The Langmuir waves associated with the 1 December 2013 type II burst

Abstract

The Langmuir waves associated with an interplanetary type II source region are presented. The type II burst was first observed on 29 November 2013 by STEREO A and B, with the shock crossing STEREO A on 1 December 2013. In the foreshock region upstream of the shock, 11 Langmuir‐like waveforms were recorded by STEREO A's Time Domain Sampler on three orthogonal antennas. The observed Langmuir wave electric fields are of large amplitude and aligned with the background magnetic field. Some of the waveforms show evidence of electrostatic decay, and several are consistent with Langmuir eigenmodes of density wells. Harmonic electric fields are observed simultaneously with the Langmuir waveforms and are consistent with fields produced by nonlinear currents. The beam speeds vb exciting the Langmuir waves are estimated from the waveform data, yielding speeds vb≈ (0.01–0.04)c. These are consistent with previous observations. The beam speeds are slower than those associated with type III solar radio bursts, consistent with the Langmuir wave electric fields being field aligned. The evidence found for electrostatic decay and against strong perpendicular fields, and so low‐wave number Langmuir/z‐mode waves, suggests that the dominant emission mechanisms for this type II foreshock involve electrostatic decay and nonlinear wave processes, rather than linear‐mode conversion. Harmonic radio emission via antenna mechanisms involving Langmuir waves remains possible.

Quantitative prediction of type II solar radio emission from the Sun to 1 AU

“…D. Bale, personal communications, 2013]. This event also had local harmonic radio emission, Langmuir waves, and accelerated electrons observed upstream of the shock crossing at STEREO A [Graham and Cairns, 2015]. The burst moves from frequencies from ∼4-2 MHz to ∼30-15 kHz, corresponding to heliocentric distances r from ∼10 R s to ∼1 AU, respectively.…”

“…This CME was launched almost in the direction of STEREO A; its driven shock reached STEREO A on 1 December 22:29 UT 2013 [Graham and Cairns, 2015], as evidenced by jumps in the density and magnetic field at STEREO A. The separation angles between the Earth and STEREO A (B) were about 149.5 ∘ anticlockwise (146.7 ∘ clockwise), with STEREO A and B separated by ≈1 AU.…”

“…A type II burst was observed by STEREO A and B (Figure 1) from near 20:00UT on 29 November until near 22:30 UT on 1 December 2013 [Graham and Cairns, 2015; S. D. Bale, personal communications, 2013]. This burst was not observed by Wind before 30 November 2013, perhaps since the event occurred on the far side of the Sun from Earth.…”

“…A type II burst was observed by STEREO A and B (Figure 1) from near 20:00UT on 29 November until near 22:30 UT on 1 December 2013 [Graham and Cairns, 2015;S. D. Bale, personal communications, 2013].…”

Parametric decay of current‐driven Langmuir waves in plateau plasmas: Relevance to solar wind and foreshock events

“…If for average solar wind conditions an electric field of E 0 = ω e V e ( m e / e ) = 1 V/m is taken, the corresponding electric field amplitudes would be E ∼ 150 mV/m and E ∼ 300 mV/m. In Langmuir events associated with solar wind type III bursts or foreshock activity, however, only values in the range between 0.1 and about 50 mV/m have been measured [ Gurnett et al , ; Hospodarsky et al , ; Soucek et al , ; Henri et al , ; Sigsbee et al , ; Malaspina et al , ; Graham and Cairns , , ] which corresponds to E / E 0 between 10 −4 and 0.05. Owing to the relation δ n i / n 0 ∼0.5( E / E 0 ) 2 , it is therefore not surprising that measurable density perturbations ( δ n i / n 0 ≥10 −4 ) simultaneously with Langmuir amplitude modulations have only been observed if the electric field amplitude was sufficiently large, i.e., E / E 0 ≥10 −2 or E ≥10 mV/m [ Soucek et al , ; Henri et al , ; Malaspina et al , ; Graham and Cairns , , ].…”