SA11A-0210
A Potential Remote Sensing Technique for Thermospheric Temperature with Ground-Based Resonant Atomic Oxygen Raman Lidar
We propose a remote sensing technique to measure temperature in the lower thermosphere with a resonant Raman lidar. A ground-based pulsed laser operating at $630.0304~(636.3776)$ nm excites $^{3}P_{2}~(^{3}P_{1})$ multiplet level of the ground electronic state of atomic oxygen in the atmosphere to the electronically excited $^{1}D_{2}$ state and the back-scattered photons at $636.3776~(630.0304)$ nm, while the atom transitions to $^{3}P_{1}~(^{3}P_{2})$, are detected. Using the backscattering Raman cross sections calculated here we show: 1. For the range of altitudes in the lower thermosphere where the fine-structure multiplets of atomic oxygen are in thermodynamic equilibrium with the local translational temperature (LTE) and the electronically excited intermediate state $^{1}D_{2}$ is relaxed primarily by collisions with $N_{2}$ and $O_{2}$, the ratio of the backscattered signals can be used to obtain temperature. 2. Higher up, for the range of altitudes where the fine-structure multiplets of atomic oxygen are in LTE but the electronically excited intermediate state $^{1}D_{2}$ is relaxed primarily by spontaneous emission of a photon, the Stokes and anti-Stokes backscattered signal can be used to obtain the atomic oxygen density and local temperature. 3.~Still higher up, for the range of altitudes where the fine-structure multiplets of atomic oxygen are not in LTE but the electronically excited intermediate state $^{1}D_{2}$ is relaxed primarily by spontaneous emission of a photon, the Stokes and anti-Stokes backscattered signal can be used to obtain the density of the $^{3}P_{2}$ and $^{3}P_{1}$ multiplet levels of the ground electronic state of atomic oxygen. For a ground-based instrument a simulation with 3~km range gate is used to show that the relative error of temperature measurements from 120 to 290 km could be less than 20 %. It is pointed out that this technique has the potential of providing unique data that addresses the modeling of satellite drag and the effects of space weather on the upper atmosphere. In addition, this technique may also permit the detection of the thickness of the temperature inversion layers as well as their temperature and density perturbations.
SA11A-0211
The Rovibronic Line fVValues of N2 in the 91.6 nm Region: High-Resolution, High-Temperature
We report measurements of the rotational f-values in the high temperature-dependent ultrahigh-resolution photoabsorption of N2 in the 91.6 nm region. One of the important issues regarding the interpretation of the NII 91.6 nm extreme ultraviolet airglow emissions of the Earth, Titan, and Triton is the effect of temperature on the atmospheric extinction due to absorption by N2 and O2. Since the temperature of the upper atmosphere of the Earth is typically in the 200 to 900 K range it is therefore important to know these molecular cross sections at such temperatures. Absorption features in this region mainly involve the (11,0) band of the b-X transition, under room temperature conditions. We have carried out high resolution photoabsorption cross section measurements of N2 with a resolution of 0.0003 nm and 0.0008 nm in the 91.5-91.728 nm region at temperatures of 600, 445, and 295 K. The 6VOPE (6.65-m vertical off-plane Eagle spectrograph) spectrometer facility available at the Photon Factory, KEK, Tsukuba, Japan, was employed in the present study. Additional intense rovibronic lines have been observed at high temperature conditions. They are tentatively identified as rovibronic transitions involving high rotational quantum numbers from the (12,1) band of the b-X, the (8,1) band of the b'-X, and the (3,1) band of the o3-X transitions. By integration over each individual absorption profile the rotational line f-values of N2 are determined for the above-mentioned spectral region and experimental conditions. The most intense component of the NII multiplets at 91.6710 nm overlap with the rovibronic line Q6 at 91.6703 nm. The NII 91.6710 nm feature is located slightly toward the line center of the Q6 line of the (11,0) band of the N2 b-X transition. However, at 445 K and 600 K this NII component completely falls inside the line shape of the Q6 of N2. Detailed results will be presented. This research is based on work supported by NSF grant ATM-0096761.
