Browsing by Author "Blake, Seán P."
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Item The Extreme Solar and Geomagnetic Storms on 20-25 March 1940(Royal Astronomical Society, 2021-12-13) Hayakawa, Hisashi; Oliveira, Denny; Shea, Margaret A.; Smart, Don F.; Blake, Seán P.; Hattori, Kentaro; Bhaska, Ankush T.; Curto, Juan J.; Franco, Daniel R.; Ebihara, YusukeIn late March 1940, at least five significant solar flares were reported. They likely launched interplanetary coronal mass ejections (ICMEs), and were associated with one of the largest storm sudden commencements (SSCs) since the year 1868, resulting in space weather hazards that today would have significant societal impacts. The initial solar activity is associated with a short geomagnetic storm and a notable SSC. Afterward, the third flare was reported in the eastern solar quadrant (N12 E37-38) at 11:30–12:30 UT on 23 March, with significant magnetic crochets (up to ≈ |80| nT at Eskdalemuir) during 11:07–11:40 UT. On their basis, we estimate the required energy flux of the source flare as X35±1 in soft X-ray class. The resultant ICMEs caused enormous SSCs (up to > 425 nT recorded at Tucson) and allowed us to estimate an extremely inward magnetopause position (estimated magnetopause standoff position ≈ 3.4 RE). The time series of the resultant geomagnetic storm is reconstructed using a Dst estimate, which peaked at 20 UT on 24 March at ≈ −389 nT. Around the storm main phase, the equatorial boundary of the auroral oval extended ≤ 46.3° at invariant latitudes. This sequence also caused a solar proton event and Forbush decrease (≈ 3%). These sequences indicate pileups of multiple ICMEs, which even achieved a record value of inward magnetopause position. Our analyses of this historical pioneer event bring more insights into possible serious space weather hazards and provide a quantitative basis for future analyses and predictions.Item Recreating the Horizontal Magnetic Field at Colaba during the Carrington Event with Geospace Simulations(AGU Pubication, 2021-03-14) Blake, Seán P.; Pulkkinen, Antti; Schuck, Peter W.; Glocer, Alex; Oliveira, Denny; Welling, Daniel; Weigel, Robert S.; Quaresima, GaryAn intriguing aspect of the famous 2 September 1859 geomagnetic disturbance (or ‘Carrington’ event) is the horizontal magnetic (B H ) dataset measured in Colaba, India (magnetic latitude approximately 20 degrees N). The field exhibits a sharp decrease of over 1600 nT and a quick recovery of about 1300 nT, all within a few hours during the daytime. The mechanism behind this has previously been attributed to magnetospheric processes, ionospheric processes or a combination of both. In this paper, we outline our efforts to replicate this low‐latitude magnetic field using the Space Weather Modelling Framework (SWMF). By simulating an extremely high pressure solar wind scenario, we can emulate the low‐latitude surface magnetic signal at Colaba. In our simulation, magnetospheric currents adjacent to the near‐Earth magnetopause and strong Region 1 field‐aligned currents (FACs) are the main contributors to the large Colaba B H . The rapid recovery of B H in our simulated scenario is due to the retreat of these magnetospheric currents as the magnetosphere expands, as opposed to ring current dynamics. In addition, we find that the scenario that best emulated the surface magnetic field observations during the Carrington event had a minimum calculated Dst value between ‐431 and ‐1191 nT, indicating that Dst may not be a suitable estimate of storm intensity for this kind of event.