Improving the twilight model for polar cap absorption nowcasts
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 riometer...
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| Veröffentlicht in: | Space Weather 2016-11, Vol.14 (11), p.950-972 |
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| creator | Rogers, N. C. Kero, A. Honary, F. Verronen, P. T. Warrington, E. M. Danskin, D. W. |
| description | 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 |
| doi_str_mv | 10.1002/2016SW001527 |
| format | Article |
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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.
Plain Language Summary
The active sun occasionally ejects streams of very high‐energy protons towards the Earth. These are guided by the geomagnetic field into the polar regions where they ionise the upper atmosphere (ionosphere). The ionised plasma strongly absorbs shortwave radio signals used for long‐distance communications and this can persist for several days. This study shows how real‐time measurements from multiple ground sensors (as well as satellites) are needed to improve the accuracy of radio absorption nowcasts. In particular, it examines and models the rapid changes in ionospheric absorption at twilight, the rate of which can vary greatly, both regionally and from day to day.
Key Points
Parameters of an empirical PCA model are optimized by using riometers
A linear twilight transition model provides a better fit than “Earth‐shadow” methods
Postsunrise delays in absorption increases are large and highly variable</description><identifier>ISSN: 1542-7390</identifier><identifier>ISSN: 1539-4964</identifier><identifier>EISSN: 1542-7390</identifier><identifier>DOI: 10.1002/2016SW001527</identifier><language>eng</language><publisher>Washington: John Wiley & Sons, Inc</publisher><subject>Absorption ; Atmosphere ; Atmospheric models ; Communication satellites ; Communications ; Correlation ; Cosmic noise ; Data assimilation ; Data collection ; Energy ; Fluctuations ; Geomagnetic field ; Geomagnetism ; HF radio propagation ; Ionosphere ; Ionospheric absorption ; Latitude ; Mathematical models ; Night ; Noise ; Noise prediction ; Optimization ; Parameters ; Polar cap absorption ; Polar caps ; Polar mesosphere ; Polar regions ; Proton flux ; Radio attenuation ; Radio waves ; Rigidity ; Riometers ; Satellites ; Sensitivity ; Sensors ; Simulation ; Solar protons ; Streams ; Sun ; Twilight ; Upper atmosphere ; Wave attenuation ; Zenith</subject><ispartof>Space Weather, 2016-11, Vol.14 (11), p.950-972</ispartof><rights>2016. The Authors.</rights><rights>2016. American Geophysical Union. All Rights Reserved.</rights><lds50>peer_reviewed</lds50><oa>free_for_read</oa><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-c4396-44a4e20d09c1020d480aedfa1da64214d975b88a1eeb20ae5cb94388f4199d23</citedby></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><linktopdf>$$Uhttps://onlinelibrary.wiley.com/doi/pdf/10.1002%2F2016SW001527$$EPDF$$P50$$Gwiley$$Hfree_for_read</linktopdf><linktohtml>$$Uhttps://onlinelibrary.wiley.com/doi/full/10.1002%2F2016SW001527$$EHTML$$P50$$Gwiley$$Hfree_for_read</linktohtml><link.rule.ids>314,776,780,1411,27901,27902,45550,45551</link.rule.ids></links><search><creatorcontrib>Rogers, N. C.</creatorcontrib><creatorcontrib>Kero, A.</creatorcontrib><creatorcontrib>Honary, F.</creatorcontrib><creatorcontrib>Verronen, P. T.</creatorcontrib><creatorcontrib>Warrington, E. M.</creatorcontrib><creatorcontrib>Danskin, D. W.</creatorcontrib><title>Improving the twilight model for polar cap absorption nowcasts</title><title>Space Weather</title><description>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.
Plain Language Summary
The active sun occasionally ejects streams of very high‐energy protons towards the Earth. These are guided by the geomagnetic field into the polar regions where they ionise the upper atmosphere (ionosphere). The ionised plasma strongly absorbs shortwave radio signals used for long‐distance communications and this can persist for several days. This study shows how real‐time measurements from multiple ground sensors (as well as satellites) are needed to improve the accuracy of radio absorption nowcasts. In particular, it examines and models the rapid changes in ionospheric absorption at twilight, the rate of which can vary greatly, both regionally and from day to day.
