Today's tutorial speakers were Paul O'Brien of Aerospace on "Space radiation climatology: A new paradigm for inner magnetosphere simulation and data analysis" and Antonius Otto of University of Alaska-Fairbanks on "Plasma transport and entropy considerations at the magnetospheric flanks".
O'Brien discussed several examples of climatology and reanalysis as applied to inner magnetospheric physics. Reanalysis can constitute an extended event study and even become a data set in itself. This allows modelers to ignore most of the subtleties inherent in analyzing space plasma data. Data assimilation can help speed up codes and are useful when the underlying physics is not understood. O'Brien illustrated these points with several examples. Wiki: http://virbo.org/wiki/index.php/GEM2007.
Meeting fatigue has caught up with me; I didn't get anything out of Otto's tutorial.
This is the last year that Rice University organizes the conference. The conference arranger, Umbe Cantú, is truly an expert at conference organization, and GEM will miss her talents. Virginia Tech takes over next year, and the rumor is it will take four people to replace Umbe.
Showing posts with label GEM. Show all posts
Showing posts with label GEM. Show all posts
Friday, June 22, 2007
GEM workshop, Thursday poster session
The Thursday poster session was less than half the size of the Tuesday poster session. Unfortunately, almost all of the posters of interest to me were in the Tuesday session, and for many of the more interesting posters in this session the presenters were not with the posters when I looked at them. Meeting burnout was also a factor; many people will be leaving in the morning.
GEM workshop, Thursday breakout sessions
In the afternoon I attended two breakout sessions on diffuse aurora, continuing the breakout session from the previous afternoon.
Speakers in the first session were Mike Schultz (Lockheed) on theoretical particle tracing in a Dungey magnetosphere, Margaret Chen (Aerospace) on simulations in the Dungey magnetosphere, Richard Thorne (UCLA, on behalf of Richard Horne and Nigel Meredith of BAS) on diffuse aurora scattering rates by chorus emissions and ECH waves, Jacob Bortnik (UCLA) on modeling the global characteristics of chorus propagation, Wen Li (UCLA) on ray tracing with the HOTRAY code, Jay Albert (AFRL) on approximations of quasilinear diffusion coefficients, and R. P. Sharma (IIT) on nonlinear kinetic Alfvén waves and their role in particle precipitation. The reason Schultz and Chen use the Dungey magnetosphere is because it is analytically tractable, and an explicit Hamiltonian can be derived from a suitable electric field model (Brice-Nishida, Volland-Stern, or AMIE). Thorne pointed out the difficulty of scattering particles with 90 degree pitch angles at the equator. Bortnik showed that the lowest frequency chorus waves can propagate to the highest latitudes. Albert showed a method for calculating approximate diffusion coefficients which is significantly more accurate than the Summers method yet still represents a substantial speedup (factor of ~200) from the full calculation, which requires an infinite sum of triple integrals.
After the break, the topic was future plans for this focus group. It was decided that at this stage it is important to gather a list of relevant available data sets, and modeling efforts will proceed later. The most relevant data set for waves is THEMIS (it is necessary for the satellite to be in an equatorial orbit). For particles there are various geosynchronous satellites as well as low altitude satellites (DMSP and FAST) to look at precipitating particles. Ground-based measurements, especially all-sky cameras and meridian scanning photometers, are also of great importance for the study.
Speakers in the first session were Mike Schultz (Lockheed) on theoretical particle tracing in a Dungey magnetosphere, Margaret Chen (Aerospace) on simulations in the Dungey magnetosphere, Richard Thorne (UCLA, on behalf of Richard Horne and Nigel Meredith of BAS) on diffuse aurora scattering rates by chorus emissions and ECH waves, Jacob Bortnik (UCLA) on modeling the global characteristics of chorus propagation, Wen Li (UCLA) on ray tracing with the HOTRAY code, Jay Albert (AFRL) on approximations of quasilinear diffusion coefficients, and R. P. Sharma (IIT) on nonlinear kinetic Alfvén waves and their role in particle precipitation. The reason Schultz and Chen use the Dungey magnetosphere is because it is analytically tractable, and an explicit Hamiltonian can be derived from a suitable electric field model (Brice-Nishida, Volland-Stern, or AMIE). Thorne pointed out the difficulty of scattering particles with 90 degree pitch angles at the equator. Bortnik showed that the lowest frequency chorus waves can propagate to the highest latitudes. Albert showed a method for calculating approximate diffusion coefficients which is significantly more accurate than the Summers method yet still represents a substantial speedup (factor of ~200) from the full calculation, which requires an infinite sum of triple integrals.
