Estimation of winter leaf area index and sky view fraction for snow modelling in boreal coniferous forests: consequences on snow mass and energy balance

Leaf area index (LAI) and canopy coverage are important parameters when modelling snow process in coniferous forests, controlling interception and transmitting radiation. Estimates of LAI and sky view factor show large variability depending on the estimation method used, and it is not clear how this is reflected in the calculated snow processes beneath the canopy. In this study, the winter LAI and sky view fraction were estimated using different optical and biomass‐based approximations in several boreal coniferous forest stands in Fennoscandia with different stand density, age and site latitude. The biomass‐based estimate of LAI derived from forest inventory data was close to the values derived from the optical measurements at most sites, suggesting that forest inventory data can be used as input to snow hydrological modelling. Heterogeneity of tree species and site fertility, as well as edge effects between different forest compartments, caused differences in the LAI estimates at some sites. A snow energy and mass balance model (SNOWPACK) was applied to detect how the differences in the estimated values of the winter LAI and sky view fraction were reflected in simulated snow processes. In the simulations, an increase in LAI and a decrease in sky view fraction changed the snow surface energy balance by decreasing shortwave radiation input and increasing longwave radiation input. Changes in LAI and sky view fraction affected directly snow accumulation through altered throughfall fraction and indirectly snowmelt through the changed surface energy balance. Changes in LAI and sky view fraction had a greater impact on mean incoming radiation beneath the canopy than on other energy fluxes. Snowmelt was affected more than snow accumulation. The effect of canopy parameters on evaporation loss from intercepted snow was comparable with the effect of variation in governing meteorological variables such as precipitation intensity and air temperature. Copyright © 2012 John Wiley & Sons, Ltd.     

Tree ring inferred summer temperature variations over the last millennium in western Himalaya, India

We report the first millennium-long reconstruction of mean summer (May–June–July–August) temperature extending back to AD 940 derived from tree-ring width data of Himalayan pencil juniper (Juniperus polycarpos C. Koch) from the monsoon-shadow zone in the western Himalaya, India. Centennial-scale variations in the reconstruction reveal periods of protracted warmth encompassing the 11–15th centuries. A decreasing trend in mean summer temperature occurred since the 15th century with the 18–19th centuries being the coldest interval of the last millennium, coinciding with the expansion of glaciers in the western Himalaya. Since the late 19th century summer temperatures increased again. However, current warming may be underestimated due to a weakening in tree growth-temperature relationship noticeable in the latter part of the 20th century. Mean summer temperature over the western Himalaya shows a positive correlation with summer monsoon intensity over north central India. Low-frequency variations in mean summer temperature anomalies over northwestern India are consistent with tree-ring inferred aridity in western North America. These far-distance linkages reported here for the first time underscore the utility of long-term temperature records from the western Himalayan region in understanding global-scale climatic patterns.     

Tectonic and climate control of oil shale deposition in the Upper Cretaceous Qingshankou Formation (Songliao Basin, NE China)

Oil shales were deposited in the Songliao Basin (NE China) during the Upper Cretaceous period, representing excellent hydrocarbon source rocks. High organic matter (OM) contents, a predominance of type-I kerogen, and a low maturity of OM in the oil shales are indicated by bulk geochemical parameters and biomarker data. A major contribution of aquatic organisms and minor inputs from terrigenous land plants to OM input are indicated by n-alkane distribution patterns, composition of steroids, and organic macerals. Strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane/phytane ratios, high C₁₄-aryl-isoprenoid contents, homohopane distribution patterns, and high V/Ni ratios. Enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values, low MTTC ratios, high β-carotene contents, low TOC/S ratios, and high Sr/Ba ratios. The stratified water column with anoxic conditions in the bottom water enhanced preservation of OM. Moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations. In this study, environmental conditions in the paleo-lake leading to OM accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics. The first Member of the Qingshankou Formation (K₂qn₁) in the Songliao Basin, containing the oil shale sequence, encompasses a third-order sequence that can be divided into three system tracts (transgressive system tract—TST, highstand system tract—HST, and regressive system tract—RST). Enrichment of OM changed from low values during TST-I to high-moderate values during TST-II/III and HST-I/II. Low OM enrichment occurs during RST-I and RST-II. Therefore, the highest enrichment of OM in the sediments is related to stages of mid-late TST and early HST.     

Evaluating sedimentary DNA for tracing changes in cyanobacteria dynamics from sediments spanning the last 350 years of Lake Tiefer See,NE Germany

Journal of Paleolimnology - Since the beginning of the Anthropocene, lacustrine biodiversity has been influenced by climate change and human activities. These factors advance the spread of harmful...     

