pyrfu.pyrf.calc_sqrtq module#

pyrfu.pyrf.calc_sqrtq.calc_sqrtq(p_xyz: DataArray) → DataArray[source]#

Computes agyrotropy coefficient as in [1]

\[Q = \frac{P_{12}^2 + P_{13}^2 + P_{23}^2} {P_\perp^2 + 2 P_\perp P_\parallel}\]
Parameters:

p_xyz (DataArray) – Time series of the pressure tensor

Returns:

Time series of the agyrotropy coefficient of the specie

Return type:

DataArray

Raises:

  • TypeError – If input is not a xarray.DataArray.

  • ValueError – If input is not a time series of a tensor (n_time, 3, 3).

References

[1]

Swisdak, M. (2016), Quantifying gyrotropy in magnetic reconnection, Geophys. Res.Lett., 43, 43–49, doi: https://doi.org/10.1002/2015GL066980.

Examples

>>> from pyrfu import mms, pyrf

Time interval

>>> tint = ["2019-09-14T07:54:00.000","2019-09-14T08:11:00.000"]

Spacecraft index

>>> ic = 1

Load magnetic field and electron pressure tensor

>>> b_xyz = mms.get_data("b_gse_fgm_srvy_l2", tint, 1)
>>> p_xyz_e = mms.get_data("pe_gse_fpi_fast_l2", tint, 1)

Rotate electron pressure tensor to field aligned coordinates

>>> p_fac_e_pp = mms.rotate_tensor(p_xyz_e, "fac", b_xyz, "pp")

Compute agyrotropy coefficient

>>> sqrt_q_e = pyrf.calc_sqrtq(p_fac_e_pp)