Colloq Abstract - Helmboldt

March 3, 2017

11am Mountain

 

Joe Helmboldt (NRL)

 

Remote sensing of disturbances within the ionosphere and plasmasphere with the Very Large Array

Abstract

While designed and predominantly used as a powerful tool for astronomy and astrophysics, the Karl G. Jansky Very Large Array (VLA) is also a unique and extremely useful ionospheric and plasmaspheric remote sensing platform.  The fidelity of any radio-frequency synthesis image is impacted to some degree by temporal and spatial variability within Earth’s ionosphere.  This is especially true at frequencies below ~500 MHz where sub-arcminute resolution imaging is nearly impossible without some form of “adaptive optics” (e.g., self-calibration).  Specifically, spatial gradients in the total electron content (TEC) perpendicular to the line of sight cause baseline phase errors that vary significantly on time scales from a few seconds to many minutes.  When observing a bright, low-frequency source, the VLA’s excellent timing stability allows for extremely precise measurements of these gradients on relatively short time scales.  This talk will describe past and current efforts to exploit this virtually unmatched precision to study disturbances in both the ionosphere and the plasmasphere.  These include irregularities associated with weather-driven gravity waves, so-called electro-buoyancy waves, naturally occurring and human-generated acoustic waves, and field-aligned plasmaspheric structures that were initially discovered with the VLA.

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