- Email: [email protected]
End-to-end study of the transfer of energy from magnetosheath ion precipitation to the cusp
ARTICLE IN PRESS
Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55 www.elsevier.com/locate/jastp
End-to-end study of the transfer of energy from magnetosheath ion precipitation to the cusp V.N. Coffeya,, M.O. Chandlera, Nagendra Singhb, Levon Avanovb,c a
NASA Marshall Space Flight Center, XD12, Huntsville, AL 35812, USA b University of Alabama in Huntsville, Huntsville, AL 35812, USA c Space Research Institute (IKI), Moscow, Russian Federation Received 31 March 2005; accepted 17 July 2006 Available online 1 December 2006
Abstract This paper describes a study of the effects of unstable magnetosheath distributions on the cusp ionosphere. A semikinetic model followed by a 2.5D particle-in-cell (PIC) model served as an end-to-end numerical system to study the evolved distributions from precipitation due to reconnection and, then secondly, the energy transfer into the high-latitude ionosphere based on these solar wind/magnetosheath inputs. Using inputs of several representative examples of magnetosheath injections, waves were generated at the lower hybrid frequency and energy transferred to the ionospheric electrons and ions. The resulting wave spectra and ion and electron particle heating was analyzed. r 2006 Elsevier Ltd. All rights reserved. Keywords: Ion heating; Magnetosheath/ionosphere coupling; Particle/wave interactions; Simulations
1. Introduction Macroscopic coupling between solar wind plasma and the magnetosphere propagates wave and particle energy along cusp magnetic field lines to the ionosphere (Reiff et al., 1977). The study of this input from solar sources into the high-latitude ionosphere and its final impact on the magnetospheric environment has recently reached a level of maturity that calls for a careful, quantitative assessment of each energy source. We conducted a preliminary study of the effects of magnetosheath precipitation on the cusp ionosphere. An end-to-end Corresponding author. Tel.: +1 256 961 7635; fax: +1 256 961 7215. E-mail address: [email protected] (V.N. Coffey).
1364-6826/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jastp.2006.07.015
numerical model was used to study the energy transfer into the high-latitude ionosphere based on these unstable magnetosheath distributions. The resulting wave generation and particle heating were analyzed. This study was addressed in two phases. 1. Modeling the evolution of the magnetosheath plasma ring distributions from their injection at the magnetopause to the ionosphere. Different reconnection events were simulated. 2. Modeling and analysis of the wave generation and the efficiency of the energy transfer from the magnetosheath precipitation to the near-earth ionospheric plasma. The modeling made use of a semi-kinetic code for plasma transport, and a 2.5D particle-in-cell (PIC)
ARTICLE IN PRESS V.N. Coffey et al. / Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55
code for wave analysis and energy transfer for an end-to-end impact. The inputs to the models were from observations and published results. Fig. 1 shows an observation from the Thermal Ion Dynamics Experiment (TIDE) on the Polar satellite of an H+ velocity distribution that resulted from the injection of D-shaped magnetosheath distributions at the reconnection site and the subsequent velocity filtering during precipitation (e.g. Lockwood and Smith, 1994). Although, the distributions appears ring-like they are actually surfaces of revolution or shells. The field-aligned ions (right side of panel) are the injected ions that have precipitated while the left half of the distribution is composed of ions that have precipitated, traveled to and mirrored in the ionosphere, and returned to the altitude of the satellite. This effect is more clearly seen in the model results shown in Fig. 4. 2. Magnetosheath input 2.1. Phase I, kinetic model description The semi-kinetic code is a one-dimensional, timedependent, plasma model (Wilson et al. 1990; Singh 1996). We defined the magnetic field using the T96 model (Tsyganenko and Stern, 1996) starting from 956 km and extending to the equatorial magnetopause (Fig. 2). This model includes the gravitational force, ambipolar electric field, and magnetic mirror 04:39:41 Vz_Bfld = 0.0 km/s
SEC3 KM−6
200
1011 1010
Vy_Bfld (km/s)
100
100 0
108 107
−100
106 −200 −200
0.0 no data
−100
0 100 Vx_Bfld (km/s)
200
Fig. 1. Observations of a shell distribution from magnetosheath precipitation on 23 April 2003 from the Thermal Ion Dynamics Experiment (TIDE).
