Can Streamer Blobs prevent the Buildup of the Interplanetetary Magnetic Field?

Coronal Mass Ejections continuously drag closed magnetic field lines away from the Sun, adding new flux to the interplanetary magnetic field (IMF). We propose that the outward-moving blobs that have been observed in helmet streamers are evidence of ongoing, small-scale reconnection in streamer current sheets, which may play an important role in the prevention of an indefinite buildup of the IMF. Reconnection between two open field lines from both sides of a streamer current sheet creates a new closed field line, which becomes part of the helmet, and a disconnected field line, which moves outward. The blobs are formed by plasma from the streamer that is swept up in the trough of the outward moving field line. We show that this mechanism is supported by observations from SOHO/LASCO. Additionally, we propose a thorough statistical study to quantify the contribution of blob formation to the reduction of the IMF, and indicate how this mechanism may be verified by observations with SOHO/UVCS and the proposed NASA STEREO and ESA Polar Orbiter missions.Comment: 7 pages, 2 figures; accepted by The Astrophysical Journal Letters; uses AASTe

Disconnecting Solar Magnetic Flux

Disconnection of open magnetic flux by reconnection is required to balance the injection of open flux by CMEs and other eruptive events. Making use of recent advances in heliospheric background subtraction, we have imaged many abrupt disconnection events. These events produce dense plasma clouds whose distinctie shape can now be traced from the corona across the inner solar system via heliospheric imaging. The morphology of each initial event is characteristic of magnetic reconnection across a current sheet, and the newly-disconnected flux takes the form of a "U"-shaped loop that moves outward, accreting coronal and solar wind material. We analyzed one such event on 2008 December 18 as it formed and accelerated at 20 m/s^2 to 320 km/s, expanding self-similarly until it exited our field of view 1.2 AU from the Sun. From acceleration and photometric mass estimates we derive the coronal magnetic field strength to be 8uT, 6 Rs above the photosphere, and the entrained flux to be 1.6x10^11 Wb (1.6x10^19 Mx). We model the feature's propagation by balancing inferred magnetic tension force against accretion drag. This model is consistent with the feature's behavior and accepted solar wind parameters. By counting events over a 36 day window, we estimate a global event rate of 1/day and a global solar minimum unsigned flux disconnection rate of 6x10^13 Wb/y (6x10^21 Mx/y) by this mechanism. That rate corresponds to ~0.2 nT/y change in the radial heliospheric field at 1 AU, indicating that the mechanism is important to the heliospheric flux balance.Comment: preprint is 20 pages with 8 figures; accepted by APJ for publication in 201

Assessment of detectability of neutral interstellar deuterium by IBEX observations

The abundance of deuterium in the interstellar gas in front of the Sun gives insight into the processes of filtration of neutral interstellar species through the heliospheric interface and potentially into the chemical evolution of the Galactic gas. We investigate the possibility of detection of neutral interstellar deuterium at 1 AU from the Sun by direct sampling by the Interstellar Boundary Explorer (IBEX). We simulate the flux of neutral interstellar D at IBEX for the actual measurement conditions. We assess the number of interstellar D atom counts expected during the first three years of IBEX operation. We also simulate observations expected during an epoch of high solar activity. In addition, we calculate the expected counts of D atoms from the thin terrestrial water layer, sputtered from the IBEX-Lo conversion surface by neutral interstellar He atoms. Most D counts registered by IBEX-Lo are expected to originate from the water layer, exceeding the interstellar signal by 2 orders of magnitude. However, the sputtering should stop once the Earth leaves the portion of orbit traversed by interstellar He atoms. We identify seasons during the year when mostly the genuine interstellar D atoms are expected in the signal. During the first 3 years of IBEX operations about 2 detectable interstellar D atoms are expected. This number is comparable with the expected number of sputtered D atoms registered during the same time intervals. The most favorable conditions for the detection occur during low solar activity, in an interval including March and April each year. The detection chances could be improved by extending the instrument duty cycle, e.g., by making observations in the special deuterium mode of IBEX-Lo.Comment: Accepted for Astronomy & Astrophysic

Bistatic LIDAR experiment proposed for the shuttle/tethered satellite system missions

