scholarly journals Spectrum of geomagnetic activity in the period range 5−60 days: possible lunar influences

1998 ◽  
Vol 16 (7) ◽  
pp. 804-811 ◽  
Author(s):  
J. Střeštík
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
High Speed ◽  
Solar Rotation ◽  
Solar Wind Speed ◽  
Frequency Resolution ◽  
Solar Activity Minimum ◽  
Activity Maximum ◽  
Average Spectrum ◽  
Significant Difference

Abstract. The series of daily Ap-indices has been subdivided into pentades (1932–1936 etc.) and spectra with fine-frequency resolution have been calculated for the indices in each of these intervals. Daily sunspot numbers have been processed in the same way. The average spectrum from all spectra in the pentades, as well as the spectrum from the whole interval have been calculated, and significant peaks have been determined. There is a significant difference between the spectra in the pentades containing the solar activity minimum (1932–1936, 1942–1946 etc.) and those containing the solar activity maximum (1937–1941, 1947–1951 etc.). Most peaks can be interpreted as a response to solar rotation and to the structure of solar wind speed (two high-speed streams per solar rotation), both modulated by the 11-year, annual and semi-annual waves. No significant peak corresponding to the period of the synodic month, or its half has been found. This result suggests that the influence of lunar cycles on some natural phenomena (if any) is not mediated by geomagnetic activity.Key words. Geomagnetism and paleomagnetism · Time variations · Diurnal to secular · Magnetospheric physics · Solar wind-magnetosphere interactions

scholarly journals The Observed Relationships Between Some Solar Rotation Parameters and the Activity Cycle

1983 ◽  
Vol 102 ◽  
pp. 99-111
Author(s):  
Robert Howard ◽  
Barry J. LaBonte
Keyword(s):  
Solar Activity ◽  
Solar Rotation ◽  
Rotational Velocity ◽  
Torsional Oscillation ◽  
Periodic Oscillation ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
Solar Activity Minimum ◽  
Activity Maximum ◽  
Open Question

Several parameters of the solar rotation show variations which appear to relate to the phase of the solar activity cycle. The latitude gradient of the differential rotation, as seen in the coefficients of the sin2 and sin4 terms in the latitude expansion, shows marked variations with the cycle. One of these variations may be described as a one-cycle-per-hemisphere torsional oscillation with a period of 11 years, where the high latitudes rotate faster at solar activity maximum and slower at minimum, and the low latitudes rotate faster at solar activity minimum and slower at maximum. Another variation is a periodic oscillation of the fractional difference in the low-latitude rotation between north and south hemispheres. The possibility of a variation in the absolute rotational velocity of the sun in phase with the solar cycle remains an open question. The two-cycle-per-hemisphere torsional waves in the solar rotation also represent an aspect of the rotation which varies with the cycle. We show that the amplitude of the fast flowing zone rises a year before the rise to activity maximum. The fast zone seems to be physically the more significant of the two zones.

Analysis of Quasistationary Solar Wind Stream Forecasts for 2010–2019

2021 ◽  
Vol 3 ◽  
pp. 58-66
Author(s):  
Yu. S. Shugai ◽  
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
High Speed ◽  
Solar Rotation ◽  
Solar Wind Speed ◽  
Coronal Holes ◽  
Slow Solar Wind ◽  
Stream Velocity ◽  
Solar Wind Stream ◽  
Time Model

A real-time model for predicting the quasistationary solar wind speed at the near-Earth orbit is presented. The forecast of the high-speed solar wind stream velocity is obtained with an empirical model linking the areas of coronal holes to the solar wind speed. The forecast of the slow solar wind is based on data on the observed solar wind speed from the previous solar rotation. Over the whole analyzed period from May 2010 to December 2019, the coefficient of correlation between the observed and predicted solar wind speed values is 0.45, and the standard deviation is 88 km/s. The accuracy of forecasting the speed of quasistationary solar wind streams is comparable to the results of foreign models.

scholarly journals Characteristics of solar wind suprathermal halo electrons

2020 ◽  
Vol 642 ◽  
pp. A130
Author(s):  
M. Lazar ◽  
V. Pierrard ◽  
S. Poedts ◽  
H. Fichtner
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
Solar Wind Speed ◽  
Substantial Reduction ◽  
Comprehensive Description ◽  
Temperature Plasma ◽  
Magnetic Focusing ◽  
Fast Wind ◽  
Outer Corona ◽  
Halo Population

A suprathermal halo population of electrons is ubiquitous in space plasmas, as evidence of their departure from thermal equilibrium even in the absence of anisotropies. The origin, properties, and implications of this population, however, are poorly known. We provide a comprehensive description of solar wind halo electrons in the ecliptic, contrasting their evolutions with heliospheric distance in the slow and fast wind streams. At relatively low distances less than 1 AU, the halo parameters show an anticorrelation with the solar wind speed, but this contrast decreases with increasing distance and may switch to a positive correlation beyond 1 AU. A less monotonic evolution is characteristic of the high-speed winds, in which halo electrons and their properties (e.g., number densities, temperature, plasma beta) exhibit a progressive enhancement already distinguishable at about 0.5 AU. At this point, magnetic focusing of electron strahls becomes weaker and may be counterbalanced by the interactions of electrons with wave fluctuations. This evolution of halo electrons between 0.5 AU and 3.0 AU in the fast winds complements previous results well, indicating a substantial reduction of the strahl and suggesting that significant fractions of strahl electrons and energy may be redistributed to the halo population. On the other hand, properties of halo electrons at low distances in the outer corona suggest a subcoronal origin and a direct implication in the overheating of coronal plasma via velocity filtration.

