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Solar Radio Emissions at HF (go direct to HF Solar Radio) and VHF/UHF (go direct to e-CALLISTO)

We started monitoring solar activity in May 2009 not long after the end of sunspot cycle 23 (fall 2008). We presently operate three systems for monitoring solar emissions, all in the HF frequency band, located at Anchorage, Cohoe and Gakona (HAARP), Alaska.

Solar radio emissions generally are associated with solar active regions and related to flare activity. Many solar radio emission have similar characteristics and are classified on the basis of their frequency and time (spectral and temporal) characteristics into seven types, Type I through Type VII with Types I through Type V being basic types and Types VI and VII being extensions of Type III and Type V. See table below for a summary of spectral classifications.

 

Solar Radio Burst Spectral Classifications ~ General (see also table notes below)

Type

Characteristics

Duration

Frequency Range (MHz)

Associated Phenomena

I

Short, narrow-bandwidth bursts. Usually occur in large numbers with underlying continuum

Single: ~1 second
Storm: hours – days

80 – 200

Active regions, flares,
eruptive prominences

II

Slow frequency drift bursts. Usually accompanied by a second harmonic

3 – 30 minutes

Fundamental:
20 – 150

Flares, proton emission, magneto-hydrodynamic shockwaves

III

Fast frequency drift bursts. Can occur singularly, in groups, or storms often with underlying continuum. Can be accompanied by a second harmonic

Single: 1 – 3 seconds
Group:  1 – 5 minutes
Storm: minutes – hours

0.01 – 1000

Active regions, flares

IV

Stationary Type IV:
Broadband continuum with fine structure

Hours – days

20 – 2000

Flares, proton emission

Moving Type IV:
Broadband, slow frequency drift, smooth continuum

0.5 – 2 hours

20 – 400

Eruptive prominences,
magneto-hydrodynamic shockwaves

Flare Continua:
Broadband, smooth continuum

3 – 45 minutes

10 – 200

Flares, proton emission

V

Smooth, short-lived continuum. Follows some type III bursts. Never occurs in isolation

1 – 3 minutes

10 – 200

Same as type III bursts

VI

Series of Type III bursts over a period of 10 minutes or more, with no period longer than 30 minutes without activity

> 10 minutes

See Type III

See Type III

VII

Series of Type III and Type V bursts over a period of 10 minutes or more, with no period longer than 30 minutes without activity

> 10 minutes

See Type III and Type V

See Type III
and Type V

Table notes:
1. Drifting bursts almost always drift from high to low frequencies
2. Frequency range is the typical range in which the bursts appear and not their bandwidth
3. Sub-types of Type IV are not universally agreed upon

 

Solar Radio Bursts ~ Summary of Major Characteristics

(source: Table 1, Radio emission from the sun and stars, Dulk, 1985, http://adsabs.harvard.edu/abs/1985ARA&A..23..169D )

 

Burst type

Duration at
100 MHz or 10 GHz

Temperature (K)

Polarization (circular)

Frequency range/ bandwidth

Height range/

magnetic topology

Association

Emission mechanism

I

≤ 1 s

≥ 1010

50 – 100%

50-300 MHz/

~1 MHz (burst)

 

0.1 – 0.6 R0/

closed

large sunspots

fundamental

plasma

I storm

days to weeks

≥ 1010

o-mode

~100 MHz (storm)

 

 

 

III storm

days to weeks

≥ 1010

o-mode

50 MHz – 30 kHz/

0.6 R0 – 1 AU/

open

Type I storms

fundamental and/or harmonic plasma

II

≥ 10 min

108 – 1011

usually unpolarized

200 → 1 MHz/

10 MHz

0.2 – 200 R0/

open

flare

shockwave

fundamental and harmonic plasma

III

few seconds

108 – 1012

(to 1013 at
~ 1 MHz)

fundamental: 30%

harmonic: 10%

o-mode

200 → 1 MHz/

10 MHz

2 harmonics

0.2 – 200 R0/

open (closed for
U or J burst)

c/3 electron stream

fundamental and harmonic plasma

IV moving

~ 30 min

108 – 109

low → high

x-mode

200 → 10 MHz/

> 10 MHz

0.5 - few R0 /

plasmoid

small flare

gyrosynchronous and/or plasma

IV flare continuum

~ 20 min

108 – 1012

0 – 40%

o-mode ?

200 → 10 MHz/

100 MHz

0.1 – 1 R0/

closed ?

moderate to large flare,

initial phase

plasma ?

IV storm continuum

few hours

> 108

60 – 100%

o-mode

50 – 300 MHz/

100 MHz

0.1 – 0.6 R0/

closed ?

flare,

late phase

fundamental plasma

V

> 1 min

108 – 1011

< 10%

x-mode

100 → 10 MHz/

50 MHz

0.5 – 2 R0/

open ?

follows some Type IIIs

harmonic plasma

Microwave impulse

> 1 min

(at 10 GHz)

107 – 109

~ 30%

x-mode

3 – 30 GHz/

10 GHz

~ 104 km

closed

small to large flares

hard x-rays

gyrosynchronous (Maxwellian or power law)

microwave IV

~ 10 min

107 – 109

~ 10%

x-mode

1 – 30 GHz/

5 GHz

104 – 105 km

closed

large flares with shocks

gyrosynchronous (power law)

microwave postburst

minutes to hours

~ 107

low

1 – 10 GHz/

5 GHz

104 – 105 km

closed

flare,

late phase

thermal bremsstrahlung

microwave spike burst

~ 10 ms (burst)

~ 10 min (group)

> 1013

~ 100%

x-mode ?

~ 0.5 – 5 GHz/

few MHz

104 – 105 km

closed

flare,

hard x-rays

cyclotron maser

  

Solar Radio Bursts ~ Frequency-Time Characteristics

(source: Figure 11, Radio emission from the sun and stars, Dulk, 1985, http://adsabs.harvard.edu/abs/1985ARA&A..23..169D )

 

Seasonal Variations in Solar Radio Observations at Anchorage, Alaska USA


The diagram immediately below shows how the geometry of our observations varies from summer to winter.

 

 

High-frequency system operating in the approximate range of 3~30 MHz (primarily 15~32 MHz) called the HF System.

Click here for information and data for our HF System.

A block diagram is shown below.

 

Solar spectrometer operating in the range of 45~870 MHz called the e-CALLISTO system.

Click here to view information and data for our e-CALLISTO System.

We participate in the e-CALLISTO solar spectrometer network sponsored by the Swiss Institute of Technology, ETH Zurich. A block diagram is shown below.