Trends in the Short-Term SSI Variability during the Declining Phase of SC23: Spectral decomposition of over 100 Carrington rotations from the UV through the near IR Lauren Bearden, Odele Coddington, Marty Snow, and Erik Richard; LASP, University of Colorado, Boulder The Sun's energy output varies on timescales ranging from minutes to decades. This variability is due to the turbulent convection-induced dynamical motions and magnetic phenomena within the Sun. The UV chromospheric irradiance, at wavelengths shorter than 300 nm, is closely related to the persistent chromospheric heating in plage and enhanced network lasting on rotational timescales with little center-to-limb variation. In contrast, at wavelengths longer than 300 nm (in the visible and near infrared) the irradiance variations are due to photospheric features related to sunspots and faculae that evolve faster. While the integrated spectral variability (TSI) varies by small amounts (typically <0.3% over days), the wavelength dependent spectral variability from the UV through the infrared spans 5 orders. For modeling Earth atmospheric response, the temporal and spectral irradiance variations across the full solar spectrum must be considered. The Spectral Irradiance Monitor (SIM) instrument has been measuring solar spectral irradiance from 200 to 2400 nm since 2003. In this work, we compute the spectral contrast, [(Imax – Imin )/ Imin]CR, in solar spectral irradiance over 109 Carrington rotations covering the declining phase of SC 23 through the last solar minimum. The periods of maximum and minimum solar activity are determined using known indices that reflect changes in chromospheric activity: the Magnesium II index (Mg II- near 280 nm) and Calcium II index (CaII- near 390 nm). We relate the rotational variability to the Solar disk location of magnetic features on the surface of the Sun using Carrington synoptic map images. In addition, we investigate case studies where the periods of maximum solar activity as defined by the MgII and CaII indices were different.