Formation of current sheets and plasmoids within corotating/stream interaction regions

2020 ◽  
Author(s):  
Timofey Sagitov ◽  
Roman Kislov
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Coronal Hole ◽  
High Speed ◽  
Solar Rotation ◽  
Coronal Holes ◽  
Rotation Period ◽  
The Sun ◽  
Current Sheets ◽  
Interaction Regions

<p>High speed streams originating from coronal holes are long-lived plasma structures that form corotating interaction regions (CIRs) or stream interface regions (SIRs) in the solar wind. The term CIR is used for streams existing for at least one solar rotation period, and the SIR stands for streams with a shorter lifetime. Since the plasma flows from coronal holes quasi-continuously, CIRs/SIRs simultaneously expand and rotate around the Sun, approximately following the Parker spiral shape up to the Earth’s orbit.</p><p>Coronal hole streams rotate not only around the Sun but also around their own axis of simmetry, resembling a screw. This effect may occur because of the following mechanisms: (1) the existence of a difference between the solar wind speed at different sides of the stream, (2) twisting of the magnetic field frozen into the plasma, and  (3) a vortex-like motion of the edge of the mothering coronal hole at the Sun. The screw type of the rotation of a CIR/SIR can lead to centrifugal instability if CIR/SIR inner layers have a larger angular velocity than the outer. Furthermore, the rotational plasma movement and the stream distortion can twist magnetic field lines. The latter contributes to the pinch effect in accordance with a well-known criterion of Suydam instability (Newcomb, 1960, doi: 10.1016/0003-4916(60)90023-3). Owing to the presence of a cylindrical current sheet at the boundary of a coronal hole, conditions for tearing instability can also appear at the CIR/SIR boundary. Regardless of their geometry, large scale current sheets are subject to various instabilities generating plasmoids. Altogether, these effects can lead to the formation of a turbulent region within CIRs/SIRs, making them filled with current sheets and plasmoids. </p><p>We study a substructure of CIRs/SIRs, characteristics of their rotation in the solar wind, and give qualitative estimations of possible mechanisms which lead to splitting of the leading edge a coronal hole flow and consequent formation of current sheets within CIRs/SIRs.</p>

Selective acceleration of O+ by drift-bounce resonance in the Earth’s magnetosphere: MMS observations

2020 ◽  
Author(s):  
Satoshi Oimatsu ◽  
Masahito Nosé ◽  
Guan Le ◽  
Stephan A Fuselier ◽  
Robert E Ergun ◽  
...  
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
Solar Wind Speed ◽  
Density Ratio ◽  
Flux Ratio ◽  
Recovery Phase ◽  
Wave Number ◽  
Azimuthal Component ◽  
Time Period ◽  
Speed Solar Wind

<p>We studied O<sup>+</sup>drift-bounce resonance using Magnetospheric Multiscale (MMS) data. A case study of an event on 17 February 2016 shows that O<sup>+</sup> flux oscillations at ~10–30 keV occurred at MLT ~ 5 hr and <em>L</em>~ 8–9 during a storm recovery phase. These flux oscillations were accompanied by a toroidal Pc5 wave and a high-speed solar wind (~550 km/s). The azimuthal wave number (<em>m</em>-number) of this Pc5 wave was found to be approximately –2. The O<sup>+</sup>/H<sup>+</sup> flux ratio was enhanced at ~10–30 keV corresponding to the O<sup>+</sup> flux oscillations without any clear variations of H<sup>+</sup> fluxes, indicating the selective acceleration of O<sup>+</sup> ions by the drift-bounce resonance. A search for the similar events in the time period from September 2015 to March 2017 yielded 12 events. These events were mainly observed in the dawn to the afternoon region at <em>L</em>~ 7–12 when the solar wind speed is high, and all of them were simultaneously identified on the ground, indicating low <em>m</em>-number. Correlation analysis revealed that the O<sup>+</sup>/H<sup>+</sup> energy density ratio has the highest correlation coefficient with peak power of the electric field in the azimuthal component (<em>E<sub>a</sub></em>). This statistical result supports the selective acceleration of O<sup>+</sup> due to the <em>N </em>= 2 drift-bounce resonance.</p>

scholarly journals Polar low-speed solar wind reappeared at the solar activity maximum of cycle 23