51
Fig. 2. The profile of normalized magnetic field strength as a function of altitude used in the simulation runs. A simple dipole configuration is shown for comparison.
force. The flux tube included H+, O+ and a neutralizing background of electrons. The electric field was turned off in these simulations because there would hardly be any effect on the magnetosheath ions. A polar wind was first established in the flux tube with an H+ and O+ background until the flux was constant. Magnetosheath H+ ions were then injected onto the field line at the equatorial plane with parameters of (defined by an observed TIDE distribution): a de Hoffman–Teller cut-off at 100 km s1, a drift velocity of 200 km s1, and a parallel and perpendicular ion temperature of 50 and 100 eV, respectively. This distribution is shown in the top left panel each of Fig. 3–5. 2.2. Phase I, simulation results Three types of magnetosheath injections were simulated: single injection event (Fig. 3), a continuous injection event (Fig. 4), and a pulsed injection event (Fig. 5). Each of the three figures consists of six panels and includes results from a selected altitude range within the flux tube. The units are arbitrary with the color range ranging from blue to red indicating low to high-velocity-phase space. The top left panel in each figure shows the initial injected magnetosheath distribution with characteristics described earlier. The remaining five panels show the evolved distribution within the selected altitude range at different elapsed times in the simulation. The distributions in Fig. 3 are observed slightly below the ‘kink’ in the field strength shown in Fig. 2. At 179 s at this altitude, the precipitating ions are
ARTICLE IN PRESS V.N. Coffey et al. / Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55
52
t = 0 sec
t = 179 sec
t = 357 sec
t = 536 sec
t = 715 sec
t = 894 sec
Vper (km/s)
400 200 0 −200 −400
Vper (km/s)
400 200 0 −200 −400 −400 −200
0
200
400
−400 −200
Vpar (km/s)
0
200
400
Vpar (km/s)
−400 −200
0
200
400
Vpar (km/s)
Fig. 3. Simulation results of the injected distribution at 90,408 km (top left panel) and the evolved H+ velocity distributions from 35,000 to 40,000 km from a single event reconnection.
t = 0 sec
t = 361 sec
t = 722 sec
t = 1083 sec
t = 1444 sec
t = 1806 sec
Vper (km/s)
400 200 0 −200 −400
Vper (km/s)
400 200 0 −200 −400 −400 −200
0
200
400
−400 −200
Vpar (km/s)
0
200
Vpar (km/s)
400
−400 −200
0
200
400
Vpar (km/s)
Fig. 4. Results of remotely observed H+ distributions ranging from 25,000 to 30,000 km altitude from a continuous reconnection simulation.
already dispersed in velocity space and there are essentially no reflected ions observed. After 357 s, the reflected ions are also observed with a loss cone. As time continues, all precipitating ions have passed
the observation point and only the mirrored ions are still observed. Fig. 4 shows simulated results from a continuous reconnection event. The notable difference between
ARTICLE IN PRESS V.N. Coffey et al. / Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55
t = 0 sec
t = 120 sec
t = 480 sec
t = 600 sec
t = 780 sec
t = 960 sec
53
Vper (km/s)
400 200 0 −200 −400
Vper (km/s)
400 200 0 −200 −400 −400 −200
0
200
400
−400 −200
Vpar (km/s)
0
200
Vpar (km/s)
400
−400 −200
0
200
400
Vpar (km/s)
Fig. 5. Results of remotely observed H+ velocity distributions ranging from 15,000 to 20,000 km in altitude from a pulsed reconnection simulation.
these results and those in Fig. 3 is the thickness of the ring that is due to the relatively long length of time the flux tube is open. The asymmetry in the distributions in the bottom row of panels shows the results of the integrated effects of velocity filtering and the spatially varying magnetic field. Fig. 5 is a simulated run of a pulsed reconnection event observed at a lower altitude range. At 120 s, with this range of velocities, there are no precipitating or reflected particles contributing to the distribution. At 780 s the ions from the first pulse can been seen at smaller velocities coincident with a ring at higher velocities composed of ions from a second pulse. While this is not expected to be a common occurrence, in that it requires multiple injections into a single flux tube, such overlapping injections have been observed (e.g. Carlson and Torbert, 1980; Woch and Lundin, 1991, 1992; Boudouridis et al., 2001).
