J. M. Castanheira

Unraveling the interactive effects of climate change and oil contamination on laboratory-simulated estuarine benthic communities.

There is growing concern that modifications to the global environment such as ocean acidification and increased ultraviolet radiation may interact with anthropogenic pollutants to adversely affect the future marine environment. Despite this, little is known about the nature of the potential risks posed by such interactions. Here, we performed a multifactorial microcosm experiment to assess the impact of ocean acidification, ultraviolet B (UV-B) radiation and oil hydrocarbon contamination on sediment chemistry, the microbial community (composition and function) and biochemical marker response of selected indicator species. We found that increased ocean acidification and oil contamination in the absence of UV-B will significantly alter bacterial composition by, among other things, greatly reducing the relative abundance of Desulfobacterales, known to be important oil hydrocarbon degraders. Along with changes in bacterial composition, we identified concomitant shifts in the composition of oil hydrocarbons in the sediment and an increase in oxidative stress effects on our indicator species. Interestingly, our study identifies UV-B as a critical component in the interaction between these factors, as its presence alleviates harmful effects caused by the combination of reduced pH and oil pollution. The model system used here shows that the interactive effect of reduced pH and oil contamination can adversely affect the structure and functioning of sediment benthic communities, with the potential to exacerbate the toxicity of oil hydrocarbons in marine ecosystems.

Wave Energy Associated with the Variability of the Stratospheric Polar Vortex

Abstract A study is performed on the energetics of planetary wave forcing associated with the variability of the northern winter polar vortex. The analysis relies on a three-dimensional normal mode expansion of the atmospheric general circulation that allows partitioning the total (i.e., kinetic + available potential) atmospheric energy into the energy associated with Rossby and inertio-gravity modes with barotropic and baroclinic vertical structures. The analysis mainly departs from traditional ones in respect to the wave forcing, which is here assessed in terms of total energy amounts associated with the waves instead of heat and momentum fluxes. Such an approach provides a sounder framework than traditional ones based on Eliassen–Palm (EP) flux diagnostics of wave propagation and related concepts of refractive indices and critical lines, which are strictly valid only in the cases of small-amplitude waves and in the context of the Wentzel–Kramers–Brillouin–Jeffries (WKBJ) approximation. Positive (negati...

Baroclinic Rossby Wave Forcing and Barotropic Rossby Wave Response to Stratospheric Vortex Variability

Abstract An analysis is performed on the dynamical coupling between the variability of the extratropical stratospheric and tropospheric circulations during the Northern Hemisphere winter. Obtained results provide evidence that in addition to the well-known Charney and Drazin mechanism by which vertical propagation of baroclinic Rossby waves is nonlinearly influenced by the zonal mean zonal wind, topographic forcing constitutes another important mechanism by which nonlinearity is introduced in the troposphere–stratosphere wave-driven coupled variability. On the one hand, vortex variability is forced by baroclinic Rossby wave bursts, with positive (negative) peaks of baroclinic Rossby wave energy occurring during rapid vortex decelerations (accelerations). On the other hand, barotropic Rossby waves of zonal wavenumbers s = 1 and 3 respond to the vortex state, and strong evidence is presented that such a response is mediated by changes of the topographic forcing due to zonal mean zonal wind anomalies progres...

Using a Physical Reference Frame to Study Global Circulation Variability

Abstract The 3D structures of the free oscillations of an adiabatic and hydrostatic atmosphere around a basic state at rest were used as a physical filtering for atmospheric data. This filtering procedure allows for the consideration of the three primitive variables (u, υ, ϕ) over the whole atmosphere simultaneously. Accordingly, the computed statistics do not simply rely on the information provided by a single variable of circulation, such as the 500-hPa geopotential field. Using this method, two classical patterns were isolated in the barotropic component of the circulation, one resembling the Pacific–North America (PNA) pattern, the other similar to the North Atlantic Oscillation (NAO) pattern in summer. Associating the barotropic and the second baroclinic components, a coupling in variability was retrieved between the strength of the winter stratospheric polar vortex and the tropospheric circulation over the North Atlantic. Until now these modes had only been recovered by means of statistical analysis...

A Detailed Normal-Mode Energetics of the General Circulation of the Atmosphere

AbstractAn energetics formulation is here introduced that enables an explicit evaluation for the conversion rates between available potential energy and kinetic energy, the nonlinear interactions of both energy forms, and their generation and dissipation rates, in both the zonal wavenumber and vertical mode domains. The conversion rates between available potential energy and kinetic energy are further decomposed into the contributions by the rotational (Rossby) and divergent (gravity) components of the circulation field. The computed energy terms allow one to formulate a detailed energy cycle describing the flow of energy among the zonal mean and eddy components, and also among the barotropic and baroclinic components. This new energetics formulation is a development of the 3D normal-mode energetics scheme. The new formulation is applied on an assessment of the energetics of winter (December–February) circulation in the 40-yr ECMWF Re-Analysis (ERA-40), the 25-yr Japan Meteorological Agency Reanalysis (JR...

Annular versus Nonannular Variability of the Northern Hemisphere Atmospheric Circulation

Abstract The annular variability of the northern winter extratropical circulation is reassessed based on reanalysis data that are dynamically filtered by normal modes. One-half of the variability of the monthly averaged barotropic zonally symmetric circulation of the Northern Hemisphere is statistically distinct from the remaining variability and is represented by its leading empirical orthogonal function (EOF) alone. The daily time series of the circulation anomalies projected onto the leading EOF is highly correlated (r ≥ 0.7) with the lower-stratospheric northern annular mode (NAM) indices showing that annular variability extends from the stratosphere deep into the troposphere. However, the geopotential and wind anomalies associated with the leading principal component (PC1) of the barotropic zonally symmetric circulation are displaced northward relative to the zonal mean anomalies associated with the PC1 of the geopotential height variability at single-isobaric tropospheric levels. The regression patt...

Diagnosis of Free and Convectively Coupled Equatorial Waves

A methodology for diagnosis of free and convectively coupled equatorial waves (CCEWs) is reviewed and illustrated for Kelvin and mixed Rossby–gravity (MRG) waves. The method is based on prefiltering of the geopotential and horizontal wind, using three-dimensional normal mode functions of the adiabatic linearized equations of a resting atmosphere, followed by space–time power and cross-spectral analysis applied to the normal-mode-filtered fields and the outgoing long-wave radiation (OLR) to identify spectral regions of coherence. The methodology is applied to geopotential and horizontal wind fields produced by European Centre for Medium-Range Weather Forecasts interim reanalysis and OLR data produced by the National Oceanic and Atmospheric Administration. The same type of data simulated by two climate models that participated in the fifth phase of the climate model intercomparison project are also used. Overall, simulation of free and CCEWs was achieved by the models with moderate success. Kelvin and MRG waves were identified in the space–time spectral domains, using both observationally based and climate model datasets. Other nonequatorial waves, classified as tropical depression and extratropical storm track activity, along with the Madden–Julian oscillation were also observed. However, significant deviations were also evident in the models, which may help identification of deficiencies in the models’ simulation schemes for some physical processes. Therefore, this diagnosis method should be a useful procedure for climate model validation and model benchmarking.