Stability Effects on Heat and Moisture Fluxes at Sea

During the 1996 ASGAMAGE experiment we measured windspeed, air temperature T_a, watertemperature T_s, humidity and the momentum,heat and moisture fluxes at a research platform offthe Dutch coast. For each quantity we used several(sets of) instruments simultaneously. This allowed usto make an extensive assessment of the quality of themeasurements and to find optimal values for thevarious quantities for each run. From these values wecalculated C_H and C_E, theStanton and Dalton numbers, and reduced them to 10-mheight and neutral conditions. For this reductionwe made a separate analysis for the effect ofinclusion or non-inclusion of the assumption that theroughness length for heat or moisture is the same forthe neutral and non-neutral cases. Differences inthe reduced data due to this assumption turned out tobe well within the measurement error.For C_H we distinguished three separategroups of data: stable (A), unstable with_{a s} (B) and unstablewith thetas;_a > _s (C), with indicating the potential temperature.The stable data separate into two groups, depending onwater temperature and/or the wave field. The data ofgroup B showed a relation with wave age. The data ofgroup C consistently gave negative values forC_H, a result that might indicate conversion oflatent heat into sensible heat through condensation ofwater vapour just above the water surface. An attemptto re-analyse the data in terms of density fluxes,combining the effects of heat and moisture, still gavenegative transfer coefficients for group C.For the moisture flux we found the more conventionalresult of a separation in stable and unstable values;these categories showed a clear difference, but notrends with, for example, wind speed.We conclude that standard Monin-Obukhov similaritytheory cannot explain our data.     

Intercomparison of snow water equivalent observations in the Northern Great Plains

In the Northern Great Plains, melting snow is a primary driver of spring flooding, but limited knowledge of the magnitude and spatial distribution of snow water equivalent (SWE) hampers flood forecasting. Passive microwave remote sensing has the potential to enhance operational river flow forecasting but is not routinely incorporated in operational flood forecasting. We compare satellite passive microwave estimates from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR‐E) to the National Oceanic and Atmospheric Administration Office of Water Prediction (OWP) airborne gamma radiation snow survey and U.S. Army Corps of Engineers (USACE) ground snow survey SWE estimates in the Northern Great Plains from 2002 to 2011. AMSR‐E SWE estimates compare favourably with USACE SWE measurements in the low relief, low vegetation study area (mean difference = ?3.8 mm, root mean squared difference [RMSD] = 34.7 mm), but less so with OWP airborne gamma SWE estimates (mean difference = ?9.5 mm, RMSD = 42.7 mm). An error simulation suggests that up to half of the error in the former comparison is potentially due to subpixel scale SWE variability, limiting the maximum achievable RMSD between ground and satellite SWE to approximately 26–33 mm in the Northern Great Plains. The OWP gamma versus AMSR‐E SWE comparison yields larger error than the point‐scale USACE versus AMSR‐E comparison, despite a larger measurement footprint (5–7 km² vs. a few square centimetres, respectively), suggesting that there are unshared errors between the USACE and OWP gamma SWE data.     

Porosity and microstructure characterization of building stones and concretes

The microstructure of building materials greatly influences engineering properties like permeability, strength and durability. To determine this microstructure, different techniques were developed, each with its own limitations. The purpose of this study on concrete and natural building stones was to compare and to combine data obtained by X-ray computed micro-tomography (micro-CT), water absorption under vacuum and mercury intrusion porosimetry (MIP). Pore-size distribution curves ranging from 10 nm to 1 mm and total porosity results were obtained. Furthermore, micro-CT revealed the presence of an interfacial transition zone (ITZ) and of micro-cracks inside the aggregates of the concrete samples after mercury intrusion. Micro-CT visualized mercury inside large air bubbles within the concrete samples. Both micro-CT and MIP were compared and their respective advantages and disadvantages discussed.     

Spatial soil moisture scaling structure during Soil Moisture Experiment 2005

Soil moisture state and variability control many hydrological and ecological processes as well as exchanges of energy and water between the land surface and the atmosphere. However, its state and variability are poorly understood at spatial scales larger than the fields (i.e. 1 km²) as well as the ability to extrapolate field scale to larger spatial scales. This study investigates soil moisture profiles, their spatial organization, and physical drivers of variability within the Walnut Creek watershed, Iowa, during Soil Moisture Experiment 2005 and relates the watershed scale findings to previous field‐scale results. For all depths, the watershed soil moisture variability was negatively correlated with the watershed mean soil moisture and followed an exponential relationship that was nearly identical to that for field scales. This relationship differed during drying and wetting. While the overall time stability characteristics were improved with observation depth, the relatively wet and dry locations were consistent for all depths. The most time stable locations, capturing the mean soil moisture of the watershed within ± 0·9% volumetric soil moisture, were typically found on hill slopes regardless of vegetation type. These mild slope locations consistently preserve the time stability patterns from field to watershed scales. Soil properties also appear to impact stability but the findings are sensitive to local variations that may not be well defined by existing soil maps. Copyright © 2010 John Wiley & Sons, Ltd.     

