Construction of a SORCE-based Solar Spectral Irradiance (SSI) Record for Input into Chemistry Climate Models

Abstract:

We present a research program to produce a solar spectral irradiance (SSI) record suitable for whole atmosphere chemistry-climate model (CCM) transient studies over the 2001-2015 time period for Solar Cycle 23 and 24 (SC23-24). Climate simulations during this time period are particularly valuable because SC23-24 represents the best-observed solar cycle in history – both from the perspective of solar physics and in terms of Earth observation systems. This record will be based predominantly on the observed irradiance of the SORCE mission as measured by the SIM and SOLSTICE instruments from April of 2003 to the present time. The SSI data record for this proposed study requires very broad wavelength coverage (115-100000 nm), daily spectral coverage, compliance of the integrated SSI record with the TSI, and well-defined and documented uncertainty estimates. While the majority of the record will be derived from SORCE observations, extensions back to the SC23 maximum time period (early 2001) and closure of critical gaps in the SORCE record will be generated employing the Fontenla et al. (2015) Solar Radiation Physical Model (SRPMv2). Since SRPM is a physics-based model, estimates of the SSI for wavelengths outside the SORCE measurement range can be meaningfully included. This model now includes non-LTE contributions from metals in the atomic number range 22-28 (i.e. titanium through nickel) as well as important molecular photo-disassociation contributions from molecules such as NH, molecular hydrogen, CH, and OH led have led to greatly improved agreement between the model and the observed 0.1 nm SOLSTICE spectrum. Thus comparative studies of the SORCE observations with SRPMv2 provide meaningful insight into the nature of solar variability critical for subsequent Earth atmospheric modeling efforts.