SA41A-0257
An improved parameterization of electron heating, with application to an X17 flare
Ionospheric models typically rely on parameterizations to account for the effects of secondary ionization and heating by photoelectrons. These parameterizations rely on an assumed form for the input solar irradiance; however, during solar flares the shape of the ionizing spectrum can change dramatically. Solomon and Qian [2005] recently updated the parameterization of secondary ionization to account for spectral changes. In this work, we describe a similar improvement to the parameterization of electron heating. The new algorithm is included in a simple ionospheric model and applied to the X17 flare of 28 Oct 2003. With these changes the modeled electron temperature and neutral gas heating rate are shown to increase significantly over previous results. This has particular relevance to the calculation of flare-induced satellite drag.
SA41A-0258
Examination of Prompt Effects of Solar X-ray Flares on Ionospheric Electrodynamics
Photons from solar X-ray flares arrive at the Earth only eight minutes after emission. The short wavelength region of the solar spectrum is effective in modifying the ionization of the dayside upper atmosphere. For periods like the 2003 Halloween Solar events, the solar flares enhanced the E and D regions significantly over the quiet time background ionosphere. The effects of these enhancements on HF and VLF signal propagation and absorption are well understood and widely known. We present studies of the space weather impacts of sustained, elevated solar x-ray and EUV levels of the background spectrum during solar active times related to the changes in the dayside conductivities. We show that not only the dayside conductivities sustain at an order of magnitude higher values than background levels, but the Pedersen-to-Hall conductivity ratio increases by a factor of 2 to 3 during high solar X-ray periods when compared to quiet periods. The effects of prompt changes of the dayside conductivities associated with a solar flare event on the dynamo electric fields and ionospheric currents are then systematically examined by using a model of the low-latitude ionospheric electrodynamics.
SA41A-0259
Electron Impact Excitation of Molecular Nitrogen
Molecular nitrogen is the main atmospheric constituent of Earth, Titan and Triton. Electron collisions with this molecule are responsible for much of the observed emission in the Earth's dayglow, nightglow, and aurora. Further, the successful insertion of the Cassini spacecraft into orbit around Saturn, and the subsequent and continuing observations of Titan's atmosphere with the onboard UVIS experiment make the determination of accurate N2 excitation parameters (e.g., cross sections, oscillator strengths, etc.) particularly timely. An overview of recent experimental investigations into electron-N2 collision properties will be presented. Particular emphasis will be placed on results with significant impact on the interpretation and modeling of atmospheric emission phenomena. Acknowledgement: This work was carried out at JPL, Caltech, under contract with NASA and at CSUF, with support from the NSF AMO Physics Division and NASA's OPR program.
SA41A-0260
Energy Transfer in Collisions of Atmospheric O and H Atoms.
The momentum-energy transfer is investigated for interacting atmospheric H and O gases. Accurate differential cross-sections are used to evaluate the energy transfer rates in collisions of fast oxygen and thermal H atoms in the upper Martian and terrestrial atmospheres. Collisionally induced escape fluxes of H and D isotopes from the Martian atmosphere are computed at different solar conditions. Rate of energy relaxation of fast H atoms in the thermal O gas in the upper Martian and terrestrial atmospheres are determined from solutions of the Boltzmann kinetic equation describing a thermalization process. We have computed parameters, characterizing the H and O energy relaxation in planetary atmospheres: the energy relaxation rate, number of collisions required for a thermalization, averaged energy transferred per collision, and thermalization time. Interaction between H and O atoms is investigated for the upper atmospheres of Mars and Earth.
SA41A-0261
Relaxation of O+(2D) and O+(2P) in Collisions with N2 and O(3P)
Atomic oxygen ions are primary charge carriers in the Earth's ionosphere. Optical emissions from the metastable excited states O+(2D) and O+(2P) provide useful diagnostics of energy deposition processes. The O+(2P{→}2D,4S) emissions near 732 and 247 nm are common features of the daytime and nighttime airglow. Previously, atmospheric O+(2D{→}4S) emissions near 373 nm were known only during cusp aurorae. We have recently analyzed sky spectra from the VLT (Very Large Telescope) in Chile during periods of large solar storms: 6-7 April, 2000, 6-7 Nov., 2001, and 28 Oct.-1 Nov. 2003. O+(2D{→}4S) 373 nm emissions are prominent and show a strong correlation with the Dst (disturbance storm time) index. Interpretation of the relative strengths of the O+(2P{→}2D) 732 and O+(2D{→}4S) 373 nm emissions requires reliable values for the rates of relaxation in collisions with the principal components of the neutral ionosphere, N2 and O(3P). In this presentation we will review the information available from laboratory experiments, quantum theory, and atmospheric modeling. Two primary conclusions have been reached, which are summarized below, along with recommended rate coefficients. (1) Of the four laboratory studies of charge-transfer, electronic-deexcitation, and ion-molecule reactions in collisions of O+(4S,2D,2P) with N2, only the most recent actually resolved the composition of the reactants, i.e., the relative abundance of O+(4S), O+(2D), and O+(2P), as well as the identity of the product ion, e.g., N2+, NO+, or N+. The most recent laboratory and airglow modeling numbers agree for O+(2P), providing strong support for each other and for the laboratory value for O+(2D). (2) There are no published laboratory or theoretical constraints for collisions with O(3P). The airglow modeling numbers similarly provide only very broad limits. We should probably expect numbers around 5×10-11cm3s for both O+(2D) and O+(2P). Qualitative theoretical analysis suggests that the rate coefficient for O+(2D) is likely to be about twice as large as that for O+(2P). The recommended rate coefficients for relaxation are (in units of 1.0{×}10-10cm3s) 2.0±0.5 for O+(2P) + N2: 0.4±0.2 for O+(2P) + O(3P) 1.5±0.4 for O+(2D) + N2 0.6±0.3 for O+(2D) + O(3P)
SA41A-0262
Determination of Absolute Plasma Electron Density and Electron Neutral Collision Frequency from Plasma Impedance Probe Measurements.
