Regions and Coordinates
Ionosphere
The region where part of the atmosphere is ionized, principally by solar radiation, leaving electrons and ions. Its properties vary with altitude, time, latitude, local time, and solar and geomagnetic activity; it is not a fixed layer with a single boundary altitude.
Plasmasphere
The relatively cool, dense plasma region in the inner magnetosphere. It is connected to the ionosphere along magnetic field lines, but the two terms refer to different regions.
Geomagnetic Coordinates
Coordinate systems that describe position relative to Earth’s magnetic field. They differ from geographic latitude and longitude, so an analysis needs to identify the model, definition, and epoch used.
Observables and Missions
GNSS-TEC
Total electron content along the signal path between a GNSS satellite and receiver. Slant values and values mapped to the vertical need to be distinguished, with elevation angle, biases, reference, and mapping assumptions checked.
Swarm Satellites
The European Space Agency mission for observing Earth’s magnetic field. When using magnetic, electric, plasma, or orbit data from its spacecraft, check the product, version, quality flags, and target interval.
Field-Aligned Current
An electric-current component flowing along Earth’s magnetic field. Estimates from satellite magnetic observations depend on the orbit, background-field removal, spatial structure, and assumptions used in the estimate.
Variation and Frequency Analysis
Magnetic Ripples
A term for short spatial- or time-scale variations seen in low-Earth-orbit magnetic data. The name does not identify their source; orbit context, frequency range, current structure, and other observations need to be considered.
Pc3 Geomagnetic Pulsation
A continuous geomagnetic pulsation classified within a conventional period range. A period within that band does not by itself establish a particular excitation source, such as the solar wind, magnetosphere, atmosphere, or solid Earth.
Power Spectral Density (PSD)
An estimate of how a signal’s variance or power is distributed across frequencies. Windowing, segment length, overlap, detrending, normalization, and units affect its shape and values.
Local Time
A time representation based on the relationship between a location’s longitude and the Sun. It changes along a satellite orbit, so check the definition used together with UTC and position.
Atmosphere-Geosphere Coupling
Acoustic-Gravity Wave
A family of atmospheric waves involving compressibility and buoyancy. Their properties vary with period, altitude, and propagation conditions. Timing agreement between ground and upper-atmosphere variation alone cannot establish a propagation path.
Lamb Wave
An atmospheric wave mode that propagates mainly horizontally in the lower atmosphere. Comparing arrival times or apparent speeds requires a source time, distance, propagation path, background atmosphere, and consistent time reference.
Reading Definitions in Context
The same term or abbreviation can have different definitions across papers, data products, and disciplines. Read an observation or analysis alongside its coordinate system, product, and processing conditions.