The precipitating distributions are highly nonMaxwellian while the background ionospheric plasma is composed of Maxwellian H+ and electron distributions. The PIC code is 3D in velocity and 2D in space and varied by Lx Ly. The electrostatic PIC model is that described previously by Singh and Leung (1999). Periodic boundary conditions on both particles and fields are used. The ambient magnetic field is in the x direction. The initial ionospheric ion and electron temperatures were equal at kT ¼ 0.3 eV, the magnetosheath and ionospheric densities were equal, and the ion to electron mass ratio M/m ¼ 1836. Distances are measured in units of Debye length, ld, where Lx ¼ 256ld and Ly ¼ 128ld. We use the following normalizations: t ¼ t*ope, ld ¼ Vte/ope, E ¼ E/En, En ¼ fn/ld, fn ¼ kBT0/e, where Vte is the electron thermal velocity, and ope is the electron plasma frequency.
3. Ionospheric input
3.2. Phase II, simulation results
3.1. Phase II, 2.5D PIC model description
An evolved magnetosheath distribution from a single pulsed reconnection event—integrated over the altitude range from 6000 to 10,000 km—was input into the PIC code. This distribution was chosen for comparison to the TIDE observations at Polar perigee around 2Re. Fig. 6 shows the wave
The simulated magnetosheath distributions were used as inputs to the 2.5D PIC code to investigate the efficiency of energy transfer from the precipitating ions to the near-earth ionospheric plasma.
ARTICLE IN PRESS V.N. Coffey et al. / Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55
Ey, pt(128,65)
54
0.6 0.4 0.2 0.0 −0.2 −0.4 −0.6 0
500
1000
1500
2000
2500
tpe 10−2
|Ey|2
10−3 10−4 10−5 10−6 0.001
0.010
0.100 /pe
1.000
10.000
Fig. 6. The electric field and wave spectrum for this simulation. The lower hybrid frequency is near 0.023o/ope.
Ionospheric
a
Ions t = 0 wpe
Electrons t = 0 wpe 2000
30 20
Vper (km/s)
1000 10 0
0
−10
−1000
−20
−2000
−30
b
t = 18600 wpe
t = 18600 wpe 2000
30 20
Vper (km/s)
1000 10 0
0 −10
−1000
−20 −30 −30 −20 −10 0 10 Vpar (km/s)
20
30
−2000 −2000 −1000 0 1000 Vpar (km/s)
2000
Fig. 7. Distributions of the ambient ionospheric H+ ions and electrons (a) before and (b) after heating by lower hybrid waves (arbitrary units).
ARTICLE IN PRESS V.N. Coffey et al. / Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55
structure and power spectrum for this simulation as a function of time. The top panel shows a growing wave in the perpendicular electric field Ey. The wave frequency peaks near the lower hybrid frequency as shown in the power spectrum in the bottom panel. Fig. 7 shows the result of the energy transfer from these waves to the electrons and ions. Electron heating occurs in the parallel direction, consistent with lower hybrid heating. The perpendicular heating of the background H+ is evident and the ratio of kTperp to kTparallel is 1.33. A simulation with a different magnetosheath distribution yielded an anisotropy ratio of 1.6. 4. Summary and conclusions The injection of magnetosheath ions onto an open, high-latitude magnetic field line results in highly non-Maxwellian distributions in the topside ionosphere. Such distributions would be expected to be a free energy source for wave generation. These preliminary results exhibit the type of simulations that can be used for an end-to-end study to interpret the remotely observed distributions from the magnetosheath, the energy transfer to the ionospheric plasma, and the final outflow from this type of excitation into the magnetosphere. We have focused on one type of ion heating mechanism peculiar to the cusp in an early study to quantify its efficiency in ion heating. The exact nature of the lower hybrid wave excitation and ion heating depends on the various density and mass parameters. Roth and Hudson (1985) found that the initial development of the waves and resulting particle distributions depends on two critical parameters: the ratio of the local ion plasma and gyro frequency and the ratio of the densities of the ionospheric ions and the injected magnetosheath ring distribution. These initial results show a small amount of heating compared to observations, however, with the conditions imposed, it represents a lower limit to the heating that may be available. A more realistic representation would provide a steadily replenished non-Maxwellian distribution in the PIC code. Therefore, this work gives a measure of the efficiency of the energy transfer but does not address the cumulative effects of long-term exposure of the ionospheric plasma to magnetosheath ions.
