Southern Aurora Research Articles

Temporal and Spectral Studies by XMM‐Newton of Jupiter's X‐ray Auroras During a Compression Event

AbstractWe report the temporal and spectral results of the first XMM‐Newton observation of Jupiter's X‐ray auroras during a clear magnetospheric compression event on June 2017 as confirmed by data from the Jovian Auroral Distributions Experiment (JADE) instrument onboard Juno. The northern and southern auroras were visible twice and thrice respectively as they rotated in and out of view during the ∼23‐hr (almost 2.5 Jupiter rotations) long XMM‐Newton Jovian‐observing campaign. Previous auroral observations by Chandra and XMM‐Newton have shown that the X‐ray auroras sometimes pulse with a regular period. We applied wavelet and fast Fourier transforms (FFTs) on the auroral light curves to show that, following the compression event, the X‐ray auroras exhibited a recurring 23‐ to 27‐min periodicity that lasted over 12.5 hr (longer than a Jupiter rotation). This periodicity was observed from both the northern and southern auroras, suggesting that the emission from both poles was caused by a shared driver. The soft X‐ray component of the auroras is due to charge exchange processes between precipitating ions and neutrals in Jupiter's atmosphere. We utilized the Atomic Charge Exchange (ACX) spectral package to produce solar wind and iogenic plasma models to fit the auroral spectra in order to identify the origins of these ions. For this observation, the iogenic model gave the best fit, which suggests that the precipitating ions are from iogenic plasma in Jupiter's magnetosphere.

Birkeland currents in Jupiter’s magnetosphere observed by the polar-orbiting Juno spacecraft

The exchange of energy and momentum between the Earth’s upper atmosphere and ionosphere, and its space environment (magnetosphere) is regulated by electric currents (called Birkeland currents) flowing along magnetic field lines that connect these two regions of space1. The associated electric currents flow towards and away from each pole primarily in two concentric conical sheets2. It has been expected that powerful sheets of magnetic-field-aligned electric currents would be found in association with the bright Jovian auroras3. The Juno spacecraft is well positioned to explore Jupiter’s polar magnetosphere and sample Birkeland or field-aligned currents and particle distributions. Since July 2016, Juno has maintained a near-polar orbit, passing over both polar regions every 53 days. From this vantage point, Juno’s complement of science instruments gathers in situ observations of magnetospheric particles and fields while its remote-sensing infrared and ultraviolet spectrographs and imagers map auroral emissions4. Here we present an extensive analysis of magnetic field perturbations measured during Juno’s transits of Jupiter’s polar regions, and thereby demonstrate Birkeland currents associated with Jupiter’s auroral emissions. We characterize the magnitude and spatial extent of the currents and we find that they are weaker than anticipated and filamentary in nature. A significant asymmetry is observed between the field perturbations and the current associated with the northern and the southern auroras. The Juno spacecraft’s observations of magnetic field perturbations in Jupiter’s polar regions show Birkeland currents associated with aurorae that are weaker than anticipated and filamentary in nature. An asymmetry is observed between the northern and southern auroras.

BLOODY “ALMAZ”: DE/CONSTRUCTION OF ONE REVOLUTION MYTH IN ODESA

In Soviet historical science during 1960s-1980s a traditional stereotype of perception of the cruiser “Almaz” as “Southern Aurora” was formed, which had to symbolize similar tendencies of the revolutionary progress in 1917- 1918 in Baltic and the Black Sea Fleets. The role of the steamship crew in events of the Russian and the Ukrainian revolutions in a limited period of time is analyzed in the article.
 In January 1918, the Bolshevist armed insurrection took place in Odesa, active participation in the preparation of which was played by the part of sailors and officers of the cruiser “Almaz”. During the existence of the Odesa Soviet republic, new authorities used the practice of the “red” terror, the symbol of which was “Almaz”. As the result of the detention and physical liquidation of people of various categories on the cruiser and at moorings of other warships, thus spreading a variety of rumours, authorities of local self-government attempted to take control of the situation in order to make facts of self-trial impossible. But judicial and investigational institutions were able to investigate the circumstances of the detention of prisoners and their subsequent fate fully only after the restoration of the Ukrainian National Republic governance in Odesa. Their conclusions dispel the heroic image of the cruiser created by Soviet historiography.

