62,775 research outputs found
Vertical Distribution of Nutrients on Transitional Season in Weda Bay, North Maluku
A vertical distribution of nutrient shows an interaction of physical processes, source, and uptake along the water column. These interactions can occur along the water column with different processes in each layer. Water samples from 17 stations were collected for nitrate, phosphate, and silicates concentration analyses during the transitional season in the Weda Bay. During the transitional season, the Weda Bay was characterized by low salinity (33.55-34.10), relatively warm temperature (30.87°C), and the relatively low nutrient concentrations (nitrate=0.03-4.87 µg at/l, phosphate=0.011-0.852 µg at/l, and silicate=0.04-1.21 µg at/l). The present of Western North Pacific Ocean (WNPO) watermass and the influence of Southern Subtropical Lower Water (SSLW) producing high salinity (>35) at the depth of 130-300 m were observed along the Weda Bay. Nutrient geochemical processes in this region were shown by nutrient utilization and regeneration across the water columns. Nutrients utilization was relatively high in the surface layer. Meanwhile, nutrients regeneration and remineralization were more dominant in the thermocline and deeper water layers. Analyses of nutrients showed that nitrate was more dominant than other nutrients with N/P ratio was 3.83-37.99 and N/Si ratio was 0.12-10.98. The effectiveness of silicate (0.25 μg at/l) that was used by phytoplankton found at a depth of 200 m when its concentration decreased at N/P ratio (16:08) close to the Redfield ratio. Due to an uptake, remineralization, and regeneration processes in each layer, a nutrient distribution pattern was formed which the nutrient concentrations decreased in mixed layer and increased in the deeper water
Wind speed vertical distribution at Mt. Graham
The characterization of the wind speed vertical distribution V(h) is
fundamental for an astronomical site for many different reasons: (1) the wind
speed shear contributes to trigger optical turbulence in the whole troposphere,
(2) a few of the astroclimatic parameters such as the wavefront coherence time
(tau_0) depends directly on V(h), (3) the equivalent velocity V_0, controlling
the frequency at which the adaptive optics systems have to run to work
properly, depends on the vertical distribution of the wind speed and optical
turbulence. Also, a too strong wind speed near the ground can introduce
vibrations in the telescope structures. The wind speed at a precise pressure
(200 hPa) has frequently been used to retrieve indications concerning the tau_0
and the frequency limits imposed to all instrumentation based on adaptive
optics systems, but more recently it has been proved that V_200 (wind speed at
200 hPa) alone is not sufficient to provide exhaustive elements concerning this
topic and that the vertical distribution of the wind speed is necessary. In
this paper a complete characterization of the vertical distribution of wind
speed strength is done above Mt.Graham (Arizona, US), site of the Large
Binocular Telescope. We provide a climatological study extended over 10 years
using the operational analyses from the European Centre for Medium-Range
Weather Forecasts (ECMWF), we prove that this is representative of the wind
speed vertical distribution at Mt. Graham with exception of the boundary layer
and we prove that a mesoscale model can provide reliable nightly estimates of
V(h) above this astronomical site from the ground up to the top of the
atmosphere (~ 20 km).Comment: 12 pages, 9 figures (whereof 3 colour), accepted by MNRAS May 27,
201
Vertical distribution of stars and gas in a galactic disk
We study the vertical density distribution of stars and gas (HI and H_2) in a
galactic disk which is embedded in a dark matter halo. The new feature of this
work is the inclusion of gas, and the gravitational coupling between stars and
gas, which has led to a more realistic treatment of a multi-component galactic
disk. The gas gravity is shown to be crucially important despite the low gas
mass fraction. This approach physically explains the observed scaleheight
distribution of all the three disk components, including the long-standing
puzzle (Oort 1962) of a constant HI scaleheight observed in the inner Galaxy.
