ALBERT

Description: [1]  Ozone changes and associated climate impacts in the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations are analyzed over the historical (1960-2005) and future (2006-2100) period under four Representative Concentration Pathways (RCP). In contrast to CMIP3, where half of the models prescribed constant stratospheric ozone, CMIP5 models all consider past ozone depletion and future ozone recovery. Multimodel mean climatologies and long-term changes in total and tropospheric column ozone calculated from CMIP5 models with either interactive or prescribed ozone are in reasonable agreement with observations. However, some large deviations from observations exist for individual models with interactive chemistry, and these models are excluded in the projections. Stratospheric ozone projections forced with a single halogen but four greenhouse gas (GHG) scenarios show largest differences in the northern midlatitudes and in the Arctic in spring (~20 and 40 DU by 2100, respectively). By 2050 these differences are much smaller and negligible over Antarctica in austral spring. Differences in future tropospheric column ozone are mainly caused by differences in methane concentrations and stratospheric input, leading to ~10 DU increases compared to 2000 in RCP 8.5. Large variations in stratospheric ozone particularly in CMIP5 models with interactive chemistry drive correspondingly large variations in lower stratospheric temperature trends. The results also illustrate that future SH summer-time circulation changes are controlled by both the ozone recovery rate and the rate of GHG increases, emphasizing the importance of simulating and taking into account ozone forcings when examining future climate projections.

Description: Here we explore the effect of a series of low-permeability tilted baffles on the ascent of a buoyant fluid injected into a porous rock from a linear well, motivated by several industrial processes, particularly CO 2 sequestration. We first consider, both theoretically and experimentally, the dynamics associated with flow past an individual inclined baffle; if the incident flux is sufficiently large then a pool of injectate grows beneath the baffle and spills over both ends, partitioning the flux, but otherwise the injectate only flows over the updip end of the baffle, leaving a stagnant zone under the downdip part of the baffle. In a multi-layered system, the flow may then be described using nonlinear recurrence relations based on the flow past an individual baffle. Using this approach, in the particular case in which there is a regular distribution of baffles, we show that, on a scale greater than individual baffles, the flow adjusts to a plume of constant width rising at an angle χ to the vertical, which depends on the geometry of the baffles. This constant-width plume may be described by an effective directional permeability (k p, 0) at angles χ, π/2-χ ) to the vertical where we find k p ≈ k, where k is the effective permeability of the regions between baffles. Within the boundaries of this plume the majority of pore space is bypassed. Indeed, the plume-scale effective porosity is largely associated with the pools of injectate which collect beneath each baffle. We show that since the constant-width plume has such a large lateral extent, the total pore space occupied by the plume, per unit height, is larger than for a homogeneous formation. Furthermore, these pools lead to a large surface area between injectate and formation water, which enhances the reaction of the injectate with the formation water. However, we also show that, in steady state, it may be hard to determine this plume-scale effective porosity since the ratio of the effective Darcy speed and the effective interstitial speed of the plume only relates to the porosity of the updip part of these pools, in which the injectate is flowing. © 2011 Cambridge University Press.

Description: We consider the buoyancy-driven flow in an inclined porous layer which results when fluid of different temperature and composition to that in the reservoir is injected from a horizontal line well. The thermal inertia of the porous matrix leads to a transition in the temperature of the injectate as it spreads from the well and heats up to reservoir temperature. Since the buoyancy and viscosity of the injectate change across this thermal transition, the alongslope characteristic speed of the current also changes. Density and viscosity typically decrease with temperature and, so, for injectate that is positively buoyant at reservoir temperature, the changes in density and viscosity with temperature have complementary effects on the characteristic speed. In contrast, for injectate that is negatively buoyant at reservoir temperature, the changes in viscosity and density with temperature have competing influences on the characteristic speed. The change in characteristic speed, combined with the change in buoyancy across the thermal transition, leads to a series of different flow morphologies with the thermally adjusted injectate either running ahead of or lagging behind the original injectate. By approximating the thermal transition as a discrete jump, we derive the leading-order structure of these currents for the different possible cases. We then build on this to develop a more detailed boundary layer description of the thermal transition based on the theory of thin gravity driven flows in porous media. Under certain injection conditions, we show that the thermal transition is gravitationally unstable and that this may lead to mixing across the thermal transition. We consider the implications of the models for several industrial processes including geothermal heat recovery, aquifer thermal storage and carbon dioxide sequestration. © 2011 Cambridge University Press.