Saturn's Atmosphere Studies with LOFAR

Saturn's Atmosphere Studies with LOFAR:
a « pot-pourri »
P. Zarka & the TKP Planet Working Group
R. Courtin and the LC0_005 team
J.-M. Griessmeier and the LC0_023 team

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Saturn’s lightning commissioning observations
• 2010/04/08 : (3h) incoherent sum of 10 stations, 30-78 MHz, 81 μsec x12 kHz, Stokes I, On only
• 2010/12/17-18 : (16h) incoherent sum of 22 stations, 15-75 MHz, 81 μsec x12 kHz, Stokes I,

Off=PSR1133 (TBB in //)
• 2011/07/07-08 : (12h) coherent sum of 5 superterp stations, 20-70 MHz, 1.3 msec x12 kHz
UIOWA 20100413
2010-04-08 (098) 19:00 2010-04-09 (099) 01:00
15,98
267,44
0,22
15,59
15,98
16,34
300,38
0,23
15,64
16,34
16,69
333,36
0,23
15,70
16,69
17,04
6,37
0,23
15,75
17,04
17,38
39,41
0,24
15,80
17,38
17,72
72,48
0,24
15,85
17,72
18,05
105,57
0,24
15,89
18,05
19:00 20:00 21:00 22:00 23:00 00:00 01:00
Orbit 129
R
S
Lon
Lat
LT
L
2,
4,
6,
8,
10,
12,
14,
16,
Frequency (Hz)
0,
2,
4,
6,
8,
10,
12,
14,
dB Above Background (30%)
Cassini Incoherent Stokes - I
0 10 20 30 40 50 60
seconds since 20:30:00
30
40
50
60
70
MHz
dB
0.2
0.4
0.6
0.8
1.0
Incoherent Stokes - I
10 20 30 40 50 60
seconds since 20:31:00
30
40
50
60
70
MHz
dB
0.2
0.4
0.6
0.8
1.0
1.2
LOFAR

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Nb of Stations f b τ σsky
1 station 30 MHz 195 kHz 82µs 104 Jy
10 stations 30 MHz 6 MHz 20ms 37 Jy
Saturn’s lightning @ Earth ~ 10-‐1000 Jy (1 Jy = 10-‐26 W.m-‐2.Hz-‐1)
σsky = 2kTsky/( A (bτ)1/2) with Tsky ~ 1.15×108/f2.5 and A1 Sta/on
~ 48λ2/3

Off=PSR1133 (TBB in //)
RFI + SED
raw data (6 MHz) "On" clean data (6 MHz)
raw data (195 kHz) "~Oﬀ"

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24 Mz On & 24 MHz Off (=PSR1133)

(TBB in //)
18/12/2010
03:00 11:00
SB#
17/12/2010 - SubBand 50
Time steps
Intensity

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(TBB in //)
UIOWA 20110627
2010-12-18 (352) 00:00 2010-12-18 (352) 16:00
27,47
292,56
-0,06
20,06
27,47
26,78
33,01
-0,06
20,11
26,78
26,08
133,41
-0,07
20,18
26,08
25,35
233,76
-0,07
20,24
25,35
24,60
334,05
-0,07
20,32
24,60
23,83
74,27
-0,07
20,39
23,83
00:00 03:00 06:00 09:00 12:00 15:00
Orbit 142
R
S
Lon
Lat
LT
L
2,
4,
6,
8,
10,
12,
14,
16,
Frequency (Hz)
0,
5,
10,
15,
20,
PSR 1133 in Off beam on 2010/12/18

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• 2010/12/17-18 : (2x8h) incoherent sum of 22 stations, 15-75 MHz, 81 μsec x12 kHz, Stokes I,


(TBB in //)
• 2011/07/07-08 : (2x6h) coherent sum of 5 superterp stations, 20-70 MHz, 1.3 msec x12 kHz
20
70
MHz
0 1600
sec
20
70
MHz
0 1600
sec

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• Statistical detection seems positive ... BUT ...
• Unsuccessful one-to-one correlation of individual ﬂashes seen by LOFAR and Cassini
(for the moment tested on 2010/04/08), in spite of severe RFI mitigation
Ex: NDA observations, 14-28 MHz, 90 sec,
20 msec x 4 kHz resolutions

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« If you torture data enough, they will confess » (޸ࢠ ~500 BC)
« Sometimes there is just too much RFI » (Ter Veen, 3/12/2012)
→ NOT NECESSARILY !
→ INDEED !

