When the 1/8th to 2/8ths of the sky is covered by with opaque (not transparent) clouds Same as Mostly Clear, except only applicable during daylight hours. definition courtesy of: NOAA

An elliptical band around each geomagnetic pole ranging from about 75 degrees magnetic latitude at local noon to about 67degrees magnetic latitude at midnight under average conditions. Those locations experience the maximum occurrence of aurorae. The aurora widens to both higher and lower latitudes during the expansion phase of a magnetic substorm. [..]

Record extremes measured on a specific calendar day.

Large Angle Spectrometric COronagraph experiment on SOHO capable of imaging CMEs from 1.1-32 solar radii. definition courtesy of: NWS Space Weather Prediction Center

A type of sunspot penumbra characteized by granular (rather than filamentary) structure, brighter intensity than the umbra, and narrow extent, and possibly only partially surrounding the umbra. Penumbrae are typically rudimentary during the sunspot formative and decay phases. definition courtesy of: NWS Space Weather Prediction Center

A sudden perturbation, positive or negative, of several nanotesla in the northward component (see geomagnetic elements) of the low-latitude geomagnetic field, not associated with a following geomagnetic storm. (An SI becomes an SC if a storm follows.) definition courtesy of: NWS Space Weather Prediction Center

That region of the Earth’s atmosphere where the neutral temperature increases with height. It begins above the mesosphere at about 80-85 km and extends to the exosphere. definition courtesy of: NWS Space Weather Prediction Center

This is the time before sunrise and after sunset where it is still light outside, but the sun is not in the sky.

The splitting of some solar spectral emission lines due to the presence of a strong magnetic field. Briefly, the lines split into three or more components of characteristic polarization. The components are circular if the local magnetic field is parallel to the line of sight, and linear if the field is perpendicular to the line of sight. The amount [..]

Record extremes measured over the course of a 24-hour period. These records most commonly apply to snow and rainfall accumulation.