Hydrodynamic Instability of Ionization Front in HII Regions: From Linear to Nonlinear Evolution

A sample of 54 6.7-GHz methanol maser sources was monitored at HartRAO for 4 years, and 11 12.2-GHz methanol masers for 3 years. The majority of the maser features display a significant degree of variability but with a wide range of timescales and behaviors. Some maser features remained unvarying throughout the monitoring programme, while others showed sporadic flares or sudden drops in flux density. Yet another group show quasi-periodic and periodic variations. In some cases the maser features dropped below the detection limit for a significant length of time before increasing in intensity and reappearing.     

TESSIN VISLab—laboratory for scientific visualization

Scientific visualization is an integral part of the modeling workflow, enabling researchers to understand complex or large data sets and simulation results. A high-resolution stereoscopic virtual reality (VR) environment further enhances the possibilities of visualization. Such an environment also allows collaboration in work groups including people of different backgrounds and to present results of research projects to stakeholders or the public. The requirements for the computing equipment driving the VR environment demand specialized software applications which can be run in a parallel fashion on a set of interconnected machines. Another challenge is to devise a useful data workflow from source data sets onto the display system. Therefore, we develop software applications like the OpenGeoSys Data Explorer, custom data conversion tools for established visualization packages such as ParaView and Visualization Toolkit as well as presentation and interaction techniques for 3D applications like Unity. We demonstrate our workflow by presenting visualization results for case studies from a broad range of applications. An outlook on how visualization techniques can be deeply integrated into the simulation process is given and future technical improvements such as a simplified hardware setup are outlined.     

Imaging DOAS for volcanological applications

The simultaneous quantitative determination of two-dimensional bromine monoxide (BrO) and sulphur dioxide (SO₂) distributions in volcanic gas plumes is described. Measurements at the fumarolic field on the island Vulcano (autumn 2004) and in the plume of Mt. Etna volcano (spring 2005) were carried out with an Imaging DOAS instrument. The SO₂ fluxes of several fumaroles were estimated from two-dimensional distributions of SO₂. Additionally, the first two-dimensional distributions of BrO within a volcanic plume were successfully retrieved. Slant column densities of up to 2.6 × 10¹⁴ molecules per square centimetre were detected in the plume of Mt. Etna. The investigation of the BrO/SO₂ ratio, calculated from the two-dimensional distributions of SO₂ and BrO, shows an increase from the centre to the edge of the volcanic plume. These results have significance for the involvement of ozone during BrO formation processes in volcanic emissions.     

A replicated 3000 yr proxy-climate record from Coom Rigg Moss and Felecia Moss,the Border Mires,northern England

Quantitative plant macrofossil and colorimetric humification analyses have been used to reconstruct proxy-climate from two paired ombrotrophic bogs in northern England (Coom Rigg Moss and Felecia Moss). Detrended correspondence analysis was used to transform the raw floral data into indices of mire surface wetness. The chronology of each peat profile was determined by radiocarbon assay, supported by pollen correlations. Palaeoclimatic reconstructions have been made by linking documented historical changes in climate, and other proxy-climate records, to those inferred from the sites investigated in the study region. Both sites contain a sensitive palaeoclimatic record, as ten periods of increased effective precipitation have been detected between ca. cal. ad 1770–1800, ad 1400–1470, ad 1110–1260, ad 920–1060, ad 550–670, ad 210–360, 30 bc to ad 80, 180–130 bc, 590–520 bc and 760–710 bc. Copyright © 1999 John Wiley & Sons, Ltd.     

CO<Subscript>2</Subscript> and He degassing at El Chichón volcano,Chiapas, Mexico: gas flux,origin and relationship with local and regional tectonics

During 2007–2008, three CO₂ flux surveys were performed on El Chichón volcanic lake, Chiapas, Mexico, with an additional survey in April 2008 covering the entire crater floor (including the lake). The mean CO₂ flux calculated by sequential Gaussian simulation from the lake was 1,190 (March 2007), 730 (December 2007) and 1,134 g m⁻² day⁻¹ (April 2008) with total emission rates of 164 ± 9.5 (March 2007), 59 ± 2.5 (December 2007) and 109 ± 6.6 t day⁻¹ (April 2008). The mean CO₂ flux estimated from the entire crater floor area was 1,102 g m⁻² day⁻¹ for April 2008 with a total emission rate of 144 ± 5.9 t day⁻¹. Significant change in CO₂ flux was not detected during the period of survey, and the mapping of the CO₂ flux highlighted lineaments reflecting the main local and regional tectonic patterns. The ³He/⁴He ratio (as high as 8.1 R _A) for gases in the El Chichón crater is generally higher than those observed at the neighbouring Transmexican Volcanic Belt and the Central American Volcanic Arc. The CO₂/³He ratios for the high ³He/⁴He gases tend to have the MORB-like values (1.41 × 10⁹), and the CO₂/³He ratios for the lower ³He/⁴He gases fall within the range for the arc-type gases. The high ³He/⁴He ratios, the MORB-like CO₂/³He ratios for the high ³He/⁴He gases and high proportion of MORB-CO₂ (M = 25 ±15%) at El Chichón indicate a greater depth for the generation of magma when compared to typical arc volcanoes.     

Geochemical evidence of the renewal of volcanic activity inferred from CO<Subscript>2</Subscript> soil and SO<Subscript>2</Subscript> plume fluxes: the 2007 Stromboli eruption (Italy)

On 27 February 2007, a new eruption occurred on Stromboli which lasted until 2 April. It was characterized by effusive activity on the Sciara del Fuoco and by a paroxysmal event (15 March). This crisis represented an opportunity for us to refine the model that had been developed previously (2002–2003 eruption) and to improve our understanding of the relationship between the magmatic dynamics of the volcano and the geochemical variations in the fluids. In particular, the evaluation of the dynamic equilibrium between the volatiles (CO₂ and SO₂) released from the magma and the corresponding fluids discharged from the summit area allowed us to evaluate the level of criticality of the volcanic activity. One of the major accomplishments of this study is a 4-year database of summit soil CO₂ flux on the basis of which we define the thresholds (low–medium–high) for this parameter that are empirically based on the natural volcanological evolution of Stromboli. The SO₂ fluxes of the degassing plume and the CO₂ fluxes emitted from the soil at Pizzo Sopra la Fossa are also presented. It is noteworthy that geochemical signals of volcanic unrest have been clearly identified before, during and after the effusive activity. These signals were found almost simultaneously in the degassing plume (SO₂ flux) and in soil degassing (CO₂ flux) at the summit, although the two degassing processes are shown to be clearly different. The interpretation of the results will be useful for future volcanic surveillance at Stromboli.     

The Alfvén wave parallel electric field in non-uniform space plasmas

We suggest a two-step mechanism for the generation of the parallel electric field at the Alfvén wave. At the first step, the coupling with the compressional mode due to the magnetic field non-uniformity and finite plasma pressure provides the parallel magnetic field of Alfvén wave. At the second step, the compressional mode acquires the parallel electric field due to coupling with the electrostatic mode as required by the quasi-neutrality condition in kinetics. The parallel electric field acquired by the Alfvén mode is considerably larger than that due to the single-step coupling between the Alfvén and electrostatic modes in kinetics.