Representation of tropical deep convection in atmospheric models - Part 1 : Meteorology and comparison with satellite observations

Published under Creative Commons Licence 3.0. Original article can be found at : http://www.atmospheric-chemistry-and-physics.net/ "The author's copyright for this publication is transferred to University of Hertfordshire".Fast convective transport in the tropics can efficiently redistribute water vapour and pollutants up to the upper troposphere. In this study we compare tropical convection characteristics for the year 2005 in a range of atmospheric models, including numerical weather prediction (NWP) models, chemistry transport models (CTMs), and chemistry-climate models (CCMs). The model runs have been performed within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The characteristics of tropical convection, such as seasonal cycle, land/sea contrast and vertical extent, are analysed using satellite observations as a benchmark for model simulations. The observational datasets used in this work comprise precipitation rates, outgoing longwave radiation, cloud-top pressure, and water vapour from a number of independent sources, including ERA-Interim analyses. Most models are generally able to reproduce the seasonal cycle and strength of precipitation for continental regions but show larger discrepancies with observations for the Maritime Continent region. The frequency distribution of high clouds from models and observations is calculated using highly temporally-resolved (up to 3-hourly) cloud top data. The percentage of clouds above 15 km varies significantly between the models. Vertical profiles of water vapour in the upper troposphere-lower stratosphere (UTLS) show large differences between the models which can only be partly attributed to temperature differences. If a convective plume reaches above the level of zero net radiative heating, which is estimated to be ~15 km in the tropics, the air detrained from it can be transported upwards by radiative heating into the lower stratosphere. In this context, we discuss the role of tropical convection as a precursor for the transport of short-lived species into the lower stratosphere.Peer reviewe

Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5

One of the major globally relevant systematic biases in previous generations of climate models has been an equatorward bias in the latitude of the Southern Hemisphere (SH) mid‐latitude tropospheric eddy driven westerly jet. The far reaching implications of this for Southern Ocean heat and carbon uptake and Antarctic land and sea ice are key reasons why addressing this bias is a high priority. It is therefore of primary importance to evaluate the representation of the SH westerly jet in the latest generation of global climate and earth‐system models that comprise the Coupled Model Intercomparison Project Phase 6 (CMIP6). In this paper we assess the representation of major indices of SH extratropical atmospheric circulation in CMIP6 by comparison against both observations and the previous generation of CMIP5 models. Indices assessed are the latitude and speed of the westerly jet, variability of the Southern Annular Mode (SAM) and representation of the Amundsen Sea Low (ASL). These are calculated from the historical forcing simulations of both CMIP5 and CMIP6 for time periods matching available observational and reanalysis datasets. From the 39 CMIP6 models available at the time of writing there is an overall reduction in the equatorward bias of the annual mean westerly jet from 1.9° in CMIP5 to 0.4° in CMIP6 and from a seasonal perspective the reduction is clearest in austral spring and summer. This is accompanied by a halving of the bias of SAM decorrelation timescales compared to CMIP5. However, no such overall improvements are evident for the ASL

Gravitational Collapse and Disk Formation in Magnetized Cores

We discuss the effects of the magnetic field observed in molecular clouds on the process of star formation, concentrating on the phase of gravitational collapse of low-mass dense cores, cradles of sunlike stars. We summarize recent analytic work and numerical simulations showing that a substantial level of magnetic field diffusion at high densities has to occur in order to form rotationally supported disks. Furthermore, newly formed accretion disks are threaded by the magnetic field dragged from the parent core during the gravitational collapse. These disks are expected to rotate with a sub-Keplerian speed because they are partially supported by magnetic tension against the gravity of the central star. We discuss how sub-Keplerian rotation makes it difficult to eject disk winds and accelerates the process of planet migration. Moreover, magnetic fields modify the Toomre criterion for gravitational instability via two opposing effects: magnetic tension and pressure increase the disk local stability, but sub-Keplerian rotation makes the disk more unstable. In general, magnetized disks are more stable than their nonmagnetic counterparts; thus, they can be more massive and less prone to the formation of giant planets by gravitational instability.Comment: Chapter 16 in "Magnetic Fields in Diffuse Media", Springer-Verlag, eds. de Gouveia Dal Pino, E., Lazarian, A., Melioli,

Tropical deep convection and its impact on composition in global and mesoscale models - Part 2: Tracer transport

