RADAR-OBSERVED ’’FINE LINES‘‘ IN THE OPTICALLY CLEAR BOUNDARY LAYER: REFLECTIVITY CONTRIBUTIONS FROM AERIAL PLANKTON AND ITS PREDATORS

Sensitive Doppler radars regularly detect fine lines ofenhanced reflectivity in mesoscale boundary-layer convergence zones. Recent studies have concludedthat these fine lines are attributable primarily to backscatter fromconcentrations of small, weakly flying insects (aerial plankton)entrained in the convergence zones. Such concentrations are likely tobe attractive to aerial predators that feed on small insects, raising thequestion of whether the presence of the predators themselves maycontribute significantly to the radar-observed fine lines.In this paper, we examine the relative contributions of aerialplankton and its predators to fine-line reflectivity, using field datafrom visual and radar studies together with a compilation of literaturedata on radar cross sections of birds and insects. Visual counts ofbirds and dragonflies in convergence zones, together withsimultaneous remote radar observations during the CaPE project inFlorida, indicated that aerial predators usually contributed little tofine-line reflectivity (median contribution 2%). Assuming thatthe size distribution of insect targets was spatially invariant, thedensity of insects composing the aerial plankton was inferred to be,on average, about one order of magnitude higher inside convergencezones than in nearby areas.These results suggest that clear-air radar reflectivity may be auseful measure of the quantity of aerial plankton in boundary-layerconvergence zones. This finding is relevant to biology because itindicates that remote sensing techniques can be usefully employed todocument patterns and processes in the distribution of aerial plankton.The results presented here also have relevance for operationalmeteorology, because most of the organisms comprising the planktonprobably serve as passive tracers of horizontal air motions, and aretherefore ideal targets for remotely detecting wind patterns. Incontrast, the aerial predators move actively and rapidly, renderingthem less useful as tracers of wind fields in studies using Dopplerradars. The influence of atmospheric structure on the ecology ofaerial predators and their prey has received little attention, but webelieve that sensitive radars with clear-air observational capabilitiesoffer great potential as research platforms for future studies of aerialplankton and aerial planktivory.     

The 1982-83 Eruption at Galunggung Volcano, Java (Indonesia): Oxygen Isotope Geochemistry of a Chemically Zoned Magma Chamber

Mount Galunggung is a historically active volcano in southwesternJava that has erupted four times in the last two centuries.During the most recent event, which occurred during a 9–monthinterval in 1982– 83, some 305 10⁶ m³ of medium–K,calc–alkaline magma was erupted. This eruption was unusualbecause of its duration, the diversity of eruption dynamicsand products, and the range of lava compositions produced. Thecomposition of juvenile material changed gradually during thecourse of the eruption from initial plagioclase (An_60–75)and two–pyrozene bearing andesites with 58% SiO₂ to finalplagioclase (An_85–90), diopside, and olivine (Fo_85–90)bearing primitive magnesium basalts with 47% SiO₂ Mineralogicaland compositional relationships indicate a magmatic evolutioninvolving differentitation of high–Mg parental melt. Theeruptive volumes of 35 10⁶ m³ andesite, 120 10⁶ m³ maficandesite, and 150 10⁶ m³ basalt are consistent with the ideathat the 1982– 83 eruption progressively tapped and draineda magma chamber that had become chemically stratified throughextensive crystal fractionation. Separates of plagioclase and pyroxene have ¹⁸O( SMO W) rangesof + 5. 6 to + 6.0 and + 5.3 to + 5.6, respectively, with ¹⁸O_plag–pxvalues of + 0.4 to + 0.6o, indicating internal O–isotopeequiliburium at temperature of 1100–850 C. The magenesianbasalts have magmatic ¹⁸O/ ¹⁶O ratios similar to those of mid–oceanridge basalt, and the O–isotope ratios of compositionallyevolved derivative melts show no evidence for contaminationof the galunggung magmas by ¹⁸O–rich crust during differentiation.Andesites and transitional mafic and sites have a more variableO–isotope character, with laves and phenocrysts havingboth higher and lower ¹⁸O values than observed in the parentalmagnesium basalts. These features are interpreted to reflectintramagma chamber processes affecting the upper portions ofthe differentiating Galunggung magma body before the 1982–83eruption.     

