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SOLID Meeting WP2 1
Solar radio spectral irradiance
Christophe Marqué
Royal Observatory of Belgium
14/10/13
SOLID Meeting WP2 2
The beginning
• Solar radio astronomy
started during WWII
• Conversion of radar
equipments into
radiotelescopes
• No choice of
frequencies
14/10/13
SOLID Meeting WP2 3
The beginningActive Sun
• Sporadic activity
linked to solar
eruptive events
• Accelerated
electrons (non
thermal
populations)
• Different spectral
types
14/10/13
SOLID Meeting WP2 4
The beginningNon active Sun
• Thermal emission
from the corona
(T~106K,
Pawsey,1946)
• Bremsstrahlung,
Gyroresonance
• 2 components:
Quiet Sun & SVC
14/10/13
SOLID Meeting WP2 5
The beginning“The excitement of the eclipse
observations
[at 10.7 cm] was soon followed by the
sobering thoughts that solar radio
emission from sunspots would be
variable…”
A. Covington, Proc. NRAO Workshop,
198314/10/13
Interplanetary medium
High corona
Low corona
Transition region
Chromosphere
Solar radio observations
The Sun is observed in radio in a large spectral window: from far I.R to km wavelengths
Plasma emission
Plasma emissionGyrosynchroton
GyrosynchrotronThermal bremsstrahlung
Thermal bremsstrahlung
Thermal bremsstrahlungGyroresonance
Thermal bremsstrahlungUnknown
SOLID Meeting WP2 7
Solar radio spectral irradiance
• Continuum emission: no lines
• Flux density: W.m-2.Hz-1
• Solar Flux Unit: 10-22 W.m-2.Hz-1 = 104
Jansky
• Intensity as Brightness Temperature
14/10/13
SOLID Meeting WP2 8
Solar Flux radio Observatories
14/10/13
2800 MHz
1000 MHz2000 MHz3750 MHz9400 MHz17000 MHz
245 MHz410 MHz610 MHz1415 MHz2695 MHz4995 MHz8800 MHz15400 MHz
SOLID Meeting WP2 9
Flux Measurement
• Full Sun
• Parabolic dish
• Horn antenna
• Pentincton:
strict
calibration
procedure 3
times per day14/10/13
SOLID Meeting WP2 10
Flux measurement: calibration
• Tanaka (1973) paper
• Toyokawa: reference
station
• Flux correction (0.9 for
F10.7)
• Standard for absolute
calibration
• Precision 1-2 %
14/10/13
SOLID Meeting WP2 11
Flux measurement: natural sources of error
14/10/13
• Atmospheric
absorption
• Rain
• Humidity (dew/snow)
on antenna
• Temperature variation
• Ionospheric
disturbances
Flux measurements: examples
calibration
Quiet Sun levelGround interference Ground
interference
Quiet sun level
Solar flare
SOLID Meeting WP2 13
Cycle 23-24
14/10/13
SOLID Meeting WP2 14
Emission mechanism
14/10/13
After Schmahl & Kundu 1998
SOLID Meeting WP2 15
Spectrum of QS &SVC
• QS : S~f2 ->
Thermal
Bremstrahlung
• SVC: ~Flat
spectrum
Gyroresonance/Fre
e-Free
14/10/13
2001-2002
SOLID Meeting WP2 16
Free-Free / Gyroresonance
14/10/13
SOLID Meeting WP2 17
Quiet Sun: essentially Free-Free
14/10/13
Zirin, 1991
SOLID Meeting WP2 18
SVC
14/10/13
S. White
SOLID Meeting WP2 19
Last words
• Long term spectral irradiance with good stability (with
proper calibration procedure)
• Care should be taken about the meaning of daily values
• No Instrument degration (apart from rust & spare parts
availability)
• Possibility to use radio data for EUV/UV calibrations
• Gold mine for long term studies of coronal evolution (n,
T, & B)
14/10/13