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Improving the twilight model for polar cap absorption nowcasts
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2016 (English)In: Space Weather: The international journal of research and applications, ISSN 1542-7390, E-ISSN 1542-7390, Vol. 14, no 11, 950-972 p.Article in journal (Refereed) Published
Abstract [en]

During solar proton events (SPE), energetic protons ionize the polar mesosphere causing HF radio wave attenuation, more strongly on the dayside where the effective recombination coefficient, αeff, is low. Polar cap absorption models predict the 30 MHz cosmic noise absorption, A, measured by riometers, based on real-time measurements of the integrated proton flux-energy spectrum, J. However, empirical models in common use cannot account for regional and day-to-day variations in the daytime and nighttime profiles of αeff(z) or the related sensitivity parameter, m=A/J. Large prediction errors occur during twilight when m changes rapidly, and due to errors locating the rigidity cutoff latitude. Modeling the twilight change in m as a linear or Gauss error-function transition over a range of solar-zenith angles (χl < χ < χu) provides a better fit to measurements than selecting day or night αeff profiles based on the Earth-shadow height. Optimal model parameters were determined for several polar cap riometers for large SPEs in 1998–2005. The optimal χl parameter was found to be most variable, with smaller values (as low as 60°) postsunrise compared with presunset and with positive correlation between riometers over a wide area. Day and night values of m exhibited higher correlation for closely spaced riometers. A nowcast simulation is presented in which rigidity boundary latitude and twilight model parameters are optimized by assimilating age-weighted measurements from 25 riometers. The technique reduces model bias, and root-mean-square errors are reduced by up to 30% compared with a model employing no riometer data assimilation.

Place, publisher, year, edition, pages
2016. Vol. 14, no 11, 950-972 p.
Keyword [en]
Polar cap ionosphere, Modeling and forecasting, Ionospheric propagation, Ionospheric effects on radio waves, polar cap absorption, HF radio propagation, riometers
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:polar:diva-3547DOI: 10.1002/2016SW001527OAI: oai:DiVA.org:polar-3547DiVA: diva2:1096857
Note

2016SW001527

Available from: 2017-05-19 Created: 2017-05-19 Last updated: 2017-05-19

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Publisher's full texthttp://dx.doi.org/10.1002/2016SW001527
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Space Weather: The international journal of research and applications
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CiteExportLink to record
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Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
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  • de-DE
  • en-GB
  • en-US
  • fi-FI
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