CaIIK imaging to understand UV irradiance variability

To identify and understand the underlying physical mechanisms of total sola r and UV irradiance variability and to estimate the contribution of various chromospheric features to UV irradiance, detailed analysis of spatially re solved data is required. The various chromospheric features have been segre gated and different parameters have been derived from Call K Spectroheliogr ams of NSO/Sac Peak and Kodaikanal Observatory and compared with UV irradia nce flux measured in MgII h and k lines by NOAA 9 satellite. The important results of this detailed analysis of Call K Images of 1992 together with UV irradiance data will be discussed in this paper.