TY - JOUR
T1 - Statistical Study of Auroral/Resonant-Scattering 427.8-nm Emission Observed at Subauroral Latitudes Over 14 Years
AU - Shiokawa, K.
AU - Otsuka, Y.
AU - Connors, M.
N1 - Funding Information:
We are grateful to Toshiro Kato, Mitsugi Sato, Yasuo Kato, Yoshiyuki Hamaguchi, Yuka Yamamoto, and Takumi Adachi, of ISEE, Nagoya University, for their continuous support of the operation of the Optical Mesosphere Thermosphere Imagers (OMTIs). We also appreciate Ian Schofield and Kyle Reiter of Athabasca University for their continuous support of the operation of the photometer at Athabasca, Canada. Athabasca University Geophysical Observatory was built and is operated using funding from the Canada Foundation for Innovation and Natural Science and Engineering Research Council, Canada. The photometer was calibrated using facilities at the National Institute of Polar Research, Japan. This work is supported by the JSPS KAKENHI (16403007, 19403010, 20244080, 23403009, 25247080, 15H05815, and 16H06286). The photometer data are available at http://stdb2.isee.nagoya‐u.ac.jp/omti/ website. The OMNI database used in this study for the solar wind parameters and geomagnetic indices was provided by https://omniweb.gsfc.nasa.gov/ow.html website.
Funding Information:
We are grateful to Toshiro Kato, Mitsugi Sato, Yasuo Kato, Yoshiyuki Hamaguchi, Yuka Yamamoto, and Takumi Adachi, of ISEE, Nagoya University, for their continuous support of the operation of the Optical Mesosphere Thermosphere Imagers (OMTIs). We also appreciate Ian Schofield and Kyle Reiter of Athabasca University for their continuous support of the operation of the photometer at Athabasca, Canada. Athabasca University Geophysical Observatory was built and is operated using funding from the Canada Foundation for Innovation?and Natural Science and Engineering Research Council, Canada. The photometer was calibrated using facilities at the National Institute of Polar Research, Japan. This work is supported by the JSPS KAKENHI (16403007, 19403010, 20244080, 23403009, 25247080, 15H05815, and 16H06286). The photometer data are available at http://stdb2.isee.nagoya-u.ac.jp/omti/ website. The OMNI database used in this study for the solar wind parameters and geomagnetic indices was provided by https://omniweb.gsfc.nasa.gov/ow.html website.
Publisher Copyright:
©2019. American Geophysical Union. All Rights Reserved.
PY - 2019/11/1
Y1 - 2019/11/1
N2 - Auroral emission at 427.8-nm from N2 + ions is caused by precipitation of energetic electrons, or by resonant scattering of sunlight by auroral N2 + ions. The latter often causes impressive purple aurora at high altitudes. However, statistical characteristics of auroral 427.8-nm emission have not been well studied. In this paper we report occurrence characteristics of high 427.8-nm emission intensities (more than 100 R) at subauroral latitudes, based on measurements by a filter-tilting photometer over 14 years (2005–2018) at Athabasca, Canada (magnetic latitude: ~62°). We divided the data set into solar elevation angles (θs) more than and less than −24° (shadow height of sunlight: 600 km) to separate the 427.8-nm emissions caused by resonant scattering of sunlight and those excited by auroral electrons, respectively. The occurrence rate of 427.8-nm emissions of more than 100 R is 10.6% and 7.65% for θs more than and less than −24°, respectively, confirming that resonant scattering of sunlight by N2 + ions is a cause of the strong 427.8-nm emissions of more than 100 R in the sunlit ionosphere. The occurrence rate is high in the postmidnight sector and increases with increasing geomagnetic activity, solar wind speed, and density. The occurrence rate is lowest in winter. A high occurrence rate was observed in 2015–2018, during the declining phase of the 11-year solar activity. Superposed epoch analysis indicates that the 427.8-nm emission exceeds 100 R when solar wind speed increases and solar wind density concurrently decreases, though the standard deviation of the data is rather large.
AB - Auroral emission at 427.8-nm from N2 + ions is caused by precipitation of energetic electrons, or by resonant scattering of sunlight by auroral N2 + ions. The latter often causes impressive purple aurora at high altitudes. However, statistical characteristics of auroral 427.8-nm emission have not been well studied. In this paper we report occurrence characteristics of high 427.8-nm emission intensities (more than 100 R) at subauroral latitudes, based on measurements by a filter-tilting photometer over 14 years (2005–2018) at Athabasca, Canada (magnetic latitude: ~62°). We divided the data set into solar elevation angles (θs) more than and less than −24° (shadow height of sunlight: 600 km) to separate the 427.8-nm emissions caused by resonant scattering of sunlight and those excited by auroral electrons, respectively. The occurrence rate of 427.8-nm emissions of more than 100 R is 10.6% and 7.65% for θs more than and less than −24°, respectively, confirming that resonant scattering of sunlight by N2 + ions is a cause of the strong 427.8-nm emissions of more than 100 R in the sunlit ionosphere. The occurrence rate is high in the postmidnight sector and increases with increasing geomagnetic activity, solar wind speed, and density. The occurrence rate is lowest in winter. A high occurrence rate was observed in 2015–2018, during the declining phase of the 11-year solar activity. Superposed epoch analysis indicates that the 427.8-nm emission exceeds 100 R when solar wind speed increases and solar wind density concurrently decreases, though the standard deviation of the data is rather large.
KW - 427.8 nm
KW - ion upflow
KW - ionosphere
KW - molecular nitrogen ion
KW - N (1NG)
KW - purple aurora
UR - http://www.scopus.com/inward/record.url?scp=85074857175&partnerID=8YFLogxK
U2 - 10.1029/2019JA026704
DO - 10.1029/2019JA026704
M3 - Journal Article
AN - SCOPUS:85074857175
SN - 2169-9380
VL - 124
SP - 9293
EP - 9301
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
IS - 11
ER -