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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Venus southern hemisphere - Geologic character and age of terrains in the Themis-Alpha-Lada region

Arecibo high-resolution radar images of the southern hemisphere of Venus extending to 78 deg S show that the surface of the Themis-Alpha-Lada region is characterized by linear deformation zones with volcanoes and corona-like features and by regional volcanic deposits (primarily plains, small shields, and large edifices). Large-scale areal deformation is limited to the tessera of Alpha Regio. Lada Terra, in the southern high latitudes, contains several large coronae, in contrast to Ishtar Terra in the northern high latitudes. The density of craters of possible impact origin is somewhat lower than that observed in the Venera 15 and 16 coverage; these data extend to 43 percent of the areas of the surface of Venus with ages of less than about 1 billion years.

Campbell, D. B.↗
NASA NTRS1991

Geology and tectonics of the Themis Regio-Lavinia Planitia-Alpha Regio-Lada Terra area, Venus - Results from Arecibo image data

Results of new radar images obtained from the Arecibo Observatory for portions of the southern hemisphere of Venus are reported. The images show that the upland of Phoebe Region contains the southern extension of Devana Chasma, a rift zone extending 4200 km south from Theia Mons and interpreted as a zone of extension. Alpha Regio, the only large region of tesserae within the imaged area, is found to be similar to tesserae mapped elsewhere on the planet; it covers a smaller percentage of the surface than that observed in the northern high latitudes. Themis Region is mapped as an ovoid chain of radar-bright arcuate single- and double-ring structures, edifices, and bright lineaments. On the basis of the present analysis, the southern hemisphere of Venus is interpreted to be characterized by regions of mantle upwelling on a variety of scales, upwelling and extension, and localized compression.

Senske, D. A.↗
NASA NTRS2002

THEMIS Surface-Atmosphere Separation Strategy and Preliminary Results

Methods refined and adapted from the TES investigation are used to develop a surface-atmosphere separation strategy for THEMIS image analysis and atmospheric temperature and opacity retrievals. Additional information is contained in the original extended abstract.

Bandfield, J. L.↗
NASA NTRS2003

THEMIS Observations of Pitted Cones in Acidalia Planitia and Cydonia Mensae

Analysis of Viking imagery revealed the presence of large numbers of pitted or cratered cones in the northern plains of Mars with the highest concentrations occurring in eastern Acidalia Planitia and Cydonia Mensae. Based largely on crater/cone diameter ratio comparisons, these features were hypothesized as being analogous to terrestrial pseudocraters (rootless cones) such as occur in the Lake Myvatn region of Iceland. Doubts remained about this connection given the disparity in mean diameters between these Martian features (mean diameter of approx. 600 m) and the Icelandic rootless cones (mean diameter of approx. 50 m). Recent analysis of MOC Narrow Angle camera images of Elysium Planitia, Amazonis Planitia and elsewhere have revealed another class of features with diameters commensurate with the Icelandic rootless cones. If the features in Acidalia and Cydonia are not rootless cones, what are they? Recent information on the thermophysical properties of these features as provided by the Mars Odyssey THEMIS instrument may help to answer this question.

W H Farrand↗
NASA NTRS2003

THEMIS Visible Imaging of the South Polar Layered Deposits, Martian Southern Spring, 2003

The polar layered deposits (PLD) of Mars have attracted considerable attention since their identification in Mariner 9 images, largely due to the possibility that these finely layered, volatile-rich deposits hold a record of recent eras in Martian climate history. The PLD have been a target of imaging and other sensors in the last several decades, but only recently has it been possible to obtain a moderately high resolution image map, using the visible sensor on 2001 Mars Odyssey s Thermal Emission Imaging System (THEMIS). We report here on the acquisition of a 36 meter/pixel contiguous single-band visible image data set of the south polar layered deposits (SPLD), obtained during early southern spring in 2003. The data will undoubtedly be applied to many problems in Mars polar studies. We will discuss here, and in more detail at the Conference, the use of these images to further characterize the population of impact craters on the SPLD, and the implications of the observed population for the age and evolution of the SPLD.

Plaut, J. J.↗
NASA NTRS2005

Evidence for Aqueously Precipitated Sulfates in Northeast Meridiani Using THEMIS and TES Data

Recently aqueously deposited sulfate-rich bedrock was found at the MER-B Meridiani landing site [1]. Additional sulfate was observed from orbit by the Mars Express OMEGA instrument [2]. In this work, I present midinfrared spectral evidence (using THEMIS and TES) for sulfate in and around a channel deposit that lies to the northeast of the hematite- strewn plains of Meridiani at approx.2degN, 1degW (Fig. 1).