SA11A-0212
Integral Cross Sections for the Electron Impact Excitation of Molecular Nitrogen
Integral cross sections for electron impact excitation out of the ground state (X $^{1}σ_{g}$$^ {+}$) to the A 3σ_{u}$$^{+}$, B 3$\Pi$$_{g}$, W 3Δ_{u}$, B$^\prime$ $^{3} σ_{u}$$^{-}$, a$^\prime$ $^{1}σ_{u}$$^{-}$, a $^{1}$$\Pi$$_{g}$, w $^{1}Δ_ {u}$, and C 3$\Pi$$_{u}$ states in N2 are reported at incident energies ranging between 10 and 100 eV. These data have been derived by integrating differential cross sections previously reported by this group [Khakoo {\it et al.}, PRA, {\bf 71}, 062703, 2005]. New differential cross section measurements for the a $^{1}$$\Pi$$_{g}$ state at 200 eV are also presented to extend the range of the reported integral cross sections for this state, which is responsible for the emissions of the Lyman- Birge- Hopfield (LBH) band system (a $^{1}$$\Pi$$_{g}$ $\rightarrow$ X $^{1}σ_{g}$$^{+}$). The present results are compared and critically evaluated against existing cross sections. Acknowledgement: This work was carried out at JPL, Caltech, under contract with NASA and at CSUF, with support from the NSF RUI program and NASA PATM program. This research was performed while CPM held a NRC Research Associateship Award at JPL.
SA11A-0213
Emission Cross Sections of the Lyman-Birge-Hopfield Band System in Molecular Nitrogen Induced by Electron Impact Excitation
Emissions from the Lyman-Birge-Hopfield (LBH) band system in N2 (a $^{1}$$\Pi$$_{g}$ $\rightarrow$ X $^{1}σ_{g}$$^{+}$) are the most prominent molecular features below 180 nm in the Earth's atmosphere [Kanik {\it et al.}, Phys. Chem. Earth (C), {\bf 25}, 573, 2000]. LBH emissions continue to be of interest as a sensitive test of N2 density distributions and photoelectron flux in the dayglow and secondary electron flux in the aurora. Furthermore, recent measurements with the onboard Ultraviolet Imaging Spectrograph (UVIS) experiment by the Cassini spacecraft of the Saturnian system, in particular Titan, have invigorated the need for improved N2 cross sections. The present work utilized a large vacuum chamber, a detector platform that provided vertical and horizontal movement, a Faraday cup, and an electron gun providing an electron beam of fixed energy. The detector platform enabled the LBH emissions to be observed, using the UVIS engineering flight spare, at multiple radial positions relative to the electron beam axis, which was used to map the glow resulting from electron impact excitation of an optically thin swarm of N2 gas. Normalization of the LBH emissions was provided by comparison with well known NI emissions. The absolute 100 eV LBH emission cross section was used to renormalize the LBH emission cross sections of [Ajello and Shemansky, JGR, {\bf 90}, 9845, 1985]. Acknowledgement: This work was carried out at JPL, Caltech, under contract with NASA and at LASP, UC (Boulder). This research was performed while CPM held a NRC Research Associateship Award at JPL.
SA11A-0214
Focused Microwave Technique for Probing the Atmosphere at 60-200 km Heights
A system for remote optical diagnostics of the atmosphere/ionosphere at heights 60-200 km is proposed. The method relies on excited-ionized N2 and N2+ molecules by electron impact during microwave pulses injected from focused ground-based transmitter. A 32 GHz gyrotron was developed at the Associate Plasma Laboratory of INPE-Brazil to this purpose. The gyrotron creates energetic electrons in the ionosphere, which excite-ionize N2 molecules to higher energy levels. These excited molecules become targets for a laser ranging system by resonantly absorbing and reradiating light at specific wavelengths. The laser return signal intensity gives information on the density of the ionospheric species under consideration, and its delay gives the height. Also, the reradiated light is detected by a ground-based photometer. A study of atmospheric species for ranging was performed, and the most suitable species were found to be N2 and N2+.
SA11A-0215
O($^{1}$$\it{D}$) Relaxation by O(3$\it{P}$)
We report laboratory experiments investigating the relaxation of O($^{1}$$\it{D}$) by O(3$\it{P}$) atoms. Rate coefficients for this process deduced from atmospheric observations and theoretical calculations have appeared in the literature that differ by more than an order of magnitude. No laboratory measurement of the rate coefficient is available, despite its importance in determining the energy flow in the upper atmosphere and controlling the intensity of atomic oxygen emissions. In the experiments, molecular oxygen is photodissociated to O($^{1}$$\it{D}$) and O(3$\it{P}$) atoms by the 157-Nm output of a fluorine laser. The temporal evolution of the O($^{1}$$\it{D}$) concentration is monitored by detection of the 630-Nm emission. Our laboratory results indicate that O($^{1}$$\it{D}$) relaxation by O(3$\it{P}$) atoms is very efficient, with a rate coefficient of approximately 2 × 10$^{-11}$ cm3s$^{-1}$ at room temperature. The relevance to atmospheric observations and ionospheric heating experiments will be discussed. The participation of Kristina D. Closser was made possible by the NSF Research Experiences for Undergraduates Program under grant PHY-0353745. This research is supported by NSF grants ATM-0209229 and ATM-0216583.
