SM13D-01 INVITED
THEMIS overview, first results and near future
Since its launch, on February 17 2007, the five-satellite (or -probe) THEMIS mission has been operating nominally in a 14.6Re apogee (low-perigee), near-equatorial orbit. Most instruments have been on since March 15. Electric field (EFI) instruments on three probes were turned on and operating nominally since mid-June. EFI instruments on the other two probes will be deployed in early winter. THEMIS nominal science operations commenced on July 1. In its early orbits through the dusk magnetotail, the THEMIS probes captured several substorms and a small storm at roughly radial alignments along the 20-23MLT meridian. The THEMIS first-light (a single orbit in nominal science mode during early operations) on March-23, was nature's welcome: Two substorm sequences were captured in fast survey mode: particle injections and dipolarization signatures were seen propagating from one probe to another. An Earthward flow pulse ahead of a predominantly duskward flow accompanied a strong field-aligned current pair signature at the THEMIS altitude. POLAR VIS,UVI imaged the global evolution of the aurora. The THEMIS GBO array captured the salient features of the largest intensification of the first substorm, concurrent with the most intense particle injection on THEMIS probes. FAST, whose orbit passed through the vicinity of the THEMIS footprints 3 min after the major intensification, made detailed observations of the field aligned currents, arc and outflowing ions. In July and August, the THEMIS probes repeatedly encountered the magnetopause and bow shock, observing FTEs, LLBL and boundary layers with the three inner, deployed-EFI-bearing probes (C,D,E) at 100-500km separations, and the two outer probes (B, A) at 5,000-10,000 km separations. Dissecting FTEs, providing evidence for simultaneous reconnection at both cusps for northward IMF orientation, and directly relating magnetopause and boundary layer motion to corresponding ULF waves in the magnetosphere, are some of the exciting findings from this dayside interlude. In September 2007 the probes commenced the series maneuvers that will place them into their final orbits with approximately 30Re, 20Re, 12Re (2) and 10Re apogees and orbital periods of 4, 2, and 1 days. In these orbits, they will be aligned along the Sun-Earth line in Earth's magnetotail in January - March 2008. Results obtained demonstrate the high data quality and the potential for scientific discovery, particularly when combined with existing ancillary data or campaigns. http://themis.ssl.berkeley.edu
SM13D-02
Local Dynamic Response of the Magnetosphere to Solar Wind Variations: First THEMIS Case Studies
During the coast phase the five spacecraft of the THEMIS mission regularly traverse the dusk-noon magnetopause boundary region. Like pearls on a string they are aligned with separations between a few hundred and a few thousand kilometres. This enables us the study in detail the local response of the magnetosphere to solar wind induced changes as observations from both sides of the magnetopause boundary region are available. This allows to infer the response function between dynamical processes in the magnetosheath, the boundary layer, and the outer magnetosphere as well as the ground. Several case studies will be presented demonstrating the large variety of local dynamic responses.
SM13D-03
Spatial Structure of Plasmaspheric Plumes Observed by THEMIS
During the first 6 months of the THEMIS mission, the five spacecraft were configured in a string-of-pearls that sampled the dayside magnetosphere revealing the dominance of cold plasma in this region. Although cold ions can only be detected when MP motion increases their energy in the spacecraft frame allowing penetration of the spacecraft potential, comparisons of electron density with ion density provide identification of the hidden cold ions. Spacecraft potential is also used to infer hidden cold plasma, supporting the plasma measurements. As expected, the largest cold plasma densities are observed in the post-noon sector where plasmaspheric plumes are convected to the magnetopause. These multi-spacecraft measurements offer a unique picture of the spatial and temporal structure of these plumes. Order of magnitude density variations over 100 km scales are observed indicating these plumes can be highly structured. Plume densities >10/cc near the magnetopause were observed on a dozen orbits, with one observation revealing 60/cc. Cold plasma is generally found to dominate the number density in the post-noon sector by a factor of 10-100 over the hot component. These measurements indicate that cold plasma must play a major role in magnetospheric dynamics, affecting wave dispersion relations, field line resonances, and reconnection. This paper will focus on structure revealed by the multi- satellite measurements.
