Solar Radiophysics with HF Radar

Workshop on Solar RadiophysicsWith the Frequency Agile Solar Radiotelescope (FASR)

23-25 May 2002Green Bank, WV

Paul RodriguezInformation Technology DivisionNaval Research LaboratoryWashington, DC The Solar & Lunar HAARP

Ionosphere

Magnetosphere

Selenosphere

Solar Wind

Solar Corona

Radial Distance

Effective Radiated

Power

Modification (growth and decay scales of irregularities)Long distance radiowave propagationDensity irregularity spectrumMeteor showers (Leonids; dusty plasmas)

Boundary and global scale dynamicsResponse to geomagnetic stormsMagnetospheric wave-particle interactions

Solar wind large scale density structuresBow shock irregularities and dynamics

Lunar surface penetration by HF radiowavesCharged lunar dust atmosphere?Lunar wake structure

Detection of near earth asteroids, comets

Detection of CMEs & prediction of geomagnetic stormsDensities, temperatures of solar coronaLarge scale structure, dynamics, wave spectrum

Range of Space Experiments with HF Radiowaves

1000 MW100 MW10 MW1 MW0.1 MW

0.05 Re

15 Re

30 Re

60 Re

1 AU

Planetary Surfaces0.5 AU

El Campo, Texas Solar Radar Antenna Array

NNNNN

SSSSS

EEEEE WWWWW

Operating Frequency: 38.25 MHzTransmitting Dipoles: 128 x 8 EW

Receiving Dipoles: 128 x 8 EW

128 x 4 NS

Total Area: 18,000 m2

Antenna Gain: 32-36 dBBeam Size (NS x EW): 1o x 6 o

Total Power: 500 kWEffect. Radiated Power: 1300 MW

Operated byMIT/Lincoln Laboratory 1961-1969

Motivation for initial solar radar experiments

• to determine radar cross section of the solar corona(however, it was recognized there was no ‘hard surface’ )

• to investigate dynamics of solar corona

Present scientific motivation

• profile of corona electron density

• backscatter from a hot, magnetized plasma

• remote sensing of wave-particle interactions in the corona(small scale dynamics)

• measurement of large scale MHD (i.e., CMEs)

• understanding of nonthermal development of variousspectra (density fluctuations, waves, radio, etc)

• direct measurements of stellar plasma and how it affectsplanetary environment

Solar Radar Performance

The radar equation is Pt Gt Ar σ p

Pr = where: 4πR2 4πR2

Pr - received power (watts) σ - scattering cross-section (m2)

Pt - transmitted power (watts) p - polarization fractionGt - transmitting antenna gain R - range to scattering cross-section (m)Ar - receiving antenna area (m2) Ro - solar radius (m)

R = 1.5 x 1011 m (1 AU)Ro = 7 x 108 m (solar radius)σ ~ 1 π Ro

2 = 1.54 x 1018 m2 ( typical value obtained by El Campo)

p = 0.5 (one of two polarizations)

N = kB T(f) B (noise power of sun), where

kB = 1.38 x 10-23 watt-s °K-1 (Boltzman’s constant)T(f) = noise equivalent temperature of sun (°K) B = receiver bandwidth (Hz)

0

10

20

30

40

50

21000 21500 22000 22500 23000 23500 24000

El Campo Solar Radar (38.25 MHz)C

ross

Sec

tion

(πR

o2 )

Serial DayDay Month Year

30 Jun 61 16 Sep 6912 Nov 62 26 Mar 64 8 Aug 65 21 Dec 66 4 May 68

El Campo Corona Echo Signal Spectrum

Typical RDA spectrum.

Among spectral typesobserved were“high corona echoes,”which may have beenCME signatures.

However, CMEs were unknown in the 1960s.

CME

SolarRadar

Solar Radar Detection of Earthward-Directed Coronal Mass Ejections

Frequency Shift

Power

Corona CME

Transmitted

Received

0

100

200

300

400

0 200 400 600 800 1000 1200 1400 1600

HF Doppler Shift from Earthward Motion of Coronal Mass Ejection

f Dp (9 MHz)f Dp (25 MHz)f Dp (38 MHz)

Fre

quen

cy S

hift

(kH

z)

CME Velocity (km/s)

The Doppler shifts expected for HF radarfrequencies of 9, 25, and 38 MHz, for the rangeof CME velocities observed with coronagraphs.

-10 0 10OFF ON

UTR-2 Return Signal Spectra UT 0927-0943

-10 0 10

Time (sec) Relative to Transition

ON OFF

10 20 30 40 50 60 seconds

0 10 20 30 40 50 60 seconds

8.920 MHz

8.880 MHz

FullPowerON/OFF

SURA Transmitted Signal UT 0911-0927

Solar Radar Experiment 21 July 1996

FrequencyShift (kHz)

8.925 MHz

FrequencyShift (kHz)

8.885 MHz

44

0

44

0

0

2

4

6

8

10

-10 -5 0 5 10

SURA / UTR-2 Solar Radar 21 July 1996

8.925 MHz

8.885 MHz

Relative Intensity

Time (sec)

ON

ON

OFF

Transmission Patterns

OFF

4500

5000

5500

6000

6500

0 5 10 15 20 25 30 35 40

SURA / UTR-2 Solar Radar 21 July 1996

8.925 spec

8.885 spec

Relative Spectral Intensity

Frequency Shift (kHz)

ReceiverFrequency

Integrated Return Signal Time Profiles and Spectra

HAARP Research Facility

Operated by Advanced Power Technologies, Inc. under contract from U. S. Air Force/ Navy

Current DesignRadiating x-dipoles: 48 180

Total area (m2): 20,000 124,000Transmitters: 96 360Power (kW): 960 3600ERP (MW): 190 3200Frequencies (MHz): 2.8 to 8 2.8 to 10

Gakona, Alaska

0

10

20

30

40

50

60

70

80

90

30 61 91 122 152 182 213 243 274 304 335 365

Sun As Seen From HAARP at UT 2000 (o), 2100 (◊), 2200 (∆), 2300 (x)LT 1100 (o), 1200 (◊), 1300 (∆), 1400 (x)

Alt

itud

e (d

eg)

Day of Year (2000)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Solar Radar Window

LOFAR: CONCEPTUALLAYOUT

EachLOFAR Station

consists of256 Active Dipolesabove their ground

screens

~ 160 m (5 acres)

LOFAR will be:

• ≥ 40 stations

• ≥ 10,000 dipoles

• ≥ 1 km2 collecting area– 20x Arecibo

• ∆ν ~ 10-250 MHz

• ≥ 2 independent beams

Possible LOFARStation sites

VLA

Los Alamos

New Mexico

Active dipole

Ground Screen

~ 1

met

er

-10

-5

0

5

10

15

20

25

30

0. 1 10 100 1000 10000

HAARP Frequency = 10 MHz

LOFAR Effective Area ~ 106 m2 Solar Radar X-Section = 1

Net

Sig

nal/

Noi

se R

atio

(dB

)

Integration Time (s)

3.2

0.9

0.3

TotalPower(MW)

5-dBThreshold

Present HAARP Power

Design HAARP Power

HALO Solar Radar

Initial HAARP Power

Summary and Conclusions

• Solar radar experiments will ‘open’ a new window onplasma physics of the sun and magnetosphere.

• Solar radar has applications to many other phenomena oflocal astrophysics.

• HAARP is capable of being a solar radar, in bistaticconfiguration with existing and planned receiving arrays.

• The CME detection problem and geomagnetic stormeffects at earth is a practical motivating issue.