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