Identification and Validation of Critical Components of Polar Mesospheric Chemistry
Abstract
Accurate simulations of the global ionosphere impact important applications such as global posi-tioning position fixes, long-distance radio communications, and satellite drag estimation, among others. The NextGen Ionospheric Model for Operations (NIMO) program has produced strong agreement between simulations and observations for the low- and mid-latitude F-region iono-sphere, especially whenincorporating satellite observations. The F-region ionosphere is only one portion of the ionosphere, however, and many important characteristics of ionospheric radio wave propagation are determined instead by the collision-dominated lower ionosphere (i.e., the D-and E-regions at ~60-120 km altitude), which is the focus of the proposed program. The majority of radio wave absorption is typically attributed to D- and E-region effects, but it is also true, for instance, that high-power radio waves can modify the lower ionosphere, sharpening its conductiv-ity profile and meaningfully changing ionospheric transmission and reflection coefficients. NIMO simulations of the lower ionosphere have not yet been validated using reliable experimental ob-servations.The University of Florida (UF)proposes a 3-year program to validate and/or improve the NIMO program, particularly for polar regions. UF is experienced at remote-sensing the lower ionosphere uses very low frequency (VLF, 3-30 kHz) radio waves, which are sensitive to small changes in ionospheric conductivity and propagate great distances (>10,000 km) within the Earth-ionosphere waveguide. A primary form of validation will thus take the form of experimental ob-servations using the North American Very Low Frequency Array of receivers, operated by UF, which monitors VLF transmitter signals some of which traverse auroral precipitation zones. Mid-latitude observations of ionospheric disturbances will also be used to quantify and characterize transient event onset and recovery times, which are governed by the photochemistry of the region. Modeling of events such as solar flares or lightning-ionosphere interactions, will benefit from em-ploying theNIMO-predicted ambient conditions. At the same time, these observations will also serve as validation for the NIMO program or identify weaknesses in the program. UF strongly recommends the deployment of additional VLF receivers to Alaska. These receivers will provide observations focused on the polar cap, auroral, and sub-auroral zones that cannot be reproduced easily elsewhere. UF also strongly recommends experimentation using the High-frequency Active Auroral Research Program ionospheric HF heater to provide unique experimental validation tests of NIMO predictions at high latitudes (sometimes auroral, other times sub-auroral). All of these experiments, in one way or another, focus on accurately representing or evaluating mesospheric chemistry, with reaction rates and heating time scales that must be consistent with the ambient predictions of the NIMO program. For this reason, this 3-year program can be described as focus-ing on the identification and validation of critical components of polar mesospheric chemistry.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 12, 2023
- Source ID
- N000142312344
Entities
People
- R. G. Moore
Organizations
- Office of Naval Research
- United States Navy
- University of Florida