Overview of Overview of the MARSIS Active the MARSIS Active Ionospheric Sounder:Ionospheric Sounder:

Data and ResultsData and Results

D. D. Morgan, D. A. Gurnett, D. D. Morgan, D. A. Gurnett,

R. L. Huff, D. L. Kirchner,R. L. Huff, D. L. Kirchner,

A. J. Kopf, F. Jaeger, A. J. Kopf, F. Jaeger,

F. Duru F. Duru

Science Objectives

Characterize the response of the Martian ionosphere to various inputs:

• Solar EUV intensity

• Energetic particles

• Areodetic effects (seasons, latitude, local time)

• Crustal magnetc fields

• Solar wind

Targets of Opportunity

• Spacecraft local electron density

• Magnetic field

• Absorption of surface reflection (indicator of energetic particles)

• Multiple ionospheric reflection (indicator of plasma trapped in crustal magnetic field cusps)

• Upper layers of ionosphere

Radar Reflections from the Ionosphere

Gurnett et al.2005, Science.

Solar wind on the ionosphere.

Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS)

• Time resolution = 91.4 μs ~ ±6.8 km

• Frequency resolution ≈10 kHz

• 80 delay time bins to 7.5 ms

• 160 frequency bins to 5.5 MHz

An Ionogram

Duru et al., 2008, SWIM, San Diego

1.25 ms

28.5 nTFor electrons B=1/28Tc

Akalin et al., 2008, SWIM, San Diego

MARSIS MARSIS Active Ionospheric Sounder:Active Ionospheric Sounder:

Processing of Ionospheric Sounding TracesProcessing of Ionospheric Sounding Traces

Ionogram inversion

• Time delay equation:

pe s ,( )

20

pe s,

2

1 ( )

jz f f

j

j

dzt

c f z f

Inverting the delay time equation: lamination method (Jackson, 1969)

• Assume fpe is monotonic function of range z

• Assume horizontal stratification • Break into segments at instrument frequencies• Chose integrable functional form:

pe pe, 1( ) ( ) exp( )j jf z f z z

Inverting (continued)

• Invert:

• Change variables

• Integrate

pe pe

pe 1 s, 1

( ) ( )1 1ln ln

( )j j j j

f z f zz

f z f

pe,

pe, 1

pedelay, delay, , 1/22

1 1pe pe s,

pe, s, pe, 1 s,

1pe, s, pe, 1 s,

2

1

1 1 1 1 /1ln

1 1 / 1 1 /

i

i

j j f

j i j fi i

i j

ji j i j

i i i j i j

dft t

c f f f

f f f f

c f f f f

P-03-14

D. D. Morgan, D. A. Gurnett, D. L. Kirchner, J. L. Fox, E. Nielsen, J. J. Plaut, G. Picardi

MARSIS MARSIS Active Ionospheric Sounding Active Ionospheric Sounding

ResultsResults

Procedure for using individual fits to Chapman model

• Order samples by some parameter, e. g., , Time, F10.7, etc.

• Place samples in bins of 100

• Take the average

1.39 AU < R < 1.48 AU14 Aug. 2005 – 31 Jan. 2007

1.38 AU < R < 1.42 AU16 Feb. 2007 – 31 Jul. 2007

1.57 AU < R < 1.67 AU31 Jan. 2006 – 16 Feb. 2007

Conclusions (Morgan et al., 2008, accepted, J. Geophys. Res.)

• d ln n0/d ln F10.7 = 0.31 ± 0.04, compared to Hantsch and Bauer (1990): 0.36Fox and Yeager(2006): 0.29 – 0.41 for 60° ≤ χ ≤ 90°

Breus et al. (2004): 0.37• n0 varies between 1.4 to 1.8 x 105 cm-3, nearly constant with solar

zenith angle and latitude• h0 varies between 110 and 140 km, falls off at χ > 60° due to

oblique insolation but increases toward poles near summer solstice

• H ~11 km for 0 < χ < 40°, increases to 15 km (270 K, 1.39 AU < R < 1.48 AU, late southern

summer) 14 km (250 K, 1.57 AU < R < 1.67 AU, northern summer) 17 km (310 K, 1.38 AU < R < 1.42 AU, southern summer)

• SEPs are associated with Δ n0/ n0 of +6%, +Δ h0 of 3 km, ΔH of 7 km (??)

