Quasi-periodic polar flares at Jupiter: A signature of pulsed dayside reconnections?

in Geophysical Research Letters (2011), 38

The most dynamic part of the Jovian UV aurora is located inside the main auroral oval. This region is known to regularly show localized but dramatic enhancements on timescales of several tens of seconds ... [more ▼]

The most dynamic part of the Jovian UV aurora is located inside the main auroral oval. This region is known to regularly show localized but dramatic enhancements on timescales of several tens of seconds, called polar flares. They have often been associated with the polar cusp, based on their location in the polar cap. The present study is based on the longest high-time resolution image sequences ever acquired by the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. We report the first observations of a regularity in the occurrence of these flares, with a timescale of 2-3 minutes. We use a magnetic flux mapping model to identify the region corresponding to these emissions in the equatorial plane: the radial distance ranges from 55 to 120 Jovian radii and the local times are between 10: 00 and 18: 00. The analogy with similar phenomena observed at Earth suggests that these quasi-periodic auroral flares could be related to pulsed reconnections at the dayside magnetopause. Indeed, the flares' projected location in the equatorial plane and their rate of re-occurrence show some similarities with the properties of the flux transfer events observed by the Pioneer and Voyager probes. [less ▲]

A layer of ozone detected in the nightside upper atmosphere of Venus

in Icarus: International Journal of Solar System Studies (2011)

Nightside reconnection at Jupiter: Auroral and magnetic field observations from 26 July 1998

in Journal of Geophysical Research. Space Physics (2011), 116

In this study we present ultraviolet and infrared auroral data from 26 July 1998, and we show the presence of transient auroral polar spots observed throughout the postdusk to predawn local time sector ... [more ▼]

In this study we present ultraviolet and infrared auroral data from 26 July 1998, and we show the presence of transient auroral polar spots observed throughout the postdusk to predawn local time sector. The polar dawn spots, which are transient polar features observed in the dawn sector poleward of the main emission, were previously associated with the inward moving flow resulting from tail reconnection. In the present study we suggest that nightside spots, which are polar features observed close to the midnight sector, are related to inward moving flow, like the polar dawn spots. We base our conclusions on the near-simultaneous set of Hubble Space Telescope (HST) and Galileo observations of 26 July 1998, during which HST observed a nightside spot magnetically mapped close to the location of an inward moving flow detected by Galileo on the same day. We derive the emitted power from magnetic field measurements along the observed plasma flow bubble, and we show that it matches the emitted power inferred from HST. Additionally, this study reports for the first time a bright polar spot in the infrared, which could be a possible signature of tail reconnection. The spot appears within an interval of 30 min from the ultraviolet, poleward of the main emission on the ionosphere and in the postdusk sector planetward of the tail reconnection x line on the equatorial plane. Finally, the present work demonstrates that ionospheric signatures of flow bursts released during tail reconnection are instantaneously detected over a wide local time sector. [less ▲]

Nightglow investigation around 1.27 µm with VIRTIS/Venus-Express

Conference (2010, December)

In this study we report about the investigation of the spectral region 1.22-1.32 µm of the night side of Venus, observed by the VIRTIS instrument (Visible and InfraRed Spectral Imaging Spectrometer) on ... [more ▼]

In this study we report about the investigation of the spectral region 1.22-1.32 µm of the night side of Venus, observed by the VIRTIS instrument (Visible and InfraRed Spectral Imaging Spectrometer) on board the Venus Express spacecraft. This spectral region is characterized by the presence of the extensively studied (a1Δg – X3Σg-) (0,0) O2 nightglow band, the most intense emission observed on the night side of Venus. However, the comparison between data and synthetic spectra from the (0,0) band only, lacks a good match at wavelengths longer than 1.27 μm, especially in the region around 1.28-1.29 μm. The effects of temperature, CO2 and the (8,5) OH emission at 1.28 µm were investigated as a possible cause to the spectral disagreement, but they all are not enough to explain the observed difference. Instrumental effects were also excluded as possible cause of the mismatch. We found that the inclusion of the (1,1) band O2 emission in the synthetic spectra, originating from the upper vibrational level ν=1 of the (a1Δg – X3Σg-) transition centered at 1.28 μm, in addition to the (0,0), significantly improves the agreement between simulated spectra and observed data in the region at 1.28-1.29 μm. A synthetic spectrum, including the (0,0) and the (1,1) is produced and compared to 4 observed VIRTIS spectra, as an example. From the analyzed data, it results that the (1,1) band with an intensity ranging from the 8 to 15% of the (0,0) band is required to best reproduce the observed VIRTIS spectra. This corresponds to a (1,1) band intensity equal to 3.1-5.8 MR, in limb view, in agreement with the upper limit set by Connes et al., (1979), on their ground-based observations of the oxygen nightglow of Venus. [less ▲]

Discovery of pulsed polar flares in the Jovian aurorae

Poster (2010, December)

The most active part of the aurora at Jupiter is certainly the polar region, i.e. the emissions located poleward of the main auroral oval. This region is known to occasionally show localized but dramatic ... [more ▼]