The Detached Auroras Induced by the Solar Wind Pressure Enhancement in Both Hemispheres From Imaging and In Situ Particle Observations

AbstractThis paper presents simultaneous detached proton auroras that appeared in both hemispheres at 11:06 UT, 08 March 2012, just 2 min after a sudden solar wind pressure enhancement (~11:04 UT) hit the Earth. They were observed under northward interplanetary magnetic field Bz condition and during the recovery phase of a moderate geomagnetic storm. In the Northern Hemisphere, Defense Meteorological Satellite Program/Special Sensor Ultraviolet Spectrographic Imager observed that the detached arc occurred within 60°–65° magnetic latitude and covered a few magnetic local time (MLT) hours ranging from 0530 to 0830 MLT with a possible extension toward noon. At the same time (11:06 UT), Polar Orbiting Environment Satellites 19 detected a detached proton aurora around 1300 MLT in the Southern Hemisphere, centering ~62° magnetic latitude, which was at the same latitudes as the northern detached arc. This southern aurora was most probably a part of a dayside detached arc that was conjugate to the northern one. In situ particle observations indicated that the detached auroras were dominated by protons/ions with energies ranging from around 20 keV to several hundreds of keV, without obvious electron precipitations. These detached arcs persisted for less than 6 min, consistent with the impact from pressure enhancement and the observed electromagnetic ion cyclotron (EMIC) waves. It is suggested that the increasing solar wind pressure pushed the hot ions in the ring current closer to Earth where the steep gradient of cold plasma favored EMIC wave growth. By losing energy to EMIC waves the energetic protons (>20 keV) were scattered into the loss cone and produced the observed detached proton auroras.

The surprising southern aurora

The discovery of Jupiter’s southern X-ray aurora reveals that it is tellingly different from the northern one, providing important clues to how Jupiter’s polar aurorae are generated.

Infrared observations of Jovian aurora from Juno's first orbits: Main oval and satellite footprints

AbstractThe Jovian Infrared Auroral Mapper (JIRAM) is an imager/spectrometer on board NASA/Juno mission for the study of the Jovian aurorae. The first results of JIRAM's imager channel observations of the H3+ infrared emission, collected around the first Juno perijove, provide excellent spatial and temporal distribution of the Jovian aurorae, and show the morphology of the main ovals, the polar regions, and the footprints of Io, Europa and Ganymede. The extended Io “tail” persists for ~3 h after the passage of the satellite flux tube. Multi‐arc structures of varied spatial extent appear in both main auroral ovals. Inside the main ovals, intense, localized emissions are observed. In the southern aurora, an evident circular region of strong depletion of H3+ emissions is partially surrounded by an intense emission arc. The southern aurora is brighter than the north one in these observations. Similar, probably conjugate emission patterns are distinguishable in both polar regions.

Observation and interpretation of energetic ion conics in Jupiter's polar magnetosphere

AbstractNASA's Juno spacecraft successfully completed its first science polar pass over Jupiter's northern and southern aurora, with all the instruments powered, on 27 August 2016. Observations of conical energetic proton distributions at low altitudes (<6 RJ) over the northern polar region are interpreted as resulting from transversely (to the local magnetic field lines) accelerated H+ at a position planetward of the point of observation. The proton conics were observed within a broad region of upward beaming electrons and were accompanied by broadband low‐frequency wave emissions as well as low‐altitude trapped magnetospheric protons and heavy ions. The characteristic energies associated with these accelerated ion conics are ~100 times more energetic than similar distributions observed in the Earth's auroral region and similar in energy to those found at Saturn. In addition, the ion conics also exhibited pitch angle dispersion with time that is interpreted as a consequence of the structure of the source location. Mapping these distributions along magnetic field lines connected from the spacecraft to the ionosphere suggests that the source region exists at altitudes between ~3 and 5 RJ. These new and exciting observations of accelerated ions over the polar region of Jupiter open up new areas for comparative planetary auroral physics.