Morgan, D. D., D. A. Gurnett, D. L. Kirchner, J. L. Fox, E. Nielsen, and J. J. Plaut, Variation of the Martian ionospheric election density from Mars Express radar soundings, J. Geophys. Res., doi:10.1029/JA013313, accepted, 2008.

Investigation on the Magnetic Field Draping Near Mars from MARSIS

F. Akalin1, D. A. Gurnett1, T. F. Averkamp1, D. L. Kirchner1, R. Modolo1, G. Chanteur2, M. H. Acuna3, J. E.

P. Connerney3, J. R. Espley3, N. F. Ness4

1University of Iowa, Iowa City, IA 52240, USA2CETP-IPSL, 10-12 Avenue de l’Europe, 78140 Velizy, France

3NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 4Inst. For Astrophysics and Computational Science, Catholic University of

America, Washington, DC 20064, USA

OUTLINE

• Electron cyclotron echoes and how they are produced.

• Comparison of electron cyclotron echoes to Cain et al. model

1-Calculating the induced draped field vector

2-Determining MPB using electron number density and magnetic field

• Statistics of all the magnetic field measurements without crustal field

1.25 ms

28.5 nTFor electrons B=1/28Tc

Gurnett et al. [2005]

Electron Cyclotron Echoes, Video/Audio

1 2

1

2

Bx=18.54±0.96 nTBy=-16.22±0.58 nTBz=-7.11±1.02 nT

Bx=11.59±0.91nTBy=4.64±0.92 nTBz=9.27±0.78 nT

B(ρ)=(By2+Bz

2)1/2

Conclusion

Limit of detectability of magnetic field by MARSIS, on dayside, coincides roughly with induced magnetosphere boundary.

F. Duru, D. A. Gurnett, D. D. Morgan, R. Modolo,

A. F. Nagy, D. Najip and J. D. Winningham

Chapman Conference on Solar Wind Interactions with Mars, Jan. 24, 2008, San Diego

Electron Densities and the Boundary Between the Ionosphere and the Solar Wind at Mars from Local

Electron Plasma Oscillations

Duru, F., D. A. Gurnett, D. D. Morgan, R. Modolo, A. F. Nagy, and D. Najib, Electron densities in the upper ionosphere of Mars from the excitation of electron plasma oscillations, J. Geophys. Res., accepted, 2008.

MARSIS on MEX(Mars Advanced Radar for Subsurface and Ionospheric

Sounding) Low-frequency radar sounder

used for sounding of the ionosphere as well as subsurface sounding.

Consists of: An antenna subsystem, 40 m tip to tip dipole antenna, 7 m monopole antenna, a radio frequency subsystem, a digital electronic subsystem.

Radar soundings are performed by transmitting a short pulse of radio waves at a fixed frequency, and then measuring the time delay of the returning echo.

MARSIS also measures local electron density from the excitation of local electron plasma oscillations.

An Ionogram

Local Electron Densities As the transmitter steps in frequency strong local electrostatic

oscillations, called Langmuir waves are excited, when f = fp.

The local electron plasma frequency can be used to obtain the electron density.

ne = (fp/8980)2 cm-3, where fp is in Hz.

One of the advantages of this method is that the electron densities can be measured at very high altitudes, where remote soundings are not obtained.

This study is done at the altitudes between 275 km and 1300 km.

Electron Plasma Oscillation Harmonics The excitation of electron plasma oscillations by the sounder

transmitter creates harmonics of the local electron plasma frequency which are seen as closely spaced vertical lines in the upper left corner of the ionograms.

