1. Overview of Results from the Radio Plasma Imager (RPI) on IMAGE James L. Green and Bodo W. Reinisch Presentation at Yosemite February 6, 2002

2. Outline Overview of magnetospheric echoes Echo observations and results –Plasmapause and trough region –Polar Cap –Magnetopause Plasma Resonances and Whistler mode Origin of kilometric continuum RPI & EUV comparisons Magnetospheric Tomography Summary of Results http://image.gsfc.nasa.gov/

3. Propagation Modes 2

4. Types of Magnetospheric Echoes

5. Plasmaspheric Echoes Two successive RPI plasmagrams in the region of the plasmapause density gradients RPI simultaneously probes the plasmasphere and field-aligned paths in the local hemisphere RPI measurements can be used to investigate N e distributions through inversion of the echo Reinisch et al., 2001 Carpenter et al., 2002

6. Probing the Plasmasphere RPI echoes received when IMAGE is outside the plasmapause can be used to: –Locate the plasmapause to within ~ 0.1 - 0.2 Re –Determine the approximate density level at the inner limit of the steep plasmapause density gradients –Observe the density profile inside the plasmapause Range spreading may be caused by coherent backscattering due to small scale density irregularities –Can yield information on both the scale and amplitude of the irregularities RangeRange

7. Echoes in the Plasmasphere Refilling Region

8. Epsilon Echoes in the Plasmasphere

9. Field-Aligned Profile Inversion N e can be obtained from an inversion technique Two traces are used to obtain N e in both hemispheres

10. Recalculated Plasmagram Traces Accuracy of derived profiles is verified by calculating the echo traces for other propagation modes, and of multiple echo traces Reinisch et al., 2001

11. Plasmasphere Refilling After the March 31, 2001 Storm Reinisch et al., 2002 Song et al., 2002

12. Kp Index 2 3 1 33 1 1

13. Pre-Storm Density Distributions

14. Empirical Plasmasphere Model Before March 31 Storm

15. Plasmagram and Profile After Storm Quiet Day Model Measured

16. Continued Refilling of the Plasmasphere Measured Quiet Day Model

17. Normalized Equatorial N 0 After Storm & Lpp

18. Storm Summary During the 31 March 2001 storm event Enhanced cross tail E field reduces plasmapause to L  2.3 Emptied the flux tubes between L=2.3 and 5 Refilling process at L = 2.8 started at 1600 UT on 1 April, and is completed before 2000UT on 2 April Refilling at 2.8 is completed in less than 28 hours Inner plasmasphere L < 2.3 shows no depletion

19. Polar Cap Observations

20. Polar Cap Density Distributions Using RPI echoes and the density inversion technique an empirical model of electron density distribution over the polar cap can be obtained Combination of individual inversions show the variations of the polar cap density during each pass Nsumei, et al., 2002 Henise, et al., 2002 July 18, 2000

21. Density Variations Over the Polar Cap

22. Radial Distance Density Model Relationship between average N e and geocentric radial distance can be modeled as a power law

23. Density and Magnetic Activity The model shows that the polar cap electron density over is strongly dependent on the geocentric distance and magnetic activity PC index (3-hourly average)Kp index (3-hourly average)

24. Magnetopause Echoes

25. Putting the “M” in IMAGE Special measurement program designed for the magnetopause (~ 10 min/plasmagram) Magnetopause boundary layer echoes are diffuse suggesting a sharp but rough reflecting surface Strong echoes observed over a 50 minutes period (Fung et al., 2002)

26. Resonances and Whistler Mode Observations

27. Overview of Plasma Resonances Qn resonances result from sounder stimulated electrostatic waves whose group velocity are nearly matched to the s/c velocity Dn resonances - two competing theories for their generation in the ionosphere –One theory has them as a new mode of plasma oscillations –On-going controversy as to their existence in planetary magnetospheres Plasma resonances are normal modes of a plasma Most are short range ES oblique echoes yielding accurate N e and |B| Ionospheric topside sounders have pioneered our knowledge of plasma resonances (Alouette, ISIS) Electromagnetic wave cutoffs at X, O, Z

28. Plasmagram with Echoes and Resonances What does RPI see? Clear X mode echo and cutoff frequency identified f x = Clear resonances at: –nfg (n = 1-3) –fqn (n = 2, 3) Determine fp/fg = 0.99 in a self consistent manner Reinisch et al., 2001

29. Stormtime Changes in the Resonances Two near apogee passes of RPI on successive quiet and disturbed days Can determine the accuracy of: –f p to ~ 1% –f g to ~ 0.1% March 30, 2001 –Clear nfg resonances (n=2-14) –fg        kHz –No fp resonance implies fp < 6 kHz March 31, 2001 –Increase of B with nfg only to n = 6 –Resonances also at D1, D1, D2+, fp, fuhr, Q3 and Q4 Benson et al., 2002 fD1- fD1

30. Results from Resonance Measurements Can obtain accurate valves of |B| (within a few tenths %) and N e (within a few %) RPI has convincingly demonstrated the existence of Dn resonances in the magnetosphere –RPI generates enough power to be able to observed the X echoes and thereby self consistently determine fp once fg has been identified –Confusion between fp and Dn resonances is resolved Resonances observed by RPI (including X, Qn, Dn) are similar to those stimulated by topside sounders in spite of the large differences in T e Previous published results from magnetospheric relaxation sounders may need to be re-examined for Dn resonances

