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Found 24 entries in the Bibliography.
Showing entries from 1 through 24
| 2015 |
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Remote sensing of Earth's limb by TIMED/GUVI: Retrieval of thermospheric composition and temperature The Global Ultraviolet Imager (GUVI) onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite senses far ultraviolet emissions from O and N2 in the thermosphere. Transformation of far ultraviolet radiances measured on the Earth limb into O, N2, and O2 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\textendash2007) 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 N2 densities are lower than the NRLMSISE-00 model, but O2 is consistent. We list some lessons learned from the GUVI program along with several unresolved issues. Meier, R.; Picone, J.; Drob, D.; Bishop, J.; Emmert, J.; Lean, J.; Stephan, A.; Strickland, D.; Christensen, A.; Paxton, L.; Morrison, D.; Kil, H.; Wolven, B.; Woods, Thomas; Crowley, G.; Gibson, S.; Published by: Earth and Space Science Published on: 01/2015 YEAR: 2015 DOI: 10.1002/2014EA000035 airglow and aurora; remote sensing; thermosphere: composition and chemistry; thermosphere: energy deposition |
| 2014 |
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Attribution of interminima changes in the global thermosphere and ionosphere We present a statistical attribution analysis of the changes in global annual average thermospheric mass density and ionospheric total electron content (TEC) between the cycle 22/23 solar minimum (which occurred at epoch 1996.4) and the prolonged cycle 23/24 minimum (2008.8). The mass density data are derived from orbital drag, and the TEC data are derived from ground-based GPS receivers. The interminima change in mass density was -36\% relative to the 1996.4 yearly average. Considering each multiplicative forcing independently, lower average geomagnetic activity during the cycle 23/24 minimum produced an interminima density change of at least -14\%, solar extreme ultraviolet (EUV) irradiance forcing produced a density change of -1\% to -13\%, and changes in thermospheric CO2concentration produced a density change of -5\%. There was essentially no interminima change in global TEC derived from ground-based GPS receivers or space-based altimeters, even though past behavior suggests that it should have changed -3\% (0.2 TEC units (1 TECU = 1016 el m-2)) in response to lower geomagnetic activity and -1\% to -9\% (0.1\textendash0.8 TECU) in response to lower EUV irradiance. There is large uncertainty in the interminima change of solar EUV irradiance; the mass density and TEC data suggest a plausible range of 0\% to -6\%. Emmert, J.; McDonald, S.; Drob, D.; Meier, R.; Lean, J.; Picone, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2014 YEAR: 2014 DOI: 10.1002/2013JA019484 ionosphere total electron content; solar minimum; thermosphere mass density |
| 2012 |
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The highly variable solar extreme ultraviolet (EUV) radiation is the major energy input to the Earth\textquoterights upper atmosphere, strongly impacting the geospace environment, affecting satellite operations, communications, and navigation. The Extreme ultraviolet Variability Experiment (EVE) onboard the NASA Solar Dynamics Observatory (SDO) will measure the solar EUV irradiance from 0.1 to 105\ nm with unprecedented spectral resolution (0.1\ nm), temporal cadence (ten seconds), and accuracy (20\%). EVE includes several irradiance instruments: The Multiple EUV Grating Spectrographs (MEGS)-A is a grazing-incidence spectrograph that measures the solar EUV irradiance in the 5 to 37\ nm range with 0.1-nm resolution, and the MEGS-B is a normal-incidence, dual-pass spectrograph that measures the solar EUV irradiance in the 35 to 105\ nm range with 0.1-nm resolution. To provide MEGS in-flight calibration, the EUV SpectroPhotometer (ESP) measures the solar EUV irradiance in broadbands between 0.1 and 39\ nm, and a MEGS-Photometer measures the Sun\textquoterights bright hydrogen emission at 121.6\ nm. The EVE data products include a near real-time space-weather product (Level\ 0C), which provides the solar EUV irradiance in specific bands and also spectra in 0.1-nm intervals with a cadence of one minute and with a time delay of less than 15\ minutes. The EVE higher-level products are Level\ 2 with the solar EUV