55
Future efforts will be in the improvement of the modeling to address the aspects of different reconnection injection events. The evolved ring distributions will be input and replenished for a parameter study in density and mass similar to the research of Roth and Hudson. The use of the realistic evolved ring distributions extends their work and affords the opportunity to study this heating mechanism quantitatively and in detail. Acknowledgments The authors acknowledge support from the GSFC Polar Mission under UPN 370-08 and from the NASA Living With a Star Program under UPN 784-50-00. References Boudouridis, A., Spence, H.E., Onsager, T.G., 2001. Investigation of magnetopause reconnection models using two collocated, low-altitude satellites: a unifying reconectin geometry. Journal of Geophysical Research 106, 29451. Carlson, C.W., Torbert, R.B., 1980. Solar wind ion injections in the morning auroral oval. Journal of Geophysical Research 85, 2903. Lockwood, M., Smith, M.F., 1994. Low and middle altitude cusp particle signatures for general magnetopause reconnection rate variations, 1: theory. Journal of Geophysical Research 99, 8531. Reiff, P.H., Hill, T.W., Burch, J.L., 1977. Solar wind injection at the dayside magnetospheric cusp. Journal of Geophysical Research 82, 479. Roth, I., Hudson, M.K., 1985. Lower hybrid heating of ionospheric ions due to ion ring distributions in the cusp. Journal of Geophysical Research 90, 4191. Singh, N., 1996. Time response of O+ to a weak transverse ion heating event in the polar ionosphere. Journal of Geophysical Research 101, 5317. Singh, N., Leung, W.C., 1999. Nonlinear features of electrostatic ion cyclotron instability driven by counterstreaming ion beams in equatorial plasmasphere. Journal of Geophysical Research 104, 28547. Tsyganenko, N.A., Stern, D.P., 1996. Modeling the global magnetic field of the large-scale Birkeland current systems. Journal of Geophysical Research 101, 27187. Woch, J., Lundin, R., 1991. Temporal magnetosheath plasma injection observed with Viking: a case study. Annals of Geophysics 9, 133. Woch, J., Lundin, R., 1992. Signatures of transient boundary layer processes observed with Viking. Journal of Geophysical Research 97, 1431. Wilson, G.R., Ho, C.W., Horwitz, J.L., Singh, N., 1990. A new kinetic model for time dependent polar plasma outflow: initial results. Geophysical Research Letters 3, 263.
Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55 www.elsevier.com/locate/jastp
End-to-end study of the transfer of energy from magnetosheath ion precipitation to the cusp V.N. Coffeya,, M.O. Chandlera, Nagendra Singhb, Levon Avanovb,c a
NASA Marshall Space Flight Center, XD12, Huntsville, AL 35812, USA b University of Alabama in Huntsville, Huntsville, AL 35812, USA c Space Research Institute (IKI), Moscow, Russian Federation Received 31 March 2005; accepted 17 July 2006 Available online 1 December 2006
Abstract This paper describes a study of the effects of unstable magnetosheath distributions on the cusp ionosphere. A semikinetic model followed by a 2.5D particle-in-cell (PIC) model served as an end-to-end numerical system to study the evolved distributions from precipitation due to reconnection and, then secondly, the energy transfer into the high-latitude ionosphere based on these solar wind/magnetosheath inputs. Using inputs of several representative examples of magnetosheath injections, waves were generated at the lower hybrid frequency and energy transferred to the ionospheric electrons and ions. The resulting wave spectra and ion and electron particle heating was analyzed. r 2006 Elsevier Ltd. All rights reserved. Keywords: Ion heating; Magnetosheath/ionosphere coupling; Particle/wave interactions; Simulations
1. Introduction Macroscopic coupling between solar wind plasma and the magnetosphere propagates wave and particle energy along cusp magnetic field lines to the ionosphere (Reiff et al., 1977). The study of this input from solar sources into the high-latitude ionosphere and its final impact on the magnetospheric environment has recently reached a level of maturity that calls for a careful, quantitative assessment of each energy source. We conducted a preliminary study of the effects of magnetosheath precipitation on the cusp ionosphere. An end-to-end Corresponding author. Tel.: +1 256 961 7635; fax: +1 256 961 7215. E-mail address: [email protected] (V.N. Coffey).
