What orientation of Bz (B sub z) increases the likelihood that charged particles from the Sun will cause disturbed conditions?

The Earth's own magnetic field points generally northward at the equator. When the Interplanetary Magnetic Field's (IMF) vertical component, Bz, points southward, it runs opposite to the Earth's magnetic field. This anti-parallel alignment causes a phenomenon called magnetic reconnection. The southward Bz effectively 'opens a door' in the Earth's magnetosphere, allowing highly energetic charged particles from the solar wind to pour into our atmosphere, which leads to geomagnetic storms, auroras, and heavily disturbed HF radio conditions.