Flow and transport modeling in the sea-breeze part II: Flow model application and pollutant transport

A modifiedE- non-hydrostatic model with non-equilibrium level 2.5 closure was applied to the flow and pollutant dynamics in the sea-breeze. The model predicts key observed characteristics of the sea-breeze, such as midday slowing of inland penetration, fast and deep inland penetration in late afternoon, and detachment of the sea-breeze from the feeding flow in early evening. In late evening when the turbulent mixing over the land subsides due to the surface cooling, a frontal density current is formed and the predicted structure is in good agreement with observations and laboratory experiments of density currents. Turbulent mixing over the land is a key parameter that controls midday slowing and late afternoon frontal development.The calculated thermal internal boundary layer and fumigation of an elevated line source show good agreement with observations and similarity theory. Calculations suggest that the residual plume aloft over the sea returns onshore at ground level during the afternoon sea-breeze and has a large impact on ground-level concentrations during the following day.     

A template for calculating rock surface roughness

This software (which accompanies McCarroll and Nesje, 1996, Earth Surface Processes and Landforms Vol. 21, 963–977) is designed to quantify the roughness of rock surfaces from profiles recorded using either a micro-roughness meter or a simple profile gauge. The roughness index used is the standard deviation of the differences between adjacent height values recorded at set horizontal intervals. Profiles are assumed to be 19 cm long with heights recorded every 5 mm. The template provided assumes that four profiles are recorded from each of ten surfaces (e.g. boulders). Roughness values are calculated using (overlapping) measurement intervals of 5 mm, 10 mm, 15 mm, 20 mm, 25 mm and 30 mm. The results are tabulated and presented as ‘deviograms’ which display both the magnitude and scale of roughness. The spreadsheet used was Quattro-pro for Windows, version 1.00. © 1997 John Wiley & Sons, Ltd.     

Role of temporal resolution of meteorological inputs for process‐based snow modelling

Accurate snow accumulation and melt simulations are crucial for understanding and predicting hydrological dynamics in mountainous settings. As snow models require temporally varying meteorological inputs, time resolution of these inputs is likely to play an important role on the model accuracy. Because meteorological data at a fine temporal resolution (~1 hr) are generally not available in many snow‐dominated settings, it is important to evaluate the role of meteorological inputs temporal resolution on the performance of process‐based snow models. The objective of this work is to assess the loss in model accuracy with temporal resolution of meteorological inputs, for a range of climatic conditions and topographic elevations. To this end, a process‐based snow model was run using 1‐, 3‐, and 6‐hourly inputs for wet, average, and dry years over Boise River Basin (6,963 km²), which spans rain dominated (≤1,400 m), rain–snow transition (>1,400 and ≤1,900 m), snow dominated below tree line (>1,900 and ≤2,400 m), and above tree line (>2,400 m) elevations. The results show that sensitivity of the model accuracy to the inputs time step generally decreases with increasing elevation from rain dominated to snow dominated above tree line. Using longer than hourly inputs causes substantial underestimation of snow cover area (SCA) and snow water equivalent (SWE) in rain‐dominated and rain–snow transition elevations, due to the precipitation phase mischaracterization. In snow‐dominated elevations, the melt rate is underestimated due to errors in estimation of net snow cover energy input. In addition, the errors in SCA and SWE estimates generally decrease toward years with low snow mass, that is, dry years. The results indicate significant increases in errors in estimates of SCA and SWE as the temporal resolution of meteorological inputs becomes coarser than an hour. However, use of 3‐hourly inputs can provide accurate estimates at snow‐dominated elevations. The study underscores the need to record meteorological variables at an hourly time step for accurate process‐based snow modelling.     

