I heard that some storm events can occur without any change in the Dst index. Significant change in solar wind parameters that are triggered by storms events, but, without any change in Dst? Is it true? If yes, can you please suggest some events (or articles) for example? I am really excited to plot them. Moreover, what are the possible reasons behind those effects?
Dear Sujan Prasad Gautam
Dst is essentially a measure of plasma pressure in the dipolar magnetosphere; it is assumed to be the strength of the Earth's ring current, but it also reacts to the partial ring current, the cross-tail current, and the Chapman-Ferraro dayside magnetopause current. While the Dst index provides an estimate of the strength of the storm-time ring current, it is an insufficient proxy for other storm-related phenomena. During storms, ionospheric Joule heating is not strongly correlated to the Dst index; rather, it is parameterized by high-latitude geomagnetic indices. Kp is often used to parameterize ionospheric ion outflow. Ionospheric models also examine the impact of geomagnetic storms using either solar wind-driven electric field models or the Kp index. Variations in thermospheric density (which is important for atmospheric drag and spacecraft reentry) are related to geomagnetic activity as parameterized by Kp. Dst does not adequately represent the particle population dynamics in the radiation belts. None of these variables have a strong correlation with Dst. In the magnetosphere, the evolution of hot-plasma ions and electrons is highly associated with the Kp index. The storm time evolution of cold plasma in the plasmasphere and plumes has a low association with Dst because it is determined by the time history of the convection electric field, which correlates better with the Kp or AE index.
More detailed information can be obtained from these papers:
1. Baumjohann, W., & Kamide, Y. (1984). Hemispherical Joule heating and the AE indices. Journal of Geophysical Research, 89, 383–388. Article Hemispherical Joule Heating and the AE Indices
2. Chun, F. K., Knipp, D. J., McHarg, M. G., Lacey, J. R., Lu, G., & Emery, B. A. (2002). Joule heating patterns as a function of polar cap index. Journal of Geophysical Research, 107(A7), 1119. https://doi.org/10.1029/2001JA000246
Generally a "magnetic storm" is defined by a decrease (negative values) in Dst from its quiet-time, near-zero baseline, something caused by an increase in the strength of the magnetospheric equatorial ring current. Magnetic disturbance can, however, be manifest in different ways, and the field is never completely still. So, you can see very mild levels of disturbance with only small decreases in Dst. Sudden commencements (that often precede storms) are manifest as an increase (positive values) in Dst.
Dear Jeffrey J. Love I really appreciate for your informative response. Thank you :)
In addition to Jeff's answer, it could be mentioned that there might be some significant local geomagnetic activity during periods without significant ring current perturbation, i.e., with low |Dst|. Such periods are named substorms. Substorms occur when electromagnetic energy is released by the magnetotail and mapped down in the nightside ionosphere. The visual consequences of this effect are the aurorae. On the ground, these effects are usually characterized by the enhancement of the westward auroral electrojet, which is commonly measured by the AL index recorded by ground magnetometers. The more depleted AL, the more intense the substorm.
Becasue DST is used as the quantitative measure of s storm my answer is no.
Based on my experience with this field, I am sure that there is no storm events can occur without any change in the Dst index. Yes, Dst might be decreased a little bit but still you will find changes in the Dst index.
Dear Denny M. Oliveira
Thank you so much for the additional information. It's quite informative. :)
Dear Essam Ghamry and Mark Pesses
Thank you for your perspective. :)
I have posted on my Researchgate page (or Dr. Wei-Hock Soon's) my co-authored book The Maunder Minimum and the Variable Sun-earth Connection. On page 167 in the section, A Particle Theory for the Sun-Earth Connection, we listed Sydney Chapman's work w/ Dst, with footnotes that will help you with your question.
Dear Steven Yaskell
Thanks for suggesting your book. It seems the book contains other a lot of information about the space weather, I will definitely read it. Thank you :)
https://doi.org/10.1029/96JA04020
Hope this clears your doubts...
- Badges
- Science topic
- Similar topics
- Engineering
- Control Theory
- Control Systems
- Control Systems Engineering