Summer time Fe depletion in the Antarctic mesopause region

We report common volume measurements of Fe densities, temperatures and ice particle occurrence in the mesopause region at Davis Station, Antarctica (69°S) in the years 2011–2012. Our observations show a strong correlation of the Fe-layer summer time depletion with temperature, but no clear causal relation with the onset or occurrence of ice particles measured as noctilucent clouds (NLC) or polar mesosphere summer echoes (PMSE). The combination of these measurements indicates that the strong summer depletion can be explained by gas-phase chemistry alone and does not require heterogeneous removal of Fe and its compounds on ice particles

Simultaneous in situ measurements of small-scale structures in neutral, plasma, and atomic oxygen densities during the WADIS sounding rocket project

In this paper we present an overview of measurements conducted during the WADIS-2 rocket campaign. We investigate the effect of small-scale processes like gravity waves and turbulence on the distribution of atomic oxygen and other species in the mesosphere-lower thermosphere (MLT) region. Our analysis suggests that density fluctuations of atomic oxygen are coupled to fluctuations of other constituents, i.e., plasma and neutrals. Our measurements show that all measured quantities, including winds, densities, and temperatures, reveal signatures of both waves and turbulence. We show observations of gravity wave saturation and breakdown together with simultaneous measurements of generated turbulence. Atomic oxygen inside turbulence layers shows two different spectral behaviors, which might imply a change in its diffusion properties. © 2019 Author(s)

Spatiotemporal modeling of microbial metabolism

Background Microbial systems in which the extracellular environment varies both spatially and temporally are very common in nature and in engineering applications. While the use of genome-scale metabolic reconstructions for steady-state flux balance analysis (FBA) and extensions for dynamic FBA are common, the development of spatiotemporal metabolic models has received little attention. Results We present a general methodology for spatiotemporal metabolic modeling based on combining genome-scale reconstructions with fundamental transport equations that govern the relevant convective and/or diffusional processes in time and spatially varying environments. Our solution procedure involves spatial discretization of the partial differential equation model followed by numerical integration of the resulting system of ordinary differential equations with embedded linear programs using DFBAlab, a MATLAB code that performs reliable and efficient dynamic FBA simulations. We demonstrate our methodology by solving spatiotemporal metabolic models for two systems of considerable practical interest: (1) a bubble column reactor with the syngas fermenting bacterium Clostridium ljungdahlii; and (2) a chronic wound biofilm with the human pathogen Pseudomonas aeruginosa. Despite the complexity of the discretized models which consist of 900 ODEs/600 LPs and 250 ODEs/250 LPs, respectively, we show that the proposed computational framework allows efficient and robust model solution. Conclusions Our study establishes a new paradigm for formulating and solving genome-scale metabolic models with both time and spatial variations and has wide applicability to natural and engineered microbial systems

Winter/summer mesopause temperature transition at Davis (69°S) in 2011/2012

We present quasi-continuous measurements of temperature profiles in the Southern Hemisphere mesopause region during the transition from winter to summer conditions in 2011/2012. In a period of 120 days around solstice, we have performed iron lidar observations at Davis (69°S), Antarctica, for a total of 736 h. The winter/summer transition is identified by a downward shift of the mesopause which occurs on 8 November 2011. Soon after transition, mesopause heights and temperatures are similar to the Northern Hemisphere (NH) colatitude summer (88 km, 130 K). Around solstice, the mesopause is elevated for several days by 4–5 km and is colder than typical NH temperatures by 10 K. In this period individual profiles show temperatures as low as 100 K. The occurrence of polar mesosphere summer echoes is closely connected to low temperatures. Below 88 to 90 km and in the main summer season of 2011/2012 temperatures at Davis are generally warmer compared to the NH by 5–15 K, whereas temperatures are generally colder above 90 km. The winter/summer transition and the first appearance of polar mesosphere summer echoes are strongly correlated to maximum zonal winds in the stratosphere which constrain gravity waves with eastward momentum reaching the mesosphere. At the breakdown of the stratospheric vortex around solstice, the mesopause is higher and, surprisingly, colder than normal