Work Description

Date: March 23, 2023

Dataset Title: Solar Cycle Dependence of Very Large Nighttime Geomagnetic Disturbances
(GMDs) Observed in Eastern Arctic Canada: Data

Dataset Creators:
Mark J. Engebretson

Dataset Contact:
Engebret@augsburg.edu

Funding:
National Science Foundation (NSF)

Abstract:
Large geomagnetic disturbances (GMDs, also denoted as MPEs - magnetic perturbation events)
have sufficient amplitude to cause geomagnetically induced currents (GICs) that can damage
technical infrastructure. In this study we present occurrence statistics for GMD / MPE
events with derivatives ≥ 6 nT/s and ≥ 20 nT/s from five stations in the MACCS and AUTUMNX
magnetometer arrays in Arctic Canada at magnetic latitudes ranging from 65° to 75°. Earlier
studies using data from these arrays (Engebretson et al., 2019a,b, 2021a,b) covered only two
years (2015 and 2017) and focused on latitude- and local time-dependent occurrence patterns and
short-term dependencies on solar wind/IMF parameters and magnetospheric activity indices.
This study presents all available data from these stations from 2011 through 2022
to analyze variations of GMD activity over a full solar cycle. Intense GMD activity did
not closely follow the sunspot cycle, but instead was lowest during its rising phase and
maximum (2011-2014), was highest during the early declining phase (2015-2017), and reached
a subsequent minimum early in the following sunspot cycle (2020). GMDs with amplitude
>20 nT/s followed the same yearly pattern but peaked even more strongly during 2015-2017.
Most of these GMDs were associated with high-speed solar wind streams
(Vsw > 600 km/s), but not with strongly negative values of the SYM/H index. The majority of
these GMDs, irrespective of the Vsw value, were accompanied within 10 min (and most often less)
by other events with amplitude ≥ 6 nT/s and showed a mostly poleward progression.
These results show that large amplitude but spatially localized nighttime GMDs are primarily
associated with high-speed stream geomagnetic drivers during the declining
phase of the solar cycle. This indicates that large GIC hazard conditions can occur for a
variety of solar wind drivers and geomagnetic conditions and not only for fast-coronal mass
ejection driven storms.

--------------------------------------------------------------------------------------------------

Methodology:

Event identification made use of a semi-automated process described in detail in
Engebretson et al. (2019a). This procedure began by displaying a daily magnetogram
(a 24-hour 3-axis plot of the magnetic field at a given station) on a computer screen.
Once a rapid (< 20 min duration) and large amplitude (> ~ 200 nT) magnetic perturbation was
visually identified, the IDL cursor function was used to select times ~15 to 60 min before and
after the perturbation to zoom in on the relatively short duration of the event and
separate it from the times of other possible activity. After application of a 10-point smoothing
to reduce noise and eliminate isolated bad data points, the data were numerically differentiated
using the 3‐point Lagrangian approximation, the times and values of extrema of B and dB/dt for
each component in this interval were recorded, and plots of the time series of data and derivatives
were produced and saved. If more than one interval with a ≥ 6 nT/s derivative in one or more
components was identified on a given day, this process was repeated as necessary.
The minimum length of each interval was chosen to be ~5 min, so multiple peak derivatives ≥ 6 nT/s
occurring within a given ~5 minute interval were not counted separately.

--------------------------------------------------------------------------------------------------

Files Contained:

The folder 'MPE Derivs GE 6' contains files for the years of 2011-2022 for 3 MACCS stations and 2
AUTUMNX stations. These files are titled with the format year + 'MPE_Derivs_' + three or four letter
station code + '.txt_ge_6'. The tail part of the title format signifies GMD events that have
derivative amplitudes greater than or equal to 6 nT/s. The files contain lists of nighttime GMD
events identified at the stations during the respective years. The GMD lists are formatted as
follows: YYDDD = year and day of year of the GMD in YYDDD format, STA = station at which the GMD
occurred, T+dxdt = time of the maximum postive dB/dt observed in the x-component of the magnetic
field, +dx/dt = maximum positive dB/dt value in the x-component that occurred at the time of
T+dx/dt, T-dx/dt = time of the maximum negative dB/dt observed in the x-component,
-dx/dt = maximum negative dB/dt value in the x-component, and so on for the y- and z-components
of the magnetic field. Each year may not contain files for all five stations, either because
there was not any available data for the respective year or because there were no GMD events
identified at the respective station for the respective year.