Sensitivity of model parameterizations for simulated latent heat flux at the snow surface for complex mountain sites

The snowcover energy balance is typically dominated by net radiation and sensible and latent heat fluxes. Validation of the two latter components is rare and often difficult to undertake at complex mountain sites. Latent heat flux, the focus of this paper, is the primary coupling mechanism between the snow surface and the atmosphere. It accounts for the critical exchange of mass (sublimation or condensation), along with the associated snowcover energy loss or gain. Measured and modelled latent heat fluxes at a wind‐exposed and wind‐sheltered site were compared to evaluate variability in model parameters. A well‐tested and well‐validated snowcover energy balance model, Snobal, was selected for this comparison because of previously successful applications of the model at these sites and because of the adjustability of the parameters specific to latent heat transfer within the model. Simulated latent heat flux and snow water equivalent (SWE) were not sensitive to different formulations of the stability profile functions associated with heat transfer calculations. The model parameters of snow surface roughness length and active snow layer thickness were used to improve latent heat flux simulations while retaining accuracy in the simulation of the SWE at an exposed and sheltered study site. Optimal parameters for simulated latent heat flux and SWE were found at the exposed site with a shorter roughness length and thicker active layer, and at the sheltered site with a longer roughness length and thinner active layer. These findings were linked to physical characteristics of the study sites and will allow for adoption into other snow models that use similar parameters. Physical characteristics of wind exposure and cover could also be used to distribute critical parameters in a spatially distributed modelling domain and aid in parameter selection for application to other watersheds where detailed information is not available. Copyright © 2012 John Wiley & Sons, Ltd.     

Psychohistory revisited: fundamental issues in forecasting climate futures

Uncertainty in the trajectories of the global energy and economic systems vexes the climate science community. While it is tempting to reduce uncertainty by searching for deterministic rules governing the link between energy consumption and economic output, this article discusses some of the problems that follow from such an approach. We argue that the theoretical and empirical evidence supports the view that energy and economic systems are dynamic, and unlikely to be predictable via the application of simple rules. Encouraging more research seeking to reduce uncertainty in forecasting would likely be valuable, but any results should reflect the tentative and exploratory nature of the subject matter.     

Evaluation of swimmer-based rip current escape strategies

Rip currents are the primary hazard on surf beaches, and early studies described them as fast, shore-normal flows that extended seaward of the surf zone. Based on this traditional view, commonly promoted safety advice was to escape a rip current by swimming parallel to the beach. However, recent studies have shown dominant rip current re-circulation within the surf zone and have endorsed floating as an appropriate escape strategy. Here, a first quantitative assessment of the efficacy of various rip current escape strategies, with a focus on the underlying physical processes, is presented. A field study was conducted at Shelly Beach, NSW, Australia, measuring three rip currents (two open beaches, one topographic) over 3 days in varying wave conditions. Floating was found to be a longer duration, more variable escape strategy ( $ \overline{t} $  = 3.8 min, σ = 2.4 min), than swimming parallel ( $ \overline{t} $  = 2.2 min, σ = 1.0 min). Neither of the scenarios is 100 % foolproof, and both fail in some scenarios, making simplified safety recommendations difficult. Swim parallel failures are related to swimming against the alongshore current of the rip circulation. Float failures related to surf zone exits, with the highest exit rate occurring in the topographic rip. Float failures also occurred due to multiple re-circulations without the person attaining safe footing on the bar. The variable spatial and temporal behaviour of rip currents suggests that a single escape strategy safety message is inappropriate. Instead, a combined approach and scenario-specific safety advice should be considered by beach safety practitioners to promote to the public.     

LINKING SEDIMENT EXPOSURE WITH EFFECTS: MODELING TECHNIQUES, ORGANIC AVAILABILITY AND UPTAKE

1 INTRODUCTION Sediments are the ultimate sink for many hydrophobic contaminants and represent biologically important environmental habitats. Exposure of the sediment-associated contaminants is not only influenced by the fate and transport of sediment but also is influenced by a variety of physical, chemical, and biological processes that involve no net movement of sediments. These processes include pore water transport processes such as advection and diffusion, and sediment mixing process…     

Spring temperature variability in northern Fennoscandia AD 1693–2011

A reconstruction of spring (April–May) temperature for northern Fennoscandia developed from the Tornionjoki (Tornio river) long cryophenological record of ice break‐up dates, back to AD 1693, is presented. The record is strongly climatically sensitive and explains 67% of the variance in the instrumental data over the last 150 years. The record exhibits a stepped decrease in the duration of the river's ice cover by 14 days, equivalent to an increase in April–May mean temperature of approximately 2.5°C over the last three centuries. The relationship between the date of ice break‐up, and accumulated daily mean temperatures (>0°C) is investigated. Uncertainty in the observation of ice break‐up is also considered in addition to the potential of this time series for regional climate model validation. Copyright © 2011 John Wiley & Sons, Ltd.