Comment on “Current understanding of magnetic storms: Storm‐substorm relationships,” by Y. Kamide et al.

Abstract

With 14 distinguished coauthors and 153 references, this recent paper [Kamide et al., 1998; hereinafter referred to as K98] symbolizes a definitive and authoritative work due a measure of respect. Considered significant enough to be assigned a separate section 7.2, the authors describe reasons that the disturbance storm time (Dst) index, the universal indicator of global magnetic storms, is not the representation of a symmetric ring current (RC) encircling the Earth in the equatorial magnetosphere, as has been supposed by most of the spacescience community since the index design was formalized 34 years ago [Sugiura, 1964]. The K98 authors enumerate a number of factors governing their reasoning: (1) the main contributions of partial ring currents, (2) the existence of strong field-aligned currents, (3) the problem of averaging just four stations for the index, (4) the artificially of making ringsymmetry latitude adjustments, (5) the introduction of false values encountered in removing a “quiet day” field on the nonquiet day of the storm, and (6) the presence of associated magnetotail currents. K98 (p. 17,723) state “Thus the present Dst contains significantly an artificially symmetric value resulting from asymmetric perturbationsz z z” Restated simply, K98 authors say that because of the listed facts it is false to assume that Dst 5 RC. I see two problems with their presentation. First, K98 neglect referencing those who have in the past produced considerable evidence for the major Dst 5 RC inconsistencies that are given in section 7.2. The K98 conclusions are not so obvious that references are unnecessary. K98 coauthors were fully aware of references disputing Dst 5 RC from my presentations of the “Ring-Current Myth”: on October 9, 1992, at the Space Environment Laboratory of NOAA (noted in the work of Campbell, [1996a]); on August 10, 1993 [Campbell, 1993], at the IAGA Assembly in Buenos Aires; and at the February 12, 1996 [Campbell, 1996b], Chapman Conference on Magnetic Storms in Pasadena. In addition to the paper by Campbell [1996a] on the Dst 5 RC myth, I produced an EOS Space Physics and Aeronomy Section News item [Campbell, 1996c] containing such information. K98 authors also could have referred to Campbell [1997, pp. 168–172], the first textbook to caution acceptance of Dst 5 RC in contrast to Mayaud’s [1980] classic rendition of the index. The second problem with the K98 paper is that the authors neglected to present these other important difficulties with the Dst 5 RC assumption: (1) satellite in situ measurements in the RC region fail to find processes paralleling the storm growth and decay phases indicated by the classic interpretation of Dst; (2) determinations within the RC region show insufficient field to account for the surface observations of Dst; (3) there are lunar-tidal effects in Dst that should not occur in Dst; (4) the enhancement of storm time ionospheric currents at the dayside dip equator indicates the existence of strong ionospheric currents providing fields to the low-latitude Dst observatories; (5) the Earth’s midnightside low-latitude fields track the seasonal position and activity changes in the storm time magnetospheric tail-current patterns; (6) the extremely high conductivity of the Earth’s interior shields observatory reception of a partial RC source field from the opposite side of the Earth; and (7) Earthmantle conductivity determinations from an assumed RC source fields are unreliable. It is the ensemble of non-ring-current contributions, not just one or two problems, that destroys the classic interpretation of Dst and begs for another explanation of the characteristic main phase to recovery phase shape of the “magnetic storm.” My publications on the ring-current myth provide accumulated referenced works showing that during a geomagnetic storm period it is wrong to suppose that Dst 5 RC (the symmetric ring current is just one of many contributors to the index) and demonstrating that with Dst showing a unique “storm time” pattern resulting from a summation of many processes and stations, the lognormal distribution characteristics possibly provide a reason for the regularly appearing storm shape (named by Chapman [1951]). The present problem with Dst is to determine how much each process is contributing to the index. Soon, using the equatorial enhancement studies, researchers may be able to extract at least the ionospheric contribution.