and thermospheric constituents. This paper details four of the RAIDS sensors that will measure spectral features in the extreme (55-110 nm), far (130-180 nm), middle (200-300 nm), and near (300-400 nm) ultraviolet bands. The radiometric and spectral recharacterization of these sensors is highlighted, along with an overview of the primary features that this combination of experiments will measure to provide an unique perspective on the response of the ionosphere and thermosphere to space weather events.

[1] ΣO/N2 ratios in the Earth's thermosphere are measured by the Global Ultraviolet Imager (GUVI) on the TIMED satellite, and demonstrate strong 9 and 7 day oscillations in 2005 and 2006, respectively, that are well correlated with the solar wind speed and Kp index. This work builds on the recently discovered connection between rotating solar coronal holes and thermospheric mass density variations. The work described here is the first description of geomagnetically forced periodicities in neutral composition. Furthermore, these observations provide the first definitive proof that the processes creating neutral composition changes during geomagnetic storms occur continuously at all activity levels and all over the world. The ΣO/N2 response versus the mass density response indicates the important role of vertical winds at high latitudes while thermal expansion dominates at lower latitudes.

[1] Near peak activity of two X-class solar flares, on 28 October and 4 November 2003, the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Solar EUV Experiment (SEE) instrument recorded order of magnitude increases in solar EUV irradiance, the TIMED/Global Ultraviolet Imager (GUVI) observed simultaneous increases in upper atmosphere far ultraviolet (FUV) dayglow, and the European Incoherent Scatter Scientific Association (EISCAT) radar and the Ionospheric Occultation Experiment onboard the PICOSat spacecraft recorded corresponding changes in E-region electron densities. Calculations of the FUV dayglow and electron density profiles using Version 8 SEE flare spectra overestimate the actual observed increases by more than a factor of 2.0. This prompted the development of an alternative approach that uses the FUV dayglow and associated E-layer electron density profiles to derive and validate, respectively, the increases in the solar EUV irradiance spectrum. The solar EUV spectrum required to produce the FUV dayglow is specified between 45 and 27 nm by SEE’s EGS measurements, between 27 and 5 nm by GUVI dayglow measurements, and between 5 and 1 nm using a combination of the GOES X-ray data and the NRLEUV model. The energy fluxes in the 5- to 27-nm bands (at 5–10, 10–15, 15–20, and 20–27 nm) are randomly varied in search of combinations such that the full spectrum (λ < 45 nm) replicates the GUVI dayglow observations. In contrast to the Version 8 SEE XPS observations, solar EUV spectra derived using the multiband yield approach produce electron densities that are consistent with those observed independently. The new multiband yield algorithm thus provides a unique tool for independent validation of solar EUV spectral irradiance measurements using FUV dayglow observations.

[1] There is great interest in understanding how the thermosphere-ionosphere system responds to geomagnetic storms. New insights are possible using the new generation of fully coupled three-dimensional models, together with extensive ionospheric databases. The period of postsolar maximum geomagnetic storms in October and November 2003 were some of the largest storms ever recorded. In this paper, we explore how the thermosphere-ionosphere system responded to the onset of the 20 November 2003 geomagnetic storm, using the NCAR TIMEGCM. The model simulates dramatic changes in the thermospheric equatorward winds, O/N 2 , and corresponding ionospheric electron densities. The model is used as a framework to interpret an increase in the observed ionospheric total electron content, and F region electron density, in the European and North African sector, in terms of changes in the neutral gas. Corresponding compositional effects observed by the GUVI instrument on the TIMED satellite lend credence to the model results. We describe some of the important physical processes that will affect planning for the utilization of measurements from the Geospace investigations in NASA's Living With a Star Program. The study illustrates the value of measuring both the neutral and ionized gases, of obtaining quasi-global views from imaging instruments, and the synergy between satellite data, ground-based measurements, and models.

