共查询到20条相似文献,搜索用时 15 毫秒
1.
Sensitivity of high-resolution tropical cyclone intensity forecasts to surface flux parameterization
Chi-Sann Liou 《Natural Hazards》2007,41(3):387-399
Surface flux parameterization schemes used in current dynamic models are primarily based upon measurements at low and moderate
wind speeds. Recent studies show that these parameterization schemes may be incorrect at high wind speeds (e.g., tropical
cyclone forecasts). Five high-resolution numerical model experiments are designed to assess the sensitivity of tropical cyclone
intensity forecasts to changes in the surface flux parameterization. The sensitivity experiments are conducted by running
48 h forecasts of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) for six selected tropical cyclones with
individual modifications to surface flux calculation that include: (1) limiting the surface stress for wind speeds greater
than 33 m s−1, or 64 knots (kt); (2) computing the stress at the top of the model bottom grid layer (MBGL) by averaging results from surface
layer similarity and turbulence mixing parameterization for wind speeds greater than 33 m s−1; (3) increasing the roughness lengths for heat and moisture transfer by a factor of ten; (4) setting the roughness lengths
for heat and moisture transfer to 1/10 of the momentum roughness length; and (5) cooling the sea surface temperature (SST)
by a prescribed rate at high winds. Averaged responses for the six storms to these sensitivity tests show that: (i) the limit
on surface stress at high winds significantly increases the cyclone intensity in 48 h forecasts; (ii) the averaged surface
layer stress at high winds increases the cyclone intensity but to a much lesser degree than limiting the surface stress; (iii)
large increases in the roughness lengths for heat and moisture transfer are needed to significantly impact the intensity forecast;
(iv) the different roughness length formula for surface transfer coefficients notably increases C
h/C
d ratio from 0.59 to 0.79 for 25 m s−1 and 0.41 to 0.75 for 50 m s−1 that significantly increases the predicted cyclone intensity; and (v) cooling of the SST by −5.8°C in 48 h reduces the maximum
surface wind speed by −32 kt, or 16.5 m s−1, at 48 h forecast. These results suggest that a surface flux parameterization scheme suitable for tropical cyclone intensity
forecast must correctly model the leveling-off character of surface stress and C
h/C
d ratio at high winds. All modifications to surface flux calculation have little influence on 48 h track forecasts, even though
they may significantly impact the intensity forecasts.
相似文献
Chi-Sann LiouEmail: |
2.
Variations in long term wind speed during different decades in Arabian Sea and Bay of Bengal 总被引:1,自引:0,他引:1
A study has been carried out by comparing the extreme wind speeds estimated based on NCEP/NCAR reanalysis data for 100 years
return period using Fischer Tippet-1 (commonly known as Gumbel) and Weibull distributions for three locations (off Goa, Visakhapatnam
and Machilipatnam) in the north Indian Ocean. The wind dataset for Goa is compared with that from ERA-40 data. For higher
wind speeds (12–20m s−1), NCEP wind speed has higher percentage of occurrence than that of ERA-40. Analysis has shown slight upward trend in the
annual maximum wind for location off Machilipatnam with an increase of 1.2 cm s−1 per year and a decreasing trend of −1.3 cm s−1 per year in the case of Goa. The Weibull distribution with shape parameter 2 fits the annual maximum wind data better than
FT-1 distribution. 相似文献
3.
