Amplitude of geomagnetic disturbances (Amp indicator)

The indicator of intensity of geomagnetic disturbances (Amp) is based on the monitoring of amplitude of the field variations. This indicator facilitates quick and clear estimation of a data record anomality rate from a specified observatory. Such approach requires preliminary definition of sporadic variations amplitude range. According to their values the intensity scale is formed. The Amp indicator is calculated for all three components and total intensity of the geomagnetic field vector as the maximal amplitude of disturbances within the three time intervals: 1, 3, and 24 hours.

The results of the application of the Amp indicator are classified within a 4-grade scale (0–3), where 0 is ‘background’; 1 is ‘weak anomaly’; 2 is ‘anomaly’; 3 is ‘strong anomaly’. The lower threshold value for the 3rd grade is determined as the value that corresponds the 1% of data maximum values for a particular observatory, time resolution and component. This threshold value is rounded to the 2nd significant digit. The lower threshold values for the 1st and the 2nd grades are determined as 1/3 and 2/3 of the lower threshold value for the 3rd grade and are rounded to the 2nd significant digit.

For an observatory or a station with no 1-minute scalar magnetometer data available, the indicator scale for the total field F is set to the ones for the observatories close to it latitudinally. For example, the F scales for KIV and LVV observatories are the same as the one for IRT observatory, and the F scale for AIA observatory is equal to the F scale for YAK observatory (considering the magnetic field symmetry in the Northern and the Southern hemispheres)*.

An example of 1-hour Amp indicator grades and corresponding threshold values for the X component data from SPG observatory is given in the following table:

Grade	Minimum value, nT	Maximum value, nT
0	0	30
1	30	59
2	59	89
3	89	100000

For more details, please check the Data Science Journal paper:

Gvishiani, A et al 2016 Automated Hardware and Software System for Monitoring the Earth’s Magnetic Environment. Data Science Journal, 15: 18, pp.1–24

*The threshold value set to 1% of maximal values was assigned based on the analysis of X or H component data from BOX, KHB, MGD and SPG magnetic observatories during March 2015. Also the threshold values of 10%, 5%, 3% were analyzed.