Magnetospheric influence on the Moon\u27s exosphere

[1] Atoms in the thin lunar exosphere are liberated from the Moon\u27s regolith by some combination of sunlight, plasma, and meteorite impact. We have observed exospheric sodium, a useful tracer species, on five nights of full Moon in order to test the effect of shielding the lunar surface from the solar wind plasma by the Earth\u27s magnetosphere. These observations, conducted under the dark sky conditions of lunar eclipses, have turned out to be tests of the differential effects of energetic particle populations that strike the Moon\u27s surface when it is in the magnetotail. We find that the brightness of the lunar sodium exosphere at full Moon is correlated with the Moon\u27s passage through the Earth\u27s magnetotail plasma sheet. This suggests that omnipresent exospheric sources (sunlight or micrometeors) are augmented by variable plasma impact sources in the solar wind and Earth\u27s magnetotail

Ionospheric storms at geophysically-equivalent sites – Part 2: Local time storm patterns for sub-auroral ionospheres

The response of the mid-latitude ionosphere to geomagnetic storms depends upon several pre-storm conditions, the dominant ones being season and local time of the storm commencement (SC). The difference between a site's geographic and geomagnetic latitudes is also of major importance since it governs the blend of processes linked to solar production and magnetospheric input, respectively. Case studies of specific storms using ionospheric data from both hemispheres are inherently dominated by seasonal effects and the various local times versus longitude of the SCs. To explore inter-hemispheric consistency of ionospheric storms, we identify "geophysically-equivalent-sites" as locations where the geographic and geomagnetic latitudes have the same relationship to each other in both hemispheres. At the longitudes of the dipole tilt, the differences between geographic and geomagnetic latitudes are at their extremes, and thus these are optimal locations to see if pre-conditioning and/or storm-time input are the same or differ between the hemispheres. <br><br> In this study, we use ionosonde values of the F2-layer maximum electron density (<I>Nm</I>F2) to study geophysical equivalency at Wallops Island (VA) and Hobart (Tasmania), using statistical summaries of 206 events during solar cycle #20. We form average patterns of Δ<I>Nm</I>F2 (%) versus local time over 7-day storm periods that are constructed in ways that enhance the portrayal of the average characteristic features of the positive and negative phases of ionospheric storms. The results show a consistency between four local time characteristic patterns of storm-induced perturbations, and thus for the average magnitudes and time scales of the processes that cause them in each hemisphere. Subtle differences linked to small departures from pure geophysical equivalency point to a possible presence of hemispheric asymmetries governed by the non-mirror-image of geomagnetic morphology in each hemisphere

Periodicities in the occurrence of aurora as indicators of solar variability

A compilation of records of the aurora observed in China from the Time of the Legends (2000 - 3000 B.C.) to the mid-18th century has been used to infer the frequencies and strengths of solar activity prior to modern times. A merging of this analysis with auroral and solar activity patterns during the last 200 years provides basically continuous information about solar activity during the last 2000 years. The results show periodicities in solar activity that contain average components with a long period (approx. 412 years), three middle periods (approx. 38 years, approx. 77 years, and approx. 130 years), and the well known short period (approx. 11 years)

Possible Evidence of Gravity Wave Coupling into the Mid-latitude F Region Ionosphere During the SEEK Campaign

On five of eight observation nights during the 1996 SEEK (Sporadic E Experiment over Kyushu) campaign, Japan, unusual “wave‐like” structures were imaged in the 630 nm thermospheric nightglow emission. Four of these events were observed to travel towards the southwest, providing new evidence in support of recent theories describing the coupling of medium‐scale gravity waves into the mid‐latitude F region ionosphere. Available ionosonde data and the visual characteristics of the wave structures indicate no association with the occurrence of mid‐latitude spread F or F region upwellings. Instead, the data support the novel concept of feedback from the ionosphere into the gravity wave, via the Perkins instability, to enhance its visibility

1999 Quadrantids and the lunar Na atmosphere

Enhancements of the Na emission and temperature from the lunar atmosphere were reported during the Leonids meteor showers of 1995, 1997 and 1998. Here we report a search for similar enhancement during the 1999 Quadrantids, which have the highest mass flux of any of the major streams. No enhancements were detected. We suggest that different chemical-physical properties of the Leonid and Quadrantid streams may be responsible for the difference.Comment: 5 pages, 1 figure, accepted for publication in MNRA

Response of Saturn's auroral ionosphere to electron precipitation: Electron density, electron temperature, and electrical conductivity

In the high-latitude regions of Saturn, the ionosphere is strongly coupled to the magnetosphere through the exchange of energy. The influx of energetic particles from Saturn's magnetosphere enhances the ionospheric densities and temperatures, affects the electrodynamical properties of the ionosphere, and contributes to the heating of the thermosphere. It is therefore critical to accurately model the energy deposition of these magnetospheric particles in the upper atmosphere in order to evaluate key ionospheric quantities of the coupled magnetosphere-ionosphere system. We present comprehensive results of ionospheric calculations in the auroral regions of Saturn using our Saturn Thermosphere-Ionosphere Model (STIM). We focus on solar minimum conditions during equinox. The atmospheric conditions are derived from the STIM 3-D General Circulation Model. The ionospheric component is self-consistently coupled to the solar and auroral energy deposition component. The precipitating electrons are assumed to have a Maxwellian distribution in energy with a mean energy E-m and an energy flux Q(0). In the presence of hard electron precipitation (1 < E-m <= 20 keV) with Q(0) > 0.04 mW m(-2), the ionospheric conductances are found to be proportional to the square root of the energy flux, but the response of the ionosphere is not instantaneous and a time delay needs to be applied to Q(0) when estimating the conductances. In the presence of soft electron precipitation (E-m < 500 eV) with Q(0) <= 0.2 mW m(-2), the ionospheric conductances at noon are found to be primarily driven by the Sun. However, soft auroral electrons are efficient at increasing the ionospheric total electron content and at heating the thermal electron population

The 1999 Quadrantids and the lunar Na atmosphere

Enhancements of the Na emission and temperature from the lunar atmosphere were reported during the Leonid meteor showers of 1995, 1997 and 1998. Here we report a search for similar enhancement during the 1999 Quadrantids, which have the highest mass flux of any of the major streams. No enhancements were detected. We suggest that different chemical-physical properties of the Leonid and Quadrantid streams may be responsible for the differenc

Characterization of a Double Mesospheric Bore Over Europe

Observations of a pair of mesospheric bore disturbances that propagated through the nighttime mesosphere over Europe are presented. The observations were made at the Padua Observatory, Asiago (45.9\ub0N, 11.5\ub0E), by the Boston University all-sky imager on 11 March 2013. The bores appeared over the northwest horizon, approximately 30 min apart, and propagated toward the southeast. Using additional satellite and radar data, we present evidence indicating the bores originated in the mesosphere from a single, larger-scale mesospheric disturbance propagating through the mesopause region. Furthermore, the large-scale mesospheric disturbance appeared to be associated with an intense weather disturbance that moved southeastward over the United Kingdom and western Europe during 10 and 11 March