Statistics – Applications
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh51b..03l&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SH51B-03
Statistics
Applications
7537 Solar And Stellar Variability, 7538 Solar Irradiance, 7549 Ultraviolet Emissions, 0355 Thermosphere: Composition And Chemistry, 0358 Thermosphere: Energy Deposition
Scientific paper
A variety of space weather models require knowledge of the Sun' s EUV spectral irradiance because this radiation is the predominant source of upper atmosphere heating and ionization. Lacking reliable observations to specify the considerable variability of the EUV spectrum during the solar activity cycle, space weather research and operational models continue to use the 10.7 cm radio flux as a proxy for variations in EUV radiation, even though its shortcomings have been recognized for some time. For example, the largest source of error in special perturbations propagation of spacecraft orbits is the parameterization of solar EUV irradiance in the density models that the codes use to estimate drag. The strongest lines in the EUV spectrum are formed in the Sun' s upper chromosphere whereas the 10.7 cm flux is formed primarily in the hotter corona. We have recently developed a composite chromospheric EUV irradiance index by combining multiple space and ground-based datasets, and are reformulating NRL' s upper atmosphere neutral density model (NRLMSISE-00) to accommodate this new index. In a parallel effort we have developed a new physics-based irradiance variability model (NRLEUV) that calculates the EUV spectrum independently of direct spectral irradiance observations. The model utilizes solar images to extract information about the fraction of the solar atmosphere occupied by different active, network and quiet regions, and coronal holes. Representative differential emission measures are constructed for each of the features and the EUV disk-integrated spectrum is calculated by combining the emission measures with theoretically determined values of plasma emissivity. We use a parameterized version of the NRLEUV model that includes both chromospheric and coronal indices to calculate variations during past solar cycles in the total EUV energy incident at the top of the earth' s atmosphere, and at selected altitude in the range 100 to 1000 km, for use in future reformulations of NRLMSIS. We compare the new chromospheric index and the physics-based EUV irradiance model products with existing EUV model estimates derived from parameterizations of direct observations, and describe how NRLMSIS will incorporate these new determinations of the EUV irradiance to provide an improved density specification for space weather applications.
Bishop James
Lean Judith L.
Mariska John T.
Picone Michael J.
Warren Harry P.
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