Comments on quiet daily variation derivation in &amp;quot;Identification of the IMF sector structure in near-real time by ground magnetic data&amp;quot; by Janzhura and Troshichev (2011)

J. Space Weather Space Clim.

2018

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-The Polar Cap (PC) indices, PCN (North) and PCS (South) are based on polar geomagnetic observations from Qaanaaq (Thule) and Vostok, respectively, processed to measure the transpolar plasma convection that may seriously affect space weather conditions. To establish reliable space weather forecasts based on PC indices, and also to ensure credibility of their use for scientific analyses of solar windmagnetosphere interactions, additional sources of data for the PC indices are investigated. In the search for alternative index sources, objective quality criteria are established here to be used for the selection among potential candidates. These criteria are applied to existing PC index series to establish a quality scale. In the Canadian region, the data from Resolute Bay magnetometer are shown to provide alternative PCN indices of adequate quality. In Antarctica, the data from Concordia Dome-C observatory are shown to provide basis for alternative PCS indices. In examples to document the usefulness of these alternative index sources it is shown that PCN indices in a real-time version based on magnetometer data from Resolute Bay could have given 6 h of early warning, of which the last 2 h were "red alert", up to the onset of the strong substorm event on 13 March 1989 that caused power outage in Quebec. The alternative PCS indices based on data from Dome-C have helped to disclose that presently available Vostok-based PCS index values are corrupted throughout most of 2011.

Section: Discussionmentioning

confidence: 99%

Multi-station basis for Polar Cap (PC) indices: ensuring credibility and operational reliability

J. Space Weather Space Clim.

2018

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“…Geophys. in a commentary, Stauning (2013a), to the paper JT2011. The commentary paper was submitted in 2012 and forwarded at that time to the authors of JT2011, but no reply has been published yet.…”

Section: Statistics For Imf B Y Modulation Of Polar Magnetic Fieldsmentioning

confidence: 98%

A critical note on the IAGA-endorsed Polar Cap index procedure: effects of solar wind sector structure and reverse polar convection

2015

Ann. Geophys.

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Abstract. The International Association of Geomagnetism and Aeronomy (IAGA) has recently endorsed a new Polar Cap (PC) index version to supersede the previous seven different versions of the PCN (North) index and the five different PCS (South) index versions. However, the new PC index has some adverse features which should be known and taken into account by users of the index. It uses in its derivation procedure an "effective" quiet day level (QDC) composed of a "basic" QDC and an added solar wind sector term related to the azimuthal component (B y ) of the interplanetary magnetic field (IMF). The added IMF B y -related terms may introduce unjustified contributions to the PC index of more than 2 index units (mV m −1 ). Furthermore, cases of reverse convection during strong northward IMF B z (NBZ) conditions included in the database for calculation of index coefficients can cause unjustified index enhancements of 0.5-1 mV m −1 during calm conditions, reduction of index values by more than 20 % during disturbed conditions, and inconsistencies between index coefficients and index values for the northern and southern polar caps. The aim here is to specify these adverse features and quantify their effects, and to suggest alternative steps for future modifications of the index procedure.

“…Data from the standard magnetic observatories for PCN and PCS calculations, Qaanaaq and Vostok, could be complemented by using data from Resolute Bay and Dome-C observatories for added reliability (Stauning, 2018b) An essential parameter for the calculation of PC index values is the reference quiet level, the so-called Quiet Day Curve (QDC), for each of the two horizontal components, from which the magnetic variation vectors, DH, are measured. The calculations performed here are based on the QDC derivation defined in and not on the methods described in Janzhura & Troshichev (2011) since their presentation is affected by grave errors (Stauning, 2013a(Stauning, , 2018a.…”

Section: The Polar Cap (Pc) Indexmentioning

confidence: 99%

Using PC indices to predict violent GIC events threatening power grids

J. Space Weather Space Clim.

2020

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The aim of the present contribution is to investigate the timing relations between enhancements in the Polar Cap (PC) indices and power grid disturbances related to geomagnetically induced currents (GIC). The polar cap indices, PCN (North) and PCS (South), are based on measurements of geomagnetic variations in the central polar caps. These variations are strongly related to the transpolar convection of plasma and magnetic fields driven by the solar wind. During cases of enhanced merging processes at the front of the magnetosphere and subsequent tailward convection of plasma and embedded magnetic fields, the magnetospheric tail configuration may accumulate excess energy, which upon release may cause violent substorm activity. Earlier reports have disclosed remarkably lengthy intervals, ranging up to several hours, of elevated PC index values preceding GIC-related power grid disruptions. The present investigation has shown that the delays of typically 3–4 h between increases in the PC indices and GIC-related power grid disturbances are related to displacements of the substorm processes responsible for strong GIC events to subauroral latitudes where vulnerable power grids reside. The results have shown that PC index values remaining above an “alert level” of 10 mV/m through more than 1 h indicate a high risk for violent GIC events that may threaten power grids and other vulnerable technical systems. These results support the application of real-time PC indices in space weather monitoring and forecast services.