1. Introducing Solar Radiophysics

3. Dynamic spectrum & Frequency drift A dynamic spectrum describes the flux density in terms of frequency and time. The time rate of change of frequency is called “frequency drift”. That is Frequency drift =

5. Understanding physical mechanisms Spectral typesAvailable theoriesConvincing or not I few no II few no III manymostly irrelevant IV no V

6. Dynamic Spectrum A conceptual interpretation

7. A simple picture of dynamic spectrum

8. Envisioned Source Region Situation

9. Observed Dynamic Spectrum

10. “Plasma Emission” In general it involves four processes: Generation of enhanced Langmuir waves Partial conversion of Langmuir waves into fundamental em waves Production of backward Langmuir waves Generation of second harmonic em waves

11. Development of Theories of “Plasma Emission” Ginzburg & Zheleznyakov (1958) Tsytovich (1967) and Kaplan & Tsytovich (1968) Melrose (1980) and others

12. Classification of Spectral Types of Radio Emission Spec. type Nature Source I StormPre-flare, decay phase II Bursts CME & shock wave IIIBursts & stormFlare-assoc. electrons IV Continuum Behind shock wave V Bursts After type III bursts

13. Difficulties with “ plasma emission ” hypothesis

14. Summary of F-wave theories Scattering of Langmuir waves by ions (Ginzburg & Zheleznyakov, 1958; Tsytovich 1967) Scattering by Ion sound waves (Melrose 1980) Collapse of Langmuir wave packets (Goldman 1980)

15. Summary of H-wave theories Coalescence of two Langmuir waves (Ginzburg & Zheleznyakov 1958) Collapse of Langmuir wave soliton (Goldman et al. 1980)

16. Difficulties with the plasma emission scenario (1) H/F ratio = 1.6 ~ 1.9

17. F-H waves are generated at the same time in the source region according to plasma emission theories.

18. H/F frequency ratio at a given time

19. Difficulties with the plasma emission scenario (2) H/F ratio = 1.6 ~ 1.9 Temporal delay of F component

20. Initial delay of F waves

21. Moreover … Observations show that the starting H wave frequency is often more than twice the starting frequency of F waves. In some cases initially F wave frequency is only one third of that of the H wave. Statistically the starting frequencies of H waves peak around 200 MHz whereas those of F waves peak around 60 MHz.

22. Difficulties with the plasma emission scenario (3) H/F ratio = 1.6 ~ 1.9 Temporal delay of F component Only a fraction of type III events have F-H pair.

23. Difficulties with the plasma emission scenario (4) H/F ratio = 1.6 ~ 1.9 Temporal delay of F component Only a fraction of type III events have F-H pair emission. F component waves are more directive than H component waves.

24. Difficulties with the plasma emission scenario (5) H/F ratio = 1.6 ~ 1.9 Temporal delay of F component Only a fraction of type III events have F-H pair emission. F component waves are more directive than H component waves. Coincidental source regions of H-F waves with same frequency

25. Expected Source Regions

26. Stewart, R. T., Proc. Astron. Soc. Aust., 2, 100 (1972)

27. Interplanetary type III emission Additional unresolved issues

28. Low-frequency interplanetary type III emission Interplanetary type III emission was not known until late 1970s. It is not observable by ground facilities. Because it is observed with satellites the results must be interpreted accordingly.

29. Comments on satellite observations When a satellite is in the source region, in principle, it can measure the distribution function of the beam electrons. However, the angular resolution is often limited. The observations enable us to examine the role of Langmuir waves in the emission process. However, we usually cannot pin point the actual source position of the waves.

30. Consensus & standard explanation In general, because of subjective reasons, researchers believe that plasma emission is the generation mechanism. However, there are difficult issues which have puzzled and mystified scientists for years.

31. Few of the difficult issues A clear electron beam is rarely observed. The best result is a weak trace of a beam which is marginally unstable according to plasma kinetic theory.

32. Observation of Langmuir waves

33. Energetic electron distribution function

35. Few of the difficult issues A clear electron beam is rarely observed. The best result is a weak trace of a beam which is marginally unstable according to plasma kinetic theory. The emission often stops suddenly in the solar wind.

