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Mega (million) electronvolt. A unit of energy used to describe the total energy carried by a particle or photon.
A radiowave signal associated with optical and/or X-ray FLAREs.
With specific reference to zones of geomagnetic activity, "middle latitudes" refers to 20 deg. to 50 deg. geomagnetic.
A unit of magnetism 10.0E-09 tesla, equivalent to a gamma (10.0E-05 gauss).
The line that separates longitudinal magnetic fields of oppo- site polarity.
The SUNSPOT area that may surround the darker UMBRA or umbrae. It consists of linear bright and dark elements radial from the sunspot umbra.
Continuation of existing conditions. When a physical parameter varies slowly, the best prediction is often persistence.
The lowest layer of the solar atmosphere; corresponds to the solar surface viewed in WHITE LIGHT. SUNSPOTs and FACULAe are observed in the photosphere.
An extended emission feature of an ACTIVE REGION that exists from the emergence of the first magnetic flux until the widely scattered remnant magnetic fields merge with the background.
A space in chromospheric (see CHROMOSPHERE) PLAGE lacking plage intensity, coinciding with polarity inversion line.
Spotless disc free of calcium plage
Any ionized gas, that is, any gas containing ions and electrons.
POLAR CAP ABSORPTION (PCA)
An anomalous condition of the polar IONOSPHERE whereby HF and VHF (3 - 300 MHz) radiowaves are absorbed, and LF and VLF (3 - 300 kHz) radiowaves are reflected at lower altitudes than normal. In practice, the absorption is inferred from the proton flux at energies greater than 10 MeV, so that PCAs and PROTON EVENTs are simultaneous. Transpolar radio paths may still be disturbed for days, up to weeks, following the end of a proton event.
A LOOP PROMINENCE SYSTEM often seen after a major TWO-RIBBON FLARE, which bridges the ribbons.