Study of charge-charge coupling effects on dipole emitter relaxation within a classical electron-ion plasma description

Studies of charge-charge (ion-ion, ion-electron, and electron-electron) coupling properties for ion impurities in an electron gas and for a two component plasma are carried out on the basis of a regularized electron-ion potential without short-range Coulomb divergence. This work is motivated in part by questions arising from recent spectroscopic measurements revealing discrepancies with present theoretical descriptions. Many of the current radiative property models for plasmas include only single electron-emitter collisions and neglect some or all charge-charge interactions. A molecular dynamics simulation of dipole relaxation is proposed here to allow proper account of many electron-emitter interactions and all charge-charge couplings. As illustrations, molecular dynamics simulations are reported for the cases of a single ion imbedded in an electron plasma and for a two-component ion-electron plasma. Ion-ion, electron-ion, and electron-electron coupling effects are discussed for hydrogen-like Balmer alpha lines.Comment: 13 figures, submitted to Phys. Rev.

An enduring rapidly moving storm as a guide to Saturn's Equatorial jet's complex structure

This work is licensed under a Creative Commons Attribution 4.0Saturn has an intense and broad eastward equatorial jet with a complex three-dimensional structure mixed with time variability. The equatorial region experiences strong seasonal insolation variations enhanced by ring shadowing, and three of the six known giant planetary-scale storms have developed in it. These factors make Saturn’s equator a natural laboratory to test models of jets in giant planets. Here we report on a bright equatorial atmospheric feature imaged in 2015 that moved steadily at a high speed of 450 ms-1 not measured since 1980–1981 with other equatorial clouds moving within an ample range of velocities. Radiative transfer models show that these motions occur at three altitude levels within the upper haze and clouds. We find that the peak of the jet (latitudes 10ºN to 10º S) suffers intense vertical shears reaching þ2.5 ms-1 km-1, two orders of magnitude higher than meridional shears, and temporal variability above 1 bar altitude level.Peer ReviewedPostprint (published version

A complex storm system in Saturn's north polar atmosphere in 2018

Saturn’s convective storms usually fall in two categories. One consists of mid-sized storms ~2,000¿km wide, appearing as irregular bright cloud systems that evolve rapidly, on scales of a few days. The other includes the Great White Spots, planetary-scale giant storms ten times larger than the mid-sized ones, which disturb a full latitude band, enduring several months, and have been observed only seven times since 1876. Here we report a new intermediate type, observed in 2018 in the north polar region. Four large storms with east–west lengths ~4,000–8,000¿km (the first one lasting longer than 200 days) formed sequentially in close latitudes, experiencing mutual encounters and leading to zonal disturbances affecting a full latitude band ~8,000¿km wide, during at least eight months. Dynamical simulations indicate that each storm required energies around ten times larger than mid-sized storms but ~100 times smaller than those necessary for a Great White Spot. This event occurred at about the same latitude and season as the Great White Spot in 1960, in close correspondence with the cycle of approximately 60 years hypothesized for equatorial Great White Spots.Peer ReviewedPostprint (author's final draft

A planetary-scale disturbance in a long-living three-vortex coupled system in Saturn's atmosphere

The zonal wind profile of Saturn has a singular structure in the latitude range 50ºN-65ºN planetocentric, with a double peak that reaches maximum zonal velocities close to 100ms-1[1]. A survey of Cassini ISS images shows that a system of three vortices formed in this latitudinal region in 2012 and has remained active until present, confirming that vortices in Saturn can be long lived [2]. In May 2015 a disturbance started to develop at the location of the triple vortex. Since at the time Cassini orbits were not favorable to the observation of the region, we were granted Director Discretionary Time of the Hubble Space Telescope to observe the region before the perturbation faded away. Here we report the dynamics and vertical structure of the three-vortex system and of the disturbance that developed at its location, based on HST and Cassini images. We also present results of numerical models to explain the stability of vortices in the region.Peer ReviewedPostprint (published version

A planetary-scale disturbance in a long living three vortex coupled system in Saturn's atmosphere

