Iver Cairns - Academia.edu (original) (raw)
Papers by Iver Cairns
EAEJA, Apr 1, 2003
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AGU Fall Meeting Abstracts, Dec 1, 2004
ABSTRACT
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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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AGUFM, Dec 1, 2001
ABSTRACT
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AGUFM, Dec 1, 2006
ABSTRACT
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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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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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AGU Fall Meeting Abstracts, Dec 1, 2013
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cosp, 2006
ABSTRACT
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Advances in Space Research, Dec 1, 2009
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Geophysical Research Letters, Oct 1, 1995
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arXiv (Cornell University), May 7, 2016
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Physical Review Letters, Jul 29, 2008
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Physical Review Letters, Nov 14, 2007
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EGUGA, Apr 1, 2009
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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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Journal of Geophysical Research, Apr 1, 2008
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The Astrophysical Journal, 2020
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2016 URSI Asia-Pacific Radio Science Conference (URSI AP-RASC), 2016
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EAEJA, Apr 1, 2003
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AGU Fall Meeting Abstracts, Dec 1, 2004
ABSTRACT
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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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AGUFM, Dec 1, 2001
ABSTRACT
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AGUFM, Dec 1, 2006
ABSTRACT
Bookmarks Related papers MentionsView impact
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
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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AGU Fall Meeting Abstracts, Dec 1, 2013
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cosp, 2006
ABSTRACT
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Advances in Space Research, Dec 1, 2009
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Geophysical Research Letters, Oct 1, 1995
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arXiv (Cornell University), May 7, 2016
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Physical Review Letters, Jul 29, 2008
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Physical Review Letters, Nov 14, 2007
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EGUGA, Apr 1, 2009
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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
Bookmarks Related papers MentionsView impact
Journal of Geophysical Research, Apr 1, 2008
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The Astrophysical Journal, 2020
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2016 URSI Asia-Pacific Radio Science Conference (URSI AP-RASC), 2016
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