TY - JOUR
T1 - Statistical study of ELF/VLF emissions at subauroral latitudes in Athabasca, Canada
AU - Martinez-Calderon, Claudia
AU - Shiokawa, Kazuo
AU - Miyoshi, Yoshizumi
AU - Ozaki, Mitsunori
AU - Schofield, Ian
AU - Connors, Martin
N1 - Funding Information:
The ELF/VLF data are available from the Solar-Terrestrial Environment Laboratory (STEL) VLF data viewer website that can be accessed at http://stdb2.stelab.nagoya-u.ac.jp/vlf/index2.html. We express our gratitude to Y. Katoh, H. Hamaguchi, and Y. Yamamoto of STEL for their continued technical support. Tsyganenko model calculations were done using the IDL Geopack Dynamic Link Module (DLM) routines by H. Korth (http://ampere.jhuapl.edu/code/idl_geopack.html) that provide access to the GEOPACK Fortran library by N.A. Tsyganenko and related routines. The OMNI data used in the superepoch analysis were obtained from the SPDF/GSFC OMNIWeb interface at http://omniweb.gsfc.nasa.gov/form/omni_min.html. Construction and operation of the Athabasca University Geophysical Observatory facilities are supported by the Canada Foundation for Innovation, and we thank Kyle Reiter for dedicated technical support. This work was supported by the Leadership Development Program for Space Exploration and Research at Nagoya University, and by the Inter-university Upper Atmosphere Global Observation NETwork (IUGONET) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. We were also supported by the grant-in-aid for Scientific Research (20244080, 23403009, 23340146, 25302006, and 25247080) from the Japan Society for the Promotion of Science.
Publisher Copyright:
©2015. American Geophysical Union. All Rights Reserved.
PY - 2015/10/1
Y1 - 2015/10/1
N2 - We present the first statistical analysis of ELF/VLF emissions observed on the ground at subauroral latitudes that includes their features, occurrences, and association with solar wind and geomagnetic variations. Using a 100 kHz sampling loop antenna located in Athabasca, Canada (54.60N, 246.36E, L = 4.3), we monitored these emissions, including chorus, quasiperiodic emissions, and hiss, from November 2012 to October 2013. We found a maximum occurrence rate in the morning sector (06-07 MLT, magnetic local time) and a minimum in the night sector (18 to 02 MLT), in agreement with previous satellite measurements in the inner magnetosphere. We also found correlation between the ongoing substorm and storm activity and the increase of occurrence rates. The observed waves usually had a central frequency 1-3 kHz lower than the half-gyrofrequency at the conjugate equatorial plane, indicating a wave source at higher latitudes. A superposed epoch analysis showed that the starting time of the ELF/VLF emissions is preceded by a rise in AE both on short (hours) and long (days) terms. Solar wind speed also started slowly rising 1.5 days before, while density and dynamic pressure decreased shortly afterward. This may signify that high-speed solar wind conditions also contribute to the generation of ELF/VLF emissions detected at subauroral latitudes.
AB - We present the first statistical analysis of ELF/VLF emissions observed on the ground at subauroral latitudes that includes their features, occurrences, and association with solar wind and geomagnetic variations. Using a 100 kHz sampling loop antenna located in Athabasca, Canada (54.60N, 246.36E, L = 4.3), we monitored these emissions, including chorus, quasiperiodic emissions, and hiss, from November 2012 to October 2013. We found a maximum occurrence rate in the morning sector (06-07 MLT, magnetic local time) and a minimum in the night sector (18 to 02 MLT), in agreement with previous satellite measurements in the inner magnetosphere. We also found correlation between the ongoing substorm and storm activity and the increase of occurrence rates. The observed waves usually had a central frequency 1-3 kHz lower than the half-gyrofrequency at the conjugate equatorial plane, indicating a wave source at higher latitudes. A superposed epoch analysis showed that the starting time of the ELF/VLF emissions is preceded by a rise in AE both on short (hours) and long (days) terms. Solar wind speed also started slowly rising 1.5 days before, while density and dynamic pressure decreased shortly afterward. This may signify that high-speed solar wind conditions also contribute to the generation of ELF/VLF emissions detected at subauroral latitudes.
KW - ELF/VLF
KW - QP
KW - chorus
KW - hiss
KW - statistics
KW - subauroral latitudes
UR - http://www.scopus.com/inward/record.url?scp=84954397567&partnerID=8YFLogxK
U2 - 10.1002/2015JA021347
DO - 10.1002/2015JA021347
M3 - Journal Article
AN - SCOPUS:84954397567
SN - 2169-9380
VL - 120
SP - 8455
EP - 8469
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
IS - 10
ER -