A plasma fluid finite difference (PFFDTD) simulation of an antenna immersed in a magneto-plasma is used to determine the absolute electron density ne and the electron neutral collision frequency νen from RF impedance probe data. The Sudden Atomic layer (SAL) mission was launched as a part of the COQUI II campaign from Puerto Rico on 19th February, 1998 at 2009 LT. The impedance data analyzed here was obtained as the SAL rocket travelled through the lower sporadic sodium layer that occured between 90 to 94 km altitude. The impedance data is analyzed at 92.37 Km, 92.40 Km, 92.44 Km altitudes on the upleg and downleg. Analytical fits obtained from a cold collisional magnetoplasma model by Balmain is compared to the PFFDTD results. The Balmain fits are in reasonable agreement to the data but over predict the electron neutral collision frequency compared to the simulation fits. The values of ne obtained from the simulation are also compared to the values obtained from IRI model.Collision frequency νen values are compared with the Schunk and Nagy(2000) model values. The simulation results are found to be in close agreement with the models.
SA41A-0263
Inferring D-Region Parameters Over Arecibo Using Incoherent Scatter Radar
We used two radar modes with the aim of measuring D-region parameters on July 23, 2006 using. One mode employed the usual practice in these experiments to measure the ion line spectra over D region altitudes. The other mode was used as a new way to calibrate the electron densities in the D-region and also to correct the ion line spectra. It used a high resolution coded long pulse (random code) transmissions to measure both the ion and plasma lines. The ion line primarily provided a power profile connecting the D-region to the altitudes where the plasma line is useful. The plasma line provided the absolute electron density, used in the lower altitudes for calibration, and at F region altitudes for determining the baseline level in the D region spectra due to the folding in of F region scattered power. These measurements allowed us to calibrate power profiles obtained from CLP data in 100 – 150 km altitude range. Electron concentration was found to be in the range of a few hundred to 5000 cm-3 between 65 – 90 km altitude ranges. In order to infer the negative ions, D-region spectras were fitted to a folded Lorentzian in accordance with the previous theoretical work and the spectral width used to calculate the ratio of negative ion to electron concentration (λ). During morning hours between 9 – 11 hrs LT, 2.5 km thick layer of negative ions was observed with λ ~ 1.6 ± 0.3 between 74 to 77 km. From spectral widths in the altitude range of 81 to 91 km, we inferred temperatures using ion-neutral frequency that are found to be in the range of 195 to 215 K.
SA41A-0264
Seasonal and Diurnal Variation of Electron and Iron Densities in the MLT Region Above Arecibo
A climatological study was performed to compare local time variation of the averaged electron and iron concentration observed at the Arecibo Observatory (18.35°N, 66.75°N) Puerto Rico. The average Fe profile between 21:00 to 24:00 LT has a single peak at about 85 km with the exception of the summer when an additional peak exists at about 95 km. It is observed that the higher Fe peak in the summer is correlated with higher electron concentrations in this season. Comparison of Fe and electron concentrations suggests that recombination of Fe+ plays an important role in determining the Fe profile in the upper part of the Fe layer. Above 93 km, the Fe concentration appears to increase after sunset if the electron concentration exceeds about 4000 electrons cm-3. The average rate of Fe production is about 0.1 atom cm-3 s-1 for all seasons at 100 km in the early evening hours. A chemical model reveals that the concentration of Fe+ must be 50 to 80 % of the total ionization over Arecibo for typical equinox conditions to explain the observed rate of Fe production. These high relative Fe+ concentrations are consistent with in situ observations that Fe+ is usually the dominant ion in sporadic E layers in the nighttime lower E region. This suggests that the source of Fe+ is provided by sporadic E layers descending over Arecibo after sunset.
SA41A-0265
Retrieval of 2-D equatorial plasma bubble images from the TIMED/GUVI data
The optical images of the ionosphere from the TIMED/GUVI and IMAGE/FUV provide the global view of the equatorial plasma bubbles. The retrieval of the bubble characteristics such as latitudinal extension, tilt, and depletion width and depth provides very useful information for the dynamics of the background ionosphere and the underlying seeding mechanism of bubbles. We develop the 2-D bubble detection algorithm from each swath of the TIMED/GUVI data by employing the directional Laplacian kernel and principal component analysis techniques. Our method is distinguished from the currently known methods such as singular value decomposition and tomographic imaging. We will compare our bubble retrievals with the tomographic bubble images and discuss the variations of the bubble characteristics with season and longitude.
SA41A-0266
Enhanced Global Coverage of the Thermosphere and Ionosphere: Adding New UV data (DMSP/SSUSI) to the TIMED/GUVI Database
The TIMED/GUVI database of ultraviolet images and derived data products has been a valuable resource for research in ionospheric and thermospheric dynamics. Given Air Force approval, this database will be augmented by UV imaging data and derived data products from the Defense Meteorological Satellite Program (DMSP) Special Sensor Ultraviolet Spectral Imager (SSUSI). There are currently two operating SSUSI instruments (DMSP F16, F17) with three more planned for launch in coming years. This database will give unprecedented spatial and temporal coverage of the ionosphere and thermosphere, extending into the next solar maximum. A summary of SSUSI sensor coverage and data products will be provided, along with a brief discussion of the calibration strategies employed to ensure consistency between the different instruments.
SA41A-0267
Excitation of mid-latitude oxygen airglow emission at 844.6 nm
Photoelectron (PE) impact on thermospheric oxygen atoms is a major source of OI 8446 Å\ emission excitation at mid-latitudes. However, historical discrepancies between observed twilight emission brightnesses and photoelectron (PE) model predictions have not only prompted speculation regarding secondary sources of excitation but also precluded the use of observed brightness as a much-needed diagnostic of thermospheric O density. In an effort to improve understanding of the physical mechanisms responsible for its excitation, we present new photometric measurements of twilight OI 8446 Å\ emission brightness acquired from Arecibo Observatory, together with calculations of expected brightness from PE-impact excitation as well as a key secondary excitation source: radiative recombination of O+ ions. Although the 8446 Å\ brightness data are fully consistent with a dominant PE impact excitation source during winter, the new data also confirm an earlier report of excess early morning brightness with respect to PE models which use a tilted-dipole approximation to the geomagnetic field. We demonstrate that the poor agreement arises simply as a consequence of inaccurate model specification of the geomagnetic field configuration and associated conjugate point location. Using the IGRF geomagnetic field model to refine Arecibo's conjugate point location specified in the Field Line Interhemispheric Plasma (FLIP) PE model yields significantly improved agreement between the modeled and observed brightness decay profiles during both morning and evening twilight intervals. This simple geometric resolution to the historical discrepancy establishes the unique favorability of 8446 Å\ airglow for mid-laittude thermospheric remote sensing.
