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J. Bland-hawthorn - One of the best experts on this subject based on the ideXlab platform.
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Multi-wavelength Observations of Galactic Winds
Publications of the Astronomical Society of Australia, 1995Co-Authors: J. Bland-hawthornAbstract:AbstractIt has long been suspected that Winds of thermal and/or relativistic particles are a common feature of both active and normal galaxies. Galactic Winds are likely to be an important mechanism, particularly at high redshift, by which energy and metals from galaxies are subsequently dumped into the intergalactic medium. Both observational and theoretical studies of Wind Processes remain in their infancy, largely because astrophysical Winds are difficult to detect. Future satellite missions will make systematic surveys possible for the first time. In this review, we summarise the current evidence for galactic-scale Winds, particularly in energy bands where the Wind emission is spatially resolved. We also discuss observational limitations and problems of interpretation.
D G Mitchell - One of the best experts on this subject based on the ideXlab platform.
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solar energetic particles sep and galactic cosmic rays gcr as tracers of solar Wind conditions near saturn event lists and applications
Icarus, 2018Co-Authors: E Roussos, C M Jackman, M F Thomsen, W S Kurth, S V Badman, C Paranicas, P Kollmann, N Krupp, R Bucik, D G MitchellAbstract:The lack of an upstream solar Wind monitor poses a major challenge to any study that investigates the influence of the solar Wind on the configuration and the dynamics of Saturn’s magnetosphere. Here we show how Cassini MIMI/LEMMS observations of Solar Energetic Particle (SEP) and Galactic Cosmic Ray (GCR) transients, that are both linked to energetic Processes in the heliosphere such us Interplanetary Coronal Mass Ejections (ICMEs) and Corotating Interaction Regions (CIRs), can be used to trace enhanced solar Wind conditions at Saturn’s distance. SEP protons can be easily distinguished from magnetospheric ions, particularly at the MeV energy range. Many SEPs are also accompanied by strong GCR Forbush Decreases. GCRs are detectable as a low count-rate noise signal in a large number of LEMMS channels. As SEPs and GCRs can easily penetrate into the outer and middle magnetosphere, they can be monitored continuously, even when Cassini is not situated in the solar Wind. A survey of the MIMI/LEMMS dataset between 2004 and 2016 resulted in the identification of 46 SEP events. Most events last more than two weeks and have their lowest occurrence rate around the extended solar minimum between 2008 and 2010, suggesting that they are associated to ICMEs rather than CIRs, which are the main source of activity during the declining phase and the minimum of the solar cycle. We also list of 17 time periods ( > 50 days each) where GCRs show a clear solar periodicity ( ∼ 13 or 26 days). The 13-day period that derives from two CIRs per solar rotation dominates over the 26-day period in only one of the 17 cases catalogued. This interval belongs to the second half of 2008 when expansions of Saturn’s electron radiation belts were previously reported to show a similar periodicity. That observation not only links the variability of Saturn’s electron belts to solar Wind Processes, but also indicates that the source of the observed periodicity in GCRs may be local. In this case GCR measurements can be used to provide the phase of CIRs at Saturn. We further demonstrate the utility of our survey results by determining that: (a) Magnetospheric convection induced by solar Wind disturbances associated with SEPs is a necessary driver for the formation of transient radiation belts that were observed throughout Saturn’s magnetosphere on several occasions during 2005 and on day 105 of 2012. (b) An enhanced solar Wind perturbation period that is connected to an SEP of day 332/2013 was the definite source of a strong magnetospheric compression which led to open flux loading in the magnetotail. Finally, we propose how the event lists can define the basis for single case studies or statistical investigations on how Saturn and its moons (particularly Titan) respond to extreme solar Wind conditions or on the transport of SEPs and GCRs in the heliosphere.
Ronald Greeley - One of the best experts on this subject based on the ideXlab platform.