Lane, Melissa D.↗
NASA NTRS2003

Themis Visible Imaging of the South Polar Layered Deposits, Martian Southern Spring, 2003

The polar layered deposits (PLD) of Mars have attracted considerable attention since their identification in Mariner 9 images, largely due to the possibility that these finely layered, volatile-rich deposits hold a record of recent eras in Martian climate history. The PLD have been a target of imaging and other sensors in the last several decades, but only recently has it been possible to obtain a moderately high resolution image map, using the visible sensor on 2001 Mars Odyssey's Thermal Emission Imaging System (THEMIS). We report here on the acquisition of a 36 meter/pixel contiguous single-band visible image data set of the south polar layered deposits (SPLD), obtained during early southern spring in 2003. The data will undoubtedly be applied to many problems in Mars polar studies.

Mariner 9↗
NASA NTRS2007

CCMC Support of Active Missions: STEREO, THEMIS

The Coordinated Community Modeling Center has been providing custom support for current active missions, such as STEREO and THEMIS. Global heliospheric and magnetospheric MHD model results and their presentation along the actual spacecraft trajectories are invaluable for the rapid contextualization of the observations. User feedback will be provided from the point of view of a mission scientist with suggestions for future improvements.

Szabeo, A.↗
NASA NTRS2008

Formation of Structured Dayside Boundary Layers under Different Solar Wind Conditions: THEMIS Observations

We have begun an investigation of the formation of the dayside low latitude boundary layer under different solar wind conditions using data from the THEMIS spacecraft. We present two cases of magnetopause/LLBL interface crossings made by the five spacecraft; one under long lasting northward IMF and a second for a period of southward IMF. All spacecraft during these observations traversed the dayside magnetosphere in a string-of-pearls configuration with the farthest distance between spacecraft less than approx.2 R(sub E). The sequence of observations from spacecraft, as they crossed the magnetopause, shows the development of a highly structured boundary layer regardless of the polarity of the IMF. We discuss possible scenarios for the development of such structured boundary layers, including low latitude reconnection under northward IMF as well as double reconnection in opposite hemispheres.

Avanov, Levon A.↗
NASA NTRS2010

Modeling Harris Current Sheets with Themis Observations

Current sheets are ubiquitous in nature. occurring in such varied locations as the solar atmosphere. the heliosphere, and the Earth's magnetosphere. The simplest current sheet is the one-dimensional Harris neutral sheet, with the lobe field strength and scale-height the only free parameters. Despite its simplicity, confirmation of the Harris sheet as a reasonable description of the Earth's current sheet has remained elusive. In early 2009 the orbits of the 5 THEMIS probes fortuitously aligned such that profiles of the Earth's current sheet could be modeled in a time dependent manner. For the few hours of alignment we have calculated the time history of the current sheet parameters (scale height and current) in the near-Earth region. during both quiet and active times. For one particular substorm. we further demonstrate good quantitative agreement with the diversion of cross tail current inferred from the Harris modeling with the ionospheric current inferred from ground magnetometer data.

Kepko, L.↗
NASA NTRS2011

THEMIS Observations of a Transient Event at the Magnetopause

This study focuses on Time History of Events and Macroscale Interactions During Substorms (THEMIS) observations of a long \duration transient event in the vicinity of the dayside magnetopause at approx.15:34 UT on 18 July 2008 that was characterized by features typical of a magnetospheric flux transfer event (FTE): a bipolar negative-positive 5-7 nT signature in the Bn component, a positive monopolar variation in the Bl and Bm components, a approx.5-7 nT enhancement in the total magnetic field strength, and a transient density and flow enhancement. The interplanetary magnetic field (IMF) was mostly radial and disturbed during the intervals studied; that is, it was favorable for the repeated formation, disappearance and reformation of the foreshock just upstream from the subsolar bow shock. We show that varying IMF directions and solar wind pressures created significant effects that caused the compressions of the magnetosphere and the bow shock and magnetopause motions and triggered the transient event. Global signatures of magnetic impulse events (MIEs) in ground magnetograms during the period suggest a widespread pressure pulse instead of a localized FTE as the cause of the event in the magnetosphere. The directions of propagation and the flow patterns associated with the event also suggest an interpretation in terms of pressure pulses.