SA41A-0268
Thermospheric O/N2 in the Sunlit Disk From More Than Five Years of GUVI/TIMED Observations
GUVI indirect observations of the thermospheric column density ratio, O/N2, in the sunlit hemisphere have been made on a nearly continuous basis from day 50 of 2002 to the present as part of the TIMED spacecraft mission. The basic large-scale spatial structure includes variations with local time (greater values in the morning), Universal Time (modulation at high latitudes due to the offset magnetic dipole), and season (greater values in the local winter hemisphere). These differences are seen to fade in the approach to solar minimum. Superposed on this reasonably well-behaved background structure are the complex, transient perturbations driven by auroral substorms and geomagnetic storms. The spatial and temporal variations are summarized in part by time-lapse movies
SA41A-0269
Analysis, Modeling and Comparison of Nitric Oxide Emissions in the Thermosphere Measured by MIPAS and SABER
A comparative study of nitric oxide (NO) 5.3 micron nighttime emissions in the thermosphere measured by the MIPAS spectrometer and the SABER radiometer satellite instruments has been conducted. The MIPAS and SABER data were inverted to retrieve NO volume emission rates. Spectral fitting of the MIPAS data was used to determine the NO(v = 1) rotational and spin-orbit temperatures, which were found to be in non-local thermodynamic equilibrium (non-LTE) above 110 km. Near 110 km, the rotational and spin-orbit temperatures converged indicating the onset of equilibrium, in agreement with the results of non-LTE modeling. Due to the onset of equilibrium, the NO rotational and spin-orbit temperatures can be used to estimate the kinetic temperature near 110 km, and the results have been compared to NRLMSISE-00 atmospheric model kinetic temperatures. The SABER instrument 5.3 micron band filter cuts off a significant fraction of the NO emission, and therefore modeling of NO is necessary to predict the total band radiance. Correction factors for the SABER filter have been directly determined from the MIPAS data, providing excellent validation of the modeled values used in SABER operational data processing for nighttime conditions. The correction factors were applied to the SABER data to calculate densities of NO(v = 1). A feasibility study was also conducted to investigate the use of NO 5.3 micron emission data to derive NO(v = 0) densities in the thermosphere.
SA41A-0270
An Analysis of Mid-Latitude Neutral Wind in the Lower Thermosphere: Comparison of Fall and Spring Equinoxes
We present an analysis of tidal structures in the altitude range of 100 to 130 km for the September 1-30, 2005 and March 6-April 6, 2006 periods using the winds measured by the Millstone Hill incoherent scatter radar (42.6N, 288.5E). The dominant signal in both zonal and meridional winds is the semidiurnal component, as expected from the tidal theory and previous experimental data. Both zonal and meridional components of semidiurnal tide are stronger during the spring equinox, reaching 70-80 m/s, and have a well defined maximum around 110-118 km. In September, amplitude of 12-h tide peaks at 112km and 60-65 m/s for the meridional component, while the zonal component exceeds 50 m/s in range of altitudes from 105 to 130 km. The diurnal tide, which has often been assumed negligible in earlier observations, is found at altitudes 105-120 km. The phase structure of the diurnal component indicates domination of the in-situ generated tide. A perfect agreement between the data and GSWM02 predictions is found in March in the phase of the semidiurnal tide. Tidal amplitudes are typically underestimated by GSWM02 by a factor of 1.5-2 for semidiurnal component and overestimated for the diurnal component, with better agreement found for the spring equinox. Similarly to GSWM02, TIMEGCM simulations underestimate the amplitude of the 12-h component and overestimate the amplitude of the 24-h component at altitudes below 110 km, with predicted phases of 12-h component lagging observed phases by 2-3 hours.
SA41A-0271
First 844.6-nm observations of neutral oxygen using the Bowen fluorescence Spatial Heterodyne Spectrometer at Millstone Hill Observatory
A Spatial Heterodyne Spectrometer (SHS) has been installed at Millstone Hill Observatory to detect mid-latitude 844.6-nm emissions from nightglow due to Bowen fluorescence, as a way of measuring thermospheric neutral oxygen density. Neutral oxygen is a dominant species in the F-region of the thermosphere, and new measurements of its density are needed to make more accurate models of that region, models which better describe responses to impulsive events such as storms and coronal mass ejections. The SHS will take readings with a time resolution of 12 minutes. It has been aligned an calibrated at 589 nm in association with a concurrent project at Scientific Solutions to perform Fraunhofer Line Discrimination spectroscopy at the sodium doublet wavelength. The SHS will presently be reset to look at 844.6 nm, which involves only a rotation of the SHS gratings to a new Littrow angle. The challenge of the mesaurement will be to separate the Bowen fluorescence 844.6-nm light from 844.6 light from other sources, most prominently photoelectron (PE) impact. It is expected that there will be characteristics of Bowen fluorescence 844.6 emissions which allow it to be distinguished from PE and other sources of 844.6. The most promising of these hallmarks is a specific intensity ratio theorized to exist between two of the three lines in the 844.6 triplet for Bowen fluorescence. It is also expected that Bowen fluorescence emissions at Millstone Hill will become more significant later at night, as the sun sets in the opposite hemisphere. First light 844.6 results and analysis will be presented.
SA41A-0272
On the Existence and Excitation of Eastward Propagating Quasi-Two Day Waves in the MLT
MLT temperature fields measured by TIMED SABER over 60 day periods have revealed the presence of eastward propagating quasi-two day wave components with zonal wavenumbers 1-4, persistent throughout the entire year. These eastward quasi-two day waves display strong enhancements in the winter high latitudes around solstice, and in the high latitudes of both hemispheres around the equinoxes extending from the stratosphere into the mesosphere and lower thermosphere. The low latitude response is dominated by Kelvin modes extending from the MLT into the lower thermosphere. Daily observations from the South Pole meteor radar system show that eastward two-day wave activity occurs in sporadic bursts, peaking around winter solstice, but also occurring with smaller amplitudes at equinox. The results of numerical experiments conducted using the NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM), and the linear mechanistic Global Scale Wave Model (GSWM) are presented in order to understand the excitation mechanisms and time evolution of the eastward propagating quasi-two day waves. The eastward quasi-two day waves are found to be excited by mechanism of mean wind instability at high latitudes, both during the winter solstice and at equinox, which are manifested as the high latitude enhancements found in the observations and model results. This mechanism can excite Kelvin modes in the low latitude MLT, thus influencing the circulation of that region. Taken together, our findings point to the eastward quasi-two day waves as a persistent global scale phenomena not limited only to solstice conditions as previously thought.
