An alternative way to identify local geomagnetically quiet days: a case study using wavelet analysis

Virginia Klausner,Margarete Oliveira Domingues,Odim Mendes,Andrés Reinaldo Rodriguez Papa,Cláudia Maria Nicole Cândido

doi:10.5194/angeo-34-451-2016

Virginia Klausner, Margarete Oliveira Domingues + Show 3 more

Open Access

https://doi.org/10.5194/angeo-34-451-2016

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Abstract

Abstract. This paper proposes a new method to evaluate geomagnetic activity based on wavelet analysis during the solar minimum activity (2007). In order to accomplish this task, a newly developed algorithm called effectiveness wavelet coefficient (EWC) was applied. Furthermore, a comparison between the 5 geomagnetically quiet days determined by the Kp-based method and by wavelet-based method was performed. This paper provides a new insight since the geomagnetic activity indexes are mostly designed to quantify the extent of disturbance rather than the quietness. The results suggest that the EWC can be used as an alternative tool to accurately detect quiet days, and consequently, it can also be used as an alternative to determine the Sq baseline to the current Kp-based 5 quietest days method. Another important aspect of this paper is that most of the quietest local wavelet candidate days occurred in an interval 2 days prior to the high-speed-stream-driven storm events. In other words, the EWC algorithm may potentially be used to detect the quietest magnetic activity that tends to occur just before the arrival of high-speed-stream-driven storms.

Highlights

A substantial part of the energy carried by the solar wind (SW) can be transferred to the terrestrial magnetosphere, and it is associated with the passage of southward-directed interplanetary magnetic fields past the Earth for sufficiently long intervals of time. Gonzalez et al (1994) discussed the energy transfer process as a conversion of the mechanical energy from the SW into magnetic energy stored in the magnetotail of Earth’s magnetosphere and its reconversion into thermal mechanical energy in the plasma sheet, auroral particles, ring current and Joule heating of the ionosphere.The increase in the SW pressure is responsible for the energy injections, and it induces global effects in the magnetosphere called geomagnetic storms
The discrete wavelet transform (DWT) can decompose the signal into different frequency variations and obtain information localized in both frequency and space domains, while in the Fourier transform, the information is only localized in the frequency domain due to the Heisenberg principle
In order to address this question, we decided to compare the results of www.ann-geophys.net/34/451/2016/

Summary

Introduction

A substantial part of the energy carried by the solar wind (SW) can be transferred to the terrestrial magnetosphere, and it is associated with the passage of southward-directed interplanetary magnetic fields past the Earth for sufficiently long intervals of time. Gonzalez et al (1994) discussed the energy transfer process as a conversion of the mechanical energy from the SW into magnetic energy stored in the magnetotail of Earth’s magnetosphere and its reconversion into thermal mechanical energy in the plasma sheet, auroral particles, ring current and Joule heating of the ionosphere.The increase in the SW pressure is responsible for the energy injections, and it induces global effects in the magnetosphere called geomagnetic storms. The characteristic signature of geomagnetic storms can be described as a depression on the horizontal component of the Earth’s magnetic field measured at low- and middle-latitude ground observatories. The decrease in the magnetic horizontal field component is due to an enhancement of the trapped magnetospheric particle population as a consequence of the enhanced ring of current. This perturbation of the H component can last from several hours to several days as described by Chapman and Bartels (1940) and Sugiura (1964)

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