Morgane Lejart Jacques Clavier Laurent Chauvaud Christian Hily 《Estuaries and Coasts》2012,35(2):622-632
Respiration and calcification rates of the Pacific oyster Crassostrea gigas were measured in a laboratory experiment in the air and underwater, accounting for seasonal variations and individual size,
to estimate the effects of this exotic species on annual carbon budgets in the Bay of Brest, France. Respiration and calcification
rates changed significantly with season and size. Mean underwater respiration rates, deducted from changes in dissolved inorganic
carbon (DIC), were 11.4 μmol DIC g−1 ash-free dry weight (AFDW) h−1 (standard deviation (SD), 4.6) and 32.3 μmol DIC g−1 AFDW h−1 (SD 4.1) for adults (80–110 mm shell length) and juveniles (30–60 mm), respectively. The mean daily contribution of C. gigas underwater respiration (with 14 h per day of immersion on average) to DIC averaged over the Bay of Brest population was 7.0 mmol DIC m−2 day−1 (SD 8.1). Mean aerial CO2 respiration rate, estimated using an infrared gas analyzer, was 0.7 μmol CO2 g−1 AFDW h−1 (SD 0.1) for adults and 1.1 μmol CO2 g−1 AFDW h−1 (SD 0.2) for juveniles, corresponding to a mean daily contribution of 0.4 mmol CO2 m−2 day−1 (SD 0.50) averaged over the Bay of Brest population (with 10 h per day of emersion on average). Mean CaCO3 uptake rates for adults and juveniles were 4.5 μmol CaCO3 g−1 AFDW h−1 (SD 1.7) and 46.9 μmol CaCO3 g−1 AFDW h−1 (SD 29.2), respectively. The mean daily contribution of net calcification in the Bay of Brest C. gigas population to CO2 fluxes during immersion was estimated to be 2.5 mmol CO2 m−2 day−1 (SD 2.9). Total carbon release by this C. gigas population was 39 g C m−2 year−1 and reached 334 g C m−2 year−1 for densely colonized areas with relative contributions by underwater respiration, net calcification, and aerial respiration
of 71%, 25%, and 4%, respectively. These observations emphasize the substantial influence of this invasive species on the
carbon cycle, including biogenic carbonate production, in coastal ecosystems. 相似文献
4.
Michael J. Durako Piotr Kowalczuk Michael A. Mallin William J. Cooper Jason J. Souza David H. Wells 《Estuaries and Coasts》2010,33(6):1430-1441
Surface water optical characteristics, nutrients, and planktonic chlorophyll a concentrations were analyzed in the Cape Fear River (CFR) plume over a 2-year period. CFR discharge during the dry year (109 ± 105 m3s−1) was only 25% of the wet year discharge (429 ± 337 m3s−1). Partitioning the contributions of phytoplankton pigments, non-pigmented particles, and colored dissolved organic matter
(CDOM) to the absorption of photosynthetically active radiation (PAR) indicated that CDOM was the dominant contributor to
PAR absorption. Particulate absorption was relatively greater during the dry year. Pigment absorption was minor and varied
little among stations or between years. Chlorophyll a concentrations were reduced at the most plume-influenced stations during the wet year, despite lower turbidity and higher
nitrate concentrations. Ammonium and orthophosphate concentrations were not different between years. CDOM absorption [a
CDOM
(412)] ranged from 0.05 to 8.25 m−1 with highest values occurring near the CFR mouth. Our results suggest that for coastal ecosystems with significant blackwater
river inputs, CDOM may exert a major limiting influence over near-shore primary production. 相似文献
5.
Paul J. Schmieder David T. Ho Peter Schlosser Jordan F. Clark S. Geoffrey Schladow 《Estuaries and Coasts》2008,31(6):1038-1051
A sulfur hexafluoride (SF6) tracer release experiment was conducted in the Stockton Deep Water Ship Channel (DWSC) to quantify mixing and transport
rates. SF6 was injected in the San Joaquin River upstream of the DWSC and mapped for 8 days. From the temporal change in SF6 distributions, the longitudinal dispersion coefficient (K
x
) was determined to be 32.7 ± 3.6 m2 s−1 and the net velocity was 1.75 ± 0.03 km day−1. Based on the decrease in SF6 inventory during the experiment, the pulsed residence time for waters in the DWSC was estimated at ∼17 days. Within the DWSC
from Stockton downstream to Turner Cut, dissolved oxygen concentrations maintained a steady state value of 4 mg l−1. These values are below water quality objectives for the time of year. The low flow rates observed in the DWSC and the inability
of oxygen-rich waters from downstream to mix into the DWSC upstream of Turner Cut contribute to the low dissolved oxygen concentration. 相似文献
6.
