Speaker
Dr
Rock Bush
(Stanford University)
Description
During the five plus years of the Solar Dynamics Observatory (SDO)
spacecraft on-orbit operation, the Helioseismic and Magnetic Imager
(HMI) instrument has been measuring the shape of the Sun. To date,
twelve roll maneuvers have been performed by the SDO spacecraft during
which the spacecraft is rotated 360 degrees around the Sun-spacecraft
line. HMI observations taken during these roll maneuvers enable the
instrument distortion to be separated from the solar shape. The mean
equator to pole radius difference over the five years of observations
is approximately 6.0 milli-arcseconds. The long term trend of the solar
oblateness, however, does not show a correlation with the current solar
sunspot cycle. Details on the HMI instrument thermal variation during
the roll maneuvers will be discussed. In particular, the thermal control
of the HMI optical bench was modified in 2013 after which there was a
statistically significant decrease in the solar oblateness determined
from the HMI observations.
Primary author
Dr
Rock Bush
(Stanford University)
Co-authors
Isabelle Scholl
(University of Hawaii)
Jeff Kuhn
(University of Hawaii)
Marcelo Emilio
(Universidade Estadual de Ponta Grossa, Parana, Brazil)
