perpendicular and parallel component

Hello all,

I have a mms data set from MMS1_FPI_BRST_L2_DES_MOMS. It is given in cartesian coordinate system (x, y, z).

It is basically electron velocity (Vx,Vy,Vz).

I want to convert it into v_perp1, v_perp2, v_parallel components.

Will you please tell me how to convert it ?

Thank you.

Answer 1

[Bjorn Gustavsson]

You have to look at the documentation of the mission and the data access etc: MMS_Data_Access_f3. We cannot tell you how to handle the data from a satellite mission (that's brilliantly interesting!) that we're not involved with. The only thing I can say is that you simply have to extract the velocity-components paralell (In swedish we have the good sense to spell it parallell, as it for visual reasons should be.) and perpendicular to the (back-ground) magnetic field:

B = read_B_field(); % you make this happen. B should be [1 x 3] for the following to work
v = read_v_cartesian(); % you make this happen. Same for v
v_par = dot(v,B)/norm(B);
v_perp = v - v_par*B/norm(B);

If you have B and v for a whole time-series the most efficient calculation might be to write out the explicit formulas for dot and norm in the above equations.

HTH

[neetasha arya]

Thanks @Bjorn Gustavsson for the suggestion.

v_perp = v - v_par*B/norm(B); This will give n x 3 matrix, which is nothing but vperp matrix.

I require vperp1 and vperp2 ie. two perpendicular components. How that can be calculated?

[Bjorn Gustavsson]

How am I to know how you have your two B-perp unit vectors oriented? Do you have some E-field perp to B that you use as reference? Some of the numerous other coordinate systems? Perp to B parallel to solar wind direction, perp to both?

Once you've settled for that you simply have to calculate the dot-product between those e1_perp and e2_perp unit-vectors and the v_perp vectors.

[neetasha arya]

Thank you @Bjorn Gustavsson

[Bjorn Gustavsson]

You're welcome @neetasha arya.