[PPRAANet] X1.5 flare/Aurora

[W0rw at aol.com]

Gang,

The sun produced another major flare tuesday afternoon, an X1.5 from

1919-1927 UTC.  SEC/NOAA has not yet released the estimated velocity of the 

shockwave for determining when it WILL arrive at planet earth (not IF).  The 

position of the flare, region 0808, is approaching the center of the sun, 

and at it's current position, we will receive pretty much the full blast 

from the shock wave.  It WILL trigger a major to severe geomagnetic storm in 

about a day and half (like we're not used to that already this week!). 


The energetic electron and proton data is also missing, since the 

instruments that measure this, such as the SOHO satellite, got thrown into 

saturation by this flare.  The instruments are currently off line.  However, 

ground-based instruments are showing very high attenuation to HF signals due 

to the D-layer.  This means the D-layer definitely got highly ionized from 

the flare.  There is an HF blackout in effect right now up to about 20MHz, 

which will likely begin to recover around 2300 UTC. 


The good news, is once the D-layer begins to recover for normal HF 

propagation (about 2300 UTC), the D and E layers will remain extra ionized 

until local sunset.  This will enhance skip propagation and the MUF will be 

raised, perhaps for 15M openings, until a bit past sundown.  This leaves a 

little time for east coast QRPers to do some DX hunting, and a couple more 

hours for those on the west coast before the sun goes down.  This temporary 

boost to the reflectivity of the D/E layers, combined with the normal 

gray-line propagation at sundown, could lead to some interesting DX on 20M 

and 15M (if open), including north-south paths. 


Flares are definitely disruptive to HF propagation, but they do generate 

short windows of opportunity for good DX, such as described above.  A few 

hours after a strong flare until local sundown is one of those windows. 

Part 2...
The most promising prospects for aurora (northern lights) is when a 

shockwave from a major flare hits the earth around midnight, YOUR local 

time, give or take a couple of hours.  All the electrons and protons riding 

along with the shockwave get deflected around earth by our magnetic field.  

But, much of it gets trapped in our polar region, fueling dramatic auroral 

displays.  The shockwave blows it right over the polar region in the 

opposite direction from the sun and into the middle latitudes.  The exact 

opposite of the sun is local midnight.  If the shockwave hits around your 

local midnight, these particles and the aurora get blown right over your 

head.  This may be the case with todays X1.5 flare. 


There are many variables trying to figure out when a shockwave will hit 

earth.  This is why SEC NOAA seldom publishes a predicted time.  However, 

QRPers can calculate it with a few hours accuracy as follows: 


SEC NOAA estimates today's X1.5 flare CME shockwave at 1500 km/sec.  As the 

shockwave travels away from the sun, it looses about 80% of it's velocity by 

the time it hits earth.  80% x 1500 km/sec. = 1200 km/sec. 


(Actually, it looses about 65-70% of it's velocity, but looses only about 

80% for estimating what the AVERAGE travel speed generally is). 


1200 km/sec = 4,320,000 km/hour (4.32 million km/hour).

The earth is about 150 million km from the sun.

Thus, 150 million km divided by 4.32 million km/hour of the shockwave yields 

a travel time of ABOUT 35 hours, or 1 day and 11 hours. 


The X1.5 flare occured on 13 SEP at about 1900 hours UTC.

Adding one day is 14 SEP at 1900 UTC.  Adding 11 hours is 14 SEP 2900 UTC,

or 15 SEP at 0500 UTC.  This is LOCAL MIDNIGHT in the midwest and west 

thursday night. 


If indeed the shockwave hits around 0500 UTC SEP 15, and the shockwave 

arrives around 1000 km/sec., it could produce nice aurora's in the upper 

tier of states and perhaps even farther to the south.  And, if it doesn't 

produce visable aurora over your head, it will certainly trigger one heck of 

a geomagnetic storm! 


For those of you night-owls interested in seeing possible aurora, checkout 

this website: 


http://umtof.umd.edu/pm/   ... and scroll down a bit to the plots 


This is the proton monitor on the SOHO satellite.  When the top velocity 

trace suddenly jumps to 800 km/sec. or more, the shockwave just arrived at 

the SOHO satellite.  It hits earth about 15 minutes later.  The higher the 

velocity of the shockwave, and the higher the particle density, (2nd trace), 

the higher the chances of auroral displays.  Also, the higher the intensity 

of the geomagnetic storm.  And lastly, if and when the 4th trace, the ANGLE, 

dips negatively, the intensity of the aurora is generally greater.  If all 

of this occurs at your local midnight to boot, the maximum effect of the 

storm and northern lights will be realized.  The only question is how far 

south the aurora is pushed as to whether you will beable to see it or not. 


This website:

http://www.sec.noaa.gov/pmap/index.html

shows approximately the extent of the current aurora. 


Looking at http://umtof.umd.edu/pm/ right now, you will clearly see what a 

shockwave looks like ... the one that hit us yesterday and triggered the 

severe geomagnetic storm, K>7 and a couple of minor ones since.  Note that 

it hit 12 SEP about 0800 UTC.  This blew nice aurora (local midnight) all 

over the uninhabited north Pacific :-( 


This is not an exact prediction, but more to show the methodology.  It does 

say *if* it does hit around midnight, it could be a nice display for some, 

likely pressing into at least the northern U.S.  Once the shockwave arrives, 

it takes several tens of minutes for the aurora to peak over your head if 

it's going to. 


Please, don't take the family out, drive 150 miles to some dark spot and 

camp the night looking for aurora because I said so.  Watching the above 

website for the arrival of the shockwave and auroral map is much easier!!!  

Then, stick your head out the back door every 10-15 minutes for any sign of 

aurora.  Then too ... if you're working 40M CW at 2300 local and the band 

just goes dead with sudden S9 noise, you can also bet the shockwave just 

arrived! 


For information purposes only.  Not approved by FEMA. 

Paul NA5N 
via  w0rw