© 2018. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The zonal wind profile of Saturn has a unique structure at 60°N with a double-peaked jet that reaches maximum zonal velocities close to 100 ms-1. In this region, a singular group of vortices consisting of a cyclone surrounded by two anticyclones was active since 2012 until the time of this report. Our observation demonstrates that vortices in Saturn can be long-lived. The three-vortex system drifts at u = 69.0 ± 1.6 ms-1, similar to the speed of the local wind. Local motions reveal that the relative vorticity of the vortices comprising the system is ~2–3 times the ambient zonal vorticity. In May 2015, a disturbance developed at the location of the triple vortex system, and expanded eastwards covering in two months a third of the latitudinal circle, but leaving the vortices essentially unchanged. At the time of the onset of the disturbance, a fourth vortex was present at 55°N, south of the three vortices and the evolution of the disturbance proved to be linked to the motion of this vortex. Measurements of local motions of the disturbed region show that cloud features moved essentially at the local wind speeds, suggesting that the disturbance consisted of passively advecting clouds generated by the interaction of the triple vortex system with the fourth vortex to the south. Nonlinear simulations are able to reproduce the stability and longevity of the triple vortex system under low vertical wind shear and high static stability in the upper troposphere of Saturn.Peer ReviewedPostprint (author's final draft

Interaction of Saturn’s Hexagon with convective storms

In March 2020 a convective storm erupted at planetographic latitude 76°N in the southern flank of Saturn’s long-lived hexagonal wave. The storm reached a zonal size of 4,500 km and developed a tail extending zonally 33,000 km. Two new short-lived storms erupted in May in the hexagon edge. These storms formed after the convective storms that took place in 2018 in nearby latitudes. There were no noticeable changes in the zonal profile of Saturn's polar winds in 2018-2020. Measurements of the longitude position of the vertices of the hexagon throughout this period yield a value for its period of rotation equal to that of System III of radio-rotation measured at the time of Voyagers. We report changes in the hexagon clouds related to the activity of the storms. Our study reinforces the idea that Saturn’s hexagon is a well rooted structure with a possible direct relationship with the bulk rotation of the planet.This work has been supported by the Spanish project AYA2015-65041-P and PID2019-109467GB444 I00 (MINECO/FEDER, UE) and Grupos Gobierno Vasco IT1366-19. EGM is Serra Hunter Fellow atUPC. This work has used data acquired from the NASA/ESA HST Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These HST observations are associated with program GO/DD 15262. EGM, MS, KAV and ASL thankfully acknowledge the computer resources at Mare Nostrum and the technical support provided by Barcelona Supercomputing Center (AECT-2019-2-0006). We thank all the observers who have contributed with their images to the monitoring of the atmospheric activity on Saturn during the years 2019 and 2020 and whose list and images can be found in the ALPO452 Japan and PVOL databases. Part of the amateur observations analyzed were obtained through a collaboration with Europlanet 2024 RI. Europlanet 2024 RI has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 871149.Peer ReviewedPostprint (author's final draft

A planetary-scale disturbance in a long living three vortex coupled system in Saturn's atmosphere

© 2018. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The zonal wind profile of Saturn has a unique structure at 60°N with a double-peaked jet that reaches maximum zonal velocities close to 100 ms-1. In this region, a singular group of vortices consisting of a cyclone surrounded by two anticyclones was active since 2012 until the time of this report. Our observation demonstrates that vortices in Saturn can be long-lived. The three-vortex system drifts at u = 69.0 ± 1.6 ms-1, similar to the speed of the local wind. Local motions reveal that the relative vorticity of the vortices comprising the system is ~2–3 times the ambient zonal vorticity. In May 2015, a disturbance developed at the location of the triple vortex system, and expanded eastwards covering in two months a third of the latitudinal circle, but leaving the vortices essentially unchanged. At the time of the onset of the disturbance, a fourth vortex was present at 55°N, south of the three vortices and the evolution of the disturbance proved to be linked to the motion of this vortex. Measurements of local motions of the disturbed region show that cloud features moved essentially at the local wind speeds, suggesting that the disturbance consisted of passively advecting clouds generated by the interaction of the triple vortex system with the fourth vortex to the south. Nonlinear simulations are able to reproduce the stability and longevity of the triple vortex system under low vertical wind shear and high static stability in the upper troposphere of Saturn.Peer Reviewe

