The Response of Planetary Ionospheres to Solar Irradiance III Posters
Presiding: S C Solomon, NCAR/High Altitude Observatory; M Galand, Center for Space Physics, Boston University
SA41A-01 0830h
ASPERA-3 ELS Measurements of Photoelectrons from Carbon Dioxide at Mars
The Mars Express Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) experiment determines the electron, ion, and neutral particle components of plasma using four instruments: Electron Spectrometer (ELS), Ion Mass Analyzer (IMA), Neutral Particle Imager (NPI), and Neutral Particle Detector (NPD). The ELS instrument determines the electron energy spectrum by collecting 128 logarithmically spaced samples of the electron spectrum between 1 eV and 20 keV every four seconds. Its 8% energy resolution is used to resolve the carbon dioxide photoelectron peaks (generated from He 30.4 nm photons) which are a dominant feature in the Martian Ionosphere. However at times, ELS oversamples the electron spectrum by conducting measurements with separation energies smaller than an 8% difference. This oversampling technique is used to improve the ELS measurement of the Mars photoelectron spectrum. During times of oversampling, ELS may be stepped in a linear fashion from 1 eV to 127 eV. In order to recover the photoelectron spectrum oversampling cases, detailed knowledge of the instrument response function must be used along with inversion methods. The procedure increases the energy resolution in the oversampled region of the energy spectrum, and thus, improves the measurement of the amplitudes of the carbon dioxide peaks.
SA41A-02 0830h
Variability of the Atmosphere/Thermosphere in the Northern Hemisphere of Mars: Analysis of the Data Obtained Onboard Mars Global Surveyor and Odyssey
The altitude of the main peak of the electron density (hpeak) and the neutral atmosphere scale-height in the vicinity of the peak (Hn) have been derived from the Mars Global Surveyor radio science data. The positive altitude gradient of Hn has been calculated. At SZA>82°, hpeak increases significantly with SZA while Hn is approximately constant. This indicates that Hn decreases with SZA when the altitude remains constant. At SZA<82°, where hpeak is approximately constant, the shape of isodensity surface of the neutral atmosphere in the vicinity of the main peak of the electron density has been derived using hpeak and Hn. The variations within the solar activity cycle have been analyzed. The isodensity of the neutral atmosphere has been compared with the longitudinal variations of the neutral atmosphere density as observed onboard Odyssey in the period Day 315-356, 2001. The difference in the phases of the non-migrating tidal waves, which were observed in the periods approximately separated by a half of Martian year: Day 344, 2000 -Day 31, 2001 and Day 315-356, 2001, may indicate either the seasonal variations or the local time effect.
SA41A-03 0830h
The Response of an Ionosphere to Changes in the solar F10.7 flux: Comparison of Venus, Earth, and Mars
There are many similarities between the terrestrial E region and the ionospheres of Venus and Mars. All are dominated by photochemical, not transport, processes. The dissociative recombination of molecular oxygen ions is an important loss mechanism for all three regions. Various workers have studied how ionospheric properties, such as the peak electron density, in these regions respond to changes in solar flux, especially as represented by the F10.7 index. Timescales of interest include the solar cycle, the solar rotation period, and shorter periods, such as one day. We shall discuss the many parameterizations of such responses that have been published and examine their consistencies with known photochemical processes.
SA41A-04 0830h
Soft X-ray Irradiance during a Solar Flare
Solar soft X-ray irradiance provides a highly variable energy source to the lower thermosphere. Solar flares are a dramatic source of this variability. Observations from the NASA satellite mission Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics - Solar Extreme Ultraviolet Experiment (TIMED-SEE) are being analyzed to determine how the solar soft X-ray energy deposition varies during a solar flare. The XUV Photometer System (XPS) aboard TIMED-SEE observes the solar soft X-ray irradiance between 0.1 and 27 nm for a 3 minute period approximately every 96 minutes. Contrary to initial assumptions based on the nature and infrequency of solar flares, XPS observations have shown that flares significantly impact the daily averaged energy input and thus the atmospheric chemistry of the lower thermosphere. The XPS observed, on average, eight solar flares of various strengths per month during a five month period in 2002 while the Student Nitric Oxide Explorer (SNOE) observed nitric oxide (NO) between 95 and 135 km. It has been shown that SNOE observed a significant increase in NO during the April 21, 2002 solar flare that was observed by the XPS. The eight XPS photodiodes are broadband detectors and a reference spectrum is required to interpret the signal because the sensitivity varies within each detector bandpass. A solar flare spectrum is inferred from the XPS detectors by an algorithm that iterates through differential emission measures until they produce a model spectrum that can reproduce the XPS detector observations. These flare spectra will be used to determine the soft X-ray energy input to Earth's lower thermosphere during a solar flare. Results and a description of this analysis will be presented.
