Midlatitude Radar Observations of the July 2004 Geomagnetic

Midlatitude Radar Observations of the July 2004 Geomagnetic Storm Melissa Meyer, Andrew Morabito, Zac Berkowitz, John Sahr University of Washington Electrical Engineering October 15, 2003 University of Washington Radar Remote Sensing Laboratory

the Manastash Ridge Radar FM Radio Transmitter E-region Plasma Density Structures 0 - 40 00 km 40 01 11 10 0 k m Remote Receivers Reference Receiver Cascade Mountains 30 km October 15, 2003 150 km University of Washington Radar Remote Sensing Laboratory 2

Radar Field of View October 15, 2003 University of Washington Radar Remote Sensing Laboratory 3

MRR Data Products Power Scale: d. B, uncalibrated Density Irregularity Ground Clutter and Airplanes October 15, 2003 University of Washington Radar Remote Sensing Laboratory 4

Electric Field Structure via Coherent Radar • Coherent scatter from density irregularities caused by Farley-Buneman instability (threshold E required) • Treat irregularities as tracers for electric field structure • Millstone Hill Group reports linear relationship between coherent backscattered power & electric field strength (valid at ~440 MHz) October 15, 2003 University of Washington Radar Remote Sensing Laboratory 5

SAPS as Cause for MRR Backscatter • Due to its midlatitude location, MRR does not often observe auroral effects. • So what causes the irregularities? • We suspect “SAPS” (Sub-Auroral Polarization Stream): – M-I feedback instability, seeded by density gradients at the plasmapause (maps to midlatitude) – Poleward E; density trough (low conductivity); sunward drift – SAPS electric field can become very structured over short time periods (Foster et al. , 2004) October 15, 2003 University of Washington Radar Remote Sensing Laboratory 6

July 2004 Magnetic Storm • MRR recorded semi-continuous data during 17 -27 July 2004 • Two frequencies (96. 5, 97. 3 MHz) • Multiple antennas (interferometry) October 15, 2003 University of Washington Radar Remote Sensing Laboratory 7

VHF Coherent Radar Backscatter Intensity vs. Range and Time ~62 o magnetic latitude 17 July 2004 (Kp 6) Mountains October 15, 2003 University of Washington Radar Remote Sensing Laboratory 8

SAPS Was There in July 2004: DMSP * DMSP High Latitude Space Weather Data courtesy of Fred Rich, AFRL, Hanscom AFB, Massachusetts October 15, 2003 University of Washington Radar Remote Sensing Laboratory 9

Auroral Precipitation Zone via DMSP SAPS Auroral Precip. Region ~61 o October 15, 2003 University of Washington Radar Remote Sensing Laboratory 10

SAPS and the Auroral Region (Further East) Characteristic SAPS Density trough; E (Ex. B drift) enhancement Auroral Precip. Region ~60 o October 15, 2003 University of Washington Radar Remote Sensing Laboratory 11

VHF Coherent Radar Backscatter Intensity vs. Range and Time horizon cutoff Entire channel motion: 140 m/s “sub structure” motion: 415 m/s October 15, 2003 University of Washington Radar Remote Sensing Laboratory 12

27 July 2004: Auroral Precip. / SAPS Channel Characteristic SAPS Density trough; E (Ex. B drift) enhancement ~59 o October 15, 2003 University of Washington Radar Remote Sensing Laboratory 13

27 July 2004: Backscatter Intensity vs. Range and Time Same quasi-periodic E field structure. (Kp 8) structure motion: ~850 m/s But faster, and no apparent “channel drift, ” as before. October 15, 2003 University of Washington Radar Remote Sensing Laboratory 14

Measured SAPS Characteristics • Equatorward drift of entire channel: – Not always seen – Measured: 100 - 200 m/s • Drift of individual features: – 400 - 1000 m/s, equatorward – Large variability, seems to respond to disturbance level • Period of electric field enhancements: – Have seen 1 - 3 minutes; 10 -20 minutes – (More observations needed. ) October 15, 2003 University of Washington Radar Remote Sensing Laboratory 15

Similar Observations from other Radars • Millstone Hill – Channel movement ~150 m/s – Feature movement ~785 m/s – 3 - 5 min period – MHR resolution used: 10 km, 1 sec – Associated |E| oscillation with density oscillations (using GPS TEC measurements) *Foster, Erickson, Lind, and Rideout: GRL, 2004. October 15, 2003 University of Washington Radar Remote Sensing Laboratory 16

Fine Range Structure ~10 km periodic features (intensifications of |E|) Look like “SAID” events October 15, 2003 University of Washington Radar Remote Sensing Laboratory 17

Fine Range Structure • Interferometer: Echoes follow aspect angle contour • Fine spatial structure persisted for ~3 hours on 17, 27 July during LT 17: 00 - 20: 00 October 15, 2003 University of Washington Radar Remote Sensing Laboratory 18

Doppler Statistics from the July 2004 Storm • Gathered Doppler moment statistics from over 330, 000 spectra • From 2 days during July 2004; disturbed conditions • Fitted each spectrum to Gaussian or Lorentzian curve via nonlinear leastsquares (Levenburg-Marquardt) October 15, 2003 University of Washington Radar Remote Sensing Laboratory 19

Doppler Statistics from the July 2004 Storm: Mean Doppler vs. Spectral Width Notes • +/- Asymmetry • Faster + wider are correlated • Narrow, fast population October 15, 2003 University of Washington Radar Remote Sensing Laboratory 20

Doppler Statistics from the July 2004 Storm: Range vs. Doppler shift Notes • Speed-up at far ranges • Other structure visible (Lloyd’s Mirror? antenna pattern effects? ) October 15, 2003 University of Washington Radar Remote Sensing Laboratory 21

Speed-up at Far Ranges: Individual Cases October 15, 2003 University of Washington Radar Remote Sensing Laboratory 22

Speed-up at Far Ranges (Why? ) • Edge of auroral convection? – DMSP does show auroral precipitation dipping into MRR field of view, – But range speed-up is not discontinuous… • Observing Geometry? – Interferometric information not available (one antenna didn’t detect the faster echoes!) October 15, 2003 University of Washington Radar Remote Sensing Laboratory 23

Speed-up at Far Ranges (Why? ) • At far ranges, shadow of Earth overtakes lower altitudes: only higher altitudes are visible. • At high E-region altitudes, temperature (cs) is greater and ions are mobile. • Electron-ion drift (and E) must be greater to drive instability. October 15, 2003 University of Washington Radar Remote Sensing Laboratory 24

Other Features in Our Data… • Narrow, fast population: Examples • Often see spectra with 2 nd, faster peak • Associated with fine range structure. October 15, 2003 University of Washington Radar Remote Sensing Laboratory 25

Other Features in Our Data… A shear in velocity / electric field over range October 15, 2003 University of Washington Radar Remote Sensing Laboratory 26

Summary • MRR often detects SAPS electric field structure (coherent radars at midlatitude are a good tool for learning about SAPS) • SAPS fields can develop very fine spatial structure (how? ) • Faster spectra tend to be wider (& vice versa) • Faster echoes occur at higher altitudes. (Larger Vd required) • Passive radar is a versatile, useful tool. October 15, 2003 University of Washington Radar Remote Sensing Laboratory 27