The ~4-ka Rungwe Pumice (South-Western Tanzania): a wind-still Plinian eruption

The ~4-ka trachytic Rungwe Pumice (RP) deposit from Rungwe Volcano in South-Western Tanzania is the first Plinian-style deposit from an African volcano to be closely documented focusing on its physical characterization. The RP is a mostly massive fall deposit with an inversely graded base. Empirical models suggest a maximum eruption column height H _T of 30.5–35 km with an associated peak mass discharge rate of 2.8–4.8 × 10⁸ kg/s. Analytical calculations result in H _T values of 33 ± 4 km (inversion of TEPHRA2 model on grain size data) corresponding to mass discharge ranging from 2.3 to 6.0 × 10⁸ kg/s. Lake-core data allow extrapolation of the deposit thinning trend far beyond onland exposures. Empirical fitting of thickness data yields volume estimates between 3.2 and 5.8 km³ (corresponding to an erupted mass of 1.1–2.0 × 10¹² kg), whereas analytical derivation yields an erupted mass of 1.1 × 10¹² kg (inversion of TEPHRA2 model). Modelling and dispersal maps are consistent with nearly no-wind conditions during the eruption. The plume corner is estimated to have been ca. 11–12 km from the vent. After an opening phase with gradually increasing intensity, a high discharge rate was maintained throughout the eruption, without fountain collapse as is evidenced by a lack of pyroclastic density current deposits.     

Development of the SAR TT-OSL procedure for dating Middle Pleistocene dune and shallow marine deposits along the southern Cape coast of South Africa

Optically stimulated luminescence (OSL) dating is now commonly used to estimate the depositional age of Quaternary landforms along the southern Cape coast of South Africa. Due to the early onset of dose saturation in the quartz-rich sediments from this region, determining the age of deposits much older than the last three glacio-eustatic sea-level high stands has been a challenge. In this study, we explored the feasibility of using the thermally-transferred OSL (TT-OSL) dating method to obtain ages for aeolian and shallow marine deposits at three different localities that hold promise to further illuminate the long and complex Late Quaternary sea-level history of this region. The bleachability and behaviour of both the recuperated OSL (ReOSL) and the basic-transferred OSL (BT-OSL) signals were investigated, and used as independent chronometers to infer (a) the degree of bleaching of the sediments and (b) the stability of the ReOSL signal for dating of older samples. We examined the sensitivity of both signals to varying preheat temperatures and further developed the single-aliquot regenerative-dose procedure for TT-OSL dating of our samples. To verify our procedures, and to understand some of the underlying mechanisms responsible for the problems we observed, modern analogues and known-age Marine Isotope Sub-stage (MIS) 5e samples from the same localities were also measured. The Middle Pleistocene deposits investigated in this study produced statistically consistent ReOSL and BT-OSL ages compatible with sea-level high stands during Marine Isotope Stage 11. This result is of considerable significance, as it may yield new insights into maximum sea-level heights during this period, which is widely considered an appropriate analogue for future environmental conditions.     

Mississippi Valley regional source of loess on the southern Green Bay Lobe land surface, Wisconsin

Loess has been recognized on the glacial land surface of the Green Bay Lobe for over 100 yr, but no systematic explanation of the source of the loess has been advanced. Intriguingly, the loess on the Green Bay Lobe land surface is thicker than predicted by regional thinning trends from the Mississippi Valley and is geographically separated from much loess of southwest Wisconsin by a sandy region devoid of loess. Mapping based on soil survey interpretation indicates that the loess occurs above an escarpment marking the eastern end of the sandy loess-free region. Particle size fining trends demonstrate that the loess was transported by northwesterly winds. Clay mineralogy of the Green Bay Lobe loess is distinctly different than glaciogenic sediments and matches loess of the Mississippi Valley, indicating a regional source and long distance transport of the loess. We propose the loess was transported from the regional source along a surface of transport produced by migration of eolian sand through low-relief landscapes including the glacial Lake Wisconsin basin. Eolian sand migration caused repeated entrainment of dust leading to east-southeastward transport. The loess accumulated above an escarpment that limited sand mobility and re-entrainment of loess beyond this topographic barrier.     

A note on multiple flow equilibria

A set of ordinary differential equations describing a mechanical system subject to forcing and dissipation is considered. A topological argument is employed to show that if all time-dependent solutions of the governing equations are bounded, the equations admitN steady solutions, whereN is a positive odd integer and where at least (N–1)/2 of the steady solutions are unstable. The results are discussed in the context of atmospheric flows, and it is shown that truncated forms of the quasigeostrophic equations of dynamic meteorology and of Budyko-Sellers climate models satisfy the hypotheses of the theorem.     

Dew formation and the drying process within a maize canopy

The amount of dew-fall and dew-rise to a maize canopy during one night, and the drying time during the early morning, were estimated by using the Bowen ratio energy budget technique (BREB) and the soil diffusivity technique (SD).In addition, the distribution of the free liquid water within the plant community was measured at sunrise by using Leick plates and blotting papers. The course of the drying process within the plant canopy was also monitored by the blotting paper technique until the received night-time free liquid water within the canopy was evaporated. The calculated total amount of dew, estimated with the BREB and SD techniques, agreed with the measured amount to within 6%, though the measured drying process lagged about 1 hour behind the calculated one. Possible causes of this difference are the dripping effect and drainage down the stems, which were not included in the calculations. Initially, the drying process was faster in the upper layers of the canopy. Later, when the moisture distribution had become more or less even through the whole canopy, the drying rate became approximately uniform.