Stratospheric influence on idealised baroclinic life cycles

<p>The importance of understanding the dynamical coupling of troposphere and stratosphere to make accurate weather and climate predictions is well-known. Over the past years and decades various signatures of such a<br>coupling have been discovered. A very robust result, for example, seems to be an equatorward shift of the tropospheric eddy driven jet following sudden stratospheric warming events, where the westerly winds of the stratospheric polar vortex weaken or even reverse. However, many aspects of this fundamental coupling are still not fully understood and research on how the state of the stratosphere can influence the tropospheric circulation and what dynamical processes are involved is still ongoing.</p><p><br>An important such process arises due to the interaction of a sharp, localised maximum in potential vorticity gradient near the tropopause with baroclinic eddies in the troposphere. Here, we analyse the sensitivity of baroclinic wave development and evolution to changes of various basic state characteristics, by performing a series of idealised baroclinic eddy life cycle experiments. Special attention is paid to sensitivities associated with the dynamical state of the stratosphere. We find that the final (steady) state of the life cycle simulations corresponds to an equatorward shift of the tropospheric jet in cases where the initial conditions do not include a stratospheric polar vortex (such as following sudden warming events) compared to those that do. These results further support the idea that the stratospheric state can strongly influence tropospheric dynamics and, in particular, highlight the robustness of the jet shift response following sudden warmings, that can be seen in a range of observations and numerical model experiments.</p>

Southern Hemisphere jet stream: emergent constraints on future shift in zonally varying framework

<p>IPCC climate models (CMIP3/5) predict a poleward shift of the Southern Hemisphere (SH) jet stream under global warming, with a large spread across the models. Efforts to find emergent constraints for the future jet shift (response) have relied on the simulated present-day jet position (observable). However, this has been investigated primarily in a zonal-mean framework, which averages out important zonal asymmetries. In this study, we revisit the problem allowing for variations in the longitude, height and season of the response to gain a better physical understanding of the nature of the future jet shift in individual models. Results from a manual data analysis will help guide an exploration of the problem using a big data approach, in particular, the application of a genetic algorithm that finds optimal solutions based on iterative random selection within large sample data spaces.</p>

Cannabis use is associated with sexually dimorphic changes in executive control of visuospatial decision-making

When the outcome of a choice is less favourable than expected, humans and animals typically shift to an alternate choice option. Several lines of evidence indicate that this “lose-shift” responding is an innate sensorimotor response strategy that is normally suppressed by executive function. Therefore, the lose-shift response provides a covert gauge of cognitive control over choice mechanisms. We report here that the spatial position, rather than visual features, of choice targets drives the lose-shift effect. Furthermore, the ability to inhibit lose-shift responding to gain reward is different among male and female habitual cannabis users. Increased self-reported cannabis use was concordant with suppressed response flexibility and an increased tendency to lose-shift in women, which reduced performance in a choice task in which random responding is the optimal strategy. On the other hand, increased cannabis use in men was concordant with reduced reliance on spatial cues during decision-making, and had no impact on the number of correct responses. These data (63,600 trials from 106 participants) provide strong evidence that spatial-motor processing is an important component of economic decision-making, and that its governance by executive systems is different in men and women who use cannabis frequently.