Evolutionary Characteristics of the Interplanetary Magnetic Field Intensity

Zhang

Monthly Notices of the Royal Astronomical Society

et al. 2019

Temporal variation of the solar coronal rotation appears to be very complex and its relevances to the eleven-year solar activity cycle are still unclear. Using the modified coronal index for the time interval from 1939 January 1 to 2019 May 31, the systematic regularities of the solar coronal rotation are investigated. Our main findings are as follows: (1) from a global point of view, the synodic coronal rotation period with a value of 27.5 days is the only significant period at the periodic scales shorter than 64 days; (2) the coronal rotation period exhibit an obviously decreasing trend during the considered time interval, implying the solar corona accelerates its global rotation rate in the long run; (3) there exist significant periods of 3.25, 6.13, 9.53, and 11.13 years in the period length of the coronal rotation, providing an evidence that the coronal rotation should be connected with the quasi-biennial oscillation, the eleven-year solar cycle, and the 22-year Hale cycle (or the magnetic activity reversal); and (4) the phase relationship between the coronal rotation period and the solar magnetic activity is not only time-dependent but also frequency-dependent. For a small range around the 11-year cycle band, there is a systematic trend in the phase, and the small mismatch in this band brings out the phase to drift. The possible mechanism for the above analysis results is discussed.

Section: Introductionmentioning

confidence: 99%

Systematic regularity of solar coronal rotation during the time interval 1939–2019

Zhang

Monthly Notices of the Royal Astronomical Society

et al. 2019

“…Many papers have found variables of near‐Earth interplanetary space and the magnetosphere approximately follow a lognormal (or similar) distribution for the great majority of the time (Dmitriev et al, ; Farrugia et al, ; Hapgood et al, ; Lockwood & Wild, ; Lotz & Danskin, ; Love et al, ; Riley & Love, ; Vaselovsky et al, ; Vörös et al, ; Weigel & Baker, ; Xiang & Qu, ). This mathematical formulation describes the core of the distribution but often fails to match the occurrence of very large or extreme events (e.g., Baker et al, ; Cliver & Dietrich, ; Lotz & Danskin, ; Riley, ).…”

Section: Introductionmentioning

confidence: 99%

The Development of a Space Climatology: 3. Models of the Evolution of Distributions of Space Weather Variables With Timescale

et al. 2019

We study how the probability distribution functions of power input to the magnetosphere P α and of the geomagnetic ap and Dst indices vary with averaging timescale, τ, between 3 hr and 1 year. From this we develop and present algorithms to empirically model the distributions for a given τ and a given annual mean value. We show that lognormal distributions work well for ap, but because of the spread of Dst for low activity conditions, the optimum formulation for Dst leads to distributions better described by something like the Weibull formulation. Annual means can be estimated using telescope observations of sunspots and modeling, and so this allows the distributions to be estimated at any given τ between 3 hr and 1 year for any of the past 400 years, which is another important step toward a useful space weather climatology. The algorithms apply to the core of the distributions and can be used to predict the occurrence rate of large events (in the top 5% of activity levels): they may contain some, albeit limited, information relevant to characterizing the much rarer superstorm events with extreme value statistics. The algorithm for the Dst index is the more complex one because, unlike ap, Dst can take on either sign and future improvements to it are suggested.Plain Language Summary This is the third in a series of three papers aimed at developing a climatology of space weather that applies to all solar conditions between grand solar minimum and grand solar maximum. We generate empirical models to enable us to predict the probability of a given level of space weather disturbance, as quantified by either the ap of the Dst geomagnetic indices, in a year with a given average level of disturbance. The models can be used with averaging/integration times anywhere between 3 hr and 1 year. , et al. (2019). The development of a space climatology: 3. Models of the evolution of distributions of space weather variables with timescale. Space Weather, 17, 180-209. https://doi.

Publ. Astron. Soc. Aust.

“…This result is similar to the findings in Badalyan & Obridko (2011), in which the authors studied the north-south asymmetry of the sunspot indices and its quasi-biennial oscillations and suggested that a great extent solar activity is generated independently in the two hemispheres. However, some studies advised that the periods shorter than 1 year (Rieger periodicity) and longer than 1 yr (in the range of 1-3 yr) have different origins (Boberg et al 2002;Vecchio et al 2012;Li et al 2012;Xiang & Qu 2018;Xiang 2019).…”

Section: Discussionmentioning

confidence: 99%

The cause of the appearance or disappearance of the Rieger-type periodicity in the northern and southern hemispheres of the sun

Xiang

Zhao

2021

Self Cite

We use a continuous wavelet transform to analyse the daily hemispheric sunspot area data from the Greenwich Royal Observatory during cycles 12–24 and then study the cause of the appearance or disappearance of the Rieger-type periodicity in the northern and southern hemispheres during a certain cycle. The Rieger-type periodicity in the northern and southern hemispheres should be developed independently in the two hemispheres. This periodicity in the northern hemisphere is generally anti-correlated with the long-term variations in the mean solar cycle strength of hemispheric activity, but the correlation of the two parameters in the southern hemisphere shows a weak correlation. The appearance or disappearance of Rieger-type periodicity in the northern and southern hemispheres during a certain solar cycle is not directly correlated with their corresponding hemispheric mean activity strength but should be related to the strength of the hemispheric activity during sunspot maximum times, which hints the Rieger-type periodicity is more related to temporal evolution of toroidal magnetic field. The Rieger-type periodicity in the two hemispheres disappears in those solar cycles with relatively weak hemispheric activity during sunspot maximum times. The reason for the disappearance of this periodicity may be due to the combined influence of relatively weak toroidal magnetic fields and torsional oscillations, the differential rotation parameters vary through the solar cycle and may not remain more or less unchanged during some time, which does not permit the strong growth of magnetic Rossby waves.