Korotova, G. I.↗
NASA NTRS2011

A THEMIS Survey of Flux Ropes and Traveling Compression Regions: Location of the Near-Earth Reconnection Site During Solar Minimum

A statistical study of flux ropes and traveling compression regions (TCRs) during the Time History of Events and Macroscale Interactions during Substorms (THEMIS) second tail season has been performed. A combined total of 135 flux ropes and TCRs in the range GSM X approx -14 to -31 R(sub E) were identified, many of these occurring in series of two or more events separated by a few tens of seconds. Those occurring within 10 min of each other were combined into aggregated reconnection events. For the purposes of this survey, these are most likely the products of reconnect ion occurring simultaneously at multiple, closely spaced x-lines as opposed to statistically independent episodes of reconnection. The 135 flux ropes and TCRs were grouped into 87 reconnection events; of these, 28 were moving tailward and 59 were moving Earthward. The average location of the near-Earth x-line determined from statistical analysis of these reconnection events is (X(sub GSM), Y*(sub GSM)) = (-30R(sub E), 5R(sub E)), where Y* includes a correction for the solar aberration angle. A strong east-west asymmetry is present in the tailward events, with >80% being observed at GSM Y* > O. Our results indicate that the Earthward flows are similarly asymmetric in the midtail region, becoming more symmetric inside - 18 R(sub E). Superposed epoch analyses indicate that the occurrence of reconnection closer to the Earth, i.e., X > -20 R(sub E), is associated with elevated solar wind velocity and enhanced negative interplanetary magnetic field B(sub z). Reconnection events taking place closer to the Earth are also far more effective in producing geomagnetic activity, judged by the AL index, than reconnection initiated beyond X approx -25 R(sub E).

Imber, S. M.↗
NASA NTRS2013

THEMIS Observations of Unusual Bow Shock Motion, Attending a Transient Magnetospheric Event

We present a multipoint case study of solar wind and magnetospheric observations during a transient magnetospheric compression at 2319 UT on October 15, 2008. We use high-time resolution magnetic field and plasma data from the THEMIS and GOES-11/12 spacecraft to show that this transient event corresponded to an abrupt rotation in the IMF orientation, a change in the location of the foreshock, and transient outward bow shock motion. We employ results from a global hybrid code model to reconcile the observations indicating transient inward magnetopause motion with the outward bow shock motion.

Korotova, Galina↗
NASA NTRS2013

THEMIS Observations of the Magnetopause Electron Diffusion Region: Large Amplitude Waves and Heated Electrons

We present the first observations of large amplitude waves in a well-defined electron diffusion region based on the criteria described by Scudder et al at the subsolar magnetopause using data from one Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite. These waves identified as whistler mode waves, electrostatic solitary waves, lower hybrid waves, and electrostatic electron cyclotron waves, are observed in the same 12 s waveform capture and in association with signatures of active magnetic reconnection. The large amplitude waves in the electron diffusion region are coincident with abrupt increases in electron parallel temperature suggesting strong wave heating. The whistler mode waves, which are at the electron scale and which enable us to probe electron dynamics in the diffusion region were analyzed in detail. The energetic electrons (approx. 30 keV) within the electron diffusion region have anisotropic distributions with T(sub e(right angle))/T(sub e(parallel)) > 1 that may provide the free energy for the whistler mode waves. The energetic anisotropic electrons may be produced during the reconnection process. The whistler mode waves propagate away from the center of the "X-line" along magnetic field lines, suggesting that the electron diffusion region is a possible source region of the whistler mode waves.

magnetopause and boundary layers↗
NASA NTRS2016

Supra Arcade Downflows with XRT Informed by Dipolarization Fronts with THEMIS

Magnetic reconnection can rapidly reconfigure the magnetic field of the corona, accelerating plasma through the site of reconnection. Ambiguities due to the nature of remote sensing have complicated the interpretation of observations of the inflowing and outflowing plasma in reconnecting regions. In particular, the interpretation of sunward moving density depletions above flare arcades (known as Supra Arcade Downflows - SADs) is still debated. Hinode/XRT has provided a wealth of observations for SADs and helped inform our current understanding of these structures. SADs have been interpreted as wakes behind newly reconnected and outflowing loops (Supra Arcade Downflowing Loops - SADLs). Models have shown the plausibility of this interpretation, though this interpretation has not yet been fully accepted. We present here observations of newly reconnected outflowing loops observed via in situ instruments in the magnetosphere. These observations, provided by five THEMIS spacecraft, show that around retracting loops (dipolarization fronts in this context) similar dynamic temperature and density structures are found as seen in SADs. We compare data from multiple SADs and dipolarization fronts to show that the observational signatures implied in the corona can be directly observed in similar plasma regimes in the magnetosphere, strongly favoring the interpretation of SADs as wakes behind retracting loops.

