Interannual-to-decadal variability of the stratosphere during the 20th century: ensemble simulations with a chemistry-climate model

摘要

Interannual-to-decadal variability in stratospheric ozone and climate have anumber of common sources, such as variations in solar irradiance,stratospheric aerosol loading due to volcanic eruptions, El NiñoSouthern Oscillation variability and the quasi-biennial oscillation (QBO).Currently available data records as well as model simulations addressingstratospheric chemical climate variability mostly cover only the past fewdecades, which is often insufficient to address naturalinterannual-to-decadal variability. Here we make use of recentlyreconstructed and re-evaluated data products to force and validate transientensemble model simulations (nine members) across the twentieth centurycomputed by means of the chemistry-climate model SOCOL (SOlar Climate OzoneLinks). The forcings include sea surface temperatures, sea ice, solarirradiance, stratospheric aerosols, QBO, changes in land properties,greenhouse gases, ozone depleting substances, and emissions of carbonmonoxides, and nitrogen oxides. The transient simulations are in goodagreement with observations, reconstructions and reanalyses and allowquantification of interannual-to-decadal variability during the 20thcentury. All ensemble members are able to capture the low-frequencyvariability in tropical and mid-latitude total ozone as well as in thestrength of the subtropical jet, suggesting a realistic response to externalforcings in this area. The region of the northern polar vortex exhibits alarge internal variability that is found in the frequency, seasonality, andstrength of major warmings as well as in the strength of the modeled polarvortex. Results from process-oriented analysis, such as correlation betweenthe vertical Eliassen Palm flux (EP flux) component and polar variables aswell as stratospheric ozone trends, are of comparable magnitude to thoseobserved and are consistent in all analysed ensemble members. Yet, trendestimates of the vertical EP flux component vary greatly among ensemblemembers precluding any robust conclusions. This suggests that internalvariability in models must be accounted for in order to quantify theatmospheric model response in wave energy upon external forcings.