Editing Ionosphere (section)

=== Geomagnetic disturbances ===
* The ''[[A-index|A]]''- and ''[[K-index|K]]''-indices are a measurement of the behavior of the horizontal component of the '''geomagnetic field'''. The ''K''-index uses a semi-logarithmic scale from 0 to 9 to measure the strength of the horizontal component of the geomagnetic field. The Boulder ''K''-index is measured at the [[Boulder Geomagnetic Observatory]].
* The geomagnetic activity levels of the Earth are measured by the fluctuation of the Earth's magnetic field in [[SI]] units called [[tesla (unit)|tesla]]s (or in non-SI [[gauss (unit)|gauss]], especially in older literature). The Earth's magnetic field is measured around the planet by many observatories. The data retrieved is processed and turned into measurement indices. Daily measurements for the entire planet are made available through an estimate of the ''A''<sub>p</sub>-index, called the ''planetary A-index'' (PAI).