Scientist Explains Whistler Turbulence in Space

Friday, March 12, 2010

Gusty winds streaming off our Sun are called solar wind and this wind propagates outwardly and develops in complicated structures, i.e. turbulence, in space and time all across the interplanetary space. The behavior of the solar wind is quite unpredictable and has long been a subject of comprehensive research because it governs numerous processes that directly impacts planet Earth.

These include geomagnetic storm, hazardous cosmic particles, space weather etc. Understanding the behavior of solar wind is therefore very critical. In situ spacecraft measurements, theory and modeling are trying to find out a fundamental question; how energy from the solar wind is transferred across many different scales (like packets or eddies of various shapes and sizes) in the interplanetary space. Unfortunately, owing to its complex nature, the problem of solar wind turbulence continues to remain one of the unresolved issues in space physics.

What is remarkably complicated is the multitude of length and time scales on which turbulence is happening throughout the interplanetary space. At very high (higher than ion cyclotron) frequency, the magnetized solar wind plasma excites whistler waves (that sounds like whistles and were first discovered by World War I radio operators) whose behavior is far more complicated than ever thought. Unfortunately their dynamics is poorly understood in the context of solar wind turbulence that transfers energy from large scale down to the scales where the wind heats up the local plasma in the interplanetary space.

A new fluid model developed by Professor Dastgeer Shaikh at the Physics Department and Center for Space Plasma and Aeronomic Research at The University of Alabama in Huntsville (UAHuntsville), links turbulence in solar wind to the transfer of energy in space and might help shed light on this mysterious process.

Dr. Shaikh discovered that the transfer of energy in solar wind occurs much quicker than predicted by earlier theories and that density of these waves do not affect the manner in which energy is transferred across the small scale high frequency whistler turbulence in the solar wind plasma. “Earlier researchers have ignored the effect of density fluctuations on whistler wave turbulence and this step was very crucial for us to take in a forward direction if are to understand the solar wind turbulence,” he said.

“Unfortunately we are not yet well equipped to measure the role of density fluctuations in the regime where whistler waves play a critical role in converting the solar wind energy into heat,” said Dr Shaikh, who added that his work is therefore very important to test observationally by in situ measurements. “Since density does not modify the general consensus of solar wind turbulence, that follows a universal power law, we like to believe that they interact weakly with the wave magnetic field at such a high frequency,” he said.

Dr. Shaikh is a leading scientist in the field of whistler and solar wind turbulence at UAHuntsville. His results agree with the spacecraft observations that measured the solar wind energy law 20 years ago. The research results of Dr. Shaikh are to appear in Monthly Notices of the Royal Astronomical Society.

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