Response of ionospheric and field-aligned currents to geomagnetic storms driven by solar wind high-speed streams and coronal mass ejections
|Author:||Pedersen, Marcus Nicolai1,2|
1University of Oulu Graduate School
2University of Oulu, Faculty of Science, Physics, Space physics and astronomy (SpaceAstro)
|Online Access:||PDF Full Text (PDF, 3.1 MB)|
|Persistent link:|| http://urn.fi/urn:isbn:9789526238784
Oulu : University of Oulu,
|Publish Date:|| 2023-11-06
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic dissertation to be presented, with the assent of the Doctoral Training Committee of Technology and Natural Science of the University of Oulu, for public discussion in the Auditorium L6, on 17th of November 2023, at 12 o’clock noon
Docent Heikki Vanhamäki
Professor Anita Aikio
Professor Emilia Kilpua
Professor Stein Haaland
Professor Lasse Clausen
Docent Heikki Vanhamäki
The behaviour of the ionospheric and ﬁeld-aligned currents (FACs) during geomagnetic storms are poorly understood, partly because the main focus of research concerning the ionospheric currents have been on time-scales of substorms and because geomagnetic storms exhibit large variations from one storm to another. To address this issue, this thesis studies the temporal and spatial development of ionospheric horizontal currents and FACs during 73 geomagnetic storms (Dstmin≤ −50 nT) from 2010 to 2017 driven by high-speed streams and associated stream interaction regions (HSS/SIRs), or sheaths and magnetic clouds (MC) associated with interplanetary coronal mass ejections (ICME).
The development of the horizontal equivalent currents (Jeq) and FACs were studied using a superposed epoch analysis (SEA) of SuperMAG and AMPERE data, respectively. The zero epoch time, t0, was set to the main phase onset, deﬁned as the time the SYM-H index in each storm crossed to less than −15 nT. Storms driven by HSS/SIR tend to begin during the dense SIR ahead of the HSS. Those storms have total FAC and Jeq that begins to slowly increase 3 hr before t0 and reach maximum at t0 + 40 min and t0 + 58 min, respectively, with total downward FAC of 8.1 MA. By separating the HSS/SIR storms into those with low and high solar wind dynamic pressure, pdyn, around t0, the total FAC, Jeq and number of substorm onsets are clearly higher for high pdyn compared to low pdyn storms for the ﬁrst 6 hours after main phase onset. This situation reversed in the storm recovery phase, when after t0 + 2 days the currents and number of substorms for low pdyn storms decay slower and become larger than for high pdyn storms. This might be due to the higher solar wind velocity for low pdyn storms at this time.
The ICME storms were separated into those driven by sheaths and MCs. Sheath-driven storms have shorter main phase durations and larger currents for the ﬁrst 4 hr of the storm main phase than MC-driven storms. During sheath-driven storms, the superposed currents increase rapidly during the passage of the dense sheath region and maximise at t0 + 50 min with a total downward FAC of 8.9 MA. On the contrary, the currents during MC-driven storms developed gradually as the interplanetary magnetic ﬁeld (IMF) rotated southward and reached maximum at t0 + 11 hrs, close to the end of the storm main phase, with a total FAC of 8.4 MA. In general, the total FAC during the ﬁrst 12 hrs of geomagnetic storms is larger for ICME-driven than HSS/SIR-driven storms, while in the recovery phase, the currents in sheath-driven storms diminishes ﬁrst. Furthermore, the Russell-McPherron (RM) eﬀect is seemingly more important for HSS/SIR than for ICME-driven storms. In total, 79% and 86% of the high and low pdyn HSS/SIR storms were aﬀected by the RM eﬀect, contrary to only 42% and 46% of the sheath and MC-driven storms.
This thesis also quantiﬁed the response time of the currents to solar wind driving at Earth’s magnetopause using cross-correlation between the total FAC and Newell coupling function (NCF). Using 10-min resolution data, the best correlation coeﬃcients (CC) were found when the total FAC lagged the NCF by 40±10 min for HSS/SIR and sheath-driven storms, and 60 ± 10 min for MC-driven storms, with CCs of 0.71, 0.84 and 0.87, respectively. The best NCF integration time was also quantiﬁed. By integrating the NCF using the preceding 90 min for HSS/SIR, 80 min for sheaths and 140 min for MC storms the CCs with total FAC reached maximum values of 0.83, 0.89 and 0.91, respectively. This shows that considering a prolonged interval of solar wind coupling better describes the currents than simply using lags.
Osajulkaisut / Original papers
Osajulkaisut eivät sisälly väitöskirjan elektroniseen versioon. / Original papers are not included in the electronic version of the dissertation.
Report series in physical sciences
|Type of Publication:||
G5 Doctoral dissertation (articles)
|Field of Science:||
115 Astronomy and space science
I gratefully acknowledge the financial support by the Academy of Finland
INGENIOUS project and the Vilho, Yrjö and Kalle Väisälä Foundation.
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