Influence of mesoscale winds on the turbulent structure of the urban boundary layer over St. Louis

Two fair weather afternoons have been examined, where the urban boundary layer over St. Louis, though exhibiting similar thermal characteristics, had a markedly different kinematic structure. The turbulent nature of the boundary layer was examined through analysis of double theodolite wind profiles at an urban and at a rural site on each day. On 14 July 1975, the winds increased with height above the inversion at both sites and on the following day, the winds decreased above the boundary layer in the same region. While the mean wind speed in the lowest 0.8 km agl was similar on both days, the turbulence characteristics of the urban boundary-layer winds were distinctly different on these two afternoons. This was evidenced by the variance of the wind and is in agreement with simultaneous aircraft measurements reported by Hildebrand and Ackerman (1984). A similar difference in turbulence was not found over the rural site. It is suggested that the enhanced turbulence at the urban site on 14 July is likely associated with the wind profile immediately above the boundary layer, where the downward flux of high momentum air from above the inversion may have resulted in stronger mechanical mixing within the boundary layer.     

Indigenous frameworks for observing and responding to climate change in Alaska

Despite a keen awareness of climate change, northern Indigenous Peoples have had limited participation in climate-change science due to limited access, power imbalances, and differences in worldview. A western science emphasis on facts and an indigenous emphasis on relationships to spiritual and biophysical components indicate important but distinct contributions that each knowledge system can make. Indigenous communities are experiencing widespread thawing of permafrost and coastal erosion exacerbated by loss of protective sea ice. These climate-induced changes threaten village infrastructure, water supplies, health, and safety. Climate-induced habitat changes associated with loss of sea ice and with landscape drying and extensive wildfires interact with northern development to bring both economic opportunities and environmental impacts. A multi-pronged approach to broadening indigenous participation in climate-change research should: 1) engage communities in designing climate-change solutions; 2) create an environment of mutual respect for multiple ways of knowing; 3) directly assist communities in achieving their adaptation goals; 4) promote partnerships that foster effective climate solutions from both western and indigenous perspectives; and 5) foster regional and international networking to share climate solutions.     

The effect of oxygen as a light element in metallic liquids on partitioning behavior

Oxygen has been considered a potentially important light element in metallic liquids during a range of planetary processes, yet the influence of O in a metallic melt on element partitioning behavior is largely unknown. To investigate the effect of O in such systems, we conducted experiments in the Fe‐S‐O system, doped with 25 trace elements, which produced two immiscible metallic liquids. Our results indicate that the presence of O in the metallic liquid produces a distinctive chemical signature for W and Ga in particular. Tungsten shows an affinity for O in the metallic liquid and partitions more strongly into the metallic melt in the presence of O. The partitioning of Ga is relatively constant despite the presence of O, which is in contrast to the majority of the other siderophile elements in the study. Our experiments from 1400 to 1600 °C show no significant effect from temperature on the partitioning behavior of any trace elements over this limited temperature range. This distinctive chemical signature due to the presence of O in the metallic liquid has potential implications for modeling core formation, evaluating isotopic signatures produced by core crystallization, and interpreting chemical assemblages observed in meteorites.     

Nutrient Limitation on Phytoplankton Growth in the Upper Barataria Basin,Louisiana: Microcosm Bioassays

The Davis Pond Diversion (DPD) was constructed to divert Mississippi River (MR) water into the Barataria Basin to reduce the salinity in support of wetland restoration on the Louisiana coast. To assess the phytoplankton nutrient limitation in adjacent water systems and potential impacts of DPD, 12 seasonal nutrient-phytoplankton bioassay experiments were conducted from October 2003 to July 2004 using the natural phytoplankton assemblages from freshwater and brackish-water lakes, Cataouatche and Salvador, LA (USA), which receive Mississippi River water from the DPD, and from a nearby freshwater lake, Lac des Allemands, that does not. Dissolved inorganic nitrogen (N), phosphorus (P), and silicate (Si) were added with different combinations at Redfield ratios in 10-l microcosms. Nitrogen was found to be the sole or primary limiting nutrient in all 12 experiments. N and P colimitations were found in seven of 12 experiments, but N was always the stronger limiting factor. P limitation was never observed to be the sole limiting nutrient. The results showed that a low concentration of P and a relatively high concentration of N do not necessarily indicate only P limitation in these lakes. Lake Cataouatche and Lake Salvador were dominated by centric diatoms, and Anabaena spp. were detected at high levels, particularly in summer. Lac des Allemands was generally dominated by N-fixing Anabaena spp. and other cyanobacteria, and their biomass responded significantly to N addition but not to P addition, indicating that nitrogen fixation in Lac des Allemands may be inhibited by other factors such as iron. Our bioassay results demonstrate that whether a water body is N- or P-limited is the consequence of the nutrient status and not the salinity regime. The results suggest that the addition of nutrient-rich waters via diversions of Mississippi River water into these lakes might increase the frequency of algal blooms, including noxious and toxic freshwater cyanobacteria.     

