Status: this discussion paper is a preprint. It has been under review for the journal Natural Hazards and Earth System Sciences (NHESS). The manuscript was not accepted for further review after discussion.
Defining scale thresholds for geomagnetic storms through statistics
Abstract. Geomagnetic storms, as part of the Sun-Earth relations, are continuously monitored with different indices and scales. These indices have some scale thresholds to quantify the severity or risk of geomagnetic disturbances. However, the most usual scale thresholds are arbitrarily chosen. In this work we aim to quantify the range of the thresholds through a new method. These new thresholds are based on statistical distribution fitting.
The data used are from a regional real-time high-cadence geomagnetic index, named LDiñ, and its derivative, LCiñ. We considered the negative part of LDiñ, as significant for geomagnetic disturbances; and the absolute value of LCiñ, significant for geomagnetically induced currents. Then we look for the best fit for different statistical continuous distributions applied to these indices.
The method yields that the beta prime is the most suitable functions for negative values of LDiñ, whereas power-law and Johnson-SU are the best fits for LCiñ and the whole distribution, respectively. We define new thresholds for intense, very intense and extreme geomagnetic disturbances as the intersects between these best fit distributions and the index complementary cumulative distribution function.
Then, thresholds for the negative part of LDiñ, are −100 nT, −205 and −475 nT. The thresholds for the absolute value of LCiñ, are 6, 18 and 32 nT min−1. The thresholds defined here provide criteria to assess the vulnerability to geomagnetic activity on design or mitigation purposes.
These threshold definitions will be applied for different products in the Spanish Space Weather Service (SeNMEs) website http://www.senmes.es/index-en.php.
Received: 16 Oct 2017 – Discussion started: 07 Nov 2017
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Geomagnetic storms are continuously monitored with different indices and scales. These indices have some scale thresholds to quantify the severity or risk of geomagnetic disturbances. However, the most usual scale thresholds are arbitrarily chosen. In this work we aim to quantify the range of the storm thresholds through a new method. These new thresholds are based on statistical distribution fitting. The provided insight can improve risk assessment on this particular natural hazard.
Geomagnetic storms are continuously monitored with different indices and scales. These indices...
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