S. A. Budzien

Quenching rate coefficients for O+(2P) derived from middle ultraviolet airglow

[i] O + ( 2 P) is produced in the sunlit thermosphere primarily by photoionization of atomic oxygen. Thermospheric atomic oxygen concentrations can be inferred from measurements of airglow produced near 732.0 nm by the transition of this excited state to the 2D state and at 247.0 nm by the transition to the 4 S ground state. The accuracy of these concentrations depends on the accuracy of the important chemical reaction rates used in the airglow model, including quenching of O + ( 2 P). We obtain coefficients for the quenching of O + ( 2 P) by O and N 2 by modeling rocket and satellite limb measurements of thermospheric middle ultraviolet (MUV) airglow at 247.0 nm. We derive a reaction rate for N 2 of 1.8 x 10- 10 cm 3 s -1 , which is lower than the value obtained by other airglow studies but in agreement with laboratory measurements. We obtain a best fit value for the O reaction rate of 5.0 x 10 -11 cm 3 s -1 , with an upper limit of 8.4 x 10 -11 cm 3 s -1 . The value of the O reaction rate determined by fits to 172 altitude profiles of the 247.0 nm emission shows a strong correlation with the magnitude of the excitation g factor. However, the airglow profile above 260 km favors the upper limit we have identified.

Electron densities determined by the HIRAAS Experiment and comparisons with ionosonde measurements

We present electron density profiles derived by inversion of ultraviolet limb scans made by the High Resolution Airglow and Aurora Spectroscopy (HIRAAS) experiment on the Advanced Research and Global Observing Satellite (ARGOS). The ultraviolet limb scans were inverted using an iterative algorithm based on discrete inverse theory. We present two comparisons with nearly coincident ionosonde measurements of the F-region peak density and peak height. Our observations took place on 24 November 1999 when the 10.7 cm radio flux was 181 × 10−22 Watt m−2 Hz−1 and the daily ap was 21, indicating moderate geomagnetic activity. The retrieved peak electron density and peak height were in good agreeent with the ionosonde measurements, demonstrating the accuracy of the ultraviolet technique for sensing the ionospheric state.

Electron densities determined by inversion of ultraviolet limb profiles

We present electron density profiles derived by inversion of ultraviolet limb radiances observed on November 24, 1999, by the Low-Resolution Airglow and Aurora Spectrograph instrument on the Advanced Research and Global Observing Satellite. The solar 10.7-cm radio flux was 181 solar flux units, and the daily ap was 21, indicating moderate geomagnetic activity. The O+ density profile, which is approximately equal to the electron density profile in the F region ionosphere, was determined by inverting the limb radiance profile of O I 911-A emission of atomic oxygen. The 911-A emission is produced by radiative recombination of O+ ions and electrons. Sounding rocket and satellite measurements of the Earths extreme ultraviolet dayglow indicated significant contamination in the 900- to 920-A passband by emissions from atomic, molecular, and ionized nitrogen [Gentieu et al., 1979, 1981; Chakrabarti et al., 1983]. As a result of these observations, the radiative recombination emission was thought to be of little use for ionospheric sensing during the daytime. Feldman et al. [2001] have recently measured spectra in the 905- to 1184-A passband and show that the contamination at F region altitudes is less than that present in the earlier observations [Gentieu et al., 1979, 1981; Chakrabarti et al., 1983]. We found the contamination of the O I 911-A emission to be negligible at F region altitudes and have been able to use the 911-A emission to accurately characterize the ionospheric state. We have compared the peak electron density and peak height determined by inversion of the 911-A altitude profiles with nearly coincident ionosonde measurements, and we find the measurements from the two techniques to be in good agreement, demonstrating the accuracy of this technique for sensing the ionospheric state.

O+, O, and O2 densities derived from measurements made by the High Resolution Airglow/Aurora Spectrograph (HIRAAS) sounding rocket experiment

We present the results of an analysis of the O II 834 A and O I 1356 A altitude profiles measured during a sounding rocket flight on March 19, 1992. The profiles were analyzed using a new set of models that used discrete inverse theory to seek a maximum likelihood fit to the data. Both profiles were fit simultaneously to ensure consistency of the retrieved ionosphere and thermospheric neutral density. During the analysis the thermospheric neutral density and temperature were modeled using the Mass Spectrometer Incoherent Scatter (MSIS-86) model [Hedin, 1987]. Two parameters were used to scale the absolute MSIS O and O2 densities; the exospheric temperature was altered by varying the 10.7 cm solar flux (an MSIS-86 input). The ionospheric O+ density was modeled by a three-parameter Chapman layer. The retrieved MSIS scalars for the O and O2 densities were 0.47 ± 0.09 and 0.58 ± 0.14, respectively. These scalars indicate that the MSIS-86 model predicted significantly higher O and O2 densities. The inferred exospheric temperature was 1125 K in good agreement with the MSIS-86 prediction. The derived O density is in good agreement with the O density inferred from midultraviolet spectra observed during the same rocket flight [Bucsela et al., 1998]. The retrieved F region peak density, 1.98 ± 0.63 × 106 cm−3, peak height, 291 ± 22 km, and plasma scale height, 138 ± 24 km, all agreed with coincident digisonde measurements. Thus we have demonstrated that the ionospheric state can be accurately determined by inversion of observed O II 834 A limb radiance profiles.

