MAGNETIC INDICES

 

The magnetic disturbances experienced by the atmosphere are measured by magnetometers placed at various stations at high latitudes, midlatitudes and equatorial regions of earth. These measurements are divided into different categories or indices according to the various characteristics and intensities.

 
In the auroral region, the indices used are Kp and AE. In the lower latitude regions, DST index is measured.

F10.7 and SSN are also a part of magnetic indices. 

1. Kp and Ap

Kp index is the measure of the irregular variations of the horizontal component of the magnetic field measurements and is used as an indicator of the general level of magnetic activity caused by the solar wind/radiation.

 
It is measured every 3 hours. The index value obtained is an average value recorded from about 12 stations located in the midlatitude zone (48° to 63°). This index ranges from a 0 to 9 scale where 0 is the least and 9 the most disturbed event. From 0 to 4 index value indicates a quite event but above 4 it indicates a storm. This scale is also divided into small segments for decimal values such as in an interval from 1.5 to 2.5 will be 2-, 20 and 2+.

 
But the Kp value is in logarithmic scale and hence it is also converted to the linear scale and those set of values are called Ap indices. Kp and Ap values are correlated by certain predefined numeric values. Ap values are useful to obtain a daily average value for this index and these indices share a linear relationship with magnetometer fluctuations as oppose to kp values.



List of Kp observatories

Northern Hemisphere

Southern Hemisphere

Observatory

Corr. Geom. Lat.

Observatory

Corr. Geom. Lat.

MEA

Meanook

62.5°

EYR

Eyrewell

50.2°

SIT

Sitka

60.0°

CAN

Canberra

45.2°

LER

Lerwick

58.9°

 

 

 

OTT

Ottawa

58.9°

 

 

 

LOV

Lovö

56.5°

 

 

 

ESK

Eskdalemuir

54.3°

 

 

 

BJE

Brorfelde

52.7°

 

 

 

FRD

Fredericksburg

51.8°

 

 

 

WNG

Wingst

50.9°

 

 

 

HAD

Hartland

50.0°

 

 

 

NGK

Niemegk(4)

48.8°

 

 

 


(4) Niemegk has replaced Witteveen in the Kp network since April 1st, 1988.

Kp


                                                                                      Distribution of Kp observatories


List of Kp observatories and figure from -  http://isgi.cetp.ipsl.fr/des_kp_ind.html


2. AE - Auroral Electrojet - This index as the term implies is mainly used for measurements of the magnetic field in the auroral regions.
3. DST - It is a measure of the ring current of the disturbance of the magnetic field.
4. F10.7 and SSN - F10.7 is a measure of the solar flux where 10.7cm is the wavelength of the wave measured. SSN is the solar sunspot     number. Both of them are correlated.



References:

1. Tascione, T.F., Introduction to the Space Environment, 2nd Ed.
2. www.noaa.gov
3. http://spidr.ngdc.noaa.gov/spidr/index.jsp


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