Iver Cairns - Academia.edu (original) (raw)

Papers by Iver Cairns

Research paper thumbnail of Predicting radio emission from lunar radio anomolies

EAEJA, Apr 1, 2003

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Research paper thumbnail of Quasilinear Simulation of Harmonic Electromagnetic Emission via Beam-driven Langmuir Waves in the Solar Wind

AGU Fall Meeting Abstracts, Dec 1, 2004

ABSTRACT

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Research paper thumbnail of Statistics of Waveform and Envelope Fields: Theory, Simulations and Initial Applications to TRICE Data

AGU Fall Meeting Abstracts, Dec 1, 2008

ABSTRACT Plasma waves in space are almost invariably bursty and widely variable in amplitude, mot... more ABSTRACT Plasma waves in space are almost invariably bursty and widely variable in amplitude, motivating statistical approaches such as stochastic growth theory. Recent wave experiments on rockets moving through Earth's auroral regions, as well as the STEREO and Wind spacecraft, have sufficient time resolution to measure the waveform as well as the envelope field. Typically, however, experiments measure the envelope field averaged over long times compared with the wave period. Four sets of new contributions are presented. First, analytic theory is used to predict the distribution of waveform fields for a single mode with known distribution of envelope fields. The distribution P(log Ew) of waveform fields Ew is shown to be proportional to the rectified field Ewa with a ≈ 1.0 for a number of special cases of the distribution P(log Ee) of envelope field Ee. This form arises due to P(log Ew) being proportional to an integral over P(log Ee) that has a square-root singularity in Ee2. Numerical calculations confirm and extend this prediction to wide range of envelope distributions. Second, ensembles of stochastically-driven waves are simulated and the distributions P(log Ew) and P(log Ee) calculated. While small differences exist between the case of a single mode and multiple modes, it is found in general that the results are independent of the product of the wave frequency and decorrelation time. Of importance here is that the distributions P(log Ew) are found to be power-law with index ≈ 1.0 at low Ew, consistent with the analytic prediction. Moreover, the envelope distribution is found to be well fit by the form P(log Ee) ∝ Ee2 exp(- Ee2 / Eth2). This form applies to one- dimensional thermal waves and now, unexpectedly, also to waves driven stochastically near marginal stability. Third, initial calculations show that averaging (boxcar and sliding averages, whether linear or logarithmic) over multiple wave periods leads to both the envelope and waveform distributions being well fitted by lognormal distributions. Fourth, initial comparisons are made with Langmuir-like waves observed in Earth's cusp region by the TRICE rocket. It appears that the foregoing analytic and numerical calculations explain semi-quantitatively the power-law form and index near 1.0 for the waveform distribution of unaveraged fields, the functional form of the envelope distribution of unaveraged fields, and the transition of the waveform and envelope distributions towards lognormal forms with averaging over multiple wave periods. The waves appear consistent with stochastic growth. The theory and simulation results extend stochastic growth theory to measurements on timescales less than or close to the wave period.

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Research paper thumbnail of Analytic and Numerical Modelling of Plasma Radiation from Earth's Foreshock

AGUFM, Dec 1, 2001

ABSTRACT

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Research paper thumbnail of Type III Solar Radio Bursts in the Inhomogeneous Corona and Interplanetary Space

AGUFM, Dec 1, 2006

ABSTRACT

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Research paper thumbnail of Waveform and envelope field statistics for waves with stochastically driven amplitudes

Physics of Plasmas, Mar 1, 2010

ABSTRACT The statistically steady distributions P(log E) and Pe(log Ee) of waveform field E and e... more ABSTRACT The statistically steady distributions P(log E) and Pe(log Ee) of waveform field E and envelope field Ee are studied for time-varying waves with stochastically driven amplitudes. The waves are represented in one dimension (1D) by a single mode or superposition of multiple independent modes, whose amplitudes follow stochastic differential equations. Both distributions at low fields follow power laws: P(log E)∝Ep and Pe(log Ee)∝Eeq 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 ≥ 2) of modes. For N ≥ 2, p ≈ +1.0, q ≈ +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 ≥ 2 agree quantitatively with the respective observations, suggesting that the Langmuir waves may be 1D and have a stochastic driver.