After the break, the topic was future plans for this focus group. It was decided that at this stage it is important to gather a list of relevant available data sets, and modeling efforts will proceed later. The most relevant data set for waves is THEMIS (it is necessary for the satellite to be in an equatorial orbit). For particles there are various geosynchronous satellites as well as low altitude satellites (DMSP and FAST) to look at precipitating particles. Ground-based measurements, especially all-sky cameras and meridian scanning photometers, are also of great importance for the study.
Thursday, June 21, 2007
GEM workshop, Thursday plenary session
Today's plenary session speakers were Vassilis Angelopoulos of UC Berkeley (soon to join the UCLA faculty) on "Maximizing substorm science on THEMIS: Probe alignments and ground conjunctions" and Eric Donovan of Calgary on "Diffuse Aurora".
Angelopoulos is PI of the THEMIS mission. He reviewed the status of the THEMIS mission and some of the scientific topics to which THEMIS can contribute. At present THEMIS is in a string-of-pearls configuration with a separation of ~10000 km between the leading and trailing satellites and ~200 km between the middle three. Electric field antennas have been successfully deployed on three of the five spacecraft, and all other instruments are working on all five spacecraft. When the spacecraft are boosted to their final orbits sometime this fall, the orbits will be phased so that there will be a five-spacecraft conjunction every four days and four-spacecraft conjunctions every two days. Apogee will be in the tail from January through March with the conjunctions over the North America sector, where ground magnetometers and all sky cameras are deployed from Alaska to Labrador. Nominal science operations will begin 1 July, and science software will be rolled out to the community 31 July. There is an open data policy (consult with PI or co-Is, and credit NASA grant NAS5-02099). Already THEMIS is obtaining useful science data, including an observation of substorm onset with westward traveling surge, a measurement of a flux transfer event, and an observation of magnetopause reconnection. THEMIS will be able to track radial motion of electrons inward from the tail and measure electric and magnetic fields and waves locally. There are also potential contributions to dayside magnetospheric physics (this summer) and tracking of solar wind interaction with the magnetopause (summer 2008). Nominal mission lasts until about March 2009, with extensions possible given consumables budget and radiation margin. There are at least two web sites of interest: data from http://themis.ssl.berkeley.edu and orbit visualization from SSCWeb at http://sscweb.gsfc.nasa.gov/tipsod. There is a removable attenuator (x50) which ensures that the particle instruments do not saturate in the radiation belt.
Donovan's talk was an overview of the breakout sessions on diffuse aurora which started yesterday and continue this afternoon. Although diffuse aurora is operationally defined as structureless precipitation, the precipitation actually reflects significant turbulence in the central plasma sheet. There are separate electron and ion aurora. On the duskside, the proton aurora is equatorward of the ion aurora, while postmidnight the proton aurora can be poleward of the electron diffuse aurora. The poleward boundary of the 630 nm oxygen line is a proxy for the open-closed field line boundary.
Angelopoulos is PI of the THEMIS mission. He reviewed the status of the THEMIS mission and some of the scientific topics to which THEMIS can contribute. At present THEMIS is in a string-of-pearls configuration with a separation of ~10000 km between the leading and trailing satellites and ~200 km between the middle three. Electric field antennas have been successfully deployed on three of the five spacecraft, and all other instruments are working on all five spacecraft. When the spacecraft are boosted to their final orbits sometime this fall, the orbits will be phased so that there will be a five-spacecraft conjunction every four days and four-spacecraft conjunctions every two days. Apogee will be in the tail from January through March with the conjunctions over the North America sector, where ground magnetometers and all sky cameras are deployed from Alaska to Labrador. Nominal science operations will begin 1 July, and science software will be rolled out to the community 31 July. There is an open data policy (consult with PI or co-Is, and credit NASA grant NAS5-02099). Already THEMIS is obtaining useful science data, including an observation of substorm onset with westward traveling surge, a measurement of a flux transfer event, and an observation of magnetopause reconnection. THEMIS will be able to track radial motion of electrons inward from the tail and measure electric and magnetic fields and waves locally. There are also potential contributions to dayside magnetospheric physics (this summer) and tracking of solar wind interaction with the magnetopause (summer 2008). Nominal mission lasts until about March 2009, with extensions possible given consumables budget and radiation margin. There are at least two web sites of interest: data from http://themis.ssl.berkeley.edu and orbit visualization from SSCWeb at http://sscweb.gsfc.nasa.gov/tipsod. There is a removable attenuator (x50) which ensures that the particle instruments do not saturate in the radiation belt.
