Title: Variability of Chromospheric Features and Implications on UV Irradiance Variability
Author: R. Kariyappa
Affil: Indian Institute of Astrophysics, Bangalore 560034, INDIA
Email: rkari@iiap.ernet.in
Abstract: The variations in the UV irradiance are produced by surface manifestation of solar magnetic activity. Considering the variations in the solar UV flux may cause significant changes in the Earth's climate, understanding the physical origin of UV irradiance changes is an extremely important issue in Solar Physics. In order to better understand the variations in UV irradiance related to various bright - magnetic chromospheric features as a function of the solar cycle, we have analyzed over 900 National Solar Observatory CaII K spectroheliograms for the years 1980, 1985, 1987, and 1992. This time period includes the maximum, minimum, and intermediate phases of the solar cycle. We derived the various morphological components (e.g., plage, network, & intranetwork that contribute to the CaII K emission, and compared with UV irradiance measured in MgII h & k lines. We estimated from the intensity time series data that about 50 % of the CaII K solar cycle variability results from plage, about 32 % from network, and about 18 % from intranetwork features.
The power spectrum analysis on the time series of intensity of plages, network, and intranetwork features show a strong 27 and 13-day rotation modulation. It is also important to note that the network and intranetwork elements behave similar to the plages in their rotation modulation, and they contribute to the 27 & 13-day rotation modulation of the CaII K irradiance.