The most active part of the aurora at Jupiter is certainly the polar region, i.e. the emissions located poleward of the main auroral oval. This region is known to occasionally show localized but dramatic enhancements of its brightness, referred to as polar flares. These emissions have been associated with the polar cusp, based on their location in the polar cap. In summer 2009, right after the refurbishment of the Space Telescope Imaging Spectrograph camera, the Hubble Space Telescope acquired the longest high-time resolution sequence ever of images of the Jovian aurora. We report the first observations of a quasi-periodicity in the occurrence of these flares, with a timescale of ~2-3 minutes. By using a magnetic flux mapping model, we show that these features originate from a region located at a radial distance ranging from 80 to 100 Jovian radii and local times between 10:00 and 15:00. As a consequence, by analogy with similar behaviors observed in the Earth aurora, we suggest that these emissions could be attributed to pulsed reconnections in the dayside magnetopause. [less ▲]

Electron-atmosphere interaction in the aurora of giant planets

Conference (2010, October 18)

All methods converge to indicate that the efficiency of the H2 (B,C states) emission is close to 10 kR/mW m-2 of electron precipitation. The UV aurora is a direct instantaneous map of the distribution of ... [more ▼]

All methods converge to indicate that the efficiency of the H2 (B,C states) emission is close to 10 kR/mW m-2 of electron precipitation. The UV aurora is a direct instantaneous map of the distribution of the electron precipitation. By contrast, the IR H3+ aurora is indirectly produced and its intensity depends on the amount of H3+ ions and the local temperature. It has the advantage to be observable from the ground The «UV color ratio » method is a powerful tool to probe the electron mean energy IF the distribution of HCs (mostly methane) is known EUV spectroscopy is very useful to determine the depth of the electron energy deposition, but so far, without spatial resolution [less ▲]

The Venus oxygen nightglow and density distributions

Conference (2010, September)

Observing Venus nightglow is a key tool to understand the composition and the dynamics of its atmosphere. Results deduced from observations can be implemented to produce a data model of Venus atmosphere ... [more ▼]

Observing Venus nightglow is a key tool to understand the composition and the dynamics of its atmosphere. Results deduced from observations can be implemented to produce a data model of Venus atmosphere. For instance, the Visible and Infra-Red Thermal Imaging Spectrometer (VIRTIS) instrument on board the Venus Express spacecraft is very useful to analyze the O2(a1Δ) nightglow at 1.27 µm in the Venus mesosphere. Nadir observations can be used to create a statistical map of the emission on Venus nightside. It appears that the maximum of the emission is located near the antisolar point. Limb observations also provide information on the altitude and on the shape of the emission layer. Combining nadir observations and vertically integrated limb observations improves the statistics of the emission map on Venus nightside. An associated limb profile can also be deduced for any point of the nightside. Given all these O2(a1Δ) intensity profiles, O2* density profiles can be calculated. O density profiles can also be calculated as long as CO2 density profiles are available. These can be retrieved either from the VTS3 model or from SPICAV stellar occultation measurements. Finally, three-dimensional maps of excited molecular and atomic oxygen densities can be generated. The oxygen density map shows significant differences from the VTS3 model predictions. [less ▲]

Jupiter's ultraviolet polar emission: a statistical study

Conference (2010, September)

Saturn's polar auroral emissions

Conference (2010, June 07)

The Venus OH Nightglow Distribution

Poster (2010, June)

The first identification of the OH airglow in the terrestrial mesosphere was made in 1950 by Meinel [1950]. Recently, the unexpected presence of the OH nightglow was observed in the Venus mesosphere by ... [more ▼]

The first identification of the OH airglow in the terrestrial mesosphere was made in 1950 by Meinel [1950]. Recently, the unexpected presence of the OH nightglow was observed in the Venus mesosphere by Piccioni et al. [2008] using a limb profile from the Visible and Infra-Red Thermal Imaging Spectrometer (VIRTIS) instrument on board the Venus Express spacecraft. They clearly identified the (1-0) and (2-1) transitions at 2.80 and 2.94 µm, respectively and the (2-0) band at 1.43 µm. Additional bands belonging to the Δv=1 sequence also appear to be present longward of the (1-0) band. In a preliminary study of characteristics of the OH emission distribution, Gérard et al. [2010] pointed out a correlation between the OH(Δv=1) and the O2(a1Δ) nightglow intensities. In Soret et al. [2010], the full dataset of VIRTIS-M limb observations of the OH Venus nightglow has been corrected from the thermal emission of the planet and analyzed to determine its characteristics. Based on 3328 limb profiles, the study shows that the emission is highly variable. No clear dependence of the airglow layer altitude versus the antisolar angle is established. The peak brightness appears to decrease away from the antisolar point even if the variability at a given location is very strong. Some correlation between simultaneous observations of the intensity of the OH and the O2(a1∆) emissions has also been detected, presumably because atomic oxygen is a common precursor to the formation of O2(a1∆) and O3, whose reaction with H produces excited OH. A relation given in the one-dimensional photochemical model of Krasnopolsky [2009] has been used to link the OH and the O2(a1∆) airglows through the hydrogen flux at 130 km. It appeared that using a constant flux did not fill well the simultaneous OH and O2 observations. Either the flux has to vary with the distance to the antisolar point or other dimensions have to be involved. [less ▲]