Space Weather
IMF Bt — live and explained
The total strength of the Sun's magnetic field reaching Earth, combining all three directional components into one number.
Current IMF Bt
Updated every few minutes from live NOAA data.
Source: NOAA DSCOVR/ACE
Why it matters
Bt sets the ceiling on how strong a geomagnetic effect is even possible. A perfectly southward Bz can't drive much of a storm if the overall field is weak — the strongest storms combine a high Bt with a strongly negative Bz, meaning nearly all of that strong field is oriented the way that connects with Earth.
Normal range
Typical quiet-time Bt sits around 3-6 nT. Elevated values above 10 nT are notable, and during major storms Bt has been observed climbing past 20-30 nT, occasionally higher during extreme events.
What today's value means
Waiting for live data to interpret…
What is IMF Bt?
The interplanetary magnetic field (IMF) is the Sun's own magnetic field, stretched out and carried through space by the solar wind. It has three directional components — Bx, By, and Bz — and Bt is their combined total strength, calculated as the square root of the sum of their squares. Typical quiet-time values sit around 3-6 nT; during a strong storm, Bt can climb past 20-30 nT.
Why Bt matters alongside Bz
Bz gets most of the attention because its direction determines whether the solar wind connects easily with Earth's magnetic field. But Bt sets the ceiling — even a perfectly southward Bz can't drive a major storm if the overall field is weak. The strongest geomagnetic storms combine a high Bt with a strongly negative Bz, meaning nearly all of that strong field is pointed the "right" way to connect with Earth.
FAQ
What's the difference between Bt and Bz?
Bz is the north-south component — its sign (positive or negative) determines whether conditions favor aurora. Bt is the total field strength regardless of direction.
What's a "high" Bt value?
Quiet conditions typically run 3-6 nT. Values above 10 nT are elevated; above 20 nT is associated with strong geomagnetic storms.