THEMIS Particle Moments (Ground)

Density, velocity, and temperature for ESA electrons.

Moments of the particle distribution may be calculated on the ground from raw ESA and/or SST particle data. This allows for manual calibration and specification of input parameters. Moments can be generated with command line routines or through the SPEDAS GUI. Some products also require magnetic field data to be present.

For command line usage see:

/projects/THEMIS/examples/basic/thm_crib_part_products.pro

For spacecraft processed moments see on-board moments.

Overview

Moments are produced with thm_part_products from raw particle data. All data products are calculated simultaneously for a particular data type. Particle data must be loaded explicitly beforehand.

SPEDAS> thm_part_load, probe='a', datatype='peif', trange=[t0,t1]

SPEDAS> thm_part_products, probe='a', datatype='peif', trange=[t0,t1], outputs = 'moments'

Support data will be used automatically if it is present. By default the software will use "th?_fgs" as the magnetic field and "th?_pxxm_pot" as the spacecraft potential ("?" denoting probe designation). If no support data is found it will be ignored; any derived quantities will not be calculated. Keywords may be used to specify support data:

SPEDAS> thm_part_products, probe='a', datatype='peif', trange=[t0,t1], outputs = 'moments', mag_name='tha_fgl', sc_pot_name='tha_peef_sc_pot'

Data Products

Products marked with a * require magnetic field data to be loaded.

All "vector" data types are 3-vectors: <x,y,z>. Symmetric tensors are stored in six dimensions: <xx, yy, zz, xy, xz, yz>.

Variable Name	Description	Units	Data type
density	Density	1/cm3	scalar
sc_current	Total number flux	1/(s·cm2)	scalar
flux	Number flux	1/(s·cm2)	vector
eflux	Energy flux	eV/(s·cm2)	vector
velocity	Velocity	km/s	vector
t3	Diagonalized temperature	eV	vector
magt3	Magnetic field aligned temperature*	eV	vector
avgtemp	Average temperature	eV	scalar
vthermal	Thermal velocity	km/s	vector
mftens	Momentum flux tensor	eV/cm3	symmetric tensor
ptens	Pressure tensor	eV/cm3	symmetric tensor
symm	Direction of pressure tensor symmetry	n/a	vector
symm_phi	Phi (longitude) direction of symmetry vector	°	scalar
symm_theta	Theta (latitude) direction of symmetry vector	°	scalar
symm_ang	Angle between symmetry vector and magnetic field*	°	scalar

Contamination

Spacecraft potential

Spacecraft potential plotted with corrected and uncorrected ESA density data

Accumulated charge on the spacecraft will affect low energy ESA data. A tplot variable containing spacecraft potential can be used to correct for this when generating ground moments. If no variable is specified then "th?_pxxm_pot" will be used automatically, if present. Spacecraft potential can be loaded with the on-board moments.

SPEDAS> thm_load_mom, probe='a', trange=[t0,t1]

SPEDAS> thm_part_products, probe='a', datatype='peef', trange=[t0,t1], output='moments', sc_pot_name='tha_pxxm_pot'

ESA background subtraction

Background subtraction for ESA data is enabled by default when producing spectra. For background removal options see ESA Background Removal. For example usage see:

/projects/THEMIS/examples/advanced/thm_crib_esa_bgnd_remove.pro

SST contamination

In most cases, contaminated SST bins should be masked and interpolated over automatically. If the default set of bins is inadequate then a list may be specified instead. For more information see SST Contamination Removal.

SPEDAS> thm_part_products, probe='a', datatype='psif', trange=[t0,t1], sst_sun_bins=[0,8,16,24,32,33,34,40,47,48,49,50,55,56,57]

Uncertainty estimates

The statistical uncertainty based on the original measurement in counts can be propagated through the moment calculation and output as tplot variables. The error is taken to be the standard deviation of the measurement assuming they are Poisson distributed.

SPEDAS> thm_part_products, probe='a', datatype='psif', trange=[t0,t1], /get_error

Resources

ESA instrument page

SST instrument page