Space-Weather Glossary

A 0–9 scale of global geomagnetic disturbance from ground magnetometers. Kp ≥ 5 marks a storm (G1 minor → G5 extreme).

A 3-hour measure of local geomagnetic disturbance at a single observatory. Kp is the planetary average of 13 K stations.

NOAA's geomagnetic storm scale: G1 (Kp 5) minor up to G5 (Kp 9+) extreme, with documented impacts on power, navigation and aurora.

The north–south component of the interplanetary magnetic field. Southward (negative) Bz enables reconnection and drives storms.

The total magnitude of the interplanetary magnetic field. Rising Bt often signals an approaching CME or stream compression.

Plasma streaming from the Sun, typically 300–800 km/s. High-speed streams from coronal holes compress the magnetosphere.

Coronal mass ejection — a billion-tonne plasma cloud hurled from the Sun, the main cause of large geomagnetic storms.

A sudden burst of X-ray and UV radiation from magnetic reconnection in an active region; classified A, B, C, M, X by X-ray flux.

Logarithmic X-ray flux scale. M-class causes R1–R2 radio fading; X-class can trigger R3+ planet-wide blackouts.

A region of open magnetic field on the Sun that releases fast solar-wind streams, recurring with the ~27-day solar rotation.

A cooler, magnetically complex region on the photosphere; the source of most flares and CMEs.

Dense plasma suspended above the Sun by magnetic fields. When it erupts it lifts off as a CME.

Solar Energetic Particles — protons and ions accelerated by flares and CME shocks; a radiation hazard for satellites and astronauts.

Disturbance storm time index tracking the equatorial ring current. Negative values signal storm main phase; below −100 nT is intense.

Trapped energetic ions drifting westward around Earth; it intensifies during storms and drives Dst negative.

The ring of aurora around each magnetic pole. It expands equatorward during storms, making aurora visible at lower latitudes.

A brief auroral intensification and magnetotail energy release, smaller and shorter than a full geomagnetic storm.

Intense high-altitude currents (auroral and equatorial) that strengthen during storms and can induce ground currents.

Absorption of high-frequency radio by an ionised D-region, caused by solar flare X-rays or polar cap absorption.

Polar Cap Absorption — HF radio blackout near the poles caused by solar energetic protons spiralling down magnetic field lines.

NOAA D-Region Absorption Prediction model mapping HF radio absorption from flares and proton events.

Geomagnetically Induced Currents in power grids, pipelines and railways, driven by rapid geomagnetic field changes during storms.

Atmospheric drag on low-Earth-orbit satellites, increased by thermospheric heating during storms (cf. the 2022 Starlink loss).

The upper atmosphere layer (~90–600 km) that absorbs solar energy and expands during storms, raising orbital drag.

The ionised layer that reflects HF radio; it is disturbed by flares and storms, degrading communications and GPS.

The Lagrange point ~1.5 million km upstream of Earth where ACE and DSCOVR sample the solar wind 30–60 min before it arrives.

Advanced Composition Explorer — NASA satellite at L1 sampling solar wind plasma and magnetic fields since 1997.

Deep Space Climate Observatory — NOAA's primary L1 solar-wind monitor since 2016, successor to ACE for real-time data.

The boundary where solar-wind pressure balances Earth's magnetic field; it compresses (to ~6 Earth radii) in severe storms.

The upstream shock where supersonic solar wind decelerates before reaching the magnetopause.

NOAA model converting solar wind drivers into auroral precipitation power per hemisphere (the GW figures on the aurora map).

The 10.7 cm solar radio flux — a stable proxy for solar activity and EUV output used in atmospheric and orbit models.

The ~11-year sunspot cycle. Cycle 25 began in December 2019 and reached solar maximum in 2025 (peak ~July 2025, NOAA/NASA confirmed October 2024). Now in declining phase.

A sharp jump in ground magnetometers when a CME-driven shock arrives; a storm follows if Bz turns southward.

Corotating Interaction Region — a compression zone ahead of a high-speed solar-wind stream that can trigger recurrent storms.

All-domain Anomaly Resolution Office — the US Department of Defence office that investigates and publishes UAP records.

A theoretical cascade where debris collisions create more debris, eventually making certain orbits unusable.

The break-up of a satellite or rocket body, creating hundreds of trackable debris pieces and thousands of untrackable ones.

The density of debris objects passing through a given area of space, used to assess collision risk for satellites.

A close approach between two space objects; major conjunctions trigger collision avoidance manoeuvres.

Low Earth Orbit — the region below 2,000 km altitude, home to the ISS, Starlink, and most space debris.

Geostationary Orbit — 35,786 km above the equator, where communications satellites match Earth's rotation.

Manoeuvres performed by satellite operators to avoid predicted close approaches with debris or other spacecraft.

Objects larger than ~10 cm in LEO or ~1 m in GEO that can be tracked by ground radar and telescopes.

The change in velocity needed for a manoeuvre; collision avoidance burns typically require just a few cm/s of delta-v.

