AAVSO Visual Sunspot Observations vs. SDO HMI Sunspot Catalog (Abstract)

Volume 42 number 1 (2014)

Rodney Howe

3343 Riva Ridge Drive, Fort Collins, CO 80526; ahowe@frii.com

Abstract

The most important issue with regard to using the SDO HMI data from the National Solar Observatory (NSO, http://www.nso.edu/staff/fwatson/STARA) is that their current model for creating sunspot counts does not split in groups and consequently does not provide a corresponding group count and Wolf number. As it is a different quantity, it cannot be mixed with the data from our sunspot networks. Although, for the AAVSO, with about seventy stations contributing each day, adding HMI sunspot data would hardly change the resulting index. Perhaps the best use of HMI data is for external validation, by exploiting the fact that HMI provides a series that is rather close to the sunspot number and is acquired completely independently. So, it is unlikely to suffer from the same problems (jumps, biases) at the same time. This validation only works for rather short durations, as the lifetime of space instruments is limited and aging effects are often affecting the data over the mission. In addition, successive instruments have different properties: for example, the NSO model has not managed yet to reconcile the series from MDI and HMI. There is a ~10–15% jump. The first challenge that should be addressed by AAVSO using HMI data is the splitting in groups and deriving group properties. Then, together with the sunspot counts and areas per group, a lot more analyses and diagnostics can be derived (such as the selective disappearance of the smallest sunspots?) that can help interpreting trends in the ratio SSN/other solar indices and many other solar effects.