Solar signals in CMIP‐5 simulations: the stratospheric pathway

Abstract

The 11 year solar-cycle component of climate variability is assessed in historical simulations of models taken from the Coupled Model Intercomparison Project, phase 5 (CMIP-5).Multiple linear regression is applied to estimate the zonal temperature, wind and annular mode responses to a typical solar cycle, with a focus on both the stratosphere and the stratospheric influence on the surface over the period ∼1850-2005. The analysis is performed on all CMIP-5 models but focuses on the 13 CMIP-5 models that resolve the stratosphere (high-top models) and compares the simulated solar cycle signature with reanalysis data. The 11 year solar cycle component of climate variability is found to be weaker in terms of magnitude and latitudinal gradient around the stratopause in the models than in the reanalysis. The peak in temperature in the lower equatorial stratosphere (∼70 hPa) reported in some studies is found in the models to depend on the length of the analysis period, with the last 30 years yielding the strongest response.A modification of the Polar Jet Oscillation (PJO) in response to the 11 year solar cycle is not robust across all models, but is more apparent in models with high spectral resolution in the short-wave region. The PJO evolution is slower in these models, leading to a stronger response during February, whereas observations indicate it to be weaker. In early winter, the magnitude of the modelled response is more consistent with observations when only data from 1979-2005 are considered. The observed North Pacific high-pressure surface response during the solar maximum is only simulated in some models, for which there are no distinguishing model characteristics. The lagged North Atlantic surface response is reproduced in both high-and low-top models, but is more prevalent in the former. In both cases, the magnitude of the response is generally lower than in observations.

Solar forcing for CMIP6 (v3.2)

“…However, there will be CMIP6 models that do not include chemistry but which resolve the stratosphere and specify SSI, and thus have some of the major ingredients for simulating a topdown pathway for solar-climate coupling (Mitchell et al, 2015b). For these models, the simulated climate response to solar variability will partly depend on the representation of the solar-ozone response in their prescribed ozone field.…”

“…If CMIP6 models opt to use an alternative ozone dataset containing a different representation of the solar-ozone response, it would be very valuable for this to be documented by modeling groups, so that differences in simulated responses to solar forcing might be better understood (Mitchell et al, 2015b).…”

“…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.…”

“…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

“…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).…”