SWG-17 Pasadena,CA
B A
Direction Finding and Triangulationfrom STEREO & Wind
M. J. Reiner
Type III burst have very characteristic intensity profiles:
• Rapid rise to a peak, followed by exponential-like decay• Peak time increases as the frequency decreases (frequency drift)• Overall duration of the profile increases with decreasing frequency
STEREO A
March 15, 2007
Type III
Direction finding provides the arrival direction of the radiation from the radio source
Auto correlations
Direction finding for STEREO is achieved from an analysis of the amplitudes (auto correlations) and phase differences (cross correlations) between pairs of antennas
STEREO Direction Finding
Ez
Ey
Ex
09:25 09:5009:4509:301.0
4.0
3.0
2.0
Time (UTC)
STEREO A
3 June 2007
type III burst time profile
Ez - Ey
Ex - Ey
Ex - Ez
09:20 09:30-1.0
Time (UTC)
STEREO A
3 June 2007
1.0
0.5
0.0
-0.5
10:0009:45
Cross correlations
EzEx
Ey
Ez
Ex Ey
sType III radio source
3 mutually orthogonalantennas
differences due to the different antenna “electrical lengths” and to
the direction of the radio source
STEREO Ahead EUVI 284
2007-08-06 02:06:30 UTCflare site
S06o W44o
WindSTEREO B STEREO A
Parker spiral interplanetarymagnetic field lines
SUN
flare siteS06o W44o
WindSTEREO B STEREO A
SUN
6o10o
16o
2007 August 6
STEREO A
2007 August 6
Wind2007 August 6
STEREO B
Lines-of-sight to the radio sourcefrom STEREO A, Wind & STEREO B
at 425 kHz
Radio source at 425 kHz locatedby STEREO/Wind triangulation
This flare produced atype III radio burst
that was “simultaneously”observed by
STEREO A, B & Wind
Spatial triangulation of a solar type III radio source
The spatial location of the radio source(0.21 AU, W48o) was determined without
using an interplanetary density model
The triangulated source location is consistentwith the 27 sec timing difference between the
type IIIs as observed at STEREO A and B
Why are these measurements important?
The DF & triangulation measurements provide:
• 3D source location - independent of a density model
• information on the size of the radio source
• information on the intrinsic source intensity
• information on the beaming characteristics of the type III radiation
• tracking of the electron beams through the interplanetary medium to 1 AU and beyond(by performing the triangulation at consecutively lower frequencies)
(needed to constrain theoretical models of type III radio generation)
(also needed to constrain theoretical models of type III radio generation)
Determining the Beaming Pattern
To deduce the intrinsic beaming pattern of the radio source, we must first factor out the 1/R2 falloff of the radiation intensity in propagating from the source to each observing s/c
To do this, we obviously need to know the location of the source from the triangulation
Since the radio source beaming pattern is a “curved surface”, we need at least 3 s/c observations
The third observation at Wind is important for distinguishing between the two possible
beaming patterns that are consistentwith the STEREO observations
A wider separation between the two STEREO s/c provides a more accurate determination of
the overall beaming pattern, but in this case the third observation at Wind is even more critical
STEREO + Wind observations can provide the first quantitative measure of the radiation beaming
Lengths of the arrows representthe observed intensity at each s/c
Lengths of the arrows representthe observed intensity at each s/c
Conclusions
• STEREO & Wind observations can be used to remotely locate radio sources in the 3D heliosphere, independently of a density model, using both timing and spatial triangulation
STEREO B STEREO A
• STEREO & Wind observations of type III bursts can be used to deduce intrinsic radiation characteristic of the radio source,
such as the beaming characteristics
Wind