Challenges. There are several scientific challenges associated with connecting the 11-year solar cycle (SC) to climate variability. Among these challenges are identifying pathways by which a small decadal change in solar irradiance (<0.1%) can be amplified beyond what current models imply to produce a significant response in the climate system, and distinguishing the SC signal from other climate signals that arise from human activities (e.g., enhanced greenhouse gases) and natural causes (e.g., volcanic activity). Adding to the challenges is the fact that these climate forcing mechanisms are subtle, nonlinearly interacting, and modulated by internal atmospheric variability.  Moreover, drawing definitive conclusions from a paucity of SC data - only about four SCs of meteorological data are currently available for statistical analysis – poses additional challenges.  Nevertheless, the observational record and output from long-term model simulations continue to grow and support a connection between the SC and several atmospheric circulation features.

The Sun-Climate Focused Science Team (FST) is combining basic research, numerical modeling and observational validation to meet the above challenges and to address its central OBJECTIVE: to provide improved understanding of sun-climate feedback mechanisms and to provide more accurate climate simulations involving the SC.

The FST’s conceptual framework for addressing its objective is shown schematically in Fig. 1. The framework hinges on examining how changes in SC irradiance and solar proton events (SPEs) alter the communication at and between “phenomenological interfaces.”  These interfaces include: (a) solar irradiance-middle atmosphere chemistry; (b) middle atmosphere chemistry-atmospheric dynamics; (c) QBO-planetary waves; (d) tropical upwelling-planetary waves; (e) mesosphere-lower thermosphere; (f) and troposphere-stratosphere.