A new experiment concept has been proposed for the shuttle/tethered satellite system missions, which can provide high resolution, global density mappings of certain ionospheric species. The technique utilizes bistatic LIDAR to take advantage of the unique dual platform configuration offered by these missions. A tuned, shuttle-based laser is used to excite a column of the atmosphere adjacent to the tethered satellite, while triangulating photometic detectors on the satellite are employed to measure the fluorescence from sections of the column. The fluorescent intensity at the detectors is increased about six decades over both ground-based and monostatic shuttle-based LIDAR sounding of the same region. In addition, the orbital motion of the Shuttle provides for quasi-global mapping unattainable with ground-based observations. Since this technique provides such vastly improved resolution on a synoptic scale, many important middle atmospheric studies, heretofore untenable, may soon be addressed

A possible generation mechanism for the IBEX ribbon from outside the heliosphere

The brightest and most surprising feature in the first all-sky maps of Energetic Neutral Atoms (ENA) emissions (0.2-6 keV) produced by the Interstellar Boundary Explorer (IBEX) is an almost circular ribbon of a ~140{\deg} opening angle, centered at (l,b) = (33{\deg}, 55{\deg}), covering the part of the celestial sphere with the lowest column densities of the Local Interstellar Cloud (LIC). We propose a novel interpretation of the IBEX results based on the idea of ENA produced by charge-exchange between the neutral H atoms at the nearby edge of the LIC and the hot protons of the Local Bubble (LB). These ENAs can reach the Sun's vicinity because of very low column density of the intervening LIC material. We show that a plane-parallel or slightly curved interface layer of contact between the LIC H atoms (n_H = 0.2 cm^-3, T = 6000-7000 K) and the LB protons (n_p = 0.005 cm^-3, T ~ 10^6 K), together with indirect contribution coming from multiply-scattered ENAs from the LB, may be able to explain both the shape of the ribbon and the observed intensities provided that the edge is < (500-2000) AU away, the LIC proton density is (correspondingly) < (0.04-0.01) cm^-3, and the LB contains ~1% of non-thermal protons over the IBEX energy range. If this model is correct, then IBEX, for the first time, has imaged in ENAs a celestial object from beyond the confines of the heliosphere and can directly diagnose the plasma conditions in the LB.Comment: Accepted by Ap.J.Lett

Lunar and Asteroid Composition Using a Remote Secondary Ion Mass Spectrometer

Laboratory experiments simulating solar wind sputtering of lunar surface materials have shown that solar wind protons sputter secondary ions in sufficient numbers to be measured from low-altitude lunar orbit. Secondary ions of Na, Mg, Al, Si, K, Ca, Mn, Ti, and Fe have been observed sputtered from sample simulants of mare and highland soils. While solar wind ions are hundreds of times less efficient than those used in standard secondary ion mass spectrometry, secondary ion fluxes expected at the Moon under normal solar wind conditions range from approximately 10 to greater than 10(exp 4) ions cm(sup -2)s(sup -1), depending on species. These secondary ion fluxes depend both on concentration in the soil and on probability of ionization; yields of easily ionized elements such as K and Na are relatively much greater than those for the more electronegative elements and compounds. Once these ions leave the surface, they are subject to acceleration by local electric and magnetic fields. For typical solar wind conditions, secondary ions can be accelerated to an orbital observing location. The same is true for atmospheric atoms and molecules that are photoionized by solar EUV. The instrument to detect, identify, and map secondary ions sputtered from the lunar surface and photoions arising from the tenuous atmosphere is discussed

Evidence of a Solar Origin for Pressure Balance Structures in the High-Latitude Solar Wind

Ulysses observations of the high-latitude solar wind have shown that on time scales of \u3c 1 day, the polar wind is dominated by pressure balance structures (PBSs). Fluctuations of the plasma beta within PBSs appear to be strongly correlated with fluctuations in the helium abundance. The correlation occurs in both the northern and southern hemispheres. In addition, a mechanism is apparently at work in the high-latitude solar wind that dissipates the beta/He correlation over a distance of a few AU. Solar wind composition is established at the base of the corona; thus, the He abundance signature strongly suggests the observed solar wind PBSs are associated with structures low in the solar atmosphere. In particular, high-beta structures appear to originate in locations of enhanced He abundance. We suggest an interpretation of the high-beta portion of PBSs as the solar wind extensions of polar plumes