This page contains a description of an anomaly in the HMI optical system that will have an ongoing impact to data obtained near the south-west limb of the Sun. This page will be updates as learn more about the problem and take corrective actions that may be available.
At about 04:52 UTC on 17 August 2016 something changed all data from a limited area of images made by the HMI instrument. The affected area is about 5% of the solar disc, lying beyond a chord in the west south-west part of the image at a minimum central distance of about 0.8 of the solar image radius and between position angles of about 75 and 145 deg measured west from north.
The HMI team is examining the situation and does still not have a full understanding of the impact of the probably permanent change to the instrument.
It is very likely that all data from outside the small effected region is not impacted and data from those regions will be OK to use for analysis of the Sun.
The effect in the impacted disk region is a pair of brighter than normal stripes surrounding a region of reduced intensity. While solar features such as supergranulation appear normal we do see scattered light off the solar limb so the change is not simply reduced intensity.
The event started over a few minutes and reduced in amplitude over the next two days. It has settled to an amplitude in a few days and has been changing slowly as of 31 August.