Can magnetic waves in the auroral region transform into acoustic waves?
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Can magnetic waves in the auroral region transform into acoustic waves?. Jada Maxwell, E.J. Zita The Evergreen State College. 14 April 2006 Photo: Dave Parkhurst Matanuska-Susitna Valley, AK. 14 April 2006 Photo: Daryl Pedersen Crow Pass, AK.

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14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Can magnetic waves in the auroral region transform into acoustic waves?

Jada Maxwell, E.J. Zita

The Evergreen State College

14 April 2006

Photo: Dave Parkhurst

Matanuska-Susitna Valley, AK

14 April 2006

Photo: Daryl Pedersen

Crow Pass, AK

Images: http://www.spaceweather.com/aurora/images2005.htm


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Abstract acoustic waves?

Aurorae are caused by geomagnetic storms created by magnetic storms from the Sun (Akasofu, 1991).  These storms drive magnetic waves in the magnetosphere (Cornilleau-Wehrlin, 2000).  Infrasonic waves have been observed to emanate from aurorae (Wilson and Olson, 2005).  This suggests that magnetic waves in Earth’s upper atmosphere may drive infrasound in Earth’s lower atmosphere.  Similar processes have been demonstrated in reverse in the Sun’s atmosphere (Johnson, et al., 2002; Bogdan, et al., 2000, 2002, 2003).  Using techniques from solar magnetohydrodynamics (MHD), we have shown that atmospheric pressure and magnetic pressure are comparable (plasma beta = 1) at 120 km, well within the auroral region, above Fairbanks, AK (Maxwell and Zita, 2005).  This is an important condition for MHD wave transformations to occur (Bogdan, et al., 2003).  We have also proposed mechanisms for the creation of infrasonic waves from electromagnetic waves (Maxwell and Zita, 2005).  Now, we investigate evidence and data from satellite and ground-based instruments to test our hypotheses.


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Overview acoustic waves?

  • How are aurorae created?

  • Magnetic Waves

  • Sound waves from the aurorae

  • Wilson model

  • Wave transformation in the Sun’s atmosphere

  • Wave transformation in Earth’s atmosphere

  • Mechanisms for transformation

  • Future work


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Solar storms cause geomagnetic storms acoustic waves?

Image by Steele Hillhttp://scijinks.jpl.nasa.gov/en/educators/gallery/spaceweather/solar_wind_comp_L.jpg


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

This Creates Aurorae acoustic waves?

Particles Spiral Down Field Lines

Image courtesy of Shawn Malonehttp://www.lakesuperiorphoto.com

Image: Fundamentals of Physics, 2005


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Types of Magnetic Waves

  • Alfvén waves (s-mode)

S-mode image courtesy of Georgia State Universityhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/tralon.html


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Can we hear aurorae? acoustic waves?

  • Anecdotal evidence

  • hissing, popping, crackling, swooshing

  • corresponds with motions of light

  • Sound takes about 6 minutes to travel from aurora to the ground

  • No recordings of audible aurorae


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Explanations of Audible Sounds acoustic waves?

  • Freezing Breath

  • “Brush discharge”

  • Psychological


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Evidence of acoustic waves?Infrasoundfrom Aurorae

  • Humans can hear between 20 and 20,000 Hertz (Hz)

  • Infrasound is below 20 Hz

  • Currently being investigated


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Charles Wilson’s Auroral Infrasonic Wave Model acoustic waves?

Figure 1. Bow wave model of the generation of AIW by auroral electrojet supersonic motion at a height h above the x,y ground plane. The aurora arc, shown in red, moves supersonically in the direction Va creating a bow wave, shown in purple, that propagates to the surface at line ab causing the AIW pressure wave to be observed if the infrasonic array is in the Front Shock Region.

From Inframatics, No. 10, June 2005, C.R. Wilson


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Sound waves on the Sun acoustic waves?

N

Sound waves

Convection

SUN


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Magnetic field acoustic waves?

N

Sound waves

Convection

SUN


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Magnetic waves acoustic waves?

