The evolution of the zodiacal dust cloud under plasma drag and lorentz forces in the latitudinally asymmetric solar wind

Orbital evolutions of zodiacal dust particles are mainly influenced by electromagnetic and by plasma Poynting-Robertson effects. Whereas the first effect acts radially symmetric, the second one depends on heliographic latitude caused by the dynamical friction of the dust particles in the ambient asymmetric solar wind flow. The solar wind mass and momentum flows vary with heliographic latitude by about 50% from the ecliptic towards the poles. Here we take into account related asymmetries in the plasma Poynting-Robertson drag. In addition, we derive formulae for a competing effect due to systematic Lorentz forces and to Lorentz scatterings of the charged dust particles at the global interplanetary magnetic field. We describe the orbital element changes occurring under these conditions. Whereas Lorentz forces by means of induced inclination drifts only cause negligible evolutionary effects, we can show that the radial migration rates due to asymmetric plasma friction forces are greater by about 5–10% for particles close to the ecliptic compared to those at high inclinations. This causes a typical variation of the inclination distribution with decreasing semimajor axis. In addition, it reveals that the dust distribution function cannot be factorized into parts solely dependent on radial distance or on inclination. We also discuss the kinetic equation for the distribution function of dust particles, and find the distribution in orbital element space from which the spatial density of the particles can then be found as an integral over this distribution function after application of a Jacobian transformation of element space differentials into configuration space differentials. Some observational consequences are drawn from this comparison and are discussed in some more detail.