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Coordinated Observations of Aeolian Features from the Mars Exploration Rovers (MER) and the Mars Express High Resolution Stereo Camera and Other Orbiters
2004Co-Authors: Ronald Greeley, S. D. Thompson, P. L. Whelley, S. Squyres, G. Neukum, R. Arvidson, M. Malin, R. Kuzmin, P. Christensen, S. C. R. RafkinAbstract:Surface features associated with aeolian (Wind) Processes at the Mars Exploration Rover (MER) landing sites for Spirit (Gusev crater) and Opportunity (Sinus Meridiani) were observed from the surface and from orbit through coordinated observations by the rovers and the Mars Express orbiter High Resolution Stereo Camera and compared with features seen in other orbiter data and with Wind vectors predicted by a numerical mesoscale model of the atmosphere.
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Aeolian Processes and their Effects on Understanding the Chronology of Mars
Space Sciences Series of ISSI, 2001Co-Authors: Ronald Greeley, Ruslan O. Kuzmin, Robert M. HaberleAbstract:Aeolian (Wind) Processes can transport particles over large distances on Mars, leading to the modification or removal of surface features, formation of new landforms, and mantling or burial of surfaces. Erosion of mantling deposits by Wind deflation can exhume older surfaces. These Processes and their effects on the surface must be taken into account in using impact crater statistics to derive chronologies on Mars. In addition, mapping the locations, relative ages, and orientations of aeolian features can provide insight into Martian weather, climate, and climate history.
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aeolian features and Processes at the mars pathfinder landing site
Journal of Geophysical Research, 1999Co-Authors: Ronald Greeley, Ruslan O. Kuzmin, Kenneth E Herkenhoff, M D Kraft, Gregory Wilson, Michael C Malin, N T Bridges, Robert Sullivan, W WardAbstract:The Mars Pathfinder landing site contains abundant features attributed to aeolian, or Wind, Processes. These include Wind tails, drift deposits, duneforms of various types, ripplelike features, and ventifacts (the first clearly seen on Mars). Many of these features are consistant with formation involving sand-size particles. Although some features, such as dunes, could develop from saltating sand-size aggregates of finer grains, the discovery of ventifact flutes cut in rocks strongly suggests that at least some of the grains are crystalline, rather than aggregates. Excluding the ventifacts, the orientations of the Wind-related features correlate well with the orientations of bright Wind steaks seen on Viking Orbiter images in the general area. They also correlate with Wind direction predictions from the NASA-Ames General Circulation Model (GCM) which show that the strongest Winds in the area occur in the northern hemisphere winter and are directed toward 209°.
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Aeolian Geology of the Mars Pathfinder Site
1998Co-Authors: Ronald Greeley, Ruslan O. Kuzmin, Kenneth E Herkenhoff, M D Kraft, Michael C Malin, Nathan T. Bridges, G. R. Wilson, R. J. Sullivan, Matthew P. Golombek, Paul S. SmithAbstract:The Mars Pathfinder landing site contains abundant features attributed to aeolian, or Wind, Processes. These include Wind tails, drift deposits, duneforms of various types, ripplelike features, and ventifacts (the first seen on Mars). Many of these features are consistent with formation involving sand-size particles. Although some features, such as the barchan dunes, could develop from saltating sand-size aggregates of finer grains, the discovery of ventifact flutes cut in rocks strongly suggests that at least some of the grains are crystalline, rather than aggregates. Excluding the ventifacts, the orientations of the Wind-related features correlate well with the orientations of bright Wind streaks seen on Viking Orbiter images in the general area. They also correlate with Wind direction predictions from the NASA-Ames General Circulation Model (GCM) which show that the strongest Winds in the area occur in the northern hemisphere winter and are directed toward 209 degrees.
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Wind Streaks on Venus: Clues to Atmospheric Circulation
Science (New York N.Y.), 1994Co-Authors: Ronald Greeley, Gerald Schubert, Daniel Limonadi, K. C. Bender, William I. Newman, P. Thomas, Catherine M. Weitz, Stephen D. WallAbstract:Magellan images reveal surface features on Venus attributed to Wind Processes. Sand dunes, Wind-sculpted hills, and more than 5830 Wind streaks have been identified. The streaks serve as local "Wind vanes," representing Wind direction at the time of streak formation and allowing the first global mapping of near-surface Wind patterns on Venus. Wind streaks are oriented both toward the equator and toward the west. When streaks associated with local transient events, such as impact cratering, are deleted, the westward component is mostly lost but the equatorward component remains. This pattern is consistent with a Hadley circulation of the lower atmosphere.
