5 research outputs found
Rapid dispersal of a hydrothermal plume by turbulent mixing
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 57 (2010): 931-945, doi:10.1016/j.dsr.2010.04.010.The water column imprint of the hydrothermal plume observed at the Nibelungen field (8°18' S 13°30' W) is highly variable in space and time. The off-axis location of the site, along the southern boundary of a non-transform ridge offset at the joint between two segments of the southern Mid-Atlantic
Ridge, is characterized by complex, rugged topography, and thus favorable
for the generation of internal tides, subsequent internal wave breaking, and
associated vertical mixing in the water column. We have used towed transects
and vertical profiles of stratification, turbidity, and direct current measurements
to investigate the strength of turbulent mixing in the vicinity of
the vent site and the adjacent rift valley, and its temporal and spatial variability
in relation to the plume dispersal. Turbulent diffusivities Kp were calculated from temperature inversions via Thorpe scales. Heightened mixing
(compared to open ocean values) was observed in the whole rift valley
within an order of Kp around 10-3 m2 s-1. The mixing close to the vent
site was even more elevated, with an average of Kp = 4 x 10-2 m2 s-1. The
mixing, as well as the flow field, exhibited a strong tidal cycle, with strong
currents and mixing at the non-buoyant plume level during ebb
flow. Periods
of strong mixing were associated with increased internal wave activity and
frequent occurrence of turbulent overturns. Additional effects of mixing on
plume dispersal include bifurcation of the particle plume, likely as a result
of the interplay between the modulated mixing strength and current speed,
as well as high frequency internal waves in the effluent plume layer, possibly
triggered by the buoyant plume via nonlinear interaction with the elevated
background turbulence or penetrative convection.This work was supported by the Priority Program
SPP1144 of the Deutsche Forschungsgemeinschaft; this is SPP 1144 contribution number 51. Funding for the ABE team from WHOI was provided by
Grant # OE-2006-218 from NOAA's Ocean Exploration Program; funding
for the MAPR work was provided by NOAA's Vents Program
The orbit and stellar masses of the archetype colliding-wind binary WR 140
We present updated orbital elements for the Wolf-Rayet (WR) binary WR 140 (HD
193793; WC7pd + O5.5fc). The new orbital elements were derived using previously
published measurements along with 160 new radial velocity measurements across
the 2016 periastron passage of WR 140. Additionally, four new measurements of
the orbital astrometry were collected with the CHARA Array. With these
measurements, we derive stellar masses of
and . We also include a discussion of the
evolutionary history of this system from the Binary Population and Spectral
Synthesis (BPASS) model grid to show that this WR star likely formed primarily
through mass loss in the stellar winds, with only a moderate amount of mass
lost or transferred through binary interactions.Comment: 10 pages, 5 figure
The orbit and stellar masses of the archetype colliding-wind binary WR 140
International audienceWe present updated orbital elements for the Wolf-Rayet (WR) binary WR 140 (HD 193793; WC7pd + O5.5fc). The new orbital elements were derived using previously published measurements along with 160 new radial velocity measurements across the 2016 periastron passage of WR 140. Additionally, four new measurements of the orbital astrometry were collected with the CHARA Array. With these measurements, we derive stellar masses of and . We also include a discussion of the evolutionary history of this system from the Binary Population and Spectral Synthesis model grid to show that this WR star likely formed primarily through mass-loss in the stellar winds, with only a moderate amount of mass lost or transferred through binary interactions
Scientific and technical challenges in remote sensing of plant canopy reflectance and fluorescence
State-of-the-art optical remote sensing of vegetation canopies is reviewed here to stimulate support from laboratory and field plant research. This overview of recent satellite spectral sensors and the methods used to retrieve remotely quantitative biophysical and biochemical characteristics of vegetation canopies shows that there have been substantial advances in optical remote sensing over the past few decades. Nevertheless, adaptation and transfer of currently available fluorometric methods aboard air- and space-borne platforms can help to eliminate errors and uncertainties in recent remote sensing data interpretation. With this perspective, red and blue-green fluorescence emission as measured in the laboratory and field is reviewed. Remotely sensed plant fluorescence signals have the potential to facilitate a better understanding of vegetation photosynthetic dynamics and primary production on a large scale. The review summarizes several scientific challenges that still need to be resolved to achieve operational fluorescence based remote sensing approaches