Sulfide Inhibition of Nitrate Removal in Coastal Sediments 总被引:1,自引:0,他引:1
Microbial nitrate (NO3−) removal via denitrification (DNF) at high sulfide (H2S) concentrations was compared in sediment from a coastal freshwater pond in a developed area that receives salt-water influx
during storm events, and a saline pond proximal to an undeveloped estuary. Sediments were incubated with added SO42− (1,000 μg per gram dry weight basis (gdw)) to determine whether acid volatile sulfides (AVS) were formed. DNF in the sediments
was measured with NO3–N (300 μg gdw−1) alone, and with NO3–N and H2S (1,000 μg S2− gdw−1). SO42− addition to the freshwater sediments resulted in AVS formation (970 ± 307 μg S gdw−1) similar to the wetland with no added SO42− (986 ± 156 μg S gdw−1). DNF rates measured with no added H2S were greater in the freshwater than the wetland site (10.6 ± 0.6 vs. 6.4 ± 0.1 μg N2O–N gdw−1 h−1, respectively). High H2S concentrations retained NH4–N in the undeveloped wetland and retained NO3–N in the developed freshwater site, suggesting that potential salt-water influx may reduce the ability of the freshwater
sediments to remove NO3–N. 相似文献
7.
Ladislaus Rybach 《Environmental Geology》2009,58(8):1645-1651
Crystalline basement can contain notable quantities of thermal/mineral waters. Knowledge about their movement and it characteristics
(fluxes, velocities, trajectories) is of great relevance for subjects like waste disposal or geothermal resources. Geothermal
methods enable to quantify these flow characteristics. The use and potential of several methods is demonstrated at three sites,
all from Hercynian basement in Western Europe. The results show rather uniform characteristics: Darcy flow velocities on the
order of 10−11–10−10 m s−1; the domain of flow ranges down to 5–7 km depth. 相似文献
8.
A comparative study on isotopic composition of precipitation in wet tropic and semi-arid stations across southern India 总被引:2,自引:0,他引:2
Isotopic composition of monthly composite precipitation samples from Kozhikode (n = 31), a wet tropic station and Hyderabad (n = 25), a semi-arid station across southern India were studied for a period of four years from 2005 to 2008. During the study
period, the Kozhikode station recorded an average rainfall of 3500 mm while the Hyderabad station showed an average rainfall
of 790 mm. The average stable isotope values in precipitation at the Kozhikode station were δ
18O = −3.52‰, d-excess = 13.72‰; δ
18O = −2.94‰, d-excess = 10.57‰; and δ
18O = −7.53‰, d-excess = 13.79‰, respectively during the pre-monsoon (March–May), monsoon (June–September) and post-monsoon
(October–February) seasons. For the Hyderabad station, the average stable isotope values were δ
18O = −5.88‰, d-excess = 2.34‰; δ
18O = −4.39‰, d-excess = 9.21‰; and δ
18O = −8.69‰, d-excess = 14.29‰, respectively for the three seasons. The precipitation at the two stations showed distinctive
isotopic signatures. The stable isotopic composition of precipitation at the Hyderabad station showed significant variations
from the global trend while the Kozhikode station almost followed the global value. These differences are mainly attributed
to the latitudinal differences of the two stations coupled with the differences in climatic conditions. 相似文献
9.
Sample cylinders of two galena ore hand specimens from Braubach, Germany were axially shortened in the strain rate range
5 × 10−5 s−1–5 × 10−7 s−1 at a confining pressure of 200 (300) MPa and at temperatures of 20 °C–600 °C. Neutron diffraction analyses of the crystallographic
preferred orientation (texture) were carried out before and after experimental deformation on the same sample cylinder. Up
to a deformation temperature of 300 °C and a strain rate of 5 × 10−6 s−1 a more or less complete <110> fiber texture develops, the strength of the fiber texture only depending on strain and the
strength of the original preferred orientation. At slower strain rate and higher temperature, there is a distinct decrease
of the fiber texture development. Diffusional mass transfer starts to become a significant deformation mechanism. Deformation
at 500 °C changes the original texture only slightly, which indicates a rapid increase of importance of diffusional flow processes.
The alteration of the accompanying sulfosalts indicates that the temperature is high enough for the movement of atoms. The
microstructure only reveals remarkable deformation structures at higher strains and in areas of locally higher stresses.
Received: 10 June 1997 / Accepted: 14 May 1998 相似文献
10.
