Evaluation of the Interpretation of Ceilometer Data with RASS and Radiosonde Data

Since 2006 different remote monitoring methods for determining mixing-layer height have been operated in parallel in Augsburg (Germany). One method is based on the operation of eye-safe commercial mini-lidar systems (ceilometers). The optical backscatter intensities recorded with ceilometers provide information about the range-dependent aerosol concentration; gradient minima within this profile mark the tops of mixed layers. Special software for these ceilometers provides routine retrievals of lower atmospheric layering. A second method, based on sodar observations, detects the height of a turbulent layer characterized by high acoustic backscatter intensities due to thermal fluctuations and a high variance of the vertical velocity component. This information is extended by measurements with a radio-acoustic sounding system (RASS) that directly provides the vertical temperature profile from the detection of acoustic signal propagation and thus temperature inversions that mark atmospheric layers. Ceilometer backscatter information is evaluated by comparison with parallel measurements. Data are presented from 2 years of combined ceilometer and RASS measurements at the same site and from comparison with a nearby (60 km) radiosonde for larger-scale humidity information. This evaluation is designed to ensure mixing-layer height monitoring from ceilometer data more reliable.     

The corridor correction concept

Atmospheric delays are contributors to the GNSS error budget in precise GNSS positioning that can reduce positioning accuracy considerably if not compensated appropriately. Both ionospheric and tropospheric delay corrections can be determined with help of reference stations in active GNSS networks. One approach to interpolate these error terms to the user’s location that is employed in Germany’s SAPOS network is the determination of area correction parameters (ACP, German: “Fl?chenkorrekturparameter—FKP”). A 2D interpolation scheme using data from at least 3 reference stations surrounding the rover is employed. A modification of this method was developed which only makes use of as few as 2 reference stations and provides 1D linear correction parameters along a “corridor” in which the user’s rover is moving. We present the results of a feasibility study portraying results from use of corridor correction parameters for precise RTK-like positioning. The differences to the reference coordinates (3D) attained in average for 1 h of data employing selected network nodes in Germany are between 0.8 and 2.0 cm, which compares well with the traditional area correction method that yields an error of 0.7 up to 1.1 cm.     

青藏高原纳木错湖阶沉积的发生特征及环境指示意义

选取的21个湖相沉积物样品分别采自纳木错湖西岸塔吉古日（剖面Nam Co 1）和纳木错湖东北岸的干玛弄附近（剖面Nam Co 2）。按照其发生特征分别将剖面从顶部到底部划分为12个和9个层次,通过分析各个层次沉积物的粒径分布特征、质地组成特点、总有机碳（TOC）、总无机碳（TIC）、总碳（TC）的百分含量、酸度值（pH）、电导率（EC）、含水量等若干环境指示因子。结果显示:无论在比较两个剖面的发生特征,还是环境指示因子特征,剖面Nam Co 1发育程度较剖面Nam Co 2更加发育;通过对测年数据结果分析,两个剖面均形成于晚更新世,并且通过比较各自剖面在垂直方向上的各项环境指示因子的变化趋势,可知纳木错湖流域在晚更新世（约40 ka BP）阶段发生过3次相对明显的冷暖交替过程.     

Continental rift-setting and evolution of Neoproterozoic Sindreth Basin in NW-India

The Neoproterozoic Sindreth Basin, NW India, and its surrounding area represent a half graben structure situated between the undeformed Malani Igneous Suite (MIS) in the west and a corridor of coeval Cryogenian ductile deformation, anatexis and granite intrusion in the east. The main lithologies observed in the basin are conglomerate, fanglomerate, debris flow and lake deposits derived from a nearby continental provenance, intercalated with concurrent mafic and felsic lava flows. Based on geological traverses across the strike of the basin, we propose a three-fold classification comprising Lower Clastic Unit and an Upper Clastic Unit and a Bimodal (basalt–rhyolite) Volcanic Unit separating the two. Tilting due to basin inversion and faulting has been observed; however, the rocks are unmetamorphosed and show undisturbed primary sedimentary features. The stratigraphic record of the basin is characteristic for deposition and magmatism in a fault-related continental setting. Implications of the findings have been discussed in the context of Neoproterozoic crustal dynamics in NW India. This study provides conclusive evidence for a continental setting for Sindreth Basin evolution and contests the recent models of active subduction setting (either back-arc basin or accretionary sediments over a subduction zone).     

