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Found 38 entries in the Bibliography.

Showing entries from 1 through 38

2018

Material flux from the rings of Saturn into its atmosphere

Perry, ME; , Waite; Mitchell, DG; Miller, KE; Cravens, TE; Perryman, RS; Moore, L; Yelle, RV; Hsu, H-W; Hedman, MM; , others;

Published by: Geophysical Research Letters Published on:

YEAR: 2018 DOI:

2013

Multiple neutral density measurements in the lower thermosphere with cold-cathode ionization gauges

Cold-cathode ionization gauges were used for rocket-borne measurements of total neutral density and temperature in the aurorally forced lower thermosphere between 90 and 200\ km. A commercial gauge was adapted as a low-cost instrument with a spherical antechamber for measurements in molecular flow conditions. Three roll-stabilized payloads on different trajectories each carried two instruments for measurements near the ram flow direction along the respective upleg and downleg segments of a flight path, and six density profiles were obtained within a period of 22\ min covering spatial separations up to 200\ km. The density profiles were integrated below 125\ km to yield temperatures. The mean temperature structure was similar for all six profiles with two mesopause minima near 110 and 101\ km, however, for the downleg profiles, the upper minimum was warmer and the lower minimum was colder by 20\textendash30\ K indicating significant variability over horizontal scales of 100\textendash200\ km. The upper temperature minimum coincided with maximum horizontal winds speeds, exceeding 170\ m/s.

Lehmacher, G.A.; Gaulden, T.M.; Larsen, M.F.; Craven, J.D.;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 01/2013

YEAR: 2013 DOI: 10.1016/j.jastp.2012.11.002

Instruments and techniques; Pressure density and temperature; thermosphere

2008

Validation of the Plasma Densities and Temperatures From the ISS Floating Potential Measurement Unit

The validation of the floating potential measurement unit (FPMU) plasma density and temperature measurements is an important step in the process of evaluating International Space Station (ISS) spacecraft charging issues including vehicle arcing and hazards to crew during extravehicular activities. The highest potentials observed on the Space Station are due to the combined Vsp times B effects on a large spacecraft and the collection of ionospheric electron and ion currents by the 160-V U.S. solar array modules. The ionospheric plasma environment is needed for input to the ISS spacecraft charging models used to predict the severity and frequency of occurrence of ISS charging hazards. The validation of these charging models requires the comparison of their predictions with measured FPMU values. The FPMU measurements themselves must also be validated for use in manned flight safety work. This paper presents preliminary results from a comparison of densities and temperatures derived from the FPMU Langmuir probes and plasma impedance probe with the independent density and temperature measurements from a spaceborne ultraviolet imager, a ground-based incoherent scatter radar, and ionosonde sites.

Coffey, Victoria; Wright, Kenneth; Minow, Joseph; Schneider, Todd; Vaughn, Jason; Craven, Paul; Chandler, Michael; Koontz, Steven; Parker, Linda; Bui, Them;

Published by: IEEE Transactions on Plasma Science Published on: Oct

YEAR: 2008 DOI: 10.1109/TPS.2008.2004271

Aeronomy science based on NASA TIMED/GUVI ultraviolet images of the Earth

Christensen, Andrew; Craven, John; Crowley, Geoff; Meier, Robert; Paxton, Larry;

Published by: 37th COSPAR Scientific Assembly Published on:

YEAR: 2008 DOI:

Solar system ionospheres

This article reviews our understanding of the ionospheres in the solar system. It provides some basic information on the sources and sinks of the ionospheric plasma, its dynamics, the energetics and the coupling to the neutral atmosphere. Ionospheres in the solar system are reviewed and comparative ionospheric topics are discussed.

Witasse, O; Cravens, T; Mendillo, M; Moses, J; Kliore, A; Nagy, AF; Breus, T;

Published by: Comparative Aeronomy Published on:

YEAR: 2008 DOI:

2007

First terrestrial soft X-ray auroral observation by the Chandra X-ray Observatory

Bhardwaj, Anil; Gladstone, Randall; Elsner, Ronald; Ostgaard, Nikolai; Waite, Hunter; Cravens, Thomas; Chang, Shen-Wu; Majeed, Tariq; Metzger, Albert;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: Jan-02-2007

YEAR: 2007 DOI: 10.1016/j.jastp.2006.07.011

Validation of ISS Floating Potential Measurement Unit Electron Densities and Temperatures

Validation of the Floating Potential Measurement Unit (FPMU) electron density and temperature measurements is an important step in the process of evaluating International Space Station spacecraft charging issues .including vehicle arcing and hazards to crew during extravehicular activities. The highest potentials observed on Space Station are due to the combined VxB effects on a large spacecraft and the collection of ionospheric electron and ion currents by the 160 V US solar array modules. Ionospheric electron environments are needed for input to the ISS spacecraft charging models used to predict the severity and frequency of occurrence of ISS charging hazards. Validation of these charging models requires comparing their predictions with measured FPMU values. Of course, the FPMU measurements themselves must also be validated independently for use in manned flight safety work. This presentation compares electron density and temperatures derived from the FPMU Langmuir probes and Plasma Impedance Probe against the independent density and temperature measurements from ultraviolet imagers, ground based incoherent scatter radar, and ionosonde sites.