Key Points
Parameters of an empirical PCA model are optimized by using riometers
A linear twilight transition model provides a better fit than “Earth‐shadow” methods
Postsunrise delays in absorption increases are large and highly variable</description><subject>Absorption</subject><subject>Atmosphere</subject><subject>Atmospheric models</subject><subject>Communication satellites</subject><subject>Communications</subject><subject>Correlation</subject><subject>Cosmic noise</subject><subject>Data assimilation</subject><subject>Data collection</subject><subject>Energy</subject><subject>Fluctuations</subject><subject>Geomagnetic field</subject><subject>Geomagnetism</subject><subject>HF radio propagation</subject><subject>Ionosphere</subject><subject>Ionospheric absorption</subject><subject>Latitude</subject><subject>Mathematical models</subject><subject>Night</subject><subject>Noise</subject><subject>Noise prediction</subject><subject>Optimization</subject><subject>Parameters</subject><subject>Polar cap absorption</subject><subject>Polar caps</subject><subject>Polar mesosphere</subject><subject>Polar regions</subject><subject>Proton flux</subject><subject>Radio attenuation</subject><subject>Radio waves</subject><subject>Rigidity</subject><subject>Riometers</subject><subject>Satellites</subject><subject>Sensitivity</subject><subject>Sensors</subject><subject>Simulation</subject><subject>Solar protons</subject><subject>Streams</subject><subject>Sun</subject><subject>Twilight</subject><subject>Upper atmosphere</subject><subject>Wave attenuation</subject><subject>Zenith</subject><issn>1542-7390</issn><issn>1539-4964</issn><issn>1542-7390</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2016</creationdate><recordtype>article</recordtype><sourceid>24P</sourceid><recordid>eNqNkE1Lw0AQhhdRsFZv_oAFL16is1_J7kWQ0mqh4KGFHpdNsmlTkmzcTS39967UQ_Hk6R2Yh2HeB6F7Ak8EgD5TIOlyDUAEzS7QiAhOk4wpuDybr9FNCLtIc0H5CL3M2967r7rb4GFr8XCom3qzHXDrStvgynncu8Z4XJgemzw43w-163DnDoUJQ7hFV5Vpgr37zTFazaaryXuy-HibT14XScGZShPODbcUSlAFgZhcgrFlZUhpUk4JL1UmcikNsTancSWKXHEmZcWJUiVlY_R4Oht__dzbMOi2DoVtGtNZtw-ayJTHgkLAP9BIZRmjMqIPf9Cd2_su9tBEgVQUFE8jRU9UVGOPuvd1a_xRE9A_zvW5c71cTykwmbJveuJz3Q</recordid><startdate>201611</startdate><enddate>201611</enddate><creator>Rogers, N. C.</creator><creator>Kero, A.</creator><creator>Honary, F.</creator><creator>Verronen, P. T.</creator><creator>Warrington, E. M.</creator><creator>Danskin, D. W.</creator><general>John Wiley & Sons, Inc</general><scope>24P</scope><scope>7TG</scope><scope>8FD</scope><scope>H8D</scope><scope>KL.</scope><scope>L7M</scope></search><sort><creationdate>201611</creationdate><title>Improving the twilight model for polar cap absorption nowcasts</title><author>Rogers, N. C. ; Kero, A. ; Honary, F. ; Verronen, P. T. ; Warrington, E. M. ; Danskin, D. W.</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c4396-44a4e20d09c1020d480aedfa1da64214d975b88a1eeb20ae5cb94388f4199d23</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2016</creationdate><topic>Absorption</topic><topic>Atmosphere</topic><topic>Atmospheric models</topic><topic>Communication satellites</topic><topic>Communications</topic><topic>Correlation</topic><topic>Cosmic noise</topic><topic>Data assimilation</topic><topic>Data collection</topic><topic>Energy</topic><topic>Fluctuations</topic><topic>Geomagnetic field</topic><topic>Geomagnetism</topic><topic>HF radio propagation</topic><topic>Ionosphere</topic><topic>Ionospheric absorption</topic><topic>Latitude</topic><topic>Mathematical models</topic><topic>Night</topic><topic>Noise</topic><topic>Noise prediction</topic><topic>Optimization</topic><topic>Parameters</topic><topic>Polar cap absorption</topic><topic>Polar caps</topic><topic>Polar mesosphere</topic><topic>Polar regions</topic><topic>Proton flux</topic><topic>Radio attenuation</topic><topic>Radio waves</topic><topic>Rigidity</topic><topic>Riometers</topic><topic>Satellites</topic><topic>Sensitivity</topic><topic>Sensors</topic><topic>Simulation</topic><topic>Solar protons</topic><topic>Streams</topic><topic>Sun</topic><topic>Twilight</topic><topic>Upper atmosphere</topic><topic>Wave attenuation</topic><topic>Zenith</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Rogers, N. C.