SA41A-0273
Temperature Dependence of OH(\upsilon) Vibrational Relaxation by Atmospheric Gases
Emission from vibrationally excited OH is a key observable in the terrestrial middle atmosphere. A detailed understanding of vibrational relaxation by collisions with other atmospheric species is required so that we can quantify the importance of these processes in controlling atmospheric OH emissions. The SABER instrument aboard the TIMED satellite monitors OH emissions that are used to evaluate the energy deposition rate for the H + O3 reaction in the mesosphere. In order to accurately retrieve this information from the SABER OH measurements, reliable measurements are needed of collisional energy transfer rate constants for the key colliders, namely, oxygen molecules, nitrogen molecules, and oxygen atoms. The dependence of the rate constants on the OH vibrational level as well as the temperature dependence must be known. We report laboratory measurements on the removal of OH(\upsilon = 9) by oxygen atoms, oxygen molecules, and nitrogen molecules at room temperature and relative rates at low temperatures. In addition, we present the first measurements of OH vibrational energy transfer below 200 K for the OH vibrational levels 3 and 4. We note a strong temperature dependence of the rate constant for OH(\upsilon = 4) + O2, whose value more than doubles when the temperature is decreased from approximately 300 K to 160 K. In the experiments, we generate O(3 P) and OH(\upsilon) by photodissociation of ozone at 248 nm in a mixture of ozone, nitrogen, oxygen, and hydrogen. We monitor the temporal evolution of the OH(\upsilon) population by laser induced fluorescence. By controlling the initial conditions of the experiments, we can extract the rate constant for OH(\upsilon) removal by the gases in the system. We will present our experimental results and discuss their atmospheric implications based on the most current modeling calculations. This work was supported by the NASA Geospace Sciences and Planetary Atmospheres Programs. The participation of Z. M. Geballe was supported the NSF Research Experiences for Undergraduates Program.
SA41A-0274
TIDAL VARIATIONS OF OH ROTATIONAL TEMPERATURES IN THE ARCTIC AND ANTARCTIC HIGH-LATITUDE
Tidal variations in OH rotational temperatures have been investigated using observations from Michelson Interferometer instruments located at Resolute Bay (74.68º N, 94.90º W), Canada, and South Pole Station, Antarctica (90o S). These stations have been making continuous measurements of temperature and airglow emissions during the six months of each polar winter night. In this paper we present multi-year data from the two sites and perform spectral analysis to retrieve wave characteristics (amplitude and phase information). From the Lomb-Scargle spectral analysis of the measured temperatures, dominant oscillations are found at various periods near tidal frequencies, i.e. 8, 12, and 24 hour. Because of periods and persistence, the observed oscillations in temperature are most likely of tidal origin. Results will be discussed in the context of short variability and long term modulation of these tidal components.
SA41A-0275
OH Meinel (3,1) Airglow Emission Model Development and Comparison With Ground-based Observations
We have developed an OH Meinel (3,1) airglow emission of the earth's middle atmosphere calculating the population at each vibrational level using the Einstein coefficients for spontaneous emission. The model was then incorporated into the Whole Atmosphere Community Climate Model (WACCM) [Garcia et. al., 2007] and a simulation of one year was completed. Model OH intensities were compared to absolute intensities from South Pole Station, Antarctica (90°S) and Resolute Bay, Canada (74.68°N, 94.90°W). Both of these stations employ identical Michelson Interferometers, which operate continuously (24 hours a day) during the polar night for each station's winter season. Model simulations and observations were compared to study temporal variations in absolute intensity of OH airglow emission.
SA41A-0276
The anomalous Mesopause region temperatures of the 2003-2004 winter season measured from Svalbard (78N 16E)
This paper reports on the temperature and dynamics of the hydroxyl layer at approx. 87km measured over Longyearbyen (78N 16E) during the 2003-2004 winter. Optical spectra obtained by a Ebert-Fastie spectrometer were used for the temperature derivation. The high number of spectra available enabled spectral analysis of both the hourly and daily averaged temperatures. We were able to identify both the presence of a 16 day wave and a quasi 27 day oscillation in the mesopause region (approx. 87 km) temperatures from this season. The average daily temperature was 228K with a standard deviation of 17K. This is exceptionally high compared to previous and later years reported in the 23 year old time series from Svalbard. The observed temperatures have been compared to temperature data from other height regions above the Arctic (troposphere and stratosphere) and to satellite data from the satellite instrument SABER. In early January 2004 a major stratospheric warming event led to a nearly 2 month long vortex disruption with high-latitude easterlies in the middle to lower stratosphere and correspondingly high temperatures. The upper stratospheric temperatures of the same period were unusually low, while mesopause temperatures were high. The regions of alternating low and high temperatures throughout the atmosphere and the dynamics of these, are clearly coupled through gravity wave activity and general atmospheric circulation. We try to put our data into context with other authors' reports on the anomalous state of the atmosphere during the 2003-2004 boreal winter.
SA41A-0277
A Semi-empirical Model of the Contribution from Sporadic Meteoroid Sources on the Meteor Input Function (MIF) Observed at Arecibo
Microgram extraterrestrial particles from the sporadic background are widely believed to be the major contributors of metals in the Mesosphere/Lower Thermosphere (MLT). It is well established that this material gives rise to the upper atmospheric metallic and ion layers observed by radars and lidars. In addition, micrometeoroids are believed to be an important source for condensation nuclei (CN), a prerequisite for the formation of NLC particles in the polar mesopause region. In order to understand how this flux gives rise to these atmospheric phenomena, accurate knowledge of the global meteoric input function (MIF) is critical. In this work, we present results from a detailed model of the diurnal and seasonal variability of the micrometeoric activity in the MLT as observed by the 430 MHz Arecibo radar. The model uses Monte Carlo simulation techniques and includes an accepted mass flux provided by six main known meteor sources (i.e. orbital families of dust) and a detailed modeling of the meteoroid atmospheric entry and ablation physics. The principal goal of this effort is to construct a more precise sporadic MIF needed for the subsequent modeling of the atmospheric chemistry of meteoric material and the origin and formation of metal layers in the MLT.