Feng Shuanglei - One of the best experts on this subject based on the ideXlab platform.
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Uncertainty Estimation of Wind Power Prediction Result Based on Wind Process Method
Power system technology, 2013Co-Authors: Feng ShuangleiAbstract:Taking Wind farms actually operated in various areas of China as the object and the implementation of optimal uncertainty estimation of Wind power prediction results as the goal,a Wind process method-based approach to estimate the uncertainty of Wind power prediction results is proposed and mathematical models for different Wind Processes are given.To effectively identify prediction errors of different characteristics,the prediction error data is divided by Wind process method and power level division method.Adopting nonparametric regression method to fit probability density distribution of the error,a better fitting result is attained.The advancement of the proposed method is verified by actual Wind farm data;and comparing the proposed estimation method with the estimation method based on normal distribution optimized fitting,the results show that the evaluation indices obtained by the proposed method are better than those from the latter.
E Roussos - One of the best experts on this subject based on the ideXlab platform.
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solar energetic particles sep and galactic cosmic rays gcr as tracers of solar Wind conditions near saturn event lists and applications
Icarus, 2018Co-Authors: E Roussos, C M Jackman, M F Thomsen, W S Kurth, S V Badman, C Paranicas, P Kollmann, N Krupp, R Bucik, D G MitchellAbstract:The lack of an upstream solar Wind monitor poses a major challenge to any study that investigates the influence of the solar Wind on the configuration and the dynamics of Saturn’s magnetosphere. Here we show how Cassini MIMI/LEMMS observations of Solar Energetic Particle (SEP) and Galactic Cosmic Ray (GCR) transients, that are both linked to energetic Processes in the heliosphere such us Interplanetary Coronal Mass Ejections (ICMEs) and Corotating Interaction Regions (CIRs), can be used to trace enhanced solar Wind conditions at Saturn’s distance. SEP protons can be easily distinguished from magnetospheric ions, particularly at the MeV energy range. Many SEPs are also accompanied by strong GCR Forbush Decreases. GCRs are detectable as a low count-rate noise signal in a large number of LEMMS channels. As SEPs and GCRs can easily penetrate into the outer and middle magnetosphere, they can be monitored continuously, even when Cassini is not situated in the solar Wind. A survey of the MIMI/LEMMS dataset between 2004 and 2016 resulted in the identification of 46 SEP events. Most events last more than two weeks and have their lowest occurrence rate around the extended solar minimum between 2008 and 2010, suggesting that they are associated to ICMEs rather than CIRs, which are the main source of activity during the declining phase and the minimum of the solar cycle. We also list of 17 time periods ( > 50 days each) where GCRs show a clear solar periodicity ( ∼ 13 or 26 days). The 13-day period that derives from two CIRs per solar rotation dominates over the 26-day period in only one of the 17 cases catalogued. This interval belongs to the second half of 2008 when expansions of Saturn’s electron radiation belts were previously reported to show a similar periodicity. That observation not only links the variability of Saturn’s electron belts to solar Wind Processes, but also indicates that the source of the observed periodicity in GCRs may be local. In this case GCR measurements can be used to provide the phase of CIRs at Saturn. We further demonstrate the utility of our survey results by determining that: (a) Magnetospheric convection induced by solar Wind disturbances associated with SEPs is a necessary driver for the formation of transient radiation belts that were observed throughout Saturn’s magnetosphere on several occasions during 2005 and on day 105 of 2012. (b) An enhanced solar Wind perturbation period that is connected to an SEP of day 332/2013 was the definite source of a strong magnetospheric compression which led to open flux loading in the magnetotail. Finally, we propose how the event lists can define the basis for single case studies or statistical investigations on how Saturn and its moons (particularly Titan) respond to extreme solar Wind conditions or on the transport of SEPs and GCRs in the heliosphere.