The above model is applied to two external galaxies: NGC 891 and NGC 4565, and
the stellar disk is shown to be not strictly flat as was long believed but
rather it shows a moderate flaring of a factor of about 2 within the optical
radius.Comment: 4 pages, 2 figures; to appear in the Proceedings of "Island
Universes: Structure and evolution of disk galaxies" (Terschelling, The
Netherlands, July 2005), ed. R. de Jon
Exploring the spatial, temporal, and vertical distribution of methane in Pluto's atmosphere
High-resolution spectra of Pluto in the 1.66 um region, recorded with the
VLT/CRIRES instrument in 2008 (2 spectra) and 2012 (5 spectra), are analyzed to
constrain the spatial and vertical distribution of methane in Pluto's
atmosphere and to search for mid-term (4 year) variability. A sensitivity study
to model assumptions (temperature structure, surface pressure, Pluto's radius)
is performed. Results indicate that (i) no variation of the CH4 atmospheric
content (column-density or mixing ratio) with Pluto rotational phase is present
in excess of 20 % (ii) CH4 column densities show at most marginal variations
between 2008 and 2012, with a best guess estimate of a ~20 % decrease over this
time frame. As stellar occultations indicate that Pluto's surface pressure has
continued to increase over this period, this implies a concomitant decrease of
the methane mixing ratio (iii) the data do not show evidence for an
altitude-varying methane distribution; in particular, they imply a roughly
uniform mixing ratio in at least the first 22-27 km of the atmosphere, and high
concentrations of low-temperature methane near the surface can be ruled out.
Our results are also best consistent with a relatively large (> 1180 km) Pluto
radius. Comparison with predictions from a recently developed global climate
model GCM indicates that these features are best explained if the source of
methane occurs in regional-scale CH4 ice deposits, including both low latitudes
and high Northern latitudes, evidence for which is present from the rotational
and secular evolution of the near-IR features due to CH4 ice. Our "best guess"
predictions for the New Horizons encounter in 2015 are: a 1184 km radius, a 17
ubar surface pressure, and a 0.44 % CH4 mixing ratio with negligible
longitudinal variations.Comment: 21 pages, 6 figure
Mt. Graham: Optical turbulence vertical distribution at standard and high vertical resolution
A characterization of the optical turbulence vertical distribution and all
the main integrated astroclimatic parameters derived from the CN2 and the wind
speed profiles above Mt. Graham is presented. The statistic includes
measurements related to 43 nights done with a Generalized Scidar (GS) used in
standard configuration with a vertical resolution of ~1 km on the whole 20-22
km and with the new technique (HVR-GS) in the first kilometer. The latter
achieves a resolution of ~ 20-30 m in this region of the atmosphere.
Measurements done in different periods of the year permit us to provide a
seasonal variation analysis of the CN2. A discretized distribution of the
typical CN2 profiles useful for the Ground Layer Adaptive Optics (GLAO)
simulations is provided and a specific analysis for the LBT Laser Guide Star
system ARGOS case is done including the calculation of the 'gray zones' for J,
H and K bands. Mt. Graham confirms to be an excellent site with median values
of the seeing without dome contribution equal to 0.72", the isoplanatic angle
equal to 2.5" and the wavefront coherence time equal to 4.8 msec. We provide a
cumulative distribution of the percentage of turbulence developed below H*
where H* is included in the (0,1 km) range. We find that 50% of the whole
turbulence develops in the first 80 m from the ground. The turbulence
decreasing rate is very similar to what has been observed above Mauna Kea.Comment: 12 pages, 6 figures, Proc. SPIE Conference "Ground-based and Airborne
Telescopes III", 27 June 2010, San Diego, California, US
Faunal response to benthic and hyporheic sedimentation varies with direction of vertical hydrological exchange
1. Sedimentation and clogging of benthic and hyporheic zone substrates is increasingly being recognised as one of the greatest threats to the ecological integrity of riverine ecosystems globally. This ex-situ study examined the influence of sedimentation (benthic and hyporheic) and pattern of hydrological exchange on the vertical distribution of the freshwater shrimp Gammarus pulex within the experimental substrates of running water mesocosms. 2. Six sediment treatments representing a continuum from a clean gravel substratum through to heavy sediment loading of both benthic and hyporheic substrates were used to examine the distribution of G. pulex in relation to the direction of hydrological exchange (downwelling, upwelling and no exchange). 3. The vertical distribution of fauna varied significantly for both sediment treatment and pattern of hydrological exchange. There was a significant interaction between the two effects indicating that the effect of sedimentation varied depending on the pattern of vertical hydrological exchange
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