Thermal Convection and Magnetic Fields in the Solar Interior

The Sun is the most familiar and closest star to Earth. While no observations allow us to see the solar interior directly, solar surface observations and theoretical studies have revealed that complicated flows fill the solar interior. Also, the physical mechanism behind the 11-year cycle in the number of sunspots, strong magnetic regions on the surface, has been a big mystery. We think understanding the details of the flows in the solar interior will allow us to solve the mystery of the cycle. Let's watch this movie of the solar interior based on computer simulations calculating the flows and the magnetic fields in the solar interior.

The Sun is very familiar, but do you know how the solar interior behaves?
Nuclear fusion generates energy near the center of the Sun. Radiation transports the energy outward to 70% of the solar radius.
In the outer 30% of the solar radius, thermal convection occurs due to the temperature difference, like hot water swirling in a bathtub. This convection transports the energy outward. In the end, the energy is emitted from the solar surface as radiation. This computer simulation calculates the thermal convection layer.
The movie shows the entire solar convection zone. The outward and inward flows are depicted in white and red, respectively. We can see a characteristic convection structure of outward and inward flow pairs. Each convection cell includes complicated small-scale flows. In this scene, one second corresponds to four days.
Now we will hide part of the Sun to look at the cross-section of the convection zone. Roughly speaking, hot, white upwellings from deep in the convection zone cool at the surface. Then the flows become red downwellings. The overall structure, however, is very complicated.
This is the cross section of the Sun at the equator. From here, let's speed up the time to see the long-term evolution. One second in the movie corresponds to about one month.
The movie shows the overall temporal evolution of the convection in the Sun. You may notice that streams around the equator flow from left to right. It is known that the Sun is rotating like the Earth. Unlike the Earth, the Sun's rotation velocity varies with location. This difference in rotation velocity is maintained by the convection and the computer simulation reproduces this phenomenon.
Now, the movie shows the magnetic field. Due to the high temperature, the material in the Sun exists as ionized gas known as "plasma." Plasma moves together with the magnetic field. From the movie, you can see that the magnetic fields trace the complicated flows in the solar interior. The red and blue colors correspond to westward (rightward) and eastward (leftward) flows, respectively.
Here we accelerate the temporal evolution to about eight months each second. The interaction between thermal convection, rotation, and magnetic fields evolves the large-scale magnetic field. Roughly speaking the magnetic field is westward (rightward) in the northern hemisphere and eastward (leftward) in the southern hemisphere. The magnetic field becomes more complicated with time, and we can observe a reversal in the magnetic field direction.

Details of Numerical Simulation

PurposeUnderstand the thermal convection and the generation of the magnetic field in the solar interior.
Calculation MethodMagneto-hydrodynamic simulation
Number of Grids256 x 384 x 1152 x 2
ComputerK Computer
Time ScaleThermal Convection: 1 month, Evolution of magnetic field: 10 years
Spatial ScaleSolar radius, 700,000 km
ReserchersHideyuki Hotta (Chiba University)
References"Large-scale magnetic fields at high Reynolds numbers in magnetohydrodynamic simulations", Hotta, H., Rempel, M., Yokoyama, M., Science, Volume 351, Issue 6280, Page 1427, (2016)

Details of Visualization

The main part of the movie is rendered from volumetric simulation data, where data are represented as a set of values on a grid. Since the Sun is spherical, this simulation is done in spherical coordinates with the grid along the latitude, longitude, and altitude directions. In the later scenes with the magnetic field, each frame is a time averaged image.Thus, short period fluctuations are smoothed out and the long-term trend can be seen clearly.

YouTube for VR

Web Browsers: You can aim the movie point-of-view in any direction you prefer by dragging the mouse over the YouTube screen.
Smartphones and Tablets: Using the YouTube App (iOS, Android), all directions can be seen by facing your device in the chosen direction. With VR viewers like Google Cardboard, you can enjoy the full effect of stereoscopic vision in all directions.
※Please note that there are some cases in which this video cannot be watched depending on your environment.


  • Simulation: Hideyuki Hotta
  • Visualization: Takaaki Takeda
  • Four-Dimensional Digital Universe Project, NAOJ

360p (.mov, zip file : 304.4 MB) (.wmv, zip file : 144.8 MB)

720p (.mov, zip file : 808.4 MB) (.wmv, zip file : 217 MB)

1080p (.mov, zip file : 1.55 GB) (.wmv, zip file : 248.9 MB)

Side-by-Side Stereovision, 1080p (.mov, zip file : 1.83 GB) (.wmv, zip file : 214.8 MB)

Panoramic Video for VR (Stereovision with Side-by-Side, .mp4, zip file : 382.1 MB) (Stereovision with Top-and-Bottom,.mp4, zip file : 608 MB) (Non-Stereo, .wmv, zip file : 1.14 GB)

Other file formats

  • 1080p GoPro CineForm Stereo/Non-Stereo (files for right and left eyes, .wmv, .mov)
  • 4096x4096 Stereo/Non-Stereo Dome Master (.mp4, .png sequence files)
If you want to use these file formats, please contact us.


  • 2020.03 Version 1.0 was released.