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อภิธานศัพท์: อภิธานศัพท์ฟิสิกส์ (อวกาศ)
P
PENUMBRA The SUNSPOT area that may surround the darker UMBRA or umbrae. It
consists of linear bright and dark elements radial from the sunspot
umbra.
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PERSISTENCE Continuation of existing conditions. When a physical parameter
varies slowly, the best prediction is often persistence.
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PHOTOSPHERE The lowest layer of the solar atmosphere; corresponds to the
solar surface viewed in WHITE LIGHT. SUNSPOTs and FACULAe are
observed in the photosphere.
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PLAGE 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.
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PLAGE CORRIDOR A space in chromospheric (see CHROMOSPHERE) PLAGE lacking
plage intensity, coinciding with polarity inversion line.
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PLAGENIL Spotless disc free of calcium plage
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PLASMA Any ionized gas, that is, any gas containing ions and electrons.
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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.
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POST-FLARE LOOPS A LOOP PROMINENCE SYSTEM often seen after a major
TWO-RIBBON FLARE, which bridges the ribbons.
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PROMINENCE A term identifying cloud-like features in the solar atmosphere.
The features appear as bright structures in the CORONA above the
solar LIMB and as dark FILAMENTs when seen projected against the
solar DISK.
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PROTON Solar activity levels with at least on high energy event (Class X
Flares)
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PROTON EVENT By definition, the measurement of at least 10
protons/sq.cm/sec/steradian at energies greater than 10 MeV.
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PROTON FLARE Any FLARE producing significant FLUXes of greater-than-10 MeV
protons in the vicinity of the earth.
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