J. Magdalena Santana-Casiano M. González-Dávila A. G. González F. J. Millero 《Aquatic Geochemistry》2010,16(3):467-482
Fe(II)-Fe(III) redox behavior has been studied in the presence of catechol under different pH, ionic media, and organic compound
concentrations. Catechol undergoes oxidation in oxic conditions producing semiquinone and quinone and reduces Fe(III) in natural
solutions including seawater (SW). It is a pH-dependent process. Under darkness, the amount of Fe(II) generated is smaller
and is related to less oxidation of catechol. The Fe(II) regeneration is higher at lower pH values both in SW with log k = 1.86 (M−1 s−1) at pH 7.3 and 0.26 (M−1 s−1) at pH 8.0, and in NaCl solutions with log k of 1.54 (M−1 s−1) at pH 7.3 and 0.57 (M−1 s−1) at pH 8.0. At higher pH values, rate constants are higher in NaCl solutions than in SW. This is due to the complexation
of Mg(II) present in the media with the semiquinone that inhibits the formation of a second Fe(II) through the reaction of
this intermediate with other center Fe(Cat)+. 相似文献
11.
We measured seasonal variations in microzooplankton grazing in Long Island Sound (LIS) and San Francisco Bay (SFB). There
was consistent evidence of nutrient limitation in LIS, but not SFB. We found higher chlorophyll a concentrations in LIS compared with SFB. In spite of differences in phytoplankton, there were no differences in microzooplankton
abundance (summer: LIS, 12.4 ± 1.8 × 103 indiv. L−1; SFB, 14.1 ± 3.0 × 103 indiv. L−1), biomass (summer: LIS, 30.4 ± 5.0 μg C L−1; SFB, 26.3 ± 5.9 μg C L−1), or grazing rates (summer: LIS, 0.66 ± 0.19 day−1; SFB, 0.65 ± 0.18 day−1) between the two estuaries. In common with many other investigators, we found many instances of saturated as well as insignificant
grazing. We suggest that saturation in some cases may result from high particle loads in turbid estuarine systems and that
insignificant grazing may result from extreme saturation of the grazing response due to the need to process non-food particles. 相似文献
12.
The aim of this interdisciplinary study is to examine a component of the hydrological cycle in Galapagos by characterizing
soil properties. Nine soil profiles were sampled on two islands. Their physical and hydrodynamic properties were analyzed,
along with their mineralogical composition. Two groups of soils were identified, with major differences between them. The
first group consists of soils located in the highlands (>350 m a.s.l.), characterized by low hydraulic conductivity (<10−5 m s−1) and low porosity (<25%). These soils are thick (several meters) and homogeneous without coarse components. Their clay fraction
is considerable and dominated by gibbsite. The second group includes soils located in the low parts of the islands (<300 m
a.s.l.). These soils are characterized by high hydraulic conductivity (>10−3 m s−1) and high porosity (>35%). The structure of these soils is heterogeneous and includes coarse materials. The physical properties
of the soils are in good agreement with the variations of the rainfall according to the elevation, which appears as the main
factor controlling the soil development. The clayey alteration products constrain soils physical and hydrodynamic properties
by reducing the porosity and consequently the permeability and also by increasing water retention. 相似文献
13.
Lars Chresten Lund-Hansen Thorbjørn Joest Andersen Morten Holtegaard Nielsen Morten Pejrup 《Estuaries and Coasts》2010,33(6):1442-1451
Optical constituents as suspended particulate matter (SPM), chlorophyll (Chl-a), colored dissolved organic matter (CDOM),
and grain sizes were obtained on a transect in the arctic fjord-type estuary Kangerlussuaq (66°) in August 2007 along with
optical properties. These comprised diffuse attenuation coefficient of downwelling PAR (K
d(PAR)), upwelling PAR (K
u(PAR)), particle beam attenuation coefficient (c
p), and irradiance reflectance R(−0, PAR). PAR is white light between 400 and 700 nm. The estuary receives melt water from the Greenland Inland Ice and stations
covered a transect from the very high turbid melt water outlet to clear marine waters. Results showed a strong spatial variation
with high values as for suspended matter concentrations, CDOM, diffuse attenuation coefficient K
d(PAR), particle beam attenuation coefficients (c
p), and reflectance R(−0, PAR) at the melt water outlet. Values of optical constituents and properties decreased with distance from the melt water
outlet to a more or less constant level in central and outer part of the estuary. There was a strong correlation between inorganic
suspended matter (SPMI) and diffuse attenuation coefficient K
d(PAR) (r
2 = 0.92) and also for particle beam attenuation coefficient (c
p; r
2 = 0.93). The obtained SPMI specific attenuation—K
d*(PAR) = 0.13 m2 g−1 SPMI—and the SPMI specific particle beam attenuation—c
p* = 0.72 m2 g−1—coefficients were about two times higher than average literature values. Irradiance reflectance R(−0, PAR) was comparatively high (0.09−0.20) and showed a high (r
2 = 0.80) correlation with K
u(PAR). Scattering dominated relative to absorption—b(PAR)/a(PAR) = 12.3. Results strongly indicated that the high values in
the optical properties were related to the very fine particle sizes (mean = 2–6 μm) of the suspended sediment. Data and results
are discussed and compared to similar studies from both temperate and tropical estuaries. 相似文献
14.
