Author Archives: admin

155. Hydrodynamic Properties of the Sun’s Giant Polar Vortices

Contributed by David H. Hathaway. Posted on April 6, 2021

The giant cellular flows, obtained through tracking HMI-observed Dopplergrams, are used to estimate kinetic helicity and Reynolds stress inside the Sun, as well as differential rotation and poleward drift near the bottom of the convection zone.

153. Computing Helioseismic Sensitivity Kernels for the Sun’s Large-scale Internal Flows Using Global-scale Wave-propagation Simulations

Contributed by Junwei Zhao. Posted on March 28, 2021

A new method to derive the helioseismic sensitivity kernels for the Sun’s large-scale internal flows is developed. The new method is based on the idea of placing a small-volume flow perturbation inside the Sun’s model, simulating the wavefield in the photosphere, and then measuring the phase shifts caused by this internal perturbation.

152. Probing the Solar Meridional Circulation using Fourier Legendre Decomposition

Contributed by Doug Braun. Posted on March 16, 2021

Fourier Legendre decomposition is applied on HMI’s long-term Doppler-velocity observations to derive the Sun’s internal meridional circulation. In addition to the well-known center-to-limb effect, a non-axisymmetric component in the northern- and southern-hemisphere is identified as another systematic effect that complicates the derivation of the internal meridional circulation.

151. Hemispheric Sign Preference of Magnetic Helicity Flux in Solar Cycle 24

Contributed by Sung-Hong Park. Posted on January 26, 2021

To study the physical processes causing the hemispheric sign preference (HSP) of helicity in the Sun, the authors surveyed active regions (ARs) observed during Solar Cycle 24 to estimate their magnetic helicity flux, and studied the HSP dependences of the magnetic helicity flux with respect to various properties of ARs.

150. Photospheric Oscillations in and around Active Region 11158, including the Polarity Inversion Line

Contributed by Aimee Norton. Posted on January 20, 2021

To search for signatures of Alfvénic waves in the solar photosphere, the authors analyze the oscillation amplitudes, phases and time-distance behavior between different observables in a sunspot umbra, its polarity inversion line, and surrounding area.

149. Activity Complexes and a Prominent Poleward Surge During Solar Cycle 24

Contributed by Zi-Fan Wang. Posted on December 15, 2020

A surface flux-transport dynamo model assimilation shows that the long-lasting active-region complexes, which appeared in the Sun’s southern hemisphere during Cycle 24, played a crucial role in the pole’s polarity reversal and the field strength at the cycle minimum.

147. Recurring Homologous Solar Eruptions in NOAA AR 11429

Contributed by Suman Dhakal. Posted on October 14, 2020

Through studying three homologous eruptive events in an active region, the authors conclude that shearing motions and magnetic flux cancellation play a dominant role leading to the recurrent eruptions, and are key processes forming the eruptive structures.