Improving the twilight model for polar cap absorption nowcasts

Rogers, Neil Christopher and Kero, Antti and Honary, Farideh and Verronen, P.T. and Warrington, Michael and Danskin, Donald W. (2016) Improving the twilight model for polar cap absorption nowcasts. Space Weather, 14 (11). pp. 950-972. ISSN 1539-4956

[thumbnail of Rogers_et_al-2016-Space_Weather]
PDF (Rogers_et_al-2016-Space_Weather)
Rogers_et_al_2016_Space_Weather.pdf - Accepted Version
Available under License Creative Commons Attribution-NonCommercial.

Download (3MB)
[thumbnail of Rogers et al. 2016 Improving the Twilight Model for PCA Nowcasts (Published Version)]
PDF (Rogers et al. 2016 Improving the Twilight Model for PCA Nowcasts (Published Version))
Rogers_et_al._2016_Improving_the_Twilight_Model_for_PCA_Nowcasts_Published_Version_.pdf - Published Version
Available under License Creative Commons Attribution.

Download (3MB)


During Solar Proton Events (SPE), energetic protons ionize the polar mesosphere causing HF radiowave attenuation, more strongly on the dayside where the effective recombination coefficient, αeff, is low. Polar cap absorption (PCA) 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 day- 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°) post-sunrise compared with pre-sunset, 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-squared errors are reduced by up to 30% compared with a model employing no riometer data assimilation.

Item Type:
Journal Article
Journal or Publication Title:
Space Weather
Additional Information:
An edited version of this paper was published by AGU. Copyright 2016 American Geophysical Union.
Uncontrolled Keywords:
?? polar cap absorptionhf radio propagationriometersatmospheric science ??
ID Code:
Deposited By:
Deposited On:
17 Oct 2016 10:26
Last Modified:
27 May 2024 00:15