Radiation belts and space weather prediction

5 problems

• Local wave acceleration or radial diffusion for radiation-belt electrons?

  Partially resolved

  Electrons in the outer radiation belt can be boosted to millions of electron volts, either by plasma waves right where they are or by being slowly pushed inward from farther out. The share of each process in a given storm is not known well enough to forecast.

• What empties the outer radiation belt during sudden electron dropouts?

  Open

  Sometimes most of the high-energy electrons in the outer belt vanish within hours. They can be lost into the atmosphere or out through the edge of the magnetic field, and which route dominates is unclear.

• Can a CME's magnetic orientation be predicted before arrival?

  Open

  A coronal mass ejection (CME, a cloud of magnetized gas thrown out by the Sun) causes a big storm only if its magnetic field points opposite to Earth's. Today that direction is measured only about an hour before arrival, by a spacecraft just upstream of Earth.

• What decides on which nights equatorial plasma bubbles form?

  Open

  After sunset, regions of thin plasma called plasma bubbles can rise through the ionosphere near the equator and disrupt GPS and radio signals. On some nights they appear and on others they do not, and forecasting that is not yet possible.

• How does upper-atmosphere density respond to geomagnetic storms?

  Open

  During magnetic storms the upper atmosphere heats and expands, increasing drag on satellites; in February 2022 a moderate storm caused the loss of dozens of newly launched satellites. Models still miss the size and timing of these density surges.