A communications satellite that collided with Cosmos 2251 in 2009, creating over 2,000 trackable debris pieces.

A defunct Russian satellite that collided with Iridium 33 in 2009, the first major accidental debris collision.

Near-Earth Asteroid — an asteroid whose orbit brings it within 1.3 AU of the Sun, close to Earth's orbit.

Potentially Hazardous Asteroid — an NEA larger than 140 m that comes within 0.05 AU of Earth's orbit.

A 0–10 scale rating the impact hazard of an asteroid, combining collision probability and kinetic energy.

A logarithmic scale comparing an asteroid's impact risk to the background risk over the same period.

When an asteroid passes near Earth; distances are measured in lunar distances (LD) or astronomical units (AU).

The average Earth–Moon distance (~384,400 km), used as a unit for asteroid close approaches.

The mean Earth–Sun distance (~149.6 million km), used to express distances in the solar system.

An asteroid's brightness if observed from 1 AU away; used to estimate its size and reflectivity.

The fraction of sunlight an asteroid reflects; combined with absolute magnitude to estimate its diameter.

The ring of persistent aurora around each magnetic pole, expanding equatorward during geomagnetic storms.

Strong horizontal currents in the ionosphere that intensify during substorms, measurable by ground magnetometers.

A sudden brightening and expansion of the aurora, lasting 1–3 hours, driven by magnetotail reconnection.

The northern lights — aurora visible in the Northern Hemisphere, typically between 60° and 75° magnetic latitude.

The southern lights — aurora visible in the Southern Hemisphere, the counterpart to the aurora borealis.

The boundary between slow and fast solar wind, often triggering geomagnetic activity.

The breaking and rejoining of magnetic field lines, converting magnetic energy into kinetic energy.

The ratio of plasma pressure to magnetic pressure; high beta means plasma dominates, low beta means magnetic field dominates.

The speed of magnetic waves in a plasma, setting the characteristic velocity for magnetohydrodynamic processes.

The maximum X-ray flux measured by GOES during a flare, used to classify its strength (A, B, C, M, X).

The density of energetic protons from the Sun, measured by GOES; elevated flux signals a radiation storm.

The current solar cycle that began in December 2019. Solar maximum was reached in 2025 (peak ~July 2025); now in the declining phase toward minimum ~2030.

Earth's magnetic shield deflecting solar wind; it stores energy in the magnetotail before releasing it in substorms.

The elongated nightside of the magnetosphere where energy builds up before substorm release.

NOAA's Space Weather Prediction Center — the official US source for space weather alerts and forecasts.

Geostationary Operational Environmental Satellite — monitors solar X-rays, EUV, and weather from geostationary orbit.

ESA's Space Weather Service Network — European space weather data and alerts complementing NOAA SWPC.

Helmholtz Centre Potsdam — German research centre providing Kp index forecasts and geomagnetic data.

ESA's three-satellite constellation measuring Earth's magnetic field with unprecedented precision since 2013.

Total Electron Content — the number of free electrons in a column of the ionosphere, key for GPS accuracy.

Loss of HF radio communication caused by solar flare X-rays ionising the D-region of the ionosphere.

NOAA D-Region Absorption Prediction model mapping HF radio absorption from flares and proton events.

A forecast combining multiple independent predictions — from models or human forecasters — into a single consensus, often weighted by past accuracy.

The process of adjusting forecast probabilities so they match observed frequencies — a forecaster who says '80%' should be right about 80% of the time.

A measure of forecast accuracy: the square of the difference between the predicted probability and the actual outcome (0 or 1). Lower is better.

Expressing predictions as probabilities rather than certainties, allowing the communication of uncertainty.

Logarithmic Market Scoring Rule — the algorithm Flarient uses to aggregate forecasts into a market probability, rewarding accurate and early predictions.

Prediction IQ — Flarient's virtual forecasting currency, representing how much conviction a forecaster has contributed to a prediction market.

A regular celestial event when Earth passes through a comet's debris trail, producing many meteors radiating from one point in the sky.

An icy body that releases gas and dust as it approaches the Sun, forming a glowing coma and sometimes a visible tail.

A planet orbiting a star outside our solar system, detected by transit, radial velocity, or direct imaging.

The number of meteors a single observer would see per hour under ideal conditions at the peak of a meteor shower.

A logarithmic measure of brightness — lower numbers are brighter. The Sun is −26.7, the full Moon −12.7, the faintest naked-eye stars around +6.

A graph of an object's brightness over time, used to track comet outbursts, variable stars, and exoplanet transits.

The point in the sky from which meteors of a particular shower appear to originate, named after the constellation it lies in.

Electric-blue clouds at ~80 km altitude, visible in summer at high latitudes, formed by ice crystals nucleating on meteoric dust.

The mass density of the upper atmosphere, which increases during geomagnetic storms and drives satellite orbital drag.

The resistance a satellite experiences from residual atmosphere, strongest in LEO and variable with solar activity.