The Remote Atmospheric and Ionospheric Detection System on the ISS: sensor performance and space weather applications from the visible to the near infrared

The RAIDS experiment is a suite of eight instruments to be flown aboard the Japanese Experiment Module-Exposed Facility on the International Space Station (ISS) in late 2009. Originally designed, built, and integrated onto the NOAA TIROS-J satellite in 1993, the original RAIDS hardware and the mission objectives have been modified for this ISS flight opportunity. In this paper we describe the four near infrared instruments on the RAIDS experiment covering the wavelength range of 630 - 870 nm. Over the past two years these instruments have undergone modification, refurbishment, and testing in preparation for flight. We present updated sensor characteristics relevant to this new ISS mission and discuss performance stability in light of the long instrument storage period. The four instruments, operating in a limb scanning geometry, will be used to observe the spectral radiance of atomic and molecular emission from the Earths upper atmospheric airglow. The passbands of the photometers are centered on the atomic lines OI(777.4), OI[630.0], and the 0-0 band of O2 Atmospheric band at 765 nm. The spectrometer scans from 725 to 870 nm. These observations will be used in conjunction with the other RAIDS instruments to investigate the properties of the lower thermosphere and to improve understanding of the connections of the region to the space environment, solar energy flux and the lower atmosphere. These studies are fundamentally important to the understanding the effects of the atmosphere and ionosphere on space systems and their operation in areas such as satellite drag, communications and navigation.

Far-UV emissions from the SL9 impacts with Jupiter

Observations with the International Ultraviolet Explorer (IUE) during the impacts of the fragments of comet D/Shoemaker-Levy 9 with Jupiter show far-UV emissions from the impact sites within a ∼10 min time scale. Positive detections of H2 Lyman and Werner band (1230–1620 A) and H-Lyα emissions are made for impacts K and S, and marginally for P2. No thermal continuum is observed. The radiated far-UV output was >1021 ergs. The H2 spectrum is consistent with electron collisional excitation if significant CH4 absorption is included. Such emissions could result from plasma processes generated by the impacts. Non-thermal excitation by the high altitude entry and explosion shocks may also be relevant. Emissions by Al+ (1671 A) and C (1657 A) of cometary origin are tentatively identified.

Ionospheric-thermospheric UV tomography: 2. Comparison with incoherent scatter radar measurements

The Special Sensor Ultraviolet Limb Imager (SSULI) instruments are ultraviolet limb scanning sensors that fly on the Defense Meteorological Satellite Program F16-F19 satellites. The SSULIs cover the 80–170 nm wavelength range which contains emissions at 91 and 136 nm, which are produced by radiative recombination of the ionosphere. We invert the 91.1 nm emission tomographically using a newly developed algorithm that includes optical depth effects due to pure absorption and resonant scattering. We present the details of our approach including how the optimal altitude and along-track sampling were determined and the newly developed approach we are using for regularizing the SSULI tomographic inversions. Finally, we conclude with validations of the SSULI inversions against Advanced Research Project Agency Long-range Tracking and Identification Radar (ALTAIR) incoherent scatter radar measurements and demonstrate excellent agreement between the measurements. As part of this study, we include the effects of pure absorption by O2, N2, and O in the inversions and find that best agreement between the ALTAIR and SSULI measurements is obtained when only O2 and O are included, but the agreement degrades when N2 absorption is included. This suggests that the absorption cross section of N2 needs to be reinvestigated near 91.1 nm wavelengths.

Oxygen aurora during the recovery phase of a major geomagnetic storm

[1] We have analyzed ultraviolet spectra measured in the postsunset auroral zone on 16 July 2000, during the recovery phase of the major geomagnetic storm of 14-16 July 2000. We find enhanced oxygen ion and neutral line emissions above 300 km in the postsunset sector of the auroral oval during the initial fast recovery phase of the storm, also called the Bastille Day storm. No comparable emissions are seen in simultaneous measurements of nitrogen and hydrogen emission features, indicating that these features are not related to electron or proton aurora. The enhancements are seen slightly equatorward of all other nitrogen line and band emissions that are presumed to comprise the nominal diffuse electron auroral oval. On the basis of the altitude profile, location, and timing of the enhancements, we interpret these oxygen emissions as a product of precipitating ring current oxygen ions in the auroral atmosphere, possibly after pitch-angle scattering by electromagnetic ion cyclotron waves. These emissions may provide an important measure of the contribution of collisions and charge exchange interactions to the loss of oxygen ions and the recovery of geomagnetic storms and substorms.

Ionospheric‐Thermospheric UV Tomography: 1) Image Space Reconstruction Algorithms

We present and discuss two algorithms of the class known as Image Space Reconstruction Algorithms (ISRAs) that we are applying to the solution of large-scale ionospheric tomography problems. ISRAs have several desirable features that make them useful for ionospheric tomography. In addition to producing non-negative solutions, ISRAs are amenable to sparse-matrix formulations and are fast, stable, and robust. We present the results of our studies of two types of ISRA: the Least-Squares Positive Definite (LSPD) and the Richardson-Lucy algorithms. We compare their performance to the Multiplicative Algebraic Reconstruction (MART) and Conjugate Gradient Least Squares algorithms. We then discuss the use of regularization in these algorithms and present our new approach based on regularization to a partial differential equation.

The Special Sensor Ultraviolet Limb Imager (SSULI) Instruments

The Special Sensor Ultraviolet Limb Imager (SSULI) instruments are ultraviolet limb scanning sensors flying on the United States Air Force Defense Meteorological Satellite Program (DMSP) Block 5D-3 satellites. The SSULIs cover the 800-1700 A wavelength range at 18 A spectral resolution. This wavelength range contains spectral signatures of all the dominant neutral and ionized species in the thermosphere and F-region ionosphere. The instruments view ahead of the spacecraft and operate as limb imagers covering the 100-750 km altitude range at 10-15 km resolution with a 90-second scan cadence. We describe these instruments and summarize their calibration and on-orbit performance. Day-to-day variability of the nighttime ionosphere at low-latitudes and longer-term variability of the global mean exospheric temperature are highlighted.