320 research outputs found
STBadman/PSP-E10-Sources: Initial-Submission
No full textThis release is for the initial iteration of this repository and the figures it creates to support submission of the associated manuscript "Prediction and Verification of Parker Solar Probe Solar Wind Sources at 13.3 R⊙" by Badman et al., submitted to JGR Space Physics on 1/31/202
Supercorotating return flow from reconnection in Saturn's magnetotail
No full textDetecting plasma dynamics in Saturn's magnetosphere is essential for understanding energy flow through the system. It has been proposed that both the Dungey and Vasyliunas cycles operate at Saturn, and the competition between these cycles has been debated. We examine data taken by the Cassini spacecraft in Saturn's post-dawn magnetosphere, similar to 17.5 Saturn radii from the planet, and identify an example of return flow from magnetotail reconnection. The flow included water group ions and had elevated ion temperatures (of order 1 keV), consistent with Vasyliunas cycle return flow. The flow was also supercorotating (similar to 200 km s(-1), similar to 120% of corotation), which is highly atypical of Saturn's outer magnetosphere. Our results suggest that return flows are time-variable, and our results concerning Dungey cycle return flows are inconclusive. We propose that supercorotating flows in Saturn's dawn magnetosphere strongly influence the current system that is responsible for the planet's main auroral emission. Citation: Masters, A., M. F. Thomsen, S. V. Badman, C. S. Arridge, D. T. Young, A. J. Coates, and M. K. Dougherty (2011), Supercorotating return flow from reconnection in Saturn's magnetotail, Geophys. Res. Lett., 38, L03103, doi: 10.1029/2010GL046149
A statistical analysis of the location and width of Saturn's southern auroras
No full textpeer reviewedA selection of twenty-two Hubble Space Telescope images of Saturn's ultraviolet auroras obtained during 1997-2004 has been analysed to determine the median location and width of the auroral oval, and their variability. Limitations of coverage restrict the analysis to the southern hemisphere, and to local times from the post-midnight sector to just past dusk, via dawn and noon. It is found that the overall median location of the poleward and equatorward boundaries of the oval with respect to the southern pole are at similar to 14 degrees and similar to 16 degrees co-latitude, respectively, with a median latitudinal width of similar to 2 degrees. These median values vary only modestly with local time around the oval, though the poleward boundary moves closer to the pole near noon (similar to 12.5 degrees) such that the oval is wider in that sector (median width similar to 3.5 degrees) than it is at both dawn and dusk (similar to 1.5 degrees). It is also shown that the position of the auroral boundaries at Saturn are extremely variable, the poleward boundary being located between 2 degrees and 20 degrees co-latitude, and the equatorward boundary between 6 degrees and 23 degrees, this variability contrasting sharply with the essentially fixed location of the main oval at Jupiter. Comparison with Voyager plasma angular velocity data mapped magnetically from the equatorial magnetosphere into the southern ionosphere indicates that the dayside aurora lie poleward of the main upward-directed field-aligned current region associated with corotation enforcement, which maps to similar to 20 degrees-24 degrees co-latitude, while agreeing reasonably with the position of the open-closed field line boundary based on estimates of the open flux in Saturn's tail, located between similar to 11 degrees and similar to 15 degrees. In this case, the variability in location can be understood in terms of changes in the open flux present in the system, the changes implied by the Saturn data then matching those observed at Earth as fractions of the total planetary flux. We infer that the broad (few degrees) diffuse auroral emissions and sub-corotating auroral patches observed in the dayside sector at Saturn result from precipitation from hot plasma sub-corotating in the outer magnetosphere in a layer a few Saturn radii wide adjacent to the magnetopause, probably having been injected either by Dungey-cycle or Vasyliunas-cycle dynamics on the nightside
Reconnection in a rotation-dominated magnetosphere and its relation to Saturn's auroral dynamics
No full textpeer reviewed[1] The first extended series of observations of Saturn's auroral emissions, undertaken by the Hubble Space Telescope in January 2004 in conjunction with measurements of the upstream solar wind and interplanetary magnetic field ( IMF) by the Cassini spacecraft, have revealed a strong auroral response to the interplanetary medium. Following the arrival of the forward shock of a corotating interaction region compression, bright auroras were first observed to expand significantly poleward in the dawn sector such that the area of the polar cap was much reduced, following which the auroral morphology evolved into a spiral structure around the pole. We propose that these auroral effects are produced by compression- induced reconnection of a significant fraction of the open flux present in Saturn's open tail lobes, as has also been observed to occur at Earth, followed by subcorotation of the newly closed flux tubes in the outer magnetosphere region due to the action of the ionospheric torque. We show that the combined action of reconnection and rotation naturally gives rise to spiral structures on newly opened and newly closed field lines, the latter being in the same sense as observed in the auroral images. The magnetospheric corollary of the dynamic scenario outlined here is that corotating interaction region- induced magnetospheric compressions and tail collapses should be accompanied by hot plasma injection into the outer magnetosphere, first in the midnight and dawn sector, and second at increasing local times via noon and dusk. We discuss how this scenario leads to a strong correlation of auroral and related disturbances at Saturn with the dynamic pressure of the solar wind, rather than to a correlation with the northsouth component of the IMF as observed at Earth, even though the underlying physics is similar, related to the transport of magnetic flux to and from the tail in the Dungey cycle
