Multimodel climate and variability of the stratosphere

Abstract

[1] The stratospheric climate and variability from simulations of sixteen chemistryclimate models is evaluated. On average the polar night jet is well reproduced though its variability is less well reproduced with a large spread between models. Polar temperature biases are less than 5 K except in the Southern Hemisphere (SH) lower stratosphere in spring. The accumulated area of low temperatures responsible for polar stratospheric cloud formation is accurately reproduced for the Antarctic but underestimated for the Arctic. The shape and position of the polar vortex is well simulated, as is the tropical upwelling in the lower stratosphere. There is a wide model spread in the frequency of major sudden stratospheric warnings (SSWs), late biases in the breakup of the SH vortex, and a weak annual cycle in the zonal wind in the tropical upper stratosphere. Quantitatively, "metrics" indicate a wide spread in model performance for most diagnostics with systematic biases in many, and poorer performance in the SH than in the Northern Hemisphere (NH). Correlations were found in the SH between errors in the final warming, polar temperatures, the leading mode of variability, and jet strength, and in the NH between errors in polar temperatures, frequency of major SSWs, and jet strength. Models with a stronger QBO have stronger tropical upwelling and a colder NH vortex. Both the qualitative and quantitative analysis indicate a number of common and long-standing model problems, particularly related to the simulation of the SH and stratospheric variability.

The Met Office HadGEM3-ES chemistry–climate model: evaluation of stratospheric dynamics and its impact on ozone

“…1 and Table 2, the metrics are divided into those that measure the mean climate of model simulations and those that measure their variability. This division follows that in Butchart et al (2010Butchart et al ( , 2011. Figure 1 demonstrates quite clearly that, whilst the nudged simulations (columns 4-7) are graded similarly to the free-running simulations (columns 2-3) in terms of mean climate metrics (an aspect in which the free-running model is already very good, though again with the exception of the Southern Hemisphere polar night jet strength), the nudged simulations outperform the free-running simulations in terms of variability.…”

“…Figure 9 demonstrates that, as shown in Fig. 1, nudging temperature and horizontal wind fields does not imply that the simulated vertical wind field will also be close to the reanalysis (and, further, there is reasonable agreement in the average magnitude of the vertical wind field across different reanalyses; Butchart et al, 2011;Abalos et al, 2015). At some locations, the biases in residual vertical velocity in the nudged simulations (Fig.…”

“…Indeed, some transport calculations (e.g. for descent in the polar stratosphere; Tegtmeier et al, 2008) use the diabatic rather than the kinematic vertical velocity (see Butchart, 2014). Thus, even though they use the same numerical advection schemes, the stratospheric transport in nudged simulations need not be more accurate than in freerunning models, as discussed in more detail below.…”

“…The metrics for dynamical processes are listed in Butchart et al (2010Butchart et al ( , 2011. These dynamical metrics include one for the polar vortex final warming time but, for reasons explained later in this section, we choose to evaluate final warming using the method of Hardiman et al (2011), and thus this metric is not directly comparable and not included here.…”

Comparative Spectral Analysis and Correlation Properties of Observed and Simulated Total Column Ozone Records

“…One of the main goals was to construct an improved scheme of ozone chemistry for global chemistry climate model (CCM). Since CCMs provide the only tool for long-time projections, their validation and the evaluation of performance are crucial aspects of predicting the time evolution of the stratospheric ozone layer on global scale [2][3][4].…”