Segmentation of EUV spectroheliograms to track and measure solar EUVI variability within a solar cycle

Solar Extreme Ultraviolet Irradiation (EUVI) is known to be the primary source of energy that drives the photochemistry, ionization and heating of the Earth's upper atmosphere above ~ 100 km, contributing to Earth's delicate heating balance and therefore its weather, and over longer periods, its climate. Changes in atmospheric density caused by EUVI (e.g. a thickening of the ionosphere) also affect space-based satellites by "dragging" them to lower orbits and lowering their expected operational lifetimes. A priori knowledge of EUVI variation in conjunction with satellite tracking models would assist satellite operators in countering such affects. Therefore, accurate determination of EUVI is useful for weather, climate and geospace modelers wishing to improve their prediction of solar EUVI effects on the Earth's thermosphere, ionosphere and atmospheric composition, as well as how it affects and modulates Earth weather and climate. It is known that the source of EUVI is the solar atmosphere, where this radiation is produced by varying ionic species of plasmas that lie at temperatures ranging from ~10^4-10^7 K. However, our understanding of the physical mechanisms that heat these plasmas to such temperatures continues to be an active area of investigation and debate, and to understand long-term EUVI effects on Earth and human engineered assets, it is necessary to see what, if any, variability is observed in the solar atmosphere that may be associated with terrestrial effects. Herein, we show initial results from the application of the Coronal Image Segmentation Algorithm (CorISA) to the SoHO EIT database to identify and segment solar features observed in EIT narrow bandpass spectroheliograms. These spectroheliograms were recorded at EUV wavelengths whose bandpasses are centered at 171, 195, 284 and 304 Å to observe line emission produced by plasmas: Fe IX/X, Fe XII, Fe XV and He II, respectively. The EIT database currently consists of observations covering a period of ~1.3 solar cycles (~16 years). Using this segmented imaging approach the goal of the study is to determine solar EUVI variability observed in each EIT bandpass, as a function of areal identification (e.g., active vs. coronal hole EUV variability), over the entire period of observations.