37. Few of the difficult issues A clear electron beam is rarely observed. The best result is a weak trace of a beam which is marginally unstable according to plasma kinetic theory. The emission often stops suddenly in the solar wind. In some cases the emission actual began in interplanetary space.

39. At very low frequencies (f < 100 kHz) the source size becomes very large.

40. The emission durations of the very low frequency radiation can be exceedingly long.

43. Energetics It is established that Thus the kinetic energy density of beam electrons is about If this total amount of energy density is converted to Langmuir waves, the waves would have an electric field ~100 mV/m.

45. Summary of major results of CMI Both O-mode and X-mode waves may be amplified. The amplified waves have frequencies close to electron gyro-frequency and its second harmonic. It turns out that O-mode is unimportant. Amplification of X-mode waves depends on the ratio of plasma frequency to gyro frequency.

46. Further Remarks In the region where both F-H waves are emitted. In the region where H waves are emitted.

47. Simultaneous observations by Wind & Ulysses spacecraft

48. Other four types of solar radio emissio type I storms, type II bursts, type IV emission, and type V bursts

51. Type I Storms J. S. Hey first observed the radiation in 1946. It is found that the radiation is connected with large sunspots. It consists of narrow band, spiky bursts and a broadband continuum. The radiation is not related to flares. It occurs for days after the appearance of large active regions. The noise storms is due to change of coronal magnetic field.

52. An example of type I storms

54. (Continuation) Occasionally there are type III storms at frequencies below type I bursts. The type I storm continuum may be due to nonthermal electrons trapped in loops. Type I bursts differs from type III bursts in that it is strongly polarized and has no harmonic band. The key issue is what produces the bursts.

55. Storms are usually associated with large sunspots

57. Type I bursts from a bipolar region For comparison, light lines show areas of plus and minus magnetic field based on Mount Wilson data.

58. A proposed model to account for erratic movement of sources

59. Type II bursts It was first identified in coronal shock wave by R. Payne-Scott and coworkers in 1947. Extremely intense and narrow bands. Fundamental and harmonic components Slow frequency drift which suggests a beam speed ~ 1000 km/s. Frequencies are close to local plasma frequency and its harmonic.

60. Payne-Scott et al. (1947): First measurement of type II bursts. Note the progressive time delay in the onset of the outburst on different frequencies.

61. Frequency drift of four type II bursts. The dotted line represents a constant drift rate of 0.22 MHz per second

62. Type II bursts with herringbone structure.

63. (Continuation) Backbone and herringbone structures The backbone is co-moving with a shock. The herringbone structure is interpreted as signatures of a beam of fast electrons associated with the shock. But herringbone structures appear only in about 20% of type II bursts. Only 65% of the shocks observed as a fast CME radiate type II bursts.

64. f t Backbone Herringbone Schematic description of a dynamic spectrum

65. (Continuation) The frequency ratio of H/F bands is closer to 2 than in the case of type III bursts. The source regions of F and H bands with a given frequency basically coincide. Lowest frequency is about 20 MHz. Type II emission usually occurs about one minute after the peak of flare associated hard X-rays.

66. H/F frequency ratio

67. Unshaded: F-H pair Shaded : One band

68. All four type II bursts contain two harmonic and split bands

69. Starting frequency of fundamental bands of type II bursts

70. Study of a compound type II and type III bursts

71. Type II bursts with harmonic feature

72. Type IV emission May be grouped into three sub-classes 1. Stationary type IV emission 2.Moving type IV emission 3.Decimetric type IV emission Early explanation: synchrotron radiation Difficulties: (i) bandwidth (ii) energetic electrons More recent notion: trapped electrons

73. Moving plasmoids scenario Loops and their evolution have important implications to the understanding of flare physics and radiophysics. Dulk & Altschuler (1971) has inferred that type IV bursts might be due to moving plasmoid. The key question is how the plasmoid id formed.

74. A suggested scenario of type VIm emission H  flare ribbons Filament Type IV bursts

76. Moving type IV emission Brightness temperature K Emission is evidently due to some kind of induced process. Most likely the emission is attributed to non-thermal trapped electrons. Moving type IV bursts is moving with nearly constant speed of a few hundred km/s.

77. Type V bursts Usually occurs immediately after type III bursts. Often has opposite sense of polarization. In general frequencies are lower than 60 MHz.

78. A type V bursts event