Ground-based FTIR Measurements of Stratospheric Trace Species from Aberdeen During Winter and Spring 1993/94 and 1994/95 and Comparison with a 3D Model

Vertical column abundances of HCl, ClONO2, HF and HNO3 have been obtained from infrared solar absorption measurements made at Aberdeen, UK (57°N, 2°W) during the periods January 13 1994 - May 8 1994 and November 23 1994 - April 19 1995. The measurements reveal the partitioning of inorganic chlorine (Cly) inside and outside the polar vortex during these two winter and spring periods. Stratospheric temperatures within the northern polar vortex during 1993/94 were not cold throughout January and most of February. The measurements reported here suggest that following a brief period of chlorine activation in late February and early March, the active chlorine within the vortex recovered rapidly to form ClONO2 resulting in in-vortex ClONO2 columns of 7 × 1015 molecules cm-2. In contrast, measurements during January 1995 suggest extensive invortex activation with in-vortex HCl + ClONO2 as low as 3.6×1015 molecules cm-2. High day-to-day variability in the ClONO2 columns observed during February is evidence for the transport of ClONO2 rich air from high to mid latitudes during the late winter. The implications for mid latitude O3 loss are discussed. A preliminary comparison of the HCl, ClONO2, and HNO3 column data from winter 94/95 with a three-dimensional chemical transport model shows that the model generally reproduces well the day-to-day variability and absolute magnitude of the observed columns, especially for HNO3 outside of the vortex.     

Wind flows and forces in a model spruce forest

Wind tunnel tests have been conducted on a 1:75 scale model of a Sitka spruce forest in a correctly scaled turbulent boundary-layer flow. 12000 tree models were manufactured with mass, flexibility and aerodynamic drag characteristics chosen to give dynamical similarity with typical 15 m trees in a 30ms^–1 gale. To measure the dynamic response of a sample tree, set within this model forest, a miniature, fast response strain-gauge balance was designed and built. Linked to a computer for on-line data sampling, this balance provided measurements of the fluctuating along-wind and acrosswind components of the overturning moment at ground level, leading to values of mean and extreme moments and the frequency spectrum of the sway motion. Associated measurements of local wind flow characteristics were made with hot-wire anemometers and a laser anemometer. The response of the tree has the characteristics of classical lightly damped vibration and there is evidence that resonant sway motion increases the extreme overturning moments significantly above the values produced by wind gust forces alone.     

Why geoengineering is not a ‘global public good’, and why it is ethically misleading to frame it as one

In early policy work, climate engineering is often described as a global public good. This paper argues that the paradigm example of geoengineering—stratospheric sulfate injection (hereafter ‘SSI’)—does not fit the canonical technical definition of a global public good, and that more relaxed versions are unhelpful. More importantly, it claims that, regardless of the technicalities, the public good framing is seriously misleading, in part because it arbitrarily marginalizes ethical concerns. Both points suggest that more clarity is needed about the aims of geoengineering policy—and especially governance—and that this requires special attention to ethics.     

Mechanisms Controlling Turbulence Development Across A Forest Edge

In this paper we discuss the development of turbulence back from the transition fromopen moorland to a forest. Data from a field study and a wind-tunnel experiment arepresented. These show that the variance in the streamwise velocity begins to adjust tothe new surface between 2 to 4 tree heights downwind of the transition. This is soonerthan either the vertical velocity variance or the shear stress, both of which begin to adjust in a zone 3 to 5 tree heights downwind of the edge. Key terms in the prognostic equations for streamwise and vertical velocity variance are evaluated in order to explain these differences. The flow distortion caused by the forest edge, which extends to 4 tree heights downwind of the forest edge, is shown to be crucial in the delayed turbulence development. Initially the shear production term, which is the dominant source for the streamwise velocity variance, is counteracted by a sink in the vertical advection term. After the flow levels out the pressure redistribution (return-to-isotropy) term becomes the main sink of streamwisevelocity variance and feeds energy into the vertical velocity component. Therefore, thedevelopment of the vertical velocity variance and shear stress cannot begin until afterdevelopment of an increase in the streamwise velocity variance. Results are comparedwith other experiments, including the flow across shelterbelts, and large-eddy simulations of forest flow.     

The Impact of Landscape Fragmentation on Atmospheric Flow: A Wind-Tunnel Study

Landscape discontinuities such as forest edges play an important role in determining the characteristics of the atmospheric flow by generating increased turbulence and triggering the formation of coherent tree-scale structures. In a fragmented landscape, consisting of surfaces of different heights and roughness, the multiplicity of edges may lead to complex patterns of flow and turbulence that are potentially difficult to predict. Here, we investigate the effects of different levels of forest fragmentation on the airflow. Five gap spacings (of length approximately 5h, 10h, 15h, 20h, 30h, where h is the canopy height) between forest blocks of length 8.7h, as well as a reference case consisting of a continuous forest after a single edge, were investigated in a wind tunnel. The results reveal a consistent pattern downstream from the first edge of each simulated case, with the streamwise velocity component at tree top increasing and turbulent kinetic energy decreasing as gap size increases, but with overshoots in shear stress and turbulent kinetic energy observed at the forest edges. As the gap spacing increases, the flow appears to change monotonically from a flow over a single edge to a flow over isolated forest blocks. The apparent roughness of the different fragmented configurations also decreases with increasing gap size. No overall enhancement of turbulence is observed at any particular level of fragmentation.     

The permanence of stream networks in britain: Some further comments

The conclusions of Ovenden and Gregory (1980) are reviewed in the context of a stream network on the blanket peat moorland of the Southern Pennines. The very great disparity between the 1:10560 map network and the present channel system suggests that the original survey only included the major tributaries. Map accuracy in areas of peat moorland must therefore be treated with some caution particularly if no air photograph or field checking can be done. Some problems of network definition in the peat moorlands are also briefly discussed.