Solar wind temperature–velocity relationship over the last five solar cycles and Forbush decreases associated with different types of interplanetary disturbance

2020 ◽  
Vol 500 (3) ◽  
pp. 2786-2797
Author(s):  
A A Melkumyan ◽  
A V Belov ◽  
M A Abunina ◽  
A A Abunin ◽  
E A Eroshenko ◽  
...  
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
Coronal Holes ◽  
Cosmic Ray ◽  
Magnetic Clouds ◽  
Solar Cycles ◽  
Forbush Decreases ◽  
Proton Temperature ◽  
Interaction Regions ◽  
Interplanetary Disturbance

ABSTRACT The behaviour of the solar wind (SW) proton temperature and velocity and their relationship during Forbush decreases (FDs) associated with various types of solar source – coronal mass ejections (CMEs) and coronal holes (CHs) – have been studied. Analysis of cosmic ray variations, SW temperature, velocity, density, plasma beta, and magnetic field (from 1965–2019) is carried out using three databases: the OMNI database, Variations of Cosmic Rays database (IZMIRAN) and Forbush Effects & Interplanetary Disturbances database (IZMIRAN). Comparison of the observed SW temperature (T) and velocity (V) for the undisturbed SW allows us to derive a formula for the expected SW temperature (Texp, the temperature given by a T–V formula, if V is the observed SW speed). The results reveal a power-law T–V dependence with a steeper slope for low speeds (V < 425 km s−1, exponent = 3.29 ± 0.02) and flatter slope for high speeds (V > 425 km s−1, exponent = 2.25 ± 0.02). A study of changes in the T–V dependence over the last five solar cycles finds that this dependence varies with solar activity. The calculated temperature index KT = T/Texp can be used as an indicator of interplanetary and solar sources of FDs. It usually has abnormally large values in interaction regions of different-speed SW streams and abnormally low values inside magnetic clouds (MCs). The results obtained help us to identify the different kinds of interplanetary disturbance: interplanetary CMEs, sheaths, MCs, corotating interaction regions, high-speed streams from CHs, and mixed events.

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>

scholarly journals Cosmic Ray Signatures of Different Types of Solar Wind Streams

1990 ◽  
Vol 142 ◽  
pp. 259-260
Author(s):  
P.K. Shrivastava ◽  
S.P. Agrawal
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
Solar Wind Speed ◽  
Coronal Holes ◽  
Cosmic Ray ◽  
Cosmic Ray Intensity ◽  
Wind Speeds ◽  
Different Types ◽  
Speed Solar Wind ◽  
High Speed Solar Wind

The earlier concept of average solar wind speed has changed with time. Besides quiet periods of low/average solar wind speeds, two different kinds of solar sources (solar flares and coronal holes) have been identified to produce high speed solar wind streams. In an earlier investigation, it was reported that the high speed streams associated to these sources produce distinctly different effects on the cosmic ray intensity (Venkatesan, et. al., 1982).

Recurrent and sporadic Forbush decreases during solar cycles 23–24

2019 ◽  
Vol 5 (1) ◽  
pp. 39-47 ◽  
Author(s):  
Анаид Мелкумян ◽  
Anaid Melkumyan ◽  
Анатолий Белов ◽  
Anatoliy Belov ◽  
Мария Абунина ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Speed ◽  
Recurrent Events ◽  
Solar Wind Velocity ◽  
High Reliability ◽  
Coronal Holes ◽  
Solar Cycles ◽  
Interplanetary Coronal Mass Ejections ◽  
Forbush Decreases ◽  
The Magnetic Field

A comparison has been made between recurrent (associated with high-speed streams from coronal holes) and sporadic (caused by interplanetary coronal mass ejections (ICMEs)) Forbush decreases (FDs) in solar cycles 23 and 24 (as well as in the maxima of these cycles and the minimum between them). Forbush Effects and Interplanetary Disturbances database created and maintained in IZMIRAN provided a large number of events (about 1700 isolated FDs, among them 350 recurrent FDs, and 207 sporadic FDs selected with high reliability), which allowed us to apply statistical methods. The results revealed that sporadic FDs prevailed in the maxima of the cycles; recurrent FDs, in the minimum between the cycles. FD parameters (magnitude, decrease rate, anisotropy) are larger for sporadic events than for recurrent ones, especially in the maxima of the cycles. FD magnitude is greater in the maxima than in the minimum for sporadic events, and it changes weakly for recurrent ones. The solar wind velocity is on average greater for recurrent events than for sporadic ones; it is larger for recurrent FDs in the minimum and for sporadic FDs in the maxima. The magnetic field is stronger for sporadic FDs than for recurrent ones in the maxima and it is approximately equal for both types of events in the minimum. The magnetic field of ICMEs is weaker in the current solar cycle than in the previous one. The duration of the FD main phase is less in the maxima for both types of events; sporadic FDs developed significantly faster than recurrent ones in the maximum of cycle 23.

scholarly journals Origins of the semiannual variation of geomagnetic activity in 1954 and 1996

