THEMIS Particle Moments (Ground)

Moments of the particle distribution may be calculated manually. This allows for manual calibration and specification of input parameters. Moments may be produced after selecting a spacecraft, particle data type, and time range. 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

Particle moments are produced by thm_part_products from raw particle data. All data products are calculated simultaneously for a particular data type. To generate the data specify "moments" in the outputs keyword:

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 quietly be ignored and any derived quantities will note 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. Symmetric tensors are stored in six dimensions: xx, yy, zz, xy, xz, yz.

Variable Name	Description	Units	Data type
density	Density	1/cm³	scalar
current	Current		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

Increased spacecraft potential may affect the lower energy bins for ESA data. A tplot variable containing spacecraft potential can be specified when producing spectra (and moments). If no variable is specified then "th?_pxxm_pot" will be used, if present. Spacecraft potential must be loaded separately:

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

Resources

ESA instrument page

SST instrument page