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The persistence and decay of springtime total ozone anomalies over the entire …


Biology Articles » Bioclimatology » Persistence and photochemical decay of springtime total ozone anomalies in the Canadian Middle Atmosphere Model » Introduction

Introduction
- Persistence and photochemical decay of springtime total ozone anomalies in the Canadian Middle Atmosphere Model

Fioletov and Shepherd (2003, hereinafter referred to as F&S 2003) showed that interannual total ozone anomalies in midlatitudes develop through the winter and spring, and then persist through summer until autumn. Weber et al. (2003) showed that these anomalies (in both spring and late summer) are related to anomalies in the dynamical forcing of the Brewer-Dobson circulation. During winter and early spring there is a buildup of ozone which is caused by the dominance of transport processes during this period. This buildup is followed by a decline through late spring and summer when transport becomes less important and photochemical loss controls the time evolution of midlatitude total ozone. During this summertime period of total ozone decline the ozone anomalies decrease in magnitude through photochemical relaxation, and then are rapidly erased when the next winter’s buildup begins. In general the persistence of the midlatitude ozone anomalies is stronger in the northern hemisphere (NH) than in the southern hemisphere (SH). This is due to the influence of springtime polar ozone depletion on midlatitude ozone after the breakup of the vortex. Fioletov & Shepherd (2005, hereinafter referred to as F&S 2005) went on to show that the persistence of the total ozone anomalies is much greater in the SH when the entire extratropics (35oS– 80oS) is included, since the region is then not sensitive to transport across 60 S. (The region poleward of 80 olatitude is not observed by TOMS or SBUV, but because of the very small area involved contributes very little to the entire extratropical amounts.)

These observed relationships provide a valuable diagnostic for process-oriented model validation. The F&S 2003 approach is used here to compare the persistence and photochemical decay of total ozone anomalies in the Canadian Middle Atmosphere Model (CMAM) with observations.


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