2004 ◽  
Vol 22 (1) ◽  
pp. 93-100 ◽  
Author(s):  
E. W. Cliver ◽  
L. Svalgaard ◽  
A. G. Ling
Keyword(s):  
Solar Wind ◽  
Geomagnetic Activity ◽  
Solar Minimum ◽  
High Speed ◽  
Solar Wind Speed ◽  
Coronal Holes ◽  
Heliospheric Current Sheet ◽  
Solar Cycles ◽  
Axial Variation ◽  
Semiannual Variation

Abstract. We investigate the cause of the unusually strong semiannual variation of geomagnetic activity observed in the solar minimum years of 1954 and 1996. For 1996 we separate the contributions of the three classical modulation mechanisms (axial, equinoctial, and Russell-McPherron) to the six-month wave in the aam index and find that all three contribute about equally. This is in contrast to the longer run of geomagnetic activity (1868-1998) over which the equinoctial effect accounts for ∼70% of the semiannual variation. For both 1954 and 1996, we show that the Russell-McPherron effect was enhanced by the Rosenberg-Coleman effect (an axial polarity effect) which increased the amount of the negative (toward Sun) [positive (away from Sun)] polarity field observed during the first [second] half of the year; such fields yield a southward component in GSM coordinates. Because this favourable condition occurs only for alternate solar cycles, the marked semiannual variation in 1954 and 1996 is a manifestation of the 22-year cycle of geomagnetic activity. The 11-year evolution of the heliospheric current sheet (HCS) also contributes to the strong six-month wave during these years. At solar minimum, the streamer belt at the base of the HCS is located near the solar equator, permitting easier access to high speed streams from polar coronal holes when the Earth is at its highest heliographic latitudes in March and September. Such an axial variation in solar wind speed was observed for 1996 and is inferred for 1954. Key words. Magnetosphere (solar wind – magnetosphere interactions; storms and substorms)

A century of geomagnetic storms, CMEs and HSS/SIRs

2021 ◽  
Author(s):  
Kalevi Mursula ◽  
Timo Qvick ◽  
Lauri Holappa
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
Geomagnetic Storms ◽  
Coronal Holes ◽  
Active Regions ◽  
Time Interval ◽  
Dst Index ◽  
Intensity Category ◽  
Interaction Regions ◽  
Storm Index

<p>Geomagnetic storms are mainly driven by the two main solar wind transients: coronal mass ejections (CME) and high-speed solar wind streams with related (corotating) stream interaction regions (HSS/SIR). CMEs are produced by new magnetic flux emerging on solar surface as active regions, and their occurrence follows the occurrence of sunspots quite closely. HSSs are produced by coronal holes, whose occurrence at the ecliptic is maximized in the declining phase of the solar cycle.</p><p>Geomagnetic storms are defined and quantified by the Dst index that measures the intensity of the ring current and is available since 1957. We have corrected some early errors in the Dst index and extended its time interval from 1932 onwards using the same stations as the Dst index (CTO preceding HER). This extended storm index is called the Dxt index. We have also constructed Dxt3 and Dxt2 indices from three/two of the longest-operating Dst stations to extend the storm index back to 1903, covering more than a century of storms.</p><p>We divide the storms into four intensity categories (weak, moderate, intense and major), and use the classification of solar wind by Richardson et al. into CME, HSS/SIR and slow wind -related flows in order to study the drivers of storms of each intensity category since 1964. We also correct and use the list of sudden storm commencements (SSC) collected by Father P. Mayaud, and divide the storms of each category into SSC-related storms and non-SSC storms.</p><p>Studying geomagnetic storms of different intensity category and SSC relation allows us to study the occurrence of CMEs and HSS/SIR over the last century. We also use these results to derive new information on the centennial evolution of the structure of solar magnetic fields.</p>

Spatial evolution of turbulent regions associated with stream interaction regions in the solar wind

2021 ◽  
Author(s):  
Roman Kislov ◽  
Timothy Sagitov ◽  
Helmi Malova
Keyword(s):  
Solar Wind ◽  
Plasma Flow ◽  
High Speed ◽  
Large Scale ◽  
Coronal Holes ◽  
Spatial Evolution ◽  
The Sun ◽  
Current Sheets ◽  
Interaction Regions ◽  
High Speed Flows

<p>High-speed flows from coronal holes are separated from the surrounding solar wind by stream or corotating interaction regions (SIRs/CIRs). The latter have a complex dynamic structure, which is determined by turbulence, the presence of current sheets and magnetic islands/flux ropes/blobs/plasmoids. As the Sun rotates, SIRs along with high-speed flows propagate in the heliosphere. A SIR can be considered as a single large-scale object resembling a magnetic tube with walls of varying thickness. In this case, one can think not only about the speed of the plasma flow inside and near the given object, but also about its movement around the Sun as a whole. Because of this rotation, SIRs can cross the orbits of two separated spacecraft, which may allow one to study the spatial evolution of their structure. We have chosen the events when SIRs were sequentially detected by ACE and one of the STEREO spacecraft. In each case, a position of the Stream Interface (SI) was found, relative to which the position of other structures within the SIR was determined. Using a newly developed method for identifying current sheets [Khabarova et al. 2021], the SIR fine structure and the properties of turbulent plasma flow were studied. The estimates of the angular velocity of rotation SIR around the Sun are given. A model is constructed that describes the motion of SIRs in the heliosphere and their main large-scale properties.</p><p>Khabarova O., Sagitov T., Kislov R., Li G. (2021), http://arxiv.org/abs/2101.02804</p>

scholarly journals Two Classes of Fast Solar Wind Streams: Their Origin and Influence on the Galactic Cosmic Ray Intensity

