ALBERT

Description: ABSTRACT Severe thunderstorms present a significant threat to property and life in Australia during the warm season (September to April). However, these relatively infrequent events are poorly understood in terms of frequency and occurrence for much of the continent due to a lack of in-situ observations. With the spectre of a changing climate, there is an increasing need to understand thunderstorms and their impact on Australia, both in the past and for the future. To facilitate this, the relationship between severe thunderstorms and their associated environments is used as a probabilistic proxy for direct observations. To establish these conditions, a proximity climatology of environments was developed for observed severe thunderstorms in Australia during the period 2003–2010 using the ERA-Interim reanalysis. Proximity soundings from the reanalysis for observed severe thunderstorms were used to develop covariate discriminants that identify the increased probability of an environment to produce severe thunderstorms. The covariates use a combination of ingredients describing instability (mixed-layer convective available potential energy) and potential for organized severe convection (deep-layer wind shear). These discriminants have been extrapolated to produce a climatology of environments favourable to the development of severe thunderstorms over the period 1979–2011 from this reanalysis. The inter-annual variations in both the spatial and temporal distribution of convective environments over Australia were analysed, with particular focus on the influence of El Niño-Southern Oscillation (ENSO) on the occurrence of severe thunderstorm environments. These results suggest that while ENSO has a substantial impact on the spatial distribution of severe thunderstorm environments over the continent, the link to frequency is more uncertain.

Description: We synthesize insights from current understanding of drought impacts at stand-to-biogeographic scales, including management options, and we identify challenges to be addressed with new research. Large stand-level shifts underway in western forests already are showing the importance of interactions involving drought, insects, and fire. Diebacks, changes in composition and structure, and shifting range limits are widely observed. In the eastern US, the effects of increasing drought are becoming better understood at the level of individual trees, but this knowledge cannot yet be confidently translated to predictions of changing structure and diversity of forest stands. While eastern forests have not experienced the types of changes seen in western forests in recent decades, they too are vulnerable to drought and could experience significant changes with increased severity, frequency, or duration in drought. Throughout the continental United States, the combination of projected large climate-induced shifts in suitable habitat from modeling studies and limited potential for the rapid migration of tree populations suggests that changing tree and forest biogeography could substantially lag habitat shifts already underway. Forest management practices can partially ameliorate drought impacts through reductions in stand density, selection of drought-tolerant species and genotypes, artificial regeneration, and the development of multistructured stands. However, silvicultural treatments also could exacerbate drought impacts unless implemented with careful attention to site and stand characteristics. Gaps in our understanding should motivate new research on the effects of interactions involving climate and other species at the stand scale and how interactions and multiple responses are represented in models. This assessment indicates that, without a stronger empirical basis for drought impacts at the stand scale, more complex models may provide limited guidance.

Description: An ensemble of eight atmospheric CO2 simulations was completed employing the National Aeronautics and Space Administration (NASA) Goddard Earth Observation System, Version 5 (GEOS-5) for the years 2000–2001, each with initial meteorological conditions corresponding to different days in January 2000 to examine internal model variability. Globally, the model runs show similar concentrations of CO2 for the two years, but in regions of high CO2 concentrations due to fossil fuel emissions, large differences among different model simulations appear. The phasing and amplitude of the CO2 cycle at Northern Hemisphere locations in all of the ensemble members is similar to that of surface observations. In several southern hemisphere locations, however, some of the GEOS-5 model CO2 cycles are out of phase by as much as four months, and large variations occur between the ensemble members. This result indicates that there is large sensitivity to transport in these regions. The differences vary by latitude—the most extreme differences in the Tropics and the least at the South Pole. Examples of these differences among the ensemble members with regard to CO2 uptake and respiration of the terrestrial biosphere and CO2 emissions due to fossil fuel emissions are shown at Cape Grim, Tasmania. Integration-based flow analysis of the atmospheric circulation in the model runs shows widely varying paths of flow into the Tasmania region among the models including sources from North America, South America, South Africa, South Asia and Indonesia. These results suggest that interhemispheric transport can be strongly influenced by internal model variability.

Description: Abstract Nitryl chloride (ClNO2) acts as a source of highly reactive chlorine atoms as well as an important NOx reservoir. Measurements of ClNO2 at an operational U.K. landfill site are reported here for the first time. A peak concentration of 4 ppb of ClNO2 was found with a peak mean nighttime maximum of 0.9 ppb. Using models based upon the photolysis of observed ClNO2 and atmospheric chlorine chemistry, chlorine atom concentrations reaching in excess of 1.20 × 105 molecules/cm3 in the early morning following sunrise are calculated. These concentrations are approximately 10 times higher than previously reported in the United Kingdom, suggesting a significant impact on the oxidizing capacity around such sites. Given the ubiquity of landfill sites regionally and globally, and the large abundances of Cl atoms from the photolysis of ClNO2, chlorine chemistry has a significant impact on ozone formation and volatile organic compounds oxidation as shown by WRF‐Chem modeling.