SA41A-05 0830h
Earth FUV Dayglow Response to the 20 January 2005 Solar Flare: TIMED and IMAGE Observations
An X-class solar flare occurred on 20 January 2005 when the TIMED and IMAGE spacecraft were both well positioned to observe the response of Earth's dayglow emission intensity. Brightness enhancements during the flare relative to just before were determined at tangent altitudes of peak emission viewed toward the limb with TIMED. The TIMED observations were made at low solar zenith angles and show flare enhancements of roughly 15%, 30%, 30%, and 60%, respectively, for OI 130.4 nm, OI 135.6 nm, N2 LBH Short, and N2 LBH Long modes of the TIMED/GUVI instrument. However, GUVI observations of HI Lyman-alpha emission brightness do not show a significant brightness change. This lack of change in HI Lyman-alpha dayglow brightness is consistent with no significant change (<2%) in the solar Lyman-alpha flux observed with TIMED/SEE. Enhancements of emissions produced by photodissociation and photoelectron impact excitation sources are studied with IMAGE observations following Immel et al., JGR, 2003. Simulations of dayglow limb profiles to compare with the observations are produced using the NRLMSIS atmosphere model, the IRI90 ionosphere model, the GLOW photoelectron model, and the REDISTER radiative transfer model. The combined datasets enable a better study of the airglow sources most affected by the EUV and x-ray components of solar irradiance variability. We report our preliminary analysis of the response of FUV dayglow emissions to this event.
SA41A-06 0830h
Observations of Solar and Magnetospheric Inputs and Atmospheric Responses to the January 2005 Long Duration Flares and Fast Coronal Mass Ejections
We report observations by the TIMED GUVI instrument of magnetospheric inputs and atmospheric responses to the remarkable series of four long-duration X-class flare events and fast coronal mass ejections that occurred from 15-22 January 2005. Magnetic activity included two magnetic storm intervals (the second accompanied by a large enhancement in solar wind dynamic pressure), and two high speed stream intervals. Unusual features seen by TIMED and discussed here include: (1) the ionospheric response to long intervals of high-energy intense polar rain (2) an excess in the mid-to-low latitude nightside atomic oxygen emissions at 130.4 and 135.6 nm and (3) enhancements in auroral electron and proton precipitation during the high dynamic pressure intervals. The intense polar rain was correlated with extremely low solar wind densities in the high-speed streams. An initial look at the observations indicates that during intervals of quieting magnetic activity (i.e., January 19-20), the polar rain was the largest energy input at high latitudes. This introduces important asymmetries into the magnetosphere-ionosphere system since the intense polar rain was confined to the northern hemisphere for the first high speed stream interval and to the southern hemisphere for the second. The excess oxygen emissions are quite extraordinary. They were seen during the 21 January magnetic storm in the high dynamic pressure interval. Similar emissions have previously been observed by TIMED but only rarely during extreme magnetic storm events.. Two possible sources of this excess emission are energetic ion and neutral precipitation from the ring current and/or a large-scale and relatively uniform enhancement in ionospheric density. Significant and correlated changes were observed in the ring current ENA by IMAGE/HENA at this time. On the other hand, DMSP observations indicate an increase in the ionospheric density most likely associated with penetration electric fields at the onset of the magnetic storm activity.. This paper will evaluate the relative contributions of these emission sources.
