Curtis R. Wood

DISPERSION EXPERIMENTS IN CENTRAL LONDON The 2007 Dapple Project

In the event of a release of toxic gas in the center of London, emergency services personnel would need to determine quickly the extent of the area contaminated. The transport of pollutants by turbulent flow within the complex streets and building architecture of London, United Kingdom, is not straightforward, and we might wonder whether it is at all possible to make a scientifically reasoned decision. Here, we describe recent progress from a major U.K. project, Dispersion of Air Pollution and its Penetration into the Local Environment (DAPPLE; information online at www.dapple.org.uk). In DAPPLE, we focus on the movement of airborne pollutants in cities by developing a greater understanding of atmospheric flow and dispersion within urban street networks. In particular, we carried out full-scale dispersion experiments in central London from 2003 through 2008 to address the extent of the dispersion of tracers following their release at street level. These measurements complemented previous studies because 1...

Radar studies of the vertical distribution of insects migrating over southern Britain: the influence of temperature inversions on nocturnal layer concentrations

Insects migrating over two sites in southern UK (Malvern in Worcestershire, and Harpenden in Hertfordshire) have been monitored continuously with nutating vertical-looking radars (VLRs) equipped with powerful control and analysis software. These observations make possible, for the first time, a systematic investigation of the vertical distribution of insect aerial density in the atmosphere, over temporal scales ranging from the short (instantaneous vertical profiles updated every 15 min) to the very long (profiles aggregated over whole seasons or even years). In the present paper, an outline is given of some general features of insect stratification as revealed by the radars, followed by a description of occasions during warm nights in the summer months when intense insect layers developed. Some of these nocturnal layers were due to the insects flying preferentially at the top of strong surface temperature inversions, and in other cases, layering was associated with higher-altitude temperature maxima, such as those due to subsidence inversions. The layers were formed from insects of a great variety of sizes, but peaks in the mass distributions pointed to a preponderance of medium-sized noctuid moths on certain occasions.

An Overview of the Urban Boundary Layer Atmosphere Network in Helsinki

The Helsinki Urban Boundary-Layer Atmosphere Network (UrBAN: http://urban.fmi.fi) is a dedicated research-grade observational network where the physical processes in the atmosphere above the city are studied. Helsinki UrBAN is the most poleward intensive urban research observation network in the world and thus will allow studying some unique features such as strong seasonality. The networks key purpose is for the understanding of the physical processes in the urban boundary layer and associated fluxes of heat, momentum, moisture, and other gases. A further purpose is to secure a research-grade database, which can be used internationally to validate and develop numerical models of air quality and weather prediction. Scintillometers, a scanning Doppler lidar, ceilometers, a sodar, eddy-covariance stations, and radiometers are used. This equipment is supplemented by auxiliary measurements, which were primarily set up for general weather and/or air-quality mandatory purposes, such as vertical soundings and t...

Wind observations above an urban river using a new lidar technique, scintillometry and anemometry

Airflow along rivers might provide a key mechanism for ventilation in cities: important for air quality and thermal comfort. Airflow varies in space and time in the vicinity of rivers. Consequently, there is limited utility in point measurements. Ground-based remote sensing offers the opportunity to study 3D airflow in locations which are difficult to observe with conventional approaches. For three months in the winter and spring of 2011, the airflow above the River Thames in central London was observed using a scanning Doppler lidar, a scintillometer and sonic anemometers. First, an inter-comparison showed that lidar-derived mean wind-speed estimates compare almost as well to sonic anemometers (root-mean-square error (rmse) 0.65-0.68 ms(-1)) as comparisons between sonic anemometers (0.35-0.73 ms(-1)). Second, the lidar duo-beam operating strategy provided horizontal transects of wind vectors (comparison with scintillometer rmse 1.12-1.63 ms(-1)) which revealed mean and turbulent airflow across the river and surrounds; in particular, channelled airflow along the river and changes in turbulence quantities consistent with the roughness changes between built and river environments. The results have important consequences for air quality and dispersion around urban rivers, especially given that many cities have high traffic rates on roads located on riverbanks.