--------------------------------------------------------------------------------------------------

Instrument and/or Software specifications:

This study utilizes instrument data from the Magnetometer Array for Cusp and Cleft Studies (MACCS)
(Engebretson et al., 1995) as well as the Athabasca University THEMIS UCLA Magnetometer
Network eXtension (AUTUMNX) (Connors et al., 2016).
MACCS stations used: CDR (Cape Dorset, NU), PGG (Pangnirtung, NU), RBY (Repulse Bay, NU)
AUTUMNX stations used: KJPK (Kuujjuarapik, NU), SALU (Salluit, NU)

MACCS magnetometers are Narod ringcore fluxgate magnetometers designed and supplied by
Dr. Barry Narod of Narod Geophysics, Ltd., Vancouver, B.C., Canada. Narod magnetometers
collect 8 samples per second in three axes, then average and record the data at two samples
per second. These magnetometers are oriented at each station so that they are aligned with the
Earth's magnetic field: X (positive magnetic North), Y (positive East), Z (postive vertically
downward).

AUTUMNX magnetometers are THEMIS-class fluxgate magnetometers provided by UCLA and based on the
design for the earlier Sino Magnetic Array at Low Latitudes (SMALL) terrestrial vector
fluxgate magnetometers. The THEMIS magnetometers record the magnetic field at 2 Hz in three axes
and the data have been rotated so that each measurement direction is in geomagnetic coordinates
(see above).

Citations:

Connors, M., Schofield, I., Reiter, K., Chi, P. J., Rowe, K. M., & Russell, C. T. (2016).
The AUTUMNX magnetometer meridian chain in Québec, Canada. Earth, Planets and Space, 68(1).
https://doi.org/10.1186/s40623-015-0354-4

Engebretson, M. J., W. J. Hughes, J. L. Alford, E. Zesta, L. J. Cahill, Jr., R. L. Arnoldy,
and G. D. Reeves (1995). Magnetometer array for cusp and cleft studies observations of the
spatial extent of broadband ULF magnetic pulsations at cusp/cleft latitudes. Journal of
Geophysical Research, 100, 19371-19386. doi:10.1029/95JA00768

Engebretson, M. J., Pilipenko, V. A., Ahmed, L. Y., Posch, J. L., Steinmetz, E. S.,
Moldwin, M. B., Connors, M. G., Weygand, J. M., Mann, I. R., Boteler, D. H., Russell,
C. T., & Vorobev, A. V. (2019a). Nighttime magnetic perturbation events observed in Arctic
Canada: 1. Survey and statistical analysis. Journal of Geophysical Research: Space Physics,
124, 7442-7458. https://doi.org/10.1029/2019JA026794

Engebretson, M. J., Steinmetz, E. S., Posch, J. L., Pilipenko, V. A., Moldwin, M. B.,
Connors, M. G., Boteler, D. H., Mann, I. R., Hartinger, M. D., Weygand, J. M., Lyons, L. R.,
Nishimura, Y., Singer, H. J., Ohtani, S., Russell, C. T., Fazakerley, A., & Kistler, L. M. (2019b).
Nighttime magnetic perturbation events observed in Arctic Canada: 2. Multiple‐instrument observations.
Journal of Geophysical Research: Space Physics, 124, 7459-7476. https://doi.org/10.1029/2019JA026797

Engebretson, M. J., Pilipenko, V. A., Steinmetz, E. S., Moldwin, M B., Connors, M. G., Boteler, D.
H., Singer, H. J., Opgenoorth, H., Schillings, A., Ohtani, S., Gjerloev, J., & Russell, C. T.
(2021a). Nighttime magnetic perturbation events observed in Arctic Canada: 3. Occurrence and
amplitude as functions of magnetic latitude, local time, and magnetic disturbances. Space
Weather, 19, e2020SW002526. https://doi.org/10.1029/2020SW002526

Engebretson, M. J., Ahmed, L. Y., Pilipenko, V. A., Steinmetz, E. S., Moldwin, M. B., Connors, M.
G., Boteler, D. H., Weygand, J. M., Coyle, S., Ohtani, S., Gjerloev, J., & Russell, C. T.
(2021b). Superposed epoch analysis of nighttime magnetic perturbation events observed in Arctic
Canada (2021). Journal of Geophysical Research: Space Physics, 126, e2021JA029465.
https://doi:10.1029/2021JA029465

Engebretson, M. J., Steinmetz, Yang, L., Pilipenko, V. A., Moldwin, M. B., McCuen, B. A.,
Connors, M. G., Weygand, J. M., Waters, C. L., Lyons, L. R., Nishimura, Y., Russell, C. T.
(2023) Solar Cycle Dependence of Very Large Nighttime Geomagnetic Disturbances (GMDs) Observed
in Eastern Arctic Canada. Journal of Geophysical Research – Space Physics. (Pending publication)