[1] We use TIMED/GUVI dayside limb observations of thermospheric far ultraviolet (FUV) dayglow to infer height profiles of total mass density during the period 2002–2004. We compare these data with total mass density derived from drag-induced changes in the orbits of satellites with perigee heights ranging from 200 to 600 km. To accommodate sampling differences, we compute the ratio of observed total mass density, filtered on a 3-day timescale, to that predicted by the NRLMSISE-00 empirical model. The GUVI densities are in good agreement with the orbit-derived densities in the 300–500 km range, where the correlation of the two independent measurements is ∼0.68 and the relative bias is less than 5%, which is within the absolute uncertainty of the drag results. Of interest is a prolonged depletion of upper thermospheric density (relative to NRLMSIS) during July 2002, when densities from both techniques were 20–35% smaller than those predicted by NRLMSIS. Our results represent the first validation of absolute densities derived from FUV limb scanning.

[1] The NASA TIMED/GUVI experiment obtained unprecedented far ultraviolet images of thermospheric composition and temperature during the intense geomagnetic storm on 20–21 November 2003. Geographic maps of the atomic oxygen to molecular nitrogen column density ratio show severe depletions that extend to the equator near the peak of the storm. This ratio is a key indicator of how the thermospheric composition is disrupted at high latitudes and how the perturbed air moves globally as a result of dynamical forcing. For example, migrating regions of low oxygen-to-nitrogen air are invariably found to correlate with high thermospheric temperatures. As well, GUVI obtained altitudinal-latitudinal (limb) images of temperature and composition, which show how the disturbances vary at different heights. The ASPEN thermospheric global circulation model was used to test our understanding of these remarkable images. The resulting simulations of thermospheric response show good agreement with GUVI data prior to the peak of the storm on 20 November. During the peak and recovery phases, serious discrepancies between data and model are seen. Although this initial attempt to model the storm is encouraging, much more detailed analysis is required, especially of the high-latitude inputs. The GUVI images demonstrate that far ultraviolet imaging is becoming a crucial component of space weather research and development.

[1] Undulations on the equatorward edge of the diffuse proton aurora have been identified by using TIMED/GUVI auroral images in the far ultraviolet wavelengths. While undulations have been previously reported on the duskside (Lui et al., 1982), GUVI observations show the undulation also occurs in the dayside, nightside, and morningside. The GUVI proton auroral images provide direct optical evidence that the undulations occur in the proton aurora. It is also the first detection of the undulation in the dayside indicating strong convection shear in the region. The undulation in the nightside, a wavy structure in the whole diffuse proton aurora, is significantly different from those in the duskside and dayside. While almost all of the undulation events are observed during magnetic storms (Dst 1000 m/s) and strong velocity shear (>0.1 s−1) within the diffuse aurora oval are necessary conditions for the undulation to occur. The SSIES data also indicate the areas with large ion drift velocity and shear move to higher latitudes in the MLT sectors toward midnight. This may explain why the undulation is rarely detected in the nightside.

[1] We present a method for measuring equatorial anomaly (EA) morphology using nighttime 135.6 nm radiance observed by the Global Ultraviolet Imager (GUVI) on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) spacecraft. The method uses the singular value decomposition to estimate an along-track intensity profile as TIMED passes over the EA. The method is unique in that it removes intensity depletions due to equatorial plasma bubbles (EPBs) from the estimated intensity profile. Thus the profiles reflect plasma distribution in response to equatorial E × B drifts and neutral winds. A set of metrics including crest maximum intensity and its latitude are extracted from the intensity profiles. EPBs are also detected. Preliminary results from this method using GUVI equinox data from 2002 are compared with results from a ground-based ionosonde EA morphology study by Whalen (2001) in the western American sector. EPB occurrence rates are also compared with results from Huang et al. (2001), who used DMSP in situ density measurements to detect EPBs. General agreement was found in both studies with some localized differences. These results indicate that this method provides a valuable means of simultaneously studying EA morphology and EPB occurrence rates. Since the TIMED spacecraft precesses through all local times in 60 days, this method can be used to extend ground-based measurements to study the global relationship between E × B drifts and plasma distribution in the EA and how these relate to the occurrence of large-scale EPBs.