Significance of Dungey-cycle flows in Jupiter's and Saturn's magnetospheres, and their identification on closed equatorial field lines
No full textWe consider the contribution of the solar wind-driven Dungey-cycle to flux transport in Jupiter's and Saturn's magnetospheres, the associated voltages being based on estimates of the magnetopause reconnection rates recently derived from observations of the interplanetary medium in the vicinity of the corresponding planetary orbits. At Jupiter, the reconnection voltages are estimated to be ~150 kV during several-day weak-field rarefaction regions, increasing to ~1 MV during few-day strong-field compression regions. The corresponding values at Saturn are ~25 kV for rarefaction regions, increasing to ~150 kV for compressions. These values are compared with the voltages associated with the flows driven by planetary rotation. Estimates of the rotational flux transport in the "middle" and "outer" magnetosphere regions are shown to yield voltages of several MV and several hundred kV at Jupiter and Saturn respectively, thus being of the same order as the estimated peak Dungey-cycle voltages. We conclude that under such circumstances the Dungey-cycle "return" flow will make a significant contribution to the flux transport in the outer magnetospheric regions. The "return" Dungey-cycle flows are then expected to form layers which are a few planetary radii wide inside the dawn and morning magnetopause. In the absence of significant cross-field plasma diffusion, these layers will be characterized by the presence of hot light ions originating from either the planetary ionosphere or the solar wind, while the inner layers associated with the Vasyliunas-cycle and middle magnetosphere transport will be dominated by hot heavy ions originating from internal moon/ring plasma sources. The temperature of these ions is estimated to be of the order of a few keV at Saturn and a few tens of keV at Jupiter, in both layers
Location of Saturn's northern infrared aurora determined from Cassini VIMS images
No full textThe location of Saturn's northern infrared aurora is described in detail using 12 selected images acquired by Cassini VIMS during 2006–2008. Bright main oval arcs and prevalent polar features are displayed, which do not exhibit a preferred local time or spatial extent. The average equatorward limit of the aurora was determined using a best fit circle method. The average circle has a radius of 16.4 ± 0.2° latitude, centred 1.6° anti-sunward of Saturn's pole. The low standard deviation of the fitted circle radii (<1°) indicates the relative stability of the equatorward auroral boundary. For the first time we show that the average location of the infrared oval is similar to that of the ultraviolet oval, suggesting that the auroral emissions at different wavelengths are very likely produced by a common driver despite the distinct emission mechanisms
Peak emission altitude of Saturn's H3+ aurora
No full textHere we present the first detailed measurement of the altitudinal profile of H3+ emission within Saturn's ionosphere, made using images taken by the VIMS instrument on Cassini on 11–12 October 2006, during a chance alignment between the visible limb of the planet and the position of the main auroral emission. Using this, we show that the emission profile of H3+ can be fitted to a reasonable accuracy with a Gaussian, producing a calculated peak emission altitude at 1155 (±25) km that differs significantly from previous observations of the UV emission profile, and also from the predictions of models that calculated the H3+ emission profile, which suggested that there would be extended emission above the peak emission altitude. This lack of extended emission is most simply explained by differences in the scale height of H and H2, suggesting that models overestimate H2 at high altitudes, with little H2 from 2000 km above the 1 bar level
1929 Roseworthy College Tennis Team
No full textBlack and white photo; mounted.Back - B.G. Walters, A. Hancock, Mr. R. Baker (Sports Master), R.H. Badman, G. Hart; front - J.L. Cuthbertson (Captain), Mr. W.R. Birks (Principal), K.A. Elliot (V. Captain)
Simultaneous Cassini VIMS and UVIS observations of Saturn's southern aurora: Comparing emissions from H, H-2 and H-3(+) at a high spatial resolution
No full textHere, for the first time, temporally coincident and spatially overlapping Cassini VIMS and UVIS observations of Saturn's southern aurora are presented. Ultraviolet auroral H and H-2 emissions from UVIS are compared to infrared H-3(+) emission from VIMS. The auroral emission is structured into three arcs - H, H-2 and H-3(+) are morphologically identical in the bright main auroral oval (similar to 73 degrees S), but there is an equatorward arc that is seen predominantly in H (similar to 70 degrees S), and a poleward arc (similar to 74 degrees S) that is seen mainly in H-2 and H-3(+). These observations indicate that, for the main auroral oval, UV emission is a good proxy for the infrared H-3(+) morphology (and vice versa), but for emission either poleward or equatorward this is no longer true. Hence, simultaneous UV/IR observations are crucial for completing the picture of how the atmosphere interacts with the magnetosphere
Roseworthy Agricultural College Second Football Team 1929
No full textMounted black and white photo.Back: WFM Appleby, KO Kitto, DH Badman, HR Hurn, SR Close; Centre: HN Clark, VA Martin, R Beckwith, DH Green, JC Kilgour, FH Wheaton, RI Herriot, Mr R Baker (Sportsmaster); Front: A Hancock, JA Hurn, AL Oppatt, WW Ellis (Capt), WLB Bell (Vice-Capt), GE Wiese, JC Sampson
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