2003 ◽  
Vol 30 (7) ◽  
Author(s):  
T. Ohmi ◽  
M. Kojima ◽  
K. Fujiki ◽  
M. Tokumaru ◽  
K. Hayashi ◽  
...  
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Activity Maximum ◽  
Low Speed ◽  
Speed Solar Wind ◽  
Polar Low

scholarly journals Implementing the MULTI-VP coronal model in EUHFORIA: Test case results and comparisons with the WSA coronal model

2021 ◽  
Vol 648 ◽  
pp. A35
Author(s):  
E. Samara ◽  
R. F. Pinto ◽  
J. Magdalenić ◽  
N. Wijsen ◽  
V. Jerčić ◽  
...  
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
High Speed ◽  
Weather Prediction ◽  
Solar Wind Plasma ◽  
High Solar Activity ◽  
Source Surface ◽  
Field Source ◽  
Magnetic Signatures

Context. In this study, we focus on improving EUHFORIA (European Heliospheric Forecasting Information Asset), a recently developed 3D magnetohydrodynamics space weather prediction tool. The EUHFORIA model consists of two parts covering two spatial domains: the solar corona and the inner heliosphere. For the first part, the semiempirical Wang-Sheeley-Arge (WSA) model is used by default; this model employs the potential field source surface and Schatten current sheet models to provide the necessary solar wind plasma and magnetic conditions above the solar surface, at 0.1 AU, which serve as boundary conditions for the inner heliospheric part. Herein, we present the first results of the implementation of an alternative coronal model in EUHFORIA, the so-called MULTI-VP model. Aims. After we replace the default EUHFORIA coronal setup with the MULTI-VP model, we compare their outputs both at 0.1 AU and 1 AU, for test cases involving high speed wind streams (HSSs). We select two distinct cases in which the standard EUHFORIA setup failed to reproduce the HSS plasma and magnetic signatures at Earth to test the performance of MULTI-VP coupled with EUHFORIA-heliosphere. Methods. To understand the quality of modeling with MULTI-VP in comparison with the default coronal model in EUHFORIA, we considered one HSS case during a period of low solar activity and another one during a period of high solar activity. Moreover, the modeling of the two HSSs was performed by employing magnetograms from different providers: one from the Global Oscillation Network Group (GONG) and the second from the Wilcox Space Observatory (WSO). This way, we were able to distinguish differences arising not only because of the different models but also because of different magnetograms. Results. The results indicate that when employing a GONG magnetogram, the combination MULTI-VP+EUHFORIA-heliosphere reproduces the majority of HSS plasma and magnetic signatures measured at L1. On the contrary, the standard WSA+EUHFORIA-heliosphere combination does not capture the arrival of the HSS cases at L1. When employing WSO magnetograms, MULTI-VP+EUHFORIA-heliosphere reproduces the HSS that occurred during the period of high solar activity. However, it is unclear if it models the HSS during the period of low solar activity. For the same magnetogram and periods of time, WSA+EUHFORIA-heliosphere is not able to capture the HSSs of interest. Conclusions. The results show that the accuracy of the simulation output at Earth depends on the choice of both the coronal model and input magnetogram. Nevertheless, a more extensive statistical analysis is necessary to determine how precisely these choices affect the quality of the solar wind predictions.

scholarly journals Seasonal features of geomagnetic activity: a study on the solar activity dependence

2021 ◽  
Vol 39 (5) ◽  
pp. 929-943
Author(s):  
Adriane Marques de Souza Franco ◽  
Rajkumar Hajra ◽  
Ezequiel Echer ◽  
Mauricio José Alves Bolzan
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Geomagnetic Activity ◽  
Annual Variation ◽  
Geomagnetic Storms ◽  
Solar Wind Speed ◽  
Solar Cycles ◽  
Annual Variations ◽  
Long Duration ◽  
Activity Dependence

Abstract. Seasonal features of geomagnetic activity and their solar-wind–interplanetary drivers are studied using more than five solar cycles of geomagnetic activity and solar wind observations. This study involves a total of 1296 geomagnetic storms of varying intensity identified using the Dst index from January 1963 to December 2019, a total of 75 863 substorms identified from the SuperMAG AL/SML index from January 1976 to December 2019 and a total of 145 high-intensity long-duration continuous auroral electrojet (AE) activity (HILDCAA) events identified using the AE index from January 1975 to December 2017. The occurrence rates of the substorms and geomagnetic storms, including moderate (-50nT≥Dst>-100nT) and intense (-100nT≥Dst>-250nT) storms, exhibit a significant semi-annual variation (periodicity ∼6 months), while the super storms (Dst≤-250 nT) and HILDCAAs do not exhibit any clear seasonal feature. The geomagnetic activity indices Dst and ap exhibit a semi-annual variation, while AE exhibits an annual variation (periodicity ∼1 year). The annual and semi-annual variations are attributed to the annual variation of the solar wind speed Vsw and the semi-annual variation of the coupling function VBs (where V = Vsw, and Bs is the southward component of the interplanetary magnetic field), respectively. We present a detailed analysis of the annual and semi-annual variations and their dependencies on the solar activity cycles separated as the odd, even, weak and strong solar cycles.

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