SA41A-0278
Laboratory Measurement of CO2(ν2) + O Temperature-Dependent Vibrational Energy Transfer
The latest results from ongoing CO2(ν2)- O vibrational energy transfer measurements will be presented. The O + CO2 → O + CO2(ν2) vibrational uppumping process is a key contributor to 15-μm earthlimb emission and to upper atmospheric cooling in the 75-120 km altitude range. Model predictions of upper atmospheric density and temperature are sensitive to the assumed rate coefficient kO(ν2) for the relaxation of CO2(ν2) by O. Accurate accounting of kO(ν2) is necessary to derive the kinetic temperature and IR cooling rates from NASA TIMED/SABER radiometric data. In the present experiment, 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 time-dependent CO2(ν2) population. A vacuum-jacketed, liquid-nitrogen cooled reaction cell permits low-temperature measurements down to approximately 140 K. A second cell is used for high-temperature measurements up to about 550 K, spanning the range typically found in the mesosphere-lower thermosphere region. The results will be compared to the ab initio results of de Lara-Castells and coworkers, including the prediction that the O(3PJ=2) spin sublevel dominates the relaxation process.
SA41A-0279
CESAR: Compact Echelle Spectrograph for Aeronomic Research
With funding from the National Science Foundation Major Research Instrumentation program, plans are underway for designing, constructing, and fielding an echelle spectrograph patterned after the HIRES instrument on the 10-m Keck I telescope on Mauna Kea. Sky spectra from this and other large telescopes have revealed many new and interesting features in the terrestrial nightglow [Cosby et al., 2006; Cosby and Slanger, 2007; Sharpee et al., 2005; Slanger et al., 2003; Slanger et al., 2006; Slanger et al., 2004; Slanger and Osterbrock, 1998], and we have concluded that full access to such an instrument, with the ability to relocate it at various sites, will have a major impact on the study of the upper atmosphere. CESAR features f/1 camera optics, CCD detection with a range of 310-1040 nm, a resolution of 20,000, and simultaneous photon accumulation over 500 nm. The anticipated sensitivity is 3 photoelectrons R-1 s-1. After commissioning in Alaska, the instrument will become available as a community facility for qualified researchers with particular interests in studying the atmosphere at high spectral resolution, with simultaneous data collection over a broad spectral range. -------------- Cosby, P.C., B.D. Sharpee, D.L. Huestis, T.G. Slanger, and R. Hanuschik, High-resolution telluric emission line atlas from UVES/VLT and HIRES Keck/I: positions, intensities, and assignments for 2810 lines at 314-1043 nm, J Geophys. Res. 111, A12307, doi:10.1029/2006JA012023, 2006. Cosby, P.C., and T.G. Slanger, OH spectroscopy and chemistry investigated with astronomical sky spectra, Can. J. Phys., 85, 77-99, 2007. Sharpee, B.D., T.G. Slanger, P.C. Cosby, and D.L. Huestis, The N(2Do-4So) 520 nm forbidden doublet in the nightglow: an experimental test of the theoretical intensity ratio, Geophys. Res. Lett., 32, L12106, doi.1029/2005GL023044, 2005. Slanger, T.G., P.C. Cosby, and D.L. Huestis, A new O2 band system: The{ \it c-b} transition in the terrestrial nightglow, J. Geophys. Res., 108 (A2), 1089, 2003. Slanger, T.G., P.C. Cosby, B.D. Sharpee, K.R. Minschwaner, and D.E. Siskind, The O(1S-1D,3P) branching ratio as measured in the terrestrial nightglow, J. Geophys. Res., 111, A12318, doi:10.1029/2006JA011972, 2006. Slanger, T.G., D.L. Huestis, P.C. Cosby, and R.R. Meier, Oxygen atom Rydberg emission in the equatorial ionosphere from radiative recombination, J. Geophys. Res., 109, A10309, doi:10.1029/2004JA010556, 2004. Slanger, T.G., and D.E. Osterbrock, Aeronomy-astronomy collaboration focuses on nighttime terrestrial atmosphere, EOS, Trans. Amer. Geophys. Union, 79, 149, 150, 154, 1998.
SA41A-0280
Doppler Ducting of Quasi-Ripple Wave Events in the Mesospheric OH and O2 Airglow Emissions
Short-lived (< 40 min) ripple events are common and well documented phenomena in the mesospheric airglow emissions. Recent coordinated studies have determined that these small-scale wave patterns are primarily due to instabilities processes as indicated by their Richardson number (Ri < 0.25, dynamic and Ri < 0, convective instability). These events are contrasted by the frequent occurrence of well-defined, much larger scale wave patterns, termed bands that are mainly associated with the passage of freely propagating short- period (< 1 hour) gravity waves through the upper mesosphere. Here we present new coordinated imaging and meteor radar measurements of spatially extensive ripple-like events that outwardly appear to be ripple but are not directly due to instability processes. The measurements were obtained as a part of the joint NSF/AFOSR Maui-MALT program using the Utah State University Mesospheric Temperature Mapper (MTM) sequentially sampling the OH and O2 airglow emissions centered at 87 and 94 km, respectively, and the University of Illinois meteor radar providing hourly wind measurements over the altitude range of 80-100 km. Using two years of data 2003-2004, we have identified 20 quasi-ripple events where the background wind measurements clearly show the events to be strongly Doppler ducted (or evanescent) in nature. These relatively rare events provide important new information on the dynamics of wave ducting at mesospheric heights.
