- Single Dish Summer School 202220 Dec, 2021
- F Region Electric Field Effects on the Intermediate Layer Dynamics During the Evening Prereversal Enhancement at Equatorial Region Over Brazil16 Dec, 2021
- Announcing a Change in Leadership of the Florida Space Institute16 Dec, 2021
- AO Scientist studies Near-Sun Asteroid 2005 UD polarimetric comparison with asteroids and meteorites15 Dec, 2021
- Near-Earth Asteroid 1999 KW4 Moshup: Planetary Defense Characterization Exercise15 Dec, 2021
- AO Scientist Contribute to European Pulsar Timing Array: Gravitational Wave Background Study15 Dec, 2021
- The Arecibo Observatory’s Big Data Program: Award Winning Preservation of AO’s Historic Dataset15 Dec, 2021
- Topical Symposium: Science and Discoveries at Arecibo Observatory 15 Dec, 2021
- Arecibo Observatory Restarts Radio Astronomy Observations15 Dec, 2021
- Beating the Noise: Arecibo and Green Bank Telescopes Detect Faint Signals from Cold Clouds in our Galaxy15 Dec, 2021
- Abrupt Change in one of the Most Precisely-Time Pulsars14 Dec, 2021
- Air Pollution Concentration Study14 Dec, 2021
- Arecibo Scientists investigate variability of Blazar J1415+132014 Dec, 2021
- Arecibo Observatory at the 239th AAS Meeting14 Dec, 2021
- Detection of the YORP Effect on the contact-binary (68346) 2001 KZ66 from combined radar and optical observations14 Dec, 2021
- AO Radar Data Used to Study NASA Mission Target Asteroid (16) Psyche14 Dec, 2021
Radio-frequency (RF) auroras, like the beautiful example shown in Figure 1 and the movie (link here), are often dancing across the night skies of Puerto Rico. Unlike their high-latitude cousins, however, these tropical phantasms do not generate optical emission and are not associated with solar activity. These are mid-latitude RF echoes observed with coherent radar and displaying radio signatures similar to those detected from the northern lights.
The Arecibo Observatory has been key to understanding the nature of these mid-latitude RF auroras. This unique cluster of diverse and highly sensitive equipment includes both radar and optical instruments. The ionized particles are observed with Arecibo’s incoherent scatter radar (ISR) and show billowy behavior as well as unexplained changes in the density and temperature distributions. At the same time, the neutral particles are observed with Arecibo’s lidars, which also show the billowy behavior and temperature changes. An example of the neutral billows using the sodium resonance lidar is shown in Figure 2. The background ionospheric medium is observed simultaneously with Arecibo’s imagers and ionosondes.
RF auroras appear to result from the interaction between neutral particles in the thermosphere and charged particles in the ionosphere. Neutral winds produce a shear that generates Kelvin-Helmholtz rolls. Current work suggests that RF auroras are produced by neutral particles that drag ions and result in coherent echoes. This finding is motivating a new area of research that focuses on the study of ion behavior to infer neutral winds. Recent work reported convective instabilities and other neutral dynamics during the daytime, opening up new possibilities to expand our understanding of ion-neutral coupling in the lower ionosphere and adding to our understanding of RF auroras.
Figure 1. Mid-latitude RF auroras observed on the night of September 30, 2008, with a coherent scatter radar located on St. Croix and looking perpendicular to the earth's magnetic field line over the Arecibo Observatory at an altitude close to 105 km. The contour corresponds to the island of Puerto Rican and the “X” to the location of the Arecibo Observatory. The color scale indicates variations in Doppler, intensity, and spectral width.
Animation related to Figure 1 Arecibo Observatory: Mid-latitude Radio-Frequency Auroras. By Eliana Nossa, Shikha Raizada, and David Hysell
Figure 2. Altitudinal and temporal distribution of Na atoms obtained using a resonance lidar over Arecibo. The main layer between 80-100 km has been saturated to reveal the structures between 101-110 km. Sarkhel et al. (2012) found atmospheric conditions to be dynamically unstable and conducive a Kelvin-Helmholtz instability during this event.Paper Title: Dynamic instability in the lower thermosphere inferred from irregular sporadic E layers
Paper Authors: D.L. Hysell, E. Nossa, M.F. Larsen, J. Munro, S. Smith, M.P. Sulzer, and S.A. González
Paper Reference: J. Geophys. Res., (2012), 117, A08305, doi:10.1029/2012JA017910.
Keywords: Ionosphere, Auroras, Aeronomy, Nossa, Hysell, Raizada, MLT Region, Mesosphere, Thermosphere, E Region, Radio Propagation, Space, Atmosphere, Earth