Donovan's talk was an overview of the breakout sessions on diffuse aurora which started yesterday and continue this afternoon. Although diffuse aurora is operationally defined as structureless precipitation, the precipitation actually reflects significant turbulence in the central plasma sheet. There are separate electron and ion aurora. On the duskside, the proton aurora is equatorward of the ion aurora, while postmidnight the proton aurora can be poleward of the electron diffuse aurora. The poleward boundary of the 630 nm oxygen line is a proxy for the open-closed field line boundary.
Wednesday, June 20, 2007
GEM workshop, Wednesday breakout sessions
This afternoon I went to the breakout sessions on the proposed solar wind structure from L1 to Earth focus group and the diffuse auroral precipitation focus group.
Speakers in the solar wind structure focus group were Joe Borovsky (Los Alamos) introducing the topic, Nicholeen Viall (Boston University) on periodic structures in the solar wind and magnetosphere, Dan Weimer (Solana Scientific) on tilted phase surfaces in the interplanetary magnetic field, Benoit Lavraud (Los Alamos) on the response of the magnetosphere to solar wind variations, Bob McPherron (UCLA) on why it is important to know the structure of the solar wind at 1 AU, and Dan Baker (Colorado) on the effect of quiet space weather conditions on the Aeronomy of Ice in the Mesosphere satellite's transmitter. This is a proposed focus group, so science definition is in progress. The most interesting talk was McPherron's; he noted that the magnetosphere's response to the solar wind is nonlinear and has histeresis; he also listed the different possible magnetospheric response modes including substorms, steady magnetospheric convection, magnetic storms, pseudobreakups, poleward boundary intensifications, and sawtooth events.
Speakers in the first session of the diffuse auroral precipitation focus group (there will be two more sessions on Thursday) were Harald Frey (UC Berkeley) on ground signatures of localized wave-particle interaction in diffuse aurora, Jay Johnson (PPPL, on behalf of Simon Wing of APL) on a magnetotail assimilation model, Michelle Thomsen (Los Alamos) on observations of plasma sheet electrons at geosynchronous orbit, Sarah Jones (UNH, on behalf of Marc Lessard) on the evolution of diffuse particle precipitation to inverted V precipitation, Emma Spanswick (Calgary) on optical and riometer signatures of diffuse aurora, Tom Sotirelis (APL) on the global character of diffuse electron aurora, and Jacob Bortnik (UCLA) on scattering of electrons by chorus waves. Highlights were Frey, who asked the key question, "What is diffuse aurora, anyway?"; Thomsen's demonstration of strong pitch angle diffusion in the geosynchronous particle data, Lessard's speculation that the latitudinal width of the substorm onset arc is determined by the overlap of precipitating plasma sheet ions and electrons, and Sotirelis's demonstration that characteristic precipitating electron energy is highest near noon--the same region where Bortnik showed the strongest off-equatorial chorus, especially at low frequencies.
Speakers in the solar wind structure focus group were Joe Borovsky (Los Alamos) introducing the topic, Nicholeen Viall (Boston University) on periodic structures in the solar wind and magnetosphere, Dan Weimer (Solana Scientific) on tilted phase surfaces in the interplanetary magnetic field, Benoit Lavraud (Los Alamos) on the response of the magnetosphere to solar wind variations, Bob McPherron (UCLA) on why it is important to know the structure of the solar wind at 1 AU, and Dan Baker (Colorado) on the effect of quiet space weather conditions on the Aeronomy of Ice in the Mesosphere satellite's transmitter. This is a proposed focus group, so science definition is in progress. The most interesting talk was McPherron's; he noted that the magnetosphere's response to the solar wind is nonlinear and has histeresis; he also listed the different possible magnetospheric response modes including substorms, steady magnetospheric convection, magnetic storms, pseudobreakups, poleward boundary intensifications, and sawtooth events.