[1] The coincident TIMED/Global Ultraviolet Imager (TIMED/GUVI) optical and DMSP particle observations have revealed new features of the optical signature of the polar cusp under a southward interplanetary magnetic field (IMF). We have found that cusp auroras usually take the shape of a thin arc with a width around 100–200 km. This provides the first far-ultraviolet evidence of the narrow cusp under a southward IMF [Newell and Meng, 1987]. The cusp auroras could extend down to 0800 magnetic local time (MLT) in the morningside and 1400 MLT in the duskside. Its length is about a few thousand kilometers. A large solar wind density, speed, and IMF are necessary conditions for GUVI to observe the cusp aurora. We found that the cusp location at 1200 MLT changes linearly (−10 nT Bz < 0 nT) and nonlinearly (Bz < −10 nT) with the IMF Bz. The nonlinear effect can be explained by an L−3 dependence of the Earth's equatorial magnetic field.

[1] The equatorial anomaly (EA) is host to the highest ionospheric densities on Earth. Disturbances within the EA result in plasma density depletions and large density gradients. This paper presents observations of global quiet time morphology of the EA as measured by images of nighttime ionospheric 135.6 nm radiation taken by the Global Ultraviolet Imager (GUVI) on NASA's Thermosphere, Ionosphere, and Mesosphere, Energetics and Dynamics (TIMED) spacecraft. It also presents equatorial plasma bubble (EPB) morphology as determined by detection of intensity depletions in GUVI images. The technique used for analysis is unique in that it allows for simultaneous characterization of the EA and detection of EPBs. This paper also presents extensive observations of EA and EPB morphology and shows that EA morphology can be well characterized by data taken from the 2030–2130 MLT range. Further, this paper identifies crest symmetry in intensity and latitude as an indicator of both EA and EPB morphology. For all longitudes, the crest-to-trough ratio (CTR) is shown to be well correlated with the EPB rate. While the CTR may drop with solar flux, EPB levels do not. Thus the absolute CTR is less an indicator than the change in the CTR as a function of longitude for a given season and solar flux. One significant exception to this correlation is observed in the Pacific sector during the June solstice. In this case the EPB rate is high despite a low CTR.

The Global Ultraviolet Imager (GUVI) is an imaging spectrometer on the NASA TIMED spacecraft which was launched on December 7, 2001. This instrument produces a far ultraviolet (FUV) data cube of spatial and spectral information at each step of a scan mirror - that scan mirror covers 140 deg in the cross track direction - a span that includes on limb. GUVI produces simultaneous monochromatic images at five "colors" (121.6 nm, 130.4 nm, 135.6 nm, and in broader bands at 140-150 nm and 165-180 nm) as its field of view is scanned from horizon to horizon. The instrument consists of a scan mirror feeding a parabolic telescope and Rowland circle spectrometer, with a wedge-and-strip detector at the focal plane. We describe the design, and give an overview of the environmental parameters that will be measured. GUVI is a modified version of the Special Sensor Ultraviolet Spectrographic Imager (SSUSI), which was launched on the DMSP Block 5D3 F16 satellite on October 18, 2003 and is slated to fly on DMSP satellites F17 through F20, as well. We present some results the science analysis of the GUVI data to demonstrate its relevance to the space weather community.

[1] On August 19, 2003, TIMED/GUVI detected, for the first time, two separated (double) dayside detached auroras (D-DDA) simultaneously in all the GUVI channels, 121.6 nm, 135.6 nm, LBHS, and LBHL. The D-DDA was located at magnetic latitudes around −57° and −63° (L shell 3.4 and 4.9) in the 0900–1030 MLT region. The high-latitude part of the D-DDA is much brighter than the low-latitude part. DMSP particle observation indicates that the source of the D-DDA is energetic (∼10 keV) precipitating protons/electrons from the ring current due to the solar wind dynamic pressure enhancements [Zhang et al., 2002] and/or northward turning of the IMF Bz. Observations of the D-DDA provide the first single-event evidence of multiple peaks in the statistical distribution of proton fluxes at energetic around and below 10 keV at low L-shells [Milillo et al., 2001].

