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Magnetic Field Unsettled Today PDF Print E-mail
Written by RC Christian   
Tuesday, 01 February 2011 17:44

Although Solar flare activity has been relatively low for the past couple days, February started off with an instability in the Earth's Magnetic Fiels.

Magnetic field monitors went berzerko today, registering a "unsettled", meaning that the Earth's Magentic Field was vastly disturbed. Many websites containing the N3KL monitor awoke this morning to a Bright Yellow indicator Showing the Earth's magnetic field as: "Unsettled"

Geomagnetic indices

Apart from the Solar Flux, another important influence on the ionosphere and hence radio propagation prediction is the level of geomagnetic activity. While the geomagnetic activity is a measure of the state of the Earth's magnetic field, this in turn is influenced by the Sun. To indicate the state of Geomagnetic activity, there are two indices that are used that are related to each other:

  • K index
  • a Index

Although different, both these indices give indications of the severity of magnetic fluctuations, and hence the level of disturbance to the ionosphere.

 

K Index: The K index is a three hourly measurement of the variation of the Earth's magnetic field compared to what are "quiet day" conditions. The measurement is made using a magnetometer. This indicates the variation of the magnetic flux in nanoTeslas. This reading is then converted to the K index. The relationship is quasi-logarithmic, i.e. an almost directly proportional on a logarithmic scale..

The K index is measured at many different places around the world. The magnetic field varies around the globe and accordingly a different value for K is created at each measurement station. Owing to the fact that the magnetic field varies in different ways around the globe dependent upon the way in which the magnetosphere is affected, it is not possible to have a simple relationship between one station and a global K index. Instead the individual K indices are averaged around the globe to give what is termed the Kp or planetary K index.

Kp Index: The planetary or Kp index has values that range between 0 and 9. The values of the index give a good indication of geomagnetic activity: values between 0 and 1 indicate quiet magnetic conditions and would give rise to virtually no degradation in HF band radio communications conditions. Values between 2 and 4 provide an indication of unsettled magnetic conditions that indicate the possibility of some degradation on the HF bands for radio communications. A value of 5 signifies a minor storm and 6 a larger one. Values through to 9 indicate steadily worsening conditions with 9 representing a major storm that is likely to result in a blackout in HF ionospheric propagation for several hours.

A Index; The A index is a linear measure of the Earth's field. As a result of this, its values extend over a much wider range. It is derived from the K index by scaling it to give a linear value which is termed the "a" index. This is then averaged over the period of a day to give the A index. Like the K index, values are averaged around the globe to give the planetary Ap index.

Values for the A index range up to 100 during a storm and may rise as far as 400 in a severe geomagnetic storm.

 

Relationship between "K" and "a" Indices

Ap Index Kp Index Description
0 0 Quiet
4 1 Quiet
7 2 Unsettled
15 3 Unsettled
27 4 Active
48 5 Minor storm
80 6 Major storm
132 7 Severe storm
208 8 Very major storm
400 9 Very major storm

 

Geomagnetic and ionospheric storms are very closely related. However they are separate effects. Geomagnetic storms relate to disturbances of the Earth's magnetic field, and ionospheric storms relate to disturbances of the ionosphere. However it is found that geomagnetic storms often lead to ionospheric ones, but not on every occasion.

 

Last Updated on Tuesday, 01 February 2011 18:24
 

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