Multiperiodic semiregular variable stars in the ASAS data base: A pilot study

Based on a search for multi‐periodic variability among the semi‐regular red variable stars in the database of the All Sky Automated Survey (ASAS), a sample of 72 typical examples is presented. Their period analysis was performed using the Discrete Fourier Transform. In 41 stars we identified two significant periods each, simultaneously present, while the remaining 31 cases revealed even three such periods per star. They occur in a range roughly between 50 and 3000 days. Inter‐relationships between these periods were analyzed using the “double period diagram” which compares adjacent periods, and the so‐called “Petersen diagram”, the period ratio vs. the shorter period. In both diagrams we could identify six sequences of accumulation of the period values. For five of these sequences (containing 97 % of all data points) we found an almost perfect coincidence with those of previous studies which were based on very different samples of semiregular red variables. Therefore, existence and locations of these sequences in the diagrams seem to be universal features, which appear in any data set of semi‐regularly variable red giants of the AGB; we conclude that they are caused by different pulsation modes as the typical and consistent properties of similar stellar AGB configurations. Stellar pulsations can be considered as the principal cause of the observed periodic variability of these stars, and not binary, rotation of a spotted surface or other possible reasons suggested in the literature. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigations on the runoff generation at the profile and plot scales,Swiss Emmental

This article describes an investigation on runoff generation at different scales in the forested catchment of the Sperbelgraben in the Emmental region (Swiss Prealps) where studies in the field of forest hydrology have a history of 100 years. It focuses on the analysis of soil profiles and the subsequent sprinkling experiments above them (1 m²), as well as on surface runoff measurements on larger plots (50 to 110 m²). In the Sperbelgraben investigation area, two very distinct runoff reactions could be observed. On the one hand, very high production of saturation overland flow was registered on wet areas of gleyic soils, with runoff coefficients between 0·39 and 0·94 for profile irrigation. On the other hand, almost no surface runoff was measured on Cambisols, with the exception at some sites of a hydrophobic reaction detected at the beginning of storms after dry periods (coefficients for profile irrigation: 0·01–0·16). This pattern was observed during 1 m² soil plot irrigation and on surface runoff plots. Apart from a less distinctive signal of the water‐repellent litter layer on the larger surface runoff plots, the dominant hydrological processes at the two scales are the same. The determined runoff reaction at the two scales corresponds well with information from a forest site type map describing soil and vegetation characteristics and used as a substitute for a soil map in this study. Theoretical considerations describing forest influence on flood discharge are discussed and evaluated to be in good agreement with observations. These findings are a sound foundation for application in hydrological catchment modelling. Copyright © 2006 John Wiley & Sons, Ltd.     

Spectral Characteristics and Correction of Long-Term Eddy-Covariance Measurements Over Two Mixed Hardwood Forests in Non-Flat Terrain

We present turbulence spectra and cospectra derived from long-term eddy-covariancemeasurements (nearly 40,000 hourly data over three to four years) and the transferfunctions of closed-path infrared gas analyzers over two mixed hardwood forests inthe mid-western U.S.A. The measurement heights ranged from 1.3 to 2.1 times themean tree height, and peak vegetation area index (VAI) was 3.5 to 4.7; the topographyat both sites deviates from ideal flat terrain. The analysis follows the approach ofKaimal et al. (Quart. J. Roy. Meteorol. Soc. 98, 563–589, 1972) whose results were based upon 15 hours of measurements atthree heights in the Kansas experiment over flatter and smoother terrain. Both thespectral and cospectral constants and stability functions for normalizing and collapsingspectra and cospectra in the inertial subrange were found to be different from those ofKaimal et al. In unstable conditions, we found that an appropriate stabilityfunction for the non-dimensional dissipation of turbulent kinetic energy is of the form ₍₎ = (1 - b^-)^-1/4 - c^-, where representsthe non-dimensional stability parameter. In stable conditions, a non-linear functionG_xy() = 1 + b_xy^c _xy (c_xy < 1) was found to benecessary to collapse cospectra in the inertial subrange. The empirical cospectralmodels of Kaimal et al. were modified to fit the somewhat more (neutraland unstable) or less (stable) sharply peaked scalar cospectra observed over forestsusing the appropriate cospectral constants and non-linear stability functions. Theempirical coefficients in the stability functions and in the cospectral models varywith measurement height and seasonal changes in VAI. The seasonal differencesare generally larger at the Morgan Monroe State Forest site (greater peak VAI) andcloser to the canopy.The characteristics of transfer functions of the closed-path infrared gas analysersthrough long-tubes for CO₂ and water vapour fluxes were studied empirically. This was done by fitting the ratio between normalized cospectra of CO₂ or watervapour fluxes and those of sensible heat to the transfer function of a first-order sensor.The characteristic time constant for CO₂ is much smaller than that for water vapour. The time constant for water vapour increases greatly with aging tubes. Three methods were used to estimate the flux attenuations and corrections; from June through August, the attenuations of CO₂ fluxes are about 3–4% during the daytime and 6–10% at night on average. For the daytime latent heat flux (Q_E), the attenuations are foundto vary from less than 10% for newer tubes to over 20% for aged tubes. Correctionsto Q_E led to increases in the ratio (Q_H + Q_E)/(Q^* - Q_G) by about 0.05 to0.19 (Q_H is sensible heat flux, Q^* is net radiation and Q_G is soil heat flux),and thus are expected to have an important impact on the assessment of energy balanceclosure.     

