A special session of the 1999 Fall Meeting of the American Geophysical Union was convened to discuss an extraordinary event: "The day of the solar wind almost disappeared." That was May 11, 1999. The doldrums lasted over 27 hours. Actually, the velocities of the particles constituting the solar wind did not slacken much: 360 kilometers/second, down just 10% from the norm. The wind's density, though dropped from 10 to 0.2 particles/cubic centimeter. Nothing untoward happened on the earth's surface. In space, the earth's magnetosphere expanded when the pressure of the solar wind diminished and more X-rays were emitted from the polar atmosphere, but these effects did not surprise anyone.
The big question is: What happened on the sun that stopped its exhalations? No one seems to have an answer.
(Lazarus, Alan J.; "The Day the Solar Wind Almost Disappeared," Science, 287: 2172, 2000.)
