A
TOMSPHERIC
W
EATHER
E
LECTROMAGNETIC
S
YSTEM FOR
O
BSERVATION
M
ODELING &
E
DUCATION
The AWESOME ELF/VLF Receiver
Stanford University
TUTORIAL
“Solar Flare Tutorial”
By Sheila Bijoor, & Benjamin Cotts
The following steps give instructions for downloading and viewing data from an AWESOME VLF
receiver at the Palmer Station in Antarctica, on December 6, 2006. A large solar flare was
detected on this day.
Step 1. View the data in Matlab
1) Open Matlab and set the current directory to the Solar Flares Tutorial Folder
2) Type command NarrowQPlot in the command window
A window should prompt you to browse for your data files.
3) Select the file “PA061206173100NLK_009A.mat,” and when prompted a second
time, select the file “PA061206173100NLK_009B.mat.”
As with your site’s data files, the filenames indicate information about the data:
PA – Station ID [Palmer, Antarctica]
06 – Year [2006]
12 – Month [December]
06 – Day [06]
173100 – Start Hour Minute Second [17:31:00]
A, B – The A and B indicate that these are low-resolution narrowband files
The “NLK” in the file name indicates that the recorded data is the NLK transmitter
frequency. The NLK transmitter is located at Jim Creek, Washington and operates at
24.8 kHz.
4) You will now have produced the figure below:
You can save this image by clicking File Æ Save on the figure menu. Note that there
are three options for dealing with the data processing of the phase using the function
removePhaseSlope.m which is included in the NarrowQplot function, therefore if the
phase plot in your figure looks different it is probably because different options were
used in making this figure than you used.. The default option is to unwrap the phase
and then to find a consistent slope to the phase and subtract it out. The second
option is to remove all jumps in the phase which are larger than some threshold and
then to subtract the phase (this is the option used in producing this plot). The third
options is just to unwrap the phase. Try changing the third variable in the function
call to removePhaseSlop on like 71. See how it changes the plot. You can also
comment out this line altogether to see what the raw data looks like. Notice in this
case that it can be very difficult to see any phase deviations because of artificial
phase wrapping and lost samples. Note that the settings used for creating all of the
figures in this exercise are: removePhaseSlope(data,freq,0,40).
5) Now produce the same plots for Palmer data at the NLM transmitter frequency by
repeating steps 2 and 3 with files “PA061206173100NLM_011A.mat” and
“PA061206173100NLM_011B.mat.” The NLM transmitter is located in LaMoure,
North Dakota and operates at 25.2 kHz.
Your plot should look like the following:
Step 2. Identify the Solar Flare
In the amplitude and phase of both plots, you should notice the sudden jumps in the
data. You may be interested to learn that this event corresponds to large solar flare
activity that occurred on the same day. A solar flare is a powerful expulsion of high
energy particles and electromagnetic energy from the sun (at energies ranging from
radio waves to gamma rays). Solar flares usually occur in regions around sunspots, and
are powered by the sudden release of magnetic energy stored in the corona. As the
high energy particles and intense radiation from the flare impact the ionosphere they
cause exceptionally high levels of ionization. When this occurs the reflection altitude of
the subionosphericlly propagating VLF transmitter signal is decreased and the
ionosphere becomes a 'better reflector' of VLF energy. The result is the significant
increase in amplitude of the received signal, and a phase advance (meaning a shorter
overall path length) as seen in the figure above.
The picture below shows the GOES satellite image of the flare. The faint ring you can
see is the outline of the sun. Because the sun is so bright, it is impossible for many
instruments to image it directly. They therefore use a type of covering for the lens that
blocks out the sun itself, and the picture shows only the outermost portion of the sun
where the solar flares can be seen. In this picture you can see a solar flare in the lowerleft hand region.
GOES Satellite Image of Solar Flare on 2005/09/07
This graph shows the X-ray counter aboard the GOES satellite. Notice the times of the
peaks in X-ray activity, and compare to the VLF Data. you just generated.
GOES Satellite X-Ray Data
GOES Event Listing for Period: 6-DEC-06 through 6-DEC-06 23:00:00
The flare classifications are as follows:
B class flares: These are the smallest flares and occur often.
C class flares: These are the next strongest flares, though they are usually still
small.
M class flares: Are larger yet and occur less frequently.
X class flares: These are huge and easy to detect. If aimed at the Earth, they
can cause major disruptions in communications, radio, and power grids.
Does the VLF data match up with the solar flare data from GOES? Why are there 3
peaks—do these each correspond to separate flares? What class flares were these?
How do the flare signatures differ at different sites for the same solar flare event?
Step 3. Download and view data from Yakutat, a VLF site in Alaska. Yakutat is at Lat/Lon:
59.8° N 139.6° W.
1) Locate Yakutat, Alaska on the maps below, which display illumination from sunlight
on the day on which the solar flare occurred. Do you think that the effects of the solar
flare would be visible in the Yakutat data?
2) Produce the same plots as you did for Palmer data for the Yakutat station at the NLM
and NLK transmitter frequencies by repeating steps 2 and 3 above with files:
a. YK061206010000NLK_006A.mat
b. YK061206010000NLK_006B.mat
Your plots should look like the following:
3) Calculate when you would expect to see the solar flare in the data above. The solar
flare jumps in the Palmer data are especially visible at ~18:31:00 UT. Zoom in on this
area in the Yakutat data using the magnified tool in the figure window.
4) Do you see any evidence of the solar flare in the Yakutat data? Does this match your
expectation of whether or not you would see the solar flare? How can you explain
these results?
Illumination from Sunlight on December 6, 2006 at 18:30:00
Illumination from Sunlight on December 6, 2006 at 19:30:00