A quasi-geostrophic diagnosis of the zonal flow associated with cut-off lows over South Africa and surrounding oceans

Climate Dynamics - The zonal flow associated with cut-off lows (COLs) comprises two jet streaks of different spatial extents. The smaller scale jet streak, located north of the COLs, forms as a...     

The Effects of Integrated Marsh Management (IMM) on Salt Marsh Vegetation,Nekton, and Birds

An integrated marsh management (IMM) project in an urbanized watershed on Long Island, New York, USA, aimed to mitigate salt marsh degradation and to reduce mosquito production by an innovative combination of restoration and open marsh water management methods. The grid ditch network at two treatment marshes was replaced with naturalized tidal channels and ponds. Effects of the hydrologic alterations were monitored utilizing a before–after–control–impact approach. The treatment marshes experienced a number of beneficial outcomes including a fourfold reduction in the invasive Phragmites australis and increased native vegetation cover in the most degraded portions of the marsh, increased abundance and diversity of marsh killifish and estuarine nekton species, higher shorebird and waterfowl densities, and increased avian species diversity. The successful implementation of IMM concept led to improved marsh health and diminished mosquito production. Therefore, this study may serve as a template for similar large-scale integrated salt marsh restoration projects.     

Monitoring food web changes in tide-restored salt marshes: A carbon stable isotope approach

Primary producer (angiosperms, macroalgae, submerged aquatic vegetation), suspended particulate matter, andFundulus heteroclitus isotope values (δ¹³C, δ¹⁵N, δ³⁴S) were examined to assess their use as indicators for changes in food web support functions in tidally-restored salt marshes. Study sites, located throughout the southern New England region (USA), ranged fromSpartina alterniflora-dominated reference marshes, marshes under various regimes and histories of tide restoration, and a severely tide-restrictedPhragmites australis marsh.Fundulus δ¹³C values were greater for fish from referenceSpartina marshes than for fish from adjacent tide-restricted or tide-restored marshes where higher percent cover of C₃ plants, lower water column salinities, and more negative dissolved inorganic δ¹³C values were observed. The difference inFundulus δ¹³C values between a tide-restrictedPhragmites marsh and an adjacent referenceSpartina marsh was great compared to the difference between marshes at various stages of tide restoration and their respective reference marshes, suggesting that food web support functions are restored as the degree of tidal restriction is lessened. While a multiple isotopic approach can provide valuable information for determining specific food sources to consumers, this study demonstrates that monitoringFundulus δ¹³C values alone may be useful to evaluate the trajectory of ecological change for marshes undergoing tidal restoration.     

Simulations of an isolated two-dimensional thunderstorm: Sensitivity to cloud droplet size and the presence of graupel

Cloud Resolving Models (CRMs) which are used increasingly to make operational forecasts, employ Bulk Microphysics Schemes (BMSs) to describe cloud microphysical processes. In this study two BMSs are employed in a new Nonhydrostatic σ-coordinate Model to perform two hour simulations of convection initiated by a warm bubble, using a horizontal grid resolution of 500 m. Different configurations of the two BMSs are applied, to test the effects of the presence of graupel with one scheme (2-configurations) and of changing the cloud droplet sizes in the second scheme (4-configurations), on the simulation of idealised thunderstorms. Maximum updrafts in all the simulations are similar over the first 40 minutes, but start to differ beyond this point. The first scheme simulates the development of a second convective cell that is triggered by the cold pool that develops from the outflow of the first storm. The cold pool is more intense in the simulation with graupel because of melting of graupel particles, which results in relatively large raindrops, decreases the temperature through latent heat absorption, causing stronger downdrafts, which all contribute to the formation of a more intense cold pool. The second scheme simulates the development of a second cell in two of its configurations, while two other configurations do not simulate the redevelopment. Two configurations that simulate the secondary redevelopment produce a slightly stronger cold pool just before redevelopment. Our results show that small differences in the microphysics formulations result in simulations of storm dynamics that diverge, possibly due nonlinearities in the model.