Colloq Abstract - Helmboldt

November 18

11am Mountain

 

Joseph 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.

Connect with NRAO

The National Radio Astronomy Observatory and Green Bank Observatory are facilities of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.

The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..."

AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public.