K-index	a	Boulder, CO observatory measurement (nT Tesla (unit) The tesla is the SI derived unit of magnetic field B . One tesla is equal to one weber per square meter, and it was defined in 1960 in honour of the inventor, physicist, and electrical engineer Nikola Tesla... )	NOAA G-scale
0	0	0 - 5	G0
1	3	5 - 10	G0
2	7	10 - 20	G0
3	15	20 - 40	G0
4	27	40 - 70	G0
5	48	70 - 120	G1
6	80	120 - 200	G2
7	140	200 - 330	G3
8	240	330 - 500	G4
9	400	>500	G5

The K-index quantifies disturbances in the horizontal component of earth's magnetic field

Earth's magnetic field

Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...

 with an integer

Integer

The integers are formed by the natural numbers together with the negatives of the non-zero natural numbers .They are known as Positive and Negative Integers respectively...

 in the range 0-9 with 1 being calm and 5 or more indicating a geomagnetic storm

Geomagnetic storm

A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by a disturbance in the interplanetary medium. A geomagnetic storm is a major component of space weather and provides the input for many other components of space weather...

. It is derived from the maximum fluctuations of horizontal components observed on a magnetometer

Magnetometer

A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...

 during a three-hour interval. The label 'K' origins from German 'Kennziffer' meaning 'characteristic digit'.

The conversion table from maximum fluctuation (nT

Tesla (unit)

The tesla is the SI derived unit of magnetic field B . One tesla is equal to one weber per square meter, and it was defined in 1960 in honour of the inventor, physicist, and electrical engineer Nikola Tesla...

) to K-index, varies from observatory to observatory in such a way that the historical rate of occurrence of certain levels of K are about the same at all observatories. In practice this means that observatories at higher geomagnetic latitude require higher levels of fluctuation for a given K-index. The real-time K-index is determined after the end of prescribed three hourly intervals (0000-0300, 0300-0600, ..., 2100-2400). The maximum positive and negative deviations during the 3-hour period are added together to determine the total maximum fluctuation. These maximum deviations may occur any time during the 3-hour period.

The K-index was introduced by Julius Bartels

Julius Bartels

Julius Bartels was a German geophysicist and statistician who made notable contributions to the physics of the Sun and Moon; to geomagnetism and meteorology; and to the physics of the ionosphere. He also made fundamental contributions to statistical methods for geophysics...

 in 1938.

The relationship between K, Kp, and estimated Kp

The official planetary Kp index is derived by calculating a weighted average of K-indices from a network of geomagnetic observatories. Since these observatories do not report their data in real-time, various operations centers around the globe estimate the index based on data available from their local network of observatories.

The Kp-index was introduced by Bartels in 1939.

The relationship between K and A

The A-index provides a daily average level for geomagnetic activity. Because of the non-linear relationship of the K-scale to magnetometer fluctuations, it is not meaningful to take averages of a set of K indices. What is done instead is to convert each K back into a linear scale called the "equivalent three hourly range" a-index (note the lower case). The daily A index is merely the average of eight "a" indices.

Thus, for example, if the K indices for the day were 3 4 6 5 3 2 2 1, the daily A index is the average of the equivalent amplitudes:

A = (15 + 27 + 80 + 48 + 15 + 7 + 7 + 3)/8 = 25.25

The Ap index is averaged planetary A-index based on data from a set of specific Kp stations.

The relationship between the NOAA G-scale and Kp

The Kp scale is a reasonable way to summarize the global level of geomagnetic activity, but it has not always been easy for those affected by the space environment to understand its significance. The NOAA G-scale was designed to correspond, in a straightforward way, to the significance of effects of geomagnetic storm

Geomagnetic storm

A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by a disturbance in the interplanetary medium. A geomagnetic storm is a major component of space weather and provides the input for many other components of space weather...

s.

External links

• http://www.sec.noaa.gov/info/Kindex.html
• http://www.sec.noaa.gov/rt_plots/kp_3d.html
• http://www.swpc.noaa.gov/SolarCycle/
• http://www.n3kl.org/sun/noaa.html
• Comprehensive radio propagation site