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The semipermanent subtropical anticyclone over the North Atlantic basin (the “Azores high”) has a major influence on the weather and climate of much of North America, western Europe, and northwestern Africa. The authors develop a climatology of the Azores high by examining its spatial and temporal changes since 1899. Using gridded surface pressure values, anticyclones are identified when the daily pressure is ≥1020 mb and frequencies are tabulated for each half month from 1899 to 1990. Principal components analysis is applied to analyze the anticyclone’s spatial variance structure. The Azores high is dominated by two spatial modes: a summer pattern, in which high pressure dominates the Atlantic basin, and a winter pattern, in which anticyclones are present over eastern North America and northwestern Africa. Century-long declines in these two modes indicate that there has been a net removal of atmospheric mass over the subtropical Atlantic. Other modes include a meridional versus zonal circulation pattern and omega blocks. Time series of the mean annual principal component scores indicate that meridional flow has been increasing over the Atlantic and that blocking anticyclones have become more prevalent over west-central Europe and less common over the northeastern Atlantic and the British Isles.

Vegetation controls aspects of climate at all scales. These controls operate through fluxes of mass (water vapour, particulates, trace gases, condensation nuclei, and ice nuclei) and energy (latent and sensible heat, radiative exchanges, and momentum dissipation) between the biosphere and the atmosphere. The role these fluxes play in controlling minimum and maximum temperature, temperature range, rainfall, and precipitation processes are detailed. On the hemispheric scale, the importance of evapotranspiration, vegetation surface roughness, and vegetation albedo in the current generation of atmospheric general circulation models is reviewed. Finally, I assess at the planetary scale the global climate effects of biogenic emissions that are well mixed throughout the troposphere. I show that daily maximum and minimum temperatures are, in part, controlled by the emission of non-methane hydrocarbons and transpired water vapour. In many regions, a substantial fraction of the rainfall arises from upstream evapotranspiration rather than from oceanic evaporation. Biosphere evapotranspiration, surface roughness, and albedo are key controls in the general circulation of the atmosphere: climate models that lack adequate specifications for these biosphere attributes fail. The biosphere modulates climate at all scales.

Aerial photographs, recording 12 positions of the shoreline and vegetation line over a 50-yr period, were used to investigate long-term ecotone displacement trends and the relationship between ecotone displacement and shoreline migration on Hog Island, Virginia. A robust regression modeling technique, originally developed for shoreline trend detection analyses, enabled examination of the direction, magnitude, and timing of changes in long-term ecotone displacement. Measurements were obtained at 277 shore normal transects spaced 50 m apart. The results show that long-term trends in ecotone displacement and shoreline movement are nonlinear for over three-fourths of the Hog Island coast. On average, the shoreline and vegetation line experienced reversals in 1972 and 1974, respectively. Rarely did the ecotones and shorelines move in tandem or synchronously. Concavity tests indicate that most of the shoreline and ecotone are currently moving seaward and the distance between the shoreline and vegetation line is decreasing through time. Evidence exists for a decennial time lag between the reversal of the shoreline and the ecotone and vice versa. The ecotone and shoreline trends apparently correspond to tidal inlet dynamics, individual storm events, storm climate, inherited topography (e.g., dune), and vegetation type.

Principal Component Analysis (PCA) was used to derive estuarine salinity zones based on field data on the salinity ranges of 316 species/life stages in the mid-Atlantic region (chiefly Chesapeake Bay and Delaware Bay species). Application of PCA to the data matrix showed that the structure underlying a diversity of salinity distributions could be represented by only five Principal Components corresponding to five overlapping salinity zones: freshwater to 4‰, 2-14‰, 11-18‰, 16-27‰, and 24‰ to marine. The derived salinity zonation showed both differences and similarities to the Venice System of estuarine zonation. However, unlike the static and essentially descriptive Venice System, the new method will allow researchers to establish biologically-relevant local salinity zones, and then develop hypotheses about the processes that give rise to the resulting patterns. Examples of this procedure are given for the mid-Atlantic region. The method used here may also be useful for studying distributions across other environmental gradients, such as temperature, pH, substrate, turbidity, vegetation, or latitude.

Selected findings from the Long Term Ecological Research (LTER) program are described in the field of biosphere–atmosphere interactions. The Palmer, Antarctic, site contributes evidence to the debate on the ecological effects of increased ultraviolet-B radiation; the ecological response to a warming trend over the past half-century has been clearly documented there. The North Temperate Lakes site in Wisconsin was the principal LTER site for an international study to document a 100-year trend of change in freeze and thaw dates of boreal lakes. A multidisciplinary approach to soil warming studies benefited from observations over decades and demonstrated the importance of initial conditions. The LTER Network permits investigation of atmosphere–ecosystem interactions over a long period encompassing storm events and quasi-periodic climate variability. LTER studies show that ecosystem dynamics often cannot be decoupled from atmospheric processes. Atmospheric processes are an integral component of the ecosystem and vice versa. Finally, we provide an example of how regionalization studies, often grounded in atmospheric data, add a spatial context to LTER sites and identify controls on ecological processes across broader environmental gradients.

