Local isotropy and anisotropy in the sheared and heated atmospheric surface layer

Longitudinal velocity and temperature measurements above a uniform dry lakebed were used to investigate sources of eddy-motion anisotropy within the inertial subrange. Rather than simply test the adequacy of locally isotropic relations, we investigated directly the sources of anisotropy. These sources, in a daytime desert-like climate, include: (1) direct interaction between the large-scale and small-scale eddy motion, and (2) thermal effects on the small-scale eddy motion. In order to explore these two anisotropy sources, we developed statistical measures that are sensitive to such interactions. It was found that the large-scale/small-scale interaction was significant in the inertial subrange up to 3 decades below the production scale, thus reducing the validity of the local isotropy assumption. The anisotropy generated by thermal effects was also significant and comparable in magnitude to the former anisotropy source. However, this thermal anisotropy was opposite in sign and tended to counteract the anisotropy generated by the large-scale/smallscale interaction. The thermal anisotropy was attributed to organized ramp-like patterns in the temperature measurements. The impact of this anisotropy cancellation on the dynamics of inertial subrange eddy motion was also considered. For that purpose, the Kolmogorov-Obukhov structure function equation, as derived from the Navier-Stokes equations for locally isotropic turbulence, was employed. The Kolmogorov-Obukhov structure function equation in conjunction with Obukhov's constant skewness closure hypothesis reproduced the measured second- and third-order structure functions. Obukhov's constant skewness closure scheme, which is also based on the local isotropy assumption, was verified and was found to be in good agreement with the measurements. The accepted 0.4 constant skewness value derived from grid turbulence experiments overestimated our measurements. A suggested 0.26 constant skewness value, which we derived from Kolmogorov's constant, was found to be adequate.     

A Note On Surface Humidity Measurements In The Cold Canadian Environment

In the cold Canadian environment, humidity measurements can be verydifficult to conduct. In this brief communication, humidity observationstaken by two different sensors at six remote Canadian Arctic locations arecompared. The observations collected by Vaisala HMP35CF sensors displaya strong tendency toward the ice saturation point whereas dew cell instrumentsexhibit significantly lower values of relative humidity with respect to ice (RH_i).Humidity data collected by HMP35CF hygrometers are therefore unreliable sincethey are subject to persistent icing that lead them to record values of RH_i near 100%, irrespective of the air temperature. The high humidity bias emerges atmeteorological stations mounted with the HMP35CF probes since these instrumentsare usually neither sheltered nor heated, and are not attended to at regular intervals. Thus, great care must be taken in utilizing humidity data recorded by HMP35CF sensors across the network of climate autostations in Canada.     

A Comparison between WCS and OPeNDAP for Making Model Results and Data Products Available through the Internet

Numerical models produce output with a large number of variables, grid cells and time steps. The same applies to algorithms that produce gridded datasets from sparse or abundant raw data. Further use of the resulting data products has been challenging, especially for dissemination outside the institute of origin. Due to the gradually increasing size of data products, simply downloading copies of them is becoming impossible. A gradual transition from traditional download methods to web services is therefore observed. Web services allow for on‐the‐fly access to subsets of data that were hitherto considered as indivisible granules. Here we compare the most mature candidates to serve gridded data through the web: the Open‐source Project for a Network Data Access Protocol (OPeNDAP) and Web Coverage Service (WCS) protocols. In the framework of the new Dutch National Model and Data Centre (NMDC.eu) a distributed data storage has been created by coupling OPeNDAP servers. A WCS service layer is provided for the same data. This allows us to compare OPeNDAP and WCS. Using several use cases, we compare the usability, performance and features of the two protocols.     

Geomasking sensitive health data and privacy protection: an evaluation using an E911 database

Geomasking is used to provide privacy protection for individual address information while maintaining spatial resolution for mapping purposes. Donut geomasking and other random perturbation geomasking algorithms rely on the assumption of a homogeneously distributed population to calculate displacement distances, leading to possible under-protection of individuals when this condition is not met. Using household data from 2007, we evaluated the performance of donut geomasking in Orange County, North Carolina. We calculated the estimated k-anonymity for every household based on the assumption of uniform household distribution. We then determined the actual k-anonymity by revealing household locations contained in the county E911 database. Census block groups in mixed-use areas with high population distribution heterogeneity were the most likely to have privacy protection below selected criteria. For heterogeneous populations, we suggest tripling the minimum displacement area in the donut to protect privacy with a less than 1% error rate.     

