Two Classes of Auroral Infrasound at I53US

By Charles R. Wilson, John V. Wilson, Curt Szuberla and Daniel L.Osborne,

Geophysical Institute, University of Alaska, Fairbanks AK

Huge AIW Bow Wave signal at I53US at15:49 UT, 04/14/03 during magnetic storm

Trace velocity = 0.602 km/s, Az = 276 deg, Cij = 0.916

Uncertainty in Vel and Theta for AIW at I53US April 14,2003,(Dr.Curt Szuberla)

Uncertainty Ellipse in Velocity Space

Vel = 614 m/sec +/- 60 m/sec

Azimuth = 276.5 +/- 5.8 deg.

Three component Magnetometer traces at Fairbanks April 14, 2003 Strong magnetic bay at 12:00 to 16:00 UT

Time of Huge AIW

All-SKY camera images at 30 second intervals at Fairbanks

AIW – Bow wave at 09:59 UT

Zenith crossingAt 09:51 UT

Bow Wave model for AIW signals fromsupersonic aurora electrojet arcs

Auroral Oval

Direction of supersonic motion of Source auroral arcs for AIW as aFunction of UT time

Azimuths of arrival ofAIW at each hour of UT at I53US

(I53US)

Inuvik N.W.T.

April 14,2003 auroral infrasound event of AIW Bow-Wave Type

MCCM

Tracevelocity

Azimuth ofarrival

AIW signals

Vel = 1.03 km/sAZ = 347 deg.

Vel = 0.875AZ = 316

Vel = 0.643AZ = 283

Vel = 0.871AZ = 280

April 14, 2003 AIW associated with auroral-electrojet supersonic motions

Azimuth versusTrace velocityIn meters/secAIW Bow Wave Signals

Mean trace velocity for Bow Wave AIW Signals is = 0.865 km/sec

New Type of Pulsating Aurora AIW

• Pulsating Aurora

• An Example of a Typical All Sky TV Camera Capture of Pulsating Aurora. Image Circle Is About 160 Degrees Edge to Edge (fisheye lens). Images are played in real speed, at 15 fps, the B&W image utilizes all visible light.

Pulsating Aurora from GI/UA’s Ester Dome Observatory

West East

North

Three images of pulsatingAurora patches above I53US On March 6, 2003 , images takenAt 20 second intervals at 12:25 to 12:26 UT

I53US Pulsating Aurora Infrasound March 06, 2003, 12:25 to 12:43 UT

Vel = 1.213 Az = 144 deg

Peak-to-peak amplitude = 0.3 Pascal

abs(fft) March 6 P-AIW signal

44.8 sec

32.2 sec

20.8 sec

Vel = 1.517 km/secAz = 202 deg.

P-AIW from March 06, 2003 at I53US 16:00 to 16:20 UT

MCCM detector output for March 6, 2003at I53US showing both MAW from 180 deg

and high velocity P-AIW signals from all azimuths

MAWsignals

High VelocityP-AIW signals

MAW signals

MCCM

Velocity

Azimuth

NorthSouth

East

West

MAW at I53US 03/06/2003 20:00 to 20:20 UT

March 6,2003, 20:00 to 20:20 UT

Simultaneous MAW EventVelocity = 0.497 km/sec, Az = 181

Trace velocitym/sec versusAzimuth for MAW And for high velocityP-AIW signals 06/03/2003

MAW

P-AIWP-AIW

Other high velocity infrasound putative pulsating aurora events

• Two examples, on Dec 15 and 25, 2002 at I53US,of infrasonic signals during magnetic storm/auroral events with the same signal characteristics of very high trace velocity, widely scattered azimuth of arrival, and similar spectra. There was no photographic aurora data available of visible pulsating auroral patches during these two events.

Phase-aligned 0verlayAll 8 sensors

15 December

abs(fft) Dec 15 P-AIW signal

41.5 sec

31.2 sec

25.4 sec

17.5 sec

Uncertainty in Velocity and Azimuth for highvelocity auroral infrasound event Dec 15,2002

Vel = 2.941 km/sec +/- 0.938 km/sec

Azimuth = 130 +/- 17 deg.Uncertainty Ellipse in Velocity Space

MCCM

Trace VelocityKm/sec

Azimuth

NorthSouth

West

East

Phase-Aligned Pulsating Aurora Infrasound I53US 12/15/02twenty minutes of data at 12,15,18 and 21 hours UT

Vel =3.35 km/sec

Vel = 5.26 km/s

Vel = 1.48 km/s

Vel =1.00 km/s

Az =127

Az = 171

Az = 229

Az = 129

Auroral Infrasound signal azimuths observed at PullmanWashington, Boulder Colorado and Washington DCThousands of kilometers away from the source region