What Is the Kp Index and How Can We Track Geomagnetic Storms in Bulgaria?

We have all heard someone say, “I have a splitting headache today - there must be a geomagnetic storm.” While some people may see this as little more than an excuse for being in a bad mood, geomagnetic disturbances are a measurable phenomenon studied by scientists and monitored by people who are sensitive to changes in the weather.

But how are these space weather events measured, and when do the values become unusually high? One of the main indicators is the Kp index.

What Is the Kp Index?

The Kp index, or Planetary K-index, is a global indicator that measures disturbances and variations in the Earth’s magnetic field. It is calculated every three hours using data from 13 geomagnetic observatories located around the world.

These disturbances are caused by solar activity. When an eruption occurs on the Sun, streams of charged particles can travel through space as part of the solar wind. When they reach the Earth, they interact with our planet’s magnetic “shield” and cause variations in the magnetic field. These variations are measured by the Kp index.

Normal and High Values: The Scale from 0 to 9

It is important to distinguish between:

• K index - shows the geomagnetic activity measured at a specific observatory;
• Kp index - a combined planetary indicator calculated using data from several observatories.

This is why the global Kp index and the local K index for Bulgaria are not always exactly the same.

How Does a Geomagnetic Storm Occur?

A geomagnetic storm is not caused directly by every solar flare.

A solar flare releases strong electromagnetic radiation, which reaches the Earth in around eight minutes. For a geomagnetic storm to occur, a coronal mass ejection - a cloud of plasma and magnetic field - or a high-speed stream of solar wind usually needs to be directed towards the Earth.

When these streams interact with the Earth’s magnetosphere, they can cause disturbances that are recorded by geomagnetic observatories.

This is why a powerful solar flare does not necessarily mean that a geomagnetic storm will follow.

How Do We Read Values from 0 to 9?

The Kp scale is quasi-logarithmic. This means that the increase from Kp 8 to Kp 9 is considerably greater than the increase between lower values.

Kp 0 to 3 - Green zone: Quiet to slightly disturbed field

The magnetic field is stable. These are normal, everyday values and no geomagnetic storm is taking place.

Kp 4 - Yellow zone: Active geomagnetic conditions

The magnetic field is more disturbed, but according to NOAA’s scale, geomagnetic storm conditions have not yet been reached. Some sensitive people may report mild fatigue or a headache.

Kp 5 or higher - Red zone: Geomagnetic storm

At Kp 5, the geomagnetic storm scale used by the US National Oceanic and Atmospheric Administration, or NOAA, begins.

Geomagnetic Storm Levels

Kp index	NOAA level	What may be observed
Kp 5	G1 - Minor storm	Weak fluctuations in power grids and minor effects on satellite operations are possible. Auroras are usually observed at high latitudes.
Kp 6	G2 - Moderate storm	High-frequency radio communication may be affected, and changes in the movement of satellites in low Earth orbit are possible.
Kp 7	G3 - Strong storm	Temporary problems with satellite navigation, including GPS, radio communication and the management of electrical power systems may occur.
Kp 8	G4 - Severe storm	More serious disruption to radio communication, navigation and satellite operations is possible. Auroras may appear at unusually low latitudes, including over Bulgaria.
Kp 9	G5 - Extreme storm	Serious problems, outages and transformer damage may occur in some power grids. Satellite navigation and radio communication may be disrupted for longer periods.

These levels primarily describe the possible effects on technological systems, satellites, radio communication and power grids. They do not indicate a corresponding level of danger to people.

Can We See the Aurora from Bulgaria?

During severe and extreme geomagnetic storms, the aurora may be visible much farther away from the polar regions, including from Bulgaria.

However, a high Kp index does not guarantee that the aurora will be visible. Other important factors include:

• the direction and strength of the interplanetary magnetic field;
• the timing and duration of the storm;
• cloud cover and light pollution;
• the location from which we are observing.

Sometimes the reddish glow of the aurora is more visible in a photograph taken with a phone or camera than it is to the naked eye.

Where Can We Track Geomagnetic Storms in Bulgaria?

