Impacts of horizontal resolution on simulated climate statistics in ECHAM4

The sensitivity of a general circulation model to changes in resolution is studied using the Max Planck Institute for Meteorology (MPI) 19-level model, ECHAM4. Simulations extending over a period between 10 and 15 years, with observed sea surface temperatures as lower boundary conditions from 1979 onward, have been performed using four different horizontal resolutions, T21, T30, T42 and T106. The atmospheric time-mean state and the intraseasonal variability are compared to the European Centre for Medium Range Weather Forecasts (ECMWF) reanalyses and a few other observational datasets. The T30, T42 and T106 simulations are similar in many respects, whereas the T21 simula- tion is qualitatively different. Several effects related to model resolution could be identi- fied, such as increasing tropical upper tropospheric warming with increasing resolution. This is due to more vigorous tropical convection, larger ice water content and, hence, increasing cirrus cloud greenhouse effect. Associated with this increasing warming at higher resolution is a poleward expansion of the zonally averaged circulation regime. On the other hand, the zonally asymmetric component of the circulation, i.e., the stationary waves, improve with higher resolution. Also, higher resolution has a positive impact on regional precipitation patterns which are affected by orography such as the summer mon- soon precipitation over India. Intraseasonal variability has been analyzed only for the higher resolution models, T42 and T106. Compared to the ECMWF reanalyses, both models are able to simulate the intrasea- sonal geopotential height variability, eddy fluxes of heat and momentum, and eddy kinetic energy with reasonable accuracy. This applies to transient eddies in both the bandpass and lowpass regime and to the stationary eddies as well. Some biases can be identified which are more or less independent of resolution. These include the mislocation of the Azores high and the overestimation of its intensity, a cold bias in the polar upper troposphere and lower stratosphere and the poleward and upward displacement of the maxima of geopotential height variability, momentum fluxes and eddy kinetic energy. An important finding is that the operational ECMWF analyses, which have been widely used for model validation, considerably overestimate the lowpass variability, as compared to the reanalyses, due to frequent changes of the forecast model and data assimilation scheme. This implies that the results from our investigations are not directly comparable to previous investigations that used operational analyses for validation

Global solutions for random vorticity equations perturbed by gradient dependent noise, in two and three dimensions

The aim of this work is to prove an existence and uniqueness result of Kato-Fujita type for the Navier-Stokes equations, in vorticity form, in $2-D$ and $3-D$, perturbed by a gradient type multiplicative Gaussian noise (for sufficiently small initial vorticity). These equations are considered in order to model hydrodynamic turbulence. The approach was motivated by a recent result by V. Barbu and the second named author in \cite{b1}, that treats the stochastic $3D$-Navier-Stokes equations, in vorticity form, perturbed by linear multiplicative Gaussian noise. More precisely, the equation is transformed to a random nonlinear parabolic equation, as in \cite{b1}, but the transformation is different and adapted to our gradient type noise. Then global unique existence results are proved for the transformed equation, while for the original stochastic Navier-Stokes equations, existence of a solution adapted to the Brownian filtration is obtained up to some stopping time

The Effect of Early Life Social Stress on Anxiety-like Behaviors and Ethanol Drinking in Female Long-Evans Rats

Among women with Alcohol Use Disorders (AUDs), women have higher rates of anxiety-disorders and are more influenced by early life stress compared to men. Preclinical models have been used to study the relationships between early life stress, anxiety-like behavior, and alcohol intake and preference. However, fewer studies have been done with female rats than male rats. To that end, chronic social instability was utilized as a model of early life stress in females. In this model Long Evans rats are placed in different pairs every day, and this has previously produced anxiety-like behavior in female rats (McCormick et al., 2008). This study extended the McCormick et al. model by including an extra experimental group and including an alcohol self-administration paradigm. Experimental groups were: (1) chronic social instability (pairhoused for 17 days with a novel cage mate introduced every 24h); (2) Social stability; pair-housed with same cage mate daily); (3) Isolated; single housed for entire study); (4) Acute social instability; pair-housed with same cage mate for 16 days but novel cage mate for 24h on last day). A well-validated model for assessment of anxiety-like behavior, the elevated plus maze, was utilized to evaluate anxiety-like behavior after the housing manipulation, and plasma corticosterone (CORT) levels were measured. Following these measures, rats were given a two bottle choice and intermittent access between alcohol and water, and alcohol consumption and preference was measured. Following these measures, no significant differences were found between experimental groups for anxiety-like behavior, CORT levels, or alcohol intake/preference. Thus, further study is needed to find a preclinical model of early life stress that promotes anxiety-like behavior and alcohol consumption

The evolution of the global aerosol system in a transient climate simulation from 1860 to 2100

