Hemispherical Power Historical

[M42Sparks]

Okay so i only recently started to keep an eye on these readings. The overal average seems quite high. Is there a rational acceptable normal level. I seem to recall it barely being 15GW per Hemisphere a year or so ago.

Edited April 29, 2023 by M42Sparks
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[Philalethes]

4 hours ago, M42Sparks said:

Okay so i only recently started to keep an eye on these readings. The overal average seems quite high. Is there a rational acceptable normal kevel. I seem to recall it barely bei g 15GW per Hemisphere a year or so ago.

I just searched around a bit and couldn't immediately find any historical data; there was supposed to be some on NOAA's site, but I could only find recent values.

I would guess, though, that the values are not that high compared to historically. A year ago we were still not that far into the cycle, and the cycle has not been that strong overall either, so lower average values at that point is what I'd expect. It's also easy to get the average wrong when eyeballing it due to e.g. higher values being more noticeable, low and sporadic sampling rate, and so on.

If someone knows where to find historical data on it (if it exists), that'd be great, then we could compare it more directly.

[hamateur 1953]

You might try GFZ in Germany as a suggestion.  

2 hours ago, Philalethes said:

I just searched around a bit and couldn't immediately find any historical data; there was supposed to be some on NOAA's site, but I could only find recent values.

I would guess, though, that the values are not that high compared to historically. A year ago we were still not that far into the cycle, and the cycle has not been that strong overall either, so lower average values at that point is what I'd expect. It's also easy to get the average wrong when eyeballing it due to e.g. higher values being more noticeable, low and sporadic sampling rate, and so on.

If someone knows where to find historical data on it (if it exists), that'd be great, then we could compare it more directly.

A note of caution if pulling data: I had difficulty with their ftp server. possibly because I am not a registered user.  Hopefully ya find whatcha are after.  Mike/Hagrid. 

Edited April 29, 2023 by hamateur 1953
ftp issues

[Philalethes]

3 hours ago, hamateur 1953 said:

You might try GFZ in Germany as a suggestion.  

A note of caution if pulling data: I had difficulty with their ftp server. possibly because I am not a registered user.  Hopefully ya find whatcha are after.  Mike/Hagrid. 

I used their data recently to plot Kp- and Ap-indices, but as far as I can see they don't have any data for hemispheric power directly; but then again it seems from reading about it for a bit that HP is typically derived in one way or another from other data, and I see SWL and NOAA uses the OVATION model based on data from the DMSP satellites, while I found some indications of other satellites being used too (POES historically, MetOp more recently), not sure if that's in addition to the DMSP data or for separate models.

That all sounds a bit too arcane for now if you ask me, and that data does not seem particularly accessible based on looking around for it a bit. Luckily this presentation has a neat little formula to estimate the HP from the Kp-index:

Using that we can use that GFZ data after all; neat. It's naturally going to be a simplistic estimate, but it should serve well for this purpose. The fact that such an association exists also hints to the fact that any long-term changes to HP would show up in the Kp-index as well. It does make sense, considering how closely related one would expect those to be, but I'd be interested if anyone with more insight knows if perhaps there are conditions under which they'd diverge. Anyway, using that formula and plotting the estimated HP, first from around last minimum:

Here we see that activity seems to have been picking up over the past few years since minimum, which is to be expected as we approach maximum.

Plotting all the way from 1932 we see that there doesn't seem to be anything remarkable about current conditions, and that we're far from the average levels of most previous recorded cycles in that time period:

It's a bit messy to plot so many data points, but at least you can see the troughs where the minima are located for a lot of the cycles. Ideally it'd probably be best to smooth out the data a bit, but it's fine for an overview.

Here are the same plots using a moving average to smooth, the same as the boxcar function used to smooth sunspot numbers (except without the tapering, which becomes rather meaningless when smoothing so many values); first the same as the first one, since around the start of SC25 to now, with ~1 month of smoothing:

And the latter longer one, with ~1 year of smoothing:

In these plots the trends become a lot clearer. We see that the average HP has indeed been rising over the past few years, but that we're still at historically low values overall.

Edited April 30, 2023 by Philalethes
added smoothed plots

[M42Sparks]

Wonderful answer in technical terms but i was hoping for an easier to confirm the "Normal" range.

[Philalethes]

1 hour ago, M42Sparks said:

Wonderful answer in technical terms but i was hoping for an easier to confirm the "Normal" range.

The bottom two plots above should give good indications of what the normal ranges are. As you can see in e.g. the very bottom one, for most of the time we've recorded the Kp-index, which is a good estimate of hemispheric power, it's been significantly higher on average; our current "high" is just barely higher than the "low" of the lowest previous cycles (except for that of SC24, which brought exceptionally low activity). If considering the overall records, it would be fair to say that a normal range would be something like 20-50 GW on average.

Edited May 11, 2023 by Philalethes