Speakers in the first session of the diffuse auroral precipitation focus group (there will be two more sessions on Thursday) were Harald Frey (UC Berkeley) on ground signatures of localized wave-particle interaction in diffuse aurora, Jay Johnson (PPPL, on behalf of Simon Wing of APL) on a magnetotail assimilation model, Michelle Thomsen (Los Alamos) on observations of plasma sheet electrons at geosynchronous orbit, Sarah Jones (UNH, on behalf of Marc Lessard) on the evolution of diffuse particle precipitation to inverted V precipitation, Emma Spanswick (Calgary) on optical and riometer signatures of diffuse aurora, Tom Sotirelis (APL) on the global character of diffuse electron aurora, and Jacob Bortnik (UCLA) on scattering of electrons by chorus waves. Highlights were Frey, who asked the key question, "What is diffuse aurora, anyway?"; Thomsen's demonstration of strong pitch angle diffusion in the geosynchronous particle data, Lessard's speculation that the latitudinal width of the substorm onset arc is determined by the overlap of precipitating plasma sheet ions and electrons, and Sotirelis's demonstration that characteristic precipitating electron energy is highest near noon--the same region where Bortnik showed the strongest off-equatorial chorus, especially at low frequencies.
GEM Workshop, Wednesday plenary session
This morning we got the agency reports via NSF program head Kile Baker. He reported two personnel changes in the Upper Atmosphere branch: Cassandra Fesen is the new Aeronomy director (replacing Bob Kerr, who is the new director at Arecibo), and Vladimir Papitashvili will return to NSF in August as a staff member heading the Antarctic program, which has been without a director for almost a year. The budget news is better than in the recent past: a 6% budget increase in FY2007 compared with 2006, with an increase of at least 4% expected for 2008. The GEM program success rate increased to 24% (6 of 25 proposals) from last year's 18% (4 of 23 proposals). The Space Weather competition news is not so good, with a success rate of around 10% expected. There are a couple of new initiatives under discussion: an interest in funding small satellites for space weather observations (i.e., nanosats and picosats) possibly starting as early as FY08, and a new initiative for computer-enabled discovery and innovation, with funding relevant to space physics available starting in 2009.
Kile relayed the following reports from other agencies: The AFOSR Young Investigator program has been expanded to include soft money scientists, with proposals due 24 July. Thomas Zurbuchen (Michigan) has proposed a collegiate space weather competition along the lines of the existing tropospheric weather competition; the first run would probably be March or April of 2009. NASA wants to speed up Explorer missions: A draft AO is (or will soon be) released, with a final AO targeted in October and three missions to be launched in 2012-2014. The Living With a Star Targeted Research and Technology deadlines may be postponed depending on when the Focused Science Topics are finalized. Magnetospheric Multiscale will likely be descoped and/or rephased to match available budget.
The tutorial speaker was Nick Omidi of Solana Scientific on "Use of hybrid and MHD models in addressing TADMAC's [the focus group on Transport at Dayside Magnetopause and Cusp] objectives". He showed that waves generated at the bow shock impinge on the magnetopause and can affect the reconnection sites if the IMF is northward. Apparently symmetric bow shocks are not. Foreshock waves can induce significant perturbations in the solar wind. Foreshock cavities (correlated dips in density and magnetic field) occur on various scales from ion gyroradius to 1 earth radius or more. A solitary shock can form when a rotational discontinuity hits the bow shock. Flux transfer events impinge on the cusps (this portion of the tutorial was shown in the breakout session yesterday). An MHD model of 3-D magnetopause reconnection shows that regions of both antiparallel and component reconnection occur.
Kile relayed the following reports from other agencies: The AFOSR Young Investigator program has been expanded to include soft money scientists, with proposals due 24 July. Thomas Zurbuchen (Michigan) has proposed a collegiate space weather competition along the lines of the existing tropospheric weather competition; the first run would probably be March or April of 2009. NASA wants to speed up Explorer missions: A draft AO is (or will soon be) released, with a final AO targeted in October and three missions to be launched in 2012-2014. The Living With a Star Targeted Research and Technology deadlines may be postponed depending on when the Focused Science Topics are finalized. Magnetospheric Multiscale will likely be descoped and/or rephased to match available budget.