Ca-H-Al exchanges and aluminium mobility in two Chinese acidic forest soils: a batch experiment

Exchange reactions between Ca²⁺, H⁺ and Al species and their effects on the aluminium mobility in two Chinese acidic forest soils were studied. The study was based on a batch experiment using extractant solutions with different base cation (calcium) concentrations and pH. The experimental data showed that increased Ca²⁺ concentrations increased the release of soil hydrogen—and aluminium ions, especially from the more acid soil. In agreement with a cation exchange process, the treatment with Ca²⁺ extracts gave significantly decreased soil aluminium saturation (AlS) and increased calcium saturation (CaS) on the ion exchanger. Geochemical calculation using AlCHEMI program showed that activities of Al³⁺ in the extracts were all strongly under-saturated with respect to any gibbsite mineral in the studied pH region (i.e. below 4.1). There were instead apparently two different mechanisms controlling the activities of Al³⁺ in extracts. At pH between about 4.1 and 3.7, the Al³⁺ activity did not change significantly with pH. This is especially the case in the more acid soil. Apparently there are no sizeable pools available to release Al in this pH region. At pH below 3.7 (induced by higher Ca²⁺concentration) the activity of Al³⁺ increased with H⁺ though not in a pattern that complies with a gibbsite solubility control. An increase of base cation deposition would therefore mainly enhance the release of hydrogen ions between pH 4.1 and 3.7 and aluminium ions below pH 3.7 from Chinese mature acidic soils. This will cause an increased acidity of soil water in the short term and a decrease in the soil acidity in the long term. More attention should be paid to this fact in Chinese acid rain studies and control options.     

A review of the thermal regime of the Eastern Alps with respect to the effects of paleoclimate and exhumation

Transient thermal signals such as Pleistocene surface temperature variations or exhumation of great rock volumes are important for the current thermal regime of the Eastern Alpine crust. In this study transient 1-D forward simulations and an analytical approach were used to estimate the order of magnitude of these effects. A comparison with numerical forward simulations and inverse analyses of steady-state heat conduction yields the following main conclusions with respect to the thermal regime of the Eastern Alps along the TRANSALP profile: (1) The change of surface temperatures in the past affects mainly the uppermost part of the Eastern Alpine crust. It results in a maximum thermal signature of more than − 6 K at a depth of 2 km. The deviations from a steady-state temperature gradient and heat flow in the region of the Tauern Window range from 0.3–4 K km^− 1 and 0–6 mW m^− 2, respectively, with maximum values at the surface. (2) Exhumation of the Eastern Alpine lithosphere may result in a thermal signature of up to 4 K at a depth of 1 km. The thermal signature increases further with depth to a maximum of approximately 80 K at a depth of 50 km. As the temperature gradient of the exhumation signal is almost zero at the base of the crust, Moho heat flow appears to be not critically perturbed. (3) The combined effect of exhumation and changing surface temperatures at the Tauern Window amounts to less than 15% of the steady-state temperatures at a depth of  8 km and to less than 10% at the base of Eastern Alpine root. The corresponding perturbation in heat flow is less than 20% at a depth of 4 km, approaching zero below 40 km.     

Environmental changes in northern New Zealand since the Middle Holocene inferred from stable isotope records (δ15N, δ13C) of Lake Pupuke

Maar lakes in the Auckland Volcanic Field are important high-resolution archives of Holocene environmental change in the Southern Hemisphere mid-latitudes. Stable carbon and nitrogen isotope analyses were applied on bulk organic matter and the green alga Botryococcus from a sediment core from Lake Pupuke (Auckland, North Island, New Zealand) spanning the period since 7,165?cal.?year BP. The origin of organic matter was established using total-organic?Ccarbon-to-nitrogen ratios (TOC/TN) as well as organic carbon (??¹³C_OM) and nitrogen (??¹⁵N) isotope composition of potential modern sources. This approach demonstrated that the contribution of allochthonous organic matter to the lake sediment was negligible for most of the record. The sedimentary TOC/TN ratios that are higher than Redfield ratio (i.e. >7) are attributed to N-limiting conditions throughout the record. Variations of nitrogen and carbon isotopes during the last 7,165?years are interpreted as changes in the dominant processes in the lake. While epilimnetic primary productivity controlled isotope composition before 6,600?cal.?year BP, microbial processes, especially denitrification and methane oxidation, caused overall shifts of the ??¹⁵N and ??¹³C values since the Mid-Holocene. Comparisons with climate reconstructions from the Northern Island suggest that changes in the wind-induced lake overturn and a shift to more pronounced seasonality were the most likely causes for lake-internal changes since 6,600?cal.?year BP.