http://guvi.jhuapl.edu
SA41A-07 0830h
On the Relationship of the Equatorial Electron Density (foF2) with Solar Soft X-ray Fluxes
We find a clear relationship between the daytime foF2 at the equator and solar X-ray fluxes during 1998-2000. The digisonde measurements of foF2 are from Jicamarca, Peru; and are compared with the solar soft X-ray fluxes from the Student Nitric Oxide Explorer (SNOE) satellite. The X-ray fluxes measurements are in wavelength bands of 2-7nm, 6-17nm and 19-21nm. After removal of trends with periods longer than 27 days, comparison of individual digisonde measurements shows a correlation of approximately 0.4 with the solar fluxes; and the effects of the sun's rotation can clearly be seen. Previous analysis of averaged Total Electron Content (TEC) from Ancon, Peru, found a correlation of 0.6, with the X-ray fluxes leading TEC approximately 1.3 days.
SA41A-08 0830h
The Correlation Between Mid-latitude Trough and the Plasmapause
We use simultaneous global observations of the mid-latitude trough and the plasmapause to experimentally prove a long-standing conjecture of magnetosphere-ionosphere coupling- namely the mid-latitude trough and plasmapause are on the same field line. Global Ionospheric Maps (GIM), generated using ground based GPS receivers, are used to detect the globally extended mid-latitude trough; while global IMAGE EUV pictures are used to estimate the plasmapause position. Observations during the equinox and solstices and during quiet and disturbed periods are analyzed. In addition, positions of the mid-latitude trough are calculated using a simple empirical model. The two independent observations (mid-latitude trough and plasmapause positions) and an empirical model have been compared on a global scale and found to be in excellent agreement.
SA41A-09 0830h
High Resolution EUV/FUV Spectral Survey of the Dayglow From ARGOS/HITS
The High Resolution Airglow and Aurora Spectroscopy (HIRAAS) experiment was successfully launched on the USAF Advanced Research and Global Observation Satellite (ARGOS) and continuously monitored the thermospheric and ionospheric airglow from May 1999 through March 2002 using three ultraviolet spectrographs. The High-resolution Ionospheric and Thermospheric Spectrograph (HITS) is a far- and extreme-ultraviolet (FUV/EUV) Rowland circle spectrograph covering the 50-150 nm spectral range at ~0.1 nm resolution in 11-nm passbands. While limb scanning, the HITS measures airglow emissions from 50 to 400 km every 130 seconds. During the mission the HITS stepped through a regular monthly sequence of passbands covering much of its spectral range. The HITS observations represents a uniquely useful dataset: high resolution, altitude-resolved global dayglow spectra. These measurements provide the capability to study new remote sensing techniques using resolved multiplet emissions (OII 83.4 nm), observed Doppler-shifted emissions from proton aurora (HI 121.6nm), and measure temperatures from molecular bandshapes (N2 Lyman-Birge-Hopfield). Moreover, the HITS spectra provide the means to disentangle complicated emission features seen at low resolution, such as NII 108.5nm emission which includes a number of nearby weak contaminating features. This analysis examines the altitude-resolved high resolution dayglow spectra acquired during June, 2000.
SA41A-10 0830h
N+ 1085Ã… Observations from the Special Sensor Ultraviolet Limb Imager (SSULI)
The first Special Sensor Ultraviolet Limb Imager (SSULI) sensor was launched on the Defense Meteorological Satellite Program (DMSP) F16 spacecraft in October of 2003 into a sun-synchronous 830 km circular orbit at a local time of 0800-2000 UT. The SSULI sensor has a field-of-view of 2.4°x0.15° and sweeps out a 2.4°x17° field-of-regard during each 90 second scan, with wavelength coverage between 800Ã… and 1700Ã… at 23Ã… resolution. The field of view scans ahead of the spacecraft in the orbital plane through a 17° field of regard, corresponding to approximately 75-750 km altitude. This paper will focus on the dayglow emission profiles of N+ 1085Ã…, generated by photo-dissociative ionization of N2. The SSULI 1085Ã… emission profiles will be compared with output from the Atmospheric Ultraviolet Radiance Integrated Code (AURIC) model spectral radiances. The period of interest for this study is the month of January, 2004.