The tutorial speaker was Nick Omidi of Solana Scientific on "Use of hybrid and MHD models in addressing TADMAC's [the focus group on Transport at Dayside Magnetopause and Cusp] objectives". He showed that waves generated at the bow shock impinge on the magnetopause and can affect the reconnection sites if the IMF is northward. Apparently symmetric bow shocks are not. Foreshock waves can induce significant perturbations in the solar wind. Foreshock cavities (correlated dips in density and magnetic field) occur on various scales from ion gyroradius to 1 earth radius or more. A solitary shock can form when a rotational discontinuity hits the bow shock. Flux transfer events impinge on the cusps (this portion of the tutorial was shown in the breakout session yesterday). An MHD model of 3-D magnetopause reconnection shows that regions of both antiparallel and component reconnection occur.
GEM workshop, Tuesday poster session
I was one of about 65 people giving posters in the Tuesday session. I can't comment too much on the other posters as I was busy giving mine, but the session seemed to go well. The venue was a semi-open exhibition hall next to the hotel.
There were a few logistical glitches. The poster boards were delivered later than expected. The poster session went until 2200 MDT, at which point a timer cut the lights abruptly. But for the most part, it went well.
I am now done with my duties for the week; I get to listen (or not) to the remaining sessions.
There were a few logistical glitches. The poster boards were delivered later than expected. The poster session went until 2200 MDT, at which point a timer cut the lights abruptly. But for the most part, it went well.
I am now done with my duties for the week; I get to listen (or not) to the remaining sessions.
GEM workshop, Tuesday breakout sessions
For the first half of the afternoon I attended the breakout session on global M-I coupling chaired by David Murr (Dartmouth). Speakers were Murr giving an overview of the selected events, G. Crowley (Astra Corp.) on AMIE runs, Jo Baker (APL) on SuperDARN data, Aaron Ridley (Michigan) on including seasonal variations of the aurora in models, and Bill Lotko (Dartmouth) on summer-winter variations in ionospheric plasma. The highlight of the session was Lotko's talk, in which he showed that both ionospheric conductivity and density can affect auroral intensity (Newell et al. focused on ionospheric conductivity in their 1996 Nature paper).
After the break I switched to the cusp session, chaired by Karlheinz Trattner (Lockheed) and Dave Sibeck (GSFC). Speakers were Antonius Otto (Alaska) on test particle simulations of cusp diamagnetic cavities, Nick Omidi (Solana Scientific) on hybrid simulations of the interaction of flux transfer events with the cusp, Masha Kuznetsova (GSFC) on MHD simulations of same, and Katariina Nykiri (Florida Tech) on particle acceleration in the high altitude cusp. Omidi's and Kuznetsova's talks were the most interesting, particularly Omidi's claim of a connection between FTEs and poleward moving auroral forms, and Kuznetsova's claims of FTE breakup due to sausage instability. Note to self: Ask Omidi about whether the FTE-cusp interaction might be related to my work with Charlie Farrugia on momentum transfer on old open field lines.
After the break I switched to the cusp session, chaired by Karlheinz Trattner (Lockheed) and Dave Sibeck (GSFC). Speakers were Antonius Otto (Alaska) on test particle simulations of cusp diamagnetic cavities, Nick Omidi (Solana Scientific) on hybrid simulations of the interaction of flux transfer events with the cusp, Masha Kuznetsova (GSFC) on MHD simulations of same, and Katariina Nykiri (Florida Tech) on particle acceleration in the high altitude cusp. Omidi's and Kuznetsova's talks were the most interesting, particularly Omidi's claim of a connection between FTEs and poleward moving auroral forms, and Kuznetsova's claims of FTE breakup due to sausage instability. Note to self: Ask Omidi about whether the FTE-cusp interaction might be related to my work with Charlie Farrugia on momentum transfer on old open field lines.
Tuesday, June 19, 2007
GEM Workshop, Tuesday plenary session
Today's plenary session speakers were Jimmy Raeder of UNH on "Quo vadis, GGCM" and Harlan Spence of Boston University on the radiation belts and the RBSP mission.