Investigation of iron sulfide impact crater residues: A combined analysis by scanning and transmission electron microscopy

Abstract– Samples returned from comet 81P/Wild 2 by the Stardust mission provided an unequaled opportunity to compare previously available extraterrestrial samples against those from a known comet. Iron sulfides are a major constituent of cometary grains commonly identified within cometary interplanetary dust particles (IDPs) and Wild 2 samples. Chemical analyses indicate Wild 2 sulfides are fundamentally different from those in IDPs. However, as Wild 2 dust was collected via impact into capture media at approximately 6.1 km s^?1, it is unclear whether this is due to variation in preaccretional/parent body processes experienced by these materials or due to heating and alteration during collection. We investigated alteration in pyrrhotite and pentlandite impacted into Stardust flight spare Al foils under encounter conditions by comparing scanning and transmission electron microscope (SEM, TEM) analyses of preimpact and postimpact samples and calculating estimates of various impact parameters. SEM is the primary method of analysis during initial in situ examination of Stardust foils, and therefore, we also sought to evaluate the data obtained by SEM using insights provided by TEM. We find iron sulfides experience heating, melting, separation, and loss of S, and mixing with molten Al. These results are consistent with estimated peak pressures and temperatures experienced (approximately 85 GPa, approximately 2600 K) and relative melting temperatures. Unambiguous identification of preserved iron sulfides may be possible by TEM through the location of Al‐free regions. In most cases, the Ni:Fe ratio is preserved in both SEM and TEM analyses and may therefore also be used to predict original chemistry and estimate mineralogy.     

Environmental and climatic reconstructions during Marine Oxygen Isotope Stage 3 from Gossau, Swiss Midlands, based on coleopteran assemblages

The well-known lower lignite layer at Gossau (15 km SE of Zürich, Switzerland) has been radiocarbon-dated to between 30 000 and 54 000 yr BP. Though these dates may be considered to be beyond the acceptable limit of the technique, there can be little doubt on stratigraphical grounds that the deposits date from some early part of MOI Stage 3. The lower lignite has yielded 49 taxa of beetles from which a detailed palaeoenvironmental picture can be reconstructed. Quantified palaeotemperature estimates using the Mutual Climatic Range method, based on this fossil assemblage, indicate that the climate was cold and considerably more continental than it is today in the Swiss Midlands and close to the thermal limit for the growth of trees. The fauna bears similarities to others from the same general period in northern Europe.     

Mercury: Mid‐infrared (3–13.5 μm) observations show heterogeneous composition,presence of intermediate and basic soil types,and pyroxene

Abstract— The Aerospace Corporation's broadband array spectrograph system (BASS) mounted on the NASA infrared telescope facility (IRTF) on Mauna Kea, Hawaii was used to obtain spectral measurements of Mercury's thermal emission on 1998 March 21 (45–85° longitude), and on 1998 May 12 (68–108° longitude). The spectra show heterogeneous composition on Mercury's surface between longitudes 45–85° and about 68–108°. These observations include measurements from 3 to 6 μm, a spectral region not previously covered by mid‐infrared spectroscopy. Excellent quality data were obtained in the atmospheric windows between 3–4.2 and 4.6–5.5 μm. These wavelength regions exhibit high emissivity characteristic of a regolith with strong thermal gradients maintained in a vacuum environment with spectra dominated by grain sizes of ?30 μm. Emission peaks are present at 3.5 and 5 μm in the 45–85° longitude data. The 5 μm peak has been tentatively attributed to clinopyroxene. Data were also obtained in the 7.5–13.5 μm spectral region. Spectra obtained during both observing periods show well‐defined emissivity maxima (EM) in the spectral vicinity (between 7.7 and 9.2 μm) of the Christiansen frequency of silicate soils. The location of the EM for longitudes 45–85° (7.9 μm) is consistent with a surface composition of intermediate SiO₂ content. The overall spectral shape is similar to that obtained previously at the same location with different instrumentation. In the region 68–108° longitude, three EM are observed at 7.8, 8.2, and 9.2 μm, indicating the presence of distinctly different surface composition from the other location. Comparisons of these data to other mid‐infrared spectra of Mercury's surface and asteroids, and of the different instrumentation used in observations are included.     

