HINT:
If the solar wind is above 600-700 km/s, it can help create a geomagnetic storm.

HINT:
If the Bz points sharply south, it may create an opening in earths magnetosphere allowing the solar wind to flow in and reach earths atmosphere.

Solar Wind Definition

A solar wind is a stream of charged particles which are ejected from the upper atmosphere of the sun. It consists mostly of high-energy electrons and protons that are able to escape the sun's gravity in part because of the high temperature of the corona and the high kinetic energy particles gain through a process that is not well understood at this time.

Bz Definition

The sun has a magnetic field which the solar wind can carry throughout the solar system. This is called the Interplanetary Magnetic Field (IMF). Earth also has a magnetic field which forms a bubble around our planet. This is called the Magnetosphere. This bubble deflects the solar wind. Earth's magnetic field comes into contact with the sun's magnetic field in a place called the magnetopause. Here is the catch. Earth's magnetic field points north. When the sun's magnetic field points south, also known as southward Bz.. it may cancel Earth's magnetic field at point of contact. When the Bz is south the 2 fields link up. This basically opens up a door that may allow energy from the solar wind to reach Earth's atmosphere.

More detailed information and illustrations found at .. http://www.spaceweather.com/glossary/imf.html

ACE Website. http://sec.noaa.gov/ace/index.html