scholarly journals Wavelet analysis of the magnetotail response to solar wind fluctuations during HILDCAA events

2019 ◽  
Vol 37 (5) ◽  
pp. 919-929
Author(s):  
Adriane Marques de Souza Franco ◽  
Ezequiel Echer ◽  
Mauricio José Alves Bolzan
Keyword(s):  
Solar Wind ◽  
Wavelet Transform ◽  
Wavelet Analysis ◽  
Geomagnetic Field ◽  
Field Component ◽  
Long Duration ◽  
Analysis Technique ◽  
Spacecraft Mission ◽  
Cross Wavelet Analysis ◽  
Cross Wavelet

Abstract. In this work a study of the effects of the high-intensity long-duration continuous AE activity (HILDCAAs) events in the magnetotail was conducted. The aim of this study was to search the main frequencies during HILDCAAs in the Bx component of the geomagnetic field in the magnetotail, as well as the main frequencies, at which the magnetotail responds to the solar wind during these events. In order to conduct this analysis the wavelet transform was employed during nine HILDCAA events that coincided with Cluster spacecraft mission crossing through the tail of the magnetosphere from 2003 to 2007. The most energetic periods for each event were identified. It was found that 76 % of them have periods ≤4 h. With the aim to search the periods that have the highest correlation between the IMF Bz (OMNI) component and the Cluster Bx geomagnetic field component, the cross wavelet analysis technique was also used in this study. The majority of correlation periods between the Bz (IMF) and Bx component of the geomagnetic field observed also were ≤4 h, with 62.9 % of the periods. Thus the magnetotail responds stronger to IMF fluctuations during HILDCCAS at 2–4 h scales, which are typical substorm periods. The results obtained in this work show that these scales are the ones on which the coupling of energy is stronger, as well as the modulation of the magnetotail by the solar wind during HILDCAA events.

scholarly journals Wavelet analysis of the magnetotail response to solar wind fluctuations during HILDCCA events

2019 ◽  
Author(s):  
Adriane Marques de Souza Franco ◽  
Ezequiel Echer ◽  
Mauricio José Alves Bolzan
Keyword(s):  
Solar Wind ◽  
Wavelet Transform ◽  
Wavelet Analysis ◽  
High Intensity ◽  
Geomagnetic Field ◽  
Long Duration ◽  
Analysis Technique ◽  
The Cross ◽  
Cross Wavelet Analysis ◽  
Cross Wavelet

Abstract. In this work a study of the effects of the High-Intensity Long-Duration Continuous AE activity events (HILDCAAs) in the magnetotail was conducted. The aim of this study was to search the main frequencies during HILDCAAs in the Bx component of the geomagnetic field, as well as at the main frequencies which the magnetotail responds to the solar wind during these events. In order to conduct this analysis the wavelet transform was employed in 9 HILDCAA events that occurred after the Cluster mission (2000) and coincided with the Cluster crossing through the tail of the magnetosphere from 2003 to 2007. Altogether, 25 most energetic periods was observed, which 76 % are ≤ 4 hours. The cross wavelet analysis technique was also used for the development of this study. It was applied to data of the Bz-IMF component and the Bx geomagnetic component, searching to obtain the periods in that had the highest correlation between these two series. To obtain these periods is important to identify frequencies on which the coupling of energy is stronger, as well the modulation of the magnetotail by the solar wind during HILDCAA events. The majority of correlation periods between the Bz (IMF) and Bx component of the geomagnetic field observed also were ≤ 4 hours, with 62.9 % of the periods. Thus the magnetotail responds stronger to IMF fluctuations during HILDCCAS at 2–4 hours scales, which are typical substorm periods.

scholarly journals Wavelet analysis on transient behaviour of tidal amplitude fluctuations observed by meteor radar in the lower thermosphere above Bulgaria

2000 ◽  
Vol 18 (3) ◽  
pp. 316-331 ◽  
Author(s):  
D. Pancheva ◽  
P. Mukhtarov
Keyword(s):  
Wavelet Transform ◽  
Wavelet Analysis ◽  
Morlet Wavelet ◽  
Neutral Wind ◽  
Bispectral Analysis ◽  
Time Intervals ◽  
Cross Wavelet Analysis ◽  
Morlet Wavelet Transform ◽  
Cross Wavelet ◽  
Mlt Region