The evolution of the global aerosol system from 1860 to 2100 is investigated through a transient atmosphere-ocean General Circulation Model climate simulation with interactively coupled atmospheric aerosol and oceanic biogeochemistry modules. The microphysical aerosol module HAM incorporates the major global aerosol cycles with prognostic treatment of their composition, size distribution, and mixing state. Based on an SRES A1B emission scenario, the global mean sulfate burden is projected to peak in 2020 while black carbon and particulate organic matter show a lagged peak around 2070. From present day to future conditions the anthropogenic aerosol burden shifts generally from the northern high-latitudes to the developing low-latitude source regions with impacts on regional climate. Atmospheric residence- and aging-times show significant alterations under varying climatic and pollution conditions. Concurrently, the aerosol mixing state changes with an increasing aerosol mass fraction residing in the internally mixed accumulation mode. The associated increase in black carbon causes a more than threefold increase of its co-single scattering albedo from 1860 to 2100. Mid-visible aerosol optical depth increases from pre-industrial times, predominantly from the aerosol fine fraction, peaks at 0.26 around the sulfate peak in 2020 and maintains a high level thereafter, due to the continuing increase in carbonaceous aerosols. The global mean anthropogenic top of the atmosphere clear-sky short-wave direct aerosol radiative perturbation intensifies to −1.1 W m^−2 around 2020 and weakens after 2050 to −0.6 W m^−2, owing to an increase in atmospheric absorption. The demonstrated modifications in the aerosol residence- and aging-times, the microphysical state, and radiative properties challenge simplistic approaches to estimate the aerosol radiative effects from emission projections

Scaling limit of stochastic dynamics in classical continuous systems

We investigate a scaling limit of gradient stochastic dynamics associated to Gibbs states in classical continuous systems on ${\mathbb R}^d, d \ge 1$. The aim is to derive macroscopic quantities from a given micro- or mesoscopic system. The scaling we consider has been investigated in \cite{Br80}, \cite{Ro81}, \cite{Sp86}, and \cite{GP86}, under the assumption that the underlying potential is in $C^3_0$ and positive. We prove that the Dirichlet forms of the scaled stochastic dynamics converge on a core of functions to the Dirichlet form of a generalized Ornstein--Uhlenbeck process. The proof is based on the analysis and geometry on the configuration space which was developed in \cite{AKR98a}, \cite{AKR98b}, and works for general Gibbs measures of Ruelle type. Hence, the underlying potential may have a singularity at the origin, only has to be bounded from below, and may not be compactly supported. Therefore, singular interactions of physical interest are covered, as e.g. the one given by the Lennard--Jones potential, which is studied in the theory of fluids. Furthermore, using the Lyons--Zheng decomposition we give a simple proof for the tightness of the scaled processes. We also prove that the corresponding generators, however, do not converge in the $L^2$-sense. This settles a conjecture formulated in \cite{Br80}, \cite{Ro81}, \cite{Sp86}

A Normal-Mode Approach to Jovian Atmospheric Dynamics

We propose a nonlinear, quasi-geostrophic, baroclinic model of Jovian atmospheric dynamics, in which vertical variations of velocity are represented by a truncated sum over a complete set of orthogonal functions obtained by a separation of variables of the linearized quasi-geostrophic potential vorticity equation. A set of equations for the time variation of the mode amplitudes in the nonlinear case is then derived. We show that for a planet with a neutrally stable, fluid interior instead of a solid lower boundary, the baroclinic mode represents motions in the interior, and is not affected by the baroclinic modes. One consequence of this is that a normal-mode model with one baroclinic mode is dynamically equivalent to a one layer model with solid lower topography. We also show that for motions in Jupiter's cloudy lower troposphere, the stratosphere behaves nearly as a rigid lid, so that the normal-mode model is applicable to Jupiter. We test the accuracy of the normal-mode model for Jupiter using two simple problem forced, vertically propagating Rossby waves, using two and three baroclinic modes and baroclinic instability, using two baroclinic modes. We find that the normal-road model provide qualitatively correct results, even with only a very limited number of vertical degrees of freedom

ENSO impact on midlatitude circulation patterns in future climate change projections

The remote influence of the leading mode of interannual variability in the Tropics, the El Niño/Southern Oscillation (ENSO), on the northern hemispheric midlatitude circulation in future climate is investigated. For this, IPCC SRES scenarios of the latest version of the coupled climate model ECHAM5/MPI-OM are used. In ensembles of future climate change projections it is found, that a changing state of ENSO with increased variability has a pronounced influence on the dominant midlatitude circulation pattern, namely the Pacific North America (PNA) pattern and the North Atlantic Oscillation (NAO). More explicitly, in the 21st and 22nd century, a positive (negative) phase of ENSO is more likely followed by a positive (negative) PNA index and negative (positive) NAO index than it is observed in the 20th century. Correlation coefficients between the winter mean Niño3.4 index and the NAO index increase substantially from the 20th centur