SA41A-0281
Laboratory Measurement of O3(v) + O Vibrational Energy Transfer
Photochemical reactions involving O3 play a key role in determining the thermal and radiative structure of the upper mesosphere/lower thermosphere. Emission detected in NASA's TIMED/SABER 9.6-μm channel is dominated by the O3(ν3) asymmetric stretch mode, including hot band and combination band emission arising from vibrationally-excited O3(v) populated by O + O2 + M three-body recombination. Rate coefficients kM(O3) for the relaxation of O3(v) by O2, N2, and O must be known to confidently model the O3 photochemistry in this region. Measurements of O3( v) quenching by O2 and N2 have been performed by several groups, including the temperature dependence. On the other hand, rate coefficients kO(O3) for quenching of O3(ν2,ν3) by O were only reported in a single published paper some 30 years ago. Those measurements were performed at room temperature, and yielded rate coefficients with factor-of-two precision. The data suggest that quenching of O3(v) by O could make a significant contribution especially at higher altitudes, motivating an updated measurement. The goal of the present work is to measure the quenching of several excited O3(v) levels by O using a temperature-jump/transient diode laser absorption experiment similar to the ongoing CO2(ν2)-O study. Ultimately a variable-temperature reaction cell will be used to measure temperature-dependent O3(v)-O relaxation rates for the first time.
SA41A-0282
Wave Damping and Accelerations Deduced from Mesospheric Airglow Perturbations
Mesospheric airglows in OH, O2 (Atmospheric), and OI (1S) responses to gravity waves have been modeled for amplitude and phase inferences to their intrinsic properties, including damping with altitude. Simple, monochromatic wave illustrations of the principles will be described. Momentum and energy fluxes with altitude, and deduced accelerations to the mean flow between layers are manifestations of wave momentum flux divergence. Examples of typical accelerations from airglow and supporting instrumentation will be described.
SA41A-0283
Predissociation Study of N2 in the 80-100 nm Region by Fluorescence Spectrometry
Fluorescence excitation spectra (FES) and dispersed fluorescence spectra (DFS) produced through photoexcitation of N2 using synchrotron radiation in the spectral region between 80 and 100 nm have been obtained. In the FES study we observe features corresponding to excitation of absorption transitions from the ground electronic state to the b, b', cn (with n = 4-8), cn' (with n = 5-9), and c4'(v') (with v' = 0-8) states of N2. The relative fluorescence production cross-sections for the observed FES features are determined. No fluorescence has been produced through excitation of the most dominant absorption features of the b-X transition except for the (1,0), (5,0), (6,0), and (7,0) bands, in excellent agreement with recent lifetime measurements and theoretical calculations. In the DFS study the EUV resonance fluorescence of the (0,v") bands of the c4'-X and the (1,v") bands of the b′-X transitions of N2 has been observed by photon excitation of N2 in the vicinity of 95.8 nm. The c4′(0) emission intensities become saturated at a N2 pressure higher than ~ 0.1 mTorr. The multiple scattering processes apparently significant reduce the c4'(0,0) emission rates. The broadband emission features in the 105-130 nm region become progressively significant as the N2 pressure increases. Many broad emission features in the 105-130 nm region observed in the DFS have been assigned to the (1,v") progression for v" up to 11 of the b'-X transition. The present results provide important information for further unraveling of complicated and intriguing interactions among the excited electronic states of N2, and may be useful in the explanation of weak c4'(0,0), but significant c4'(0,v") features in the dayglow of the Earth observed by the FUSE Explorer. Detailed results will be presented. This research is based on work supported by NSF grant ATM-0096761.
SA41A-0284
Mesospheric Winds and Magnetic Fields from the South Pole
We show how carbon monoxide (CO) can be used as a tracer of mesospheric neutral wind speeds, by measuring small Doppler shifts in its rotational emission spectrum. Since the altitude range we are most sensitive to is generally inaccessible to many other measurement techniques, this fills a significant experimental gap. Using this method, high-resolution ground-based measurements of mesospheric CO taken from the AST/RO sub-millimeter telescope, located at Amundsen-Scott South Pole Station have been used to calculate wind speeds and column densities over the Antarctic from 2002 to 2005. For more information see Burrows et al. JGR-Atmospheres doi:10.1029/2006JD007993. In addition, the 2→ 1 rotational transition of O18O has been measured and used as a tracer of the mesospheric magnetic field over the Antarctic. We demonstrate how the Zeeman splitting of this molecule was used to measure the Earth's magnetic field during the geomagnetic storm of January 2003.
SA41A-0285
SIMULTANEOUS OBSERVATION OF GRAVITY WAVES IN TEMPERATURE BY USING RAYLEIGH LIDAR AND SODIUM LIDAR
One night(Oct 28,2003)temperature measurements by a resonance Sodium Wind/Temperature lidar at Maui (20.7oN,156.3oW,84-104km) and by a Rayleigh temperature Lidar at Mauna Loa (19.5oN, 155.6oW, 35 - 80 km) are used to study gravity waves (GWs) from the lower stratosphere up to the lower thermosphere. The overlapped time series of these two datasets starts from 5:28UT and ends at 15:13UT. Mean and fluctuations of temperatures are derived and one dominating vertical wavelength is found to be around 10 km for both lidar measurements.Three other wave components are identified from the Rayleigh lidar measurement, but not from the Sodium Lidar.Gravity waves with smaller vertical wavelength(around 5km)seem to be filtered out when they propagate upward to the mesosphere.The wave amplitudes generally increase with altitude except for some areas characterized by reduced convective instabilities.The observed waves are partly dissipated and their amplitudes increase with a scale height of 14km.The maximum amplitudes increase from 0.6%(1.5K) at the lower layer(35-52km) to 4.7%(9K) at the upper layer(84-103km),which suggests that the observed quasi-10-km GWs can propagate upward even after experiencing certain dissipation in the middle layer(52-58 km).The wave period is around 5.5 hours,and the same period wave is also identified in the OH airglow observed at Maui on the same night.