1980 ◽  
Vol 91 ◽  
pp. 399-401
Author(s):  
N. Iucci ◽  
M. Parisi ◽  
M. Storini ◽  
G. Villoresi
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
Cosmic Ray ◽  
Mean Value ◽  
Proton Density ◽  
Fast Solar Wind ◽  
Cosmic Ray Intensity ◽  
Proton Temperature ◽  
The Mean ◽  
Galactic Cosmic Ray

The analysis of solar wind (bulk velocity v, proton density n, proton temperature T) and magnetic field (B) data in the years 1964-1974 makes possible to identify two main classes of high-speed streams (ΔV = (vm - vo)≥ 100 km/sec, vm being the maximum daily mean speed and vo the mean value between the speeds immediately preceding and following the stream; duration Δt ≥ 2 days):

scholarly journals The effect of the high-speed stream following the corotating interaction region on the geomagnetic activities

1997 ◽  
Vol 15 (6) ◽  
pp. 662-670 ◽  
Author(s):  
S. Watari
Keyword(s):  
Solar Wind ◽  
Coronal Hole ◽  
High Speed ◽  
Coronal Holes ◽  
Geomagnetic Disturbance ◽  
Seasonal Effect ◽  
Solar Cycles ◽  
Geomagnetic Disturbances ◽  
High Speed Stream ◽  
Long Duration

Abstract. The high-speed stream following the corotating interaction regions (CIRs) was analyzed. As a result of the analysis, it is found that the geomagnetic field is continuously disturbed in the high-speed stream in question. The geomagnetic disturbances with long duration recurred several rotations between December 1993 and June 1994. These disturbances were associated with a large recurrent coronal hole expanding from the south pole of the Sun. High-speed solar wind from this coronal hole was observed by the IMP-8 satellite during this period. However, the observed intensities of the geomagnetic disturbances were different for each recurrent period. This is explained by the seasonal effect. The disturbed geomagnetic condition continued in the high-speed stream after the passage of the CIRs. The long duration of these disturbances can be explained by the continuous energy input into the Earth's magnetosphere from the high-speed regions following the CIRs. This kind of long-duration geomagnetic disturbance in association with coronal holes has been observed in the declining phase of other solar cycles. The relation between the coronal-hole area and the maximum solar-wind velocity is not good for the well-developed large coronal hole analyzed here.

scholarly journals Recurrent and sporadic Forbush decreases during solar cycles 23–24

2019 ◽  
Vol 5 (1) ◽  
pp. 28-34 ◽  
Author(s):  
Анаид Мелкумян ◽  
Anaid Melkumyan ◽  
Анатолий Белов ◽  
Anatoliy Belov ◽  
Мария Абунина ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Speed ◽  
Recurrent Events ◽  
Solar Wind Velocity ◽  
High Reliability ◽  
Coronal Holes ◽  
Solar Cycles ◽  
Interplanetary Coronal Mass Ejections ◽  
Forbush Decreases ◽  
The Magnetic Field

A comparison has been made between recurrent (associated with high-speed streams from coronal holes) and sporadic (caused by interplanetary coronal mass ejections (ICMEs)) Forbush decreases (FDs) in solar cycles 23 and 24 (as well as in the maxima of these cycles and the minimum between them). Forbush Effects and Interplanetary Disturbances database created and maintained in IZMIRAN provided a large number of events (about 1700 isolated FDs, among them 350 recurrent FDs, and 207 sporadic FDs selected with high reliability), which allowed us to apply statistical methods. The results revealed that sporadic FDs prevailed in the maxima of the cycles; recurrent FDs, in the minimum between the cycles. FD parameters (magnitude, decrease rate, anisotropy) are larger for sporadic events than for recurrent ones, especially in the maxima of the cycles. FD magnitude is greater in the maxima than in the minimum for sporadic events, and it changes weakly for recurrent ones. The solar wind velocity is on average greater for recurrent events than for sporadic ones; it is larger for recurrent FDs in the minimum and for sporadic FDs in the maxima. The magnetic field is stronger for sporadic FDs than for recurrent ones in the maxima and it is approximately equal for both types of events in the minimum. The magnetic field of ICMEs is weaker in the current solar cycle than in the previous one. The duration of the FD main phase is less in the maxima for both types of events; sporadic FDs developed significantly faster than recurrent ones in the maximum of cycle 23.

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