SA11A-0216
Removal Rate Constants for OH and OH(v=4) by O and O2
The temperature dependence of the OH + O -> H + O2 reaction was measured using a laser photolysis - laser induced fluorescence technique. A known excess of O atoms is prepared by complete 248 nm laser photolysis of a monitored O3 flow in N2, with small amounts of H2 to provide an OH source. The window-equipped flow cell is enclosed in a Dewar by which temperatures of 140K (LN2), 235K (dry ice), and 365K (heated cell) were produced. Modeled results for OH(v=0) + O under various conditions agree with the NASA-JPL panel recommendation at 298 K, independent of OH source, with a slightly larger temperature dependence. k(140K) = 2.5 k(298K). Measured decays for OH(v=4) reflect reaction, and vibrational relaxation by O and by the O2(1-delta) also created by the O3 photolysis. Results show a considerable increase in decay rate for v=4 at all temperatures, likely from vibrational relaxation processes. k(228K) = 1.9 x 10(-10). Interpreting the results from the perspective of an HO2 intermediate and past theoretical efforts reveals some challenges. We also measured a removal rate constant of 1.2 x 10(-12) (298K) by added O2. Experiments were performed at 140 K for trace amounts of OH and O (<1 mtorr) in 40 torr O2 or N2 to search for evidence of the proposed weakly bound HO3 atmospheric complex. Signal intensities and slow decays are identical, which provides an upper limit of 7 kcal/mole for the stability of this species. Research supported by the NSF Aeronomy Program and NASA Geoscience ITM Physics Program.
SA11A-0217
Modeling Altitude Profiles of the N2 Lyman-Birge-Hopfield Band Emissions
Space-based remote sensing of the N2 Lyman-Birge-Hopfield (LBH) band emissions provides valuable insight about the Earth's environment. In this study we investigate the ability of the cascade model to reproduce the LBH limb profiles, by comparing model calculations with observations from the High resolution Ionospheric and Thermospheric Spectrograph (HITS) aboard the Advanced Research and Global Observation Satellite (ARGOS). Also, we examine how the different models existing to infer the LBH emissions match in different altitude regions. While most models only take direct excitation into account, the cascade code also includes radiative and collisional cascade contributions.
SA11A-0218
An EUV Photometer for tomographic observations of the ionosphere
A relatively simple far ultraviolet (FUV) scanning photometer named TOROID (TOmographic Reconstruction Of Ionospheric Disturbances), is being developed to observe the night glow of the ionosphere. The nightglow, which correlates with ionospheric density, is dynamic with disturbances depending on the geomagnetic field topography, neutral thermospheric winds and ultimately the solar activity. The goal is to develop an instrument which is optimized to produce data for tomographic reconstruction with approximately a 20 km cubic volume pixel from a 600 km orbit altitude. The instrument will be sensitive to two wavelengths: 91.1 and 135.6 nm, both resulting from the recombination of atomic oxygen and electrons. These wavelengths were selected because they are optically thin and to provide information on interference signals due to positive and negative oxygen ion recombination and hydrogen emissions. Night side radiation at the selected wavelengths is measured within the plane of the spacecraft's orbit continuously by way of an external rotating scanning mirror. Data from these measurements allows the application of a tomographic reconstruction algorithm to characterize the plasma densities below, and potentially above, the spacecraft's orbit altitude. This windowless instrument makes use of multiple spectrally selective mirrors for high radiometric sensitivity. The detectors and corresponding instrument mechanisms are selected for high reliability and compatibility with both potential spacecraft and sounding rocket missions.
SA11A-0219
Quantum-mechanical investigations of the N$(^4S)$ + O$_2(X^3\Sigma^-_g)$ $\rightarrow$ NO$(X^2\Pi)$ + O$(^3P)$ reaction
The reaction between energetic nitrogen atoms and oxygen molecules has received important attention in connection with nitric oxide chemistry in the lower thermosphere. We report time-independent quantum mechanical calculations of the N($^4S$)+O$_2\to$NO+O reaction employing the $X^2A'$ and $a^4A'$ electronic potential energy surfaces Sayós et al. [J. Chem. Phys. {\bf 117}, 670 (2002)]. We confirm the production of highly vibrationally excited NO molecules, consistent with previous semiclassical and more recent time-dependent quantum wave packet calculations. Calculations are carried out for total angular momentum quantum number $J=0$ and cross sections and rate coefficients are extracted using the $J$-shifting approximation. Results are compared with available experimental and theoretical data.
