Filtered screens and augmented Teichm\"uller space

We study a new bordification of the decorated Teichm\"uller space for a multiply punctured surface F by a space of filtered screens on the surface that arises from a natural elaboration of earlier work of McShane-Penner. We identify necessary and sufficient conditions for paths in this space of filtered screens to yield short curves having vanishing length in the underlying surface F. As a result, an appropriate quotient of this space of filtered screens on F yields a decorated augmented Teichm\"uller space which is shown to admit a CW decomposition that naturally projects to the augmented Teichm\"uller space by forgetting decorations and whose strata are indexed by a new object termed partially oriented stratum graphs.Comment: Final version to appear in Geometriae Dedicat

Interference effects during burning in air for stationary n-heptane, ethyl alcohol, and methyl alcohol droplets

Experiments have been conducted for the determination of the evaporation constant and flame shapes of two and of five closely spaced droplets burning in air. Droplets of approximately the same and of different diameters were used at various distances between the droplet centers. The apparent flame shape, which was observed only for n-heptane droplets, changes very little during burning. The square of the droplet diameter decreases linearly with time for fixed spacing between droplet centers, at least within the experimental limits of accuracy. In general, the average evaporation constant for two droplets, K', must be assumed either to vary continuously during burning or else to be a function of average initial drop diameter, D^0. The change of K' with time corresponds to the second derivative in plots of the square of the diameter vs. time. These second derivatives are not defined in our work because of unavoidable scatter of the experimental data. Attempts at understanding the observed results by considering published theories for single droplets, as well as groupings obtained from dimensional analysis, have been unsuccessful. It appears that the diffusion model for the heterogeneous burning of single fuel droplets will require serious revision and extension before the burning of droplets arrays and sprays can be understood quantitatively. Furthermore, the effective value of K' for a spray probably depends not only on the fuel-oxidizer system but also on the injection pattern. For this reason additional studies had best be carried out under conditions corresponding to those existing in service models

Uncertainty analysis for estimates of the first indirect aerosol effect

International audienceThe IPCC has stressed the importance of producing unbiased estimates of the uncertainty in indirect aerosol forcing, in order to give policy makers as well as research managers an understanding of the most important aspects of climate change that require refinement. In this study, we use 3-D meteorological fields together with a radiative transfer model to examine the spatially-resolved uncertainty in estimates of the first indirect aerosol forcing. Uncertainties in the indirect forcing associated with aerosol and aerosol precursor emissions, aerosol mass concentrations from different chemical transport models, aerosol size distributions, the cloud droplet parameterization, the representation of the in-cloud updraft velocity, the relationship between effective radius and volume mean radius, cloud liquid water content, cloud fraction, and the change in the cloud drop single scattering albedo due to the presence of black carbon are calculated. The cloud fraction is found to be the most important source of uncertainty and causes an overestimation of the indirect forcing by almost 0.8 Wm?2 in the reference case. Uncertainties associated with aerosol and aerosol precursor emissions are the next most important uncertainty followed closely by uncertainties in the calculation of aerosol burden by chemical transport models and uncertainties in the representation of the aerosol size distribution (including the representation of the pre-industrial size distribution). There are significant regional differences in the uncertainty associated with the first indirect forcing with largest uncertainties in regions associated with the major biomass burning regions followed by uncertainties in Asia and Europe

Enumeration of chord diagrams on many intervals and their non-orientable analogs

Two types of connected chord diagrams with chord endpoints lying in a collection of ordered and oriented real segments are considered here: the real segments may contain additional bivalent vertices in one model but not in the other. In the former case, we record in a generating function the number of fatgraph boundary cycles containing a fixed number of bivalent vertices while in the latter, we instead record the number of boundary cycles of each fixed length. Second order, non-linear, algebraic partial differential equations are derived which are satisfied by these generating functions in each case giving efficient enumerative schemes. Moreover, these generating functions provide multi-parameter families of solutions to the KP hierarchy. For each model, there is furthermore a non-orientable analog, and each such model likewise has its own associated differential equation. The enumerative problems we solve are interpreted in terms of certain polygon gluings. As specific applications, we discuss models of several interacting RNA molecules. We also study a matrix integral which computes numbers of chord diagrams in both orientable and non-orientable cases in the model with bivalent vertices, and the large-N limit is computed using techniques of free probability.Comment: 23 pages, 7 figures; revised and extended versio

Climate change - The cloud conundrum

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62779/1/432962a.pd

Aerosol effects on ice clouds: can the traditional concept of aerosol indirect effects be applied to aerosol-cloud interactions in cirrus clouds?