Aeolian sediment transport on a recovering storm‐eroded foredune with sand fences

Studies of sediment transport on developed coasts provide perspective on how human adjustments alter natural processes. Deployment of sand‐trapping fences is a common adjustment that changes the characteristics of the dune ramp and its role in linking sediment transfers from the backshore to the foredune. Fence effects were evaluated in the field using anemometer arrays and vertical sediment traps placed across a beach and dune at Seaside Park, New Jersey, USA during onshore and longshore winds. The foredune is 18 m wide and 4.5 m above the backshore. The mean speed of onshore winds at 0.5 m elevation decreased by 17% from the berm crest to the upper ramp and 36% in the lee of a fence there. Sediment transport during mean wind speeds up to 8.0 m s^?1 at 0.5 m elevation was < 0.06 kg m^?1 h^?1 on the berm crest and backshore where fetch distances were < 45 m and surface sediment was relatively coarse (0.74–0.85 mm) but increased to 5.63 kg m^?1 h^?1 on the upper ramp aided by the longer fetch distances (up to 82 m) and finer grain size of the source sediment there (0.52 mm). Sediment transport along the berm crest and backshore during longshore winds, where fetch distances were > 200 m, was up to 58.69 kg m^?1 h^?1, about three orders of magnitude greater than during the onshore winds. Fences can displace the toe of the ramp farther seaward than would occur under natural conditions. They can create a gentler slope and change the shape of the ramp to a more convex form. A fence on the ramp can cut off a portion of sediment supply to the upper slope. Decisions about fence placement thus should consider these morphologic changes in addition to the effects on dune volume. Copyright © 2017 John Wiley & Sons, Ltd.     

Shock melts in QUE 94411, Hammadah al Hamra 237, and Bencubbin: Remains of the missing matrix?

Abstract— We have studied the CB carbonaceous chondrites Queen Alexandra Range (QUE) 94411, Hammadah al Hamra (HH) 237, and Bencubbin with an emphasis on the petrographical and mineralogical effects of the shock processing that these meteorite assemblages have undergone. Iron‐nickel metal and chondrule silicates are the main components in these meteorites. These high‐temperature components are held together by shock melts consisting of droplets of dendritically intergrown Fe,Ni‐metal/sulfide embedded in silicate glass, which is substantially more FeO‐rich (30–40 wt%) than the chondrule silicates (FeO <5 wt%). Fine‐grained matrix material, which is a major component in most other chondrite classes, is extremely scarce in QUE 94411 and HH 237, and has not been observed in Bencubbin. This material occurs as rare, hydrated matrix lumps with major and minor element abundances roughly similar to the ferrous silicate shock melts (and CI). We infer that hydrated, fine‐grained material, compositionally similar to these matrix lumps, was originally present between the Fe,Ni‐metal grains and chondrules, but was preferentially shock melted. Other shock‐related features in QUE 94411, HH 237, and Bencubbin include an alignment and occasionally strong plastic deformation of metal and chondrule fragments. The existence of chemically zoned and metastable Fe,Ni‐metal condensates in direct contact with shock melts indicates that the shock did not substantially increase the average temperature of the rock. Because porphyritic olivine‐pyroxene chondrules are absent in QUE 94411, HH 237, and Bencubbin, it is difficult to determine the precise shock stage of these meteorites, but the shock was probably relatively light (S2–S3), consistent with a bulk temperature increase of the assemblages of less than ?300 °C. The apparently similar shock processing of Bencubbin, Weatherford, Gujba (CB_a) and QUE 94411/HH 237 (CB_b) supports the idea of a common asteroidal parent body for these meteorites.     