A regional groundwater-flow model for sustainable groundwater-resource management in the south Asian megacity of Dhaka,Bangladesh

The water resources that supply most of the megacities in the world are under increased pressure because of land transformation, population growth, rapid urbanization, and climate-change impacts. Dhaka, in Bangladesh, is one of the largest of 22 growing megacities in the world, and it depends on mainly groundwater for all kinds of water needs. The regional groundwater-flow model MODFLOW-2005 was used to simulate the interaction between aquifers and rivers in steady-state and transient conditions during the period 1981–2013, to assess the impact of development and climate change on the regional groundwater resources. Detailed hydro-stratigraphic units are described according to 150 lithology logs, and a three-dimensional model of the upper 400 m of the Greater Dhaka area was constructed. The results explain how the total abstraction (2.9 million m³/d) in the Dhaka megacity, which has caused regional cones of depression, is balanced by recharge and induced river leakage. The simulated outcome shows the general trend of groundwater flow in the sedimentary Holocene aquifers under a variety of hydrogeological conditions, which will assist in the future development of a rational and sustainable management approach.

     

Modelling biofilm growth in the presence of carbon dioxide and water flow in the subsurface

The concentration of greenhouse gases – particularly carbon dioxide (CO₂) – in the atmosphere has been on the rise in the past decades. One of the methods which have been proposed to help reduce anthropogenic CO₂ emissions is the capture of CO₂from large, stationary point sources and storage in deep geological formations. The caprock is an impermeable geological layer which prevents the leakage of stored CO₂, and its integrity is of utmost importance for storage security. Due to the high pressure build-up during injection, the caprock in the vicinity of the well is particularly at risk of fracturing. Biofilms could be used as biobarriers which help prevent the leakage of CO₂ through the caprock in injection well vicinity by blocking leakage pathways. The biofilm could also protect well cement from corrosion by CO₂-rich brine.     

Southern hemispheric westerlies control the spatial distribution of modern sediments in Laguna Potrok Aike,Argentina

We studied the internal lake processes that control the spatial distribution and characteristics of modern sediments at the ICDP (International Continental Scientific Drilling Program) deep drilling site in Laguna Potrok Aike, southern Patagonia, Argentina. Sediment distribution patterns were investigated using a dense grid of 63 gravity cores taken throughout the lake basin and 40 additional shoreline samples. Analysis of the surficial sediment distribution points to distinct internal depositional dynamics induced by wind-driven lake internal currents. Distribution maps illustrate that the spatial characteristics of analysed variables are linked to high erosional wave activity. Persistent wave action and littoral erosion along all shores, especially the eastern shore, is caused by prevailing Southern Hemispheric Westerlies. Several sediment variables (grain size, benthic diatoms, total inorganic carbon and calcium) indicate re-suspension of littoral sediment followed by re-distribution to profundal accumulation areas near the eastern shore. Variations within the catchment influence sediment characteristics in the north-eastern bay. That area is characterized by different mineralogical and sedimentological conditions as well as greater accumulation of pollen, inorganic carbon and diatoms. These findings are related to the influence of episodic inflow into this bay. Spatial differences in stable isotope values throughout the lake suggest that ephemeral tributaries around the lake basin may also contribute to the detected spatial sediment variations.     

