Small-scale Spatial Changes Research Articles

Subpixel Characterization of HIRS Spectral Radiances Using Cloud Properties from AVHRR

AbstractThis paper describes a cloud type radiance record derived from NOAA polar-orbiting weather satellites using cloud properties retrieved from the Advanced Very High Resolution Radiometer (AVHRR) and spectral brightness temperatures (Tb) observed by the High Resolution Infrared Radiation Sounder (HIRS). The authors seek to produce a seamless, global-scale, long-term record of cloud type and Tb statistics intended to better characterize clouds from seasonal to decadal time scales. Herein, the methodology is described in which the cloud type statistics retrieved from AVHRR are interpolated onto each HIRS footprint using two cloud classification methods. This approach is tested over the northeast tropical and subtropical Pacific Ocean region, which contains a wide variety of cloud types during a significant ENSO variation from 2008 to 2009. It is shown that the Tb histograms sorted by cloud type are realistic for all HIRS channels. The magnitude of Tb biases among spatially coincident satellite intersections over the northeast Pacific is a function of cloud type and wavelength. While the sign of the bias can change, the magnitudes are generally small for NOAA-18 and NOAA-19, and NOAA-19 and MetOp-A intersections. The authors further show that the differences between calculated standard deviations of cloud-typed Tb well exceed intersatellite calibration uncertainties. The authors argue that consideration of higher-order statistical moments determined from spectral infrared observations may serve as a useful long-term measure of small-scale spatial changes, in particular cloud types over the HIRS–AVHRR observing record.

Does the resolution of megacity emissions impact large scale ozone?

Abstract The importance of using high resolution when modelling the impact of megacity emission on large scale tropospheric ozone has been investigated using the regional WRF-Chem model. Two 3-day summer periods in July and August 2003 have been simulated for three megacities; London, Ruhr, and Cairo. Simulations have been performed with constant model resolution (9 × 9 km2) and with megacity emission resolutions at 9 × 9 km2, 27 × 27 km2, and 81 × 81 km2, by using detailed emission inventories averaged to the appropriate resolution. In order to quantify the megacities’ contributions to regional ozone, simulations without megacity emissions were also performed. In general, results from the six case studies show that the inaccuracies that arise on a large scale when using megacity emission resolution at a typical scale of a global Chemistry-Transport Model (81 × 81 km2) were relatively small (12% or less). However, the impact of resolution on ozone changes caused by megacity emissions depends strongly on meteorological conditions. The case with the largest impact (London, July 2003) showed that net ozone formed from the megacity were 12% higher when using 81 × 81 km2 rather than 9 × 9 km2 emission resolution, due to stronger ozone production since the NOx emissions were more rapidly diluted to regions where the ozone production was NOx limited in the coarse resolution case. Our study suggests that high resolution is more important for local air pollution studies than for large scale ozone changes relevant for climate studies, since a change in megacity emission resolution induces small-scale spatial changes in ozone fields, but relatively small changes when integrating over a large volume. These results indicate that parameterization of megacity emissions in large scale models may be unnecessary. However, the impact of a finer resolution of the meteorology is not studied here and could possibly give larger effects seen from a climate perspective.

Floating and fixed artificial habitats: Spatial and temporal patterns of benthic communities in a coral reef environment

While natural marine habitats with motion capabilities, e.g., kelps and seaweeds, have been studied alongside their associated fouling communities, little is known of the effect of motion on the communities of floating artificial habitats such as buoys, rafts, and pontoons, particularly in tropical systems. Hydrodynamic features greatly differ between floating and fixed artificial substrata, which in turn affect the structure of their associated communities. This study tested the hypothesis that floating and fixed artificial installations in a tropical reef system (Eilat, Red Sea) would support different benthic communities throughout space and time. Specifically, we examined differences in communities recruited onto settlement plates between floating and fixed installations deployed at three different sites, along a two-year monitoring period. The three sites exhibited distinct differences in species assemblages between the monitoring dates (6, 12, 18 and 24 months post deployment), mainly between the first and the last two dates. The average level of dissimilarity between floating and fixed installations increased over time at all sites. Over 50% of the dissimilarity between the floating and fixed installations resulted from five taxonomic groups i.e., bryozoans, bivalves, barnacles, sponges, including the amount of bare space on the settlement plates. The contribution of these groups to the dissimilarity changed both temporally within each site, and spatially among sites. The observed differences were related to the hydrodynamic characteristics of floating and fixed habitats, interacting with biotic features such as predation, successional processes and seasonality; and abiotic features including small-scale spatial changes, light, and position in the water column.

Small-scale spatial changes in estuarine fish: subtidal assemblages in tropical Brazil

Monthly sampling was conducted during one year in three zones along the estuarine gradient of Baía de Vitória, Brazil. Within each zone, unreplicated night trawls were done in deep subtidal flats located 130–210 m away and 2–3 m deeper than shallow ones. Twenty-one taxa represented 97.5% of the total mean fish abundance. The taxa Achirus lineatus (mean±SD: 2076±1269 10−4 m2), Eucinostomus spp. (694±807), Symphurus tessellatus (400±626), Sphoeroides testudineus (367±597) and Lutjanus synagris (323±445) dominated the deep assemblage (N=36) while Eucinostomus spp. (3649±4913), A. lineatus (1287±1569), S. testudineus (1208±1986), L. synagris (1101±927) and Sphoeroides greeleyi (569±1404) dominated the shallow assemblage (N=35). Taxa exclusive of one or the other depth showed extremely low abundance. The low-salinity shallow flats showed higher total abundance and taxa number than the high salinity deep locales but richness, diversity and equitability showed no significant differences among the six stations. The assemblage structure was significantly correlated to the depth structure but not to physico-chemical characteristics of the water. However, the spatial distribution of individual species varied greatly, from depth-dependent pattern to estuarine gradient-dependent pattern, with several intermediates. The community structure is singular in comparison to that of other tropical Brazilian estuaries studied to date. This is probably related to its geographical position in a transitional zone between the northern, tropical Brazilian oceanic domain and the southern, subtropical-temperate domain.

The influence of parent material on small-scale spatial changes in streamwater chemistry in Scottish upland catchments

Spatial changes in streamwater chemistry in seven upland catchments in NE Scotland have been studied using samples collected at 250 m intervals from the stream source to the catchment outlet. The catchments contain a number of different parent materials including granites and diorite from the Lochnagar Complex, and metasediments and metabasites from the Argyll and Appin Groups of the Dalradian Supergroup. Samples were collected under low flow conditions between June 1989 and January 1990 and ten component ions were determined; this paper concentrates on pH, Ca, Mg, Na and K. All seven catchments show major changes in stream solute concentrations along their length. Samples collected immediately downstream of the source typically show a rapid increase in pH with distance, reflecting degassing in the stream of CO 2 from the soil solution. Further down the catchment small-scale spatial changes in streamwater chemistry appear to be strongly influenced by the underlying geology. As the stream flows over parent materials with distinctly different geochemical characteristics, the pH, and Ca and Mg concentrations in the stream show rapid changes, reflecting changes in the underlying lithology. In a number of the catchments K also exhibits significant spatial variability along the length of the stream. The underlying geology appears to have little effect on Na concentrations, which typically increase from the source to the bottom of the catchment. These data suggest that small-scale spatial changes in streamwater chemistry may provide a useful tool for identifying changes in the underlying geology in poorly exposed areas. In addition, they also have implications for regional critical load mapping and prediction of streamwater sensitivity to acidification.