Cirrus clouds cover approximately 20–25% of the globe and thus play an important role in the Earth's radiation budget. Therefore the effect of aerosols on cirrus clouds can have a substantial impact on global radiative forcing if either the ice-water path (IWP) and/or the cloud ice number concentration (CINC) changes. This study examines the aerosol indirect effect (AIE) through changes in the CINC and IWP for a cirrus cloud case. We use a cloud-system resolving model (CSRM) coupled with a double-moment representation of cloud microphysics. Intensified interactions among CINC, deposition and dynamics play a critical role in increasing the IWP as aerosols increase. Increased IWP leads to a smaller change in the outgoing LW radiation relative to that for the SW radiation for increasing aerosols. Increased aerosols lead to increased CINC, providing increased surface area for water vapor deposition. The increased deposition causes depositional heating which produces stronger updrafts, and leads to the increased IWP. The conversion of ice crystals to aggregates through autoconversion and accretion plays a negligible role in the IWP response to aerosols, and the sedimentation of aggregates is negligible. The sedimentation of ice crystals plays a more important role in the IWP response to aerosol increases than the sedimentation of aggregates, but not more than the interactions among the CINC, deposition and dynamics

Comparison of a global-climate model to a cloud-system resolving model for the long-term response of thin stratocumulus clouds to preindustrial and present-day aerosol conditions

The response of a case of thin, warm marine-boundary-layer (MBL) clouds to preindustrial (PI) and present-day (PD) conditions is simulated by a cloud-system resolving model (CSRM). Here, both the aerosol conditions and environmental conditions match those of a general circulation model (GCM). The environmental conditions are characterized by the initial condition and the large-scale forcings of humidity and temperature, as well as the surface fluxes. The response of the CSRM is compared to that simulated by the GCM. <br><br> The percentage increase of liquid-water path (LWP) due to a change from the PI to PD conditions is ~3 times larger in the CSRM than that in the GCM due to the formation of cumulus clouds. The formation of cumulus clouds is controlled by a larger increase in the surface latent-heat (LH) flux in the PD environment than in the PI environment rather than by the change in aerosols. However, the aerosol increase from the PI to PD level determines the LWP response in the stratocumulus clouds, while the impacts of changes in environmental conditions are negligible for stratocumulus clouds. The conversion of cloud liquid to rain through autoconversion and accretion plays a negligible role in the CSRM in the response to aerosols, whereas it plays a role that is as important as condensation in the GCM. Also, it is notable that the explicit simulation of microphysics in the CSRM leads to a smaller LWP in the CSRM than that in the GCM using heavily parameterized microphysics for stratocumulus clouds. The smaller LWP in the CSRM is closer to an observed LWP than the LWP in the GCM for stratocumulus clouds. <br><br> Supplementary simulations show that increasing aerosols increase the sensitivity of the cloud responses to the PI and PD environmental conditions. They also show that aerosol effects on clouds depend on the cloud type. The LWP of warm cumulus clouds is more sensitive to aerosols than that of stratocumulus clouds

Simulation of the global contrail radiative forcing: A sensitivity analysis

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96352/1/grl29839.pd

Development of a secondary organic aerosol formation mechanism: comparison with smog chamber experiments and atmospheric measurements

International audienceA new mechanism to simulate the formation of secondary organic aerosols (SOA) from reactive primary hydrocarbons is presented, together with comparisons with experimental smog chamber results and ambient measurements found in the literature. The SOA formation mechanism is based on an approach using calculated vapor pressures and a selection of species that can partition to the aerosol phase from a gas phase photochemical mechanism. The mechanism has been validated against smog chamber measurements using ?-pinene, xylene and toluene as SOA precursors, and has an average error of 17%. Qualitative comparisons with smog chamber measurements using isoprene were also performed. A comparison against SOA production in the TORCH 2003 experiment (atmospheric measurements) had an average error of only 12%. This contrasts with previous efforts, in which it was necessary to increase partition coefficients by a factor of 500 in order to match the observed values. Calculations for rural and urban-influenced regions in the eastern U.S. suggest that most of the SOA is biogenic in origin, mainly originated from isoprene. A 0-dimensional calculation based on the New England Air Quality Study also showed good agreement with measured SOA, with about 40% of the total SOA from anthropogenic precursors. This mechanism can be implemented in a general circulation model (GCM) to estimate global SOA formation under ambient NOx and HOx levels