Constraints on the age and dilution of Pacific Exploratory Mission-Tropics biomass burning plumes from the natural radionuclide tracer 210Pb

During the NASA Global Troposphere Experiment Pacific Exploratory Mission-Tropics (PEM-Tropics) airborne sampling campaign we found unexpectedly high concentrations of aerosol-associated 210Pb throughout the free troposphere over the South Pacific. Because of the remoteness of the study region, we expected specific activities to be generally less than 35 μBq m−3 but found an average in the free troposphere of 107 μBq m−3. This average was elevated by a large number of very active (up to 405 μBq m−3) samples that were associated with biomass burning plumes encountered on nearly every PEM-Tropics flight in the southern hemisphere. We use a simple aging and dilution model, which assumes that 222Rn and primary combustion products are pumped into the free troposphere in wet convective systems over fire regions (most likely in Africa), to explain the elevated 210Pb activities. This model reproduces the observed 210Pb activities very well, and predicts the ratios of four hydrocarbon species (emitted by combustion) to CO to better than 20% in most cases. Plume ages calculated by the model depend strongly on the assumed 222Rn activities in the initial plume, but using values plausible for continental boundary layer air yields ages that are consistent with travel times from Africa to the South Pacific calculated with a back trajectory model. The model also shows that despite being easily recognized through the large enhancements of biomass burning tracers, these plumes must have entrained large fractions of the surrounding ambient air during transport

Pine Tip Moth (Lepidoptera: Tortricidae) Infestation Rates as Influenced by Site and Stand Characteristics in Loblolly Pine Plantations in East Texas

Three young loblolly pine plantations grown on contrasting soil types produced quantitatively and qualitatively different host material for pine tip moths during 1985 and 1986. Amounts, periodicity, and availability of soil moisture regulated internal moisture conditions within host trees. Host xylem moisture potential in conjunction with soil nutrient status governed tree growth and influenced pine tip moth infestation rates. Pines on a sandy site exhibited the poorest growth with lowest infestation rates, indicative of low-quality hosts with little if any tolerance to damage. A clayey site produced vigorous plant growth with moderate infestation rates. The less apparent hosts appeared capable of withstanding pine tip moth attack and overcoming damage. Pines on a loamy site grew at moderate rates and received the highest infestation rates. This moderate growth indicated susceptible stand conditions

Site/stand factors influencing Nantucket pine tip moth in loblolly pine plantations

Tip moth infestation and loblolly pine growth were examined on sandy, loamy and clayey sites in 2-3 year old plantations. Infestations were greatest on loamy sites. Following fertilizer and herbicide applications, tip moth infestations were lowest on fertilized plots following application of phosphorus

Estimation of stratospheric input to the Arctic troposphere: 7Be and 10Be in aerosols at Alert, Canada

Concentrations of 7Be and 210Pb in 2 years of weekly high-volume aerosol samples collected at Alert, Northwest Territories, Canada, showed pronounced seasonal variations. We observed a broad winter peak in 210Pb concentration and a spring peak in 7Be. These peaks were similar in magnitude and duration to previously reported results for a number of stations in the Arctic Basin. Beryllium 10 concentrations (determined only during the first year of this study) were well correlated with those of 7Be; the atom ratio 10Be/7Be was nearly constant at 2.2 throughout the year. This relatively high value of 10Be/7Be indicates that the stratosphere must constitute an important source of both Be isotopes in the Arctic troposphere throughout the year. A simple mixing model based on the small seasonal variations of 10Be/7Be indicates an approximately twofold increase of stratospheric influence in the free troposphere in late summer. The spring maxima in concentrations of both Be isotopes at the surface apparently reflect vertical mixing in rather than stratospheric injections into the troposphere. We have merged the results of the Be-based mixing model with weekly O3 soundings to assess Arctic stratospheric impact on the surface O3 budget at Alert. The resulting estimates indicate that stratospheric inputs can account for a maximum of 10-15% of the 03 at the surface in spring and for less during the rest of the year. These estimates are most uncertain during the winter. The combination of Be isotopic measurements and O3 vertical profiles could allow quantification of the contributions of O3 from the Arctic stratosphere and lower latitude regions to the O3 budget in the Arctic troposphere. Although at present the lack of a quantitative understanding of the temporal variation of O3 lifetime in the Arctic troposphere precludes making definitive calculations, qualitative examples of the power of this approach are given

Greenland ice core “signal” characteristics: An expanded view of climate change

The last millenium of Earth history is of particular interest because it documents the environmental complexities of both natural variability and anthropogenic activity. We have analyzed the major ions contained in the Greenland Ice Sheet Project 2 (GISP 2) ice core from the present to ∼674 A.D. to yield an environmental reconstruction for this period that includes a description of nitrogen and sulfur cycling, volcanic emissions, sea salt and terrestrial influences. We have adapted and extended mathematical procedures for extracting sporadic (e.g., volcanic) events, secular trends, and periodicities found in the data sets. Finally, by not assuming that periodic components (signals) were “stationary” and by utilizing evolutionary spectral analysis, we were able to reveal periodic processes in the climate system which change in frequency, “turn on,” and “turn off” with other climate transitions such as\u27that between the little ice age and the medieval warm period

Analysis of ultrasonic transducers with fractal architecture

Ultrasonic transducers composed of a periodic piezoelectric composite are generally accepted as the design of choice in many applications. Their architecture is normally very regular and this is due to manufacturing constraints rather than performance optimisation. Many of these manufacturing restrictions no longer hold due to new production methods such as computer controlled, laser cutting, and so there is now freedom to investigate new types of geometry. In this paper, the plane wave expansion model is utilised to investigate the behaviour of a transducer with a self-similar architecture. The Cantor set is utilised to design a 2-2 conguration, and a 1-3 conguration is investigated with a Sierpinski Carpet geometry