Assessment of heavy-metal contamination of floodplain soils due to mining and mineral processing in the Harz Mountains, Germany 总被引:9,自引:2,他引:7
2 study area was assessed with respect to its heavy-metal load on the basis of the current guideline values. The heavy-metal
loads of the soils in the study area have ranges of <0.2–200 mg kg−1 for Cd, <10–30,000 mg kg−1 for Pb, 7–10,000 mg kg−1 for Cu and 50–55,000 mg kg−1 for Zn. Mobility of the heavy metals was determined by extraction at different pH values. The acid neutralisation capacity
(ANCx) at these pH values was also determined to estimate the probability that the pH can drop to pH=x. The ANC values in the study area ranged from 6 to 3000 mmol H+ kg−1, from −33 to 800 mmol H+ kg−1 and from −74 to 160 mmol H+ kg−1 for ANC3.5, ANC5.0 and ANC6.2, respectively. Together with pedological data, the extraction experiments permit differentiation between soil units that
have been placed in the same environmental hazard class on the basis of total heavy-metal loads.
Received: 10 August 1998 · Accepted: 14 August 1999 相似文献
15.
Xi Bin Ji Wen Zhi Zhao Er Si Kang Zhi Hui Zhang Bo Wen Jin 《Environmental Earth Sciences》2011,64(3):619-629
Fluxes of carbon dioxide, water vapor, and heat were measured above crop canopy using the eddy covariance method during the
2008 maize growing season, over an agricultural field within an oasis located in the middle reaches of Heihe River basin,
northwest China. The values for friction velocity, the Monin–Obukhov stability parameter, and energy balance closure indicated
that the eddy covariance system at this study site provided reliable flux estimates. Results from measurements showed that
the mean sensible heat flux was 70 W m−2 with a maximum value of 164 W m−2 (May) and a minimum value of 45 W m−2 (July) during the maize growing season. In contrast, the mean latent heat was 278 W m−2 with a maximum value of 383 W m−2 (July) and minimum of 101 W m−2 (May). The mean downward soil heat flux was 55 W m−2 with a maximum value of 127 W m−2 (May) and minimum of 49 W m−2 (July). The magnitude of mean daytime net CO2 uptake was −11.50 μmol m−2 s−1 with a maximum value of −28.32 μmol m−2 s−1 (18 and 19 July) and a minimum values of −0.32 μmol m−2 s−1 (18 and 19 May). Correlation was observed between daytime half-hourly carbon dioxide flux and canopy conductance. In addition,
the relationship between carbon dioxide flux and photosynthetically active radiation for selected days during different stages
of maize growing season indicated the carbon dioxide flux uptake by the canopy was controlled by actual photosynthetic activity
related to the variation of green leaf area index for the different growing stages. 相似文献
16.
Huan-Xin Weng Ya-Chao Qin Xiang-Wei Sun Xun-Hong Chen Jing-Feng Chen 《Environmental Geology》2009,57(1):9-15
Laboratory culture experiments have been conducted to evaluate the effects of light intensity on the growth of Cryptomonas sp. (Cryptophyceae) and the discrepancy in absorption of iron and phosphorus under different light conditions. Results show
that there is an exponential correlation between algal growth rate and light intensity. The saturating and semi-saturating
light values for Cryptomonas sp. cells are 150 and 47 μmol photons m−2 s−1, respectively. More uptake of Fe, P, and other trace elements such as Zn, Mn, Co, and Mo is observed in the low light cultures,
although the algal growth rates are slow. The growth rate at 10 μmol photons m−2 s−1 is only 10% of that at 150 μmol photons m−2 s−1, whereas Fe and P uptake increases by 150 and 100%, respectively. These results suggest potential implications of differentiation
in absorption of iron and phosphorus at different light intensities for the occurrence of harmful algal blooms (HABs). The
mechanisms of light intensity regulating nutrient uptake as well as the occurrence of HABs are also discussed. 相似文献
17.
