[PPRAANet] Propagation Info

[W0rw at aol.com]

Speaking of Propagation did you see the Prop discussion from Paul na5n
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Bill, VA3OL / VE3KGJ writes: 

 has anyone actually charted the SFI, A and K indexes to try and understand 

 them?


There was a relatively small sized long duration C-class flare around

1700 UTC on May 6.  This flare produced a coronal mass ejection (CME).

Because this particular flare was located near the center of the sun,

the outflow of mass and gasses, and the shockwave, was directed at earth.

Not all flares and CME's will effect the earth ... only those that are

"geoeffective," or, those whose trajectory is pointed at the earth. 


The SEC NOAA site reported this flare produced a type II sweep measured

at about 1250 km/sec.  A type II sweep is caused by the shockwave of the

solar flare punching through the magnetic field lines of the sun, and

in so doing, produce bursts of radio energy.  The farther out the shock-

wave travels, the LOWER the frequency of the bursts.  Scientist measure

the time it takes for the bursts to travel from one frequency to

another.  This tells them the speed of the shockwave.  In this case, it

was determined to be about 1250 km/sec. 


Let's do some math. 


1250 km/sec., divided by 1.6 = 781 miles per second.

Times 360 = 2,812,500 miles per hour.

However, the shockwave slows down as it travels away from the sun and

rides along with the solar wind.  The average speed tends to be around

75-80% of the Type II measured speed.

So, multiply 2,812,500 mph times 80% = 2,249,600 mph 


The earth is approximately 93 million miles from the sun.  Divide this

by 2,250,000 mph = 41 hours.  This is the APPROXIMATE travel time of the

CME from the flare to hit the earth and trigger a geomagnetic storm. 


The flare occured about 1700 UTC May 6.  Adding 41 hours, or 7 hours

less than two days, would be ABOUT 1000 UTC May 8.  The solar wind and

proton monitors on the SOHO satellite recorded the shockwave at 0907 UTC

on 8 May.  Because SOHO is far out in space at the Lagrange point, it

gives us about 15 minutes warning before the shockwave hits our 

magnetosphere.  So, the shockwave hit the earths magnetic field about

0920 UTC May 8, or about 40 minutes before we calculated using the above.  

Not bad, aye? 


The shockwave that hit us was about 850 km/sec. with a density of about

10 particles per cubic cm., or fairly dense (normal is 1-2 p/cm^3), or,

about the density of a light dust storm on earth.  The "normal" solar wind 

is about 350 km/sec.  Thus, we got hit with something similar to a desert

dust storm traveling at 2 million miles per hour - and you're complaining

that poor old earth reacted when she got hit in the face by that? :-) 


This tremendous shockwave compressed the earth's magnetic field, generating

huge currents via the dynamo effect (our wiggling magnetic field moving

about the earth's metalic core).  Tens of thousands of amps of electrons

are moving along our magnetic field lines directly above our heads ...

naturally generating GOBS of white noise in the HF bands centered around

10 MHz.  That is, above 10 MHz, the intensity of this noise is LESS, and

below 10 MHz it is GREATER.  This is why a geomagnetic storm produces

more noise on 40M than it does on 20M, and hardly noticed much above 20M. 


> I see a SFI of 100 and an A of 46 , K 2 and figure it is a bad report but 

> the forcast says conditions are normal.


The SFI (solar flux index) is merely a measure of the ionizing radiation

received from the sun.  It is related to our daily MUF, and how reflective 

the E and F layers are for that day ... meaning, how reflective the E/F

layers are to signals around the MUF.  Thus, SOLAR FLUX tells you what

is happening on 30M, 20M and above.  Since 40M is ALWAYS below the MUF,

this band (and 80, 160M) are NOT effected by the solar flux.  The solar

flux can be 50 or 500, and 40M will be pretty much the same.  Please,

quit citing the SFI as an indicator of how tonight's 40M fox hunt will be.

Absolutely unrelated.  If that don't make sense, look at it this way.

40M is generally a NIGHT-TIME BAND.  At night ... THERE IS NO SOLAR 

RADIATION HITTING ANYTHING ABOVE YOUR HEAD.  Right?  That lack of solar 

flux, or lack of ionizing radiation, is why the D-layer goes away at night.

