@article{1f902b15c744491899a642569819e51f,
title = "Extreme Positive Ionosphere Storm Triggered by a Minor Magnetic Storm in Deep Solar Minimum Revealed by FORMOSAT-7/COSMIC-2 and GNSS Observations",
abstract = "This study examines an unexpected and extreme positive ionospheric response to a minor magnetic storm on August 5, 2019 by using global ionosphere specification (GIS) 3D electron density profiles obtained by assimilating radio occultation total electron content (TEC) measurements of the recently launched FORMOSAT-7/COSMIC-2 satellites, and ground-based global navigation satellite system (GNSS) TEC. The results reveal ∼300% enhancement of equatorial ionization anomaly (EIA) crests, appearing over 200–300 km altitudes, and a much intense localized density enhancement over the European sector. These are the most intense ionospheric response that has ever been detected for a small magnetic storm with Dst ∼ −53 nT (SYM-H ∼ −64 nT). The enhancements are validated by using global ionosphere map (GIM) TEC and ground-based GNSS TEC. The GIS vertical electron density structures during the storm are examined to understand the physical processes giving rise to such an intense ionosphere response during deep solar minimum conditions when the background electron density is very low. Altitude variations and poleward shifts of the locations of the EIA crests indicate that prompt penetration electric fields (PPEF) play an important role in producing the observed positive storm responses, with the storm-induced equatorward circulation supporting the plasma accumulation against recombination losses. Additional physical mechanisms are required to fully explain the unexpected electron density enhancements for this minor storm event.",
author = "Rajesh, {P. K.} and Lin, {C. H.} and Lin, {C. Y.} and Chen, {C. H.} and Liu, {J. Y.} and T. Matsuo and Chen, {S. P.} and Yeh, {W. H.} and Huang, {C. Y.}",
note = "Funding Information: This work was supported by the Ministry of Science and Technology (MOST), Taiwan under project MOST 108‐2638‐M‐006‐001‐MY2 and part of the work was supported by the National Space Organization (NSPO) under project NSPO‐S‐108004. C. H. Chen is supported by MOST and NSPO projects MOST‐107‐2111‐M‐006‐002‐MY3, MOST‐108‐2621‐M‐006‐014, and NSPO‐S‐109059 to National Cheng Kung University, Taiwan. The authors acknowledge Space Physics Data Facility (SPDF) for Interplanetary magnetic field (IMF Bz), symmetric disturbance index (SYM‐H), and solar wind speed (Vsw) data ( https://omniweb.gsfc.nasa.gov ), Kyoto University geomagnetic data service for Disturbance Storm‐time index (Dst) values ( http://wdc.kugi.kyoto-u.ac.jp ), International GNSS Service (IGS) for Global Positioning System (GPS) data ( http://garner.ucsd.edu/pub/rinex ), Global Ultraviolet Imager (GUVI) science team for the O/N ratio ( http://guvitimed.jhuapl.edu ), and Lowell Global Ionosphere Radio Observatory (GIRO) Data Center for digisonde data ( http://giro.uml.edu ). Note that, to access the GPS data, the IGS site requires to sign in using “anonymous” as username and a valid email address as password. Additionally, the GPS data used in this study are made available at the link https://figshare.com/s/16f8b268bc81ce305039 . The authors also acknowledge Center for Orbit Determination in Europe (CODE) Global Ionospheric Map (GIM) for the total electron content data ( http://ftp.aiub.unibe.ch/CODE ) used in this study, which could be accessed using the link https://figshare.com/s/30c1988c90a22be8eb92 . The authors acknowledge the constructive and encouraging comments and suggestions by the reviewers that have helped to enrich the discussion. 2 Funding Information: This work was supported by the Ministry of Science and Technology (MOST), Taiwan under project MOST 108-2638-M-006-001-MY2 and part of the work was supported by the National Space Organization (NSPO) under project NSPO-S-108004. C. H. Chen is supported by MOST and NSPO projects MOST-107-2111-M-006-002-MY3, MOST-108-2621-M-006-014, and NSPO-S-109059 to National Cheng Kung University, Taiwan. The authors acknowledge Space Physics Data Facility (SPDF) for Interplanetary magnetic field (IMF Bz), symmetric disturbance index (SYM-H), and solar wind speed (Vsw) data (https://omniweb.gsfc.nasa.gov), Kyoto University geomagnetic data service for Disturbance Storm-time index (Dst) values (http://wdc.kugi.kyoto-u.ac.jp), International GNSS Service (IGS) for Global Positioning System (GPS) data (http://garner.ucsd.edu/pub/rinex), Global Ultraviolet Imager (GUVI) science team for the O/N2 ratio (http://guvitimed.jhuapl.edu), and Lowell Global Ionosphere Radio Observatory (GIRO) Data Center for digisonde data (http://giro.uml.edu). Note that, to access the GPS data, the IGS site requires to sign in using ?anonymous? as username and a valid email address as password. Additionally, the GPS data used in this study are made available at the link https://figshare.com/s/16f8b268bc81ce305039. The authors also acknowledge Center for Orbit Determination in Europe (CODE) Global Ionospheric Map (GIM) for the total electron content data (http://ftp.aiub.unibe.ch/CODE) used in this study, which could be accessed using the link https://figshare.com/s/30c1988c90a22be8eb92. The authors acknowledge the constructive and encouraging comments and suggestions by the reviewers that have helped to enrich the discussion. The Global Ionospheric Specification (GIS) electron density profiles used in this study are available online at the National Cheng Kung University web-platform for providing FORMOST-7/COSMIC-2 ionospheric data products (http://formosat7.earth.ncku.edu.tw). The institutional policy regulations require the researchers to sign-up for a free user account to access the data. Once logged-in with the account, users can select GIS among the other data products available for download. Alternatively, the GIS data used in this study could also be accessed by using the link https://figshare.com/s/7a83fe1b10b0880961e7. The example RO data in Figure?1a and the digisonde validation data used for Figure?1b are available at the links https://figshare.com/s/f22073b853b76cca09a5 and https://figshare.com/s/4043fbd5b6fa96df1699, respectively. Publisher Copyright: {\textcopyright} 2021. American Geophysical Union. All Rights Reserved.",
year = "2021",
month = feb,
doi = "10.1029/2020JA028261",
language = "English",
volume = "126",
journal = "Journal of Geophysical Research: Space Physics",
issn = "2169-9402",
number = "2",
}