Description: Enhanced vertical gradients in benthic foraminiferal δ 13 C and δ 18 O in the Atlantic and Pacific during the last glaciation have revealed that ocean overturning circulation was characterized by shoaling of North-Atlantic sourced interior waters; nonetheless our understanding of the specific mechanisms driving these glacial isotope patterns remains incomplete. Here we compare high-resolution depth transects of Cibicidoides spp. δ 13 C and δ 18 O from the Southwest Pacific and the Southwest Atlantic to examine relative changes in northern and southern sourced deep waters during the Last Glacial Maximum (LGM) and deglaciation. During the LGM, our transects show that water mass properties and boundaries in the South Atlantic and Pacific were different from one another. The Atlantic between ~1.0 and 2.5 km was more than 1 ‰ enriched in δ 13 C relative to the Pacific and remained more enriched through the deglaciation. During the LGM, Atlantic δ 18 O was ~ 0.5 ‰ more enriched than the Pacific, particularly below 2.5 km. This compositional difference between the deep portions of the basins implies independent deep water sources during the glaciation. We attribute these changes to a ‘deep gateway’ effect whereby northern sourced waters shallower than the Drake Passage sill were unable to flow southward into the Southern Ocean because a net meridional geostrophic transport cannot be supported in the absence of a net east-west circumpolar pressure gradient above the sill depth. We surmise that through the LGM and early deglaciation, shoaled northern-sourced waters were unable to escape the Atlantic and contribute to deep water formation in the Southern Ocean.

Description: Effective and accurate communication of scientific findings is essential. Unfortunately, scientists are not always well trained in how to best communicate their results with other scientists nor do all appreciate the importance of speaking with the public. Here, we provide an example of how the development of oral communication skills can be integrated with research experiences at the undergraduate level. We describe our experiences developing, running, and evaluating a course for undergraduates that complemented their existing undergraduate research experiences with instruction on the nature of science and intensive training on the development of science communication skills. Students delivered science talks, research monologues, and poster presentations about the ecological and evolutionary research in which they were involved. We evaluated the effectiveness of our approach using the CURE survey and a focus group. As expected, undergraduates reported strong benefits to communication skills and confidence. We provide guidance for college researchers, instructors, and administrators interested in motivating and equipping the next generation of scientists to be excellent science communicators. In a world that is quickly changing its views on the significance of science, it is more important than ever to train young scientists in the art of science communication so that our community can accurately and effectively disseminate the importance of research. Here, we describe our experiences developing, implementing, and evaluating a course that developed undergraduates’ oral science communication skills. We provide guidance to those that are interested in developing courses like ours that mutually benefit the researcher and the undergraduate students.

Description: Calligonum mongolicum is a successful pioneer shrub to combat desertification, which is widely used for vegetation restoration in the desert regions of northwest China. In order to reveal the limitations to natural regeneration of C. mongolicum by asexual and sexual reproduction, following the process of sand dune stabilization, we assessed clonal shoots, seedling emergence, soil seed bank density, and soil physical characteristics in mobile and stabilized sand dunes. Controlled field and pot experiments were also conducted to assess germination and seedling emergence in different dune soil types and seed burial depths. The population density of mature C. mongolicum was significantly different after sand dune stabilization. Juvenile density of C. mongolicm was much lower in stabilized sand dunes than mobile sand dune. There was no significant difference in soil seed bank density at three soil depths between mobile and stabilized sand dunes, while the emergence of seedlings in stabilized dunes was much lower than emergence in mobile dunes. There was no clonal propagation found in stabilized dunes, and very few C. mongolicum seedlings were established on stabilized sand dunes. Soil clay and silt content, air-filled porosity, and soil surface compaction were significantly changed from mobile sand dune to stabilized dunes. Seedling emergence of C. mongolicm was highly dependent on soil physical condition. These results indicated that changes in soil physical condition limited clonal propagation and seedling emergence of C. mongolicum in stabilized sand dunes. Seed bank density was not a limiting factor; however, poor seedling establishment limited C. mongolicum's further natural regeneration in stabilized sand dunes. Therefore, clonal propagation may be the most important mode for population expansion in mobile sand dunes. As a pioneer species C. mongolicum is well adapted to propagate in mobile sand dune conditions, it appears unlikely to survive naturally in stabilized sand dune plantations. Natural propagation of the pioneering shrub C. mongolicum by asexual and sexual reproduction following the process of sand dune stabilization was limited. Changes in soil physical condition limited clonal propagation and seedling emergence of C. mongolicum in stabilized sand dunes. Seed bank density was not a limiting factor; however, poor seedling establishment limited C. mongolicum's further natural propagation in stabilized sand dunes.

Description: A leading Data Assimilation (DA) technique in meteorology is 4DVAR which relies on the Tangent Linear Model (TLM) of the non-linear model and its adjoint. The difficulty of building and maintaining traditional TLMs and adjoints of coupled ocean-wave-atmosphere-etc models is daunting. On the other hand, coupled model ensemble forecasts are readily available. Here, we show how an ensemble forecast can be used to construct an accurate Local Ensemble TLM (LETLM) and adjoint of the entire coupled system. The method features a local influence region containing all the variables that could possibly influence the time evolution of some target variable(s) near the center of the region. We prove that high accuracy is guaranteed provided that (i) the ensemble perturbations are governed by linear dynamics, and (ii) the number of ensemble members exceeds the number of variables in the influence region. The approach is illustrated in a simple coupled model. This idealized coupled model has some realistic features including reasonable predictability limits in the upper-atmosphere, lower-atmosphere, upper-ocean and lower-ocean of 10, 96, 160 and 335 days, respectively. In addition, the length scale of eddies in the ocean is about one fifth of those in the atmosphere. The easy manner in which the adjoint is obtained from the LETLM is also described and illustrated by demonstrating how the LETLM adjoint predicts the high sensitivity of oceanic boundary layer evolution to changes in the atmosphere. Finally, the feasibility of LETLMs for 4DVAR is demonstrated. Specifically, a case is considered with a 5 day data assimilation window in which non-linear terms play a significant role in the evolution of forecast error; it is shown that the posterior mode delivered by 4DVAR with an LETLM, its adjoint and 10 outer loops approximately recovers the true state in spite of a spatially sparse observational network.