Geomagnetic Daily Magnetograms
We represent regular up-to-date information about the current state of the geomagnetic field in the form of graphical magnetograms and local K-indexes.
Learn moreThe page is under construction! The graphs shown here are for test purposes only and should not be regarded as a meaningful piece of information!
Geomagnetic intensity variations
F: ±50 nT
X: ±50 nT
Y: ±50 nT
Z: ±50 nT
The graph shows the relative variations in the local components of the Earth's magnetic field. The three components of the magnetic intensity vector X, Y, Z and the total intensity F in nT (nanotesla) are shown. The observations are performed continuously using a geophysical vector magnetometer MG-01, located near the city of Stara Zagora, in the central region of Bulgaria (42°25′N; 25°38′E). The sampling period is 1 minute and data are updated every 10 minutes. The raw values are filtered using a bidirectional low-pass filter. The mean is subtracted and the scale is determined for the field intensity axis (Oy axis). Thus, the graph shown represents the variations in the field relative to the mean value for a period of one day. Time is UTC and is measured in hours.
K-index
To estimate the amplitude of the local variations in the intensity of the geomagnetic field, the calculation of the so-called K-index has been internationally adopted. It shows the correspondence, expressed in quasi-logarithmic scale, between the amplitude of the disturbances in the horizontal component of Earth's magnetic field and an integer number, in the range from 0 to 9. As the value of the K-index increases by one unit, the amplitude increases approximately twice. The index is calculated every three hours. The amplitude is determined using the difference between the maximal and minimal intensity values measured for the last three hours.
A higher value of the K-index corresponds to a greater disturbance in the magnetic field. Values of 0, 1, 2, 3 indicate a quiet field or low geomagnetic activity and are usually shown in green color. A value of 4 means a moderate activity and is displayed in yellow. Values of 5 and higher mean a magnetic storm and are displayed in red color.
The Earth's magnetic field has different intensities in the different latitude regions. The same process (or perturbation) in the magnetosphere can be detected having a different amplitude in two magnetic observatories located on the surface. As we approach the magnetic poles, the amplitude increases. An individual table is calculated for each observational location, showing the relationship between the amplitudes of the geomagnetic disturbances and a given index number. Thus, a correlation between the values of the K-index for the various magnetic observatories around the world is ensured. The following table is used in the region of Bulgaria:
| K-index | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Value | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| Disturbance, [nT] | <4 | [4, 8) | [8, 16) | [16, 30) | [30, 50) | [50, 85) | [85, 140) | [140, 230) | [230, 350) | >350 |
In geophysical science, the so-called planetary index or Kp-index is used. It is estimated as a weighted mean of the local K-indexes calculated in 13 geomagnetic observatories located in the mid-latitude region. The accuracy of the Kp-index is 1/3. The index values are published daily by international geomagnetic centers.