irradiance at higher time cadence (0.25\ seconds for photometers and ten seconds for spectrographs) and Level\ 3 with averages of the solar irradiance over a day and over each one-hour period. The EVE team also plans to advance existing models of solar EUV irradiance and to operationally use the EVE measurements in models of Earth\textquoterights ionosphere and thermosphere. Improved understanding of the evolution of solar flares and extending the various models to incorporate solar flare events are high priorities for the EVE team. Woods, T.; Eparvier, F.; Hock, R.; Jones, A.; Woodraska, D.; Judge, D.; Didkovsky, L.; Lean, J.; Mariska, J.; Warren, H.; McMullin, D.; Chamberlin, P.; Berthiaume, G.; Bailey, S.; Fuller-Rowell, T.; Sojka, J.; Tobiska, W.; Viereck, R.; Published by: Solar Physics Published on: 01/2012 YEAR: 2012 DOI: 10.1007/s11207-009-9487-6 |
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SAMI3 Simulations of Ionospheric Variability from 1996 to 2011 McDonald, SE; Lean, J; Huba, JD; Emmert, JT; Drob, DP; Siefring, CL; Meier, RR; Picone, J; Published by: Published on: |
| 2011 |
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Global and regional trends in ionospheric total electron content Lean, J.; Emmert, J.; Picone, J.; Meier, R.; Published by: Journal of Geophysical Research Published on: Jan-01-2011 YEAR: 2011 DOI: 10.1029/2010JA016378 |
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Ionospheric total electron content: Global and hemispheric climatology Lean, J.; Meier, R.; Picone, J.; Emmert, J.; Published by: Journal of Geophysical Research Published on: Jan-01-2011 YEAR: 2011 DOI: 10.1029/2011JA016567 |
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Solar extreme ultraviolet irradiance: Present, past, and future Lean, J.; Woods, T.; Eparvier, F.; Meier, R.; Strickland, D.; Correira, J.; Evans, J.; Published by: Journal of Geophysical Research Published on: Jan-01-2011 YEAR: 2011 DOI: 10.1029/2010JA015901 |
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Simulating Ionospheric Variability in the Descending Phase of Solar Cycle-23 using SAMI3 McDonald, SE; Lean, J; Huba, JD; Joyce, GR; Emmert, JT; Drob, DP; Stephan, AW; Siefring, CL; Meier, RR; Picone, J; Published by: Published on: |
| 2010 |
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Record-low thermospheric density during the 2008 solar minimum Emmert, J.; Lean, J.; Picone, J.; Published by: Geophysical Research Letters Published on: Jan-06-2010 YEAR: 2010 DOI: 10.1029/2010GL043671 |
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Integrating the Sun-Earth System for the Operational Environment (ISES-OE) Lean, J.; Huba, J.; McDonald, S.; Slinker, S.; Drob, D.; Emmert, J.; Meier, R.; Picone, J.; Joyce, G.; Krall, J.; Stephan, A.; Roach, K.; Knight, H.; Plunkett, S.; Wu, C.-C.; Wood, B.; Wang, Y.-M.; Howard, R.; Chen, J.; Bernhardt, P.; Fedder, J.; Published by: Published on: |
| 2007 |
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Strickland, D.; Lean, J.; Daniell, R.; Knight, H.; Woo, W.; Meier, R.; Straus, P.; Woods, T.; Eparvier, F.; McMullin, D.; Christensen, A.; Morrison, D.; Paxton, L.; Published by: Journal of Geophysical Research Published on: Jan-01-2007 YEAR: 2007 DOI: 10.1029/2006JA012074 |
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Strickland, DJ; Lean, JL; , Daniell; Knight, HK; Woo, WK; Meier, RR; Straus, PR; Woods, TN; Eparvier, FG; McMullin, DR; , others; Published by: Journal of Geophysical Research: Space Physics Published on: |
| 2006 |
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Thermospheric densities derived from spacecraft orbits: Application to the Starshine satellites Lean, J.; Picone, J.; Emmert, J.; Moore, G.; Published by: Journal of Geophysical Research Published on: Jan-01-2006 YEAR: 2006 DOI: 10.1029/2005JA011399 |
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Emmert, JT; Meier, RR; Picone, JM; Lean, JL; Christensen, AB; Published by: Journal of Geophysical Research Published on: YEAR: 2006 DOI: 10.1029/2005JA011495 |
