Abstract
The tropospheric and stratospheric temperature trends and uncertainties in the fifth Coupled Model Intercomparison Project (CMIP5) model simulations in the period of 1979–2005 have been compared with satellite observations. The satellite data include those from the Stratospheric Sounding Units (SSU), Microwave Sounding Units (MSU), and the Advanced Microwave Sounding Unit-A (AMSU). The results show that the CMIP5 model simulations reproduced the common stratospheric cooling (−0.46–−0.95 K/decade) and tropospheric warming (0.05–0.19 K/decade) features although a significant discrepancy was found among the individual models being selected. The changes of global mean temperature in CMIP5 simulations are highly consistent with the SSU measurements in the stratosphere, and the temporal correlation coefficients between observation and model simulations vary from 0.6–0.99 at the 99% confidence level. At the same time, the spread of temperature mean in CMIP5 simulations increased from stratosphere to troposphere. Multiple linear regression analysis indicates that the temperature variability in the stratosphere is dominated by radioactive gases, volcanic events and solar forcing. Generally, the high-top models show better agreement with observations than the low-top model, especially in the lower stratosphere. The CMIP5 simulations underestimated the stratospheric cooling in the tropics and overestimated the cooling over the Antarctic compared to the satellite observations. The largest spread of temperature trends in CMIP5 simulations is seen in both the Arctic and Antarctic areas, especially in the stratospheric Antarctic.
Highlights
As an important aspect of climate change, the vertical structure of temperature trends from the troposphere to stratosphere has received a great deal of attention in the climate change research community [1,2,3,4,5,6,7,8,9]
To facilitate the inter-comparison study, all data are first interpolated to the same horizontal resolution of 5-degrees in longitude and latitude, the temperature of the pressure levels in CMIP5 are converted to the equivalent brightness temperatures of the six Stratospheric Sounding Units (SSU)/Microwave Sounding Units (MSU) layers (SSU3, SSU2, SSU1, MSU4, MSU3, MSU2) based on the vertical weighting function of the SSU/MSU measurements in Figure 1
Research iscoupled-ocean-atmosphere needed to understand the forcing internal variability principleFurther of the coupled is needed to understand the forcing of internal variability and the principle of the coupled ocean–atmosphere system to improve the performance of the CMIP5 models in the troposphere
Summary
As an important aspect of climate change, the vertical structure of temperature trends from the troposphere to stratosphere has received a great deal of attention in the climate change research community [1,2,3,4,5,6,7,8,9]. The World Climate Research Program (WCRP) made an incredible effort to understand the variability in the stratosphere based on climate model simulations [10]. Many of the climate models do not include all the physical and chemical processes necessary for simulating the stratospheric climate [11]. Santer and his co-authors compared CMIP5 model simulations with satellite observations to conduct attribution studies on atmospheric temperature trends [13,14], and they found that CMIP5 models underestimate the observed cooling of the lower stratosphere and overestimate the warming of the troposphere. As a consequence, evaluating the climate model results with integrated observational data sets is necessary to understand the model capabilities and limitations in representing long term climate change and short term variability
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