Statistics of auroral Langmuir waves

Samara, M.; LaBelle, J.; Cairns, Iver H.

doi:10.5194/angeo-26-3885-2008

Cited by 5 publications

(13 citation statements)

References 52 publications

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“…For a random distribution of γ i and/or δt i , log S will have a normal distribution, according to the central limit theorem. Such distributions have already been observed in the intensity of terrestrial auroral Langmuir waves [ Samara et al , 2008] or visible emissions [ Shefov et al , 2006]. The above results establish that this also the case for the CMI instability.…”

Section: Akr Stokes Parameterssupporting

confidence: 82%

Auroral kilometric radiation diurnal, semidiurnal, and shorter‐term modulations disentangled by Cassini

et al. 2010

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[1] During the flyby of the Earth by Cassini in 1999, the Radio and Plasma Wave Science (RPWS) instrument recorded a month of quasi-continuous observations of auroral kilometric radiation (AKR). Analyzing the full polarization of incoming radio waves, we found AKR to be 100% circular left-handed (LH) or right-handed (RH). As AKR is emitted predominantly on the extraordinary mode, we analyzed separately the northern (RH) emission, from the southern (LH) one with respect to the magnetic equator. AKR power variations reveal (1) a log-normal distribution at time scales of minutes, (2) bursts of emission at time scales of a few hours, and (3) a clear overall modulation at 24 h, together with a weaker modulation at 12 h (especially visible for LH emissions). The prominent 24 h modulation is found to modulate LH and RH AKR in phase opposition. This is interpreted as being due to visibility effects related to the precession of the terrestrial magnetic dipole, making Cassini oscillate relative to the average AKR beaming pattern from each hemisphere. We accordingly quantified the AKR beaming as a function of explored latitudes. On time scales shorter than a few hours, LH and RH emissions are found to be correlated. This is attributed to the actual conjugacy of the corresponding sources, simultaneously turned on by substorm occurrence. The geometrical anticorrelation (at 24 h) dominates close to Earth, while the short-term correlation (substorms) dominates far from Earth, where the detection threshold makes the visibility less important than the occurrence of substorms. Finally, the 12 h modulation is detected when it is not masked by strong visibility effects, namely, for the LH emission, which is observed mostly near the magnetic equator along the path of Cassini. As a 12 h modulation of some geomagnetic indices was also observed, we suggest that the AKR semidiurnal modulation may have a physical cause, for which we favor the variable geometry and efficiency of the reconnection between interplanetary and geomagnetic fields, or magnetotail oscillations.Citation: Lamy, L., P. Zarka, B. Cecconi, and R. Prangé (2010), Auroral kilometric radiation diurnal, semidiurnal, and shorter-term modulations disentangled by Cassini,

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Section: Akr Stokes Parameterssupporting

confidence: 82%

Auroral kilometric radiation diurnal, semidiurnal, and shorter‐term modulations disentangled by Cassini

et al. 2010

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“…Therefore these distributions are intrinsic to the waves. Statistical analyses of the waveform distributions for auroral Langmuir waves, 44 and of both the waveform and envelope distributions for Langmuir waves in the cusp region, 32 showed that time averaging has significant effects on the distributions. For in- stance, LaBelle et al 32 found that sufficient averaging leads to lognormal distributions for both P͑log E͒ and P e ͑log E e ͒, in contrast to the power-law forms in the absence of averaging.…”

Section: Discussionmentioning

confidence: 99%

Waveform and envelope field statistics for waves with stochastically driven amplitudes

Cairns

Robinson

et al. 2010

Physics of Plasmas

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The statistically steady distributions P͑log E͒ and P e ͑log E e ͒ of waveform field E and envelope field E e are studied for time-varying waves with stochastically driven amplitudes. The waves are represented in one dimension ͑1D͒ by a single mode or superposition of multiple independent modes, whose amplitudes follow stochastic differential equations. Both distributions at low fields follow power laws: P͑log E͒ ϰ E p and P e ͑log E e ͒ ϰ E e q with distinct exponents p and q. Transitions in both distributions are found between the single-mode and multimode cases, with the distributions in the latter essentially independent of the number N ͑provided N Ն 2͒ of modes. For N Ն 2, p Ϸ +1.0, q Ϸ +2.0, and both distributions agree quantitatively with independent analytic predictions. Applications to Langmuir waves observed in Earth's polar cusp ionosphere show that both distributions for N Ն 2 agree quantitatively with the respective observations, suggesting that the Langmuir waves may be 1D and have a stochastic driver.