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Thermospheric density 2002–2004: TIMED/GUVI dayside limb observations and satellite drag We use TIMED/GUVI dayside limb observations of thermospheric far ultraviolet (FUV) dayglow to infer height profiles of total mass density during the period 2002–2004. We compare these data with total mass density derived from drag-induced changes in the orbits of satellites with perigee heights ranging from 200 to 600 km. To accommodate sampling differences, we compute the ratio of observed total mass density, filtered on a 3-day timescale, to that predicted by the NRLMSISE-00 empirical model. The GUVI densities are in good agreement with the orbit-derived densities in the 300–500 km range, where the correlation of the two independent measurements is ∼0.68 and the relative bias is less than 5\%, which is within the absolute uncertainty of the drag results. Of interest is a prolonged depletion of upper thermospheric density (relative to NRLMSIS) during July 2002, when densities from both techniques were 20–35\% smaller than those predicted by NRLMSIS. Our results represent the first validation of absolute densities derived from FUV limb scanning. Emmert, JT; Meier, RR; Picone, JM; Lean, JL; Christensen, AB; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2006 DOI: https://doi.org/10.1029/2005JA011495 |
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Thermospheric density 2002—2004: TIMED/GUVI dayside limb observations and satellite drag Emmert, JT; Meier, RR; Picone, JM; Lean, JL; Christensen, AB; Published by: Journal of Geophysical Research: Space Physics Published on: |
| 2005 |
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Emmert, JT; Meier, RR; Picone, JM; Lean, JL; Published by: Published on: |
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E-Layer Variations During an X-Class Flare Inferred from Far Ultraviolet Dayglow Observations Strickland, D.; Daniell, R.; Meier, R.; Lean, J.; Published by: Published on: |
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E-Layer Variations During X-Class Flares Inferred from Far Ultraviolet Dayglow Observations A study is reported that addresses dayglow and ionospheric response to X-class flares that occurred on Oct 28 and Nov 4 2003. Data of interest are 1) the dayglow observations by GUVI and solar EUV/X-ray observations by SEE (both on NASA\textquoterights TIMED satellite), 2) E-region measurements made by the EISCAT radar (on Oct 28) located at Troms\o, Norway, and 3) E-region/F-region IOX GPS occultation measurements (on Nov 4). The timing of the flares was fortunate in that TIMED was on the dayside portion of its orbit when activity peaked for both flares. During the Oct 28 flare, the EISCAT measurements were made near local noon under low geomagnetic activity conditions. Key results are the modeled and measured preflare and flare E-region electron densities. The basis of the modeled densities is QEUV, an integrated measure of solar EUV/XUV energy flux from 0 to 45 nm (that portion of the irradiance spectrum responsible for far ultraviolet dayglow). Use is made of spectra from SEE and the NRLEUV model along with GUVI nadir dayglow observations within its 135.6 and LBHS spectral channels to derive preflare and flare QEUV. The GUVI data are used to derive QEUV with the use of lookup tables, each distinguished by solar EUV/X-ray spectral shape, not by magnitude. Lookup tables have been produced using SEE and NRLEUV flare and preflare spectral shapes. The AURIC model is used to calculate the E-layer with the key input being a solar spectrum with a given shape (those discussed above) and magnitude (set by QEUV). The two sets of ionospheric measurements on their respective flare days show increases in NmE (E-layer peak density) by approximately a factor of three. The QEUV-based NmE agrees well with the measurements before and during these flares. NmE based on SEE spectra, on the other hand, exceeds the observed values, especially during the flares. The favorable agreement supports the derived GUVI QEUV values and argues for a significant reduction in SEE energy fluxes during periods of eruptive solar activity. Strickland, D.~J.; Daniell, R.~E.; Meier, R.~R.; Lean, J.~L.; Straus, P.~R.; Morrison, M.~D.; Paxton, L.; Published by: AGU Fall Meeting Abstracts Published on: 2479 Solar radiation and cosmic ray effects; 7519 Flares; 7549 Ultraviolet emissions; 7974 Solar effects |
