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High-resolution Solar irradiance EUV Spectrum Forecast


OBJECTIVE: Develop a solar irradiance spectrum forecast toolset that can accurately determine current and future high-resolution solar extreme ultraviolet irradiance spectra using near real-time solar observations. DESCRIPTION: The solar spectral irradiance at the top of the atmosphere is the main energy input to Earth"s thermosphere. It excites, dissociates and ionizes the neutral constituents in the thermosphere. It is important to accurately determine the solar irradiance spectrum at very high-resolution to make it possible to compute the effects of radiation on the various absorbing species. Thermosphere density is a critical factor in determining orbital drag used for providing collision avoidance warnings for manned spaceflight and other high-value assets, accurately cataloging orbiting objects, predicting reentry times, and estimating satellite lifetimes, on-board fuel requirements, and attitude dynamics. Uncertainties in neutral density variations are the major limiting factor for precise low-Earth orbit determination at altitudes below about 700 km. Long-standing shortfalls in satellite drag prediction have been, in large part, due to inadequate prediction capability for solar EUV spectra. R & D effort in this area has recently been enhanced by an AFOSR-supported Multi-University Research Initiative entitled"Neutral Atmosphere Density Interdisciplinary Research."It has greatly improved the understanding of the neutral density profiles under various solar and geomagnetic conditions. While near real time data and indices including EUV data and solar flux are now becoming available, thermospheric models have not yet taken advantage of the data for improving neutral density modeling. Empirical solar irradiance specification models (e.g. HEUVAC and SOLAR2000 models) have provided proxy-based solar EUV for characterizing solar irradiance variability across the solar spectrum. Current EUV forecast models commonly rely on time series analysis of past solar measurements. Forecasts of the daily F10.7 cm solar radio data adjusted to 1 AU, the E10.7 EUV proxy index, and a Lyman-alpha index (from Mg II index) are now routinely available. Recent research has indicated the feasibility of forecasting the solar F10.7 index utilizing advanced predictions of the global solar magnetic field generated by a flux transport model. Other researchers have shown that daily solar irradiance spectra can be efficiently constructed based on a set of semi-empirical physical models of solar features and their emitted spectra as a function of viewing angle, combined with solar images. A challenging R & D effort beyond the current state of art is to be able to efficiently nowcast and forecast of high-resolution EUV spectra in the range of 0.1 to 100 nm using the available near real-time observations of solar features. This topic thus requests innovative R & D to develop a semi-empirical physical model of solar atmosphere that can be assimilated with near real-time solar observations. The objective of this STTR is to establish technical feasibility of specification and forecast of high-resolution EUV spectra that can be used to drive thermospheric neural density modeling for near real-time operations. This STTR will also provide motivation for improving EUV-driven ionospheric processes. Successful proposals will help develop innovative algorithms employing new physical models and near real time solar data and indices. The new algorithms will eventually be utilized in the modeling of satellite drag by the Air Force Space Command (AFSPC) and the Joint Space Operations Center (JSpOC). PHASE I: Develop and assess a solar irradiance spectrum modeling system of empirical and/or physical models of solar atmosphere using near real-time solar observations. Demonstrate that the proposed physical model is feasible to achieve the goal of accurately determining current and future high-resolution solar extreme ultraviolet irradiance spectra. PHASE II: Develop a system of tools that can assimilate semi-empirical physical model of solar atmosphere with the available near real-time solar observations. Develop innovative algorithms that forecast high-resolution EUV spectra. Demonstrate that the developed model can be used as input to improve thermosphere and ionospheric physical modeling. Deliverables will include at least the models, prediction algorithms, software system, and validation reports. PHASE III: Results of this work can be used to improve AF space catalog accuracy, a critical component for space situational awareness. The developed model can be utilized in DoD operational centers. New algorithms under this grant can be used in high accuracy collision avoidance in commercial applications. REFERENCES: 1. NOAA Solar Ultraviolet Spectral Irradiance website: 2. Henney, C. J., W. A. Toussaint, S. M. White, and C. N. Arge (2012), Forecasting F10.7 with solar magnetic flux transport modeling, Space Weather, 10, S02011, doi:10.1029/2011SW000748. 3. Fontenla, J. M., J. Harder, W. Livingston, M. Snow, and T. Woods (2011), High-resolution solar spectral irradiance from extreme ultraviolet to far infrared, J. Geophys. Res., 116, D20108, doi:10.1029/2011JD016032. 4. Richards, P. G., T. N. Woods and W. K. Peterson, HEUVAC: A new high resolution EUV proxy model, Adv. Space Res., 37, 315, 2006. 5. Codrescu, M. V., C. Negrea, M. Fedrizzi, T. J. Fuller-Rowell, A. Dobin, N. Jakowsky, H. Khalsa, T. Matsuo, and N. Maruyama (2012), A real-time run of the Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe) model, Space Weather, 10, S02001, doi:10.1029/2011SW000736.
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