[1] Previous multiple regression analyses of the solar cycle variation of stratospheric ozone are improved by (1) analyzing three independent satellite ozone data sets with lengths extending up to 25 years and (2) comparing column ozone measurements with ozone profile data during the 1992-2003 period when no major volcanic eruptions occurred. Results show that the vertical structure of the tropical ozone solar cycle response has been consistently characterized by statistically significant positive responses in the upper and lower stratosphere and by statistically insignificant responses in the middle stratosphere ($28-38 km altitude). This vertical structure differs from that predicted by most models. The similar vertical structure in the tropics obtained for separate time intervals (with minimum response invariably near 10 hPa) is difficult to explain by random interference from the QBO and volcanic eruptions in the statistical analysis. The observed increase in tropical total column ozone approaching the cycle 23 maximum during the late 1990s occurred primarily in the lower stratosphere below the 30 hPa level. A mainly dynamical origin for the solar cycle total ozone variation at low latitudes is therefore likely. The amplitude of the solar cycle ozone variation in the tropical upper stratosphere derived here is somewhat reduced in comparison to earlier results. Additional data are needed to determine whether this upper stratospheric response is or is not larger than model estimates.Citation: Soukharev, B. E., and L. L. Hood (2006), Solar cycle variation of stratospheric ozone: Multiple regression analysis of longterm satellite data sets and comparisons with models,

At northern midlatitudes over the 1979-2002 time period, column ozone trends are observed to have maximum negative amplitudes in February and March. Here, the portion of the observed ozone interannual variability and trends during these months that can be attributed to two specific dynamical transport processes is estimated using correlative and regression methods. In approximate agreement with a recent independent study, 18%-25% of the observed maximum negative trend is estimated to be due to long-term changes in the diabatic (Brewer-Dobson) circulation driven by global-scale changes in planetary wave [Eliassen-Palm (EP) flux] forcing. In addition, 27%-31% of the observed maximum midlatitude trend during these months is estimated to be due to long-term changes in local nonlinear synoptic wave forcing as deduced from correlated interannual variations of zonal mean ozone and Ertel's potential vorticity. Like long-term decreases in the Brewer-Dobson circulation, this trend component reflects an overall net increase in the polar vortex strength, which is associated with increased numbers of anticyclonic, poleward-breaking Rossby waves at northern midlatitudes. Together, these components can explain approximately 50% of the observed maximum negative column ozone trend and interannual variance at northern midlatitudes in February and March. The combined empirical model also approximately simulates a leveling off or slight increase in column ozone anomalies that has been observed for some months and latitudes since the mid-1990s.

Abstract.The results from three 45-year simulations of a coupled chemistry climate model are analysed for solar cycle influences on ozone and temperature. The simulations include UV forcing at the top of the atmosphere, which includes a generic 27-day solar rotation effect as well as the observed monthly values of the solar fluxes. The results are analysed for the 27-day and 11-year cycles in temperature and ozone. In accordance with previous results, the 27-day cycle results are in good qualitative agreement with observations, particularly for ozone. However, the results show significant variations, typically a factor of two or more in sensitivity to solar flux, depending on the solar cycle.In the lower and middle stratosphere we show good agreement also between the modelled and observed 11-year cycle results for the ozone vertical profile averaged over low latitudes. In particular, the minimum in solar response near 20 hPa is well simulated. In comparison, experiments of the model with fixed solar phase (solar maximum/solar mean) and climatological sea surface temperatures lead to a poorer simulation of the solar response in the ozone vertical profile, indicating the need for variable phase simulations in solar sensitivity experiments. The role of sea surface temperatures and tropical upwelling in simulating the ozone minimum response are also discussed.

[1] A decadal variation of tropical lower stratospheric ozone and temperature has previously been identified that correlates positively with the 11 year solar activity cycle. However, the El Niño-Southern Oscillation (ENSO) also influences lower stratospheric ozone and temperature. It is therefore legitimate to ask whether quasi-decadal ENSO variability can contribute to this apparent solar cycle variation, either accidentally because of the short measurement record or physically because solar variability affects ENSO. Here we present multiple regression analyses of available data records to compare differences in results obtained with and without including an ENSO term in the statistical model. In addition, simulations are performed using the NRL NOGAPS-ALPHA GCM for warm/cold ENSO conditions to test for consistency with the ENSO regression results. We find only very minor changes in annual mean solar regression coefficients when an ENSO term is included. However, the observed tropical ENSO response provides useful insights into the origin of the unexpected vertical structure of the tropical solar cycle ozone response. In particular, the ENSO ozone response is negative in the lower stratosphere due to increased upwelling but changes sign, becoming positive in the middle stratosphere (5-10 hPa) due mainly to advective decreases of temperature and NO x , which photochemically increase ozone. A similar mechanism may explain the observed lower stratospheric solar cycle ozone and temperature response and the absence of a significant response in the tropical middle stratosphere.

Abstract. Extreme ozone minima represent localized and temporally brief (several days) reductions in column ozone amounts below some chosen absolute level.