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Found 25 entries in the Bibliography.

Showing entries from 1 through 25

2015

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

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

2013

Theoretical tools for studies of low-frequency thermospheric variability

[1]\ This paper supports studies of low-frequency variability (LFV) within the thermosphere by deriving approximate integral and closed-form solutions of a nontrivial model of thermospheric temperature, density, and composition depending on altitude and time. We also provide a paradigm for applying dimensional analysis in such studies. The domain is the region between the mesopause and the exobase. The solutions emphasize the connectedness of the thermosphere, i.e., nonlocal influences of LFV in key physical parameters and phenomena. The present focus is seasonal variability, within which the origin of a sizable semiannual variation in the thermosphere remains under active investigation. Following from the thermodynamic differential equation for temperature is a filtered, integral solution consistent with the Π theorem of dimensional analysis. A key result is the explicit demonstration that lower thermospheric boundary conditions affect low-frequency variability throughout the thermosphere, making accurate boundary conditions essential to modeling LFV. In addition, LFV of the temperature varies inversely with variability of the net heating profile and has directly and inversely proportional contributions from variations in the thermal conductivity profile, which can include an \textquotedbllefteddy diffusivity\textquotedblright component. Given a temperature profile, diffusive equilibrium defines model composition. For rapid calculations and transparency, we develop an approximate, closed-form solution for temperature, density, and composition depending only on a minimal set of observable parameters, and from that, we demonstrate the essential role of the phase and amplitude profile of the temperature LFV in determining the corresponding profile of variability in composition and density.

Picone, J.; Meier, R.; Emmert, J.;

Published by: Journal of Geophysical Research: Space Physics Published on: 09/2013

YEAR: 2013 DOI: 10.1002/jgra.v118.910.1002/jgra.50472

dimensional analysis; low frequency variation; Pi Theorem; seasonal variation; semi-annual variation; thermospheric variability

2012

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:

YEAR: 2012 DOI:

2011

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

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

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:

YEAR: 2011 DOI:

2010

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

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:

YEAR: 2010 DOI:

2008

Thermospheric global average density trends, 1967--2007, derived from orbits of 5000 near-Earth objects

We use orbit data on ∼5000 near-Earth space objects to investigate long-term trends in thermospheric total mass density, which has been predicted to decrease with time due to increasing CO2 concentrations. We refine and extend to 2007 previous density trend estimates, and investigate solar cycle-dependent bias in empirical density models previously used to filter out solar irradiance effects. We find that the bias is caused in part by the solar cycle dependence of the long-term trends, and we develop a new representation of solar cycle, seasonal, and geomagnetic activity effects. At 400 km, we estimate an overall trend of –2.68 ± 0.49 % per decade and trends of ∼–5 and –2 % per decade at solar minimum and maximum, respectively, in fair quantitative agreement with theoretical predictions. The global average density trends also depend on the phase of the year, with the strongest trends around October and weak trends in January.

Emmert, JT; Picone, IM; Meier, RR;

Published by: Geophysical Research Letters Published on:

YEAR: 2008 DOI: 10.1029/2007GL032809

Influence of systematic error on least squares retrieval of upper atmospheric parameters from the ultraviolet airglow

This paper investigates the effect of simple systematic error, or bias (i.e., in the magnitude of data or an associated model), on physical parameters retrieved by least squares algorithms from observations that are indexed by an independent variable. This factor is now of critical interest with the advent of global, space-based ultraviolet remote sensing of thermospheric and ionospheric composition by experimental and operational systems. A finite bias between an observed intensity profile and the parametric physical model used to compute a least squares solution will contaminate the values of retrieved physical parameters. The simplest mitigation method is to retrieve an additional bias adjustment parameter (additive or multiplicative) as part of the solution. The result is a measurably superior fit. The utility of this approach can depend on the particular spectral feature of interest. The discussion includes derivation of relevant equations and diagnostic tests. An illustrative application concerns recent observations of the dayside O II 834 A airglow, which contains information on O+, the dominant ion in the ionospheric F region.

Picone, J.;

Published by: Journal of Geophysical Research: Space Physics Published on:

YEAR: 2008 DOI: https://doi.org/10.1029/2007JA012831

systematic error; discrete inverse theory; airglow

Long-term climatology and trends of global average thermospheric density

Emmert, John; Picone, Michael; Meier, Robert;

Published by: 37th COSPAR Scientific Assembly Published on:

YEAR: 2008 DOI:

2006

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

TIMED Contributions to Mesosphere, Lower Thermosphere, and Ionosphere Science-A10S16 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 Published on:

YEAR: 2006 DOI: 10.1029/2005JA011495

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

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:

YEAR: 2006 DOI:

2005

Comparison of Thermospheric Density Derived From TIMED/GUVI Limb Observations with Total Mass Density Derived From Satellite Orbits

Emmert, JT; Meier, RR; Picone, JM; Lean, JL;

Published by: Published on:

YEAR: 2005 DOI:

Orbital Drag-Atmospheric Density Concept of Operations2004 Update

The Global UV Imager (GUVI), a predecessor instrument to SSUSI, has shown promising, though limited, comparison to orbit-based densities. Current operations at the SCC rely on

Buell, Diane; Walterscheid, Richard; Marcos, Frank; Fuller-Rowell, Tim; Picone, J; Storz, Mark; Owens, Jerry;

Published by: Published on:

YEAR: 2005 DOI:

SSUSI and GUVI limb scans of thermospheric neutral density changes during a geomagnetic storm

Stephan, AW; Picone, JM; Meier, RR; Emmert, JT; Paxton, LJ; Morrison, D; Wolven, B; Kil, H;

Published by: Published on:

YEAR: 2005 DOI:

2004

Picone, Michael; Meier, Robert;

Published by: Published on: 3

YEAR: 2004 DOI:

2003