Ring current simulation in connection with interplanetary space conditions

Abstract

A ring current model has been obtained which permits calculations of D st variations on the Earth's surface during magnetic storms. The changes in D st are described by the equation d dt D sto = F(EM)− D sto tau; where D sto = D st-bp 1 2 +~tc ; p = mnv 2 is solar wind pressure; F( EM) is the function, controlled by the electromagnetic parameters of interplanetary medium, of injection into ring current ; τ is the constant of ring current decay. C = C u τϕ=18 nT , where C is the level of the D st-variation field measurements; ϕ is the injection function characterizing the quasisteady-state injection of energy into the ring-current region. The constant Ç is determined from the condition that the change of the ring current energy from magnetic storm commencement to end should equal the difference between the injected and dissipated energy throughout the storm. The values of the factors b and τ were found by the method of minimizing the sum of the quadratic deviations of the calculated D st from the values observed throughout the storm : b = 0.23 nT/(eV cm −3) 1 2 , τ = 8.2 h at D st ⩾ − 55 nT and τ = 5.8 h at -120 ⩾ D st ⩾ — 55 nT. The injection function F( EM) is of the form F( EM) = d( E y − A) at the values of the azimuthal component of the solar wind electric field E y ⩾ A, and F( EM) =0 at A⩾ E y . d = − 1.2 × 10 −3 Ts −1 (mV/m) −1 and A = − 0.9 mV m −1 . Thus, the injection to ring current is possible at the northward B z component of the IMF.