Why simulate cities?

This paper consists of three parts. After an introduction that stresses the historical progression of modeling methods, the motivation for urban modeling and simulation is explored, and the terms defined. Next, a meta-review of the literature is conducted, partially in an attempt to show that urban models resemble, and indeed share many overlapping issues with models in parallel fields such as economics and ecology. Lastly, the specific lessons learned from the author’s fifteen-year experience developing and supporting a cellular urban growth and land use change model (SLEUTH) are shared, in the interest of making these issues generic to current and future modeling and simulation efforts. The conclusion stresses that future models face new computing power, new theoretical paradigms, vastly improved ways of visualizing simulations, and a rapidly changing audience for modeling and simulation.     

On the interactions between planetary geostrophy and mesoscale eddies

Multiscale asymptotics are used to derive three systems of equations connecting the planetary geostrophic (PG) equations for gyre-scale flow to a quasigeostrophic (QG) equation set for mesoscale eddies. Pedlosky (1984), following similar analysis, found eddy buoyancy fluxes to have only a small effect on the large-scale flow; however, numerical simulations disagree. While the impact of eddies is relatively small in most regions, in keeping with Pedlosky’s result, eddies have a significant effect on the mean flow in the vicinity of strong, narrow currents.First, the multiple-scales analysis of Pedlosky is reviewed and amplified. Novel results of this analysis include new multiple-scales models connecting large-scale PG equations to sets of QG eddy equations. However, only introducing anisotropic scaling of the large-scale coordinates allows us to derive a model with strong two-way coupling between the QG eddies and the PG mean flow. This finding reconciles the analysis with simulations, viz. that strong two-way coupling is observed in the vicinity of anisotropic features of the mean flow like boundary currents and jets. The relevant coupling terms are shown to be eddy buoyancy fluxes. Using the Gent-McWilliams parameterization to approximate these fluxes allows solution of the PG equations with closed tracer fluxes in a closed domain, which is not possible without mesoscale eddy (or other small-scale) effects. The boundary layer width is comparable to an eddy mixing length when the typical eddy velocity is taken to be the long Rossby wave phase speed, which is the same result found by Fox-Kemper and Ferrari (2009) in a reduced gravity layer.     

The climate of Scotland over the last 5000 years inferred from multiproxy peatland records: inter‐site correlations and regional variability

The mid to late‐Holocene climates of most of Scotland have been reconstructed from seven peat bogs located across north–south and east–west geographical and climatological gradients. The main techniques used for palaeoclimatic reconstruction were plant macrofossil, colorimetric humification, and testate amoebae analyses, which were supported by a radiocarbon‐based chronology, aided by markers such as tephra isochrons and recent rises in pine pollen and in spheroidal carbonaceous particles (SCPs). Field stratigraphy was undertaken at each site in order to show that the changes detected within the peat profiles were replicable. Proxy climate records were reconstructed using detrended correspondence analysis (DCA) of the plant macrofossil data and a mean water table depth transfer function on the testate amoebae data. These reconstructions, coupled with the humification data, were standardised for each site and used to produce a composite record of bog surface wetness (BSW) from each site. The results show coherent wet and dry phases over the last 5000 years and suggest regional differences in climate across Scotland, specifically between northern and southern Scotland. Distinct climatic cycles are identified, all of which record a millennial‐scale periodicity which can be correlated with previously identified marine and ice core Holocene cycles. The key role of the macrofossil remains of Sphagnum imbricatum, a taxon now extinct on many sites, is discussed in relation to the identified climatic shifts. Copyright © 2005 John Wiley & Sons, Ltd.     

Preserving the unpreservable: a lost world rediscovered at Christian Malford, UK

The small village of Christian Malford, Wiltshire (UK) is known to palaeontologists the world over because of the chance discovery of an astonishing fossil bonanza in the mid-nineteenth century. Pits in the Jurassic Oxford Clay yielded thousands of specimens of exquisitely preserved ammonites, fish and crustaceans, but became most famous for squid-like cephalopods and belemnites (collectively termed coleoids) with fossilized soft-parts. The precise location of the find has remained obscure, until now, and a new attempt is underway to understand the ancient environment that triggered this unusual preservation.     

The 2dF Galaxy Redshift Survey: luminosity dependence of galaxy clustering

We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using the Anglo-Australian two degree field galaxy redshift survey (2dFGRS). The 2dFGRS is over an order of magnitude larger than previous redshift surveys used to address this issue. We measure the projected two-point correlation function of galaxies in a series of volume-limited samples. The projected correlation function is free from any distortion of the clustering pattern induced by peculiar motions and is well described by a power law in pair separation over the range     . The clustering of     galaxies in real space is well-fitted by a correlation length     and power-law slope     . The clustering amplitude increases slowly with absolute magnitude for galaxies fainter than M *, but rises more strongly at higher luminosities. At low luminosities, our results agree with measurements from the Southern Sky Redshift Survey 2 by Benoist et al. However, we find a weaker dependence of clustering strength on luminosity at the highest luminosities. The correlation function amplitude increases by a factor of 4.0 between     and −22.5, and the most luminous galaxies are 3.0 times more strongly clustered than L * galaxies. The power-law slope of the correlation function shows remarkably little variation for samples spanning a factor of 20 in luminosity. Our measurements are in very good agreement with the predictions of the hierarchical galaxy formation models of Benson et al.     

Interactions between groundwater and surface water in a virginia coastal plain watershed. 1. Hydrological flowpaths

A field study of surface water and groundwater interactions during baseflow and stormflow conditions was performed at the Reedy Creek watershed in the Virginia Coastal Plain. Three estimates of the average saturated hydraulic conductivity (K_s) of the unconfined aquifer were in reasonable agreement (ranging from 0.0033 to 0.010 cm/s), indicating that baseflow in the creek is entirely from the drainage of shallow groundwater from the relatively thin (1–6 m thick) unconfined aquifer. This relatively permeable surficial aquifer was found to be underlain by dark, olive grey, clay-silt and diatomaceous Miocene deposits of low permeability known as the Calvert Formation, which is believed to function as a confining bed in the area. A chemical hydrograph separation technique was used to resolve the contributions of [old] (pre-event) and [new] (event) water to stormflow. Results from a major rainstorm indicated that old water dominated the stormflow response of the watershed, although the new water contribution approached 40% at the hydrograph peak. Stormflow at Reedy Creek appears to result from saturation overland flow from variable source areas which include the stream channels and a significant part of the riparian wetland area. This response appears to be attributable to the transient dynamics of the shallow groundwater flow system and to the formation of localized groundwater mounds which raise the water-table to the wetland surface.