1364-6826/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jastp.2006.07.015
numerical model was used to study the energy transfer into the high-latitude ionosphere based on these unstable magnetosheath distributions. The resulting wave generation and particle heating were analyzed. This study was addressed in two phases. 1. Modeling the evolution of the magnetosheath plasma ring distributions from their injection at the magnetopause to the ionosphere. Different reconnection events were simulated. 2. Modeling and analysis of the wave generation and the efficiency of the energy transfer from the magnetosheath precipitation to the near-earth ionospheric plasma. The modeling made use of a semi-kinetic code for plasma transport, and a 2.5D particle-in-cell (PIC)
ARTICLE IN PRESS V.N. Coffey et al. / Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55
code for wave analysis and energy transfer for an end-to-end impact. The inputs to the models were from observations and published results. Fig. 1 shows an observation from the Thermal Ion Dynamics Experiment (TIDE) on the Polar satellite of an H+ velocity distribution that resulted from the injection of D-shaped magnetosheath distributions at the reconnection site and the subsequent velocity filtering during precipitation (e.g. Lockwood and Smith, 1994). Although, the distributions appears ring-like they are actually surfaces of revolution or shells. The field-aligned ions (right side of panel) are the injected ions that have precipitated while the left half of the distribution is composed of ions that have precipitated, traveled to and mirrored in the ionosphere, and returned to the altitude of the satellite. This effect is more clearly seen in the model results shown in Fig. 4. 2. Magnetosheath input 2.1. Phase I, kinetic model description The semi-kinetic code is a one-dimensional, timedependent, plasma model (Wilson et al. 1990; Singh 1996). We defined the magnetic field using the T96 model (Tsyganenko and Stern, 1996) starting from 956 km and extending to the equatorial magnetopause (Fig. 2). This model includes the gravitational force, ambipolar electric field, and magnetic mirror 04:39:41 Vz_Bfld = 0.0 km/s
SEC3 KM−6
200
1011 1010
Vy_Bfld (km/s)
100
100 0
108 107
−100
106 −200 −200
0.0 no data
−100
0 100 Vx_Bfld (km/s)
200
Fig. 1. Observations of a shell distribution from magnetosheath precipitation on 23 April 2003 from the Thermal Ion Dynamics Experiment (TIDE).
51
Fig. 2. The profile of normalized magnetic field strength as a function of altitude used in the simulation runs. A simple dipole configuration is shown for comparison.
force. The flux tube included H+, O+ and a neutralizing background of electrons. The electric field was turned off in these simulations because there would hardly be any effect on the magnetosheath ions. A polar wind was first established in the flux tube with an H+ and O+ background until the flux was constant. Magnetosheath H+ ions were then injected onto the field line at the equatorial plane with parameters of (defined by an observed TIDE distribution): a de Hoffman–Teller cut-off at 100 km s1, a drift velocity of 200 km s1, and a parallel and perpendicular ion temperature of 50 and 100 eV, respectively. This distribution is shown in the top left panel each of Fig. 3–5. 2.2. Phase I, simulation results Three types of magnetosheath injections were simulated: single injection event (Fig. 3), a continuous injection event (Fig. 4), and a pulsed injection event (Fig. 5). Each of the three figures consists of six panels and includes results from a selected altitude range within the flux tube. The units are arbitrary with the color range ranging from blue to red indicating low to high-velocity-phase space. The top left panel in each figure shows the initial injected magnetosheath distribution with characteristics described earlier. The remaining five panels show the evolved distribution within the selected altitude range at different elapsed times in the simulation. The distributions in Fig. 3 are observed slightly below the ‘kink’ in the field strength shown in Fig. 2. At 179 s at this altitude, the precipitating ions are
ARTICLE IN PRESS V.N. Coffey et al. / Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55
52
t = 0 sec
t = 179 sec
t = 357 sec
t = 536 sec
t = 715 sec
t = 894 sec
Vper (km/s)
400 200 0 −200 −400
Vper (km/s)
400 200 0 −200 −400 −400 −200
0
200
400
−400 −200
Vpar (km/s)
0
200
400
Vpar (km/s)
−400 −200
0
200
400
Vpar (km/s)
Fig. 3. Simulation results of the injected distribution at 90,408 km (top left panel) and the evolved H+ velocity distributions from 35,000 to 40,000 km from a single event reconnection.
t = 0 sec
t = 361 sec
t = 722 sec
t = 1083 sec
t = 1444 sec
t = 1806 sec
Vper (km/s)
400 200 0 −200 −400
Vper (km/s)
400 200 0 −200 −400 −400 −200
0
200
400
−400 −200
Vpar (km/s)
0
200
Vpar (km/s)
400
−400 −200
0
200
400
Vpar (km/s)
Fig. 4. Results of remotely observed H+ distributions ranging from 25,000 to 30,000 km altitude from a continuous reconnection simulation.
