Schematic drawing, not real data. The live chart looks noisier, but it has the same layout.
- 1 Time. Three days side by side, hours 0 to 24 per day. Tomsk local time, 7 hours ahead of UTC.
- 2 Frequency. 0 Hz at the top, 40 Hz at the bottom. Lower tones sit higher up.
- 3 Schumann bands. Soft horizontal bands near 8, 14, 20 and 26 Hz. The top one is the 7.8 Hz fundamental.
- 4 White stripe. Bright column through every frequency: usually a thunderstorm near the station.
- 5 Black stripe. No data was recorded for that period.
- 6 Thin line. A sharp line at one exact frequency: man-made interference.
- 7 Black block. The rest of today, not recorded yet.
- 8 Colour bar. Weak at the bottom, strong at the top. No numbers, no unit.
Where the chart comes from
The spectrogram on our homepage is a copy of the live chart published by the Space Observing System station in Tomsk, Russia (sos70.ru; the station’s older site, sosrff.tsu.ru, now points there). The station has recorded extremely low frequency signals continuously since March 1997 (Tomsk).
It listens with a 5 metre vertical antenna, which picks up the vertical part of the electric field, and filters the signal to below 40 Hz. Every 3 minutes it averages many short spectra into one column of the chart, which makes 480 columns per day (Tomsk method). Our copy checks the station for a new image every minute.
The two axes
Across: three days of time
The chart shows three days side by side. The dates sit along the top, and each day runs from hour 0 to hour 24 along the bottom. The Russian word час on the axis means “hour”. The hours are local time in Tomsk, 7 hours ahead of UTC. To convert, subtract 7 hours: 15:00 on the chart is 08:00 UTC. You can check this yourself: the newest data at the right edge always sits about seven hours ahead of the current UTC time. The black block after it is simply the rest of today, which has not been recorded yet.
Down: frequency in hertz
The Russian label Гц means Hz. Zero sits at the top and 40 Hz at the bottom, so lower tones appear higher up on the image. That is the opposite of most charts, so it is worth a second look: the band a fifth of the way down is the 7.8 Hz fundamental, not a high frequency.
What the colours mean (and why they are not picotesla)
Colour shows how strong the signal is at a given time and frequency. The bar on the right runs from black and dark blue for weak signals, through light blue, green, yellow and red, to white for the strongest. The bar has no numbers and no unit. The colours tell you where the signal is stronger or weaker compared with the rest of the chart. They do not give a physical value.
Colour is not picotesla. Picotesla is a unit of magnetic field. The Tomsk antenna records the electric field, and the colour scale is not calibrated, so no colour on this chart converts into picotesla. If you see a Schumann “amplitude” quoted from this chart, for example a number on a scale from 10 to 300, it is a relative reading of the colour scale. It can show that one period looked brighter than another. It is not a measurement.
The Schumann bands
The resonance appears as soft horizontal bands running across the whole chart. The strongest sits near 7.8 Hz, about a fifth of the way down. Fainter bands follow near 14, 20 and 26 Hz. The Tomsk station describes its chart the same way: the first four modes show up as bright horizontal bands (Tomsk method).
The bands stay at roughly the same height day after day. That steadiness is the point: the frequency of the resonance barely moves, while its brightness changes all the time. The measured values of each mode are in the harmonics table of our Schumann resonance guide.
White stripes (“whiteouts”)
Tall white, red or yellow columns that cut through every frequency at once are often called whiteouts. According to the Tomsk station, white vertical stripes are usually a local thunderstorm near the station (Tomsk). Lightning radiates across a wide range of frequencies (Wikipedia), so a storm close by lights up the whole column.
A whiteout does not mean the Schumann resonance jumped to 30 or 40 Hz. Look at the 7.8 Hz band on either side of the stripe: it is still where it was. Treat a single bright column at one station as a local event until a second station shows the same thing (see Cumiana below).
Black stripes and gaps
Black vertical stripes mean that no data was recorded for that period, for whatever reason (Tomsk). The black block at the right-hand end is different: it is the part of the current day that has not happened yet. If the whole image stops changing for hours, the station feed has paused, and our homepage then shows a notice with the time of the last update.