Raeder discussed some details of how global models work in situations involving reconnection. Ideal MHD should have a zero reconnection rate, but real-world implementations will have numerical diffusion which can produce reconnection (as well as form shocks, something else that ideal MHD should not do). Numerical diffusion can also counteract the tendency of numerical dispersion (diffusion and dispersion are due to even and odd error terms, respectively, in the truncation) to drive the code unstable. If the Hall term is included, GGCMs even manage to get close to observed reconnection rates (and if they are off, the models usually get higher rates). The implication is that reconnection rates on the dayside are set by boundary conditions, not the microphysics of the reconnection region. On the nightside, average reconnection rates (over periods of an hour or more) must equal dayside reconnection rates. Substorms are the result of short-term deviations from this balance. It is not clear whether GGCMs produce genuine substorms (there are plasmoids, but some of the other signatures are absent). Tail reconnection in the GGCM models is much more fragmented than the classic substorm models. High ionospheric conductance can suppress convection.
Spence is the lead scientist on the Radiation Belt Storm Probes mission. He reviewed the history of radiation belt paradigms and science and advertised the mission. The goal is to be able to understand, and predict, the variation of relativistic particle populations in response to energy inputs from the Sun. The satellite can make in situ measurements of high energy astrophysical phenomena.
It seems that there are capacity limits on connections from the conference center. I'm posting this from my room.
Raeder discussed some details of how global models work in situations involving reconnection. Ideal MHD should have a zero reconnection rate, but real-world implementations will have numerical diffusion which can produce reconnection (as well as form shocks, something else that ideal MHD should not do). Numerical diffusion can also counteract the tendency of numerical dispersion (diffusion and dispersion are due to even and odd error terms, respectively, in the truncation) to drive the code unstable. If the Hall term is included, GGCMs even manage to get close to observed reconnection rates (and if they are off, the models usually get higher rates). The implication is that reconnection rates on the dayside are set by boundary conditions, not the microphysics of the reconnection region. On the nightside, average reconnection rates (over periods of an hour or more) must equal dayside reconnection rates. Substorms are the result of short-term deviations from this balance. It is not clear whether GGCMs produce genuine substorms (there are plasmoids, but some of the other signatures are absent). Tail reconnection in the GGCM models is much more fragmented than the classic substorm models. High ionospheric conductance can suppress convection.
Spence is the lead scientist on the Radiation Belt Storm Probes mission. He reviewed the history of radiation belt paradigms and science and advertised the mission. The goal is to be able to understand, and predict, the variation of relativistic particle populations in response to energy inputs from the Sun. The satellite can make in situ measurements of high energy astrophysical phenomena.
It seems that there are capacity limits on connections from the conference center. I'm posting this from my room.
Monday, June 18, 2007
GEM Workshop, Monday breakout sessions
I attended two breakout sessions devoted to the focus group on Magnetosphere-Ionosphere Coupling Electrodynamics and Transport. Bill Lotko of Dartmouth and Josh Semeter of Boston University led the discussion. I spoke in the morning session, the second-to-last talk before lunch. Other speakers in the morning session were Yi-Jiun Su (UT Arlington) on the electron cyclotron maser instability in the Alfvénic acceleration region, R. P. Sharma (India Institute of Technology) on nonlinear kinetic Alfvén waves, Peter Damiano (St. Andrews) on Alfvén wave induced electron precipitation, Joo Hwang (Colorado) on test particle simulations of the effect of moving double layers on ion outflow, and Alex Glocer (Michigan) on ion outflow modeling in the "gap" region. Speakers in the afternoon session were Matt Zettergren on a kinetic-fluid coupled model for computing ion outflow, Bill Lotko on the importance of 0.1-1 Hz Alfvén waves in ion outflow, Andrew Wright (St. Andrews) on the effects of field-aligned currents on the ionosphere, Josh Semeter on an observational perspective of M-I coupling in the auroral region, Jo Baker (APL) on midlatitude ionospheric convection as observed with the SuperDARN Wallops radar, and Jerry Goldstein on "SAPpy musings" about M-I coupling.
Some highlights of the sessions:
Damiano showed that at least 40% of Alfvén wave energy in a field line resonance is lost every half period due to induced electron beam precipitation (the loss is higher with hotter electrons). He can derive a Knight-like I-V relation for warm electrons in a field line resonance; as Lotko pointed out, this implies that the wave period is much longer than the electron transit time. The initial current perturbation must broaden so that the electric field can replenish the loss cone.
