A statistical study of underestimates of wind speeds by VHF radar

International audienceComparisons are made between horizontal wind measurements carried out using a VHF-radar system at Aberystwyth (52.4°N, 4.1°W) and radiosondes launched from Aberporth, some 50 km to the south-west. The radar wind results are derived from Doppler wind measurements at zenith angles of 6° in two orthogonal planes and in the vertical direction. Measurements on a total of 398 days over a 2-year period are considered, but the major part of the study involves a statistical analysis of data collected during 75 radiosonde flights selected to minimise the spatial separation of the two sets of measurements. Whereas good agreement is found between the two sets of wind direction, radar-derived wind speeds show underestimates of 4?6% compared with radiosonde values over the height range 4?14 km. Studies of the characteristics of this discrepancy in wind speeds have concentrated on its directional dependence, the effects of the spatial separation of the two sets of measurements, and the influence of any uncertainty in the radar measurements of vertical velocities. The aspect sensitivity of radar echoes has previously been suggested as a cause of underestimates of wind speeds by VHF radar. The present statistical treatment and case-studies show that an appropriate correction can be applied using estimates of the effective radar beam angle derived from a comparison of echo powers at zenith angles of 4.2° and 8.5°

PRESERVING RURAL HISTORIC PROPERTIES: HELPING OWNERS HELP THEMSELVES

Advisory Committee: Dennis J. Pogue and Brent Leggs

Mangrove Restoration Potential: A global map highlighting a critical opportunity

Rapid losses of mangroves over the past 50 years have had negative consequences on the environment, the climate, and humanity, through diminished benefits such as carbon storage, coastal protection and fish production. Restoration of mangrove forests is possible, and has already been undertaken in many settings, but such efforts have been piecemeal, and many have failed. The current work describes the findings from an entirely new effort to locate and map, on a global scale, the places where mangroves can be restored, and to calculate the potential benefits from such restoration. The work has generated the Mangrove Restoration Potential Map, which provides a critical tool for encouraging restoration and enabling robust, data-driven policy changes and investments.This work forms part of a project supported by the International Climate Initiative (IKI). The German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) supports this initiative on the basis of a decision adopted by the German Bundesta

Subduction on the northern and southern flanks of the Gulf Stream

Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 40 (2010): 429-438, doi:10.1175/2009JPO4187.1.Sections of temperature, salinity, dissolved oxygen, and velocity were made crossing the Gulf Stream in late January 2006 to investigate the role of frontal processes in the formation of Eighteen Degree Water (EDW), the Subtropical Mode Water of the North Atlantic. The sections were nominally perpendicular to the stream and measured in a Lagrangian frame by following a floating spar buoy drifting in the Gulf Stream’s warm core. During the survey, EDW was isolated from the mixed layer by the stratified seasonal pycnocline, suggesting that EDW was not yet actively being formed at this time in the season and at the longitudes over which the survey was conducted (64°–70°W). However, in two of the sections, the seasonal pycnocline in the core of the Gulf Stream was broken by an intrusion of cold, fresh, weakly stratified water, nearly saturated in oxygen, that appears to have been subducted from the surface mixed layer north of the stream. The intrusion was identified in three of the sections in profiles with a nearly identical temperature–salinity relation. From the western-to-easternmost sections, where the intrusion was observed, the depth of the intrusion’s salinity minimum descended by 90 m in the 71 h it took to complete this part of the survey. This apparent subduction occurred primarily on the upstream side of a meander trough, where the cross-stream velocity was confluent and frontogenetic. Using a variant of the omega equation, the vertical velocity driven by the confluent flow was inferred and yielded downwelling in the vicinity of the intrusion spanning 10–40 m day−1, a range of values consistent with the intrusion’s observed descent, suggesting that frontal subduction was responsible for the formation of the intrusion. In the easternmost section located downstream of the meander trough, the flow was diffluent, driving an inferred vertical circulation that was of the opposite sense to that in the section upstream of the trough. In transiting the two sides of the trough, the intrusion was observed to move toward the center of the stream between the downwelling branches of the opposing vertical circulations, resulting in a downward Lagrangian mean vertical velocity and net subduction. Hydrographic evidence of the subduction of weakly stratified surface waters was seen in the southern flank of the Gulf Stream as well. The solution of the omega equation suggests that this subduction was associated with a relatively shallow vertical circulation confined to the upper 200 m of the water column in the proximity of the front marking the southern edge of the warm core.Support came from the National Science Foundation Grant OCE-0424865 (TJ and LT). LT was also supported by NSF Grant OCE- 0549699 and the Worzel Assistant Scientist Endowed Fund at WHOI

