I: Interannual variability of stratospheric ozone and temperature. II: Seasonal cycle of N2O

Abstract

This dissertation is a collection of empirical and modeling studies focusing on the interannual variability (IAV) of the stratospheric ozone and temperature. The IAV of O3 in the high latitude is characterized by four main modes in both hemispheres. Similar spatial patterns and trends are simulated by the Goddard Earth Observation System, Version 4 (GEOS-4) chemistry-climate model (CCM). The El Nino-Southern Oscillation signal in column ozone is also simulated well by the GEOS-4 CCM in the tropics. To study the Quasi-biennial oscillation (QBO) and QBO-Annual Beat (QBO-AB) in column ozone, the Caltech/JPL two-dimensional (2-D) chemistry and transport model (CTM) has been used. The 2-D CTM provides realistic simulations of the seasonal and IAV of ozone in the tropics. The phase and amplitude of the QBO are well captured by the model. The QBO-AB found in the simulated ozone agrees well with that in the observed data. An idealized 2-D interactive chemistry, radiation, and dynamic model (CRDM) is used to investigate the spatial patterns of, and mechanism for, the QBO-AB signal in ozone in the tropics and subtropics. An extended EOF analysis reveals the characteristic pattern of the downward propagation of QBO and upward propagation of QBO-AB. The model results are compared to those from the Merged Ozone Data. To understand the IAV and trend in the stratospheric temperature, we apply principal component analysis to observations and global climate model simulations. The cooling trend in the stratosphere is associated with a spatially uniform pattern of stratospheric variability, which is isolated from more common modes of natural IAV such as the Northern Annular Mode. These results are supported by a number of coupled ocean-atmosphere climate model simulations. Finally, a systematic study of the seasonal cycle and its latitudinal variation is carried out for the nitrous oxide data. In order to confirm the weak seasonal signal in the observations, we applied the multi-taper method for the spectrum analysis. The amplitude (peak to peak) of the seasonal cycle of N2O varies from 0.29 ppb (parts-per-billion by mole fraction in dry air) at the South Pole to 1.15 ppb at Alert.