already dispersed in velocity space and there are essentially no reflected ions observed. After 357 s, the reflected ions are also observed with a loss cone. As time continues, all precipitating ions have passed
the observation point and only the mirrored ions are still observed. Fig. 4 shows simulated results from a continuous reconnection event. The notable difference between
ARTICLE IN PRESS V.N. Coffey et al. / Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55
t = 0 sec
t = 120 sec
t = 480 sec
t = 600 sec
t = 780 sec
t = 960 sec
53
Vper (km/s)
400 200 0 −200 −400
Vper (km/s)
400 200 0 −200 −400 −400 −200
0
200
400
−400 −200
Vpar (km/s)
0
200
Vpar (km/s)
400
−400 −200
0
200
400
Vpar (km/s)
Fig. 5. Results of remotely observed H+ velocity distributions ranging from 15,000 to 20,000 km in altitude from a pulsed reconnection simulation.
these results and those in Fig. 3 is the thickness of the ring that is due to the relatively long length of time the flux tube is open. The asymmetry in the distributions in the bottom row of panels shows the results of the integrated effects of velocity filtering and the spatially varying magnetic field. Fig. 5 is a simulated run of a pulsed reconnection event observed at a lower altitude range. At 120 s, with this range of velocities, there are no precipitating or reflected particles contributing to the distribution. At 780 s the ions from the first pulse can been seen at smaller velocities coincident with a ring at higher velocities composed of ions from a second pulse. While this is not expected to be a common occurrence, in that it requires multiple injections into a single flux tube, such overlapping injections have been observed (e.g. Carlson and Torbert, 1980; Woch and Lundin, 1991, 1992; Boudouridis et al., 2001).
The precipitating distributions are highly nonMaxwellian while the background ionospheric plasma is composed of Maxwellian H+ and electron distributions. The PIC code is 3D in velocity and 2D in space and varied by Lx Ly. The electrostatic PIC model is that described previously by Singh and Leung (1999). Periodic boundary conditions on both particles and fields are used. The ambient magnetic field is in the x direction. The initial ionospheric ion and electron temperatures were equal at kT ¼ 0.3 eV, the magnetosheath and ionospheric densities were equal, and the ion to electron mass ratio M/m ¼ 1836. Distances are measured in units of Debye length, ld, where Lx ¼ 256ld and Ly ¼ 128ld. We use the following normalizations: t ¼ t*ope, ld ¼ Vte/ope, E ¼ E/En, En ¼ fn/ld, fn ¼ kBT0/e, where Vte is the electron thermal velocity, and ope is the electron plasma frequency.
3. Ionospheric input
3.2. Phase II, simulation results
3.1. Phase II, 2.5D PIC model description
An evolved magnetosheath distribution from a single pulsed reconnection event—integrated over the altitude range from 6000 to 10,000 km—was input into the PIC code. This distribution was chosen for comparison to the TIDE observations at Polar perigee around 2Re. Fig. 6 shows the wave
The simulated magnetosheath distributions were used as inputs to the 2.5D PIC code to investigate the efficiency of energy transfer from the precipitating ions to the near-earth ionospheric plasma.
ARTICLE IN PRESS V.N. Coffey et al. / Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55
Ey, pt(128,65)
54
0.6 0.4 0.2 0.0 −0.2 −0.4 −0.6 0
500
1000
1500
2000
2500
tpe 10−2
|Ey|2
10−3 10−4 10−5 10−6 0.001
0.010
0.100 /pe
1.000
10.000
Fig. 6. The electric field and wave spectrum for this simulation. The lower hybrid frequency is near 0.023o/ope.
Ionospheric
a
Ions t = 0 wpe
Electrons t = 0 wpe 2000
30 20
Vper (km/s)
1000 10 0
0
−10
−1000
−20
−2000
−30
b
t = 18600 wpe
t = 18600 wpe 2000
30 20
Vper (km/s)
1000 10 0
0 −10
−1000
−20 −30 −30 −20 −10 0 10 Vpar (km/s)
20
30
−2000 −2000 −1000 0 1000 Vpar (km/s)
2000
Fig. 7. Distributions of the ambient ionospheric H+ ions and electrons (a) before and (b) after heating by lower hybrid waves (arbitrary units).
