Charles D. Camp

The Influence of the Solar Cycle and QBO on the Late-Winter Stratospheric Polar Vortex

Abstract A statistical analysis of 51 years of NCEP–NCAR reanalysis data is conducted to isolate the separate effects of the 11-yr solar cycle (SC) and the equatorial quasi-biennial oscillation (QBO) on the Northern Hemisphere (NH) stratosphere in late winter (February–March). In a four-group [SC maximum (SC-max) versus minimum (SC-min) and east-phase versus west-phase QBO] linear discriminant analysis, the state of the westerly phase QBO (wQBO) during SC-min emerges as a distinct least-perturbed (and coldest) state of the stratospheric polar vortex, statistically well separated from the other perturbed states. Relative to this least-perturbed state, the SC-max and easterly QBO (eQBO) each independently provides perturbation and warming as does the combined perturbation of the SC-max–eQBO. All of these results (except the eQBO perturbation) are significant at the 95% confidence level as confirmed by Monte Carlo tests; the eQBO perturbation is marginally significant at the 90% level. This observational res...

Temporal and spatial patterns of the interannual variability of total ozone in the tropics

The recently constructed gridded Merged Ozone Data (MOD) set, combining the monthly mean column abundances collected by the Total Ozone Mapping Spectrometer (TOMS) and the Solar Backscatter Ultraviolet (SBUV and SBUV/2) instruments, provides a nearly continuous record from late 1978 to 2000 on a 5° × 10° latitude-longitude grid. The precision of these measurements and their calibration allow very small signals, ∼1% of total column ozone, to be clearly seen. Using MOD, we have carried out an empirical orthogonal function (EOF) study of the temporal and spatial patterns of the interannual variability of total column ozone in the tropics. The first four EOFs of our study capture over 93% of the variance of the deseasonalized data. The leading two EOFs of our study, respectively accounting for 42% and 33% of the variance, display structures attributable to the quasi-biennial oscillation(QBO), with influence from a decadal oscillation. The third EOF (15% of the variance) represents an interaction between the QBO and an annual cycle. The fourth EOF (3% of the variance) is related to the El Nino - Southern Oscillation. This EOF decomposition is robust; nearly identical patterns occur in the decomposition of various equatorial latitude bands of MOD and similar patterns occur in the analysis of the deseasonalized TOMS data set, a shorter record with a more finely resolved spatial grid. For comparison, similar decompositions were performed for dynamical fields from the reanalysis product from the National Centers for Environmental Prediction and the National Center for Atmospheric Research. Using these analyses, we found possible connections between the deduced patterns in ozone and the climate variables.

Solar cycle warming at the Earth's surface in NCEP and ERA-40 data: A linear discriminant analysis

[1] The total solar irradiance (TSI) has been measured by orbiting satellites since 1978 to vary on an 11-year cycle by about 0.08%. Because of previous controversies on the reality of solar cycle response at the surface, in this work we discuss the robustness of the solar response with respect to analysis methods, data sets and periods used. Furthermore we concentrate on the globally coherent signal. Two reanalysis data sets are used: one is from National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP for short) and the other is the European Centre for Medium-Range Weather Forecasts (ECMWF)’s most recent reanalysis denoted by ERA-40. Three analysis methods are considered, with increasing sophistication. Within each data set the analysis results are consistent with each other (i.e., each within the other’s error bars), with the method of linear discriminant analysis (LDA) yielding the smallest error bar and the unfiltered global mean data yielding the largest error bar in the temperature amplitude. All three methods and both data sets are able to demonstrate that the 11-year signal is statistically significant and attributable (i.e., related) to the solar cycle. We deduce the spatial surface pattern over the globe which best distinguishes the solar maximum years from the solar minimum years using the LDA method. The resulting warming pattern shows clearly the polar amplification of warming and the preference for continents over oceans. We propose that the magnitude of the surface warming is consistent with direct solar radiative forcing if positive feedback processes such as ice albedo, water vapor/lapse rate and cloud feedbacks, similar to some of those studied for the greenhouse warming problem, are incorporated. It does not appear to be necessary to invoke some previously proposed exotic indirect mechanisms for an explanation of the observed solar signal. Citation: Tung, K. K., and C. D. Camp (2008), Solar cycle warming at the Earth’s surface in NCEP and ERA-40 data: A linear discriminant analysis, J. Geophys. Res., 113, D05114, doi:10.1029/2007JD009164.