SA11A-0220
Relative Yield of O2($b^1\Sigma^+_g$, $v$ = 0 and 1) in O($^1D$) + O2 Collisions
In the thermosphere, energy transfer from excited O-atoms leads to production of O2 molecules in the first two vibrational levels of the O2($b^1\Sigma^+_g$) state: O($^1D$) + O2 $\rightarrow$ O($^3P$) + O2($b^1\Sigma^+_g$, $v$ = 0, 1). Subsequent radiative decay of O2($b^1\Sigma^+_g$, $v$ = 0 and 1) to the ground state, O2($X^3\Sigma^-_g$), results in the Atmospheric Band emission. The relative yield for production of O2($b^1\Sigma^+_g$, $v$ = 0 and 1) in the above process, k$_{1}$/k$_{0}$, is an important parameter in modeling of the observed Atmospheric Band emission intensities. We report laboratory measurements of k$_{1}$/k$_{0}$, in which the output of a pulsed fluorine laser at 157 nm is used to photodissociate molecular oxygen in a O2/N2 mixture. Photodissociation of O2 produces a ground-state O($^3P$) atom and an excited O($^1D$) atom. O($^1D$) rapidly transfers energy to the remaining O2 to produce O2($b^1\Sigma^+_g$, $v$ = 0, 1). The temporal evolution of the O2($b^1\Sigma^+_g$, $v$ = 0 and 1) populations is monitored by observing emissions in the O2($b$--$X$) 0-0 and 1-1 bands at 762 and 771 nm, respectively. The value of k$_{1}$/k$_{0}$ is extracted from the time-dependent O2($b^1\Sigma^+_g$, $v$ = 0 and 1) fluorescence signals, based on a detailed understanding of the kinetics involved. Two published studies reported that energy transfer to O2($b^1\Sigma^+_g$, $v$ = 0) is favored, with a k$_{1}$/k$_{0}$ ratio in the range 0.3--1 [1, 2]. In contrast, our more direct measurements clearly indicate that production of O2($b^1\Sigma^+_g$, $v$ = 1) dominates that of O2($b^1\Sigma^+_g$, $v$ = 0), with a value of k$_{1}$/k$_{0}$ in the range 3--4. Comparisons with high-altitude spectra of the O2($b$--$X$) 0-0 and 1-1 bands obtained during the Arizona Airglow Experiment (GLO) support our experimental finding and suggest that a major revision of the input for k$_{1}$/k$_{0}$ in atmospheric models is warranted. This work was supported by the NSF Aeronomy Program under grant ATM-0209229. The fluorine laser was purchased under grant ATM-0216583 from the NSF Major Research Instrumentation Program. 1. M. J. E. Gauthier and D. R. Snelling, Can. J. Chem. 52, 4007 (1974). 2. L. C. Lee and T. G. Slanger, J. Chem. Phys. 69, 4053 (1978).
SA11A-0221
Laboratory Measurements of Ozone - M Vibrational Energy Transfer
In preliminary work, we explore using a temperature-jump method, similar to what has been used in our ongoing CO2($\nu2)-O energy transfer studies, to measure vibrational energy transfer efficiencies in O3-M encounters, where M=O2, N2, or O. A lingering concern in the analysis of NASA's TIMED/SABER data involves the 9.6 micron channel, where the observed radiance is dominated by intense emission from the O3($\nu3) asymmetric stretch level. Hot band emission trailing to longer wavelengths is also present, arising from vibrationally excited O3 initially populated by O + O2 three-body recombination. Poor knowledge of the relevant collisional quenching rate coefficients constitutes one of the most significant deficiencies in the non-LTE models used to retrieve ozone densities from SABER data. Specifically, accurate rate parameters for the relaxation of vibrationally-excited O3 by the major atmospheric species in the mesosphere and lower thermosphere, N2, O2, and O, are required. The O3(v)-O2, N2quenching rate coefficients derived from existing laboratory measurements vary over a substantial range, and there exists only a single published measurement of O-atom quenching coefficients. The proposed method involves a slow-flowing, dilute mixture of O3 in Xe bath gas. A 266 nm laser pulse is used to dissociate a small fraction of the O3, forming O atoms and stimulating a modest temperature increase. The O3 vibrational level populations redistribute according to the new temperature, and the excited vibrational level populations are monitored via transient diode laser absorption spectroscopy as they return to equilibrium. Rate parameters are determined by effectively plotting the redistributions rates against the quencher concentration. Any promising data or experimental progress will be discussed.