Diatom,pollen, and geochemical evidence for the palaeosalinity of Medicine Lake,S. Dakota,during the late-Wisconsin and early Holocene

Medicine Lake is a highly saline meromictic lake in eastern South Dakota. A lithostratigraphic and biostratigraphic study of the late-glacial and early post-glacial sediments shows that it was a relatively deep dilute freshwater lake during the period of the Picea pollen zone. When spruce forest changed to a Betula and then to a Quercus/Ulmus woodland in the early post-glacial period, the lake water became more concentrated but remained fresh. However, during the subsequent rapid transition to prairie in the early Holocene, when Gramineae, Ambrosia, and Artemisia dominated dry-land vegetation, the freshwater diatom flora was progressively replaced by a saline assemblage characterized by Cyclotella quillensis, Chaetoceros, and eventually Cyclotella caspia. The lake became permanently saline at about 9000 yr BP. A comparison of the fossil diatom assemblages with surface-sediment samples from a range of lakes in the Dakotas indicates that the change involved an increase in conductivity from about 500 S cm^–1 in the late-glacial period to > 10 000 S cm^–1 in the early Holocene. This rapid change is also marked by an abrupt increase in sulphate concentration in the sediment, the first appearance of bands of gypsum crystals, and the beginning of a well-laminated core sequence that continues through the remaining sediment record. Conditions of high salinity have prevailed to the present day.Contribution 299, Limnological Research Center.     

Cross-shore distribution of longshore sediment transport rates on a barred non-tidal beach

This study was conducted to relate the cross-shore distribution of longshore sediment transport and grain size characteristics to cross-shore and longshore current velocities on a sandy low-energy beach in a non-tidal embayment of the Baltic Sea. Simultaneous measurements of current velocities and amount of sand caught in streamer traps were made on 31 sampling runs on 6 d in April 1999 at three fixed sites including the swash zone on the upper foreshore, the lower foreshore, and the crest of the most landward of four bars. Spilling waves broke frequently on the bar but rarely on the lower foreshore, even during onshore wind speeds up to 11.0 m s⁻¹. Waves always broke as plunging waves at the step at the base of the upper foreshore and were converted directly into swash. The greatest longshore current velocities in the swash occurred when wind speeds and water levels were greatest, but wind direction was nearly directly onshore. Longshore velocities were greater in the swash zone than at other sites except when relatively strong winds blew nearly parallel to the shoreline, causing a pronounced wind-induced current at the other two sites. Calculated longshore shear stress and rate of sediment trapped were highly correlated on the bar (r=0.90), less highly correlated in the swash zone, and least highly correlated (r=0.66) on the lower foreshore. Mean trapping rates in the swash were 14.6 times greater than on the lower foreshore and 7.2 times greater than on the bar. Greater trapping rates in the swash are attributed to the greater turbulence mobilizing sediments in the uprush and backwash. Little of the finer-grained sediment on the offshore sites was reworked under low energy conditions. The study reveals the dominance of swash transport on steep, reflective, low-energy beaches where wave energy dissipation takes place over small distances on the upper foreshore.     

Jupiter's White Oval turns red

Jupiter's remaining White Oval changed color in late 2005 and became noticeably red in early 2006, as reported by amateur observers. We present wind and color analyses from high spatial resolution images taken with the Hubble Space Telescope Advanced Camera for Surveys in April 2006. These images suggest that the recent color change was tied to a strengthening of this storm, as implied by increased vorticity, causing it to become more like the Great Red Spot. From a historical perspective, the current activity may be consistent with the generation of new anticyclones at this latitude in the coming months and years.     

The Galileo star scanner observations at Amalthea

In November of 2002, the Galileo spacecraft passed within 250 km of Jupiter's moon Amalthea. An onboard telescope, the star scanner, observed a series of bright flashes near the moon. It is believed that these flashes represent sunlight reflected from 7 to 9 small moonlets located within about 3000 km of Amalthea. From star scanner geometry considerations and other arguments, we can constrain the diameter of the observed bodies to be between 0.5 m to several tens of kilometers. In September of 2003, while crossing Amalthea's orbit just prior to Galileo's destruction in the jovian atmosphere, a single additional body seems to have been observed. It is suspected that these bodies are part of a discrete rocky ring embedded within Jupiter's Gossamer ring system.