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THEMIS-A: On Board moments: ESA and SST Electron/Ion moments density, flux, velocity, pressure and temperature.

ResourceID
spase://SMWG/Instrument/THEMIS/A/MOM

Description

THEMIS-A: The On Board Moments (MOM) system, part of the Instrument Data Processing Unit (IDPU), is used for on board calculations of electron and ion moments from a combination of ESA and SST data. On board data outputs include number density, number and energy flux, and a six component symetric momentum flux tensor. Total pressure, velocity, plasma temperature, and momentum flux are calculated on the ground via a combination of the other partial moments. Velocity is calculated in DSL, GSE, GSM, and MFA coordinates (coordinate descriptions are listed below in Table 1). Pressure and temperature are also calculated in MFA coordinates. All quantities are calculated for both ions and electrons. Moments data is taken at spin resolution in all ESA survey modes except burst. The spacecraft potential, as measure by the EFI, is used to correct for spacecraft charging, thereby eliminating contamination from photo-electrons. Other corrections are made for instrument specific efficiency variations.

Table 1: Coordinate Descriptions.

Despun Sun - L-vector (DSL): Z-axis points towards the spin axis, the Y-axis is obtained from the cross product of Z and the Spacecraft-Sun direction as viewed from the probe. The X-axis sits in the Z-axis-Sun plane and completes a right handed system.
Geocentric Solar Ecliptic (GSE): Z-axis is normal to the solar ecliptic, the X-axis points from earth towards the Sun, and Y complets a right handed system.
Geocentric solar Magnetosphereic (GSM): X-axis points from Earth to the Sun, the Y-axis is orthogonal to the Earth's magnetic dipole and points towards the dusk side, and the X-Z plane contains the dipole axis.
Magnetic Field Aligned (MFA): Z-axis points along magnetic field lines, the Y-axis is the orthonormal cross product of the Z-axis and a vector pointing towards the Sun, and the X-axis completes the right handed system.

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Details

Version:2.0.0

Instrument

ResourceID
spase://SMWG/Instrument/THEMIS/A/MOM
ResourceHeader
ResourceName
THEMIS-A: On Board moments: ESA and SST Electron/Ion moments density, flux, velocity, pressure and temperature.
AlternateName
THEMIS-A MOM
ReleaseDate
2019-05-05 12:34:56Z
Description

THEMIS-A: The On Board Moments (MOM) system, part of the Instrument Data Processing Unit (IDPU), is used for on board calculations of electron and ion moments from a combination of ESA and SST data. On board data outputs include number density, number and energy flux, and a six component symetric momentum flux tensor. Total pressure, velocity, plasma temperature, and momentum flux are calculated on the ground via a combination of the other partial moments. Velocity is calculated in DSL, GSE, GSM, and MFA coordinates (coordinate descriptions are listed below in Table 1). Pressure and temperature are also calculated in MFA coordinates. All quantities are calculated for both ions and electrons. Moments data is taken at spin resolution in all ESA survey modes except burst. The spacecraft potential, as measure by the EFI, is used to correct for spacecraft charging, thereby eliminating contamination from photo-electrons. Other corrections are made for instrument specific efficiency variations.

Table 1: Coordinate Descriptions.

Despun Sun - L-vector (DSL): Z-axis points towards the spin axis, the Y-axis is obtained from the cross product of Z and the Spacecraft-Sun direction as viewed from the probe. The X-axis sits in the Z-axis-Sun plane and completes a right handed system.
Geocentric Solar Ecliptic (GSE): Z-axis is normal to the solar ecliptic, the X-axis points from earth towards the Sun, and Y complets a right handed system.
Geocentric solar Magnetosphereic (GSM): X-axis points from Earth to the Sun, the Y-axis is orthogonal to the Earth's magnetic dipole and points towards the dusk side, and the X-Z plane contains the dipole axis.
Magnetic Field Aligned (MFA): Z-axis points along magnetic field lines, the Y-axis is the orthonormal cross product of the Z-axis and a vector pointing towards the Sun, and the X-axis completes the right handed system.

Acknowledgement
NASA contract NAS5-02099, V. Angelopoulos for use of data from the THEMIS Mission, C.W. Carlson, and J. McFadden.
Contacts
RolePersonStartDateStopDateNote
1.PrincipalInvestigatorspase://SMWG/Person/Vassilis.Angelopoulos
2.CoInvestigatorspase://SMWG/Person/Charles.W.Carlson
3.CoInvestigatorspase://SMWG/Person/James.P.McFadden
InformationURL
Name
THEMIS-A Spacecraft
URL
Description

Spacecraft description from NSSDC database

InformationURL
Name
THEMIS-A Electrostatic Analyzer
URL
Description

Instrument (ESA) description from NSSDC database.

InformationURL
Name
THEMIS-A Solid-State Telescope
URL
Description

Instrument (SST) description from NSSDC database.

InstrumentType
Unspecified
InstrumentType
ElectrostaticAnalyser
InstrumentType
ParticleDetector
InvestigationName
THEMIS On Board Moments
ObservatoryID
Caveats
Due to bit errors and data misdirection, ESA data (including moments) before April 27, 2007 should be considered dubious. Other data loss and formatting errors in the moments calculations and ETC were not corrected until Aug. 6, 2007. Potential data from the EFI was not properly included in calculations between Nov. 18-22, 2007. EFI booms on THEMIS-A were not deployed until Jan. 14, 2008, 17:00:00 UT. Moments data before this date is suspect to error due to photoelectrons and spacecraft charging.