N

SUN


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Can the inverse happen in acoustic waves?Earth’s atmosphere?

Earth


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Plasma is like… acoustic waves?

Gas Pressure

Beta = β =

Magnetic Field Pressure

Acoustic and magnetic waves couple where

β ≈ 1


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

β acoustic waves?= 1 in Earth’s atmosphere?


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

y (B acoustic waves?0, k)

y (B0)

x (v1, B1)

x (v1, B1, k)

z (E1)

z (E1)

Mechanism for Transformation

Alfvén waves

Magnetosonic waves


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Mechanism for Transformation acoustic waves?

y (B0, k)

y (B0)

x (v1, B1)

x (v1, B1, k)

E1 p

E1 p

z (E1)

z (E1)

Alfvén waves to

Acoustic waves

Magnetosonic waves to

Acoustic waves


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Mechanism for Transformation acoustic waves?

y (B0, k)

y (B0)

v1 p

v1 p

x (v1, B1)

x (v1, B1, k)

E1 p

E1 p

z (E1)

z (E1)

Alfvén waves to

Acoustic waves

Magnetosonic waves to

Acoustic waves



14 april 2006 photo 3a daryl pedersen crow pass 2c ak

*Wilson – origin of waves 110 km acoustic waves?

*From Inframatics, No. 10, p 1, June 2005, C.R. Wilson

Beta ≈ 1 at altitude lower than 120 km

Wavelength should increase


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

What’s next? acoustic waves?

  • Apply temperature data

  • Access satellite data (FAST)

    • Magnetic and electric field fluctuations

    • Magnetic waves

  • Access infrasound data

  • Compare ground and auroral waves ( )


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Acknowledgements: acoustic waves?

  • Dr. E.J. Zita for her guidance, input and helpful discussions

  • Dr. Charles Wilson for providing resources

  • Dr. Kristine Sigsbee for her generous insight regarding Polar satellite data

  • Dr. Charles Carlson for direction to useful FAST satellite data

  • All of my classmates in Physics of Astronomy for their good questions and suggestions

  • The Evergreen State College Foundation for Activity Grant


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

Sources & References acoustic waves?

  • Akasofu, S.-I. “Auroral Phenomena.” In: Meng, C.-I., M.J. Rycroft, and L.A. Frank (editors). Auroral Physics. Cambridge Univ. Press, 1991

  • Cornilleau-Wehrlin, N. “Magnetosphere of Earth: Waves.” Encyclopedia of Astronomy & Astrophysics [online], Nature Publishing Group, 2001/IoP Publishing, 2005

  • Bogdan, T.J., et al. “Waves in the Magnetized Solar Atmosphere. II. Waves from Localized Sources in Magnetic Flux Concentrations.” Astrophys. J., 599, 626-660, 2003

  • Johnson, M.C., S. Petty-Powell, and E.J. Zita. “Energy Transport by MHD Waves Above the Photosphere Numerical Simulations.” 17 Oct 2002, http://192.211.16.13/z/zita/students/matt/researchmatt.html

  • Israelevich, P.L. and L. Ofman. “Parallel Electric Field in the Auroral Ionosphere: Excitation of Acoustic Waves by Alfvén Waves.” Ann. Geophys., 22, 2797-2804, 2004

  • Maxwell, J.F. and E.J. Zita. “Can magnetic waves in aurorae transform into acoustic waves?” APS NW Section Meeting, 13 May 2005

  • Wilson, C.R. "Infrasound from Auroral Electrojet Motions at I53US." Inframatics, 10, 1-13, 2005

  • Wilson, C.R. and J.V. Olson. “Auroral Infrasound Observed at I53US at Fairbanks, Alaska.” American Geophysical Union, Fall Meeting, 2003


14 april 2006 photo 3a daryl pedersen crow pass 2c ak

http://academic.evergreen.edu/m/maxjad02 acoustic waves?

3 April 2006, Aldersundet, Norway

Photo: Eskil Olsen

http://www.spaceweather.com/aurora/gallery_01apr06.htm