Hwang showed significantly enhanced (by an order of magnitude), but episodic, ion outflow in the presence of moving double layers as compared with the extended static parallel electric field structure examined by Gorney et al. (1985). She pointed out that the outflowing ions need not pass through a moving double layer.
Lotko noted that if ion parallel dynamics are properly included, the ion density depletion in the lower F region can be ~80%, rather than ~1% if the ion dynamics are not included. The extra depletion is due to a nonlinear coupling of Alfvén waves to ion sound waves. The ions are pushed upward.
Wright noted that a downward parallel current can deplete the E region on time scales of ~30 seconds. The parallel current region must broaden to compensate. The reflection coefficient, and therefore the ionospheric Alfvén resonator, are significantly modified. He derived a parameter which determines whether depletion is (nearly) complete and a time scale for the depletion. He raised the question of whether the depletion of E region plasma implies current closure in the F region.
Semeter showed that the apparent motion of auroral arcs may be due to dispersive propagation of Alfvén wave packets.
Some highlights of the sessions:
Damiano showed that at least 40% of Alfvén wave energy in a field line resonance is lost every half period due to induced electron beam precipitation (the loss is higher with hotter electrons). He can derive a Knight-like I-V relation for warm electrons in a field line resonance; as Lotko pointed out, this implies that the wave period is much longer than the electron transit time. The initial current perturbation must broaden so that the electric field can replenish the loss cone.
Hwang showed significantly enhanced (by an order of magnitude), but episodic, ion outflow in the presence of moving double layers as compared with the extended static parallel electric field structure examined by Gorney et al. (1985). She pointed out that the outflowing ions need not pass through a moving double layer.
Lotko noted that if ion parallel dynamics are properly included, the ion density depletion in the lower F region can be ~80%, rather than ~1% if the ion dynamics are not included. The extra depletion is due to a nonlinear coupling of Alfvén waves to ion sound waves. The ions are pushed upward.
Wright noted that a downward parallel current can deplete the E region on time scales of ~30 seconds. The parallel current region must broaden to compensate. The reflection coefficient, and therefore the ionospheric Alfvén resonator, are significantly modified. He derived a parameter which determines whether depletion is (nearly) complete and a time scale for the depletion. He raised the question of whether the depletion of E region plasma implies current closure in the F region.
Semeter showed that the apparent motion of auroral arcs may be due to dispersive propagation of Alfvén wave packets.
GEM Workshop, Monday plenary session
Today's plenary session speakers were Joe Huba of NRL on M-I coupling from the ionosphere point of view and Joachim Birn of Los Alamos on transport of plasma and particles from the tail to the inner magnetosphere.
Huba's talk gave a different perspective on global modeling from that of most people in the audience; he is an ionospheric modeler, whereas many magnetospheric modelers treat the ionosphere as an annoying boundary condition. His talk covered a number of points of interest, including coupling his model (SAMI3) to the Rice Convection Model, the penetration of magnetospheric electric fields to low latitudes (when the Region 2 current should shield them out), and Total Electron Content and its effect on GPS signals. A comment by Bob McPherron pointed out an implication of Huba's work that the standard ionospheric correction to the Dst index may be in the wrong direction.
Birn gave an overview of how plasma is transported from the tail to the inner magnetosphere. He gave arguments for why the average transport from the distant tail to the inner magnetosphere should be 0, as observed. Unfortunately, lack of sleep caught up to me and I dozed through about half of the talk.
Huba's talk gave a different perspective on global modeling from that of most people in the audience; he is an ionospheric modeler, whereas many magnetospheric modelers treat the ionosphere as an annoying boundary condition. His talk covered a number of points of interest, including coupling his model (SAMI3) to the Rice Convection Model, the penetration of magnetospheric electric fields to low latitudes (when the Region 2 current should shield them out), and Total Electron Content and its effect on GPS signals. A comment by Bob McPherron pointed out an implication of Huba's work that the standard ionospheric correction to the Dst index may be in the wrong direction.
Birn gave an overview of how plasma is transported from the tail to the inner magnetosphere. He gave arguments for why the average transport from the distant tail to the inner magnetosphere should be 0, as observed. Unfortunately, lack of sleep caught up to me and I dozed through about half of the talk.
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