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Research paper thumbnail of Quasilinear-based simulations of bidirectional type III bursts

Journal of Geophysical Research, Oct 1, 2008

Quasilinear‐based simulations are presented of bidirectional type III bursts that originate in th... more Quasilinear‐based simulations are presented of bidirectional type III bursts that originate in the corona and are observed at Earth, assuming plasma emission. By extending a recent simulation model to more realistic three‐dimensional source structures and including Langmuir collisional damping, dynamic spectra of both the normal‐drifting (normal) and the reverse‐slope‐drifting (RS) bursts are simulated and studied in detail for realistic electron‐release and coronal parameters. The radio flux, brightness temperature, frequency drift rate, and time duration of the bursts agree semiquantitatively with typical observations. The flux of 2fp emission is significantly higher than that of fp emission, which is below the noise thresholds of typical radio instruments. This is mainly because the fp emission is strongly free‐free absorbed and further damped by scattering off density fluctuations. The 2fp emission is asymmetric between the normal and RS bursts, with the normal burst stronger and lasting longer than the RS burst, consistent with observations. This occurs primarily because of the downgoing beam being weaker, not faster, and narrower in velocity space than the upgoing beam, and because of stronger free‐free absorption for the RS burst than for the normal burst, consistent with a semiquantitative theory. Furthermore, the RS burst terminates at frequencies lower than the maximum simulated, and the normal burst extends to lower frequencies not simulated because of computational limitations. Collisional damping reduces the Langmuir wave levels and consequently suppresses the flux levels and washes out the dynamic spectral structures associated with successive wave‐wave interactions when the damping is switched off.

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Research paper thumbnail of MHD-kinetic Simulation of the Heliospheric Interface and Related 2-3 kHz Radio Emission

AGU Fall Meeting Abstracts, Dec 1, 2013

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Research paper thumbnail of Solar cycle variation of dynamic spectra predicted for radiation from the outer heliosphere

cosp, 2006

ABSTRACT

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Research paper thumbnail of Heliospheric asymmetries due to the action of the interstellar magnetic field

Advances in Space Research, Dec 1, 2009

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Research paper thumbnail of Maximum Langmuir fields in planetary foreshocks determined from the electrostatic decay threshold

Geophysical Research Letters, Oct 1, 1995

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Research paper thumbnail of On the Directivity of Low-Frequency Type IV Radio Bursts

arXiv (Cornell University), May 7, 2016

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Research paper thumbnail of Eigenmode Structure in Solar-Wind Langmuir Waves

Physical Review Letters, Jul 29, 2008

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Research paper thumbnail of Laboratory Evidence for Stochastic Plasma-Wave Growth

Physical Review Letters, Nov 14, 2007

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Research paper thumbnail of Type II and type III radiation from Langmuir wave eigenmodes

EGUGA, Apr 1, 2009

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Research paper thumbnail of Heliospheric structure due to magnetic fields and neutral particles from the three- dimensional MHD-kinetic model

