Search

• 3D test-particle simulation model is developed to examine trapped particle dynamics. • RK4 can simulate only bounce motion of the protons due to more numerical dissipation. • RK6 can simulate trapped particle motion of energy 5 keV to 250 MeV at L = 2–6. • The simulation results of bounce and drift periods are in agreement with theory. • RK6 can be applied to the time-varying and non-analytical magnetospheric studies. This article aims to understand the motion of the charged particles trapped in the Earth's inner magnetosphere. The emphasis is on identifying the numerical scheme, which is appropriate to characterize the trajectories of the charged particles of different energies that enter the Earth's magnetosphere and get trap along the magnetic field lines. These particles perform three different periodic motions, namely: gyration, bounce, and azimuthal drift. However, often, the gyration of the particle is ignored, and only the guiding center of the particle is traced to reduce the computational time. It is because the simulation of all three motions (gyro, bounce, and drift) together needed a robust numerical scheme, which has less numerical dissipation. We have developed a three-dimensional test particle simulation model in which the relativistic equation of motion is solved numerically using the fourth and sixth-order Runge-Kutta methods. The stability of the simulation model is verified by checking the conservation of total kinetic energy and adiabatic invariants linked with each type of motion. We found that the sixth-order Runge-Kutta method is suitable to trace the complete trajectories of both proton and electron of a wide energy range, 5 keV to 250 MeV for L = 2 – 6. We have estimated the bounce and drift periods from the simulations, and they are found to be in good agreement with the theory. The study implies that a simulation model with sixth-order Runge-Kutta method can be applied to the time-vary, non-analytical form of magnetic configuration in future studies to understand the dynamics of charged particles trapped in Earth's magnetosphere. [ABSTRACT FROM AUTHOR]

Recent solar cycles (SCs) 21–24 have experienced a gradual decrease in their activity with considerable weakening during current SC 24. This is a unique opportunity to examine the long-term response of Earth's low-latitude ring-current and high latitude auroral electrojet current systems during such systematically decreasing solar activity. With the advancement in technology, continuous recordings of ground/space magnetic field are available for the last few decades that allow us to explore the behaviour of probability distribution functions (PDFs) linked with the ring-current and auroral electrojet current systems for past five SCs (20–24). Also, PDFs linked with solar wind parameters that drive these current systems like magnetic field and velocity at Earth's bow shock are examined. We noticed the significant narrowing of PDF of ring-current and auroral electrojet during SC 24. The number of one-hour intervals with Dst < - 150 nT are less than 600 for SCs 20–23, which constitutes less than 0.7% of respective PDF, and number of one-hour intervals with Dst < - 250 nT are less than 100 for SCs 20–23, which corresponds to less than 0.1% of respective PDF. But for SC 24 the Dst < - 150 nT encountered only for 58 h, which corresponds to 0.06% of PDF and there are no intervals when Dst was < −250 nT. For auroral electrojet, the number of one-hour intervals with AE > 750 nT and AE > 1500 nT are less than 3060 and 70, respectively for SCs 20–23, which corresponds to < 4% and < 0.06% of respective PDFs. But for SC 24 the AE > 750 nT encountered only for 1398 h, which corresponds to 1.7% of PDF and there are only 9 intervals when AE increased above 1500 nT, which is 0.01% of PDF. It implies that the probability of intense ring-current and auroral electrojet current during SC 24 was unusually low. Such narrowing is seen in PDFs of the interplanetary magnetic field and solar wind velocity as well. This fair quiet space weather experienced during SC 24 is attributed to the weakening of solar activity, which has subsequently influenced the strength of the interplanetary magnetic field and solar wind velocity at Earth's bow shock. [ABSTRACT FROM AUTHOR]

The knowledge about future solar activity is necessary to plan our space-based missions. As yet, several prediction models (statistics- or dynamo-based) have been developed to forecast the peak smoothed sunspot number (SSN) of the upcoming solar cycle. Many of these data-based prediction models require sunspot number until the end of n th solar cycle to predict the peak of the solar cycle n + 1. However, one prefers to have the predictions well in advance. We propose a new data-based model that can provide information about the peak SSN (or amplitude) of solar cycle n ​+ ​1, and sum of peak SSN of solar cycle n ​+ ​2 and n ​+ ​3 ​at the end of each n th solar cycle. The solar cycles are paired using even-odd cycles, therefore in this model n is allowed to take even number. We used recently updated, Version-2, daily and monthly sunspot-number data. The area under the curve of each n th solar cycle [ A n ] is estimated and used in the model together with its length and peak SSN [ S max n ]. We noticed that difference in the area under the curve of solar cycles n and n + 1 can be used to predict the summation of peak SSN of n + 2 and n + 3 solar cycles (i.e., S max n + 2 + S max n + 3). We have tested this prediction model with both daily and monthly sunspot numbers. Our model predicts; S max 24 + S max 25 ​= ​219.7 ​± ​31 and S max 26 + S max 27 ​= ​229.4 ​± ​31. As the peak SSN of solar cycle 24 is known, we get S max 25 ​= ​103.3 ​± ​15. Further, model suggest that the solar cycle 26 and 27 would be similar or slightly stronger than solar cycle 24 and 25. [Display omitted] • A new model of peak sunspot number is presented, which is based on the recently updated Version-2 sunspot-number data. • This model provides the summation of peak smooth sunspot number (SSN) of even-odd pair of solar cycles. • Our model predicts the peak SSN of solar cycle 25 as 103 ​± ​15, and sum of peak SSN of solar cycle 26 and 27 as 229.4 ​± ​31. [ABSTRACT FROM AUTHOR]