Blooms of the toxic dinoflagellate Alexandrium fundyense in the western Gulf of Maine in 1993 and 1994: A comparative modeling study

Blooms of the toxic dinoflagellate Alexandrium fundyense commonly occur in the western Gulf of Maine but the amount of toxin observed in coastal shellfish is highly variable. In this study, a coupled physical–biological model is used to investigate the dynamics underlying the observed A. fundyense abundance and shellfish toxicity in 1993 (a high toxicity year) and 1994 (low toxicity year). The physical model simulates the spring circulation, while the biological model estimates the germination and population dynamics of A. fundyense based on laboratory and field data. The model captures the large-scale aspects of the initiation and development of A. fundyense blooms during both years, but small-scale patchiness and the dynamics of bloom termination remain problematic. In both cases, the germination of resting cysts accounts for the magnitude of A. fundyense populations early in the spring. Simulations with low net A. fundyense growth rates capture the mean observed concentration during the bloom peak, which is of similar magnitude during both years. There is little evidence that large-scale changes in biological dynamics between 1993 and 1994 were a primary driver of the differences in shellfish toxicity. Results instead suggest that the persistent southwesterly flow of the western Maine Coastal Current led to A. fundyense populations of similar alongshore extent by late May of both years. This period coincides with peak cell abundance in the region. Variations in wind forcing (downwelling favorable in 1993, upwelling favorable in 1994) and subsequent cell transport (inshore in 1993, offshore in 1994) in early June then provides a plausible explanation for the dramatic mid-June differences in shellfish toxicity throughout the western Gulf of Maine.     

Spatial and temporal expression of vegetation and atmospheric variability from stable carbon and nitrogen isotope analysis of bat guano in the southern United States

Stable isotopes of faeces contain information related to the animals feeding ecology. The use of stable isotope values from subfossil faeces as a palaeoenvironmental indicator depends on how faithfully the animal records their local environment. Here we present insectivorous bat guano δ¹³C and δ¹⁵N values from a precipitation gradient across the southern United States and northern Mexico to compare with local vegetation and climate. We find δ¹³C values to be an excellent predictor of expected C₄/CAM vegetation, indicating that the bats are non-selective in their diet. Moreover, we find bat guano δ¹³C values to be strongly correlated with summer precipitation amount and winter precipitation ratio. We also find evidence for a significant relationship with mean annual temperature. In general, we do not find δ¹⁵N values to be related to any parameters along the climatic gradient we examined. Additionally, we measured δ¹³C and δ¹⁵N values of bulk guano deposited annually from 1968 to 1987 in a varved guano deposit at Eagle Creek Cave, Arizona. Neither δ¹³C nor δ¹⁵N values were significantly related to various local meteorological variables; however, we found δ¹³C values of guano to be significantly related to drought and to the North American Monsoon indicating bat guano δ¹³C values preserve an interpretable record of large-scale atmospheric variability.     

The spectral composition of fluxes and variances over land and sea out to the mesoscale

We discuss the accuracy requirements for measuring mesoscale (roughly horizontal scales > 10 km or 5 to 10 times the planetary boundary-layer (PBL) depth) fluxes in the convective PBL, and the ability of current research aircraft to achieve this accuracy. We conclude that aircraft equipped with inertial nagivation systems capable of < 3 km hr⁻¹ navigational accuracy are able to resolve mesoscale fluctuations in velocity, and thus variances and fluxes on the mesoscale. We then discuss measurements of velocity and scalar spectra, and cospectra of vertical velocity with horizontal velocity components and scalars, obtained from long flight legs with the National Center for Atmospheric Research Electra aircraft over the boreal forest of Canada in summer during the BOreal Ecosystem-Atmosphere Study (BOREAS), over the tropical Pacific Ocean from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE), and over the East China Sea during wintertime cold-air outbreaks from the Air Mass Transformation Experiment (AMTEX). Each of these studies has somewhat different forcings and boundary conditions, so we can compare their consequences on the spectra and cospectra. On average, we found no significant scalar or momentum fluxes for horizontal scales > 10 km. We also develop a simple model based on observed thermal structure to explain the phase angle between vertical velocity and the along-wind horizontal velocity as a function of height, which shows good agreement with the observed phase angle in AMTEX. The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Zero velocity hypersurfaces for the general three-dimensional three-body problem

In a recent paper by Sergysels with the same title, he describes a problem concerning these surfaces. In this brief commentary, we resolve this problem.     