AGU Fall Meeting Abstracts, Dec 1, 2007

ABSTRACT Neutral particles play a major role in determining the structure of the outer heliospher... more ABSTRACT Neutral particles play a major role in determining the structure of the outer heliosphere. This is primarily due to the low degree of ionization of the local interstellar medium (LISM). Charge exchange and collisions among atoms and solar wind (SW) ions results in the deceleration of the latter. It is responsible for the birth of pickup ions (PUIs). Secondary neutrals can propagate far upstream of the LISM and modify its parameters. By decreasing the ratio of the SW and LISM ram pressures neutral particles decrease the distance of the heliopause to the Sun, so affecting the location and strength of the SW termination shock (TS). We have shown recently that charge exchange considerably decreases the effect of the interstellar magnetic field (ISMF) on the TS asymmetry -- the phenomenon very well known from ideal MHD simulations performed over the last decade. Since the mean free-path of neutral hydrogen, which is the most important atomic component of the LISM, is comparable with the characteristic lengths (the distances between major discontinuities) of the solar wind (SW) interaction with the LISM, a physically-consistent way to model its behavior is based on the solution of the kinetic Boltzmann equation. An efficient way to solve the Boltzmann equation is provided by stochastic simulations with a direct simulation Monte Carlo method. We apply the Riverside MHD-kinetic model of the heliospheric interface, incorporated into a parallel, adaptive mesh refinement code MS-FLUKSS (Multi-Scale FLUid-Kinetic Simulation Suite) to investigate the the structure of the heliosphere under the assumption that the plane formed by the ISMF and the LISM velocity vectors belongs to the hydrogen deflection plane (HDP) identified in the recent observations from the SOHO SWAN experiment. The actual deflection of the neutral hydrogen flow from its original orientation in the LISM is determined in the presence of the interplanetary magnetic field and ISMF. We present the results in the form of distributions of the plasma and magnetic field quantities in the directions of the Voyager 1 and Voyager 2 spacecraft. Connection of different points on the Voyager trajectories to the TS is investigated. We also analyze the regions of favorable 2-3 kHz radio emission occurring in the outer heliosheath due to charge exchange of the LISM plasma and hot secondary H atoms born in the inner heliosheath.

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Research paper thumbnail of Langmuir-like waves and radiation in planetary foreshocks

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Research paper thumbnail of Draping of the local interstellar magnetic field over the heliopause

Journal of Geophysical Research, Apr 1, 2008

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Research paper thumbnail of A Flare-type IV Burst Event from Proxima Centauri and Implications for Space Weather

The Astrophysical Journal, 2020

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Research paper thumbnail of On the directivity of low-frequency type IV radio bursts

2016 URSI Asia-Pacific Radio Science Conference (URSI AP-RASC), 2016

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Research paper thumbnail of Predicting radio emission from lunar radio anomolies

EAEJA, Apr 1, 2003

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Quasilinear Simulation of Harmonic Electromagnetic Emission via Beam-driven Langmuir Waves in the Solar Wind

AGU Fall Meeting Abstracts, Dec 1, 2004

ABSTRACT

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Statistics of Waveform and Envelope Fields: Theory, Simulations and Initial Applications to TRICE Data

AGU Fall Meeting Abstracts, Dec 1, 2008

ABSTRACT Plasma waves in space are almost invariably bursty and widely variable in amplitude, mot... more ABSTRACT Plasma waves in space are almost invariably bursty and widely variable in amplitude, motivating statistical approaches such as stochastic growth theory. Recent wave experiments on rockets moving through Earth's auroral regions, as well as the STEREO and Wind spacecraft, have sufficient time resolution to measure the waveform as well as the envelope field. Typically, however, experiments measure the envelope field averaged over long times compared with the wave period. Four sets of new contributions are presented. First, analytic theory is used to predict the distribution of waveform fields for a single mode with known distribution of envelope fields. The distribution P(log Ew) of waveform fields Ew is shown to be proportional to the rectified field Ewa with a ≈ 1.0 for a number of special cases of the distribution P(log Ee) of envelope field Ee. This form arises due to P(log Ew) being proportional to an integral over P(log Ee) that has a square-root singularity in Ee2. Numerical calculations confirm and extend this prediction to wide range of envelope distributions. Second, ensembles of stochastically-driven waves are simulated and the distributions P(log Ew) and P(log Ee) calculated. While small differences exist between the case of a single mode and multiple modes, it is found in general that the results are independent of the product of the wave frequency and decorrelation time. Of importance here is that the distributions P(log Ew) are found to be power-law with index ≈ 1.0 at low Ew, consistent with the analytic prediction. Moreover, the envelope distribution is found to be well fit by the form P(log Ee) ∝ Ee2 exp(- Ee2 / Eth2). This form applies to one- dimensional thermal waves and now, unexpectedly, also to waves driven stochastically near marginal stability. Third, initial calculations show that averaging (boxcar and sliding averages, whether linear or logarithmic) over multiple wave periods leads to both the envelope and waveform distributions being well fitted by lognormal distributions. Fourth, initial comparisons are made with Langmuir-like waves observed in Earth's cusp region by the TRICE rocket. It appears that the foregoing analytic and numerical calculations explain semi-quantitatively the power-law form and index near 1.0 for the waveform distribution of unaveraged fields, the functional form of the envelope distribution of unaveraged fields, and the transition of the waveform and envelope distributions towards lognormal forms with averaging over multiple wave periods. The waves appear consistent with stochastic growth. The theory and simulation results extend stochastic growth theory to measurements on timescales less than or close to the wave period.