Coffey, V.; Minow, J.; Schneider, T.; Vaughn, J.; Craven, P.; Parker, L.; Bui, T.; Wright, K.; Koontz, S.;

Published by: Published on: 06/2007

YEAR: 2007 DOI:

Thermospheric O/N2 in the Sunlit Disk From More Than Five Years of GUVI/TIMED Observations

Craven, JD; Christensen, AB; Paxton, LJ;

Published by: Published on:

YEAR: 2007 DOI:

2006

Effect of IMF By on thermospheric composition at high and middle latitudes: 2. Data comparisons

Immel, Thomas; Crowley, Geoff; Hackert, Chris; Craven, John; Roble, Ray;

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

YEAR: 2006 DOI:

Thermospheric O/N2 ratio observations obtained over more than four years with the GUVI instrument in the TIMED spacecraft mission

Craven, JD; Christensen, AB; Paxton, LJ; Strickland, DJ;

Published by: Published on:

YEAR: 2006 DOI:

The importance of high latitude inputs in correctly modeling the magnitude and extend of thermospheric storms

Immel, Thomas; Crowley, Geoff; Craven, John;

Published by: Adv. Space Res Published on:

YEAR: 2006 DOI:

Effect of IMF BY on thermospheric composition at high and middle latitudes: 1. Numerical experiments

Magnetic storms and their effects on the thermosphere and ionosphere have been studied for many years, yet there are many aspects of the thermospheric and ionospheric responses that are not understood. The purpose of this paper is to show how the high-latitude composition depends on the sign of the IMF BY component, using controlled simulations with a global first principles model. Because the high-latitude convection and neutral wind systems are strongly controlled by the IMF BY component, it seems likely that the compositional response that is driven by high-latitude forcing should also be sensitive to the BY component. To date, no first-principles modeling has been performed to test the idea of IMF BY effects on composition. Numerical experiments using model simulations provide insight into this important scientific question, since the thermospheric compositional response to the convection patterns for different IMF BZ and BY can be studied in isolation in a model. In this paper we use a first-principles model to determine the effect of the IMF BY component on the compositional response of the high-latitude thermosphere. We show for the first time that a clockwise rotation of the potential pattern resulting from a change from BY-negative to BY-positive drives a corresponding rotation in the wind, neutral density, and composition distributions. BY control of thermospheric composition has been invoked in the literature to explain an apparent variability in the effectiveness of auroral activity in causing thermospheric storm effects at middle latitudes, as observed in global images of the far-ultraviolet (FUV) OI 130.4-nm emission from the DE-1 auroral imager. However, the effect in the simulations presented here is opposite from that suggested by earlier work based on DE data, indicating another explanation must be sought for the DE results. These simulations are highly relevant for interpreting data being provided by more modern UV imaging instruments on the DMSP, TIMED, and IMAGE satellites.

Crowley, G.; Immel, T.; Hackert, C.; Craven, J.; Roble, R.;

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

YEAR: 2006 DOI: https://doi.org/10.1029/2005JA011371

composition; thermospheric

2005

The High-Latitude Knee of the O/N2 Ratio Profile: Latitudinal Variations with UT, Local Time, Season, and Magnetic Activity

Craven, JD; Christensen, AB; Meier, RR; Paxton, LJ; Strickland, DJ;

Published by: Published on:

YEAR: 2005 DOI:

2004

Quiet-time seasonal behavior of the thermosphere seen in the far ultraviolet dayglow

