Reconnection Of Open Field Lines Research Articles

Structure and statistical properties of plasmoids in Jupiter's magnetotail

AbstractPlasmoids and other reconnection‐related signatures have been observed in Jupiter's magnetotail through analysis of magnetic field and energetic particle data. Previous studies have established the spatial distribution and recurrence period of tail reconnection events, and identified the location of a statistical X‐line separating inward and outward flow. Here we present new analysis focusing specifically on 43 plasmoid signatures observed in magnetometer data in order to establish the average properties and internal structure of Jovian plasmoids. We present statistics on the observed plasmoid length scale, duration, radial position, and local time distribution. On average, the observed plasmoids have a ~3 RJ radial extent and ~7 min duration and result in the closure of ~4–8 GWb of open flux from reconnection of open field lines in the postplasmoid plasma sheet. We also determine the amount of mass released and the magnetic flux closed in order to understand the role of tail reconnection in the transport of mass and flux in Jupiter's magnetosphere. The observed plasmoid properties are consistent with a mass loss rate of ~0.7–120 kg/s and a flux closure rate of ~7–70 GWb/d. We conclude that tail reconnection and plasmoid release is an important method of flux transport at Jupiter but likely cannot account for the mass input from Io, suggesting that additional mass loss mechanisms may be significant. Finally, we examine the plasmoid interior structure through minimum variance analysis and find that most plasmoids lack a core field and are better described by magnetic loops rather than flux ropes.

Statistical Analysis of Low-latitude Pi2 Pulsations Observed at Bohyun Station in Korea

We statistically investigated the properties of low-latitude Pi2 pulsations using Bohyun (BOH, Mlat = <TEX>$29.8^{\circ}$</TEX>, L = 1.35) ground magnetometer data in 2008. For this 1-year interval, 582 Pi2 events were identified when BOH was in the nightside from 1800 to 0600 local times. We found the following Pi2 characteristics. (1) The occurrence distribution of Pi2s is relatively constant in local times. (2) The Pi2 frequency varies in local times. That is, Pi2 pulsations in postmidnight sector had higher frequency than in premidnight sector. (3) Pi2 power in premidnight sector is stronger than in postmidnight sector. (4) Pi2 frequency has positive correlation with solar wind speed and AE index. (5) Pi2 power has not a clear correlation with solar wind parameters. This indicates that Pi2 power is not controlled by external sources. (6) It is found that the most probable-time between Pi2 onsets is <TEX>${\Delta}t$</TEX> ~ 37.5 min: This is interpreted to be the period between Pi2 pulsations when they occur cyclically. We suggest that <TEX>${\Delta}t$</TEX> ~ 37.5 min is the occurrence rate of reconnection of open field lines in the tail lobe.

Enhancement of Photospheric Meridional Flow by Reconnection Processes

We simulate the two-dimensional transport of the open magnetic flux on the surface of the Sun. The temporal evolution of the flux density depends on the advective motions due to solar differential rotation and poleward meridional flow and on an effective spatial diffusive motion. The latter is a result of the uniform diffusion of field line footpoints in the network lanes and a nonuniform diffusion offield lines due to reconnection of open field lines with closed loops on the solar surface. The gradient of the diffusion coefficient represents an effective velocity in addition to the advective velocity. We investigate the behavior of the steady state solution for solar minimum and solar maximum conditions with spatially uniform and nonuniform diffusion coefficients. We find that for solar minimum conditions, the effect of spatial diffusion resulting from reconnection processes enhances the poleward meridional flow due to the large-scale preferred direction in the gradient of the diffusion coefficient. For solar maximumconditions,theneteffectofspatialdiffusionisminimalbecauseoftheisotropicandlocalgradientsofthe diffusion coefficient. Our simulation demonstrates that magnetic reconnection processes on the solar surface can be a mechanism to vary motions on the photosphere, in particular, poleward meridional flow.

Acceleration of the solar wind as a result of the reconnection of open magnetic flux with coronal loops

There are compelling observations of a clear anticorrelation between solar wind flow speed and coronal electron temperature, as determined from solar wind ionic charge states. A simple theory is presented which can account for these observations, including the functional form of the correlation: Solar wind flow speed squared varies essentially linearly as the inverse of the coronal electron temperature. In this theory, magnetic field lines in the corona that open into the heliosphere reconnect with coronal loops near their base. This process displaces the open field line and disturbs and imparts energy into the overlying corona, thereby determining the Poynting vector into the corona. This process releases mass from the loop into the corona and determines the mass flux of the solar wind. The Poynting vector and mass flux into the corona determine the final speed of the solar wind and yield a relationship that provides an excellent fit to observations. The reconnection of open field lines with coronal loops, and their subsequent displacements, also results in a diffusive transport of open field lines, which influences the configuration of the heliospheric magnetic field.