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Research paper thumbnail of Analytic and Numerical Modelling of Plasma Radiation from Earth's Foreshock

AGUFM, Dec 1, 2001

ABSTRACT

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Research paper thumbnail of Type III Solar Radio Bursts in the Inhomogeneous Corona and Interplanetary Space

AGUFM, Dec 1, 2006

ABSTRACT

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Waveform and envelope field statistics for waves with stochastically driven amplitudes

Physics of Plasmas, Mar 1, 2010

ABSTRACT The statistically steady distributions P(log E) and Pe(log Ee) of waveform field E and e... more ABSTRACT The statistically steady distributions P(log E) and Pe(log Ee) of waveform field E and envelope field Ee are studied for time-varying waves with stochastically driven amplitudes. The waves are represented in one dimension (1D) by a single mode or superposition of multiple independent modes, whose amplitudes follow stochastic differential equations. Both distributions at low fields follow power laws: P(log E)∝Ep and Pe(log Ee)∝Eeq 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 ≥ 2) of modes. For N ≥ 2, p ≈ +1.0, q ≈ +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 ≥ 2 agree quantitatively with the respective observations, suggesting that the Langmuir waves may be 1D and have a stochastic driver.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Quasilinear-based simulations of bidirectional type III bursts

Journal of Geophysical Research, Oct 1, 2008

Quasilinear‐based simulations are presented of bidirectional type III bursts that originate in th... more Quasilinear‐based simulations are presented of bidirectional type III bursts that originate in the corona and are observed at Earth, assuming plasma emission. By extending a recent simulation model to more realistic three‐dimensional source structures and including Langmuir collisional damping, dynamic spectra of both the normal‐drifting (normal) and the reverse‐slope‐drifting (RS) bursts are simulated and studied in detail for realistic electron‐release and coronal parameters. The radio flux, brightness temperature, frequency drift rate, and time duration of the bursts agree semiquantitatively with typical observations. The flux of 2fp emission is significantly higher than that of fp emission, which is below the noise thresholds of typical radio instruments. This is mainly because the fp emission is strongly free‐free absorbed and further damped by scattering off density fluctuations. The 2fp emission is asymmetric between the normal and RS bursts, with the normal burst stronger and lasting longer than the RS burst, consistent with observations. This occurs primarily because of the downgoing beam being weaker, not faster, and narrower in velocity space than the upgoing beam, and because of stronger free‐free absorption for the RS burst than for the normal burst, consistent with a semiquantitative theory. Furthermore, the RS burst terminates at frequencies lower than the maximum simulated, and the normal burst extends to lower frequencies not simulated because of computational limitations. Collisional damping reduces the Langmuir wave levels and consequently suppresses the flux levels and washes out the dynamic spectral structures associated with successive wave‐wave interactions when the damping is switched off.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of MHD-kinetic Simulation of the Heliospheric Interface and Related 2-3 kHz Radio Emission