Thin horizontal lines
Sharp, thin lines that stay at one exact frequency are man-made. The Tomsk station names nearby power lines, transformer substations and machinery as typical sources (Tomsk). They are narrow and steady, which makes them easy to tell apart from the broad, soft Schumann bands.
The daily rhythm
The bands brighten and fade over the day. Most of the energy comes from thunderstorms in the tropics, which build up in the local afternoon. Measured intensity peaks near 08:00, 14:00 and 20:00 UTC, when the thunderstorm centres over Asia, Africa and the Americas are most active (Musur and Beggan 2019). On the Tomsk chart that is roughly 15:00, 21:00 and 03:00 local time.
Seasons matter too. At the Eskdalemuir observatory in Scotland the resonance is strongest in the northern summer and weakest in winter (Musur and Beggan 2019), and at Tomsk each mode has its own daily and seasonal pattern (Tomsk). Local weather around the station adds to this, so no single day looks exactly like the textbook.
Cross-check with a second station: Cumiana
Further down our homepage you will find the Cumiana station in north-west Italy, maintained by Renato Romero (vlf.it). Comparing it with Tomsk is the simplest way to tell a global change from a local one. Three differences matter when you read it:
- Frequency runs the other way: low at the bottom, high at the top.
- Times are UTC. One image covers the last 8 hours and is updated every 30 minutes. The daily strip chart stacks one day per row.
- The colour bar is labelled in decibels, from -100 dB to 0 dB. That is also a relative scale, not picotesla.
The sharp line at 50 Hz on the Cumiana chart comes from the European power grid, which runs at 50 Hz. The station also sits near an industrial area, and its operator notes that machinery sometimes shows up as strong tones on the geophone channel.
Three common misreadings
“The frequency spiked to 40 Hz.”
A bright column that covers every frequency is a burst of energy, usually a storm near the station. The 7.8 Hz band has not moved.
“Brighter means a higher frequency.”
Brightness is strength. Frequency is the height on the chart, and on the Tomsk chart higher up means lower in frequency.
“The colours show picotesla.”
They are the uncalibrated colours of an electric field recording. Any number derived from them is a relative index.
What the chart does not show
The chart shows an electromagnetic signal and the weather around one station. It does not show effects on people, and a bright day is not a warning. What research does and does not support about people and the resonance is summarised in the research section of our guide. For the Sun’s influence, the Kp index is a separate measurement from NOAA that you can read next to the chart.
Sources
We checked each source below before citing it. The line under each entry says what we use it for on this page.
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Space Observing System, Tomsk. Live ELF noise sonogram, with notes on how to interpret it (in Russian). sos70.ru
Black stripes are missing data, white stripes are a local thunderstorm, thin horizontal lines are man-made interference.
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Space Observing System, Tomsk. Measurement method for ELF noise (in Russian). sos70.ru/?page_id=43
A 5 metre vertical antenna, a filter at 40 Hz, one averaged spectrum every 3 minutes (480 per day), and the first four modes seen as bright horizontal bands.
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Space Observing System, Tomsk. Seasonal and daily variations of the resonance frequencies (in Russian). sos70.ru/?page_id=256
Continuous recording since March 1997; each mode has its own daily and seasonal pattern.
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Romero, R. Cumiana (NW Italy) VLF monitoring station, live data. vlf.it
Each image covers the last 8 hours and is updated every 30 minutes, all times in UTC; the station sits near an industrial area.
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Musur, M. A., and Beggan, C. D. (2019). Seasonal and Solar Cycle Variation of Schumann Resonance Intensity and Frequency at Eskdalemuir Observatory, UK. Sun and Geosphere, 14(1), 81-86. doi:10.31401/SunGeo.2019.01.11
Intensity peaks near 08:00, 14:00 and 20:00 UT, tied to the thunderstorm centres over Asia, Africa and the Americas; strongest in the northern summer.
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Wikipedia. Schumann resonances. English edition, read on 25 September 2026. en.wikipedia.org
Lightning is the main natural source of the resonance and radiates across a wide range of frequencies.