The SABER instrument on TIMED continuously measures certain infrared limb radiance profiles with unprecedented sensitivity. Among these are emissions of CO 2 Q 3 at 4.3 µ m, routinely recorded to tangent heights of ~140-150 km, and NO at 5.3 µ m, seen to above 200 km. Both of these are greatly enhanced during periods of strong auroral activity, when they can be measured to ~200 km and ~300 km, respectively. We use these infrared channels of SABER and coincident far ultraviolet (FUV) measurements from GUVI on TIMED, to study the geomagnetic storm of April 2002. These all give a consistent measure of auroral energy input into the lower thermosphere at high latitudes. Emission in yet another SABER channel, near 2.0 µ m, correlates well with enhanced electron energy deposition. We also have, in the 5.3-µ m emissions from the long-lived population of aurorally produced NO, a tracer of how this energy is transported equator-ward and released over an extended period of time, a few days. In this paper, we discuss the global patterns of energy deposition into the expanded auroral oval, its transport to lower latitudes, and its loss as revealed by the NO 5.3-µ m emissions. Keywords: Aurora, CO

[1] In this work we will present a method for retrieving nighttime electron density profiles from OI 135.6 nm limb emissions measured by the Global Ultraviolet Imager (GUVI) aboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission spacecraft. The primary mechanism for 135.6 nm radiance in the nighttime thermosphere is recombination of O+ ions, and the volume emission rate is approximately proportional to the square of the electron density. Herein we describe a two-step inversion method in which we first determine the volume emission rate as a function of altitude from the radiance measurements and then use the inferred volume emission rates to determine the electron density profile. There are two important factors that we have addressed in constructing the retrieval algorithms for this problem. First, the GUVI instrument was primarily designed for day side measurements. Consequently, the signal levels on the night side are very low, and our retrieval algorithms must therefore be able to function in regions where the signals are weak. Second, since we must take the square root of the volume emission rate, it must be everywhere positive in order for the electron density to be deduced. For this reason, we have imposed nonnegativity constraints (using the methods described by Menke [1989]) on what might otherwise be discrete linear retrievals of volume emission rate. After describing the retrieval method we present an error analysis and a preliminary comparison with coincident measurements by incoherent scatter radars (ISRs). In general, the retrieved electron densities from the GUVI data agree well with the ISR data, although more coincident measurements would increase our confidence in the resulting electron density profiles.

[1] The TIMED/GUVI instrument is a far ultraviolet spectrograph that obtains images in five spectrally resolved wavelength channels. These images yield information on the dayside composition, temperature, solar EUV flux, large-scale wave structures, and auroral processes. In this paper we present an overview analysis of Earth-disk images for four seasons (March, July, and September 2002 and January 2003). Days were selected during geomagnetically quiet periods when the Sun was nearly in the orbital plane (noon orbits). Two of GUVI's five channels (designated as 135.6 and LBHS and dominated by OI 135.6 nm and short wavelength N2 LBH band emission, respectively) are used when the instrument is in its imaging mode. These data are used to derive O/N2 (column density ratio referenced to an N2 column density of 1017 cm−2). The AURIC model is used to generate a lookup table that relates O/N2 to the ratio of 135.6 to LBHS for a given solar zenith angle. Global images of derived O/N2 (designated as GUVI O/N2) are presented for the 4 days. The initial validation of the retrieved composition ratio comes from comparison with the NRLMSIS model. Good overall qualitative agreement is obtained between GUVI and NRLMSIS. Both data and model exhibit similar latitudinal behaviors on the near-solstice days, namely a distinct gradient with O/N2 decreasing from the winter to the summer hemisphere. Reductions in O/N2 in the vicinity of magnetic poles are seen in both GUVI and NRLMSIS images. Globally, O/N2 is smaller at the solstices and may be explained by the “thermospheric spoon” mechanism discussed by Fuller-Rowell [1998]. Alternatively, the greater overall values at the equinoxes may arise in part from global response to greater Joule heating at these times of the year. The sensitivity of O/N2 to scalings of the N2 LBH cross section and solar EUV below 20 nm is also addressed in response to recent papers on these topics. This initial look at the GUVI data demonstrates great promise of FUV remote sensing as a way to observe thermospheric composition changes over broad geographic scales.

