El Niño-Southern Oscillation in Tropical Column Ozone and A 3.5-year signal in Mid-Latitude Column Ozone Jingqian Wang, 1* Steven Pawson, 2 Baijun Tian, 3 Run-Lie Shia, 4 Yuk L. Yung, 4 and Xun Jiang 1 1 Department of Earth and Atmospheric Sciences, University of Houston, TX 77204, USA. 2 Global Modeling and Assimilation Office, NASA GSFC, Code 610.1, Greenbelt, MD 20771, USA. 3 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA. 4 Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA Abstract In this work, the impact of El Niño-Southern Oscillation (ENSO) on the tropical column ozone, tropical tropopause pressure, and the 3.5-year ozone signal in the mid-latitude column ozone are examined by Version 1 of the Goddard Earth Observation System Chemistry-Climate Model (GEOS CCM) [Pawson et al., 2008]. Observed monthly-mean sea surface temperature and sea ice between 1951 and 2004 were used as boundary conditions for the model. The ENSO signal is the dominant mode in the tropical column ozone variability in the GEOS CCM, capturing 65.8% of the total variance. The spatial pattern of this mode is similar to that in Total Ozone Mapping Spectrometer (TOMS) observations between Nov 1978 and Apr However, there are some discrepancies in ozone spatial pattern in the southern hemisphere between the GEOS CCM and TOMS. There is also a clear ENSO signal in the tropical tropopause pressure in the GEOS CCM, which may be the cause of the ENSO signal in the column ozone in the GEOS CCM. The regression coefficient between the model O 3 and the model tropopause pressure is 0.78 DU/hPa, which is consistent with observations. A 3.5-yr signal is found in the monthly mean ozonesonde data in the mid-latitude. The 3.5-yr signal is also found in the column ozone simulated by the GEOS CCM when similar analysis is applied. Using Empirical Mode Decompostion (EMD) analysis method, the 3.5-yr signal is very significant in both ozonesonde data and model data, which suggests that the model with realistic ENSO can reproduce the 3.5-yr signal. So it is likely that the 3.5-yr signal is from the ENSO signal.  Data and Model: I: Goddard Earth Observation System, Version 4 (GEOS-4) Chemistry-Climate Model (GEOS CCM)  Column Ozone: Ω S  Tropopause Pressure: P T II: Ozonesonde Data ( ) III: Sea Surface Temperature: SST [Rayner et al., 2003]  Methods: I: Remove seasonal cycle and trend from data. II: Apply Principal Component Analysis [Preisendorfer, 1988] to the deseasonalized and detrended data. III: Power Spectral Analysis will be applied to Principal Component (PC) timeseries. IV: Independent Method, Empirical mode decomposition (EMD) [Huang et al., 1998], will be applied to ozonesonde and model outputs ENSO Signals Table 1: Variances, spectral peaks, and correlations (Lag = 0) for the first modes of the sea surface temperature, tropopause pressure, and column ozone. The numbers in parentheses denote significance levels.  The first modes of variability determined by the PCA capture 46.9%, 33.9%, and 63.8% of the total variance in SST, P T, and Ω S, respectively.  Evidence is first presented that the first modes of variability captured by the PCA are related to ENSO. Time Series of PC1 Power Spectrum of PC1 Spatial Pattern of Mode 1 Conclusions  The first modes in the model Ω S and P T are related to ENSO, which capture 63.8% and 33.9% of the total variances.  ENSO spatial pattern are well captured in the model column ozone.  The 3.5-yr ozone signal was found in both observations and GEOS-CCM model data.  EMD method was also used to analysis the data. Consistent results are found in observations and model column ozone.  The possible source for 3.5-y period is related to ENSO signal. Figure 4: (a) First mode of column O 3 averaged in Niño-3.4 region (solid line) and first mode of tropopause pressure in Niño-3.4 region (dotted line). (b) Scatter plot of O 3 against the tropopause pressure. Solid line is the linear fitting of the dots. Power Spectra Ozonesonde Data Figure 5: Power spectra of ozonesonde data (left) and GEOS-CCM result (right). Dash-dot lines and dashed lines correspond to 10% and 5% significance levels, respectively.  Figure 1 shows PC1 time series for the first modes of sea surface temperature (black solid line), tropopause pressure (blue dotted line), and column ozone (red dashed line). SOI index is shown by green dash-dotted line. Data and Methods Figure 2: (a) Power spectrum of PC1 for the first mode of SST from GEOS-4 CCM. (b) Power spectrum of PC1 for the first mode of tropopause pressure from GEOS-4 CCM. (c) Power spectrum of PC1 for the first mode of column ozone from GEOS-4 CCM. Mode 1 of Variance captured Spectral PeaksCorrelations (significance level) with: SOISST (PC1)P T (PC1) SST46.9%4-5 years0.88 (0.1%)  PTPT 33.9% 17 months 5 years 0.65 (0.1%)0.72 (0.1%)  ΩSΩS 63.8%17 months 2-5 years 0.53 (0.1%)0.57 (0.1%)0.82 Regression Between O 3 and Tropopause Pressure GEOS-CCM Data Hradec Belsk Potsdam Hohenpeissenberg ArosaToronto Sapporo Nashville Potsdam HohenpeissenbergHradec Belsk ArosaToronto NashvilleSapporo Figure 3: (a) The spatial pattern of the first mode for SST in the tropics. (b) The spatial pattern of the first mode for tropopause pressure from GEOS-4 CCM in the tropics. (c) The spatial pattern of the first mode for column ozone from GEOS-4 CCM in the tropics.  Power spectra of the PC1s of SST, P T and Ω S all reveal strong spectral peaks near 3-7 years, which are typical of ENSO variations.  For observation data, there are significant peaks between 3-4 years: The power spectra of Potsdam, Hohenpeissenberg, and Sappor are within 10% to 5% significance levels; In the other five stations, Belsk, Hradec, Arosa, Toronto, Nashiville, 3.5-yr signals are within 5% significance level.  The 3.5-yr signal could also be found in the model column ozone and is significant.  3.5-yr signals of observation and model ozone both appear in the fourth mode of EMD results.  Spatial pattern in Fig. 3a corresponds to the SST anomalies in the Niño-3.4 region.  Large anomalies in P T over the subtropics is the Rossby- wave response of ENSO convection anomaly.  The Ozone spatial pattern is very similar to the ENSO spatial pattern in the TOMS column ozone data in Camp et al. [2003].  The two time series of mean value for the first mode of the column ozone in the Niño-3.4 region and the tropopause pressure correlate well.  The correlation coefficient is  The regression coefficient between the O 3 and tropopause pressure is 0.71 DU/hPa.