Can magnetic waves in the auroral region transform into acoustic waves?
Download
1 / 25

14 April 2006 Photo: Daryl Pedersen Crow Pass, AK - PowerPoint PPT Presentation


  • 89 Views
  • Uploaded on

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.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about '14 April 2006 Photo: Daryl Pedersen Crow Pass, AK' - vivienne


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

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


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.


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


Solar storms cause geomagnetic storms acoustic waves?

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


This Creates Aurorae acoustic waves?

Particles Spiral Down Field Lines

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

Image: Fundamentals of Physics, 2005


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


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


Explanations of Audible Sounds acoustic waves?

  • Freezing Breath

  • “Brush discharge”

  • Psychological


Evidence of acoustic waves?Infrasoundfrom Aurorae

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

  • Infrasound is below 20 Hz

  • Currently being investigated


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


Sound waves on the Sun acoustic waves?

N

Sound waves

Convection

SUN


Magnetic field acoustic waves?

N

Sound waves

Convection

SUN


Magnetic waves acoustic waves?

N

SUN


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

Earth


Plasma is like… acoustic waves?

Gas Pressure

Beta = β =

Magnetic Field Pressure

Acoustic and magnetic waves couple where

β ≈ 1


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


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


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


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



*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


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 ( )


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


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


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

3 April 2006, Aldersundet, Norway

Photo: Eskil Olsen

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


ad