The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The tested models range from the regional to the global scale, and include numerical weather prediction (NWP), chemistry transport, and climate chemistry models. Idealised tracers were used in order to prevent the model's chemistry schemes from influencing the results substantially, so that the effects of modelled transport could be isolated. We find large differences in the vertical transport of very short lived tracers (with a lifetime of 6 hours) within the tropical troposphere. Peak convective outflow altitudes range from around 300 hPa to almost 100 hPa among the different models, and the upper tropospheric tracer mixing ratios differ by up to an order of magnitude. The timing of convective events is found to differ between the models, even among those which source their forcing data from the same NWP model (ECMWF). The differences are less pronounced for longer lived tracers, however they could have implications for the modelling of the halogen burden of the lowermost stratosphere through species such as bromoform, or for the transport of short lived hydrocarbons into the lowermost stratosphere. The modelled tracer profiles are found to be strongly influenced by the convective transport parameterisations, and boundary layer mixing parameterisations of the models. The location of rapid transport into the upper troposphere is similar among the models, and is mostly concentrated over the western Pacific, the Maritime Continent and the Indian Ocean. In contrast, none of the models indicates significant enhancement in upward transport over western Africa. The mean mixing ratios of an idealised CO like tracer in the upper tropical troposphere are found to be sensitive to the surface CO mixing ratios in the regions with the most active convection, revealing the importance of correctly modelling both the location of convective transport and the geographical pollutant emission patterns

Rap1 regulates the formation of E-cadherin-based cell-cell contacts

In epithelial tissues, cells are linked to their neighbors through specialized cell-cell adhesion proteins. E-cadherin is one of the most important membrane proteins for the establishment of intimate cell-cell contacts, but the molecular mechanism by which it is recruited to contact sites is largely unknown. We report here that the cytoplasmic domain of E-cadherin interacts with C3G, a guanine nucleotide exchange factor for Rap1. In epithelial cell cultures, ligation of the extracellular domain of E-cadherin enhances Rap1 activity, which in turn is necessary for the proper targeting of E-cadherin molecules to maturing cell-cell contacts. Furthermore, our data suggest that Cdc42 functions downstream of Rap1 in this process. We conclude that Rap1 plays a vital role in the establishment of E-cadherin-based cell-cell adhesion

Goodness of fit of probability distributions for sightings as species approach extinction

Estimating the probability that a species is extinct and the timing of extinctions is useful in biological fields ranging from paleoecology to conservation biology. Various statistical methods have been introduced to infer the time of extinction and extinction probability from a series of individual sightings. There is little evidence, however, as to which of these models provide adequate fit to actual sighting records. We use L-moment diagrams and probability plot correlation coefficient (PPCC) hypothesis tests to evaluate the goodness of fit of various probabilistic models to sighting data collected for a set of North American and Hawaiian bird populations that have either gone extinct, or are suspected of having gone extinct, during the past 150 years. For our data, the uniform, truncated exponential, and generalized Pareto models performed moderately well, but the Weibull model performed poorly. Of the acceptable models, the uniform distribution performed best based on PPCC goodness of fit comparisons and sequential Bonferroni-type tests. Further analyses using field significance tests suggest that although the uniform distribution is the best of those considered, additional work remains to evaluate the truncated exponential model more fully. The methods we present here provide a framework for evaluating subsequent models. © 2008 Society for Mathematical Biology

Rationale for an international consortium to study inherited genetic susceptibility to childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia is the major pediatric cancer in developed countries. To date most association studies of acute lymphoblastic leukemia have been based on the candidate gene approach and have evaluated a restricted number of polymorphisms. Such studies have served to highlight difficulties in conducting statistically and methodologically rigorous investigations into acute lymphoblastic leukemia risk. Recent genome-wide association studies of childhood acute lymphoblastic leukemia have provided robust evidence that common variation at four genetic loci confers a modest increase in risk. The accumulated experience to date and relative lack of success of initial efforts to identify novel acute lymphoblastic leukemia predisposition loci emphasize the need for alternative study designs and methods. The International Childhood Acute Lymphoblastic Leukaemia Genetics Consortium includes 12 research groups in Europe, Asia, the Middle East and the Americas engaged in studying the genetics of acute lymphoblastic leukemia. The initial goal of this consortium is to identify and characterize low-penetrance susceptibility variants for acute lymphoblastic leukemia through association-based analyses. Efforts to develop genome-wide association studies of acute lymphoblastic leukemia, in terms of both sample size and single nucleotide polymorphism coverage, and to increase the number of single nucleotide polymorphisms taken forward to large-scale replication should lead to the identification of additional novel risk variants for acute lymphoblastic leukemia. Ethnic differences in the risk of acute lymphoblastic leukemia are well recognized and thus in assessing the interplay between inherited and non-genetic risk factors, analyses using different population cohorts with different incidence rates are likely to be highly informative. Given that the frequency of many acute lymphoblastic leukemia subgroups is small, identifying differential effects will realistically only be possible through multi-center pooled analyses. Here, we review the rationale for identifying genetic risk variants for acute lymphoblastic leukemia and our proposed strategy for establishing the International Childhood Acute Lymphoblastic Leukaemia Genetics Consortium. ©2011 Ferrata Storti Foundation