From local to global deformation quantization of Poisson manifolds

We give an explicit construction of a deformation quantization of the algebra of functions on a Poisson manifolds, based on Kontsevich's local formula. The deformed algebra of functions is realized as the algebra of horizontal sections of a vector bundle with flat connection.Comment: 16 pages. Reference and dedication added. Sign corrected, remark on Poisson vector fields adde

Fedosov connections on jet bundles and deformation quantization

We review our construction of star-products on Poisson manifolds and discuss some examples. In particular, we work out the relation with Fedosov's original construction in the symplectic case.Comment: Contribution to the proceedings of the conference "Deformation Quantization", Strasbourg, May 31-June 2, 200

Dolbeault and JJ-invariant cohomologies on almost complex manifolds

In this paper we relate the cohomology of $J$-invariant forms to the Dolbeault cohomology of an almost complex manifold. We find necessary and sufficient condition for the inclusion of the former into the latter to be true in different cases. We also extend some results obtained by J. Cirici and S.O. Wilson about the computation of the left-invariant cohomology of nilmanifolds to the setting of solvmanifolds. Various examples are given, for manifolds of dimension $4$ and $6$

Tropical moist convection an important driver of Atlantic Hadley circulation variability

The exact role of moist deep convection and associated latent heating in the tropical Hadley circulation has been debated for many years. This study investigates the connection between moist convection and the strength of the upper-level meridional circulation over the tropical Atlantic, focusing mainly on one particular boreal winter season. There is a close relationship between events of strong organised deep convection and enhanced meridional upper-level wind on many occasions. A process-based analysis of specific events suggests that moist convection impacts Hadley circulation variability on time-scales of days to months through equatorial wave dynamics. Equatorial waves play an important role, both directly by contributing to the Hadley circulation via their meridional wind component and also indirectly by triggering moist convection through low-level convergence. Specific Hadley circulation surge events, short-term, regionally confined intensifications of the upper-level meridional circulation, can be attributed to enhanced organised moist convection and equatorial wave activity in many cases, with implications for trade wind cloudiness. The findings thus elucidate how the mean Hadley circulation is shaped by and composed of temporally and spatially varying convection–circulation interactions

Climate feedback efficiency and synergy

The Author(s) 2013. This article is published with open access at Springerlink.com Abstract Earth’s climate sensitivity to radiative forcing induced by a doubling of the atmospheric CO2 is deter-mined by feedback mechanisms, including changes in atmospheric water vapor, clouds and surface albedo, that act to either amplify or dampen the response. The climate system is frequently interpreted in terms of a simple energy balance model, in which it is assumed that individual feedback mechanisms are additive and act independently. Here we test these assumptions by systematically control-ling, or locking, the radiative feedbacks in a state-of-the-art climate model. The method is shown to yield a near-perfect decomposition of change into partial temperature contri-butions pertaining to forcing and each of the feedbacks. In the studied model water vapor feedback stands for about half the temperature change, CO2-forcing about one third, while cloud and surface albedo feedback contributions are relatively small. We find a close correspondence between forcing, feedback and partial surface temperature response for the water vapor and surface albedo feedbacks, while the cloud feedback is inefficient in inducing surface tempera-ture change. Analysis suggests that cloud-induced warming in the upper tropical troposphere, consistent with rising convective cloud anvils in a warming climate enhances the negative lapse-rate feedback, thereby offsetting some of the warming that would otherwise be attributable to this positive cloud feedback. By subsequently combining feedback mechanisms we find a positive synergy acting between the water vapor feedback and the cloud feedback; that is, the combined cloud and water vapor feedback is greater than the sum of its parts. Negative synergies sur-round the surface albedo feedback, as associated cloud and water vapor changes dampen the anticipated climate change induced by retreating snow and ice. Our results highlight the importance of treating the coupling between clouds, water vapor and temperature in a deepening troposphere