SA41A-11 0830h
Comparison of Thermospheric Density Derived From TIMED/GUVI Limb Observations with Total Mass Density Derived From Satellite Orbits
We use TIMED/GUVI limb observations of thermospheric far UV dayglow to derive height profiles of O, N2, and O2 number densities. From these, we calculate the total mass density for comparison with total mass density derived from changes in the orbits of satellites with varying perigee heights. To accommodate sampling differences, we compare the ratio, averaged over ~3 days, of observed total mass density to that predicted by the NRLMSISE-00 empirical model. Our results represent the first validation of absolute densities derived from FUV limb scanning. The GUVI densities in the 300-500 km range are in good agreement with the orbit-derived densities, with both showing variations on solar rotation time scales. Of particular interest is a substantial depletion of upper thermospheric density around day 200 of 2002, when observed densities were 40% smaller than those predicted by NRLMSISE-00.
SA41A-12 0830h
Molecular Nitrogen Carroll-Yoshino c4' (v'=0, v">2) Fluorescence in the Thermospheric Dayglow as seen by the Far Ultraviolet Spectroscopic Explorer
N2 Carroll-Yoshino c4' excitation has been of considerable interest in the analysis of EUV-FUV observations of several solar system objects: Earth, Titan and Triton. The fundamental v'=0, v"=0 band is characterized by strong transition strengths with relatively weak predissociation. However, the associated large optical depths lead to enhancement of predissociation and fluorescence. Past work on the intricacies of c4' multiple scattering and the interaction of v'=0, v"=1 branching with the b(2,0) transition illustrated the complexities of the problem and provided insight into the differences seen among observed thermospheres; however, the role of v'=0, v">2 fluorescence has until now been considered very minor. High-resolution dayglow measurements by the Far Ultraviolet Spectroscopic Explorer (FUSE) made in September 1999 reveal c4' fluorescence bands at wavelengths > 1100 Ã… much stronger than previously expected. The results of a careful analysis of the FUSE measurements -- fluorescence band intensities along with intensities of features blended in lower resolution observations -- are presented and the implications of the observed emission ratios are discussed. The c4' (0,9) band at 1183 Ã… in particular stands out as a viable remote sensing observable.
SA41A-13 0830h
Measurement of Atomic and Molecular Parameters of Nitrogen for Earth, Planetary and Astrophysical Applications
For the purpose of providing accurate atomic and molecular data for applications to the Earth's ionosphere and astrophysical plasmas, this project will provide measurements of: the radiative lifetime of the 5S metastable level of N+, the dissociation rate of doubly charged molecular nitrogen ions, electron capture rates from molecular nitrogen for both these ions, and the cross section for dissociative electron impact ionization of molecular nitrogen into metastable 5S N+, which is responsible for auroral 214 nm emission. Preliminary data and results are be presented. Ions are created in a radiofrequency ion trap by electron bombardment on nitrogen gas, and the UV radiation emitted by the stored ion population is then measured as a function of time. The primary source of radiation is the decaying metastable N+ ions, which emit photons at a wavelength of 214 nm. In addition to the atomic N+, doubly charged molecular ions (dications) are created and stored. Electron capture from neutral molecules into excited states of singly charged molecular nitrogen results in emission in bands that overlap with 214 nm. The decay rate of these two sources of radiation is measured as a function of nitrogen gas pressure to determine: the electron capture rates for both ions, the radiative decay rate of the metastable N+, and the dissociation rate of the dications. The photon observations are corrected for ion losses using the technique presented in Daw, Parkinson, Smith, & Calamai, ApJ 533, L179, 2000. Limits on the cross section for dissociative electron impact ionization of molecular nitrogen into metastable 5S N+ will be determined relative to the (well-known) cross section for dication production, by comparing the photon rate at 214 nm to the photon rate generated in different bandpasses as a result of dication electron capture.