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Storms & Probability
Click on images to enlarge
The emissions from Jupiter are not continous in time, nor in frequency.
The upper cutoff frequency is about 39.5MHz, while the lower cutoff frequency
is dependend on the conditions in the ionosphere, which is usually from
5 to 10MHz. The best frequency for picking up storms is around 20MHz.
The storms, which we will discuss in this page, have durations from some
minutes to several hours. Furthermore the bursts are ranked in short (S)
and long (L) bursts. Short bursts sound sometimes like a piece of cardboard
you mounted on your bikes wheel when you were a child - the long burst sound
like a wave rolling onto the beach, lasting from a few seconds to several
tens of seconds with a bandwith of a few MHz. Short bursts occur a few to
several hundred times per second and have a bandwith of a few kHz to a few
tens of kHz. The drift rate of such short bursts is typical -20MHz/sec.
Due the high drift frequency, S bursts are very short in duration in a narrow-band
receiver.
This does not mean that you must tune your narrow-band receiver to an exact frequency
to hear S-burst activity - this means that the burst is drifting thru the
narrow-band of your receiver and is causing a very short increase of noise.
So tuning the receiver around 20Mhz is accurate enough to receive S-bursts.
If we want to determine the probability of detecting a burst, we have to
consider 3 values:
- Jovian
Central Meridian Longitude -> CML (System III facing to the Earth)
- Phase
of Io with respect to superior geocentric conjunction
- Jovicentric
declination of the Earth (discussed in another page)
Jovian
Central Meridian Longitude (CML):
 The
3 types of storms A, B and C are strongly dependent on the CML.
NOTE: The radio rotation period of System III ( 9h 55' 29.685" - see 'A New Determination
of Jupiter's Radio Rotation Period' in 'Planetary Radio Emissions IV'
p.43+) is sligthly different than the usual rotation periods determined
by visual observations (System I + II).
Phase
of Io
In addition to the normal A, B and C bursts, there are Io related sources
- Io-A, Io-B and Io-C.
 In
the graph on the right one can see the dependence on the geocentric phase
of Io.
Io-A are RH polarized
mostly L bursts
Io-B are RH polarized
mostly S bursts and
Io-C are LH polarized
L
and S bursts.
 A
combination of 2 graphs is shown here. There one can see 3 hot-spots,
which are the 3 Io-related burst types.
Actually there are 3 other hot-spots, but
those don't produce storms in the 20MHz band.
| Storm |
CML-SysIII |
Io-Phase |
Discription |
| A |
200-290 |
|
|
| B |
90-200 |
|
|
| C |
290-10 |
|
|
| Io-A |
200-290 |
195-265 |
RH
pol., mostly L-Bursts |
| Io-B |
90-200 |
75-105 |
RH
pol., mostly S-Bursts |
| Io-C |
290-10 |
225-250 |
LH
pol., L and S Bursts |
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