AGU Fall Meeting Abstracts, Dec 1, 2013

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Solar cycle variation of dynamic spectra predicted for radiation from the outer heliosphere

cosp, 2006

ABSTRACT

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Heliospheric asymmetries due to the action of the interstellar magnetic field

Advances in Space Research, Dec 1, 2009

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Maximum Langmuir fields in planetary foreshocks determined from the electrostatic decay threshold

Geophysical Research Letters, Oct 1, 1995

Bookmarks Related papers MentionsView impact

Research paper thumbnail of On the Directivity of Low-Frequency Type IV Radio Bursts

arXiv (Cornell University), May 7, 2016

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Eigenmode Structure in Solar-Wind Langmuir Waves

Physical Review Letters, Jul 29, 2008

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Laboratory Evidence for Stochastic Plasma-Wave Growth

Physical Review Letters, Nov 14, 2007

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Type II and type III radiation from Langmuir wave eigenmodes

EGUGA, Apr 1, 2009

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Heliospheric structure due to magnetic fields and neutral particles from the three- dimensional MHD-kinetic model

AGU Fall Meeting Abstracts, Dec 1, 2007

ABSTRACT Neutral particles play a major role in determining the structure of the outer heliospher... more ABSTRACT Neutral particles play a major role in determining the structure of the outer heliosphere. This is primarily due to the low degree of ionization of the local interstellar medium (LISM). Charge exchange and collisions among atoms and solar wind (SW) ions results in the deceleration of the latter. It is responsible for the birth of pickup ions (PUIs). Secondary neutrals can propagate far upstream of the LISM and modify its parameters. By decreasing the ratio of the SW and LISM ram pressures neutral particles decrease the distance of the heliopause to the Sun, so affecting the location and strength of the SW termination shock (TS). We have shown recently that charge exchange considerably decreases the effect of the interstellar magnetic field (ISMF) on the TS asymmetry -- the phenomenon very well known from ideal MHD simulations performed over the last decade. Since the mean free-path of neutral hydrogen, which is the most important atomic component of the LISM, is comparable with the characteristic lengths (the distances between major discontinuities) of the solar wind (SW) interaction with the LISM, a physically-consistent way to model its behavior is based on the solution of the kinetic Boltzmann equation. An efficient way to solve the Boltzmann equation is provided by stochastic simulations with a direct simulation Monte Carlo method. We apply the Riverside MHD-kinetic model of the heliospheric interface, incorporated into a parallel, adaptive mesh refinement code MS-FLUKSS (Multi-Scale FLUid-Kinetic Simulation Suite) to investigate the the structure of the heliosphere under the assumption that the plane formed by the ISMF and the LISM velocity vectors belongs to the hydrogen deflection plane (HDP) identified in the recent observations from the SOHO SWAN experiment. The actual deflection of the neutral hydrogen flow from its original orientation in the LISM is determined in the presence of the interplanetary magnetic field and ISMF. We present the results in the form of distributions of the plasma and magnetic field quantities in the directions of the Voyager 1 and Voyager 2 spacecraft. Connection of different points on the Voyager trajectories to the TS is investigated. We also analyze the regions of favorable 2-3 kHz radio emission occurring in the outer heliosheath due to charge exchange of the LISM plasma and hot secondary H atoms born in the inner heliosheath.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Langmuir-like waves and radiation in planetary foreshocks

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Draping of the local interstellar magnetic field over the heliopause

Journal of Geophysical Research, Apr 1, 2008

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A Flare-type IV Burst Event from Proxima Centauri and Implications for Space Weather

The Astrophysical Journal, 2020

Bookmarks Related papers MentionsView impact

Research paper thumbnail of On the directivity of low-frequency type IV radio bursts

2016 URSI Asia-Pacific Radio Science Conference (URSI AP-RASC), 2016

Bookmarks Related papers MentionsView impact