2011 THEMIS NUGGETS

SUMMARIES OF THEMIS RESEARCH

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Mitsuo Oka, 13 September 2011. Magnetic reconnection X-line retreat associated with dipolarization of the Earth's magnetosphere.

The magnetic reconnection X-line has previously been detected and studied when it retreats tailward and passes by the spacecraft. But why does it move tailward in the first place? This article presents a multi-probe observation of the entire magnetotail to understand a possible relationship between the X-line retreat motion and the dipolarization of the Earth's magnetosphere. Read more.


Michael Hartinger, 4 May 2011. Energy transfer associated with a field line resonance.

The Earth's magnetosphere is an inhomogeneous medium where the fast and shear Alfvèn magnetohydrodynamic (MHD) wave modes can couple. A case of resonant mode coupling known as field line resonance (FLR) is particularly important for large scale energy transfer. We present observations from multiple THEMIS probes and IMAGE ground magnetometers, tracing the energy transfer from magnetopause boundary undulations to an FLR and finally to the ionosphere. Read more.


Yao Yao, 5 April 2011. Electromagnetic waves on ion gyro-radii scales across the magnetopause.

Kinetic Alfven waves (KAWs) are considered as an important entry mechanism of plasma transport across the magnetopause. In this paper, we present the first study of the global distribution and properties of kinetic scale electromagnetic waves on the Earth's magnetopause by THMIS observations. Read more.


Wen Li, 16 March 2011. Modulation of Whistler-mode Chorus waves: 1. Role of Compressional Pc4-5 Pulsations.

We investigate the modulation of whistler-mode chorus waves in the magnetosphere by compressional Pc4-5 pulsations with an anti-correlation between the total electron density and the background magnetic field intensity. We find that such compressional pulsations are frequently associated with modulations of chorus wave intensity. Statistical result shows that the modulation of whistler-mode wave intensity caused by compressional Pc4-5 pulsations predominantly occur at large L-shells of 8-12 in the dawn sector. Read more.


Wen Li, 16 March 2011. Modulation of Whistler-mode Chorus waves: 2. Role of Density Variations.

We present the role of density variations in the modulation of the whistler-mode chorus wave amplitude, which forms a complementary study to the modulation of chorus by compressional Pc4-5 pulsations, discussed in a companion article. Our results show that both density depletions and enhancements are frequently correlated remarkably well with modulated chorus intensity, and typically occur on a timescale of a few seconds to tens of seconds. Read more.


Tetsuo Motoba, 9 March 2011. In situ evidence for interplanetary magnetic field induced tail twisting associated with relative displacement of conjugate auroral features

We report here for the first time in situ observations of a twisted magnetic field configuration in the near-Earth tail region, associated with relative displacement of conjugate auroral features during a weak substorm. Our results indicate that the IMF-induced magnetotail variation (twisting) coincides well with the temporal variation of relative MLT displacement of the nightside conjugate auroral locations in both hemispheres, and that the time scale (reconfiguration time) for both variations to respond to IMF changes is 52±1 min. Read more.


Rumi Nakamura, 25 February 2011. Observations and modeling of forward and reflected chorus waves captured by THEMIS.

Changes in the current sheet configuration are obtained during a double-onset onset substorm, which is a substorm that consists of two distinct onsets of auroral expansion and magnetotail disturbances, based on multi-point observations by THEMIS and GOES spacecraft and ground-based observations. We show how the internal redistribution of magnetic flux after the first onset results in production of a thin current sheet in the midtail that leads to favorable conditions for lobe reconnection during the second onset. Read more.


Oleksiy Agapitov, 23 February 2011. Observations and modeling of forward and reflected chorus waves captured by THEMIS.