Aerial photographs, recording 12 positions of the shoreline and vegetation line over a 50-yr period, were used to investigate long-term ecotone displacement trends and the relationship between ecotone displacement and shoreline migration on Hog Island, Virginia. A robust regression modeling technique, originally developed for shoreline trend detection analyses, enabled examination of the direction, magnitude, and timing of changes in long-term ecotone displacement. Measurements were obtained at 277 shore normal transects spaced 50 m apart. The results show that long-term trends in ecotone displacement and shoreline movement are nonlinear for over three- fourths of the Hog Island coast. On average, the shoreline and vegetation line experienced reversals in 1972 and 1974, respectively. Rarely did the ecotones and shorelines move in tandem or synchronously. Concavity tests indicate that most of the shoreline and ecotone are currently moving seaward and the distance between the shoreline and vegetation line is decreasing through time. Evidence exists for a decennial time lag between the reversal of the shoreline and the ecotone and vice versa. The ecotone and shoreline trends apparently correspond to tidal inlet dynamics, individual storm events, storm climate, inherited topography (e.g., dune), and vegetation type.

Environmental scientists are exploring how tree morbidity, mortality, reproductive success, and consequent community change can be explained by effects of climate. The dynamic relationship between tree mortality and the atmospheric environment can be resolved on a number of scales, but a large-scale synthesis relating community distribution and dynamics to atmospheric circulation systems is emphasized. Widely used circulation, successional and scale interaction models are examined. A research protocol is proposed that could begin to relate the atmospheric and ecological scale matrices.

Due to the complexity of coastal barrier vegetation, it is useful to apply a functional-type approach to assess the response of barrier island vegetation to climate change. In this paper, a simple clustering analysis is applied to a group of 19 plant associations, based on six plant attributes and six environmental constraints. This analysis results in the suggestion that the main division of the vegetation types at Virginia Coast Reserve is between herbaceous and woody types, which differs from the existing classification which recognizes three groups: xeric-mesic herbaceous, woody and hydric-halophytic herbaceous. Considerations about grouping plant functional types are also addressed in this paper. At a global scale, inclusion of barrier plant functional types may not be so important for the climate-change response of vegetation, but it may be necessary to consider these important systems for spatially explicit modelling of landscape responses.

The high-water-shoreline positions in 1852, 1871, 1910, 1919, 1943, 1955, 1967, 1980, and 1990 for Hog Island, a barrier island located at the eastern shore of Virginia, were determined with the NOS T-sheets and aerial photographs. Shrub thicket distributions for northern Hog Island were extracted from black/white and infrared color aerial photographs for the years of 1949, 1962, 1974, and 1989. The overlay operations between shrub age and land age data layers indicated that shrub coverage on Hog Island was closely related with shoreline changes. By examining 138-year shoreline changes on 50-m-interval transects of Hog Island, it was found that the sine function could describe shoreline change patterns better than earlier used simple models. The overlay between old NOS T-sheets and 1993 TM satellite image suggested that there would be at least three types of shoreline changes for different barrier islands. All these three types of shoreline change patterns could be interpreted with the sine function model. The potential distribution of shrub thickets on Hog Island was simulated based on the shoreline change model. The shrub line and shoreline positions were closely related with each other, but there were time lags between shrub thicket expansion and shoreline accretion.

The objective of this study is to investigate hydrocarbon species and amounts released by red mangrove foliage and determine if these quantities warrant future research on atmospheric chemical processing of these compounds. The field investigation took place during July 2001 at Key Largo, Florida Bay, Florida. Foliage still attached to plants was enclosed in cuvettes while air of known flow rates circulated around leaves to study hydrocarbon emissions. Cuvette air samples underwent gas chromatographic analyses to determine species and amounts of hydrocarbons released by mangrove foliage. Red mangrove foliage emits isoprene and trace amounts of the monoterpenes of α-pinene, β-pinene, camphene, and d-limonene. The mangrove flowers released these latter compounds in amounts ranging from 0.5 to 10 mg (monoterpene) per gram of dry biomass per hour. These fluxes are normalized to the foliage temperature of 30 °C. When normalized to the foliage temperature of 30 °C and light levels of 1000 µmol m−2 s−1, isoprene emission rates as high as 0.092 ± 0.109 µg (isoprene) per gram of dry biomass per hour were measured. Compared to terrestrial forest ecosystems, red mangroves are low isoprene emitters. During peak flowering periods in the summertime, however, red mangroves may emit sufficient amounts of monoterpenes to alter ground-level ozone concentrations and contribute to biogenic aerosol formation.