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Homework Help: Subsolar magnetopause distance

  1. Feb 10, 2016 #1
    1. The problem statement, all variables and given/known data

    I need to calculate the subsolar magnetopause distance (r_mp) when the distance to Earth is 0.4 AU. I have all the formulas and the data, but I still don’t get a reasonable value (it’s too small!)
    Here is what I know:

    Solar wind density: 5 cm^-3 (rho_sw)
    Solar wind speed=400 km/s (u_sw)
    Magnetic field at Earth’s surface= 5*10^-6 T (B_E)
    u_0= magnetic constant permeability= 4*pi*10-7 T m/A

    2. Relevant equations

    3. The attempt at a solution
    First I start to calculate the thermal pressure:

    p= rho_sw*(u_sw)^2

    next, the magnetic field when the distance is 0.4 AU, where r= 1AU * 0.4:


    And finally I use the following equation to get the distance I am searching for in term of Earth radius R_E:

    (r_mp/R_E)=[(2*B(r)^2)/( u_0*p)]^1/6

    But as I mentioned, the value is not “the right one”. Can I get help from someone?
  2. jcsd
  3. Feb 10, 2016 #2
    I solved it, so no need to help me :)
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