magnetism↗
NASA NTRS2016

Supra Arcade Downflows with XRT Informed by Dipolarization Fronts with THEMIS

Magnetic reconnection can rapidly reconfigure the magnetic field of the corona, accelerating plasma through the site of reconnection. Ambiguities due to the nature of remote sensing have complicated the interpretation of observations of the inflowing and outflowing plasma in reconnecting regions. In particular, the interpretation of sunward moving density depletions above flare arcades (known as Supra Arcade Downflows - SADs) is still debated. Hinode/XRT has provided a wealth of observations for SADs and helped inform our current understanding of these structures. SADs have been interpreted as wakes behind newly reconnected and outflowing loops (Supra Arcade Downflowing Loops - SADLs). Models have shown the plausibility of this interpretation, though this interpretation has not yet been fully accepted. We present here observations of newly reconnected outflowing loops observed via in situ instruments in the magnetosphere. These observations, provided by five THEMIS spacecraft, show that around retracting loops (dipolarization fronts in this context) similar dynamic temperature and density structures are found as seen in SADs. We compare data from multiple SADs and dipolarization fronts to show that the observational signatures implied in the corona can be directly observed in similar plasma regimes in the magnetosphere, strongly favoring the interpretation of SADs as wakes behind retracting loops.

corona↗
NASA NTRS2017

THEMIS Satellite Observations of Hot Flow Anomalies at Earth's Bow Shock

Hot flow anomalies (HFAs) at Earth's bow shock were identified in Time History of Events and Macroscale Interactions During Substorms (THEMIS) satellite data from 2007 to 2009. The events were classified as young or mature and also as regular or spontaneous hot flow anomalies (SHFAs). The dataset has 17 young SHFAs, 49 mature SHFAs, 15 young HFAs, and 55 mature HFAs. They span a wide range of magnetic local times (MLTs) from approximately 7 to 16.5MLT. The largest ratio of solar wind to HFA core density occurred near dusk and at larger distances from the bow shock. In this study, HFAs and SHFAs were observed up to 6.3 RE and 6.1 RE (Earth radii), respectively, upstream from the model bow shock. HFA-SHFA occurrence decreases with distance upstream from the bow shock. HFAs of the highest event core ion temperatures were not seen at the flanks. The ratio of HFA ion temperature increase to HFA electron temperature increase is highest around 12MLT and slightly duskward. For SHFAs, (Tihfa=Tisw)/(Tehfa=Tesw) generally increased with distance from the bow shock. Both mature and young HFAs are more prevalent when there is an approximately radial interplanetary magnetic field. HFAs occur most preferentially for solar wind speeds from 550 to 600 km s-1. The correlation coefficient between the HFA increase in thermal energy density from solar wind values and the decrease in kinetic energy density from solar wind values is 0.62. SHFAs and HFAs do not show major differences in this study.

Interplanetary physics (planetary bow shocks; sola↗
NASA NTRS2019

Local Time Variation of Water Ice Clouds on Mars as Observed by THEMIS

The move of the Odyssey spacecraft during Mars Years 31 and 32 to an orbit with local time near 7:00 AM and PM has enabled the systematic retrieval of water icecloud optical depth using THEMIS thermal infrared images at a time of day not accessible from Mars Global Surveyor, Mars Reconnaissance Orbiter, or previousOdyssey observations. Because water ice clouds form by condensation, relatively small changes in atmospheric temperature can cause clouds to form or sublimatequickly, and there can be large changes in water ice cloud optical depth over the course of a day. Retrievals of water ice cloud optical depth using THEMISobservations show significant differences in cloud locations and optical depth as a function of local time and season. Cloud optical depth generally increases from theearliest (14:30) to latest (19:30) observations. During the aphelion season the increase from afternoon to evening is primarily associated with the thickening ofexisting clouds, while during the equinoctial and perihelion seasons there is a proportionally greater increase associated with the formation of clouds in the eveningat locations where clouds were not present during the afternoon.

Michael D Smith↗