Bibliography

A Globally Averaged Thermospheric Density Data Set Derived From Two-Line Orbital Element Sets and Special Perturbations State Vectors

We describe a long-term data set of global average thermospheric mass density derived from orbit data on ∼7,700 objects in low Earth orbit, via the effect of atmospheric drag. The data cover the years 1967–2019 and altitudes 250–575 km, and the temporal resolution is 3–4 days for most years. The data set is an extension and revision of a previous version. The most important change is the use of more precise orbit data: special perturbation state vectors are now used starting in 2001, instead of mean Keplerian orbital elements. The data are suitable for climatological studies of thermospheric variations and trends, and for space weather studies on time scales longer than 3 days.

Emmert, J.; Dhadly, M.; Segerman, A.;

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

YEAR: 2021     DOI: 10.1029/2021JA029455

orbital elements; spacecraft drag; thermosphere density

Improving Neutral Density Predictions Using Exospheric Temperatures Calculated on a Geodesic, Polyhedral Grid

A new model of exospheric temperatures has been developed, with the objective of predicting global values with greater spatial and temporal accuracy. From these temperatures, the neutral densities in the thermosphere can be calculated, through use of the Naval Research Laboratory Mass Spectrometer and Incoherent Scatter radar Extended (NRLMSISE-00) model. The exospheric temperature model is derived from measurements of the neutral densities on several satellites. These data were sorted into triangular cells on a geodesic grid, based on location. Prediction equations are derived for each grid cell using least error fits. Several versions of the model equations have been tested, using parameters such as the date, time, solar radiation, and nitric oxide emissions, as measured with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. Accuracy is improved with the addition of the total Poynting flux flowing into the polar regions, from an empirical model that uses the solar wind velocity and interplanetary magnetic field. Given such inputs, the model can produce global maps of the exospheric temperature. These maps show variations in the polar regions that are strongly modulated by the time of day, due to the daily rotation of the magnetic poles. For convenience the new model is referred to with the acronym EXTEMPLAR (EXospheric TEMperatures on a PoLyhedrAl gRid). Neutral densities computed from the EXTEMPLAR-NRLMSISE-00 models combined are found to produce very good results when compared with measured values.

Weimer, D.; Mehta, P.; Tobiska, W.; Doornbos, E.; Mlynczak, M.; Drob, D.; Emmert, J.;

Published by: Space Weather      Published on: 12/2019

YEAR: 2020     DOI: 10.1029/2019SW002355

How might the thermosphere and ionosphere react to an extreme space weather event?

This chapter explores how the thermosphere and ionosphere (T-I) might respond to extreme solar events. Three different scenarios are considered: (1) an increase in solar UV and EUV radiation for a number of days, (2) an extreme enhancement in the solar X-rays and EUV radiation associated with a flare, and (3) an extreme CME driving a geomagnetic storm. Estimating the response to the first two scenarios is reasonably well defined, and although they would certainly impact the T-I system, those impacts could potentially be mitigated. In contrast, the response to an extreme geomagnetic storm is significantly more complicated, making the response much more uncertain, and mitigation more challenging.

Fuller-Rowell, Tim; Emmert, John; Fedrizzi, Mariangel; Weimer, Daniel; Codrescu, Mihail; Pilinski, Marcin; Sutton, Eric; Viereck, Rodney; Raeder, Joachim; Doornbos, Eelco;

Published by:       Published on:

YEAR: 2018     DOI: 10.1016/B978-0-12-812700-1.00021-2

Thermospheric mass density: A review

The mass density of Earth\textquoterights thermosphere (\~90\textendash600\ km altitude) is a critical parameter for low Earth orbit prediction because of the atmospheric drag on satellites in this region. In this review, we first survey techniques for measuring thermospheric density, empirical models that provide a synthesis of historical data, and physical models that simulate the environment by solving fluid equations. We then review the climate and weather features that are observed in thermospheric density (including its response to solar forcing) and summarize recent studies of these features. The review is focused on results published between 2000 and 2014, which coincides with a period of extensive accelerometer measurements of density and accompanying research; some historical context is also provided.

Emmert, J.T.;

Published by: Advances in Space Research      Published on: 09/2015

YEAR: 2015     DOI: 10.1016/j.asr.2015.05.038

thermosphere; ~Mass density

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

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

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

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:

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

A study of space shuttle plumes in the lower thermosphere

Meier, R.; Stevens, Michael; Plane, John; Emmert, J.; Crowley, G.; Azeem, I.; Paxton, L.; Christensen, A.;

Published by: Journal of Geophysical Research      Published on: Jan-01-2011

YEAR: 2011     DOI: 10.1029/2011JA016987

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:

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

Dynamical Properties of Shuttle Plumes in the Lower Thermosphere

Meier, RR; Stevens, MH; Plane, JM; Emmert, JT; Crowley, G; Paxton, LJ; Christensen, AB; Azeem, SI;

Published by:       Published on:

YEAR: 2010     DOI:

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:

Satellite Observations of Space Shuttle Main Engine Exhaust: Vertical Diffusion and Meridional Transport

Stevens, MH; Meier, RR; Plane, JM; Emmert, JT; Russell, J;

Published by:       Published on:

YEAR: 2010     DOI:

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

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:

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:

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:

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: