Author Archives: admin

70. Magnetic Flux Emergence & Decay Rates for Sunspots Observed with HMI

Contributed by Aimee Norton. Posted on May 23, 2017

We quantify the emergence and decay rates of ten bipolar active regions using vector magnetic field data from HMI. Our results, placed in context with other observational and modeling results in the literature, confirm a trend that higher flux regions emerge faster and the rate is dependent on the total flux of that region.

66. A Poynting-Robertson-Like Drag at the Sun’s Surface

Contributed by Jeff Kuhn. Posted on February 14, 2017

A new analysis using about 4 years of HMI 5-min solar p-mode limb oscillations as a rotation “tracer” finds a large velocity gradient at the top of the photosphere. It is suggested that the net effect of the photospheric angular momentum loss is similar to Poynting-Robertson “photon braking” on, for example, Sun-orbiting dust.