Glossary

Scienception uses operational language. These are the short versions.

Planetary K-index (Kp)

A 0–9 scale of geomagnetic activity over three-hour windows. Quiet is low single digits. Storms live at the top. BGS observatories are how the UK actually measures the field. See BGS geomagnetism.

X-ray flare classes

A, B, C, M and X, each ten times the last. C is common at solar maximum. M can disturb HF radio. X is major. A letter plus a number (C3, M1) is the size within the class.

G-scale storms

G1 minor through G5 extreme describes geomagnetic storm intensity. A G1 watch for the UK is mainly a high-latitude aurora and radio story. Severe grid impacts live at the rare end of the scale.

Sunspot number

A weighted count of spots and groups. It is famous, observer-dependent, and a cousin of the 10.7 cm radio flux rather than a substitute for solar-wind data.

Coronal holes

Open magnetic regions. Fast solar wind streams from them and can rattle Earth's field a few days after the hole faces us.

10.7 cm flux (F10.7)

Daily radio brightness of the Sun at 10.7 cm, in solar flux units. Ionospheric models consume it. See the left-hand rail on the homepage.

Coronal mass ejection (CME)

A magnetic cloud thrown off the Sun. It may glance Earth, miss, or drape. Geometry, not the size of the flare, decides whether Britain gets an oval, a Forbush decrease, both, or neither.

Forbush decrease

A drop in galactic cosmic-ray intensity at the ground when a CME's magnetic field sweeps particles aside. Neutron monitors see it. Aurora cameras may not. Longer explainer.

Ionosonde

A radar that looks up and times echoes from the E and F layers. Critical frequency is the operational number. The UK series around Chilton is how Britain remembers the ionosphere. Chilton and UKSSDC.

Magnetopause

The moving wall where the solar wind meets Earth's magnetic field. In-situ craft pierce it. SMILE is designed to image it. SMILE at MSSL.

Noctilucent clouds

Ice at about 80 km, lit after the ground is dark in high-latitude summer. Not aurora. Not tropospheric cirrus. Scotland still has the best UK seats.

F10.7 explainer · G1 watch explained in place · JUICE as planetary space weather