10:15 AM - 10:30 AM
[PEM14-05] Understanding differential rotation by spatial scale decomposition of angular momentum transport
Keywords:sun, turbulence, differential rotation
We investigated the turbulent scales that carry angular momentum by analyzing the spectra of turbulent thermal convection in 3D magnetohydrodynamic calculations for the solar convection zone.
It is known that the Sun has differential rotation with a fast equator and slow poles. The differential rotation is formed by turbulent thermal convection in the Sun interior. The turbulence is influenced by the Coriolis force and becomes anisotropic, carrying angular momentum and creating differential rotation. There have been many studies of differential rotation using numerical simulations. Most of them simply divide the turbulence into two types, mean flow and turbulence. The former is the azimuthal average, and the latter is the deviation. However, there are many scales of "turbulence". It is difficult to discuss the dominant scale that carries angular momentum if we use "turbulence" as a single term.
In this study, we investigated the efficiency of angular momentum transport for each scale of turbulence by performing Fourier transforms in the longitude at each latitude and radial position. Since simple Fourier transforms show different scales at different locations, we adjusted them to offer the same scales. In this study, we analyzed three calculations with different rotation rates. The calculation results include the solar-like rotation with a fast equator and the anti-solar rotation with a fast pole.
We compared the results with solar-like and anti-solar differential rotation. We found a characteristic distribution on a specific spatial scale in the solar-like case. When the turbulence of the anti-solar rotation is decomposed into spatial scales, it is found that the radial inward angular momentum transport becomes dominant from the equator to mid-latitudes as the scale decreases. In the solar-like case, outward angular momentum transport in the radial direction is found to occur on a large scale of about 100 Mm at mid-latitudes. The outward radial angular momentum transport around the equator is thought to form a meridional flow distribution with multiple cells and a differential rotation of a fast equator. On the other hand, we concluded that in the anti-solar case, the single-cell meridional flow is formed by the radial inward angular momentum transport that exists from the equator to mid-latitudes. The angular momentum transport by the meridional flow is poleward, which results in the formation of the anti-solar rotation.
It is known that the Sun has differential rotation with a fast equator and slow poles. The differential rotation is formed by turbulent thermal convection in the Sun interior. The turbulence is influenced by the Coriolis force and becomes anisotropic, carrying angular momentum and creating differential rotation. There have been many studies of differential rotation using numerical simulations. Most of them simply divide the turbulence into two types, mean flow and turbulence. The former is the azimuthal average, and the latter is the deviation. However, there are many scales of "turbulence". It is difficult to discuss the dominant scale that carries angular momentum if we use "turbulence" as a single term.
In this study, we investigated the efficiency of angular momentum transport for each scale of turbulence by performing Fourier transforms in the longitude at each latitude and radial position. Since simple Fourier transforms show different scales at different locations, we adjusted them to offer the same scales. In this study, we analyzed three calculations with different rotation rates. The calculation results include the solar-like rotation with a fast equator and the anti-solar rotation with a fast pole.
We compared the results with solar-like and anti-solar differential rotation. We found a characteristic distribution on a specific spatial scale in the solar-like case. When the turbulence of the anti-solar rotation is decomposed into spatial scales, it is found that the radial inward angular momentum transport becomes dominant from the equator to mid-latitudes as the scale decreases. In the solar-like case, outward angular momentum transport in the radial direction is found to occur on a large scale of about 100 Mm at mid-latitudes. The outward radial angular momentum transport around the equator is thought to form a meridional flow distribution with multiple cells and a differential rotation of a fast equator. On the other hand, we concluded that in the anti-solar case, the single-cell meridional flow is formed by the radial inward angular momentum transport that exists from the equator to mid-latitudes. The angular momentum transport by the meridional flow is poleward, which results in the formation of the anti-solar rotation.