Disturbance Storm Time Index (Geomagnetic)...

... The measurement of which gives information about the strength of the ring current surrounding the earth. This in turn provides information about the affect solar storms might have on the Earth's magnetic field such as the occurence of aurorae and subsequently other outcomes for the Earth in extreme cases.
I have read where the limit of the dst Index is -2500 nT.
Does anyone know why this is the limit? If it is.
Could this be when a storm is so powerful that it destroys the ring current and the Earth's magnetic field?
Apologies if this has already been addressed in a previous thread.

Terra Australis
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Thanks Cat (reliable as ever) :)
I realise the Halloween storms are the largest in recent history with dst index at -500 nT nowhere near -2500 nT I mentioned.
I'm not sure if there is an estimated value for dst index of the storms associated with the Carrington event.
Certainly to reach -2500 nT is purely hypothetical and truly I hope we never find out. I just wonder why this is the limit.
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"Science begets knowledge, opinion ignorance.
The ring current lies at a distance of approximately 6,200 to 37,000 miles (10,000 to 60,000 km) from Earth. The ring current was hypothesized in the early 20th century to explain observed global decreases in the Earth's surface magnetic field, which can be measured by ground magnetometers.19 May 2016

Van Allen Probes Reveal Behaviors of Earth's Ring Current

Cat :)
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"Science begets knowledge, opinion ignorance.
The Disturbance Storm Time Index
The Dst index is an index of magnetic activity derived from a network of near-equatorial geomagnetic observatories that measures the intensity of the globally symmetrical equatorial electrojet (the "ring current").

Disturbance Storm-Time (Dst) Indices | NCEI
https://www.ngdc.noaa.gov › stp › geomag › dst

Disturbance storm time index - Wikipedia
https://en.wikipedia.org › wiki › Disturbance_storm_ti...

The disturbance storm time (Dst, Kyoto Dst) index is a measure in the context of space weather. It gives information about the strength of the ring current ...

Cat :)
Concerning the limit of -2500 nT for dst I have read that this is likely a theoretical figure.
Early research classified the Carrington storms as being around ~ -1700 nT but later investigations have them at around ~ -800 nT, others may have read lower estimates, of course the exact figure may never be known. To compare, the Halloween storms have been listed as -500 nT but I have read lower figures for those as well ~ -700 - 800 nT. It all depends on the modelling and the math. Most large solar storms have been studied.
Further I have read of at least two things that come into play during a solar storm which determine how negative the dst becomes.
The ring current, which is an electric current carried by charged particles trapped in the Earth's magnetosphere (which overflow from the Van Allen belt)
The cross polar cap potential difference. Ionospheric electric potential in the polar region mostly generated through the interaction between the solar wind and the magnetosphere. It is this polar cap potential difference which results in ionospheric plasma flow by which (under extreme and unlikely conditions) may become saturated due to the overabundance of solar wind particles. It may be this that is the limiting aspect of dst.
During a solar storm the ring current expands, the effect of this is to suppress the Earth's magnetic field. The more negative the dst, the more the magnetic field is weakened allowing solar material to enter in. When the storm subsides the magnetic field bounces back again.
Research in the area of Sun - Earth interaction is ongoing, far from complete and not fully understood.
(I wrote this in another forum I thought I would include it here)