Preliminary JIRAM results from Juno polar observations: 2. Analysis of the Jupiter southern H3+ emissions and comparison with the north aurora

AbstractThe Jupiter InfraRed Auroral Mapper (JIRAM) aboard Juno observed the Jovian South Pole aurora during the first orbit of the mission. H3+ (trihydrogen cation) and CH4 (methane) emissions have been identified and measured. The observations have been carried out in nadir and slant viewing both by a L‐filtered imager and a 2–5 μm spectrometer. Results from the spectral analysis of the all observations taken over the South Pole by the instrument are reported. The coverage of the southern aurora during these measurements has been partial, but sufficient to determine different regions of temperature and abundance of the H3+ ion from its emission lines in the 3–4 μm wavelength range. Finally, the results from the southern aurora are also compared with those from the northern ones from the data taken during the same perijove pass and reported by Dinelli et al. (2017).

Saturn’s northern auroras as observed using the Hubble Space Telescope

We discuss the features of Saturn’s northern FUV auroras as observed during a program of Hubble Space Telescope observations which executed over 2011–2013 and culminated, along with Cassini observations, in a comprehensive multi-spectral observing campaign. Our 2011–2013 observations of the northern aurora are also compared with those from our 2007–2008 observation of the southern aurora. We show that the variety of morphologies of the northern auroras is broadly consistent with the southern, and determine the statistical equatorward and poleward boundary locations. We find that our boundaries are overall consistent with previous observations, although a modest poleward displacement of the poleward boundaries is due to the increased prevalence of poleward auroral patches in the noon and afternoon sectors during this program, likely due to the solar wind interaction. We also show that the northern auroral oval oscillates with the northern planetary period oscillation (PPO) phase in an elongated ellipse with semi-major axis ∼1.6° oriented along the post-dawn/post-dusk direction. We further show that the northern auroras exhibit dawn-side brightenings at zero northern magnetic PPO phase, although there is mixed evidence of auroral emissions fixed in the rotating frame of the northern PPO current system, such that overall the dependence of the auroras on northern magnetic phase is somewhat weak.

Longitude dependences of Saturn's ultraviolet aurora

AbstractBased on periodicities in the kilometric radio emissions, the Saturn Longitude System 4 (SLS4) was used to organize the far ultraviolet (120–150 nm) aurora observed by the Ultraviolet Imaging Spectrograph on the Cassini spacecraft. Individual Ultraviolet Imaging Spectrograph pixels were projected onto the ionosphere of Saturn, transformed into the SLS4 north and SLS4 south longitude systems, accumulated over all over auroral observations from 2007 to early 2009, and binned into 1°×1° bins of colatitude. The intensity of the northern aurora showed little variation in its SLS4 north system, but the intensity of the southern aurora exhibited an enhancement of over ~10 kR between ~140–280° SLS4 south longitude. This enhancement may represent the auroral signature of a southern ionospheric vortex proposed in MHD models of Saturn's magnetosphere to explain its periodicities. The loci of the northern intensity peaks and the 3 kR boundaries varied little over 360° of longitude, while the equatorward boundary of the southern aurora varied by ~5° in SLS4 south longitude, reaching its most equatorward location of ~23° colatitude between 100° and 180° longitude. The polygonal centroids of the aurora in both north and south were consistent with offsets of no more than ~1° in both hemispheres.

The morphology of Saturn's ultraviolet aurora

Spectrographic images in the far ultraviolet, obtained from observations made from 2007 to 2009, are used to quantify and compare the morphology of Saturn's northern and southern aurora in local time. Made by the UVIS imager on the Cassini spacecraft, these observations differ from previous UV observations of Saturn's aurora by offering complete local time coverage of the aurora from small zenith angles. A statistical picture emerges after combining over 105 spectrographic images of the north and south aurora. From its composite, the northern aurora exhibits an intensity peak of ∼40 kR near 05 h local time, while the southern aurora peaks at ∼60 kR near the same local time. Aurora intensities in the post‐noon sectors are essentially constant at ∼10 kR. The half‐power points of latitudinal profiles reveal widths of ∼4° near dawn and ∼8° near dusk in both north and south. The aurora has an approximately circular shape (not oval!), although harmonic fits suggest the northern aurora is more nearly circular than the southern. The center of the northern aurora has an offset of ∼1–2° from the pole, while the southern center is offset by ∼2–3°, with both offsets in the midnight‐to‐dawn quadrant. When mapped to the polar regions, precipitation of field‐aligned energetic electrons (>20 keV) generally lies equatorward of the main auroral intensity at all local times.

