Solar signals in CMIP‐5 simulations: effects of atmosphere–ocean coupling

Abstract

The surface response to the 11 year solar cycle is assessed in ensemble simulations of the twentieth century climate performed in the framework of the fifth phase of the Coupled Model Inter‐Comparison Project (CMIP5). A lead/lag multiple linear regression analysis identifies a multi‐model mean (MMM) global mean surface warming of about 0.07 K, lagging the solar cycle by 1–2 years on average. The anomalous warming penetrates to approximately the first 80–100 m depth in the ocean. Solar signals in the troposphere show a similar time lag of 1–2 years and the strongest MMM warming is simulated in the Tropics above 300 hPa. At the surface, the MMM response in a subset of models that show statistically significant global mean warming (CMIP5‐SIG95) is characterized by an anomalous warming in the west equatorial Pacific Ocean and the Arctic, at 1–2 years after solar maximum. The Arctic warming is twice as strong as the global mean response and appears in the winter months only. The surface warming in the equatorial Pacific Ocean is related to dynamical/thermodynamical processes. Different increase rates of global mean precipitation and atmospheric water vapour in response to a warmer surface lead to a weaker Walker circulation and anomalous westerly winds over the equatorial Pacific in the years following the solar maximum. Owing to atmosphere–ocean coupling, the anomalous westerly winds cool the subsurface and warm the surface in the western equatorial Pacific by ∼0.14 K. The CMIP5‐SIG95 MMM surface warming in the equatorial Pacific and Arctic is weak but qualitatively similar compared with solar signals in the HadCRUT4 dataset.

Solar forcing for CMIP6 (v3.2)

“…Recent modeling efforts have made progress in defining the prerequisites to simulate solar influence on regional climate more realistically (e.g., Gray et al, 2013;Scaife et al, 2013;Thieblemont et al, 2015), but the lessons learned from CMIP5 show that a more process-based analysis of climate models within CMIP6 is required to better understand the differences in model responses to solar forcing (e.g., Mitchell et al, 2015b;Misios et al, 2016;Hood et al, 2015). In particular, the role of solar-induced ozone changes and the need for a suitable resolution of climate model radiation schemes to capture SSI variations is becoming increasingly evident, and will be touched upon in this paper.…”

“…Analysis of model simulations and observations have shown a response of global surface temperature to TSI variations over the 11-year solar cycle of about 0.1 K Misios et al, 2016). However, the observed lag and the spatial pattern of the solar-cycle response are poorly represented in CMIP5 models (e.g., Mitchell et al, 2015b;Misios et al, 2016;Hood et al, 2015).…”

“…However, the observed lag and the spatial pattern of the solar-cycle response are poorly represented in CMIP5 models (e.g., Mitchell et al, 2015b;Misios et al, 2016;Hood et al, 2015).…”

Climate responses to SATIRE and SIM-based spectral solar forcing in a 3D atmosphere-ocean coupled GCM

“…Since the ocean has large heat capacity, the surface temperature will have a delayed response to the solar forcing. We performed a regression analysis to the global average temperature anomalies to the TSI variations using a similar method to that in Misios et al (2015). Since we are only interested in 11-year solar cycle variation, we filter out long-term trends of both TSI and temperature.…”

“…Climate model results are often used to estimate the climate responses to solar variations and to understand associated mechanisms (e.g., Haigh 1996Haigh , 2003Shindell et al 1999;Matthes et al 2006;Meehl et al 2009;Rind et al 2008Rind et al , 2013Ineson et al 2011;Frame & Gray 2010;Gray et al 2013;Misios et al 2015;Hood et al 2015;Kidston et al 2015;Mitchell et al 2015). The earlier modeling studies to assess the implication of SORCE SIM measurements mainly focused on the time scale of the 11-year solar cycle by comparing the responses to the out-of-phase SORCE SSI and the in-phase SSI (e.g., NRLSSI and SATIRE SSI).…”