Measurement of wind parameters and heat flux with the sensitron Doppler SODAR

The authors present the results of a comparison of wind parameters and heat flux inferred from Doppler SODAR (Sensitron/Sweden) with direct measurements using an acoustic anemometer (Kaijo-Denki, DAT 300) and a platinum wire thermometer. Rather important are the results of a calibration method for c _t ² from measurements of temperature standard deviation, and of an underestimation of the wind speed by Doppler SODAR. An operational means to calculate the flux of sensible heat on the basis of SODAR measurements is studied.     

Synthetic spectra of simulated terrestrial atmospheres containing possible biomarker gases.

NASA's proposed Terrestrial Planet Finder, a space-based interferometer, will eventually allow spectroscopic analyses of the atmospheres of extrasolar planets. Such analyses would provide information about the existence of life on these planets. One strategy in the search for life is to look for evidence of O3 (and hence O2) in a planet's atmosphere; another is to look for gases that might be present in an atmosphere analogous to that of the inhabited early Earth. In order to investigate these possibilities, we have calculated synthetic spectra for several hypothetical terrestrial-type atmospheres. The model atmospheres represent four different scenarios. The first two, representing inhabited terrestrial planets, are an Earth-like atmosphere containing variable amounts of oxygen and an early Earth-type atmosphere containing methane. In addition, two cases representing Mars-like and early Venus-like atmospheres were evaluated, to provide possible "false positive" spectra. The calculated spectra suggest that ozone could be detected by an instrument like Terrestrial Planet Finder if the O2 concentration in the planet's atmosphere is > or = 200 ppm, or 10(-3) times the present atmospheric level. Methane should be observable on an early-Earth type planet if it is present in concentrations of 100 ppm or more. Methane has both biogenic and abiogenic sources, but concentrations exceeding 1000 ppm, or 0.1% by volume, would be difficult to produce from abiogenic sources alone. High methane concentrations in a planet's atmosphere are therefore another potential indicator for extraterrestrial life.     

Complex formation in the ternary system Mg(II)-CO2-H2O

The carbonato and hydrogencarbonato complexes of Mg²⁺ were investigated at 25 and 50° in solutions of the constant ClO₄^? molality (3 M) consisting preponderantly of NaClO₄. The experimental data could be explained assuming the following equilibria: Mg²⁺ + CO_2B + H₂O ag MgHCO⁺₃ + H⁺, $\text{log}{}^1\text{β}{}_1\text{= ?7.64}{}_4\text{± 0.01}{}_7\text{(25°), ?7.46}{}_2\text{± 0.01}{}_1\text{(50°)}$, Mg²⁺ + 2 CO_2g + 2 H₂Oag Mg(HCO₃)⁰₂ ± 2 H⁺, $\text{log}{}^1\text{β}{}_2\text{= ?15.00 ± 0.14 (25°)}$, ?15.37 ± 0.39 (50°), Mg²⁺ + CO_2g + H₂Oag MgCO⁰₃ + 2 H⁺, $\text{log}{}^1\text{k}{}_1\text{= ?15.64 ± 0.06 (25°)}$,?15.23 ± 0.02 (50°), with the assumption γ_MgCO3⁰ = γ_Mg(HCO3)⁰2, ΔG⁰(I = 0) for the reaction MgCO⁰₃ + CO_2g + H₂O = Mg(HCO₃)⁰₂ was estimated to be ?3.9₁ ± 0.8₆ and 0.6 ± 2.4 kJ/mol at 25 and 50°C, respectively. The abundance of carbonate linked Mg(II) species in fresh water systems is discussed.     

Paleoecological investigation of recent lake acidification in the northern Great Lakes states

Paleoecological analyses of sediments from nine northern Great Lakes states (NGLS) lakes reveal small pH changes in seven of these lakes since 1860, four of these being declines. The largest diatom-inferred (DI) pH declines of 0.5 pH units were found in Brown L. and Denton L., Wisconsin. Two other lakes with suspected total alkalinity declines (based on an acidification model and on historical water chemistry, respectively), McNearney L., Michigan, and Camp 12 L., Wisconsin, have not acidified recently according to diatom-inference techniques. Many of the observed trends of increasing pH are coincident with logging; floristic composition of diatom assemblages also changed coincident with fisheries manipulations in some lakes, but these floristic trends did not affect DI pH. Sediment core profiles of Pb, S, and polycyclic aromatic hydrocarbons provide a record of atmospheric deposition of fossil fuel combustion products beginning around the turn of the century; onset is later and accumulation rates are smaller than for other northeastern study regions of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) Project. The response of diatom species to lakewater pH in the NGLS region is very strong and similar to response in other regions. Overall, there is little paleoecological evidence that acidic deposition has caused significant acidification of lakes in the NGLS region.This is the twelfth of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D.F. Charles and D.R. Whitehead are guest editors for this series.     

Stability of two-dimensional pre-flare structures

Several theoretical approaches to the problem of the onset of solar flares identify the point of onset as a ‘critical’ point, where the solution curve turns back. In other theories, a flare occurs at a conventional transition from stability to instability. The present paper provides stability results relevant for both types of approaches. Restricting the discussion to two-dimensional configurations (e.g. models for two-ribbon flares) stability is discussed in the framework of ideal magnetohydrodynamics, resistive magnetohydrodynamics and Vlasov theory. In most (but not all) cases the perturbation modes considered are restricted to two spatial dimensions in the same sense as the equilibrium. Several rather general criteria for stability of the lower part of the solution curve (‘minimal solutions’) are derived. Our results provide support to the concept of flare onset at a critical point.     

Tearing modes in the magnetopause current sheet

A simple method is proposed to investigate the stability of a charge neutral magnetopause current sheet with respect to the tearing-mode instability. This method may serve as a useful tool in understanding the processes of local opening of the closed magnetosphere.     

A theory of the onset of solar eruptive processes

The present theory assumes that solar eruptive processes - such as flares or eruptive prominences - occur at a critical stage when a configuration evolves in a quasi-static way. The onset criterion is not based on standard linear stability considerations but on the fact that under suitable conditions static equilibrium configurations cease to exist. This starting point leads us to present a general discussion of existence properties of the corresponding set of equations. It turns out that the existing mathematical literature provides very useful pertinent information. In fact, some important questions of the existence can be answered without even solving the equations. Nevertheless, several explicit examples are discussed for reasons of illustration.For the major part of the paper the configurations are characterized by a single parameter. In a particularly simple (one-dimensional) case we also discuss solutions depending on two parameters. The results can be discussed in terms of catastrophe theory.The theory is valid for two space dimensions and contains topological changes of the magnetic field, although the latter feature is not necessary for the theory to apply. The theory of two-dimensional force-free fields is contained as a special case.