Uncertainty and risk in climate projections for the 21st century: comparing mitigation to non-intervention scenarios

Probabilistic climate projections based on two SRES scenarios, an IMAGE reference scenario and five IMAGE mitigation scenarios (all of them multi-gas scenarios) using the Bern2.5D climate model are calculated. Probability distributions of climate model parameters that are constrained by observations are employed as input for the climate model. The sensitivity of the resulting distributions with respect to prior assumptions on climate sensitivity is then assessed. Due to system inertia, prior assumptions on climate sensitivity play a minor role in the case of temperature projections for the first half of the 21st century, but these assumptions have a considerable influence on the distributions of the projected temperature increase in the year 2100. Upper and lower probabilities for exceeding 2°C by the year 2100 are calculated for the different scenarios. Only the most stringent mitigation measures lead to low probabilities for exceeding the 2°C threshold. This finding is robust with respect to our prior assumptions on climate sensitivity. Further, probability distributions of total present-value damages over the period 2000-2100 for the different scenarios are calculated assuming a wide range of damage cost functions, and the sensitivity of these distributions with respect to the assumed discount rate is investigated. Absolute values of damage costs depend heavily on the chosen damage cost function and discount rate. Nevertheless, some robust conclusions are possibl

Neurovascular coupling during visual stimulation in Multiple Sclerosis: a MEG-fMRI study

The process of neurovascular coupling ensures that increases in neuronal activity are fed by increases in cerebral blood flow. Evidence suggests that neurovascular coupling may be impaired in multiple sclerosis (MS) due to a combination of brain hypoperfusion, altered cerebrovascular reactivity and oxygen metabolism, and altered levels of vasoactive compounds. Here, we tested the hypothesis that neurovascular coupling is impaired in MS. We characterised neurovascular coupling as the relationship between changes in neuronal oscillatory power within the gamma frequency band (30-80 Hz), as measured by magnetoencephalography (MEG), and associated haemodynamic changes (blood oxygenation level dependent, BOLD, and cerebral blood flow, CBF) as measured by functional MRI. We characterised these responses in the visual cortex in 13 MS patients and in 10 matched healthy controls by using a reversing checkerboard stimulus at five visual contrasts. There were no significant group differences in visual acuity, P100 latencies, occipital grey matter (GM) volumes and baseline CBF. However, in the MS patients we found a significant reduction in peak gamma power, BOLD and CBF responses. There were no significant differences in neurovascular coupling between groups, in the visual cortex. Our results suggest that neuronal and vascular responses are altered in MS. Gamma power reduction could be an indicator of GM dysfunction, possibly mediated by GABAergic changes. Altered hemodynamic responses confirm previous reports of a vascular dysfunction in MS. Despite altered neuronal and vascular responses, neurovascular coupling appears to be preserved in MS, at least within the range of damage and disability studied here

The atmospheric boundary layer and the "gray zone" of turbulence: a critical review

Recent increases in computing power mean that atmospheric models for numerical weather prediction are now able to operate at grid spacings of the order of a few hundred meters, comparable to the dominant turbulence length scales in the atmospheric boundary layer. As a result, models are starting to partially resolve the coherent overturning structures in the boundary layer. In this resolution regime, the so‐called boundary‐layer "gray zone", neither the techniques of high‐resolution atmospheric modeling (a few tens of meters resolution) nor those of traditional meteorological models (a few kilometers resolution) are appropriate because fundamental assumptions behind the parameterizations are violated. Nonetheless, model simulations in this regime may remain highly useful. In this paper, a newly‐formed gray‐zone boundary‐layer community lays the basis for parameterizing gray‐zone turbulence, identifies the challenges in high‐resolution atmospheric modeling and presents different gray‐zone boundary‐layer models. We discuss both the successful applications and the limitations of current parameterization approaches, and consider various issues in extending promising research approaches into use for numerical weather prediction. The ultimate goal of the research is the development of unified boundary‐layer parameterizations valid across all scales