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[Konovalenko et al., Icarus, 2012]
Ground-based detection of Saturn’s lightning
• Dec. 2010 observation at UTR-2/Kharkov with DSP receivers
10 microsec resolution
(from waveform capture)
DM ~ 3x10-5 pc.cm-3
∫1
10(5/L2)dL ~ 5 cm-3/Lmin(UA)

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Jean-Mathias Griessmeier LPC2E / OSUC France
Philippe Zarka LESIA / Observatoire de Paris France
Julien Girard LESIA / Observatoire de Paris France
Walid Majid JPL / Caltech USA
Heino Falcke Radboud Univ. Nijmegen NL
Alexander Konovalenko IRA Kharkov Ukraine
LC0_023 : Measuring the energy of Saturn's lightning
LOFAR TAB data analysis / LOFAR TBB / UTR-2 observations
Semester : LOFAR Cycle 0
Abstract
Lightning-generated radio emission from Saturn has been observed by spacecraft missions (1980,
1981, and since 2004) and from the ground (since 2006). The highest frequency covered by these
instruments is 40 MHz; at higher frequencies, the spectrum of Saturn lightning remains unknown.
LOFAR observations at >40 MHz with high time resolution (5 microsec) would allow to measure the
slope of the SED spectrum, the fine structure of discharges, and thus determine the energy of the
discharge, which is currently unknown by many orders of magnitude. This energy is an important input
for atmospheric chemistry. Extending the observation to lower frequencies (10-40 MHz) would allow to
study the ionosphere of Saturn.
Telescopes
Telescope Modes
LOFAR Beam Observation
Applicants
Name Affiliation Email Country Potential
observer
Dr Jean-Mathias Griessmeier LPC2E & OSUC & Obs.
Paris Nancay
[email protected]
-orleans.fr
France Pi Yes
Dr Philippe Zarka CNRS - Observatoire de
Paris (LESIA)
[email protected] France
Phd student Julien Girard LESIA - Observatoire de
Paris Meudon (LESIA -
Griessmeier LC0_023
Measuring the energy of Saturn's lightning
[Farrell et al., 2007]
- ToO / Saturn (Cassini)
- measure spectrum across LBA band with 5 microsec
resolution + TBB (5 nsec on bright spikes)
- « HF » (>30 MHz) spectrum + hi-res time proﬁle
㱺 ﬂash energy
- Mars ?

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After the giant storm in 2011 ...
• Storm lasted from 12/2010 to 8/2011, in Northern (summer) hemisphere
• up to 10 ﬂashes / sec, intensity up to 104 Earth's
[Fischer et al., 2011]

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After the giant storm in 2011 ...
2011-07-01 (182) 00:00 2011-07-10 (191) 00:00
44,47
152,56
0,27
15,37
44,47
41,05
328,05
0,29
15,77
41,05
35,07
141,94
0,32
16,28
35,08
25,68
311,35
0,35
17,09
25,68
10,14
93,49
0,33
19,72
10,14
2011-07-02 2011-07-04 2011-07-06 2011-07-08 2011-07-10
R
S
Lon
Lat
LT
L
2,
4,
6,
8,
10,
12,
14,
16,
Frequency (Hz)
0,
2,
4,
6,
8,
10,

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... Saturn’s amosphere has been quiet for months ...
2012-11-20 (325) 00:00 2012-12-04 (339) 00:00
27,72
321,97
-44,55
18,03
54,59
11,49
157,00
28,24
11,29
14,80
28,34
192,96
-31,35
15,14
38,86
2012-11-23 2012-11-28 2012-12-03
R
S
Lon
Lat
LT
L
2,
4,
6,
8,
10,
12,
14,
16,
Frequency (Hz)
0,
2,
4,
6,
8,
10,

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But there is more about Saturn’s atmosphere
with LOFAR ...

