FUNCTION: cal_bsn2(sx,sy,sz,bx,by,bz,vmag,bow=bow) INPUT: sx,sy,sz: x, y, and z coodinates of spacecraft in GSE with units of Re bx,by,bz: magnetic field direction OPTIONS: bow: structure containing {L,ecc,x0} L: standoff parameter with units of Re ecc: eccentricity of shock x0: focus location in Re hyperbolic bow shock, see JGR 1981, p.11401, Slavin Fig.7 r = L/(1+ecc*cos(theta)) 1 = (x-x0-c)^2/a^2 - (y^2+z^2)/b^2 default L = b^2/a = 23.5 ecc = c/a = 1.15 xoffset= 3 c = (a^2 + b^2)^.5 = L*e/(e^2-1) = 83.8 a = L/(e^2-1) = 72.87 b = L/(e^2-1)^.5 = 41.38 PURPOSE: Function returns a structure that describes the interaction of a B-field with a hyperboloid bow shock model. Returned structure elements include: th_bn: the angle (in degrees) between shock normal and the field line that passes through the spacecraft l1: the distance along the field line to the shock l2: the distance from a point that is missdist from the spacecraft in x to the tangent point d,m: the distance along x from the spacecraft to a point where the B field line would be tangent to the bow shock. A postive d means that the field line has already intersected the shock. A positive m indicates that the field line has not yet intersected the shock. intpos: position vector in GSE of point where field line originating at spacecraft intersects bow shock All distances are in Re. CREATED BY: P. Schroeder LAST MODIFICATION: L. Winslow 9/15/00 LAST MODIFICATION: %W% %E%