The field guide · Moon & methods
A plain-language space weather glossary.
Use this glossary to decode a chart or bulletin without confusing the quantity, its unit and its interpretation. Each term links to a guide where the measurement and its limitations are explained in context.
Earth and resonance
Schumann resonances. Broad electromagnetic resonant modes in the Earth–ionosphere cavity, excited by lightning. Start with the resonance guide.
Ionosphere. A region of the upper atmosphere containing charged particles. Its electrical properties matter for radio propagation and the resonance environment. See the Earth–Sun distinction.
ELF. Extremely low frequency. In an instrument description, check the actual numerical range; an acronym alone does not specify the sensor bandwidth.
Hertz, Hz. Cycles per second. A unit of frequency, not amplitude. Frequency and amplitude explained.
Spectrogram. A display showing how spectral content changes over time, commonly using color for intensity. Read a worked example.
Sun and solar wind
Solar flare. A burst of electromagnetic radiation from the Sun. Its A/B/C/M/X class refers to peak soft X-ray flux in a defined band. Flare classes.
Coronal mass ejection, CME. An eruption of plasma and magnetic field from the corona. It is not another word for a flare. CME guide.
Solar wind. The continuous outward flow of solar plasma carrying a magnetic field. Speed, density and field direction.
Bz. The z component of a magnetic field in the specified coordinates. For solar-wind interpretation, the coordinate system and sign matter. Reading Bz.
Nanotesla, nT. A unit of magnetic flux density. A magnetic measurement in nT and a dimensionless index are not the same quantity.
Geomagnetic activity and bulletins
Kp. A planetary geomagnetic index with three-hour intervals and a 0–9 scale. Kp guide.
G scale. NOAA’s classification of geomagnetic-storm severity. G1 through G5.
R scale. NOAA’s classification of radio blackouts associated with flare-related effects. Solar-flare and radio context.
S scale. NOAA’s classification of solar radiation storms using energetic-proton measurements. S1 through S5.
Watch, warning, alert. Distinct message types concerning potential, imminent or observed activity. Bulletin-reading guide.
Aurora. Upper-atmospheric light produced following particle excitation of atoms and molecules. Northern and southern lights.
Time, data and interpretation
UTC. Coordinated Universal Time, used to align observations across time zones. Preserve the stated zone when comparing charts.
Missing data. An interval without an available measurement. It is not interchangeable with a measured zero.
Nowcast. An estimate of current or very recent conditions. It may differ from a later definitive product.
Correlation. A statistical relationship between variables. It does not, on its own, identify a cause.
Waxing / waning. Increasing / decreasing visible lunar illumination. Moon phase guide.
People and experiments
Hertz. One cycle per second; named for Heinrich Hertz.
Terrella. A small magnetized sphere used as a laboratory Earth model; see Birkeland’s experiment.
Global electric circuit. A large-scale atmospheric current system; see Wilson’s contribution.
Correlated magnetic noise. Related magnetic disturbances at separated sites; a concern studied in gravitational-wave background searches.
Sources
Definitions summarize the primary sources linked throughout the individual guides. For agency terminology and index specifications, consult:
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