Plasma sheet dynamics observed by the Polar spacecraft in association with substorm onsets

We present observations of the Polar spacecraft of magnetospheric substorm signatures in the plasma sheet midway along auroral field lines between the ionosphere and the equatorial plasma sheet. On October 17, 1997, Polar was located in the onset meridian in conjunction with the Scandinavian magnetometer chain (International Monitor for Auroral Geomagnetic Effects; IMAGE). In addition, a geostationary spacecraft, LANL‐97A, was located near the onset meridian. On August 29, 1997, Polar was magnetically conjugate to the Canadian magnetometer chain (Canadian Auroral Network for the OPEN Program Unified Study; CANOPUS) ∼ 5 hours east of the onset meridian. In both cases, substorm activity was manifested as strong magnetic (20 nT) and electric (40 mV m−1) field variations with bursts of parallel Poynting flux (∼ 1 erg cm−2 s−1), predominantly directed toward the ionosphere. In the first event Polar was located in the plasma sheet near the plasma sheet boundary, and the field variations were initiated at the ground onset. In the second event, Polar crossed the plasma sheet boundary to the tail lobes a few minutes prior to a local plasma sheet expansion. As Polar was engulfed by the plasma sheet, the field variations occurred in the previously quiet plasma sheet boundary. This coincided with the auroral bulge reaching the CANOPUS stations. We compare these two events and argue that the field variations were most probably signatures of the reconnection of open field lines and the subsequent enhanced earthward flows. Furthermore, weak flow bursts were observed at Polar in both events ∼ 9 min before the onset. In the first event, a gradual development toward a negative bay and a burst of Pi2 pulsations were associated with the flow bursts. We anticipate that these signatures, often described in terms of pseudobreakups, were a precursor of the substorm onset, the initiation of the reconnection of closed field lines.

Observation of the magnetospheric “sash” and its implications relative to solar‐wind/magnetospheric coupling: A multisatellite event analysis

Using a unique data set from the Wind, Polar, Interball 1, Magion 4, and Defense Meteorological Satellite Program (DMSP) F11 satellites, comparisons with the Integrated Space Weather Model (ISM) have provided validation of the global structure predicted by the ISM model, which in turn has allowed us to use the model to interpret the data to further understand boundary layers and magnetospheric processes. The comparisons have shown that the magnetospheric “sash” [White et al., 1998], a region of low magnetic field discovered by the MHD modeling which extends along the high‐latitude flank of the magnetopause, is related to the turbulent boundary layer on the high‐latitude magnetopause, recently mapped by Interball 1. The sash in the data and in the model has rotational discontinuity properties, expected for a reconnection site. At some point near or behind the terminator, the sash becomes a site for reconnection of open field lines, which were previously opened by merging on the dayside. This indicates that significant reconnection in the magnetotail occurs on the flanks. Polar mapped to the high‐density extension of the sash into the tilted plasma sheet. The source of the magnetosheath plasma observed by Polar on closed field lines behind the terminator was plasma entry through the low field connection of the sash to the central plasma sheet. The Polar magnetic field line footprints in each hemisphere are moving in different directions. Above and below the tilted plasma sheet the flows in the model are consistent with the corresponding flows in the ionosphere. The turbulence in the plasma sheet allows the convection patterns from each hemisphere to adjust. The boundary layer in the equatorial plane on the flank for this interplanetary magnetic field BY condition, which is below the tilted central plasma sheet, is several RE thick and is on tailward flowing open field lines. This thick boundary layer shields the magnetopause from viscous forces and must be driven by magnetic tension. Above the plasma sheet the boundary layer is dominated by the sash, and the model indicates that the open region inside the sash is considerably thinner.

GEOTAIL observations on the reconnection process in the distant tail in geomagnetically active times

A statistical study is made on the reconnection process in the distant tail by using the GEOTAIL observations at x≈ −150 Re and −95 Re in geomagnetically active times with Kp≥3. Occurrence frequencies of various combinations of the field polarity and the convection direction suggest that at least 75% of the reconnection of open field lines occurs inside 150 Re and at least 39% occurs inside 95 Re. At 150 Re the convection of closed field lines constituting the viscous‐like cell is at most 25% of the convection generated by the reconnection of open field lines. The reconnection rate of open field lines varies across the tail and is a few times higher near the tail axis than at the flanks.

Magnetic reconnection ahead of a coronal mass ejection

On 29 November 1990 the Ulysses spacecraft passed through a series of interplanetary structures which suggest that reconnection had occurred on open field lines ahead of a coronal mass ejection (CME), changing the magnetic topology of the upstream region. We observe in sequence 1) a heat flux dropout, 2) a region of counterstreaming halo electrons which does not appear to be a CME, and 3) a region of counterstreaming halo electrons which is a CME. We suggest an interpretation in which upstream of the CME Ulysses passed first through a region magnetically disconnected from the Sun and then through a region magnetically connected back to the solar corona at both ends, both of which were created by reconnection of open field lines ahead of the CME. Such reconnection provides a method for producing a heat flux dropout / counterstreaming suprathermal electron pair of signatures in interplanetary space that has not been previously described.