Simultaneous Cassini VIMS and UVIS observations of Saturn's southern aurora: Comparing emissions from H, H2 and H3+ at a high spatial resolution

Here, 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 H2 emissions from UVIS are compared to infrared H3+ emission from VIMS. The auroral emission is structured into three arcs – H, H2 and H3+ are morphologically identical in the bright main auroral oval (∼73°S), but there is an equatorward arc that is seen predominantly in H (∼70°S), and a poleward arc (∼74°S) that is seen mainly in H2 and H3+. These observations indicate that, for the main auroral oval, UV emission is a good proxy for the infrared H3+ 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.

Phase relation of oscillations near the planetary period of Saturn's auroral oval and the equatorial magnetospheric magnetic field

Previous analyses of Hubble Space Telescope (HST) images of Saturn's southern auroras obtained during two campaigns, in January 2007 and February 2008, have revealed that the auroral oval oscillates at a period close to the planetary rotation period, with its center describing an elongated ellipse of semimajor axis ∼2° colatitude aligned along the prenoon to premidnight direction. Previous analyses of Cassini magnetic field data from Saturn's near‐equatorial quasi‐dipolar magnetosphere have also established the presence of a rotating pattern of magnetic field perturbations near the planetary period, a phase model which has been derived from data over the interval from mid‐2004 to the end of 2007, whose extrapolation is verified here for use during the February 2008 HST campaign. In this paper we compare the phases of these oscillatory phenomena and show that the southern oval displacement was directed approximately opposite to the rotating equatorial perturbation field during both HST campaign intervals. We also examine the relation of the southern oval oscillations to the periodic power modulations in Saturn kilometric radiation (SKR) and show that the southern oval was displaced sunward at SKR maxima. It is suggested that the oval displacements are related to magnetospheric field line distortions associated with the rotating magnetic field perturbations, this picture also being consistent with recently reported periodic tilting of the equatorial plasma sheet. We note, however, that this picture provides no immediate explanation for the significantly elliptical nature of the observed oval motion.

IMF dependence of the open-closed field line boundary in Saturn's ionosphere, and its relation to the UV auroral oval observed by the Hubble Space Telescope

Abstract. We study the dependence of Saturn's magnetospheric magnetic field structure on the interplanetary magnetic field (IMF), together with the corresponding variations of the open-closed field line boundary in the ionosphere. Specifically we investigate the interval from 8 to 30 January 2004, when UV images of Saturn's southern aurora were obtained by the Hubble Space Telescope (HST), and simultaneous interplanetary measurements were provided by the Cassini spacecraft located near the ecliptic ~0.2 AU upstream of Saturn and ~0.5 AU off the planet-Sun line towards dawn. Using the paraboloid model of Saturn's magnetosphere, we calculate the magnetospheric magnetic field structure for several values of the IMF vector representative of interplanetary compression regions. Variations in the magnetic structure lead to different shapes and areas of the open field line region in the ionosphere. Comparison with the HST auroral images shows that the area of the computed open flux region is generally comparable to that enclosed by the auroral oval, and sometimes agrees in detail with its poleward boundary, though more typically being displaced by a few degrees in the tailward direction.

A statistical analysis of the location and width of Saturn's southern auroras

Abstract. A 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 ~14° and ~16° co-latitude, respectively, with a median latitudinal width of ~2°. These median values vary only modestly with local time around the oval, though the poleward boundary moves closer to the pole near noon (~12.5°) such that the oval is wider in that sector (median width ~3.5°) than it is at both dawn and dusk (~1.5°). It is also shown that the position of the auroral boundaries at Saturn are extremely variable, the poleward boundary being located between 2° and 20° co-latitude, and the equatorward boundary between 6° and 23°, 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 ~20°–24° 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 ~11° and ~15°. 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.

