Magnetic Rossby waves on the Sun

Solar activity, which governs the plasma dynamics in the solar interior/atmosphere over long time scales and short- term energetic processes in the solar corona (solar flares, CMEs), is not yet completely understood despite of significant effort of scientific community in recent decades. Generation of magnetic cycles, mechanisms for solar flares/CMEs and chromospheric/coronal heating still are far from the final solution. Along with that the forecasting of solar flares/CMEs also appears an essential task for developing of space weather predictions. The complete understanding of those processes requires increasing both, observational and theoretical efforts in the study of fundamental processes of magnetized plasmas. Rossby waves determine the large-scale dynamics of planetary atmospheres. These waves arise because of the latitudinal variation of the Coriolis parameter and are widely used in the geophysical context. However, large-scale magnetic field in the solar interior and the atmosphere may significantly change the dynamics of Rossby waves, which may explain various observed phenomena on The Sun. The present project is particularly aimed to study the effects of magnetic Rossby waves in the large-scale dynamics of the solar interior and photosphere. The main research directions (project tasks) of the project are: 1) instability of magnetic Rossby waves in the solar tachocline and its possible relation to observed midrange periodicities in the solar activity (on the time scales of months), 2) estimation of plasma parameters in the solar tachocline using the midrange periodicities, 3) large-scale dynamics of magnetic Rossby waves in the solar atmosphere. Expected results of the project will have tremendous importance for further study of large-scale dynamics of the solar tachocline and atmosphere. The unstable harmonics of magnetic Rossby waves can be responsible for midrange periodicities of the solar activity, which may provide a clue for further study of solar dynamo and consequently magnetic cycles. The observed midrange periodicities can be used to estimate the magnetic field strength and differential rotation rate in the solar tachocline. With the help of helioseismology, this will further develop the tachocline seismology. Nonlinear dynamics of magnetic Rossby waves may lead to the explanation of observed large scale cyclonic motions in the solar atmosphere.

The main scientific goal of the project was to study large-scale motions in the solar magnetized atmosphere/interior caused by magnetic Rossby (planetary) waves and their connection to the observed variations in solar activity. Recent direct observations of Rossby waves on the Sun indeed confirmed the importance of the waves for solar plasma dynamics. The project included the theoretical study of magnetic Rossby waves by analytical and numerical calculations and the statistical analysis of long-term sunspot (on the Sun) and radionuclide (on the Earth) data records. It is shown that the magnetic Rossby waves in the solar tachocline, a thin layer below the solar convection zone, are responsible for the observed long-term variations of solar activity with the periods of hundreds of years. All observed periodicities were explained by the magnetic Rossby wave spherical harmonics and the future long-term behavior of solar cycle strength was predicted. It is also found that the Rossby waves are responsible for the observed short-term variations of solar activity with periods of hundreds of days. Our result showed that the observed periodicity is anti-correlated with the solar cycle strength: stronger cycles displayed shorter periodicity. Observed short-term periodicity and the theory of magnetic Rossby waves were used to estimate the magnetic field strength in the solar interior, which is novel and promising method to test different dynamo models of solar cycle generation. Using this method it was also found that the magnetic field strength is with 25 % stronger in more active hemisphere on the Sun, which provides a challenge for the dynamo theory. The results obtained under the projects are ground breaking and provide unique opportunity to study solar activity. The methodology and the theory can be applied to other solar-like stars, which show solar-type activity variations. Observations of solar-like stars at different evolutionary phases alongside with the theory of magnetic Rossby waves allow to study the evolution of stellar internal magnetic field and hence the stellar dynamo. Therefore, the project results open new interdisciplinary research areas in different branches of astrophysics. Long-term prediction of solar activity based on the magnetic Rossby wave theory has enormous importance for the long-term planning of future scientific-technological activity, which is a key point for further development of our civilization.