The term “real time” is relative, as the traditional Kp index covers three-hour periods. Some websites display preliminary or forecast values, which may later be updated.

To understand the current state of the magnetic field over Bulgaria, it is best to use local data. The global Kp index represents average planetary activity, but conditions can vary between different regions.

1. NIGGG-BAS

The most suitable source for local geomagnetic conditions in Bulgaria is the website of the National Institute of Geophysics, Geodesy and Geography at the Bulgarian Academy of Sciences, or NIGGG-BAS.

The Bulgarian Academy of Sciences operates its own Geomagnetic Observatory in the town of Panagyurishte, where the magnetic field is measured every 15 minutes. The website includes a graph of the local K index for Bulgaria. Green indicates quiet conditions, while yellow or red shows increased geomagnetic activity.

The institute publishes estimated local K indices from the Panagyurishte Geomagnetic Observatory, as well as daily magnetograms.

On the website, http://www.geophys.bas.bg/, look for the following sections:

• “Real-time information”;
• “Geomagnetic activity”;
• “Estimated local K indices”.

The local K index is particularly useful when you want to understand the activity measured in Bulgaria rather than relying only on the global planetary value.

2. NOAA Space Weather Prediction Center

NOAA provides:

• the current planetary Kp index;
• a three-day forecast;
• warnings of expected geomagnetic storms;
• information about the solar wind and coronal mass ejections.

It is one of the main international sources for monitoring space weather.

3. GFZ Helmholtz Centre for Geosciences

The German GFZ Helmholtz Centre for Geosciences is the official producer of the Kp index. Its website provides the latest recorded values and forecasts.

It is a useful source when you want to check the primary data for the planetary index.

4. Magnitni-Buri.BG

If the BAS website appears too technical or difficult to interpret, you can also use magnitni-buri.bg.

The website combines information from BAS and the US agency NOAA and presents it in a clear and accessible visual format, together with a three-day forecast.

5. Mobile App

To access the information directly from your phone, you can download the “Геомагнитна Прогноза БГ” app from the App Store or Google Play.

It shows geomagnetic activity over the past few hours and provides a short-term forecast using data from NIGGG-BAS. The app has been developed independently and is not an official application of the Bulgarian Academy of Sciences.

Do Geomagnetic Storms Affect Our Health?

Some people report headaches, changes in sleep, fatigue or fluctuations in blood pressure during periods of increased geomagnetic activity.

Scientific studies have investigated possible links between geomagnetic activity and certain physiological indicators. However, the available results remain limited and are not always consistent. An observed statistical association does not necessarily prove that a geomagnetic storm is the direct cause of a particular symptom.

The Kp index should therefore not be used as a medical indicator or as an explanation for every health complaint.

What Should We Do If We Feel Unwell?

There is no special routine that has been proven to “protect” people from a geomagnetic storm. We can, however, follow the usual habits that support general wellbeing:

• drink enough fluids;
• eat regular, balanced meals;
• limit alcohol if we are not feeling well;
• get enough sleep and rest;
• check our blood pressure if we commonly experience problems with it;
• take prescribed medication according to our doctor’s instructions.

Taking a break from phones, computers and other screens may help with fatigue, eye strain or difficulty falling asleep, but it does not stop or neutralise a geomagnetic storm.

In the event of a severe or sudden headache, chest pain, difficulty breathing, weakness, numbness or other unusual symptoms, we should not wait for the storm to pass. We should seek medical advice.

How Can We Use the Kp Index Sensibly?

The Kp index is a useful tool for monitoring space weather. It helps us understand when the Earth’s magnetic field is quiet and when it is experiencing significant disturbances.

When checking forecasts:

• compare the global Kp index with the local K index for Bulgaria;
• distinguish between measured values and forecast values;
• check when the information was last updated;
• do not assume that every solar flare is a certain sign of an approaching geomagnetic storm;
• use official sources when unusually high values are reported.

Most importantly, treat the Kp index as an indicator of the condition of the Earth’s magnetic field, not as a medical diagnosis.