Open flux estimates in Saturn's magnetosphere during the January 2004 Cassini‐HST campaign, and implications for reconnection rates

During 8–30 January 2004, a sequence of 68 UV images of Saturn's southern aurora was obtained by the Hubble Space Telescope (HST), coordinated for the first time with measurements of the upstream interplanetary conditions made by the Cassini spacecraft. Using the poleward edge of the observed aurora as a proxy for the open‐closed field line boundary, the open flux content of the southern polar region has been estimated. It is found to range from ∼15 to ∼50 GWb during the interval, such a large variation providing evidence of a significant magnetospheric interaction with the solar wind, in particular with the interplanetary structures associated with corotating interaction regions (CIRs). The open flux is found to decline slowly during a rarefaction region in which the interplanetary magnetic field remained very weak, while decreasing sharply in association with the onset of CIR‐related solar wind compressions. Such decreases are indicative of the dominating role of open flux closure in Saturn's tail during these intervals. Increases in open flux are found to occur in the higher‐field compression regions after the onsets, and in a following rarefaction region of intermediate field strength. These increases are indicative of the dominating role of open flux production at Saturn's magnetopause during these intervals. The rate of open flux production has been estimated from the upstream interplanetary data using an empirical formula based on experience at Earth, with typical values varying from ∼10 kV during the weak‐field rarefaction region, to ∼200 kV during the strong‐field compression. These values have been integrated over time between individual HST image sets to estimate the total open flux produced during these intervals. Comparison with the changes in open flux obtained from the auroral images then allows us to estimate the amount of open flux closed during these intervals, and hence the averaged tail reconnection rates. Intermittent intervals of tail reconnection at rates of ∼30–60 kV are inferred in rarefaction regions, while compression regions are characterised by rates of ∼100–200 kV, these values representing averages over the ∼2‐day intervals between HST image sequences. The forms of the aurorae observed are also discussed in relation to the deduced voltage values.

Simultaneous images of the northern and southern auroras from the Polar spacecraft: An auroral substorm

The first simultaneous images of the auroras in the Northern and Southern Hemispheres with a single camera have been gained with the Earth Camera onboard the Polar spacecraft with sufficient angular resolution to provide maps of the intensities. An auroral substorm was fortuitously observed on 1 November 2001 when the spacecraft was favorably positioned to observe both auroras. The auroral intensities during the onset and the early expansive phase were mapped into corrected geomagnetic coordinates. The onset brightening at far‐ultraviolet wavelengths was first detected in the southern auroras and subsequently seen in the northern auroras about 1 min later on L‐shells of about 5 RE. During the early phases of the auroral expansive phase, the southern aurora continued to be brighter. The unequal auroral intensities in the two hemispheres suggest that there is strong coupling of the ionosphere and magnetosphere. The mapping of the auroras revealed that there is a local time difference between the onset positions of about 40 min, with the southern auroras positioned to the east relative to those in the north. This displacement was also similarly detected in the quiet auroral regions, which were not participants in the auroral substorm. Such displacements may be useful in developing improvements in the accuracy of global magnetic models that are important for determination of the position of the in situ particle and field measurements in the magnetosphere. The greater brightness of the northern quiet time auroras by tens of percent as first reported by aircraft observations at visible wavelengths in both hemispheres has been verified by the more global view from the Polar spacecraft.

