We present the first results of a systematic analysis of radially truncated exponential discs for four galaxies of a complete sample of disc-dominated edge-on spiral galaxies. The discs of our sample galaxies are truncated at similar radii on either side of their centres. With possible the exception of the disc of ESO 416-G25, it appears that the truncations in our sample galaxies are closely symmetric, in terms of both their sharpness and the truncation length. However, the truncations occur over a larger region and not as abruptly as found in previous studies. We show that the truncated luminosity distributions of our sample galaxies, if also present in the mass distributions, comfortably meet the requirements for longevity. The formation and maintenance of disc truncations are likely closely related to stability requirements for galactic discs.Comment: 11 pages LaTeX, incl. 7 postscript figures, MNRAS, accepted; major revisions include

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Abstract. This study is the first to contrast two similarity theory methods, the flux variance and the half-order time derivative, over a wide range of atmospheric stability and surface roughness conditions. These two methods were selected because they require only single-level temperature measurement to estimate sensible heat flux. The data used were collected over bare soil, a grass-covered forest clearing, and an even-aged pine forest. For all three sites the flux variance method estimated the sensible heat flux relatively well for unstable atmospheric conditions. The half-order time derivative method was found to be sensitive to the parameterization of the eddy diffusivity, especially for the grass and bare soil field sites. Overall, the flux variance method was able to reproduce the measured sensible heat flux with greater accuracy than the half-order time derivative methods for the three experiment sites.

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It is becoming clear that the description of water exchange over vegetated surfaces can bene t from a simultaneous consideration of heat and C O 2 exchanges, as all these exchange processes are intertwined at the most fundamental level. Over the last two decades, several approaches have been developed to infer scalar sources and sinks within canopies without resorting to gradient-di usion theory. This study investigates recent developments in multi-layer methods to compute distributions and strengths of scalar sources and sinks within the canopy volume. Two types of model formulations are considered: 1 forward methods which require vertical foliage distribution along with canopy radiative, physiological, biochemical, and drag properties and 2 inverse methods which require measured mean scalar concentration distribution within the canopy. These approaches are able to reproduce measured turbulent uxes above the canopy without relying on an empirical relationship between turbulent scalar uxes and mean concentration gradients. However, both approaches share the need for accurate description of the second moments of the velocity statistics inside the canopy.