SA41A-0286
Inter-annual and Long-term Temperature Variations in the Mesopause Region at High Latitudes Generated by the Stratospheric QBO
The Numerical Spectral Model (NSM) simulates the Quasi-biennial Oscillation (QBO) that dominates the zonal circulation of the lower stratosphere at low latitudes. In the model, the QBO is generated with parameterized small-scale gravity waves (GW), which are partially augmented in 3D with planetary waves owing to baroclinic instability. Due to GW filtering, the QBO extends into the upper mesosphere, evident in UARS zonal wind and TIMED temperature measurements. While the QBO zonal winds are confined to equatorial latitudes, even in simulations with latitude-independent wave source, the associated temperature variations extend to high latitudes. The meridional circulation redistributes some of the QBO energy to focus it partially onto the Polar Regions. The resulting QBO temperature variations away from the equator tend to increase at higher altitudes to produce inter-annual variations that can exceed 5 K in the polar mesopause region -- and our 3D model simulations show that the effect is variable from year to year and can produce large differences between the two hemispheres, presumably due to interactions involving the seasonal variations. Modeling studies with the NSM have shown that long-term variations can also be generated by the QBO interacting with the seasonal cycles through GW node-filtering. A 30-month QBO, optimally synchronized by the 6-month Semi-Annual Oscillation (SAO), thus produces a 5-year or semi-decadal (SD) oscillation -- and observational evidence for that has been provided by a recent analysis of stratospheric NCEP data. In a simulation with the 2D version of the NSM, this SD oscillation extends into the upper mesosphere, and we present results to show that the related temperature variations could contribute significantly to the long-term variations of the polar mesopause region. Quasi-decadal variations could furthermore arise from the modeled solar cycle modulations of the QBO and 12-month annual oscillation. Our numerical results are discussed in the context of the observed low summer temperatures reproduced by the model, to demonstrate that the above inter-annual and long-term variations could contribute significantly to the climatology of Polar Mesospheric Clouds (PMC) investigated by the Aeronomy of Ice in the Mesosphere (AIM) mission.
SA41A-0287
Seasonal nocturnal temperature structure of the mesopause over Arecibo and comparisons with TIMED-SABER
In a recently published paper, Friedman and Chu (2007 JGR, doi:10.1029/2006JD008220) presented the nocturnal climatology for the mesopause region over Arecibo Observatory (18.35°N, 66.75°W). Continuing this study, we have brought in the sampling effects of the nocturnal-only observations by looking at tidal amplitudes and phases as measured by the TIMED SABER instrument. In this presentation, we discuss the implications of combining the SABER measurements with the nocturnal lidar measurements. We will present the initial results of diurnal lidar temperature measurements from Arecibo, with the long-term goal of fully resolving the thermal structure and making extensive comparisons with SABER measurements.
SA41A-0288
Tidal Variability in a Whole Atmosphere Model (WAM): Comparison With SABER Observations on TIMED
The upper atmosphere and ionosphere exhibit spatial and temporal variability characteristic of planetary waves and tides originating in the lower atmosphere. To study the origin, vertical propagation, and possible effects of these planetary-scale perturbations on the coupled thermosphere-ionosphere-electrodynamics system, a new model of Integrated Dynamics through Earth's Atmosphere (IDEA) is being developed under a NASA sponsored collaborative project between the University of Colorado and National Weather Service's (NWS) Environmental Modeling and Space Environment Centers. The neutral-atmosphere component of the coupled system, WAM, is a 150-layer general circulation model based on NWS's operational weather prediction Global Forecast System (GFS), extended from its nominal top altitude of about 60 km to over 600 km. WAM incorporates relevant physical processes in the extended domain, ranging from the hydrological cycle, cloud physics, and atmosphere-surface exchanges in the troposphere, to solar and Joule heating, ion drag, and mutual diffusion of major species in the thermosphere. First extended simulations reveal the presence of various tidal waves modulated at planetary wave periods in the mesosphere and lower thermosphere (MLT). Substantial contribution from non-migrating tidal modes, recently implicated in the observed spatial morphology of the ionosphere, is also evident. Comparisons with a recent analysis of multi-year MLT observations by the SABER instrument on TIMED will be presented.
SA41A-0289
Seasonal variation of multi-day wave activity at Adelaide and Alice Springs
Aerospace imagers operating at Alice Springs (23° E) and Adelaide (34°S, 138° E) have collected more than five years of OH and O2A emission data. Images were taken over the course of each night at 5-minute intervals and used to determine OH Meinel (6,2) and O2 Atmospheric (0,1) band emission intensities and temperatures, as well as atmospheric gravity wave parameters. The NCAR general circulation model TIME-GCM was run for years 2002-2005 for comparison with these data. We present and discuss the seasonal variation of the two-day and quasi five-day waves at Adelaide and Alice Springs derived from airglow intensity measurements. Results from TIME-GCM runs, which include forcing from NCEP analysis fields, are presented for comparison, although the two-day wave is suppressed in the model. While the model often predicts the five-day waves, the observations show much greater year-to-year intensity variation. Explanations for this intensity variation will be explored, including the effects of gravity wave activity on both the two-day and five-day waves.
SA41A-0290
Results from and upgrades to the triple-etalon Fabry-Perot interferometer for OI 630-nm dayglow observations at Cerro Tololo
The Scientific Solutions triple-etalon air-gap Fabry-Perot Interferometer (FPI) has been installed at Cerro Tololo Interamerican Observatory (CTIO) in Chile to measure dayglow emissions from neutral oxygen at 630 nm, as a way of tracking thermospheric neutral winds. The instrument is designed to be operated remotely, using internet controls. It has yet to make the difficult dayglow Doppler measurements via remote operation, but analysis and equipment updates in 2007 have brought it much closer to that goal. A diffusion plate, to obtain diffuse integrated sunlight for data analysis, was delivered to Chile in Summer 2007. New instrument and data analysis in association with the University of Illinois has revealed more information about the remote operation parameters of the instrument. In addition, a new FPI calibration source was sent to Chile in Fall 2007. Previously, the instrument had used only a Helium-Neon laser (632.8 nm) for calibration, but a Cerium hollow cathode lamp, with an emission line at about 630.4 nm, will be added to the system. This will allow the system to be wavelength-calibrated and set much closer to the line of interest, making it significantly easier to detect the 630-nm emission. Both calibration sources will be active at the same time, and remotely switchable. The next step in data collection is to seek the 630-nm emission from nightglow, where the emission is very much easier to detect because of the lack of background light. This will show how the system responds to simple 630- nm emission, and make detecting that emission in dayglow (where it is surrounded by Solar Fraunhofer lines and copious background light) much easier. Instrument updates and current data analysis results will be presented in this talk.