[1] Remotely sensed ultraviolet emissions from the Earth's upper atmosphere are shown to mirror fluctuations in solar EUV irradiance during July 2002, including the overall increase and decrease as the Sun rotated, and episodic increases associated with multiple solar flares. The TIMED/GUVI dayglow observations are used to derive a new quantity, QEUVGUVI, which is a measure of integrated solar EUV electromagnetic energy shortward of 45 nm. Both the absolute QEUVGUVI values and their modulation by solar rotation agree well with the corresponding solar EUV energy estimated by the NRLEUV irradiance variability model. The QEUVGUVI values do not support recent suggestions that the solar EUV irradiances estimated by the model of Hinteregger et al. be increased by a factor of four, nor even a factor of two.

[1] The Global Ultraviolet Imager (GUVI) instrument carried aboard the NASA TIMED satellite measures the spectral radiance of the Earth’s far ultraviolet airglow in the spectral region from 120 to 180 nm using a cross-track scanning spectrometer design. Continuous operation of the instrument provides images of the Earth’s disk and limb in five selectable spectral bands. Also, spectra at fixed scanning mirror position can be obtained. Initial results demonstrate the quantitative functionality of the instrument for studies of the Earth’s dayglow, aurora, and ionosphere. Moreover, through forward modeling, the abundance of the major constituents of the thermosphere, O, N2, and O2 and thermospheric temperatures can be retrieved from observations of the limb radiance. Variations of the column O/N2 ratio can be deduced from sunlit disk observations. In regions of auroral precipitation not only can the aurora regions be geographically located and the auroral boundaries identified, but also the energy flux Q, the characteristic energy Eo, and a parameter fo that scales the abundance of neutral atomic oxygen can be derived. Radiance due to radiative recombination in the ionospheric F region is evident from both dayside and nightside observations of the Earth’s limb and disk, respectively. Regions of depleted F-region electron density are evident in the tropical Appleton anomaly regions, associated with so-called ionospheric ‘‘bubbles.’’ Access to the GUVI data is provided through the GUVI website www.timed.jhuapl.edu\guvi. INDEX TERMS: 0310 Atmospheric Composition and Structure: Airglow and aurora; 0355 Atmospheric Composition and Structure: Thermosphere—composition and chemistry; 0358 Atmospheric Composition and Structure: Thermosphere—energy deposition; 2407 Ionosphere: Auroral ionosphere (2704); KEYWORDS: airglow, aurora, ultraviolet, imaging, satellite, atmosphere

The Solar Ultraviolet Radiation and Correlative Emissions (SOURCE) mission is intended to advance our ability to specify the spectral irradiance of the Sun in the extreme ultraviolet (EUV) wavelength range through simultaneous, radiometrically accurate measurements of the solar EUV spectral irradiance and measurements, including EUV and visible images, of solar parameters that are correlated with the EUV flux. The data will be used in combination with empirical modelling to develop and validate a more accurate system of proxy, or surrogate, indices for the solar EUV flux.

The Remote Atmospheric and Ionospheric Detection System (RAIDS) is a new NASA experiment studying the Earth's thermosphere and ionosphere from a vantage point on the International Space Station (ISS). The RAIDS mission focuses on the coupling and transition from the coldest part of the atmosphere, the mesopause near 85 kilometers, up to the hottest regions of the thermosphere, above 300 kilometers in altitude. Built jointly by the Naval Research Laboratory (NRL) and The Aerospace Corporation, RAIDS also is serving as a pathfinder experiment for atmospheric remote sensing aboard the ISS. RAIDS and a companion experiment, NRL's Hyperspectral Imager for the Coastal Ocean (HICO), make up the HICO-RAIDS Experiment Payload (HREP), the first U.S. payload on the Japanese Experiment Module—Exposed Facility (JEM-EF). The experience developing and operating RAIDS for this mission provides useful insights for utilizing the ISS as a platform for atmospheric science.

