Is the Dst Index Sufficient to Define All Geospace Storms?

Abstract

The purpose of this commentary is (1) to raise awareness about some shortcomings of the use of the Dst index to identify storms, to gauge storm intensity, and to represent storm time space‐weather phenomena and (2) to initiate discussions about different types of storms and about improved identifiers for different types of storms.

Geoeffectiveness of Stream Interaction Regions From 1995 to 2016

“…The intensity of a geomagnetic storm can be described by the disturbance storm time ( D s t ) index. The D s t index shows the H‐component perturbation on equatorial magnetometers and was initiated more than 60 years ago (e.g., Borovsky & Shprits, ; Mayaud, , and references therein). Using minimum values of the D s t indices ( D s t min ) of geomagnetic storms, intensities of geomagnetic storms can be described in different levels, such as minor geomagnetic storms (−50 nT < D s t min ≤−30 nT), moderate geomagnetic storms (−100 nT < D s t min ≤−50 nT) and intense geomagnetic storms ( D s t min ≤−100 nT; e.g., Gonzalez et al, ).…”

Exploration of a Composite Index to Describe Magnetospheric Activity: Reduction of the Magnetospheric State Vector to a Single Scalar

“…As pointed out in Borovsky and Shprits (), specific types of storms (e.g., high‐speed stream‐driven storms, cloud‐driven storms, and cloud‐sheath‐driven storms) could be identified by examining the products of the magnetospheric state vector E with various coefficient vectors defined to highlight the specific properties of the different types of storms (cf. Borovsky & Denton, ).…”

“…In Figure the Earth index E (1) (expression ) is plotted as a function of the universal driver function S (1) (expression ) for different measures of activity in the magnetosphere in 1991–2007. The red points in Figure are hours when Dst < −50 nT, defined as Dst storms (Borovsky & Shprits, ; Loewe & Prolss, ; Sugiura & Chapman, ), and the red line is a linear regression fit to the red points given by E (1) = 0.834 S (1) + 0.421. The green points in Figure are a sampling of hours during the first 2 days of high‐speed stream‐driven storms, and the green line is a linear regression fit to the green points given by E (1) = 0.824 S (1) + 0.0547: The green points are taken from the Borovsky and Denton () collection of high‐speed stream‐driven storms, which are defined by elevated Kp , a 27‐day periodicity, and an absence of ejecta in the solar wind.…”

Dynamical Properties of Peak and Time‐Integrated Geomagnetic Events Inferred From Sample Entropy

“…It is determined by both solar wind forcing and internal magnetospheric processes (Daglis et al, ; Kozyra & Liemohn, ; O'Brien & McPherron, ). But alone cannot provide a full account of the complexity of geomagnetic storms, nor can it provide an appropriate measure of the strength of all strong disturbances induced by the solar wind (Borovsky, ; Borovsky & Shprits, ; Mourenas et al, ). The index (varying linearly from 0 to 400) is obtained from 3‐hr measurements of the disturbance range of the horizontal component of the Earth's magnetic field at middle latitude stations; it can serve as a proxy of magnetospheric convection and substorm‐associated field‐aligned currents flowing in and out of the ionosphere (Borovsky & Shprits, ; Mayaud, ; Thomsen, ).…”

“…But alone cannot provide a full account of the complexity of geomagnetic storms, nor can it provide an appropriate measure of the strength of all strong disturbances induced by the solar wind (Borovsky, ; Borovsky & Shprits, ; Mourenas et al, ). The index (varying linearly from 0 to 400) is obtained from 3‐hr measurements of the disturbance range of the horizontal component of the Earth's magnetic field at middle latitude stations; it can serve as a proxy of magnetospheric convection and substorm‐associated field‐aligned currents flowing in and out of the ionosphere (Borovsky & Shprits, ; Mayaud, ; Thomsen, ). and are high‐latitude range indices similar to , related to auroral electrojet field‐aligned currents and energetic particle injections from the plasma sheet (Gabrielse et al, ; Mayaud, ).…”