A planetary-scale disturbance in a long-living three-vortex coupled system in Saturn's atmosphere

The zonal wind profile of Saturn has a singular structure in the latitude range 50ºN-65ºN planetocentric, with a double peak that reaches maximum zonal velocities close to 100ms-1[1]. A survey of Cassini ISS images shows that a system of three vortices formed in this latitudinal region in 2012 and has remained active until present, confirming that vortices in Saturn can be long lived [2]. In May 2015 a disturbance started to develop at the location of the triple vortex. Since at the time Cassini orbits were not favorable to the observation of the region, we were granted Director Discretionary Time of the Hubble Space Telescope to observe the region before the perturbation faded away. Here we report the dynamics and vertical structure of the three-vortex system and of the disturbance that developed at its location, based on HST and Cassini images. We also present results of numerical models to explain the stability of vortices in the region.Peer Reviewe

A complex storm system in Saturn's north polar atmosphere in 2018

Saturn’s convective storms usually fall in two categories. One consists of mid-sized storms ~2,000¿km wide, appearing as irregular bright cloud systems that evolve rapidly, on scales of a few days. The other includes the Great White Spots, planetary-scale giant storms ten times larger than the mid-sized ones, which disturb a full latitude band, enduring several months, and have been observed only seven times since 1876. Here we report a new intermediate type, observed in 2018 in the north polar region. Four large storms with east–west lengths ~4,000–8,000¿km (the first one lasting longer than 200 days) formed sequentially in close latitudes, experiencing mutual encounters and leading to zonal disturbances affecting a full latitude band ~8,000¿km wide, during at least eight months. Dynamical simulations indicate that each storm required energies around ten times larger than mid-sized storms but ~100 times smaller than those necessary for a Great White Spot. This event occurred at about the same latitude and season as the Great White Spot in 1960, in close correspondence with the cycle of approximately 60 years hypothesized for equatorial Great White Spots.Peer Reviewe

The Dynamic Environment of Jezero Crater, Mars

International audienceSince the Perseverance rover's arrival in February 2021, atmospheric and aeolian observations by a wide range of rover instruments have revealed a highly dynamic environment in Jezero crater. The Mars Environmental Dynamics Analyzer (MEDA) carries a large suite of meteorological sensors, including pressure, surface temperature and atmospheric temperature at three heights, relative humidity, and wind speed and direction, as well as sensors dedicated to measuring aerosol abundance and properties, and (for the first time on Mars) upward and downward visible and infrared radiative fluxes. The SuperCam instrument has been used to measure atmospheric gas and aerosol abundances and aerosol properties, and also carries the first microphone operating on the martian surface, which has been used to measure very high frequency wind variations. Further, Mastcam-Z and the rover's engineering cameras have been used to retrieve aerosol abundances and properties, to observe clouds, dust devils, and dust lifting, and to observe aeolian features at the surface.Perseverance's wind measurements reveal diurnal and seasonal patterns of winds driven by the global and regional Isidis basin circulation, as well as significant sol-to-sol variability and strong wind gusts that may be associated with vigorous daytime convection cells being advected over the crater. These may also be linked to several strong dust lifting events imaged since landing. Measurements of pressure, temperature, wind, and radiative fluxes by MEDA sensors have been used to identify and even track the passage of vortices and dust devils, while rover cameras have caught numerous dust devils in images. Surface features such as regolith wind tails and ventifacts also indicate major aeolian activity inside the crater, although their orientations and morphology suggest the ventifacts may have formed under past climate conditions.Collectively, these observations show Jezero crater to be one of the most dynamic environments we have visited on Mars. In this presentation we will examine the diurnal, sol-to-sol, and seasonal variations of winds, wind gusts, and vortices; explore how these changes may be controlled by solar insolation, local topography, atmospheric waves, and regional and global-scale circulations; and relate these observations to observed dust lifting and aeolian features