The interaction between solar wind and the Earth's magnetic field (Earth's magnetosphere) may lead to a transference proces of matter and energy between these two systems. This interaction can significantly modify the shape, size and even the intensity of the Earth's magnetosphere on a planetary scale during periods of hours or days. These effects of the solar wind on the Earth's magnetic field are known as geomagnetic activity.

The effects of geomagnetic activity will depend on the characteristics of the interaction of the solar wind with the Earth's magnetosphere. Geomagnetic activity regularly affects the highest regions of the Earth's atmosphere. In addition, geomagnetic activity can also negativelly affect technology in space such as artificial satellites and services associated with them such as telecommunications and geopositioning services.

Due to the relevance geomagnetic activity has, scientists have developed geomangetic indices. Geomagnetic indices are tools whose objectives are to identify, describe, classify and quantify geomagnetic activity, as well as its characteristics. There are a number of geomagnetic indices, and the calculation method for each of them defines the phenomenon of the Earth's magnetic field that it describes, as well as its characteristic cadence (time) and region (latitude) of validity.

Space Weather National Laboratory (LANCE) uses the geomagnetic indices Kp and Dst for operational processes. Kp and Dst are tow of the International Association of (IAGA)'s endorsed geomagnetic indices.

Kp - Nowcast

The Planetary-K index or Kp, broadly speaking, characterizes the intensity of geomagnetic activity on a planetary scale. However, due to the historical context at the time of its creation, the Kp index measurement network is heavily biased towards Europe and North America. Additionally, because the measurement network of this index is located in middle geomagnetic latitudes, its values are highly conditioned to the geomagnetic activity of these regions.

The Kp index measurement network is made up of 11 stations located in the northern hemisphere and 2 in the southern hemisphere. All of them located between 44° and 60° north or south geomagnetic latitude.

Kp is the arithmetic mean of the standardized 3-hour K indices for the 13 Kp observatories. Standardization is achieved through standardization tables for each observatory with the aim of eliminate UT and seasonal variations in geomagnetic disturbances.
 
The GFZ website dedicated to Kp and related geomagnetic indices, like ap. The ap index is a linearization of Kp.

Text adapted from Kp page at ISGI.

Dst - Near Real-Time

Disturbance storm-time index or Dst, aims to monitor the axis-symmetric magnetic signature of magnetosphere currents, including mainly the ring current, the tail currents and also the magnetopause Chapman-Ferraro current.

The network to compute Dst index is made of 4 low latitude magnetic observatories distribuited arround the globe. The observatories are sufficiently distant from the auroral and equatorial electrojets to inhibit noise from these two sources.

Dst is computed using 1-hour values from each one the four observatories. In each observatory a local Dst values are computed using the following protocol:
(i) contributions to horizontal field (H) from the background field (non-transient field of core and crustal origin) and the solar regular daily variation are subtracted from the observed value of H ; (ii) the so-obtained residual (ΔH) is normalized to the dipole equator thorugh the geomagnetic latited in which each observatory is located at; (iii) for each 1-hour UT interval, the Dst index is the average of the local Dst hourly mean values at the four observatories.

Dst values are publisched in real-time by WDC for Geomagnetism - Kyoto, Japan.

Text adapted from Dst page at ISGI.