31. Low Frequency, Low Altitude Observations Three RPI measurement programs linked together to reveal low frequency plasma waves Note in the Z mode emission observed at fg is of unknown origin Auroral Hiss fpfp fgfg f uhr Z mode Carpenter et al., 2002

32. Whistler Mode Observations Perigee passes of IMAGE show range spreading of the whistler mode waves Quasi-electrostratic waves generated at the boundaries of field-aligned density irregularities from the initial RPI whistler mode pulse Similar to spectral broadening of narrowband signals observed in low altitude polar s/c Not completely understood a b Z Z Carpenter et al., 2001

33. Kilometric Continuum Observations

34. Source of Kilometric Continuum KC is high frequency banded emission RPI measurements within the bite-out show that Kilometric Continuum is: –Generated deep inside the bite-out at the plasmapause –Beamed along the magnetic equator from a confined source region –Not generated over a broad source region as previously reported –Also observe field-aligned echoes EUV observes distinct plasmaspheric bite-out structures; an unknown feature prior to IMAGE

36. Correlative Geotail Measurements with EUV Geotail within 10 o of magnetic equator 01-11UT Enters KC beam at 1 UT leaves at ~6 UT June 24, 2000

37. Characteristics of KC Correlative Geotail observations confirm that: –KC is generated in very narrow latitudinal beams (within ~10 o of magnetic equator) –Magnetic longitude extent of ~50 o –KC is also observed coming from inside of a plasma tail region

38. Generation of Kilometric Continuum Banded spectral characteristics of KC and its source region near the magnetic equator at the plasmapause is strong evidence for this emission to be generated by the same mechanism as the lower frequency non-thermal continuum (5-100 kHz) Favored mechanism is the linear or non-linear mode conversion theory (electrostatic Z mode to electromagnetic O mode) when f uhr = (n+ 1/2 ) f g

39. EUV & RPI Comparisons

40. Plasmasphere Density Measurements Extreme Ultraviolet (EUV) imager uses resonance scattering He + at 30.4 nm to observe the plasmasphere He + is typically the second most important ion in the plasmasphere; however, there can be large H + / He + variations RPI can be used to measure the electron density (which much be equal to the total ion density) by radio sounding or by insitu measurements RPI insitu measurement and EUV data are compared during the month of June 2001 to determine how the N e and N He+ are related Goldstein et al., 2002

41. Extracting (L, MLT) of the Helium Edge Map He + edge down to equator to obtain the L value RPI insitu measurements occur at a later or earlier time Assume strict corotation of the plasmasphere Plasmapause? Extracted He+ Edge

42. Plasmapause Results During June, 2001 50%of the events are within 0.125 L of perfect agreement; almost all of the points are within 0.5 L Average plasmapause position from EUV observations #1 and #4 Interpolate in time and account for erosion or refilling Horizontal segment shows width of RPI segment

43. Fuzzy EUV Edge Extraction Fuzzy edges (low counts) from EUV produce subjective plasmapause locations Larger scatter in the results Variation can be as great as 0.5 L June 12, 21:04

44. What’s the lower threshold of EUV? “Fuzzy” edges in EUV data correspond to much more gradual plasmapauses Lower density threshold of EUV appears to be ~48-50 /cc Fuzzy Edge June 17, 12:38 ~ 48/cc

45. EUV & RPI Comparisons: Conclusions Sharp edges in EUV images of the plasmasphere have a good correlation with the plasmaspause L shell observed by RPI Sharp edges correspond to steep plasmapause gradients “Fuzzy” edges in EUV data correspond to much more gradual plasmapauses Lower density threshold of EUV appears to be ~48-50 /cc

46. IMAGE/RPI Transmissions and Wind/Waves Receptions

47. Experiment in Radio Tomography RPI generated pulse were observed by the Wind/Waves instrument during several perigee passes (Aug 3 & 15, 2000; Oct 23, Dec 2, 2001) Faraday rotation was measured and occurs when the received electric field is observed to rotate with time due to the changing density of plasma and magnetic field strength Many future multi-spacecraft missions propose to use Faraday rotation to obtain global density pictures of the magnetosphere Cummer, et al., 2001; 2002

48. Data Analysis and Interpretation 828 kHz RPI Signal Modulation Signal modulation gives Faraday rotation Single-frequency FR gives relative path- integrated N e B product Recent experiments produced dual frequency Faraday measurements Path-Integrated Magnetospheric Parameters

49. Summary of RPI Results 1.Pervasiveness of the ducted echoes in the plasmasphere, plasmapause, trough, and polar cap regions Field-aligned density structures are prevalent throughout the magnetosphere Could this be a consequence of persistent ionospheric outflow? 2.Determine (nearly instantaneously) the density distribution along field lines in the plasmasphere refilling region Refilling is faster than any models predicted by a factor of ~2 No discontinuities in the density observed as part of the filling process 3.Observed diffuse echoes from plasmapause and magnetopause BL Key magnetospheric boundaries are actually rough surfaces 4.Determine polar cap density distributions below the s/c within one pass Demonstrates the variable nature of the polar cap ionosphere as a source of plasma for the tail 5.Measurement of fundamental plasma resonances Like the ionosphere, the magnetosphere has clear D and Q resonances 6.KC emanating from plasmapheric bite-outs Are bite-out structures a sufficient conditions for the generation of KC? 7.Reception of RPI pulses by Wind from distance of over 12 RE Provides validity to future tomographic missions

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