Wintertime observations of Subtropical Mode Water formation within the Gulf Stream

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L02607, doi:10.1029/2008GL035918.We study the structure of Subtropical Mode Water (STMW) within the eastward-flowing Gulf Stream as it forms during strong winter cooling. Shipboard observations using SeaSoar and ADCP reveal that while active mixing by gravitational instabilities is common, large vertical and lateral shears of the Gulf Stream play a central role in determination of the modes of active mixing. Evidence is presented that low static stability and large vertical shear can combine to cause slantwise convection/symmetric instabilities, while the large anticyclonic shears to the south of the Gulf Stream core can cause low absolute vorticity and precondition the Ertel potential vorticity to be small and more susceptible to instabilities. The area of active mixing driven by surface forcing in the presences of shear occupies a swath 50–90 km wide immediately south of the Gulf Stream core at the northern edge of the Sargasso Sea.Support came from the National Science Foundation grants OCE-0424865 (TJ and FB) and OCE-0549699 (LT)

Passive Integrated Transponder Tags: Review of Studies on Warmwater Fishes With Notes on Additional Species

Although numerous studies have assessed retention and survival of passive integrated transponder (PIT) tags, data are scattered and information gaps remain for many diminutive fishes. Our study objectives were to 1) systematically review PIT tag studies and summarize retention, growth, and survival data for warmwater fishes; and 2) conduct a laboratory study to evaluate the retention, survival, and growth effects of intracoelomic-placed, half duplex PIT tags on six small-bodied species common to warmwater streams. Our systematic review suggested small sample sizes were common within PIT tag retention and survival studies (39% with n ≤ 20) and that many experiments (15%, 14 of 97) failed to use control fish as part of their evaluations. Studies focused primarily on short-term changes (15 d to 2 y) in tag retention and survival. Tag retention was equal to or greater than 90% in 85% of the experiments reviewed and median survival was 92%. Growth was reported by fishes in the majority of reviewed studies. We found similar results after PIT tagging (peritoneum tagging using 12- or 23-mm half duplex tags) adult Cardinal Shiner Luxilus cardinalis, Central Stoneroller Campostoma annomalum, Greenside Darter Etheostoma blennioides, Orangethroat Darter Etheostoma spectabile, Slender Madtom Noturus exilis, and juvenile Smallmouth Bass Micropterus dolomieu. Tag retention for all species was high, with only one tag loss recorded after 60 d. Survival was also high (≥88%) for all of our species with the exception of Orangethroat Darter (56% survival). No significant difference in mean growth between treatment and control groups was found. Both our results and the findings of the literature review suggested generally high tag retention and low mortality in tagged fishes (across 31 species reviewed). However, within our study (e.g., Orangethroat Darter) and from the literature, examples of negative effects of PIT tagging on fishes were apparent, suggesting methodological testing is necessary before using PIT tags in field studies. We suggest future studies would benefit from addressing the behavioral implications that may be associated with tagging and examination of longer-term tag retention. Furthermore, standard reporting (i.e., sample sizes) in PIT tag studies would be beneficial, and use of control subjects or groups for statistical comparisons is needed

Modified technique to fabricate a hollow light-weight facial prosthesis for lateral midfacial defect: a clinical report

Large oro-facial defects result from cancer treatment consequences in serious functional as well as cosmetic deformities. Acceptable cosmetic results usually can be obtained with a facial prosthesis. However, retention of a large facial prosthesis can be challenging because of its size and weight. This article describes prosthetic rehabilitation of a 57-year-old man having a right lateral mid-facial defect with intraoral-extraoral combination prosthesis. A modified technique to fabricate a hollow substructure in heat-polymerizing polymethyl-methacrylate to support silicone facial prosthesis was illustrated. The resultant facial prosthesis was structurally durable and light in weight facilitating the retention with magnets satisfactorily. This technique is advantageous as there is no need to fabricate the whole prosthesis again in case of damage of the silicone layer because the outer silicone layer can be removed and re-packed on the substructure if the gypsum-mold is preserved