1. In general, the minute given is that in/during which the crossing is observed. For 'extended' crossings, the minute given generally corresponds to the beginning of the magnetopause interval. For multiple crossings in the early IMP data submitted by Fairfield, sometimes an 'average position' was selected by visually determining the point that equalized the magnetosphere time outside the point with the magnetosheath time inside the point; the minute given corresponds to the 'average position'.

2. The field intensity is [Bx**2+By**2+Bz**2]**0.5 (wds 13-15 --> wd 12)

3. The Xgse component of the solar wind velocity vector is negative. To avoid negative values for this component, we have chosen to give components for the vector anti-aligned with the velocity vector.

Further explanations of some equations below are given here

4. Flow pressure = (2.0/10**6) * N * V**2 (wds 23, 18 --> wd 24) (note that this 2.0 includes a 5% alpha contribution)

5. Electric field = V(km/s) * Bz (nT; GSM) * 10**-3

6. Plasma beta = [(T*4.16/10**5) + 5.34] * N / B**2 (wds 22, 23, 12 --> wd 26)

7. The Alfven speed = 20. * B / N**0.5 (wds 12, 23 --> wd 27)

8. The sound speed = 0.12 * [T + 1.28*10**5]**0.5 (wd 22 --> wd 28)

9. Magnetosonic speed = [(sound speed)**2 + (Alfv speed)**2]**0.5 (wds 28, 27 --> wd 29)

10. IMF cone angle = 57.3 * arc cos [|Bx|/Bt] (wds 13, 12 --> wd 33)

11. IMF clock angle = 57.3 * arc tan [|Bygsm|/Bzgsm] (wds 16, 17 --> wd 34)

This note addresses the derived parameters found in the IMP bowshock records.

Consider first the multi-species nature of the solar wind plasma: protons, alphas, electrons. We use subscripts p, a and e for these. N is density, T temperature, V flow speed, m mass.

Rewrite:Where

Now, some issues.

1. f is typically in the range 0.04-0.05, although there are significant differences for different flow types.

2. Ta/Tp is typically in the range 4-6.

3. What about Te? Feldman et al, JGR, 80, 4181, 1975 says that Te is almost always in the range 1-2*10**5 deg K. Te rises and falls with Tp, but with a much smaller range of variability. Kawano et al (JGR, 105, 7583, 2000) cites Newbury et al (JGR, 103, 9553, 1998) recommending Te = 1.4E5 based on 1978-82 ISEE 3 data. So we'll use Te = 1.4E5 deg K for our analysis.

4. What about (Va/Vp)**2? We should probably let this be unity always.

If we let f=0.05, Ta=4*Tp, Va=Vp, and Te=1.4*10**5, we'd have Characteristic speeds: With the above assumptions for f, Ta, Va, and Te, and with gamma = 5/3, we'd get With the above assumptions, we'd get Since C=speed of light in this expression, So Vms**2 = VA**2 + Vs**2

Mach numbers: Plasma beta: With above assumptions, we'd get
Flow pressure
With above assumptions, we'd get Converting units, this becomes Shock strength

IMF Clock and Cone Angles

We'll provide the cone angle as the arc-cotan of the abs value of Bx over Btotal. This assumes the cone angle's value is just in measuring the extent of non-radialness of the IMF. We'll provide the clock angle as the arc cotan of Bz over Bt, or clock angle = 0 for IMF due north and 180 for IMF due south.

Joe King, 2002