Investigation of Space/Ionospheric Plasma Turbulence caused by Anomalous Large-Scale Thermal Fronts


Rezy Pradipta (PhD Student) , Manuel Martinez-Sanchez (Professor), Min-Chang Lee (Professor)


Motivation 


This research is aimed at investigating the possibility that large-scale anomalous heat source (e.g. heat wave event) might be capable of triggering widespread turbulence in the space/ionospheric plasma layer through the excitation of acoustic-gravity waves (AGWs).  This hypothesis was motivated by the observation of intense traveling ionospheric disturbances (TIDs) over Arecibo Observatory, Puerto Rico, for several consecutive days in the summer 2006.  At that time, the geomagnetic condition was relatively quiet, and there were no major earthquake, tsunami, or volcanic eruptions.  However, we note that during this time period, a relatively severe and prolonged heat wave was steadily sweeping eastward across the mainland United States [1].  These findings therefore suggest that the thermal gradients associated with the heat wave fronts are generating AGWs that could propagate through long distances to induce space plasma turbulence in the form of TIDs over an extended region [2].

 


Through this work, we hope to better understand the behavior of space plasma environment as the earth climate changes.  This is especially intriguing because, according to some climate models, we could expect severe and prolonged heat waves to occur more frequently in a warmer earth climate [3].


Approach / Tools 


We are employing two separate approaches to investigate this hypothesis:

- study the level of fluctuations in total electron content (TEC) over the North American sector in response to heat wave events.
- physically simulate AGW/TID excitation by thermal gradients under controlled conditions in a set of ionospheric HF heating experiments.

In the first approach (i.e. mapping of TEC fluctuations), we are looking for possible correlation between the heat wave event and the increase in the level of ionospheric plasma disturbance within the area of interest.  In the second approach (i.e. HF heating experiments), we aim to generate some artificial time-varying thermal
gradients directly at ionospheric heights and see if AGWs/TIDs are being generated.

 


In this HF heating experiment, we utilize a number of ground-based and satellite diagnostics (which include HF and UHF radars, as well as GPS and LEO satellites).  We aim to detect the plasma disturbances
generated by the modulated heating, and to be able to distinguish it from natural ionospheric disturbances that might happen to pass overhead during the experiments.  Possible contamination from naturally-occurring disturbances generally can be minimized by conducting the experiments during geomagnetically quiet times.

References


[1]  NASA Earth Observatory Newsroom, Heat Wave in North America and Western Europe, National Aeronautics and Space Administration (August 2006).http://earthobservatory.nasa.gov/IOTD/view.php?id=6803 (last accessed
16 December 2011).

[2]  R. Pradipta (2007), Could Global Warming Affect Space Weather? Case Studies of Intense Ionospheric Plasma Turbulence Associated with Natural Heat Sources, MS Thesis, MIT.

[3]  G.A. Meehl et al. (2004), More Intense, More Frequent, and Longer Lasting Heat Waves in the 21st Century, Science, 305, 994, doi:10.1126/science.1098704.