The TIMED/GUVI instrument is a far ultraviolet spectrograph that obtains images in five spectrally resolved wavelength channels. These images yield information on the dayside composition, temperature, solar EUV flux, large-scale wave structures, and auroral processes. In this paper we present an overview analysis of Earth-disk images for four seasons (March, July, and September 2002 and January 2003). Days were selected during geomagnetically quiet periods when the Sun was nearly in the orbital plane (noon orbits). Two of GUVI\textquoterights five channels (designated as 135.6 and LBH_S and dominated by OI 135.6 nm and short wavelength N₂ LBH band emission, respectively) are used when the instrument is in its imaging mode. These data are used to derive O/N₂ (column density ratio referenced to an N₂ column density of 10¹⁷ cm^-2). The AURIC model is used to generate a lookup table that relates O/N₂ to the ratio of 135.6 to LBH_S for a given solar zenith angle. Global images of derived O/N₂ (designated as GUVI O/N₂) are presented for the 4 days. The initial validation of the retrieved composition ratio comes from comparison with the NRLMSIS model. Good overall qualitative agreement is obtained between GUVI and NRLMSIS. Both data and model exhibit similar latitudinal behaviors on the near-solstice days, namely a distinct gradient with O/N₂ decreasing from the winter to the summer hemisphere. Reductions in O/N₂ in the vicinity of magnetic poles are seen in both GUVI and NRLMSIS images. Globally, O/N₂ is smaller at the solstices and may be explained by the \textquotedblleftthermospheric spoon\textquotedblright mechanism discussed by Fuller-Rowell [1998]. Alternatively, the greater overall values at the equinoxes may arise in part from global response to greater Joule heating at these times of the year. The sensitivity of O/N₂ to scalings of the N₂ LBH cross section and solar EUV below 20 nm is also addressed in response to recent papers on these topics. This initial look at the GUVI data demonstrates great promise of FUV remote sensing as a way to observe thermospheric composition changes over broad geographic scales.

Strickland, D.; Meier, R.; Walterscheid, R.; Christensen, A.; Paxton, L.; Morrison, D.; Craven, J.; Crowley, G.;

Published by: Journal of Geophysical Research Published on: 01/2004

YEAR: 2004 DOI: 10.1029/2003JA010220

far ultraviolet; remote sensing; seasonal behavior; thermosphere

Thermospheric Composition Changes in the Morning Sector near Local Midnight in Association with Substorm Activity and IMF Orientation

Craven, JD; Christensen, AB; Meier, RR; Paxton, LJ; Strickland, DJ;

Published by: Published on:

YEAR: 2004 DOI:

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

Automatic Detection of Equatorial Plasma Bubbles in GUVI Data

Henderson, S; Swenson, C; Straus, P; Kil, H; Christensen, A; Paxton, L; Morrison, D; Crowley, G; Meier, R; Craven, J; , others;

Published by: Published on:

YEAR: 2003 DOI:

The Sun-Earth Connection as Viewed from GUVI on TIMED

Paxton, L; Christensen, A; Avery, S; Craven, J; Crowley, G; Meier, R; Meng, C; Srickland, D; Swenson, C; Walterscheid, R; , others;

Published by: Published on:

YEAR: 2003 DOI:

Search for thermospheric composition changes in the morning sector near local midnight in association with intense substorm activity

Craven, JD; Strickland, DJ; Meier, RR; Crowley, G; Christensen, AB; Paxton, LJ; Morrison, D; Avery, SK; Meng, C; Straus, PR; , others;

Published by: Published on:

YEAR: 2003 DOI:

Retrieval of thermospheric temperature and N2, O, and O2 concentrations from GUVI limb scans

Meier, RR; Strickland, DJ; Picone, JM; Christensen, AB; Paxton, LJ; Morrison, D; Kil, H; Bishop, J; Drob, D; Craven, JD; , others;

Published by: Published on:

YEAR: 2003 DOI:

Initial observations with the Global Ultraviolet Imager (GUVI) in the NASA TIMED satellite mission

The Global Ultraviolet Imager (GUVI) instrument carried aboard the NASA TIMED satellite measures the spectral radiance of the Earth\textquoterights far ultraviolet airglow in the spectral region from 120 to 180 nm using a cross-track scanning spectrometer design. Continuous operation of the instrument provides images of the Earth\textquoterights disk and limb in five selectable spectral bands. Also, spectra at fixed scanning mirror position can be obtained. Initial results demonstrate the quantitative functionality of the instrument for studies of the Earth\textquoterights dayglow, aurora, and ionosphere. Moreover, through forward modeling, the abundance of the major constituents of the thermosphere, O, N₂, and O₂\ and thermospheric temperatures can be retrieved from observations of the limb radiance. Variations of the column O/N₂\ ratio can be deduced from sunlit disk observations. In regions of auroral precipitation not only can the aurora regions be geographically located and the auroral boundaries identified, but also the energy flux Q, the characteristic energy E_o, and a parameter f_o\ that scales the abundance of neutral atomic oxygen can be derived. Radiance due to radiative recombination in the ionospheric F region is evident from both dayside and nightside observations of the Earth\textquoterights limb and disk, respectively. Regions of depleted F-region electron density are evident in the tropical Appleton anomaly regions, associated with so-called ionospheric \textquotedblleftbubbles.\textquotedblright Access to the GUVI data is provided through the GUVI website\ www.timed.jhuapl.edu\guvi.

Christensen, AB; Paxton, LJ; Avery, S; Craven, J; Crowley, G; Humm, DC; Kil, H; Meier, RR; Meng, C-I; Morrison, D; , others;