Abstract
Powerful ‘space weather’ events caused by solar activity pose serious risks to human health, safety, economic activity and national security. Spikes in deaths due to heart attacks, strokes and other diseases occurred during prolonged power outages. Currently it is hard to prepare for and mitigate the impact of space weather because it is impossible to forecast the solar eruptions that can cause these terrestrial events until they are seen on the Sun. However, as recently reported in Nature, eruptive events like coronal mass ejections and solar flares, are organized into quasi-periodic “seasons”, which include enhanced bursts of eruptions for several months, followed by quiet periods. We explored the dynamics of sunspot-producing magnetic fields and discovered for the first time that bursty and quiet seasons, manifested in surface magnetic structures, can be caused by quasi-periodic energy-exchange among magnetic fields, Rossby waves and differential rotation of the solar interior shear-layer (called tachocline). Our results for the first time provide a quantitative physical mechanism for forecasting the strength and duration of bursty seasons several months in advance, which can greatly enhance our ability to warn humans about dangerous solar bursts and prevent damage to satellites and power stations from space weather events.
Highlights
Recent observations indicate that variability within a sunspot cycle consists of quasi-periodic bursts of activity followed by quieter intervals; these are called the “seasons” of solar activity[1]
To investigate how robust the Tachocline Nonlinear Oscillations (TNOs) periodicity is, we study the nonlinear evolution of shallow-water tachocline dynamics as functions of the parameters of the model, namely the differential rotation amplitude, the effective gravity (Geff), toroidal magnetic band’s latitude-location and its band-strength, with initial perturbations to the system of no more than 16% with respect to the DR energy
We showed that the dynamics of the solar tachocline shear-layer produces nonlinear oscillations (TNO’s) that periodically exchange energy among differential rotation, magnetic fields and Rossby waves
Summary
Recent observations indicate that variability within a sunspot cycle consists of quasi-periodic bursts of activity followed by quieter intervals; these are called the “seasons” of solar activity[1]. No method exists to make a reliable prediction of when, or where, the burst of solar activity will occur Global organization of these persistent, longitude-dependent, oscillating magnetic signals suggests their origin lies in the solar tachocline[3], a thin shear-layer that separates the solidly rotating radiative core and differentially rotating convective envelope. Zaqarashvili[14,15] et al suggested, by employing linearized dynamics of an MHD shallow-water tachocline model, that the interactions of oscillatory neutral modes and growing modes can explain the Rieger-type periodicities and QBO Motivated by these results, Dikpati[16] developed a nonlinear shallow-water tachocline model to study the evolution of the differential rotation and Rossby wave disturbances with low longitudinal wave numbers that perturb the system. What is the physical origin of these Tachocline Nonlinear Oscillations (TNOs), and how robust is their periodicity? Does it agree with the observed range of periodicities of solar seasons? Can these seasons be forecast?
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