ARTICLE IN PRESS V.N. Coffey et al. / Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 50–55
structure and power spectrum for this simulation as a function of time. The top panel shows a growing wave in the perpendicular electric field Ey. The wave frequency peaks near the lower hybrid frequency as shown in the power spectrum in the bottom panel. Fig. 7 shows the result of the energy transfer from these waves to the electrons and ions. Electron heating occurs in the parallel direction, consistent with lower hybrid heating. The perpendicular heating of the background H+ is evident and the ratio of kTperp to kTparallel is 1.33. A simulation with a different magnetosheath distribution yielded an anisotropy ratio of 1.6. 4. Summary and conclusions The injection of magnetosheath ions onto an open, high-latitude magnetic field line results in highly non-Maxwellian distributions in the topside ionosphere. Such distributions would be expected to be a free energy source for wave generation. These preliminary results exhibit the type of simulations that can be used for an end-to-end study to interpret the remotely observed distributions from the magnetosheath, the energy transfer to the ionospheric plasma, and the final outflow from this type of excitation into the magnetosphere. We have focused on one type of ion heating mechanism peculiar to the cusp in an early study to quantify its efficiency in ion heating. The exact nature of the lower hybrid wave excitation and ion heating depends on the various density and mass parameters. Roth and Hudson (1985) found that the initial development of the waves and resulting particle distributions depends on two critical parameters: the ratio of the local ion plasma and gyro frequency and the ratio of the densities of the ionospheric ions and the injected magnetosheath ring distribution. These initial results show a small amount of heating compared to observations, however, with the conditions imposed, it represents a lower limit to the heating that may be available. A more realistic representation would provide a steadily replenished non-Maxwellian distribution in the PIC code. Therefore, this work gives a measure of the efficiency of the energy transfer but does not address the cumulative effects of long-term exposure of the ionospheric plasma to magnetosheath ions.
55
Future efforts will be in the improvement of the modeling to address the aspects of different reconnection injection events. The evolved ring distributions will be input and replenished for a parameter study in density and mass similar to the research of Roth and Hudson. The use of the realistic evolved ring distributions extends their work and affords the opportunity to study this heating mechanism quantitatively and in detail. Acknowledgments The authors acknowledge support from the GSFC Polar Mission under UPN 370-08 and from the NASA Living With a Star Program under UPN 784-50-00. References Boudouridis, A., Spence, H.E., Onsager, T.G., 2001. Investigation of magnetopause reconnection models using two collocated, low-altitude satellites: a unifying reconectin geometry. Journal of Geophysical Research 106, 29451. Carlson, C.W., Torbert, R.B., 1980. Solar wind ion injections in the morning auroral oval. Journal of Geophysical Research 85, 2903. Lockwood, M., Smith, M.F., 1994. Low and middle altitude cusp particle signatures for general magnetopause reconnection rate variations, 1: theory. Journal of Geophysical Research 99, 8531. Reiff, P.H., Hill, T.W., Burch, J.L., 1977. Solar wind injection at the dayside magnetospheric cusp. Journal of Geophysical Research 82, 479. Roth, I., Hudson, M.K., 1985. Lower hybrid heating of ionospheric ions due to ion ring distributions in the cusp. Journal of Geophysical Research 90, 4191. Singh, N., 1996. Time response of O+ to a weak transverse ion heating event in the polar ionosphere. Journal of Geophysical Research 101, 5317. Singh, N., Leung, W.C., 1999. Nonlinear features of electrostatic ion cyclotron instability driven by counterstreaming ion beams in equatorial plasmasphere. Journal of Geophysical Research 104, 28547. Tsyganenko, N.A., Stern, D.P., 1996. Modeling the global magnetic field of the large-scale Birkeland current systems. Journal of Geophysical Research 101, 27187. Woch, J., Lundin, R., 1991. Temporal magnetosheath plasma injection observed with Viking: a case study. Annals of Geophysics 9, 133. Woch, J., Lundin, R., 1992. Signatures of transient boundary layer processes observed with Viking. Journal of Geophysical Research 97, 1431. Wilson, G.R., Ho, C.W., Horwitz, J.L., Singh, N., 1990. A new kinetic model for time dependent polar plasma outflow: initial results. Geophysical Research Letters 3, 263.