7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

High-intensity long-duration continuous auroral electrojet (AE) activity(HILDCAA) events and associated space weather impacts
Rajkumar Hajra1, and Bruce T. Tsurutani2
1
CAS Key Laboratory of Geospace Environment, School of Earth and Space
Sciences, University of Science and Technology of China
2
Retired, Pasadena, CA, USAe-mail (speaker): rhajra@ustc.edu.cn

High-intensity
long-duration
continuousauroralelectrojet (AE) activity (HILDCAA) events[1] areassociated with high-speed streams (HSSs) emanatedfrom solar coronal holes. While HILDCAAs representvery intense AE activity (AE peak > 1000 nT) continuing
for several days to week (minimum duration > 2 days)
when AE does not fall below 200 nT for more than 2hours at a time, they are not associated with significant
ring current development. HILDCAAs are generally
recorded during the recovery phase of a geomagnetic
storm or during geomagnetic quiet condition (withSYM-H > -50 nT). Statistically, HILDCAAs arerecorded more frequently during the solar cycle
descending phase compared to the ascending phases andthe solar maximum[2].
Sporadic magnetic reconnection between daysidegeomagnetic field and the Alfvén wave southward
component
embeddedinHSSs
leads
tosubstorm/convection events and energetic (10–100 keV)electron injection into the nightside sector of themagnetosphere during HILDCAAs. Plasma instability

caused by the temperature anisotropy of the electrons
generates electromagnetic chorus waves. Resonantinteractions of the chorus waves with the electrons leadto the acceleration of electrons to relativistic energies[3,4],
which can damage satellite electronics.
Figure 1 shows an example of geomagnetic activity
during an HILDCAA event, causative solar
wind/interplanetary variations, generation of chorus
waves and acceleration of magnetospheric relativistic
electrons in the geosynchronous orbit of the Earth. The
present talk will discuss origin, features, solar cycle
variations, and different impacts of HILDCAA events.
References[1] B.T. Tsurutani & W.D. Gonzalez, Planet. Space Sci.
35, 405 (1987)[2] R. Hajra et al., J. Geophys. Res. 118, 5626 (2013)[3] R. Hajra et al., Geophys. Res. Lett. 41, 1876 (2014)[4] R. Hajra et al., Earth Planets Space 67, 109 (2015)

Figure 1. Solar wind/interplanetary dependence and geomagnetic/radiation belt effects during a HILDCAA event on 6–
10 June 2006. From top to bottom, the panels show the frequency (Hz)–time (UT) spectrogram of the magnetic fieldcomponent of the electromagnetic plasma waves (nT2 Hz−1) measured by the Cluster 1 spacecraft, the variations of E >
0.6 (E1), E > 2.0 (E2), and E > 4.0 MeV (E3) electron fluxes (cm−2 s−1 sr−1) from GOES-12, and solar wind speed (Vswin km s−1), IMF magnitude (B0 in nT), and Bz (nT) component in geocentric solar magnetospheric coordinate system,and the SYM-H (nT) and AE (nT) indices, respectively. Perigee passes of Cluster 1 through the dusksidemagnetosphere are marked by black rectangles in the upper panel. The horizontal arrow in the AE panel indicates theHILDCAA interval. The vertical dash-dot line shows the initiation time of the HILDCAA.