SA11A-0222
Quenching of CO2($\nu2) by O: New Results and Analysis
New results from ongoing laboratory measurements of CO2($\nu2) + O vibrational energy transfer (VET) will be presented. The process is a key contributor to both the CO2 15-μm emission intensity and to upper atmospheric cooling in the 75-120 km altitude range. A 266-Nm laser pulse photolyzes O3, producing O atoms and initiating a temperature jump, while transient diode laser absorption spectroscopy is used to monitor the CO2($\nu2) level population. We report the latest measurement results, including improvements in the experiment that have mitigated vibrational cascading effects, and the development of a powerful global kinetic fitting routine to allow the simultaneous determination of the appropriate rate parameters from a large body of data. Predictions of upper atmospheric density and temperature are sensitive to the input value of the CO2($\nu2) + O relaxation rate constant {\it k}$_{O}$($\nu2), including its temperature dependence. Aeronomic models imply that increasing CO2 levels from anthropogenic sources will cause the thermosphere to cool and contract over time. The model results are supported by analyses of satellite orbital motion data over the past 40 years, which are consistent with a few percent thermospheric density decrease per decade. This has important implications for spacecraft drag and orbital longevity. It also provides an interesting connection between a molecular-level parameter, the CO2 + O VET efficiency, and the macroscopic effects of atmospheric density and temperature.
SA11A-0223
Theoretical Analysis of the Temperature Variations and the Krassovsky Ratio for Long Period Gravity Waves
Based on the assumption that they are caused by atmospheric gravity waves rather than atmospheric tides, this study aims at developing a theoretical analysis of the long period (~ 8 hour) fluctuations of both the Meinel OH band intensity and the rotational temperature. Eddy thermal conduction and eddy viscosity is included in the calculation. In addition, to account for the very long periods, Coriolis force due to earth's rotation will also be taken into account by employing the "shallow atmosphere" approximation. For the first time the height varying background wind is also included in the discussion. Long period fluctuations in the airglow have been measured in many recent experimental observations (Taylor M.J., Gardner L.C., Pendleton W.R., Adv. Space Res., 2001). The Krassovsky ratio which determines the efficiency of producing an intensity fluctuation for a given temperature fluctuation, and also the phase difference between the intensity and temperature fluctuation will also be calculated based on the gravity wave assumption.
SA11A-0224
Continual 24-hour Observations of Thermospheric Winds and Temperatures Made With the Second-Generation Optimized Fabry-Perot Doppler Imager (SOFDI)
The Second generation Optimized Fabry-Perot Doppler Imager (SOFDI), a state-of-the-art triple-etalon Fabry-Perot interferometer, has been constructed, tested, and is now making continual 24-hour observations in upstate New York. The 630 nm data, originating from layer-integrated OI emission with centroid heights of 250 km at night and 220 km during the day, are analyzed so as to obtain measurements of horizontal winds and temperatures in the thermosphere. In this paper we report the most recent results from continuous 24-hour observations of these thermospheric parameters.
SA11A-0225
Seasonal and Interannual Variability of the Atmospheric Tides Observed over South Pole
A meteor radar system was installed at Amundesen-Scott South Pole station in 2001 and became fully operational in 2002. This radar has operated nearly continuously since and is providing horizontal wind measurements in four separate azimuth directions. This feature provides the ability to determine the zonal wavenumber and direction of propagation for the observed perturbations. With multiple years of observations we now have the opportunity to investigate the coherent seasonal structure of the large scale observations over South Pole. These include large 12 and 24 hour oscillations propagating westward with zonal wavenumber one and associated with the non-migrating semidiurnal and migrating diurnal tides respectively. The observations show a clear annual variation in these perturbations with maximum amplitudes observed in the Austral summer as has been previously reported. Previously unreported and particularly interesting features appear in the observed phases of these tidal perturbations. Analysis of the phases for the four separate observing directions indicates a clear phase progression of these perturbations to later times in the spring and early times in the fall, which could indicate change in the vertical wavelength of the tides. Additionally the phase difference between the four observing directions is not exactly a quarter of a wave period as expected, indicating the possibility that these disturbances could be propagating around an offset dynamical pole. Both of these features observed in the phases are clearly repeatable from year to year. These results will be presented and possible mechanisms will be described.