The Telescope of Extreme Ultraviolet (TEX) aboard Japan's lunar orbiter Kaguya has succeeded in imaging of the plasmaspheric helium ions by detecting resonantly scattered emission at 30.4 nm. After ...the initial instrumental check was completed, TEX has been operated routinely, and EUV images from TEX have become available from the perspective of the lunar orbit. The view afforded by the Kaguya orbit encompasses the plasma (He+) distribution in a single exposure, enabling us to examine for the first time the globally averaged properties of the terrestrial plasmasphere from the “side” (meridian) perspective. In this paper we report the inward motion of the nightside plasmapause on 2 May 2008 as seen from this remote meridian view of the Earth. The southward turning of the IMF initiated the inward motion of the plasmapause, and the nightside plasmasphere shrunk at a rate of 0.2 Re/h. Simultaneous solar wind velocity measurements provide a possible explanation for the total radial displacement of the plasmasphere observed in the EUV images.
An ensemble of twenty four coupled ocean-atmosphere models has been compared with respect to their performance in the tropical Pacific. The coupled models span a large portion of the parameter space ...and differ in many respects. The intercomparison includes TOGA (Tropical Ocean Global Atmosphere)-type models consisting of high-resolution tropical ocean models and coarse-resolution global atmosphere models, coarse-resolution global coupled models, and a few global coupled models with high resolution in the equatorial region in their ocean components. The performance of the annual mean state, the seasonal cycle and the interannual variability are investigated. The primary quantity analysed is sea surface temperature (SST). Additionally, the evolution of interannual heat content variations in the tropical Pacific and the relationship between the interannual SST variations in the equatorial Pacific to fluctuations in the strength of the Indian summer monsoon are investigated. The results can be summarised as follows: almost all models (even those employing flux corrections) still have problems in simulating the SST climatology, although some improvements are found relative to earlier intercomparison studies. Only a few of the coupled models simulate the El Nino/Southern Oscillation (ENSO) in terms of gross equatorial SST anomalies realistically. In particular, many models overestimate the variability in the western equatorial Pacific and underestimate the SST variability in the east. The evolution of interannual heat content variations is similar to that observed in almost all models. Finally, the majority of the models show a strong connection between ENSO and the strength of the Indian summer monsoon.
A statistical study comparing the plasmapause location determined using extreme ultraviolet (EUV) and cross‐phase measurements was performed over 50 days in May–July 2000 and 1 day in May 2008. In ...EUV images the plasmapause location was estimated using the sharp gradient in the brightness of 30.4 nm He+ emission. We have taken EUV images obtained by the IMAGE and the Kaguya satellites, which were operated in a solar maximum and minimum periods, respectively. In the ground‐based cross‐phase measurement, the plasmapause was defined as a steep drop of mass density in its radial profile. Mass density was inferred from the eigenfrequency of field line resonances in the ULF band (∼1–1000 mHz), which was deduced from geomagnetic field data using cross‐phase analysis. The two measurements of the plasmapause have been compared in a same meridian at the same time and very good agreement was found in 18 of 19 events. Our result clearly indicates that the He+ and mass density plasmapause are usually detected at the same place with the error range of ± 0.4 RE. In only one event, the He+ and the mass density defined plasmapauses were not colocated. This event may be due to the difference of refilling time between He+ and other dominant species.
BepiColombo, a mission of ESA (European Space Agency) in cooperation with JAXA (Japan Aerospace Exploration Agency), will explore Mercury, the planet closest to the Sun. BepiColombo will launch in ...2014 on a journey lasting up to six and a half years; the data gathering phase should occupy a one year nominal mission, with a possible extension of another year. The data which will be brought back from the orbiters will tell us about the Hermean surface, atmospheric composition, and magnetospheric dynamics; it will also contribute to understanding the history and formation of terrestrial planets. The PHEBUS (Probing of Hermean Exosphere by Ultraviolet Spectroscopy) instrument will be flown on MPO: Mercury Planetary Orbiter, one of the two BepiColombo orbiters. The main purpose of the instrument is to reveal the composition and the distribution of the exosphere of Mercury through EUV (Extreme Ultraviolet: 55–155nm) and FUV (Far Ultraviolet: 145–315nm) measurements. A consortium composed of four main countries has been formed to build it. Japan provides the two detectors (EUV and FUV), Russia implements the scanning system, and France and Italy take charge of the overall design, assembly, test, integration, and also provide two small NUV (Near Ultraviolet) detectors (for the light from calcium and potassium molecules). An optical prototype of the EUV detector which is identical to the flight configuration has been manufactured and evaluated. In this paper, we show the first spectra results observed by the EUV channel optical prototype. We also describe the design of PHEBUS and discuss the possibility of detecting noble gases in Mercury’s exosphere taking the experimental results so far into account.