Discrete ELF/VLF chorus emissions are the most intense electromagnetic plasma waves observed in the radiation belts of the Earth's magnetosphere. Chorus emissions, whistler-mode wave packets propagating roughly along magnetic field lines from a well-localized source in the vicinity of the magnetic equator to polar regions, can be reflected at low altitudes. After reflection, wave packets can return to the equatorial plane region. Understanding of whistler wave propagation and reflection is critical to correctly describe wave-particle interaction in the radiation belts. Read more.


Xin Tao, 17 February 2011. Evolution of electron pitch angle distributions following injection from the plasma sheet.

We use a combination of numerical modeling and observational data from THEMIS and CRRES satellite to demonstrate the dominant role of chorus waves in shaping energetic electron pitch angle distributions after their injection to the inner magnetosphere during disturbed times. Read more.


Drew L. Turner, 8 February 2011. Multi-spacecraft observations of a foreshock-induced magnetopause disturbance exhibiting distinct plasma flows and an intense density compression.

We present multipoint THEMIS observations of a foreshock cavity event that resulted in a significant magnetopause disturbance. Four of the THEMIS probes observe this event from different locations in the solar wind just upstream of the bow shock, in the magnetosheath, and within the magnetosphere just inside of the magnetopause. This event provides unprecedented, multi-point views of a foreshock cavity, which reveal an unusually high compression of plasma density within the sheath (>7x that of the near-Earth solar wind), very rapid magnetopause motion (~450 km/s), a complex boundary layer along the magnetopause, coherent transport with a discontinuity in the IMF, and distinct flows in the magnetospheric plasma being displaced around it. Read more.


Suping Duan, 11 January 2011. Multiple magnetic dipolarizations observed by THEMIS during a substorm.

Observations from multiple probes of THEMIS indicate the magnetic dipolarization having complex features during substorms. There are multiple magnetic dipolarizations occurring during a substorm in the near-Earth plasma sheet. Dipolarization at substorm onset is a local and small scale phenomenon, while dipolarizations during the substorm expansion phase have larger spatial scale and are correlative with the azimuthal expansion of plasma sheet or high speed earthward ion bulk flow. Read more.


Xu-Zhi Zhou, 5 January 2011. On the nature of precursor flows upstream of advancing dipolarization fronts.

One of the most interesting observational signatures associated with the earthward propagating dipolarization fronts is the appearance of earthward plasma flows well before front arrival. Both THEMIS observations and numerical simulations suggest that the precursor flows are caused by the gradual emergence of a new ion population composed of ions that have been accelerated and reflected by the front. The reflected ions would be confined to a region comparable to their thermal gyroradius over the background Bz upstream of the advancing front. Read more.


Jean-André Sauvaud, 4 January 2011. Far tail (255 RE) fast response to very weak magnetic activity.

Substorms are known to be initiated in the tail of the magnetosphere, close to the Earth, at around 10 Earth's radii in the nightside and propagate tailward. In February 2007, the STEREO-B spacecraft passed through the distant tail of the magnetosphere which allowed searching for substorm effects at 1,500,000 km from the Earth. Furthermore, during this period, ground stations were operating in the frame of the THEMIS multi-satellite missions and provided a precise timing of the onset of substorms as they are linked to the break-up of auroral forms in the Earth's atmosphere/ionosphere. Read more.


Binbin Ni, 3 January 2011. Analysis of Radiation Belt Energetic Electron Phase Space Density Using THEMIS SST Measurements: Cross-satellite Calibration and a Case Study

With a broad energy coverage from the radiation belt electron source population to hazardous relativistic electrons as well as available pitch angle information for each energy channel, the SST data from the five-probe THEMIS mission has enormous potential for studying radiation belt electron dynamics. While various calibration efforts have continued to improve the absolute accuracy of the SST electron fluxes, in this study we follow the Liouville's theorem to perform empirical cross-satellite calibration of THEMIS SST data based upon electron phase space density (PSD) conjunctions with high-quality LANL SOPA measurements. Read more.


Please send comments/suggestions to
Emmanuel Masongsong / emasongsong@igpp.ucla.edu