Characteristics of air flow above and within soybean canopies

Air flow was observed above and within canopies of a number of kinds of soybeans. The Clark cultivar and two isolines of the Harosoy cultivar were studied in 1979 and 1980, respectively. Wind speed above the canopy was measured with cup anemometers. Heated thermistor anemometers were used to measure air flow within the canopy. Above-canopy air flow was characterized in terms of the zero-plane displacement (d), roughness parameter (z _o) and drag coefficient (C _d). d and z _o were dependent on canopy height but were independent of friction velocity in the range 0.55 to 0.75 m s^?1 · C _d for the various canopies ranged from 0.027 to 0.035. Greater C _d values were measured over an erectophile canopy than over a planophile canopy. C _d was not measurably affected by differences in leaf pubescence. Within-canopy wind profiles were measured at two locations: within and between rows. The wind profile was characterized by a region of great wind shear in the upper canopy and by a region of relatively weak wind shear in the middle canopy. Considerable spatial variability in wind speed was evident, however. This result has significant implications for canopy flow modeling efforts aimed at evaluating transport in the canopy. In the lower canopy, wind speed within a row increased with depth whereas wind speed between two rows decreased with depth. The wind speeds at the two locations tended to converge to a common value at a height near 0.10 m. The attenuation of within-canopy air flow was stronger in canopies with greater foliage density. Canopy flow attenuation seemed to decrease with increasing wind speed, suggesting that high winds distorted the shape of the canopy in such a manner that the penetration of wind into the canopy increased.     

Radiocarbon dating of Danube Delta deposits

The Holocene history of the Danube Delta has been studied using ¹⁴C analyses of faunal material. The principal phases of development include: (1) initial Letea Caroarman spit, 11,700–9800 yr B.P. in its central part, 8800-5500 yr B.P. in its southern part; (2) Sf. Gheorghe I Delta, 8900-7200 yr B.P.; (3) Sulina Delta, 7200-2000 yr B.P., and (4) Sf. Gheorghe II Delta-Chilia Delta 2000 yr B.P.-present. Other smaller-scale features have also been dated, including secondary deltas (Co?na and Sinoe Deltas) and littoral bars. Age determinations carried out on whole samples were erratic and it was found that individual species had to be separated and dated. In all cases, the older dates were of transported material whereas the younger dates gave the true age of the formation.     

Lithosphere formation in the central Slave Craton (Canada): plume subcretion or lithosphere accretion?

Major-element compositions of minerals in peridotite xenoliths from the Lac de Gras kimberlites provide constraints on the mode of lithosphere formation beneath the central Slave Craton, Canada. Magnesia contents of reconstructed whole rocks correlate positively with NiO and negatively with CaO contents, consistent with variable partial melt extraction. Alumina and Cr₂O₃ contents are broadly positively correlated, suggestive of melt depletion in the absence of a Cr–Al phase. Garnet modes are high at a given Al₂O₃ content (a proxy for melt depletion), falling about a 7 GPa melt depletion model. These observations, combined with high olivine Mg# and major-element relationships of FeO-poor peridotites (<7.5 wt%) indicative of melt loss at pressures >3 GPa (residual FeO content being a sensitive indicator of melt extraction pressure), and similar high pressures of last equilibration (∼4.2 to 5.8 GPa), provide multiple lines of evidence that the mantle beneath the central Slave Craton has originated as a residue from high-pressure melting, possibly during plume subcretion. Apparent low melt depletion pressures for high-FeO peridotites (>7.5 wt%) could suggest formation in an oceanic setting, followed by subduction to their depth of entrainment. However, these rocks, which are characterised by low SiO₂ contents (<43 wt%), are more likely to be the result of post-melting FeO-addition, leading to spuriously low estimates of melt extraction pressures. They may have reacted with a silica-undersaturated melt that dissolved orthopyroxene, or experienced olivine injection by crystallising melts. A secular FeO-enrichment of parts of the deep mantle lithosphere is supported by lower average Mg# in xenolithic olivine (91.7) compared to olivine inclusions in diamond (92.6).     

The impact of hurricanes on sedimenting particulate matter in the semi-arid Bahía de La Paz,Gulf of California

From 2002 through 2004, time-series sediment trap samples were collected from a depth of 410 m in Cuenca Alfonso, Bahía de La Paz, on the SW coast of the Gulf of California. The instrument recorded the impact of the local passage of hurricanes “Ignacio” (24–26 August) and “Marty” (21–23 September) in 2003. These two events accounted for 82% of the total rainfall measured in 2003, equivalent to the annual average precipitation in years without hurricanes. Mean total mass fluxes (TMFs) of 2.88 and 3.58 g m⁻² d⁻¹ were measured during the week of each hurricane as well as the following week. This may have been enough to produce a lamina in the underlying sediment with characteristics peculiar to such events. The terrigenous component was particularly abundant, with notably higher concentrations of Fe, Sc, Co and Cs and REEs. In contrast, TMFs throughout 2002–2004 (excluding the hurricane periods) averaged only 0.73 g m⁻² d⁻¹ and had a larger marine biogenic component. The extraordinary elemental fluxes during the 29 days of hurricane-influenced sedimentation represented a great proportion of the totals over an entire “normal” year: Co (67.8%) >Sc (62.6) >Fe (59.6) >Cs (53.4)>Lu (51.5)>La (51.3)>Yb (51.0)>Ce (49.5) >Tb (48.4) >Sm (44.7)>Cr (36.5) >Ca (31.0)>Eu (25.4%). The terrigenous fraction was calculated using (a) TMF minus the sum of CaCO₃, biogenic silica and organic matter and (b) the ratio of Sc in the trap samples to the average in the Earth's crust. The latter was consistently smaller, but the two methods offered similar results following hurricanes (78% vs. 63%, respectively). For normal sedimentation, however, the difference method yielded values twice as large as the Sc method (58% vs. 30%) This suggests that the mineralogy of the terrigenous fraction may also vary, with unsorted dessert soil being carried to sea by the powerful flash floods associated with hurricanes. Eolian supply of particles, particularly Sc-free quartz grains, possibly from beyond the limited fluvial drainage basin, apparently dominates normal sedimentation.     

A technical comment: Analysis of ‘examination of “global atmospheric temperature monitoring with satellite microwave measurements”’

The potential for residual hydrometeor contamination effects in the global temperature time series produced by Spencer and Christy from MSU channel 2 (MSU2) data has been addressed by Prabhakara et al. (1995, 1996). They use tropical oceanic MSU channel l (MSU1) data to estimate the hydrometeor effects on MSU2. We present several lines of evidence to show that their technique greatly overestimates the hydrometeor effects on MSU2. This overestimation is due to the faulty assumption that the hydrometeors that cause MSU1 warming are the same as (or always exist with) the hydrometeors that cause cooling in MSU2. Instead, the hydrometeors responsible for MSU1 warming are liquid phase, while those responsible for MSU2 cooling are large ice particles. Because liquid phase clouds are much more widespread than the large-ice portions of deep convective systems, their method greatly overestimates the areal coverage of contaminated tropical MSU2 data. In addition, we show that the convective screening procedure of Spencer and Christy removes the negative correlation between MSU1 and MSU2 their conclusions rest upon. Radiosonde validation of monthly tropical MSU2 anomalies over the tropical West Pacific also support these conclusions.     

A useful tool for image enhancement

Image enhancement provides a means to facilitate information transfer without altering the image information. A plug-in for the commonly used image capture and manipulation program Photoshop is discussed as one useful tool.