Water chemistry and its diversity in relation to local factors in the Latnjavagge drainage basin, arctic–oceanic Swedish Lapland

The chemistry of precipitation, snow pack and surface water has been analysed on 205 samples collected during the 2001 field season at 25 selected sites within the Latnjavagge drainage basin in arctic–oceanic northern Swedish Lapland. Additionally, daily discharge and yield of dissolved solids have been calculated for several subcatchments and the entire Latnjavagge catchment during the years 2000, 2001 and 2002. Chemical water analysis included the components Ca²⁺, Mg²⁺, Na⁺, K⁺, Fe²⁺, Mn²⁺, Cl⁻, NO₃⁻, SO₄²⁻ and PO₄³⁻, with SO₄²⁻ and Ca²⁺ being the dominant ones in the surface water. Solute concentrations and chemical denudation were low, but showed significant differences within the basin. In areas of shade, longer snow cover, frozen ground and thin regolith, concentrations over the summer were perceptible but so low that solutes brought into the basin from precipitation could be detected in the surface water. In one locality, it was even found that lake water could reflect snowmelt to such an extent that the solute concentration was less than that of summer precipitation. The highest concentrations were found at a radiation-exposed, W-facing, vegetated, moderately steep slope with relatively thick regolith that was thawed at the time of snowmelt in early June. In such well-drained sites with continuous subsurface water flow, a maximum of contact between water and mineral particles could take place. The concentration values revealed differences in the rate of thawing of frozen ground between shaded areas and/or areas at higher altitude on the one hand and radiation-exposed areas on the other. A comparison with published results from Kärkevagge a few kilometres to the northwest as well as from other periglacial locations indicates that the chemical denudation values from Latnjavagge are more representative of periglacial oceanic environments than the values from the Kärkevagge catchment, which shows especially high chemical denudation rates. The investigation in Latnjavagge stresses the importance of spatial variability within even small catchments of homogeneous lithology as it demonstrates that solute concentrations from different subbasins can differ substantially dependent on exposure to radiation, duration of snow cover and frozen ground conditions, regolith thickness and possibly also to vegetation cover and slope angle as factors steering water turbulence and retention of drainage.     

Insights into Holocene relative sea-level changes in the southern North Sea using an improved microfauna-based transfer function

In light of global warming and rising relative sea level (RSL), detailed reconstructions of RSL histories and their controlling processes are essential in order to manage coastal-protection challenges. This study contributes to unravelling Holocene RSL change on the East Frisian North Sea coast in high resolution and with a new approach for the German Bight. For the first time, a transfer function (vertical error: 29.7 cm ? ~11% of the mean tidal range) for RSL change based on a combined training set of benthic foraminifers and ostracods from the back-barrier tidal basin of Spiekeroog is applied to the Holocene record of the back-barrier tidal basin of Norderney. The resulting RSL curve for the Norderney tidal basin is corrected for decompaction and shows a deceleration in RSL rise between 6000 and 5000 cal bp. The smallest possible error envelope (~1 m) results from the good suitability of salt-marsh layers between 5000 and 4000 cal bp. The RSL curve provides an approach towards the closure of the common data gap of peat-based curves for the southern North Sea related to a lack of basal peats in the youngest age range, and verifies regional differences in glacial isostatic adjustment.     

Determining the dependence of the power supply to the ocean on the length and time scales of the dynamics between the meso-scale and the synoptic scale,from satellite data

Ocean Dynamics - The input of mechanical power to the ocean due to the surface wind stress, in regions which correspond to different regimes of ocean dynamics, is considered using data from...     

DME/TACAN interference mitigation for GNSS: algorithms and flight test results

The Galileo E5a/E5b signals and the Global Positioning System (GPS) L5 signal lie within the aeronautical radionavigation services (ARNS) band. They suffer interference from the services in this frequency band, in particular, pulsed signals from distance measuring equipment (DME) and tactical air navigation (TACAN) systems. To maintain system accuracy and integrity, interference mitigation is beneficial and necessary. We first present the real DME/TACAN environment at Stanford, CA as an example to illustrate the need for mitigating DME/TACAN interference. We then propose a time and frequency joint mitigation algorithm—Hybrid Blanking and its simplified version, frequency domain adaptive filtering (FDAF) for hardware implementation. Finally, a flight measurements campaign was performed over a European DME/TACAN hotspot near Frankfurt, Germany, to record a worst-case DME interference environment. Recorded data from the flight tests mixed with injected GNSS signals verify the effectiveness of the proposed mitigation algorithm.