Abstract. On the basis of bispectral analysis applied to the hourly data set of neutral wind measured by meteor radar in the MLT region above Bulgaria it was demonstrated that nonlinear processes are frequently and regularly acting in the mesopause region. They contribute significantly to the short-term tidal variability and are apparently responsible for the observed complicated behavior of the tidal characteristics. A Morlet wavelet transform is proposed as a technique for studying nonstationary signals. By simulated data it was revealed that the Morlet wavelet transform is especially convenient for analyzing signals with: (1) a wide range of dominant frequencies which are localized in different time intervals; (2) amplitude and frequency modulated spectral components, and (3) singular, wave-like events, observed in the neutral wind of the MLT region and connected mainly with large-scale disturbances propagated from below. By applying a Morlet wavelet transform to the hourly values of the amplitudes of diurnal and semidiurnal tides the basic oscillations with periods of planetary waves (1.5-20 days), as well as their development in time, are obtained. A cross-wavelet analysis is used to clarify the relation between the tidal and mean neutral wind variability. The results of bispectral analysis indicate which planetary waves participated in the nonlinear coupling with the atmospheric tides, while the results of cross-wavelet analysis outline their time intervals if these interactions are local.Key words: Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides) - Radio science (nonlinear phenomena)

scholarly journals Cross-correlation and cross-wavelet analyses of the solar wind IMF <i>B</i><sub><i>z</i></sub> and auroral electrojet index AE coupling during HILDCAAs

2018 ◽  
Vol 36 (1) ◽  
pp. 205-211 ◽  
Author(s):  
Adriane Marques de Souza ◽  
Ezequiel Echer ◽  
Mauricio José Alves Bolzan ◽  
Rajkumar Hajra
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
Cross Correlation ◽  
Auroral Electrojet ◽  
Long Duration ◽  
Ae Index ◽  
Speed Solar Wind ◽  
Wavelet Analyses ◽  
Cross Wavelet ◽  
High Speed Solar Wind

Abstract. Solar-wind–geomagnetic activity coupling during high-intensity long-duration continuous AE (auroral electrojet) activities (HILDCAAs) is investigated in this work. The 1 min AE index and the interplanetary magnetic field (IMF) Bz component in the geocentric solar magnetospheric (GSM) coordinate system were used in this study. We have considered HILDCAA events occurring between 1995 and 2011. Cross-wavelet and cross-correlation analyses results show that the coupling between the solar wind and the magnetosphere during HILDCAAs occurs mainly in the period ≤ 8 h. These periods are similar to the periods observed in the interplanetary Alfvén waves embedded in the high-speed solar wind streams (HSSs). This result is consistent with the fact that most of the HILDCAA events under present study are related to HSSs. Furthermore, the classical correlation analysis indicates that the correlation between IMF Bz and AE may be classified as moderate (0.4–0.7) and that more than 80 % of the HILDCAAs exhibit a lag of 20–30 min between IMF Bz and AE. This result corroborates with Tsurutani et al. (1990) where the lag was found to be close to 20–25 min. These results enable us to conclude that the main mechanism for solar-wind–magnetosphere coupling during HILDCAAs is the magnetic reconnection between the fluctuating, negative component of IMF Bz and Earth's magnetopause fields at periods lower than 8 h and with a lag of about 20–30 min. Keywords. Magnetospheric physics (solar-wind–magnetosphere interactions)

Ultra-Low Frequency (ULF) waves originating in solar wind dynamic pressure oscillations and propagating through the magnetosheath to the inner magnetosphere

2020 ◽  
Author(s):  
Marina Georgiou ◽  
Christos Katsavrias ◽  
Ioannis Daglis ◽  
Georgios Balasis
Keyword(s):  
Solar Wind ◽  
Wavelet Transform ◽  
Dynamic Pressure ◽  
Solar Wind Dynamic Pressure ◽  
Slow Solar Wind ◽  
Ulf Waves ◽  
Pressure Oscillations ◽  
Inner Magnetosphere ◽  
Cross Wavelet ◽  
Wave Properties

&lt;p&gt;Several observational studies have shown that ULF oscillations of the solar wind dynamic pressure can drive periodic fluctuations in magnetic field measurements at corresponding frequencies. In this study, we use multi-spacecraft (Cluster, GOES, THEMIS and Van Allen Probes) mission measurements to investigate the propagation of pressure fluctuations-driven pulsations within the Pc5 and Pc4 frequency range (from ~0.5 to 25 mHz) into the magnetosphere. During intervals of slow solar wind &amp;#8212; to exclude waves generated by velocity shear at the magnetopause &amp;#8212; common periodicities in electromagnetic fields in the magnetosphere and the solar wind driver are first detected in Lomb-Scargle periodograms. Then, using the cross-wavelet transform, we examine the causal relationship and specifically, in cross-wavelet spectra and wavelet transform coherence. Lastly, spatial and temporal variations of wave properties are mapped from beyond the magnetopause to the inner magnetosphere through frequency, polarisation and power signatures of waves detected at the various probes. The observed dependence of wave properties on their localisation offers an excellent source for verification of the role that solar wind dynamic pressure oscillations as driver of ULF waves propagating through the magnetosheath into the dayside and nightside magnetosphere.&lt;/p&gt;

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