We developed light requirements for eelgrass in the Pacific Northwest, USA, to evaluate the effects of short- and long-term
reductions in irradiance reaching eelgrass, especially related to turbidity and overwater structures. Photosynthesis-irradiance
experiments and depth distribution field studies indicated that eelgrass productivity was maximum at a photosynthetic photon
flux density (PPFD) of about 350–550 μmol quanta m−2 s−1. Winter plants had approximately threefold greater net apparent primary productivity rate at the same irradiance as summer
plants. Growth studies using artificial shading as well as field monitoring of light and eelgrass growth indicated that long-term
survival required at least 3 mol quanta m−2 day−1 on average during spring and summer (i.e., May-September), and that growth was saturated above about 7 mol quanta m−2 day−1. We conclude that non-light-limited growth of eelgrass in the Pacific Northwest requires an average of at least 7 mol quanta
m−2 day−1 during spring and summer and that long-term survival requires a minimum average of 3 mol quanta m−2 day−1. 相似文献
18.
Dagma Derdau Robert Freer Kate Wright 《Contributions to Mineralogy and Petrology》1998,133(1-2):199-204
Oxygen exchange experiments have been performed between single crystals of sanidine feldspar and oxygen gas enriched in 18O, at temperatures in the range 869–1053 °C, total pressure 1 atmosphere, for times up to 28 days. Oxygen isotope diffusion
profiles in a direction perpendicular to (001) were determined with an ion microprobe. The experimental data obey a single
Arrhenius relationship of the form D = 8.4 × 10−11 exp. (−245 ± 15 kJ mol−1/RT) m2s−1. The results indicate that oxygen diffusion in anhydrous sanidine feldspar is marginally slower than oxygen diffusion in
anhydrous anorthite. Comparison with published atomistic simulation studies suggests that oxygen transport in feldspar is
by an interstitial mechanism.
Received: 17 October 1997 / Accepted: 6 July 1998 相似文献
19.
Phytoplankton Biomass and Production in Subtropical Hong Kong Waters: Influence of the Pearl River Outflow 总被引:1,自引:0,他引:1
Alvin Y. T. Ho Jie Xu Kedong Yin Yuelu Jiang Xiangcheng Yuan Lei He Donald M. Anderson Joseph H. W. Lee Paul J. Harrison 《Estuaries and Coasts》2010,33(1):170-181
The size-fractionated phytoplankton biomass and primary production were investigated in four contrasting areas of Hong Kong
waters in 2006. Phytoplankton biomass and production varied seasonally in response to the influence of the Pearl River discharge.
In the dry season, the phytoplankton biomass and production were low (<42 mg chl m−2 and <1.8 g C m−2 day−1) in all four areas, due to low temperatures and dilution and reduced light availability due to strong vertical mixing. In
contrast, in the wet season, in the river-impacted western areas, the phytoplankton biomass and production increased greater
than five-fold compared to the dry season, especially in summer. In summer, algal biomass was 15-fold higher than in winter,
and the mean integrated primary productivity (IPP) was 9 g C m−2 day−1 in southern waters due to strong stratification, high temperatures, light availability, and nutrient input from the Pearl
River estuary. However, in the highly flushed western waters, chl a and IPP were lower (<30 mg m−2 and 4 g C m−2 day−1, respectively) due to dilution. The maximal algal biomass and primary production occurred in southern waters with strong
stratification and less flushing. Spring blooms (>10 μg chl a L−1) rarely occurred despite the high chl-specific photosynthetic rate (mostly >10 μg C μg chl a
−1 day−1) as the accumulation of algal biomass was restricted by active physical processes (e.g., strong vertical mixing and freshwater
dilution). Phytoplankton biomass and production were mostly dominated by the >5-μm size fraction all year except in eastern
waters during spring and mostly composed of fast-growing chain-forming diatoms. In the stratified southern waters in summer,
the largest algal blooms occurred in part due to high nutrient inputs from the Pearl River estuary. 相似文献