Overview of Results from the R Plasma Imager

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

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/

Propagation Modes 2

Types of Magnetospheric Echoes

Plasmaspheric Echoes • Two successive RPI plasmagramsin 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 Ne distributions through inversion of the echo Reinisch et al. , 2001 Carpenter et al. , 2002

Probing the Plasmasphere R a n g e • RPI echoes received when IMAGE is outside theplasmapause 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

Echoes in the Plasmasphere Refilling Region

Epsilon Echoes in the Plasmasphere

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

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

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

Kp Index 1 2 3 1 3

Pre-Storm Density Distributions

Empirical Plasmasphere Model Before March 31 Storm

Plasmagramand Profile After Storm Quiet Day Model Measured

Continued Refilling of the Plasmasphere Quiet Day Model Measured

Normalized Equatorial N After Storm & Lpp 0

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 2000 UT on 2 April • Refilling at 2. 8 is completed in less than 28 hours • Inner plasmasphere L < 2. 3 shows no depletion

Polar Cap Observations

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 July 18, 2000 Nsumei, et al. , 2002 Henise, et al. , 2002

Density Variations Over the Polar Cap

Radial Distance Density Model • Relationship between average Ne and geocentric radial distance can be modeled as a power law

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

Magnetopause Echoes

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)

Resonances and Whistler Mode Observations

Overview of Plasma Resonances • Plasma resonances are normal modes of a plasma • Most are short range ES oblique echoes yielding accurate Ne and |B| • Ionospheric topside sounders have pioneered our knowledge of plasma resonances (Alouette, ISIS) • Electromagnetic wave cutoffs at X, O, Z • 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

Plasmagramwith Echoes and Resonances • What does RPI see? • Clear X mode echo and cutoff frequency identified fx = • 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

Stormtime Changes in the Resonances • Two near apogee passes of RPI on successive quiet and disturbed days • Can determine the accuracy of: – fp to ~ 1% – fg to ~ 0. 1% • March 30, 2001 – Clear nfg resonances (n=2 -14) – fg k. H z – No fp resonance implies fp < 6 k. Hz f. D 1 - • March 31, 2001 – Increase of B with nfg only to n = 6 – Resonances also at D 1, D 2+, fp, fuhr, Q 3 and Q 4 Benson et al. , 2002

Results from Resonance Measurements • Can obtain accurate valves of |B| (within a few tenths %) and. Ne (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 Te • Previous published results frommagnetospheric relaxation sounders may need to be re-examined for Dn resonances

Low Frequency, Low Altitude Observations Auroral Hiss fp fg fuhr Z mode • 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 Carpenter et al. , 2002

Whistler Mode Observations Z Z b • 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 Carpenter et al. , 2001

Kilometric Continuum Observations

Source of Kilometric Continuum • EUV observes distinct plasmaspheric bite-out structures; an unknown feature prior to IMAGE • 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

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

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

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 nonthermal continuum (5 -100 k Hz) • Favored mechanism is the linear or non-linear mode conversion theory (electrostatic Z mode to electromagnetic O mode) when fuhr = (n+1/2 ) fg

EUV & RPI Comparisons

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 e N and NHe+ are related Goldstein et al. , 2002

Extracting (L, MLT)of the Helium Edge Extracted He+ Edge Plasmapause? • 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 Results During June, 2001 • Average plasmapause position from EUV observations #1 and #4 • Interpolate in time and account for erosion or refilling • Horizontal segment • 50%of the events are within 0. 125 L of perfect shows width of RPI agreement; almost all of the points are within 0. 5 L segment

Fuzzy EUV Edge Extraction June 12, 21: 04 • Fuzzy edges (low counts) from EUV produce subjective plasmapause locations • Larger scatter in the results • Variation can be as great as 0. 5 L

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

EUV & RPI Comparisons: Conclusions • Sharp edges in EUV images of the plasmasphere have a good correlation with theplasmaspause L shell observed by RPI • Sharp edges correspond to steepplasmapause gradients • “Fuzzy” edges in EUV data correspond to much more gradualplasmapauses • Lower density threshold of EUV appears to be ~48 -50 /cc

IMAGE/RPI Transmissions and Wind/Waves Receptions

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 occurs when the received electric field and 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

Data Analysis and Interpretation 828 k. Hz RPI Signal Modulation Path-Integrated Magnetospheric Parameters • Signal modulation gives Faraday rotation • Single-frequency FR gives relative pathintegrated Ne. B product • Recent experiments produced dual frequency Faraday measurements

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

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