SA41A-0291
Mesospheric Water Vapor Retrieved From SABER/TIMED Measurements
The SABER instrument on board the TIMED Satellite is a limb scanning infrared radiometer designed to measure temperature and minor constituent vertical profiles and energetics parameters in the mesosphere and lower thermosphere (MLT). The H2O concentrations are retrieved from 6.3 micron band radiances. The interpretation of this radiance requires developing a non-LTE H2O model that includes energy exchange processes with the system of O3 and O2 vibrational levels populated at the daytime through a number of photoabsorption and photodissociation processes. We developed a research model based on an extended H2O non-LTE model of Manuilova et al, 2001 coupled with the novel model of the electronic-vibrational kinetics of the O2 and O3 photolysis products suggested by Yankovsky and Manuilova, 2006. The performed study of this model helped us to develop and test an optimized operational model for interpretation of SABER 6.3 micron band radiances. The sensitivity of retrievals to the parameters of the model is discussed. The H2O retrievals are compared to other measurements for different seasons and locations.
SA41A-0292
Seasonal variations of semidiurnal tidal-period perturbations in mesopause region temperature, zonal and meridional winds above Fort Collins, CO (40.6°N, 105.1°W)
Based on Colorado State University (CSU) Na lidar observations over full diurnal cycles from May 2002 to April 2006, harmonic analysis was performed to extract semidiurnal perturbations in mesopause region temperature, zonal and meridional winds over Fort Collins, CO (40.6°N, 105.1°W). The observed monthly semidiurnal amplitudes and phases are compared to predictions of the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA) for the CSU Na lidar location. Both show similar tidal seasonal variations: a) propagating mode dominance in winter and equinoctial months and evanescent mode behavior in summer months; b) large amplitude during the winter months with a larger growth rate above ~ 85 km and minimum amplitudes during the summer months around a constant value. The lidar observed a considerable tidal amplitude enhancement in September, a phenomenon previously reported at high latitudes. By calculating the vertical wavenumber squared, m2, of the major semidiurnal modes, (2, 2), (2, 3), and (2, 4), we evaluated the effect of mean temperature and zonal wind on semidiurnal tidal behavior. Considering the amplitude ratio, RP/E, between a propagating mode and the evanescent (2, 2) mode with different amplitude growth rates, and the seasonal dependence of thermal excitation of the major semidiurnal tidal modes in the troposphere and stratosphere, a simplified explanation of the upward propagation of major tidal modes is provided to explain qualitatively the seasonal and altitude variation of semidiurnal tidal amplitudes and phases.
SA41A-0293
Self-consistent Non-LTE Model of Infrared Molecular Emissions and Oxygen Dayglows in the Mesosphere and Lower Thermosphere
We describe the new version of the ALI-ARMS (for Accelerated Lambda Iterations for Atmospheric Radiation and Molecular Spectra) model. The model allows simultaneous, self-consistent calculations of the non-LTE populations of the electronic- vibrational levels of ozone and O2 photolysis products and the vibrational level populations of CO2, N2, O2, O3, H2O, CO, and other molecules with a detailed accounting of electronic-vibrational, vibrational-vibrational and vibrational-translational energy exchange processes. The model is used as the reference for modeling O2 dayglow experiments and for the infrared molecular emissions measured by the multi-channel observations of MLT in the SABER experiment on TIMED. It also permits the re-evaluation of the thermalization efficiency of absorbed solar ultraviolet energy and infrared radiative cooling/heating of MLT through a detailed accounting of the electronic-vibrational relaxation of excited photolysis products via a complex chain of collisional energy conversion processes down to the vibrational energy of optically active trace gas molecules.
SA41A-0294
Ducting Conditions for Observed Bore-Like Events in the Upper Mesosphere and Lower Thermosphere
Instances of traveling airglow fronts in the upper mesosphere and lower thermosphere (MLT) have been identified as mesospheric bores. They are ducted phenomena and have been observed in association with mesospheric inversions and strong wind shears. Airglow fronts often show an out-of-phase relation between OH and O2 (the former brightens while the latter dims). This talk reports on a numerical study of ducted waves in the upper mesosphere and focuses on conditions (e.g., inversion thickness and strength, wind shear) that give ducting in altitude regions where the upper mesospheric-lower thermospheric airglow layers are found. We analyze the vertical modal structure and the airglow signature of ducted waves for two events. The first is the dramatic event described and analyzed by Smith et al. (2003) that occurred in the south western United States. The second is an event observed over Alice Springs, Australia with the Aerospace airglow imager. Under typical conditions there is a stable layer in the lower thermosphere and ducted modes can involve both layers to a greater or lesser extent. We find ducted modes that resemble observed modes in terms of phase speeds and wavelengths, but (unlike for tropospheric bores) the waves are not necessarily the lowest mode the system can support. These modes include but are not necessarily confined to the upper mesospheric stable layer. Smith, S. M., et al., A multidiagnostic investigation of the mesospheric bore phenomenon, J. Geophys. Res., 108, 2003
SA41A-0295
The Terrestrial O2(1delta) 1.27 micron Airglow Emissions
The O2(1Δ) 1.27 micron emission is one of the brightest airglow emissions observed in the Earth airglow spectrum and provides an ideal light source for passively sensing the atmosphere. It is known that the excited O2(1Δ) molecules in the daytime are produced by ozone photolysis by solar UV radiation. Its measured emission rates have thus been used to obtain the abundances of ozone. The exact night time excitation mechanisms, however, are still not well-understood. However, atomic oxygen recombination and oxidation of vibrationally excitation OH have been proposed. Observations by instruments onboard TIMED have provided a unique opportunity to examine the spatial and temporal morphology of this emission and its excitation mechanisms. We will use the O2(1Δ) and OH(v) measurements by SABER and O2(1Σ) measurements by TIDI to investigate the O2(1Δ) excitation mechanisms. In addition, because of its relatively long chemical relaxation time, the O2(1Δ), could potentially not be in the steady-state chemical balance. In this paper, we will discuss the importance of this effect and its impact on the utility of this emission for composition retrievals (i.e. ozone and atomic oxygen).
SA41A-0296
Dynamical flux of constituents in the mesopause region estimated from heat flux measurement
The vertical transport of constituents in the mesopause region due to dissipating waves is a significant transport process but the dynamical fluxes cannot be easily measured. We show that under fairly general conditions, constituent fluxes can be related to the heat flux in a simple way. This relation is verified by comparing the directly measured sodium flux and heat flux with a sodium wind/temperature lidar at Starfire Optical Range. The annual mean, as well as the seasonal variation of the sodium and heat fluxes are consistent with theory. The results suggest that for many constituents in the mesopause region, their vertical dynamical flux fluxes can be estimated from the measured heat flux, and the mean profiles of the temperature and constituent.