Radio emission observed by Galileo in the inner Jovian magnetosphere during orbit A-34

The Galileo spacecraft encountered the inner magnetosphere of Jupiter on its way to a flyby of Amalthea on November 5, 2002. During this encounter, the spacecraft observed distinct spin modulation of plasma wave emissions. The modulations occurred in the frequency range from a few hundred hertz to a few hundred kilohertz and probably include at least two distinct wave modes. Assuming transverse EM radiation, we have used the swept-frequency receivers of the electric dipole antenna to determine the direction to the source of these emissions. Additionally, with knowledge of the magnetic field some constraints are placed on the wave mode of the emission based on a comparative analysis of the wave power versus spin phase of the different emissions. The emission appears in several bands separated by attenuation lanes. The analysis indicates that the lanes are probably due to blockage of the freely propagating emission by high density regions of the Io torus near the magnetic equator. Radio emission at lower frequencies (<40 kHz) appears to emanate from sources at high latitude and is not attenuated. Emission at is consistent with O-mode and Z-mode. Lower frequency emissions could be a mixture of O-mode, Z-mode and whistler mode. Emission for shows bands that are similar to upper hybrid resonance bands observed near the terrestrial plasmapause, and also elsewhere in Jovian magnetosphere. Based on the observations and knowledge of similar terrestrial emissions, we hypothesize that radio emission results from mode conversion near the strong density gradient of the inner radius of the cold plasma torus, similar to the generation of nKOM and continuum emission observed in the outer Jovian magnetosphere and in the terrestrial magnetosphere from source regions near the plasmapause.     

A chromospheric temperature inversion and its implications on millimeter brightness distribution

The brightness temperature curve of the quiet Sun at millimeter wavelengths suggests a possible inversion in the mid-millimeter range. Interpreting this as a result of an actual inversion in the chromospheric temperature structure, and example of a model chromoshere is presented whose calculated temperature curve exhibits such an inversion. This model is then tested for radial brightness distribution at millimeter wavelengths. Comparing the calculated distributions at 3.2 mm and 6 mm with eclipse measurements made with parabolic cylinders at 3.2 mm and 8.6 mm shows qualitative agreement, allowing for instrumental smoothing. It is conluded that a chromospheric temperature inversion, either actual or effective, could account for the inversion suggested by millimeter data and also the complex brightness distributions measured during eclipses with parabolic cylinders.     

On the formation of energy spectra in synchrotron sources

The observed energy spectra in synchrotron sources are power laws,N (E)=KE ^–, with the distribution in peaked around 2.5. These are consistent with initially injected spectra with between 1 and 2, subsequently steepened by synchrotron losses. Contrary to the results of Kardashev (1962), it is shown that statistical acceleration when coupled with synchrotron losses lead naturally to the formation of flat stationary spectra with 1. These stationary spectra have bends near the energy at which synchrotron losses balance the energy gains by acceleration. Above this bend the spectrum tends to =2. The time evolution of an initial spectrum towards the stationary spectrum is investigated. It is suggested that the initially flat spectra with 1 to 1.5 observed in some variable sources result from an incomplete approach to the stationary spectrum, and that in sources with constant acceleration spectra with 2 are to be expected.     

On oscillatory motion in the problem of three bodies

In the case of oscillatory motion in the problem of three bodies it is shown that ast the mutual distances between particles cannot separate faster thanCt ^2/3 whereC is some positive constant. As bounding functions of time exist for the other classifications of motion in the three body problem, it follows in general that the mutual distances between particles is 0(t) ast.