Long-term changes and variability in a transient simulation with a chemistry-climate model employing realistic forcing

[摘要] A transient simulation with the interactively coupled chemistry-climate model(CCM) E39/C has been carried out which covers the 40-year period between1960 and 1999. Forcing of natural and anthropogenic origin is prescribed wherethe characteristics are sufficiently well known and the typical timescales areslow compared to synoptic timescale so that the simulated atmospheric chemistryand climate evolve under a "slowly" varying external forcing. Based onobservations, sea surface temperature (SST) and ice coverare prescribed. The increase of greenhouse gasand chlorofluorocarbon concentrations, as well as nitrogen oxide emissionsare taken into account. The 11-year solar cycle is considered in the calculation ofheating rates and photolysis of chemical species. The three major volcaniceruptions during that time (Agung, 1963; El Chichon, 1982;Pinatubo, 1991) are considered. The quasi-biennial oscillation (QBO) is forcedby linear relaxation, also known as nudging, of the equatorial zonal wind inthe lower stratosphere towards observed zonal wind profiles. Beyond areasonable reproduction of mean parameters and long-term variabilitycharacteristics there are many apparent features of episodic similaritiesbetween simulation and observation: In the years 1986 and 1988 the Antarcticozone holes are smaller than in the other years of that decade. Inmid-latitudes of the Southern Hemisphere ozone anomalies resemble thecorresponding observations, especially in 1985, 1989, 1991/1992, and 1996.In the Northern Hemisphere, the episode betweenthe late 1980s and the first half of the 1990s is dynamically quiet, inparticular, no stratospheric warming is found between 1988 and 1993.As observed, volcanic eruptions strongly influencedynamics and chemistry, though only for few years. Obviously, planetarywave activity is strongly driven by the prescribed SST and modulated by theQBO. Preliminary evidence of realistic cause and effectrelationships strongly suggests that detailed process-oriented studies will bea worthwhile endeavour.

[学科分类] 大气科学