The Global Ultraviolet Imager (GUVI) onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite senses far ultraviolet emissions from O and N 2 in the thermosphere. Transformation of far ultraviolet radiances measured on the Earth limb into O, N 2 , and O 2 number densities and temperature quantifies these responses and demonstrates the value of simultaneous altitude and geographic information. Composition and temperature variations are available from 2002 to 2007. This paper documents the extraction of these data products from the limb emission rates. We present the characteristics of the GUVI limb observations, retrievals of thermospheric neutral composition and temperature from the forward model, and the dramatic changes of the thermosphere with the solar cycle and geomagnetic activity. We examine the solar extreme ultraviolet (EUV) irradiance magnitude and trends through comparison with simultaneous Solar Extreme EUV (SEE) measurements on TIMED and find the EUV irradiance inferred from GUVI averaged (2002-2007) 30% lower magnitude than SEE version 11 and varied less with solar activity. The smaller GUVI variability is not consistent with the view that lower solar EUV radiation during the past solar minimum is the cause of historically low thermospheric mass densities. Thermospheric O and N 2 densities are lower than the NRLMSISE-00 model, but O 2 is consistent. We list some lessons learned from the GUVI program along with several unresolved issues.
The launch of the Defense Meteorological Satellite Program (DMSP) satellite F16 in 2003 provided the first opportunity to analyze extensive sets of high‐quality coincident auroral particle and FUV data obtained by the onboard sensors Special Sensor Ultraviolet Spectrographic Imager (SSUSI) and Special Sensor Auroral Particle Sensor (SSJ/5). Features of interest are Ly α (121.6 nm), Lyman‐Birge‐Hopfield short (LBHS, the SSUSI 140–150 nm channel), and Lyman‐Birge‐Hopfield long (LBHL, 165–180 nm). We report on comparisons of column emission rates (CERs) by deriving simulated SSUSI values using SSJ/5 electron and ion (treated as proton) spectra. Field‐line tracing is performed to determine the locations of coincidences. CERs are obtained by integrating the products of particle spectra and monoenergetic emission yields. A technique is reported for deriving these yields from nonmonoenergetic CERs obtained by our particle transport model. SSJ/5 ion spectra are extrapolated above 30 keV using a statistical representation based on Polar Orbiting Environmental Satellites particle data. Key quantities of interest are ratios of SSUSI to SSJ/5‐based CERs (S‐S ratios) and corresponding ratios of proton‐produced to total emission (unity for Ly α and from 0 to 1 for LBHS and LBHL). SSJ/5‐based CERs are used to derive the latter ratios. Median ratio values are determined in order to reduce the error budget to primarily calibration and model errors. The median LBH S‐S ratios increase by a factor of ∼2.5 from electron to proton aurora and support significantly higher proton LBH emission efficiencies (3 times the electron efficiencies) assuming reported calibration uncertainties. This calls for significant increases in proton and/or H‐atom LBH cross sections. In turn, FUV auroral remote‐sensing algorithms must explicitly address both electron and proton aurora.
[1] The NASA TIMED/GUVI experiment obtained unprecedented far ultraviolet images of thermospheric composition and temperature during the intense geomagnetic storm on 20-21 November 2003. Geographic maps of the atomic oxygen to molecular nitrogen column density ratio show severe depletions that extend to the equator near the peak of the storm. This ratio is a key indicator of how the thermospheric composition is disrupted at high latitudes and how the perturbed air moves globally as a result of dynamical forcing. For example, migrating regions of low oxygen-to-nitrogen air are invariably found to correlate with high thermospheric temperatures. As well, GUVI obtained altitudinallatitudinal (limb) images of temperature and composition, which show how the disturbances vary at different heights. The ASPEN thermospheric global circulation model was used to test our understanding of these remarkable images. The resulting simulations of thermospheric response show good agreement with GUVI data prior to the peak of the storm on 20 November. During the peak and recovery phases, serious discrepancies between data and model are seen. Although this initial attempt to model the storm is encouraging, much more detailed analysis is required, especially of the high-latitude inputs. The GUVI images demonstrate that far ultraviolet imaging is becoming a crucial component of space weather research and development.
[1] Thermospheric O/N 2 column density ratios referenced at a N 2 column density of 10 17 cm À2 are obtained using the IMAGE SI-13 and TIMED/GUVI far-ultraviolet (FUV) dayglow data, AURIC simulation results, and MSIS86 model. Each of the magnetic storms occurring during a 4-day period (1-4 October 2002) caused significant O/N 2 depletion that was detected by both of the IMAGE SI-13 and GUVI instruments. The depletion extended down to latitudes of 10°and À5°in the Northern and Southern Hemispheres, respectively. Simultaneous measurements show an excellent agreement between the SI-13 and GUVI O/N 2 on both global and local scales. The IMAGE SI-13 O/N 2 data provide direct optical evidence that the O/N 2 depletion corotates with the Earth. The GUVI O/N 2 indicate the depletion in both of the hemispheres is not symmetric owing to the seasonal effect and differences in heating and convection induced winds. Both the IMAGE SI-13 and GUVI O/N 2 maps also provide a good opportunity for future modeling efforts.
Despite the importance of health information seeking, not all people engage in such behaviors, especially when thinking about the disease is distressing. The focus of this paper is to examine the antecedents of information seeking and retention. Based on individuals' risk perception and efficacy beliefs, the risk perception attitude framework is used to formulate four groups: responsive (high risk, high efficacy), avoidance (high risk, low efficacy), proactive (low risk, high efficacy), and indifference (low risk, low efficacy). In Study 1, a 2 (risk) 3 2 (efficacy) between-subjects experiment, participants' perceived risk to skin cancer and skin cancer-related efficacy beliefs were induced to determine their information seeking, retention, and intentions to engage in future seeking. The responsive group, as predicted, was associated with the most information-seeking behaviors and information-seeking intentions. The avoidance group, however, sought information but exhibited the lowest retention scores. These results were used to derive two predictions-the incredulity hypothesis and the anxiety-reduction hypothesis-that were then tested in Study 2. Study 2, also a 2 (risk) 3 2 (efficacy) betweensubjects experiment dealing with diabetes, found support for the anxiety-reduction hypothesis, which argues that the high-risk, low-efficacy group experiences more anxiety, which leads to high motivations to seek, but lower ability to retain information.
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