Aluminum‐26 in calcium‐aluminum‐rich inclusions and chondrules from unequilibrated ordinary chondrites

Abstract— In order to investigate the distribution of ²⁶A1 in chondrites, we measured aluminum‐magnesium systematics in four calcium‐aluminum‐rich inclusions (CAIs) and eleven aluminum‐rich chondrules from unequilibrated ordinary chondrites (UOCs). All four CAIs were found to contain radiogenic ²⁶Mg (²⁶Mg*) from the decay of ²⁶A1. The inferred initial ²⁶Al/²⁷Al ratios for these objects ((²⁶Al/²⁷Al)₀ ? 5 × 10^?5) are indistinguishable from the (²⁶Al/²⁷Al)₀ ratios found in most CAIs from carbonaceous chondrites. These observations, together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of CAIs, imply that CAIs in UOCs and carbonaceous chondrites formed by similar processes from similar (or the same) isotopic reservoirs, or perhaps in a single location in the solar system. We also found ²⁶Mg* in two of eleven aluminum‐rich chondrules. The (²⁶Al/²⁷Al)₀ ratio inferred for both of these chondrules is ～1 × 10^?5, clearly distinct from most CAIs but consistent with the values found in chondrules from type 3.0–3.1 UOCs and for aluminum‐rich chondrules from lightly metamorphosed carbonaceous chondrites (～0.5 × 10^?5 to ～2 × 10^?5). The consistency of the (²⁶Al/²⁷Al)₀ ratios for CAIs and chondrules in primitive chondrites, independent of meteorite class, implies broad‐scale nebular homogeneity with respect to ²⁶Al and indicates that the differences in initial ratios can be interpreted in terms of formation time. A timeline based on ²⁶Al indicates that chondrules began to form 1 to 2 Ma after most CAIs formed, that accretion of meteorite parent bodies was essentially complete by 4 Ma after CAIs, and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 Ma after CAIs formed. Type 6 chondrites apparently did not cool until more than 7 Ma after CAIs formed. This timeline is consistent with ²⁶Al as a principal heat source for melting and metamorphism.     

Geomorphology and palaeoecology of the Mark valley (southern Netherlands): palaeoecology, palaeohydrology and climate during the Weichselian Late Glacial

Bohncke, Sjoerd, Vandenberghe, Jef, Coope, Russell & Reiling, Rudo 1987 03 01: Geomorphology and palaeoecology of the Mark valley (southern Netherlands): palaeoecology, palaeohydrology and climate during the Weichselian Late Glacial. Boreas , Vol. 16, pp. 69–85. Oslo. ISSN 0300–9483.
A backswamp peat, located on an Upper Pleniglacial terrace, has been analysed in detail with respect to its pollen content, its macroscopic plant remains and its fossil insect fauna. The analyses permitted a detailed reconstruction of the Late Glacial palaeoenvironment besides an estimation of fluctuations in the local humidity and fluctuations in the palaeotemperatures. The main boundaries in the sequence have been radiocarbon dated, indicating a peat accumulation from c .12,600 B.P. to 10,970 B.P. The Bölling s.l . shows a clear migration of vegetation belts, starting with a shrub vegetation and passing into a birch wood. This progressive vegetation development culminates in a short lasting Pinus maximum early in the Alleröd, without being hampered by events during the Older Dryas. Up to and including the Alleröd no serious climate deterioration is registered. The humidity curve reveals a semiterrestrial phase in the local hydrosere that correlates with the Older Dryas and that is explained by the geomorphological evolution of the adjacent river system. The transition to the Younger Dryas coincides with a return to fluvial conditions and a marked change in the pollen record and insect fauna, indicating a decline in the average July temperature from between 18 and 15°C to 11 and 10°C.     

Late Glacial environmental changes indicated by a coleopteran succession from North Wales

This investigation was designed to compare the environmental inferences that can be made from fossil Coleoptera with those that can be made from palynological data. In the Glanllynnau kettle hole, sedimentation began at 14,000 BP and continued until about 10,000 BP. The Coleoptera from these deposits show that during this period there was only one climatic oscillation and that this differed in both timing and intensity from oscillations inferred from palynological evidence. Thus, at about 13,000 BP, an intensely cold continental climate suddenly gave place to a period with summer temperatures at least as warm as those at the present day, but during this episode the landscape was entirely without trees. From 12,000 BP to about 10,000 BP there was a progressive deterioration in the temperature, and the period of Betula forest, broadly equivalent to the Allerød, is shown to have a less thermophilous fauna than that of the previous pollen Zone I. An attempt is made to explain this anomaly in terms of the differential rate of response of the plants and animals to rapid climatic changes.