</creatorcontrib><creatorcontrib>Kero, A.</creatorcontrib><creatorcontrib>Honary, F.</creatorcontrib><creatorcontrib>Verronen, P. T.</creatorcontrib><creatorcontrib>Warrington, E. M.</creatorcontrib><creatorcontrib>Danskin, D. W.</creatorcontrib><collection>Wiley Online Library Open Access</collection><collection>Meteorological & Geoastrophysical Abstracts</collection><collection>Technology Research Database</collection><collection>Aerospace Database</collection><collection>Meteorological & Geoastrophysical Abstracts - Academic</collection><collection>Advanced Technologies Database with Aerospace</collection><jtitle>Space Weather</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Rogers, N. C.</au><au>Kero, A.</au><au>Honary, F.</au><au>Verronen, P. T.</au><au>Warrington, E. M.</au><au>Danskin, D. W.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Improving the twilight model for polar cap absorption nowcasts</atitle><jtitle>Space Weather</jtitle><date>2016-11</date><risdate>2016</risdate><volume>14</volume><issue>11</issue><spage>950</spage><epage>972</epage><pages>950-972</pages><issn>1542-7390</issn><issn>1539-4964</issn><eissn>1542-7390</eissn><abstract>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.
Plain Language Summary
The active sun occasionally ejects streams of very high‐energy protons towards the Earth. These are guided by the geomagnetic field into the polar regions where they ionise the upper atmosphere (ionosphere). The ionised plasma strongly absorbs shortwave radio signals used for long‐distance communications and this can persist for several days. This study shows how real‐time measurements from multiple ground sensors (as well as satellites) are needed to improve the accuracy of radio absorption nowcasts. In particular, it examines and models the rapid changes in ionospheric absorption at twilight, the rate of which can vary greatly, both regionally and from day to day.
Key Points
Parameters of an empirical PCA model are optimized by using riometers
A linear twilight transition model provides a better fit than “Earth‐shadow” methods
Postsunrise delays in absorption increases are large and highly variable</abstract><cop>Washington</cop><pub>John Wiley & Sons, Inc</pub><doi>10.1002/2016SW001527</doi><tpages>23</tpages><oa>free_for_read</oa></addata></record> |
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| source | Wiley Online Library Journals Frontfile Complete; Elektronische Zeitschriftenbibliothek - Frei zugängliche E-Journals |
| subjects | Absorption Atmosphere Atmospheric models Communication satellites Communications Correlation Cosmic noise Data assimilation Data collection Energy Fluctuations Geomagnetic field Geomagnetism HF radio propagation Ionosphere Ionospheric absorption Latitude Mathematical models Night Noise Noise prediction Optimization Parameters Polar cap absorption Polar caps Polar mesosphere Polar regions Proton flux Radio attenuation Radio waves Rigidity Riometers Satellites Sensitivity Sensors Simulation Solar protons Streams Sun Twilight Upper atmosphere Wave attenuation Zenith |
| title | Improving the twilight model for polar cap absorption nowcasts |
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