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

Radar Remote Sensing Laboratory University of Washington October 15, Remote Receivers FM Radio Transmitter Reference Receiver 30 km150 km E-region Plasma Density Structures km Cascade Mountains the Manastash Ridge Radar

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

Radar Remote Sensing Laboratory University of Washington October 15, MRR Data Products Ground Clutter and Airplanes Density Irregularity Power Scale: dB, uncalibrated

Radar Remote Sensing Laboratory University of Washington October 15, 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) Electric Field Structure via Coherent Radar

Radar Remote Sensing Laboratory University of Washington October 15, 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)

Radar Remote Sensing Laboratory University of Washington October 15, July 2004 Magnetic Storm MRR recorded semi-continuous data during July 2004 Two frequencies (96.5, 97.3 MHz) Multiple antennas (interferometry)

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

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

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

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

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

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

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

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

Radar Remote Sensing Laboratory University of Washington October 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.

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

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

Radar Remote Sensing Laboratory University of Washington October 15, 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 least- squares (Levenburg-Marquardt)

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

Radar Remote Sensing Laboratory University of Washington October 15, 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?)

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

Radar Remote Sensing Laboratory University of Washington October 15, 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!)

Radar Remote Sensing Laboratory University of Washington October 15, 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 (c s ) is greater and ions are more mobile. Electron-ion drift (and E) must be greater to drive instability.

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

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

Radar Remote Sensing Laboratory University of Washington October 15, 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 V d required) Passive radar is a versatile, useful tool.