The Relationship of Umiray Dumaget to Other Philippine Languages

The Relationship of Umiray Dumaget to Other Philippine Languages Ronald S. Himes Abstract Most scholars who have addressed the problem of categorizing Philippine languages have related Umiray Dumaget (DGTU) most closely to other languages spoken by Negritos in northeastern Luzon, languages in the Cordilleran microgroup. Reid (1994) suggests that DGTU is not a Cordilleran language but rather that it is relatable to Bikol, a Central Philippine language. While the evidence from phonological changes and the pronominal system does not compel us to favor one subgrouping over the other, the lexical data do show that DGTU is most closely related to the Central Philippine languages. Culturally, we can infer that DGTU results from very early contact between the non-Austronesian-speaking Negrito population and speakers of that variety of Central Philippine that evolved into Tagalog, Bikol, and the Bisayan languages. A consequence of this grouping is that any inherited lexeme that DGTU shares with non-Central Philippine languages must be assigned to a higher level. 1. Background.1 East Central Luzon is the homeland of the group of about 3,000 people speaking Umiray Dumaget (DGTU). "Dumagat" is an exonym applied to a wide variety of groups of the Negrito physical type, most of whom prefer the term Agta, Alta, Ayta, or some other derivative of the Proto-Philippines (PPH(Z)) *qaRta[ ] 'person'.2 Local names for the group in question abound—tagi kellogen, tagi bulus, tagi kabuluwen, tagi depoynga, and so forth—but the designation Umiray has most often been used in the literature (Macleod 1972, McFarland 1980, Walton 1979, Thomas and Gieser 1973, Reid 1994). This language covers a relatively wide area of eastern Luzon from southern Aurora, just south of Baler, along the coast to at least Infanta in Quezon, and westward [End Page 275] into Nueva Ecija, Bulacan, and Rizal provinces. Some speakers of this language are found in communities along the northern coast of Polillo Island (Reid, pers. comm.). There is only minor dialect variation among DGTU speaking communities. DGTU is not mutually intelligible with any other Philippine language. Thomas and Gieser (1973:65) grouped the "Dingalan Bay Dumaget group: Umiray, Diteki, tagi Kabuluwen, Depoynga, Anglat" with other Agta languages under "Northern Negrito group and Luzon various." On the basis of lexicostatistics, Walton (1979:81) subgrouped DGTU with Casiguran Dumagat (DGTC), the pair splitting off from Northern Cordilleran at 45% of shared cognates. This percentage of shared cognates is high, at least as far as DGTU is concerned, undoubtedly because of unexcluded borrowings; Headland and Headland (1974) calculate the percentage of cognates shared by DGTC and DGTU as 36 %, and this writer at 35%. McFarland (1980) also links DGTU with DGTC and the latter's close relatives East Cagayan Negrito, Paranan, and Kasiguranin. The latter are classified together as the Northern Dumagat languages, and DGTU is separated into a class by itself. "Dumagat (Umirey) is very different from the other four, and may actually belong to a different subgroup (such as Northern Cordilleran) or constitute a subgroup by itself" (66). He nevertheless states that the "Dumagat languages are part of the Northern Philippine group, within which their closest relatives are probably the Northern Cordilleran languages" (66). Reid, in contrast, holds that the closest relatives of DGTU are not to be found in the northern Philippines. Rather, "a cursory inspection of sound changes and verb morphology suggests that it is probably a Central Philippine language, related fairly remotely to the Bikol languages" (1994:41). 2. The Problem. In his 1994 article "Possible non-Austronesian lexical elements in Philippine Negrito languages," Reid argues convincingly that languages spoken by modern Negrito populations are the descendants of creolized Austronesian speech acquired by the Negritos soon after coming into contact with the invading population. If these languages, indeed, developed from creoles, then they should not appear in a family tree of true Austronesian languages. Reid acknowledges this, writing (39): "I shall continue, however, to refer to them as members of particular subfamilies of Philippine Austronesian languages...

The [FORMULA][F][RM]H[/RM][SUP]+[/SUP][INF]3[/INF][/F][/FORMULA] Latitudinal Profile of Saturn

We present an H latitudinal profile of Saturn, obtained in 1998 October using the CSHELL spectrometer on the NASA Infrared Telescope Facility. The profile, measured at 3.953 μm, shows that the majority of the emission is concentrated in the auroral ovals, making Saturn similar to Jupiter and different from Uranus. The spatial resolution is sufficient to resolve the southern auroral oval, currently fully displayed around the south pole, into two peaks separated by 12. At the time of the observations reported here, the emission flux in the H line is 8.3 (±1.7) × 10-18 W m-2 for the intensity integrated over a 10 swath along the southern aurora and 5.8 (±1.3) × 10-18 W m-2 for the northern aurora. There may also be some mid- to low-latitude emission, similar to that on Jupiter. We suggest that planetwide H emission from Saturn is between 1.2 and 3.6 × 1011 W.

Solar Wind Control of Jupiter's H+3Auroras

A program of observations of Jupiter's H+3auroras was conducted during the first 4 months of 1992, a period that spanned the Ulysses encounter. Daily variations of auroral intensity are small in magnitude (∼20%) and well correlated with variations in the solar wind ram pressure arriving at Jupiter. A much larger (factor of 3) time variation is observed to occur on a time scale of approximately 2 months. During the first 2 months of observation, the inferred total intrinsic intensity of the northern aurora exceeded that of the southern aurora by a factor of 2. Throughout the latter 2 months, characterized by less intense auroral activity, the intensity of the northern aurora was comparable to that of the southern aurora.