The Mercury Sodium Atmosphere Spectral Imager (MSASI) on the Mercury Magnetospheric Orbiter (MMO) of the JAXA/ESA Bepi-Colombo (BC) Mission will address a range of fundamental scientific questions ...pertaining to Mercury's exosphere. The measurements will provide new information on regolith–exosphere–magnetosphere coupling as well as new understanding of the dynamics governing the exosphere bounded by the planetary surface, the solar wind and interplanetary space. MSASI is a high-dispersion visible spectrometer working in the spectral region near the sodium D
2 emission (589
nm), a major constituent of the Mercury exosphere. A single high-resolution Fabry–Perot etalon is used in combination with a narrow-band interference filter to achieve a compact and efficient instrument design. The etalon and filter are extremely stable with respect to long-term aging and temperature variations. Full-disk images of the planet are obtained by means of a single-axis scanning mirror in combination with the spin of the MMO spacecraft. This paper presents an overview of the MSASI and the design of the Fabry–Perot interferometer used as its spectral analyser.
It is concluded that:
(1)
The MSASI optical design is practical and can be implemented without new or critical technology developments.
(2)
The thermally stable etalon design is based on concepts, designs and materials that have a good space heritage.
(3)
The MSASI instrument will achieve a high signal-to-noise ratio (SNR) (>10) in the range of 2
K–10
M Rayleigh.
An Earth-orbiting small satellite “EXtreme ultraviolet spectrosCope for ExosphEric Dynamics” (EXCEED) which will be launched in 2012 is under development. The mission will carry out spectroscopic and ...imaging observation of EUV (Extreme Ultraviolet: 60–145
nm) emissions from tenuous plasmas around the planets (Venus, Mars, Mercury, and Jupiter). It is essential for EUV observation to put on an observing site outside the Earth’s atmosphere to avoid the absorption. It is also essential that the detection efficiency must be very high in order to catch the faint signals from those targets. In this mission, we employ cesium iodide coated microchannel plate as a 2 dimensional photon counting devise which shows 1.5–50 times higher quantum detection efficiency comparing with the bared one. We coat the surface of the grating and entrance mirror with silicon carbides by the chemical vapor deposition method in order to archive the high diffraction efficiency and reflectivity. The whole spectrometer is shielded by the 2
mm thick stainless steel to prevent the contamination caused by the high energy electrons from the inner radiation belt. In this paper, we will introduce the mission overview, its instrument, and their performance.
Using the Extreme Ultraviolet Spectroscope for Exospheric Dynamics (EXCEED) aboard Hisaki and the Solar Extreme Ultraviolet Monitor on the Solar and Heliospheric Observatory, we investigate ...variations of the extreme ultraviolet (EUV) dayglow brightness for OII 83.4 nm, OI 130.4 nm, and OI 135.6 nm in the Venusian upper atmosphere observed in March–April (period 1), April–May (period 2), and June–July (period 3) in 2014. The result shows that characteristic periodicities exist in the dayglow variations other than the ~27 day solar rotational effect of the solar EUV flux: 1.8, 2.8, 3.1, 4.5, and 9.9 day in period 1; 1.1 day in period 2; and 1.0 and 11 day in period 3. Many of these periodicities are consistent with previous observations and theory. We suggest these periodicities are related to density oscillations of oxygen atoms or photoelectrons in the thermosphere. The cause of these periodicities is still uncertain, but planetary‐scale waves and/or gravity waves propagating from the middle atmosphere, and/or minor periodic variations of the solar EUV radiation flux may play a role. Effects of the solar wind parameters (velocity, dynamic pressure, and interplanetary magnetic field's intensity) on the dayglow variations are also investigated using the Analyser of Space Plasma and Energetic Atoms (ASPERA‐4) and magnetometer aboard Venus Express. Although clear correlation with the dayglow variations is not found, their minor periodicities are similar to the dayglow periodicities. Contribution of the solar wind to the dayglow remains still unknown, but the solar wind parameters might affect the dayglow variations.
Key Points
Periodic variations of the EUV oxygen dayglow are observed at Venus
The solar EUV flux controls main periodic variations of the oxygen dayglow
Atmospheric waves and the solar wind may control minor dayglow periodicities
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