This is because, with voltage amplitudes on the antenna much greater than the power supply voltage in the preamplifier, the received waveforms are usually severely clipped.

In many cases, the fundamental of the electron plasma frequency cannot be observed, since it is below the lower limit of the frequency of the receiver. However, it can still be determined from the spacing of the harmonics which occur at higher frequencies.

Measurement Technique

Possible Effect of Temperature

For Te = 5000 K, no = 10 cm-3, λDe = 1.5 m.

ω2 = ω2pe[1 + 3λ2

Dek2]

λDe = 6.9 √(Te/no)

k = 2π / λ

The wavelength excited is approximately the length of the antenna, λ ~ 40 m.

For these parameters 3λ2Dek2 ~ 0.176, which is negligible.

Why are Plasma Oscillations Sometimes not Detected?

Low electron density (n < 10 cm-3)

If the electron density is too low, such as in the solar wind, the frequency is below the low frequency limit of the instrument (100 kHz).

Landau damping

If the temperature is high, such as in the solar wind, kλDe ≥ 1, then Landau damping prevents the detection of the wave.

High flow velocity

If the velocity of the plasma is high, such as in the solar wind, the wave packet will be carried away before it can be detected by the antenna. (VSW > ~160 km/s.)

When the flow speed is high:

The Local Electron Density for a Full Pass

Another Pass: Lots of Fluctuations

Percentage of the Ionograms with Plasma Oscillations (Introduces Sampling Bias)

Measured Electron Density Profiles

Electron Density Profiles Corrected for Sampling Bias

Median Electron Density Versus SZA

Electron Density Versus SZA at the peak in the Electron Density Profiles

Gurnett et al., 2005

The importance of Plasma flow at High Altitudes (Ma et al., 2004)

Plasma Flow Simulations

A 3D Hybrid simulation model (Modolo et al., 2005). - A fluid description for the electrons and a fully kinetic

description for the ions. - Particles and fields are treated self-consistently. - Particles are represented by a set of macro-particles, which

obey the laws of motion of physical particles.

A 3-D Magnetohydrodynamic (MHD) model (Ma et al., 2004). - Four species, high resolution model. - Ideal MHD equations are used to define electrons, ions and

their motion.

Comparison of Data and Simulations

Does the Disappearance of Plasma Oscillations Correspond to the Ionopause?

The fact that the electron plasma oscillations appear and disappear suddenly through a given pass, can be used to obtain the boundary between the ionosphere of Mars and shocked solar wind (ionopause).

o Plasma oscillations disappear as the spacecraft goes to high altitudes.

o Disappearance of the plasma oscillations can be explained by the high temperatures, high flow velocities, and low electron densities in the magnetosheath.

Joint plot: Aspera-3 and MARSIS

Comparison with Magnetic Pileup Boundary (MPB)

Comparison with Solar Wind Speed Simulations

Summary and Conclusions

Over 500 passes are studied and electron density profiles are obtained between 275 and 1300 km and 10o and 140o.

Individual passes have highly fluctuating profiles. There is an exponential relationship between the median electron

density and the altitude. The median electron density is almost constant on the dayside. It

decreases dramatically around the terminator. Our data are consistent with the MHD and Hybrid simulation models

and also with the inversion data. The data are highly variable at a given SZA or altitude. The fact that the electron plasma oscillations start and end suddenly

through a given pass, can be used to identify the ionopause. On the dayside, the data from MARSIS are compared to ASPERA-3

ELS data. They agree 93 % of the time. On the dayside, the boundary where the plasma oscillations disappear

is in agreement with the MPB. The boundary deviates from MPB on the nightside.

From Transient layers in the topside ionosphere of Mars, A. J. Kopf, D. A. Gurnett, D. D. Morgan, and D. L. Kirchner, Submitted to GRL, June 2008.