Quasi‐biennial oscillation and quasi‐biennial oscillation–annual beat in the tropical total column ozone: A two‐dimensional model simulation

The National Centers for Environmental Prediction–Department of Energy Reanalysis 2 data are used to calculate the monthly mean meridional circulation and eddy diffusivity from 1979 to 2002 for use in the California Institute of Technology–Jet Propulsion Laboratory two-dimensional (2-D) chemistry and transport model (CTM). This allows for an investigation of the impact of dynamics on the interannual variability of the tropical total column ozone for all years for which the Total Ozone Mapping Spectrometer and the Solar Backscatter Ultraviolet merged total ozone data are available. The first two empirical orthogonal functions (EOFs) of the deseasonalized and detrended stratospheric stream function capture 88% of the total variance on interannual timescales. The first EOF, accounting for over 70% of the interannual variance, is related to the quasi-biennial oscillation (QBO) and its interaction with annual cycles, the QBO-annual beat (QBO-AB). The 2-D CTM provides realistic simulations of the seasonal and interannual variability of ozone in the tropics. The equatorial ozone anomaly from the model is close to that derived from the observations. The phase and amplitude of the QBO are well captured by the model. The magnitude of the QBO signal is somewhat larger in the model than it is in the data. The QBO-AB found in the simulated ozone agrees well with that in the observed data.

Interannual Variability and Trends of Extratropical Ozone. Part I: Northern Hemisphere

The authors apply principal component analysis (PCA) to the extratropical total column ozone from the combined merged ozone data product and the European Centre for Medium-Range Weather Forecasts assimilated ozone from January 1979 to August 2002. The interannual variability (IAV) of extratropical O3 in the Northern Hemisphere (NH) is characterized by four main modes. Attributable to dominant dynamical effects, these four modes account for nearly 60% of the total ozone variance in the NH. The patterns of variability are distinctly different from those derived for total O3 in the tropics. To relate the derived patterns of O3 to atmospheric dynamics, similar decompositions are performed for the 30–100-hPa geopotential thickness. The results reveal intimate connections between the IAV of total ozone and the atmospheric circulation. The first two leading modes are nearly zonally symmetric and represent the connections to the annular modes and the quasi-biennial oscillation. The other two modes exhibit in-quadrature, wavenumber-1 structures that, when combined, describe the displacement of the polar vortices in response to planetary waves. In the NH, the extrema of these combined modes have preferred locations that suggest fixed topographical and land–sea thermal forcing of the involved planetary waves. Similar spatial patterns and trends in extratropical column ozone are simulated by the Goddard Earth Observation System chemistry–climate model (GEOS-CCM). The decreasing O3 trend is captured in the first mode. The largest trend occurs at the North Pole, with values 1 Dobson Unit (DU) yr 1 . There is almost no trend in tropical O3. The trends derived from PCA are confirmed using a completely independent method, empirical mode decomposition, for zonally averaged O3 data. The O3 trend is also captured by mode 1 in the GEOS-CCM, but the decrease is substantially larger than that in the real atmosphere.

The sensitivity of tropospheric methane to the interannual variability in stratospheric ozone

The dominant processes affecting the concentration of tropospheric methane on interannual timescales are the biospheric and anthropogenic sources and changes in the abundance of the hydroxyl radical caused by the changes in the UV flux which result from changes in stratospheric ozone abundance. We have carried out an empirical study of the sensitivity of the methane to fluctuations in ozone column abundance. This analysis was carried out using monthly mean surface methane concentrations measured by the National Oceanic and Atmospheric Administration – Climate Monitoring and Diagnostics Laboratory (NOAA-CMDL) Global Cooperative Air Sampling Network from 1983 to 1998 and ozone column abundances obtained by the Total Ozone Mapping Spectrometer (TOMS) and the EP TOMS instruments over the same time period. We focused on interannual variability with periods between 15 and 60 months, in which interval the dominant ozone fluctuation is the quasi-biennial oscillation (QBO), with a period of approximately 29 months. In order to isolate the response of methane to ozone from the effects of variability in the sources and transport of methane, we restricted our analysis to data at mid-latitudes in the southern hemisphere. A statistical study shows that the sensitivity factor α≡−d(ln[CH_4])/d(ln[O_3])=−0.038±0.009. The response of CH_4 lags approximately 6 months behind the forcing by O_3. A simple model was used to interpret the empirical results. Our results confirm that any mechanism that affects stratospheric ozone impacts the oxidizing potential of the troposphere. CH_4 fluctuations provide a quantitative measure of this important effect linking the upper and the lower atmosphere.