Macroalgal survival in ballast water tanks

Despite a large amount of research into invasive species and their introductions, there have been no studies focused on macroalgal transport in ballast water. To address this, we collected replicate samples of ballast water from 12 ships in two Mediterranean harbours (Naples and Salerno). Filtered samples were kept in culture for a month at Mediterranean mean conditions (18 degrees C, 12:12h LD, 60micromol photons m(-2)s(-1)). Fifteen macroalgal taxa were cultured and differed according to the geographic origin of the ballast water. Most of the cultured algae were widely distributed species (e.g. Ulva spp. and Acinetospora-phase). However, Ulva ohnoi Hiraoka and Shimada, described from Japan, was hitherto unknown in the Mediterranean Sea. We show for the first time that ballast water can be an important vector for the transport of microscopic stages of macroalgae and that this can be a vector for the introduction of alien species.     

The radio frequency dielectric properties of the stratified UG1–UG2 geological unit in the Bushveld Complex

A new measurement technique enables the complex dielectric properties of the geological strata comprising the UG1–UG2 (Upper Group 1–Upper Group 2) unit of the Bushveld Complex in South Africa to be determined with unprecedented detail at radio frequencies (RF). Results of non-destructive laboratory measurements of representative diamond drill core samples from the UG1–UG2 unit are presented at 25 MHz. These data establish that the UG1 and UG2 chromitite layers are embedded in rock strata (norite, pyroxenite and anorthosite) which are translucent in the HF spectral band, whereas the chromitite layers themselves exhibit significant velocity contrast, making them good radar reflectors. The data presented here is useful for calibration of the radar system, and for predicting the range and resolution performance of borehole radars operating in both the hanging and footwalls of the economically important platiniferous UG2 reef.     

Towards Improved Remedial Outcomes in Categorical Aquifers with an Iterative Ensemble Smoother

Categorical parameter distributions consisting of geologic facies with distinct properties, for example, high-permeability channels embedded in a low-permeability matrix, are common at contaminated sites. At these sites, low-permeability facies store solute mass, acting as secondary sources to higher-permeability facies, sustaining concentrations for decades while increasing risk and cleanup costs. Parameter estimation is difficult in such systems because the discontinuities in the parameter space hinder the inverse problem. This paper presents a novel approach based on Traveling Pilot Points (TRIPS) and an iterative ensemble smoother (IES) to solve the categorical inverse problem. Groundwater flow and solute transport in a hypothetical aquifer with a categorical parameter distribution are simulated using MODFLOW 6. Heads and concentrations are recorded at multiple monitoring locations. IES is used to generate posterior ensembles assuming a TRIPS prior and an approximate multi-Gaussian prior. The ensembles are used to predict solute concentrations and mass into the future. The evaluation also includes an assessment of how the number of measurements and the choice of the geological prior determine the characteristics of the posterior ensemble and the resulting predictions. The results indicate that IES was able to efficiently sample the posterior distribution and showed that even with an approximate geological prior, a high degree of parameterization and history matching could lead to parameter ensembles that can be useful for making certain types of predictions (heads, concentrations). However, the approximate geological prior was insufficient for predicting mass. The analysis demonstrates how decision-makers can quantify uncertainty and make informed decisions with an ensemble-based approach.     

The role of aridification in constraining the elevation range of Holocene solifluction processes and associated landforms in the periglacial belt of the Sierra Nevada (southern Spain)

Climate variability during the Mid‐Late Holocene has influenced the activity of geomorphic processes in the current periglacial belt of the Sierra Nevada. We studied two types of sedimentary records that reveal a synchronous timing for slope instability in this high semi‐arid massif: solifluction landforms and mountain lake sediments. Lithological and sedimentological properties of both records have recorded numerous cycles of different magnitude of slope processes in the massif. Solifluction deposits record seven phases of solifluction activity and soil development during the last 7 ka bp and lake sediments show evidence of eight periods with increased geomorphic activity in the catchments over the last 6 ka bp . Although present‐day climate conditions do not promote active solifluction processes in the Sierra Nevada, colder and wetter periods during the Holocene triggered solifluction and transported coarse‐grained sediments into the lakes. By contrast, warm phases favoured soil formation and spread an incipient vegetation cover over the headwaters of the highest valleys, diminishing the grain size of the particles reaching the lakes. Lake sediments record an aridification trend in the massif intensifying since 4·2 ka bp that has conditioned solifluction activity to shift gradually to higher elevations. During major cooler phases such as the Little Ice Age active solifluction was recorded back down to 2500 m altitude. Copyright © 2010 John Wiley & Sons, Ltd.