The Global UV imager (GUVI) is an imaging spectrometer on the NASA TIMED spacecraft. GUVI produces simultaneous monochromatic images at five 'colors' as its field of view is scanned from horizon to horizon. The instrument consists of a scan mirror feeding a parabolic telescope and Rowland circle spectrometer, with a wedge-and-strip detector at the focal plane. We describe the design, and give an overview of the environmental parameters that will be measured. GUVI is a modified version of the Special Sensor UV Spectrographic Imager (SSUSI), which will fly on the DMSP Block 5D3 satellites S-16 through S-20, We present some results from the optical calibration of the five SSUSI units.

The global ultraviolet imager (GUVI) investigation is designed to provide quantitative observations and interpretation of the Earth's airglow and auroral emissions in support of the NASA thermosphere, ionosphere, mesosphere, energy and dynamics (TIMED) mission. It addresses TIMED objectives dealing with energetics, dynamics, and the specification of state variables. The instrument provides multiple-wavelength, simultaneous `monochromatic' images of the far-ultraviolet emission (115 to 180 nm) using a scan mirror to sweep the instantaneous field of view of a spectrographic imager through an arc of up to 140 degree(s) aligned perpendicular to the orbit plane of the spacecraft. The instantaneous field of view is 11.8 degree(s) by 0.37 degree(s) (adjustable) along the slit and perpendicular to the slit, respectively. The field of view is mapped to a two-dimensional image plane with up to 64 spatial pixels by 160 spectral pixels of spectral width 0.4 nm per pixel. Binning of pixels can be performed along both the spatial and spectral axes of the array to reduce the demands on the downlink telemetry. The f/3 Rowland circle scanning spectrographic imager is outfitted with a toroidal grating ruled at 1200 grooves per millimeter. The fore-optics consists of a plane scanning mirror and an off-axis parabolic telescope. The detector is a photon-counting microchannel plate with a wedge and strip anode mounted in a sealed tube.

Radiation at He+ at 30.4 nm, which is emitted close to the Earth, comes from three distinct regions; the ionosphere, the plasmasphere and the polar cap. Published observational data on He+ 30.4 nm have shown that the intensities from polar regions are relatively smaller than the other regions. Polar emissions are believed to be due to resonant scattering of ion outflow in sunlight. A 1982 rocket flight from Poker Flat, Alaska has shown that line-of-sight 30.4 nm emission rates are relatively strong in the direction of the pole. Since the roll of the rocket afforded many different observing directions, we have used the variety of viewing geometries to extract ionospheric source densities from the photometric intensity data. We have assumed that the He+ densities vary with distance along dipole field lines according to a particular functional form, and then we proceeded to extract the source densities by a matrix inversion method. The results give density variations over a range of latitudes including samples from each of the regions mentioned above. The method obtains good fits of the observed profiles of intensity versus observation angle.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The RAIDS experiment is an optical remote sensing platform consisting of eight sensors (spectrographs, spectrometers and photometers) covering the wavelength range 550 A to 8744 A. RAIDS employs a mechanical scan platform to view the Earth's limb and measure vertical profiles of atmospheric dayglow and nightglow from the mesosphere to the upper regions of the F region ionosphere (75 -750 km). RAIDS will be flown on the NOAA J weather satellite through the auspices of the Air Force Space Test Program (STP). The RAIDS wavelength and altitude coverage allows remote sensing of the major, and many minor constituents in the thermosphere and ionosphere. These measurements will be used as part of a proof-of-concept for remote sensing of ionospheric and neutral density profiles. The RAIDS database will be used to study composition, thermal structure and couplings between the mesosphere, thermosphere and ionosphere. RAIDS is a joint venture of the Naval Research Laboratory (NRL) and The Aerospace Corporation. This paper describes the subset of RAIDS instruments developed at NRL covering the far to near ultraviolet (1300 A - 4000 A). A companion paper describes the balance of the experiment complement.