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What indicator to tell the current sign of polarity for (CH HSS)?


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Referring to following articles, I would like to know on what indicator to tell the current sign of polarity for (CH HSS), Positive or Negative at current status and forecast status.

Does anyone have any suggestions?
Thanks in advance for any suggestions



Geomagnetic field activity is expected to be reach G3 (Strong)
geomagnetic storm levels on 09 May and G1 (Minor) storm levels on 10
May due to the influence of a negative polarity coronal hole high
speed stream (CH HSS). G1 (Minor) storm levels are likely on 20 May
due to the influence of a positive polarity CH HSS as well as on 29
May and 04 Jun due to the influence of negative polarity CH HSSs. 
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  • 2 months later...
Guest EI2KK

Hi there..

I am trying to analyze solar wind's parameters from radio amateur perspective (not a visual aurora).

I understand all you wrote above about Phi and polarity, no problem to calculate Phi using Bx and By, results are the same as on NOAA chart


Can't find clear info how Phi affects aurora..


What Phi gives better chance for aurora - 90 to 270 (-Bx) or 0-90 and 270-360 (+Bx)?

Better if Phi is closer to 180 (or 0) or doesn't matter as long as is between 90 and 270? (or 270 and 90)

Does ratio of Bx to Btot matter or not? (i.e. Phi 170 but small vector BxBy big vector Bz)



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The Phi angle has no influence on auroral activity. It just shows us if the Sun's magnetic field at Earth points away or towards us. The phi value can be used to know if there was a solar sector boundary crossing but it does not have any influence on the geomagnetic activity at Earth. Solar sector boundary crossings are sometimes associated with slighly elevated solar wind/IMF conditions but that has nothing to do with the Phi itself. That the Phi angle has a direct influence on the aurora here is a hard to crack myth that keeps popping up occasionally on some social media unfortunately.

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Guest EI2KK

Thanks Marcel,

Yes, there is a lot of myths unfortunately.. I've seen 'somewhere' a theory says one of polarities provides better connection between Sun-Earth magnetic fields and more particles are carried by the solar wind, but never found anything to proove or even to support such theory.

I've observed yesterday's changing of polarity and it was followed by increase of solar wind density, but one separate observation proves nothing :)


Many Thanks


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I also seen it somewhere... multiple somewheres actually. Even tried to explain this ''somewhere'' and got my post deleted for no apparent reason... but that's another story. :P

NOAA often talks about the Phi angle as negative (towards) or positive (away) and this is confusing for some people who mix it up the with the Bz (north-south direction of the IMF) which has an important influence on the geomagnetic activity where the Phi angle does not have any influence. It is important for people to understand the difference between the Phi and the Bz. If they think they understand it but in reality they do not, there is a real risk that they will inform other people incorrectly and this will only create more confusion in the long run. 

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Guest EI2KK

Yes.. I understand difference betwen Bz and Phi - that is clear

... but have a look at the last Weekly Highlights and Forecasts from NOAA:


The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at normal to moderate levels for the majority of the
period with high levels from 05-15 August due to recurrent CH HSS

Geomagnetic field activity is expected to reach active levels on
25-27 July due to lingering CME effects and the arrival of a
positive polarity
Active to minor storm levels are expected
on 29 July, 03-05, 08, and 10 August due to recurrent CH HSS
. Mostly quiet to unsettled conditions are expected for the
remainder of the period. 

It looks like CH HSS can affect geomagnetic field - this is long-term prediction, nothing mesured @ DSCOVR so has to be related to CH HSS polarity...

I have not enough data but given above, 'arrival of a positive polarity CH HSS' can affect geomagnetic field it sounds interesting..

Does the positive polarity cause geomagnetic activity or only the transition from negative to positive?

Predicted period is between 5th and 15th August - looks like it is not the transition which will occur around 1st August.



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They just mean they expect an increase in geomagnetic activity due to the arrival of a coronal hole high speed solar wind stream. That's it's a positive polarity CH HSS is extra information unrelated to the expected geomagnetic increase. A sector boundary crossing can be accompanied by a slight change in the solar wind environment but it is usually minor at best.

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  • 4 weeks later...

Theta or Beta??

 There NOAA explains:

(theta) = cos-1(BZ/B)

So,  (BZ/B) can have values between -1 and 1, that means Theta can have a value between 0deg and 180deg..

(0deg if (BZ/B) = 1; 90deg if (BZ/B) = 0; 180deg if (BZ/B) = -1)


On the chart Theta has values between -90deg and 90deg  - it seems to be a Beta..

 (beta) = 90 - theta degrees


Looks like a bug?




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