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Saturn’s observable atmosphere
from the UV to the microwave domains

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Saturn’s temperature proﬁle
as a function of the H2
O abundance

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LOFAR is expected to probe much deeper
in Saturn’s atmosphere
down to pressures of a few kbar
ν=300 MHz ; λ=100 cm
Opacity: NH3
+ H2
O
ν=100 MHz ; λ=300 cm
Opacity: neutral & weakly-ionized H2
O

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LOFAR HBA
H2
O = 0.2×VF (O/H~0.7×solar)
H2
O = 5×VF (O/H~17×solar)
H2
Briggs and Sackett (1989)
Saturn’s brightness temperature spectrum
between 10 cm and 300 cm

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H2
O = 0.2×VF (O/H~0.7×solar)
H2
H2
Saturn’s disk-integrated ﬂux density
in the LOFAR HBA range
Δt = 5h per band

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1 MeV 0.028 MeV
Flux (cm-2.sr-1.s-1.MeV-1)
Flux (cm-2.sr-1.s-1.MeV-1)
!
Electrons ﬂuxes
Salammbô-3D
Modeled synchrotron radiation in the LOFAR HBA range
Computed 2-D maps
at 110-300 MHz
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
100 150 200 250 300 350
Fréquence (MHz)
Densité de flux (mJy)
DE=0°
DE=26°
@ 8.8 UA
Computed disk-
integrated spectrum

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Objectives
• Determine the deep atmospheric water vapor abundance,
hence the O/H ratio in Saturn’s interior
• Obtain better constraints for interior models of Saturn,
i.e. the contribution of H2
O to the heavy-element component (z)
• Check the prediction of a negligible level of synchrotron radiation
• Assess the existence of a weakly-ionized region below 30 kbar
Expectations
• good signal-to-noise is expected at least in 3 of the bands
above 160 MHz (160-172 + 210-222 + 238-250 MHz)
• a 10% accuracy should allow us to discriminate between
"under-solar" and "over-solar" H2
O distributions
• the accuracy of the O/H determination will strongly depend on
the quality of the imaging processing and calibration

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Régis Courtin LESIA / Observatoire de Paris France
Daniel Gautier LESIA / Observatoire de Paris France
Franck Hersant LAB / Observatoire de Bordeaux France
Mark Hofstadter Jet Propulsion Laboratory USA
Tobias Owen IfA / University of Hawaii USA
Nadine Nettelmann Rostock University Germany
Philippe Zarka LESIA / Observatoire de Paris France
Cyril Tasse GEPI / Observatoire de Paris France
Julien Girard LESIA / Observatoire de Paris France
Jean-Mathias Griessmeier LPC2E / OSUC France
Angélica Sicard-Piet ONERA Toulouse France
Lise Lorenzato ONERA / IRAP Toulouse France
Daniel Santos-Costa SWRI San Antonio USA
LC0_005 : A determination of the abundance of water
in Saturn’s deep atmosphere with LOFAR
Saturn’s Atmosphere & Interior / LOFAR Imaging / Saturn’s Synchrotron Radiation
Semester : LOFAR Cycle 0
Abstract
Lightning-generated radio emission from Saturn has been observed by spacecraft missions (1980,
1981, and since 2004) and from the ground (since 2006). The highest frequency covered by these
instruments is 40 MHz; at higher frequencies, the spectrum of Saturn lightning remains unknown.
LOFAR observations at >40 MHz with high time resolution (5 microsec) would allow to measure the
slope of the SED spectrum, the fine structure of discharges, and thus determine the energy of the
discharge, which is currently unknown by many orders of magnitude. This energy is an important input
for atmospheric chemistry. Extending the observation to lower frequencies (10-40 MHz) would allow to
study the ionosphere of Saturn.
Telescopes
Telescope Modes
LOFAR Beam Observation
Applicants
Name Affiliation Email Country Potential
observer
Dr Jean-Mathias Griessmeier LPC2E & OSUC & Obs.
Paris Nancay
[email protected]
-orleans.fr
France Pi Yes
Dr Philippe Zarka CNRS - Observatoire de
Paris (LESIA)
Phd student Julien Girard LESIA - Observatoire de
Paris Meudon (LESIA -
Griessmeier LC0_023
Measuring the energy of Saturn's lightning

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Saturn's Atmosphere Studies with LOFAR

Saturn's Atmosphere Studies with LOFAR

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