MAJOR SNOWFALL EVENTS IN THE GREAT PLAINS: TEMPORAL ASPECTS AND RELATIVE IMPORTANCE

The purpose of this research is to develop a better understanding of the spatial and temporal aspects of central Great Plains snowstorms by: (1) identifying trends in the frequency of snow events, (2) determining the relative importance of significant snowfalls (those producing snowfall amounts of 10 cm or more), and (3) identifying temporal and/or latitudinal variations in the frequency of significant snowstorms. Using NCDC data from cooperative program weather stations along a north-south transect, summary statistics, correlation coefficients, and frequency histograms were generated. The results provided evidence of a highly variable spatial and temporal record. Significant snowstorms are more critical to total snowfall amounts in Nebraska, Kansas, and Texas. Although strong, regionally coherent temporal trends were not detected, a predominance of January through March snow events was observed. The greater frequency of January snowstorms coincides with the mean position of the polar front, while February and March snowfall frequency reflects the increased incidence of Colorado cyclones. Decadally, snowfall variability corresponds with a change in mean temperatures and predominant upper atmospheric flow that occurred around 1950. This change brought less snow to the Southern and Central Plains states, but more snow to the north. [Key words: snowfall, Great Plains, temporal/spatial variability.]     

Variational data assimilation for parameter estimation: application to a simple morphodynamic model

Data assimilation is a sophisticated mathematical technique for combining observational data with model predictions to produce state and parameter estimates that most accurately approximate the current and future states of the true system. The technique is commonly used in atmospheric and oceanic modelling, combining empirical observations with model predictions to produce more accurate and well-calibrated forecasts. Here, we consider a novel application within a coastal environment and describe how the method can also be used to deliver improved estimates of uncertain morphodynamic model parameters. This is achieved using a technique known as state augmentation. Earlier applications of state augmentation have typically employed the 4D-Var, Kalman filter or ensemble Kalman filter assimilation schemes. Our new method is based on a computationally inexpensive 3D-Var scheme, where the specification of the error covariance matrices is crucial for success. A simple 1D model of bed-form propagation is used to demonstrate the method. The scheme is capable of recovering near-perfect parameter values and, therefore, improves the capability of our model to predict future bathymetry. Such positive results suggest the potential for application to more complex morphodynamic models.     

Salinity history of coastal marshes reconstructed from diatom remains

Sediment cores were collected from three Louisiana coastal marsh ponds, dated with radioisotopes, and analyzed for diatom remains to determine if long-term salinity changes were evident in the sediment record. A diatom-based salinity index formulated from a statistical comparison of available salinity data and changing diatom assemblages demonstrated that diatom remains appear to preserve salinity signals in coastal brackish and salt marsh environments. The salinity index was applied to sediment cores spanning the late 1600s to the 1990s and provided a more complete record of salinity than field data, which were temporally and spatially incomplete. The salinity reconstructions indicated that salinity has increased at two sites and decreased at a third since the early 1900s. The salinity changes are less than 1‰ per decade in all cases, and may be due to natural variability as depicted by the wide range of salinities observed between the late 1600s and 1900. Salinity regimes may be very localized (<2 km from a hydrologic source), indicating single-site studies may not be applicable to regional inferences. This study demonstrates that diatoms can be used to reconstruct past salinity in coastal marsh environments and can provide a useful tool with which to study the changing hydrology of river-influenced ecosystems.     

Spectroscopic survey of field Type II Cepheids

A sample of relatively bright, short- and intermediate-period ( P =1–10 d) Type II Cepheids in the Galactic field have been observed spectroscopically with an intermediate-resolution (λ/Δλ=11000) spectrograph. The wavelength region was 6500–6700 Å, including the Hα line and some photospheric iron lines. The signal-to-noise ratio (S/N) was usually between 50 and 100, depending on weather conditions and the brightness of target stars. Radial velocities were determined by cross-correlating the Cepheid spectra with those of selected IAU velocity standard stars having F–G spectral types. The internal error of the velocity determination process was calculated to be about 1 km s⁻¹. Hα emission and strong line splitting were observed in BL Her during the expansion phase, but no similar phenomenon was detected in any other stars in this programme, except for AU Peg which has an unusual Hα line showing a P Cygni-like profile. The velocity curve agrees well with recent CORAVEL measurements. The velocity gradients in Cepheid atmospheres are studied using the Hα minus metallic velocities. Similar data are collected from the literature. It seems that having large velocity differences ( v _Hα− v _metal>40 km s⁻¹) is a characteristic feature of the very short-period ( P <1.5 d) and longer period ( P >10 d) Cepheids. Between these period regions the Cepheid atmospheres exhibit smaller velocity differences. Most of the Type II Cepheids observed in the present study fall into this latter category. There might be a tendency for classical Cepheids of intermediate period to have larger maximum velocity differences.     

Array technology as a tool to monitor exposure of fish to xenoestrogens

A variety of anthropogenic chemicals are capable of binding to the estrogen receptor of vertebrate species. Binding of these compounds can interfere with homeostasis by disrupting normal gene expression patterns. The purpose of this study was to investigate the feasibility of applying array technology as a monitoring tool for detecting the presence and distribution of estrogenic compounds in coastal habitats using sheepshead minnows as our model. cDNA clones that were isolated from differential display, including vitellogenin alpha and beta, vitelline envelope protein (ZP2), and transferrin, among others, were spotted on the macroarray. The results of these experiments demonstrate a characteristic expression pattern of estrogen responsive genes in sheepshead minnows exposed to 17 beta-estradiol (E2).     

Multiple “stable” states and the conservation of marine ecosystems

Marine ecosystems were among the first to provide potential examples of multiple stable states. However, remarkably few of these have been explored in detail, and none have been rigorously confirmed. This may be because differences between alternative states are too subtle to document in the context of regular disturbance, because one state is naturally far more likely to occur than any other, or because most environments naturally support only one type of stable community. It is also possible that the temporal and spatial criteria required to document alternate stable states rigorously may be too difficult to meet in most circumstances. Nevertheless, the possibility of alternative stable states has recently received renewed attention in the context of marine conservation biology. People may be widening the range of habitats in which alternate stable states are possible, or they may be shifting communities to new domains of attraction that rarely occur in the absence of massive anthropogenic perturbations. The ability of people now to alter ocean ecosystems on global scales may eliminate “edge effects” that might otherwise rescue perturbed communities. Ecosystems with alternate stable states are characterized by positive feedback mechanisms that stabilize transitions; even if return to original conditions is predicted (that is, the alternate states are not stable), the same mechanisms will retard recovery. This may explain in part why return to original conditions following anthropogenic disturbance is slower than expected. Slow recovery times and transitions to new states are both potentially costly to human societies. Thus, from a conservation perspective the indefinite persistence of an alternate state may be less important than the presence of feedback loops that slow recovery. Both possibilities reinforce the arguments for application of the precautionary principle in managing marine ecosystems.     

Periscoping as a Feminist Methodological Approach for Researching the Seemingly Hidden

This article proposes the metaphor of the periscope to guide an innovative approach to researching topics obstructed from view or out of range of more traditional approaches. Periscoping, it suggests, combines a feminist focus on the everyday with the recognition that no space, even those intentionally obscured, can be fully contained. Drawing on research on U.S. immigration enforcement policies, the article explores how feminist geographers can think creatively about how to arrange the “prisms” and “mirrors” at their disposal to obtain an image of what was previously thought to be unknowable. It then explores potential problems inherent to a periscopic strategy alongside tools it offers to researchers.