Seasonality in the North Sea during the Allerød and Late Medieval Climate Optimum using bivalve sclerochronology

Seasonal temperature patterns may have changed through time in response to current global warming. However, the temporal resolution of available proxy records is not sufficient to quantify paleotemperature seasonality prior to anthropogenic forcing of the climate. In the present study, we reconstructed seasonal and inter-annual temperature patterns of the North Sea during the last 140 years, the Allerød Interglacial and the Late Medieval Climate Optimum using sclerochronological and δ¹⁸O_aragonite data from bivalve shells, Arctica islandica. On average, the climate during 1278–1353 AD was ca. 1.1°C colder and seasonality was ca. 60% less than today. During the Allerød, long-term temperatures remained about 3.2°C below present values, and absolute summer and winter anomalies were ca. ?4 and ?2.7°C, respectively. However, seasonality was statistically indistinguishable from today. Long-term average temperatures compare well with existing data for the Late Medieval and Allerød, but detailed information on seasonality during the studied time intervals has never been presented before. Our data also demonstrated that annual instrumental and δ¹⁸O_aragonite-derived temperatures did not always match. This difference is explained by (1) NAO-driven salinity changes, which influence the temperature estimation from δ¹⁸O_aragonite and (2) food-driven changes in growth rates; portions of the shell that formed more rapidly are overrepresented in carbonate samples. Our study indicated that individual bivalve shells can open discrete, near-century long, ultra-high-resolution windows into the climate past. Such information can be vital for testing and verifying numerical climate models.     

A late Holocene paleo-productivity record in the western Gulf of Maine,USA, inferred from growth histories of the long-lived ocean quahog (<Emphasis Type="Italic">Arctica islandica</Emphasis>)

To investigate environmental variability during the late Holocene in the western Gulf of Maine, USA, we collected a 142-year-old living bivalve (Arctica islandica) in 2004, and three fossil A. islandica shells of the Medieval Warm Period (MWP) and late MWP / Little Ice Age (LIA) period (corrected ¹⁴C_AMS = 1030 ± 78 ad; 1320 ± 45 ad; 1357 ± 40 ad) in 1996. We compared the growth record of the modern shell with continuous plankton recorder (CPR) time-series (1961–2003) from the Gulf of Maine. A significant correlation (r ² = 0.55; p < 0.0001) exists between the standardized annual growth index (SGI) of the modern shell and the relative abundance of zooplankton species Calanus finmarchicus. We therefore propose that SGI data from A. islandica is a valid proxy for paleo-productivity of at least one major zooplankton taxa. SGIs from these shells reveal significant periods of 2–6 years (NAO-like) based on wavelet analysis, multitaper method (MTM) analysis and singular spectrum analysis (SSA) during the late Holocene. Based on established physical oceanographic observation in the Gulf of Maine, we suggest that slope water variability coupled with North Atlantic Oscillation (NAO) dynamics is primarily responsible for the observed SGI variability. Special Issue: AGU OS06 special issue “Ocean’s role in climate change—a paleo perspective”.     

Development of Emission Models and Improvement of Emission Data for Germany

Measurements and model developments with the objective to improve the quality and resolution of estimations of anthropogenic emissions are described. Measurement results on a chassis dynamometer were used to determine VOC profiles for exhaust gas emissions of passenger cars for different vehicle and fuel types and different driving modes. Further measurements resulted in emission factors and VOC profiles for lignite burning in residential stoves. Using remote sensing techniques benzene emission factors of gas stations and the efficiency of gasoline vapour recovery systems were measured.To improve the quality and the spatial and temporal resolution of emission data, emission models were improved or modified. This was done by elaborating and applying new methods for important emission source categories (e.g., solvent use, road traffic, small combustion) as well as including new data sources in the calculation routines (e.g. emission statements, land use data, import/export indices of solvents). Simultaneously considerable progress was made improving temporal and spatial allocation functions and VOC profiles. With these improvements a large number of anthropogenic emission data sets for 14 different grid projections in Germany and Europe have been generated. An emission scenario for Germany for 2010 suggests that considering air quality directives from the EU and Germany which are in force or in pipeline, German emissions of VOC and NO_x will decrease, but still exceed the national emission ceilings of the EU-NEC directive.