SM13D-04
Dayside Magnetospheric Electric Field Observations from the THEMIS Electric Field Instrument
The five-satellite NASA THEMIS Mission was launched on 17 February 2007 into a common set of low-inclination, high apogee (~15-Re) orbits, pending placement into their final mission orbits starting in September 2007. Each satellite carries a full complement of electromagnetic and particle instruments, including a three-axis Electric Field Instrument (EFI) covering the range from DC to 8 kHz with both waveform and spectral data, with limited spectral coverage from 100-400 kHz. The EFI was fully-deployed on three of the five THEMIS spacecraft in May-June 2007, and have observed various electromagnetic phenomena at spacecraft separations of a few hundred to 1000 km separations. Once deployed on all five probes, the EFI will form an essential component of the substorm and auroral-related observations provided by THEMIS. The initial results from EFI operations in the dayside magnetosphere are quite promissing, both in terms of quasi-DC observations of Hall electric fields at the magnetopause, as well as wave observations of various whistler-mode phenomena throughout the magnetosphere, magnetosheath, and solar wind. Significant electrostatic wake effects due to the presence of cold plasma throughout the dayside magnetosphere suggest that such effects will be very important for future missions, such as MMS and RBSP. Examples of each sort of phenomena will be presented and interpreted.
SM13D-05
Multi-scale and Multi-spacecraft Plasma Measurements in the Vicinity of an Quasi-periodic Magnetospheric Structures
During the first 6 months of its mission, the 5 THEMIS spacecraft have been operating in a "string of pearls" orbit that provides multi-spacecraft observations of magnetospheric processes on distance scales of .1 - 2 RE. The large gyro radii of the energetic particles measured by the Solid State Telescope (SST) experiment provide an additional means of determining spatial gradients from a single spacecraft. In this study we examine a ~2 hour interval on August 28, 2007 with large (+/-100 km/sec) periodic (~5 minute period) velocity fluctuations observed while the spacecraft where just inside the pre-noon magnetopause.
SM13D-06
Relation between electromagnetic waves and FTE's
On May 20, 2007, the 5 THEMIS spacecraft passed by a FTE, in the post-noon sector. Spacecraft configuration was particularly interesting since the satellites bracketed the FTE structure, with Thb and Thc on the magnetospheric side, Tha and The on the magnetosheath side, while Thd was close to the magnetopause current layer. The geometry and the general characteristics of this event will be discussed elsewhere by Sibeck et al. Here we look for possible wave-particle interactions. The spacecraft in the magnetosphere observe (i) a bipolar magnetic field signature normal to the nominal magnetopause, (ii) a crater-like variation in the magnetic field strength, (iii) enhanced densities, (iv) enhanced ion flow velocities, (v) intense fluxes of medium energy electrons, and (vi) enhanced magnetic components of the ULF waves. Densities and ion velocities in the core region are comparable to those in the magnetosheath, but electrons are apparently heated/accelerated well above magnetosheath values. Near the magnetopause, and in the magnetosheath, electron heating/acceleration is not limited to the vicinity of the FTE magnetic field signature, but rather extends over a broader region, where it still coincides with ULF waves. Densities and ion flow velocities vary little as the FTE passes the spacecraft in the magnetosheath. However, in conjunction with large amplitude ULF waves, the magnetosheath electrons are heated/accelerated significantly These preliminary observations suggest that electromagnetic waves interact with electrons, inside the FTE, on the magnetospheric side, and in a broader region, in the current layer and magnetosheath side. We will analyse wave characteristics, as well as the shape of the electron distribution function, and investigate possible signatures of wave particle interactions as a potential heating mechanism.
SM13D-07
THEMIS Education and Public Outreach: Multi-point investigations of Earth's magnetic field changes from ground-based magnetometers by teachers and students
The THEMIS ground-based magnetometer array together with an extensive THEMIS all-sky camera array in Canada and Alaska, will be used to determine the onset of substorms when the five THEMIS satellites are conjugate to these stations in the magnetotail. The magnetometer array is unique in that 12 of the 20 magnetometers are located at schools (primarily high schools) in the Northern United States as part of the THEMIS Education and Public Outreach program. This is the first NASA mission to place research-grade scientific instruments at schools and to have students and their teachers use the data from these instruments. Because the twelve magnetometers that are housed in schools are research-grade magnetometers, teachers and students are learning about substorms using the same data which scientists use. The magnetometer data and being part of the THEMIS team have inspired students and teachers around the country to learn about multipoint measurements, magnetism, auroral physics, and space physics in general. We will present an overview of this program including the teacher guides developed for this program, discuss the positive impact of the program on the participating teachers and students, and describe how we will broaden the participation in the program in the future years. We will also discuss the research that the teachers and students have undertaken using multipoint magnetometer measurements. THEMIS has several other components to its E/PO program, but we will focus on this magnetometer school network. Scientists interested in contributing to THEMIS E/PO should contact us. Visit http://ds9.ssl.berkeley.edu/themis for more information on the THEMIS E/PO program. http://ds9.ssl.berkeley.edu/themis