So, what does the solar flux have to do with the night time bands again?

Nothing! 


When the shockwave hit earth and sent our magnetic field into this wiggling

motion for several hours, earthborne instruments measure the amount of this 

geomagnetic disturbance.  This is the source of the K-INDEX, a scale

from 1-9.  The K-Index is the AVERAGE disturbance measured over the past

3-hours by numerous reporting stations.  Keep in mind, the stations facing 

the sun will see more disturbance of the geomagnetic field (where the

shockwave just hit) than stations on the back (dark) side of earth, where

the magnetic field lines are not as disturbed (they are NOT being fueled

by the solar wind).  The K-index is an average of all of these reporting

stations.  The CURRENT K-index is more or less telling you what is happening 

on planet earth RIGHT NOW (at least, the past 3 hours). 


At the end of the UTC day, all of the K-indexes from around the planet are 

added up to form the A-Index, or Ap, the PLANETARY A-index.  Thus, (and

this is a biggie) ... the CURRENT A-INDEX tells you what planet earth

experienced YESTERDAY ... not right now. 


So ... conditions are nice (say K=2, A=8) and a shockwave hits.  K=5 or 6

for a major storm, 7,8,9 for a severe geomagnetic storm.  But ... the

A-Index will remain at 8 for the remainder of the day, while every 3

hours, the K index is bouncing all over the place.  Then ... the storm

is over, K=2.  The next day, you get on your trusty computer and check out 

conditions. K=2, A=46.  Yikes, conditions are awful.  NO THEY ARE NOT!

K=2 means the CURRENT geomagnetic field (read: 10MHz and below) is normal.  

The A=46 is what happened to our geomagnetic field YESTERDAY. 


The daily solar flux is the ionizing radiation being experienced TODAY.

It effects 10MHz and above, up to the MUF. 


The K-index is a measure of our magnetic field.  The current K-index is

CURRENT conditions, being averaged over the past 3 hours.  It tends to

reflect what HF noise levels are, below about 10 MHz. 


The A-Index is a measure of YESTERDAY'S disturbances to our magnetic field. 


The solar flux and K and A-indices are not really related.  One's an

apple, the other is an orange. 


> I just don't understand when is the best day that I should be on the 

> air; so I look to the propogation forecast. and it confuses me.


The most disruptive time for QRPers is during a geomagnetic storm.  This

produces huge noise levels on the lower bands, gobbling up your signals

into the higher than normal noise floor.  For operating 20M during the

day, you are at the mercy of the solar flux.  For operating 30M and

below, you are at the mercy of our magnetic field, i.e., the K-index. 


When a solar flare occurs, it generally does NOT effect HF conditions

until the shockwave arrives, then keeps things pretty noisy for many hours.

Thus, the best time to operate is right after a solar flare, and right

after the geomagnetic storm subsides.  Using the example above, or the

forecasts from NOAA, you can calculate about when the geomagnetic storm

will occur, and likely mess up conditions for the next 12 hours. 


However, geomagnetic storms are also triggered by other things, such as

coronal hole streams and magnepause crossings, often more difficult to

predict.  Weather, humidity of our upper atmosphere, the gazillions of

watts of 60Hz power being dumped into our environment by power lines and

machinery, etc. all contribute to the noise levels on HF as well.  You

can not blame the sun on all of it, all of the time.  Those things are

not measurable, and thus not reflected in the K or A indices. 


Hope this helps, Bill, and others, to explain what these things mean.  It's

only the tip of the iceberg. This, of course, is similar to what I will be 

talking about at FDIM in Dayton next week.  Plan to attend and you can ask 

all the questions you want, plus go home with a really nifty 8-page

handout in the compendium.  Perhaps the compendium will be made

available after FDIM (I just don't know), as it will be full of very

useful information from a host of many of the top QRPers today on a wide

variety of subjects. 


The ARRL Handbook does a reasonable job explaining the mechanics of HF

propagation, in terms of the D, E and F layers, daytime this and nighttime

that.  However, there is nothing available that I know of that explains

the recent advances and understanding of solar physics, and how solar

flares and CME's effect earth, except in the professional astrophysics

journals.  I attempted to explain it in my FDIM compendium paper, and

will continue to explain it, time permitting, on qrp-l. 


72, Paul NA5N