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“…Two types of statistical analyses of the wavefields are considered here: statistics of the absolute values of the wavefields and statistics of the envelopes of the fields. The former are the type presented by Samara et al [2008] for the case of nightside auroral Langmuir waves detected during the PHAZE II rocket experiment. The latter are the type applied to Langmuir waves in the electron foreshock [ Cairns and Robinson , 1997, 1999], solar type III source regions [ Robinson et al , 1993], and the auroral magnetosphere [ Cairns and Menietti , 2001].…”

Section: Data Presentationmentioning

confidence: 86%

“…Another previous study relevant to the observations reported below is a recent statistical analysis of waveforms of auroral Langmuir wave packets observed with the PHAZE‐2 rocket, launched into active nighttime aurora [ Samara et al , 2008]. Inspired by statistical analyses of Langmuir wave packets in Earth's electron foreshock [ Cairns and Robinson , 1997, 1999], Samara et al [2008] compute histograms of log N versus log E for nine selected 2–13 s intervals of Langmuir wave activity, where N is the number of measurements for each value of wave electric field E . Averaging the wavefields over varying time intervals reveals a transition in the shapes of the resulting histograms for averaging times of 50–100 μ s, although the data have insufficient resolution to determine the cause of this transition.…”

Section: Introductionmentioning

confidence: 99%

Electric field statistics and modulation characteristics of bursty Langmuir waves observed in the cusp

2010

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[1] HF wave receivers on the Twin Rockets to Investigate Cusp Electrodynamics (TRICE) detect numerous 20-250 ms duration Langmuir wave bursts. Investigation of 41 bursts at 967-984 km, where the gyrofrequency exceeds the plasma frequency, reveals a characteristic signature whereby the Langmuir wave bandwidth and highest frequency maximize at the center of the bursts, suggesting that bursts coincide with density enhancements. The Langmuir waveforms are modulated at frequencies up to 50 kHz, with significant modulation at frequencies <1 kHz about 10% of the time. Where amplitudes of the modulated waves pass through zero, the phase of the carrier wave shifts by 180°, consistent with a superposition of interfering waves. The corresponding wave spectrum has multiple <1 kHz bandwidth peaks separated by <1-50 kHz. For no averaging, the wave E field statistics, dominated by the carrier Langmuir wave, show an E +1 dependence at small E fields as expected for rectified sine waves. For moderate averaging, the statistics, dominated by the envelope field, show a spectral index of ≈ +2 at small E fields, consistent with numerical simulations of independent stochastically driven waves. The wave statistics, absence of VLF waves, lack of transition in the modulation occurrence as a function of frequency, and tendency of the spread spectrum to cut off at the ambient plasma frequency outside the density enhancement associated with the wave burst suggest that linear growth and mixing of Langmuir modes provides a more natural explanation of modulated Langmuir waves than do wave-wave processes previously proposed, at least for cusp waves encountered by TRICE.Citation: LaBelle, J., I. H. Cairns, and C. A. Kletzing (2010), Electric field statistics and modulation characteristics of bursty Langmuir waves observed in the cusp,

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Statistics of auroral Langmuir waves

Cited by 5 publications

References 52 publications

Auroral kilometric radiation diurnal, semidiurnal, and shorter‐term modulations disentangled by Cassini

Auroral kilometric radiation diurnal, semidiurnal, and shorter‐term modulations disentangled by Cassini

Waveform and envelope field statistics for waves with stochastically driven amplitudes

Electric field statistics and modulation characteristics of bursty Langmuir waves observed in the cusp

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