The influence of solar variability on the atmosphere and ocean dynamics

The sun is well-known as the fundamental energy source that drives the global climate system. It has been suggested that the 11-year cycle of solar forcing is associated with various phenomena in both atmosphere and ocean from the observation. However, the amplitude of the solar cycle is relatively small, about 0.2 W m-2 globally averaged (Lean 2005), and the change of observed global sea surface temperature response to solar variation is less than 0.1°C, there has always been a question that how this small variation could be amplified to produce significant responses in the earth system.

There are two major mechanisms proposed to explain the response of climate system to solar forcing. One is the “top-down” stratospheric ozone mechanism [Haigh, 1996; Balachandran et al., 1999; Shindell et al., 1999] which emphasizes the variation in stratospheric ozone in response to solar ultraviolet (UV) variability. The other is the “bottom-up” air-sea coupling mechanism [Meehl et al., 2003; Van Loon et al., 2007] which suggests that the increased net solar radiation over cloud-free regions in the subtropics translates into greater evaporation and moisture convergence. This strengthens the trades and cooler SSTs in eastern equatorial Pacific. We will use two state-of-the-art fully coupled earth system models, COSMOS (Community system Earth models) and CCSM4 (Community Climate System Model), to investigate the influence of the 11-year solar activity on the global climate system. The sensitivity of including 11-year solar forcing is examined. The preliminary results indicate that the atmosphere temperature may indeed response according to the additional solar forcing for both models. Also, the “bottom-up” air-sea coupling mechanism can be reproduced in the COSMOS model. We will further examine and quantify the possibly amplification resulting from the small solar variation in the future work.