On the Temperature Structure Parameter and Sensible Heat Flux over Helsinki from Sonic Anemometry and Scintillometry

Two commercial large-aperture scintillometers, Scintec BLS900, were tested on pathlengths of 1840 and 4200m at about 45–65m above ground in Helsinki, Finland. From July 2011 through June 2012, large variability in diurnal and annual cycles of both the temperature structure parameter C 2 and sensible heat flux H were observed. Scintillometer data were compared with data from two eddy-covariance stations. A robust method was developed for the calculation ofC 2 from raw sonic-anemometer data. In contrast to many earlier studies that solely present the values of H, the main focus here is on comparisons of C 2 T itself. This has advantages, because optical-wavelength scintillometers measure C 2 with few assumptions, while the determination of H implies the applicability of the Monin–Obukhov similarity theory, which has several inherent limitations.The histogramsofC2 comparewell between sonic andscintillometer. In-depthanalysis is focused on one of the scintillometer paths: both C2 T and H comparisons gave similar and surprisingly high correlation coefficients (0.85 for C2 and 0.84–0.95 for H in unstable conditions), given the differences between the two measurement techniques, substantial sensor separation, and different source areas.

Layers of nocturnal insect migrants at high-altitude: the influence of atmospheric conditions on their formation.

1 Radar studies of nocturnal insect migration have often found that the migrants tend to form well‐defined horizontal layers at a particular altitude. 2 In previous short‐term studies, nocturnal layers were usually observed to occur at the same altitude as certain meteorological features, most notably at the altitudes of temperature inversion tops or nocturnal wind jets. 3 Statistical analyses are presented of 4 years of data that compared the presence, sharpness and duration of nocturnal layer profiles, observed using continuously‐operating entomological radar, with meteorological variables at typical layer altitudes over the U.K. 4 Analysis of these large datasets demonstrated that temperature was the foremost meteorological factor that was persistently associated with the presence and formation of longer‐lasting and sharper layers of migrating insects over southern U.K.

Sensitivity analysis of the meteorological pre-processor MPP-FMI 3.0 usingalgorithmic differentiation

The meteorological input parameters for urban and local scale dispersion models can be evaluated by pre-processing meteorological observations, using a boundary-layer parametrization model. This study presents a sensitivity analysis of a meteorological pre-processor model (MPPFMI) that utilises readily available meteorological data as input. The sensitivity of the pre-processor to meteorological input was analysed using algorithmic differentiation (AD). The AD tool used was TAPENADE. The AD method numerically evaluates the partial derivatives of functions that are implemented in a computer program. In this study, we focus on the evaluation of vertical fluxes in the atmosphere, and in particular on the sensitivity of the predicted inverse Obukhov length and friction velocity on the model input parameters. The study shows that the estimated inverse Obukhov length and friction velocity are most sensitive to wind speed, and second most sensitive to solar irradiation. The dependency on wind speed is most pronounced at low wind speeds. The presented results have implications for improving the meteorological pre-processing models. AD is shown to be an efficient tool for studying the ranges of sensitivities of the predicted parameters on the model input values quantitatively. A wider use of such advanced sensitivity analysis methods could potentially be very useful in analysing and improving the models used in atmospheric sciences.

The Sensitivity of the Predictions of a Roadside Dispersion Model to Meteorological Variables: Evaluation Using Algorithmic Differentiation

Dispersion and transformation of air pollution originated from a network of vehicular sources can be evaluated using the CAR-FMI model, combined with a meteorological pre-processor, MPP-FMI. The aim of this study is to analyse the sensitivities of both the meteorological pre-processor and the roadside dispersion model to the variations of model input values, taking especially into account the meteorological variables. Comprehensive and systematic analyses of the sensitivities of atmospheric dispersion models have been scarce in the literature. Such sensitivity analyses can be used in the refinement of both categories of models. The sensitivity analyses have been performed using an algorithmic differentiation (AD) tool called TAPENADE. We present selected illustrative results on the sensitivities of the meteorological pre-processing model MPP-FMI and the roadside dispersion model CAR-FMI on the model input variables. However, the AD method in general could also be applied for analysing the sensitivities of any other atmospheric modelling system.