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Solar EUV Experiment (SEE): Mission overview and first results [1]\ The Solar EUV Experiment (SEE) is one of four scientific instruments on the NASA Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) spacecraft, which has been simultaneously observing the Sun and Earth\textquoterights upper atmosphere since January 2002. The SEE instrument measures the irradiance of the highly variable, solar extreme ultraviolet (EUV) radiation, one of the major energy sources for the upper atmosphere. The primary SEE data product is the solar spectral irradiances from 0.1 to 194 nm in 1 nm intervals that are fundamental for the TIMED mission\textquoterights investigation of the energetics in the tenuous, but highly variable, layers of the Earth\textquoterights atmosphere above 60 km. The TIMED mission began normal operations on 22 January 2002, a time when the Sun displayed maximum levels of activity for solar cycle 23, and has provided daily measurements as solar activity has declined to moderate levels. Solar irradiance variability observed by SEE during the 2 years of the TIMED prime mission includes a variety of moderate and large flares over periods of seconds to hours and dozens of solar rotational cycles over a typical period of 27 days. The SEE flare measurements provide important, new results because of the simultaneous spectral coverage from 0.1 to 194 nm, albeit limited temporal coverage due to its 3\% duty cycle. In addition, the SEE measurements reveal important, new results concerning phase shifts of 2\textendash7 days in the intermediate-term variations between different UV wavelengths that appear to be related to their different center-to-limb variations. The new solar EUV irradiance time series from SEE are also important in filling the \textquotedblleftEUV Hole,\textquotedblright which is the gap in irradiance measurements in the EUV spectrum since the 1980s. The solar irradiances measured by SEE (Version 7, released July 2004) are compared with other measurements and predictions from models of the solar EUV irradiance. While the measurement comparisons show reasonable agreement, there are significant differences between SEE and some of the models in the EUV range. The data processing algorithms and calibrations are also discussed. Woods, Thomas; Eparvier, Francis; Bailey, Scott; Chamberlin, Phillip; Lean, Judith; Rottman, Gary; Solomon, Stanley; Tobiska, Kent; Woodraska, Donald; Published by: Journal of Geophysical Research: Space Physics (1978\textendash2012) Published on: YEAR: 2005 DOI: 10.1029/2004JA010765 thermosphere; solar activity cycle; solar irradiance; ultraviolet emissions; solar effects |
| 2004 |
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Solar EUV irradiance variability derived from terrestrial far ultraviolet dayglow observations Remotely sensed ultraviolet emissions from the Earth s upper atmosphere are shown to mirror fluctuations in solar EUV irradiance during July 2002, including the overall increase and decrease as the Sun rotated, and episodic increases associated with multiple solar flares. The TIMED/GUVI dayglow observations are used to derive a new quantity, QEUVGUVI, which is a measure of integrated solar EUV electromagnetic energy shortward of 45 nm. Both the absolute QEUVGUVI values and their modulation by solar rotation agree well with the corresponding solar EUV energy estimated by the NRLEUV irradiance variability model. The QEUVGUVI values do not support recent suggestions that the solar EUV irradiances estimated by the model of Hinteregger et al. be increased by a factor of four, nor even a factor of two. Strickland, D.J.; Lean, J.L.; Meier, R.R.; Christensen, A.B.; Paxton, L.J.; Morrison, D.; Craven, J.D.; Walterscheid, R.L.; Judge, D.L.; McMullin, D.R.; Published by: Geophysical research letters Published on: YEAR: 2004 DOI: 10.1029/2003GL018415 |
| 2003 |
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Lean, JL; Strickland, DJ; Meier, RR; Christensen, AB; Woods, TN; Eparvier, FG; McMullin, D; Judge, DL; Published by: Published on: |
| 2002 |
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Ionospheric and dayglow responses to the radiative phase of the Bastille Day flare Meier, RR; Warren, HP; Nicholas, AC; Bishop, J; Huba, JD; Drob, DP; Lean, JL; Picone, JM; Mariska, JT; Joyce, G; , others; Published by: Geophysical research letters Published on: |
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Parameterizations of solar EUV irradiance variations for use in upper atmosphere density models Lean, JL; Picone, JM; Mariska, JT; Warren, HP; Knowles, S; Bishop, J; Meier, RR; Published by: Advances in the Astronautical Sciences Published on: |
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