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1
Kenyon, Kern E. "Downwelling by Surface Gravity Waves?" Natural Science 09, n. 05 (2017): 143–44. http://dx.doi.org/10.4236/ns.2017.95015.
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2
Blue, Charles. "Mantle downwelling causes continental depressions". Eos, Transactions American Geophysical Union 74, n. 9 (2 marzo 1993): 98. http://dx.doi.org/10.1029/93eo00359.
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Cenedese, Claudia. "Downwelling in Basins Subject to Buoyancy Loss". Journal of Physical Oceanography 42, n. 11 (1 novembre 2012): 1817–33. http://dx.doi.org/10.1175/jpo-d-11-0114.1.
Testo completoAbstract (sommario):
Abstract Recent observational, theoretical, and modeling studies all suggest that the upper part of the downwelling limb of the thermohaline circulation is concentrated in strong currents subject to buoyancy loss near lateral boundaries. This is fundamentally different from the traditional view that downwelling takes place in regions of deep convection. Even when resolving the buoyant boundary currents, coarse-resolution global circulation and climate models rely on parameterizations of poorly known turbulent mixing processes. In this study, the first direct measurements of downwelling occurring within a basin subject to buoyancy loss are obtained. Downwelling is observed near the basin’s vertical wall within the buoyant boundary current flowing cyclonically around the basin. Although the entire basin is cooled, large-scale mean downwelling is absent in the basin interior. Laboratory rotating experiments are conducted to explicitly resolve the turbulent mixing due to convective plumes and the baroclinic eddies generated by the boundary current, and to identify where downwelling takes place. Small vertical velocities can be measured more reliably in the laboratory than in many numerical calculations, whereas the measurement of these small vertical velocities is still a challenge for field experiments. Downwelling is observed near the vertical wall within a boundary layer with a thickness that scales with the baroclinic Rossby radius of deformation, consistent with the dynamical balance proposed by a previous numerical study. Hence, downwelling in the Labrador Sea and Lofoten Basin cyclonic boundary currents may be concentrated in a baroclinic Rossby radius of deformation thick boundary layer in regions with large eddy generation.
4
Fan, Wei, Dongdong Pan, Canbo Xiao, Tiancheng Lin, Yiwen Pan e Ying Chen. "Experimental Study on the Performance of an Innovative Tide-Induced Device for Artificial Downwelling". Sustainability 11, n. 19 (25 settembre 2019): 5268. http://dx.doi.org/10.3390/su11195268.
Testo completoAbstract (sommario):
Hypoxia has been increasingly observed in estuaries and coastal marine ecosystems around the world. In this paper, a tide-powered artificial downwelling device is proposed to potentially alleviate hypoxia in bottom waters. The downwelling device mainly consists of a vertical square tube, a 90° bend sitting on the top of the tube, two symmetrical-guide plates which installed alongside the vertical tube, a static mixer, and an artificial reef. Scale model experiments are performed with respect to different density difference heads, horizontal current velocities, and tube geometries. The results show that the downwelling flow rate is dependent on horizontal current velocity, tube geometry parameters, and the density profile of ambient water. In addition, increasing the equivalent diameter and bend radius of the device can decrease the total loss coefficient in the tube, which in turns enhance the downwelling efficiency. The two symmetrical-guide plates also generate obvious downwelling of surface water which further improves the whole performance of the device. Further work will need to determine the influence of the other parts of the device, such as the static mixer and artificial reef, on the downwelling efficiency.
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Brüggemann, Nils, e Caroline A. Katsman. "Dynamics of Downwelling in an Eddying Marginal Sea: Contrasting the Eulerian and the Isopycnal Perspective". Journal of Physical Oceanography 49, n. 11 (novembre 2019): 3017–35. http://dx.doi.org/10.1175/jpo-d-19-0090.1.
Testo completoAbstract (sommario):
AbstractIn this study, we explore the downward branch of the Atlantic meridional overturning circulation (AMOC) from a perspective in depth space (Eulerian downwelling) as well as from a perspective in density space (diapycnal downwelling). Using an idealized model, we focus on the role of eddying marginal seas, where dense water is formed by deep convection due to an intense surface heat loss. We assess where diapycnal mass fluxes take place, investigate the pathways of dense water masses, and elucidate the role of eddies. We find that there are fundamental differences between the Eulerian and diapycnal downwelling: the strong Eulerian near-boundary downwelling is not associated with substantial diapycnal downwelling; the latter takes place in the interior and elsewhere in the boundary current. We show that the diapycnal downwelling appears to be more appropriate to describe the pathways of water masses. In our model, dense water masses are exported along two routes: those formed in the upper part of the boundary current are exported directly; those formed in the interior move toward the boundary along isopycnals due to eddy stirring and are then exported. This study thus reveals a complex three-dimensional view of the overturning in a marginal sea, with possible implications for our understanding of the AMOC.
6
Spall, Michael A. "Buoyancy-Forced Downwelling in Boundary Currents". Journal of Physical Oceanography 38, n. 12 (1 dicembre 2008): 2704–21. http://dx.doi.org/10.1175/2008jpo3993.1.
Testo completoAbstract (sommario):
Abstract The issue of downwelling resulting from surface buoyancy loss in boundary currents is addressed using a high-resolution, nonhydrostatic numerical model. It is shown that the net downwelling is determined by the change in the mixed layer density along the boundary. For configurations in which the density on the boundary increases in the direction of Kelvin wave propagation, there is a net downwelling within the domain. For cases in which the density decreases in the direction of Kelvin wave propagation, cooling results in a net upwelling within the domain. Symmetric instability within the mixed layer drives an overturning cell in the interior, but it does not contribute to the net vertical motion. The net downwelling is determined by the geostrophic flow toward the boundary and is carried downward in a very narrow boundary layer of width E1/3, where E is the Ekman number. For the calculations here, this boundary layer is O(100 m) wide. A simple model of the mixed layer temperature that balances horizontal advection with surface cooling is used to predict the net downwelling and its dependence on external parameters. This model shows that the net sinking rate within the domain depends not only on the amount of heat loss at the surface but also on the Coriolis parameter, the mixed layer depth (or underlying stratification), and the horizontal velocity. These results indicate that if one is to correctly represent the buoyancy-forced downwelling in general circulation models, then it is crucial to accurately represent the velocity and mixed layer depth very close to the boundary. These results also imply that processes that lead to weak mixing within a few kilometers of the boundary, such as ice formation or freshwater runoff, can severely limit the downwelling forced by surface cooling, even if there is strong heat loss and convection farther offshore.
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Meneghello, Gianluca, John Marshall, Mary-Louise Timmermans e Jeffery Scott. "Observations of Seasonal Upwelling and Downwelling in the Beaufort Sea Mediated by Sea Ice". Journal of Physical Oceanography 48, n. 4 (aprile 2018): 795–805. http://dx.doi.org/10.1175/jpo-d-17-0188.1.
Testo completoAbstract (sommario):
AbstractWe present observational estimates of Ekman pumping in the Beaufort Gyre region. Averaged over the Canada Basin, the results show a 2003–14 average of 2.3 m yr−1 downward with strong seasonal and interannual variability superimposed: monthly and yearly means range from 30 m yr−1 downward to 10 m yr−1 upward. A clear, seasonal cycle is evident with intense downwelling in autumn and upwelling during the winter months, despite the wind forcing being downwelling favorable year-round. Wintertime upwelling is associated with friction between the large-scale Beaufort Gyre ocean circulation and the surface ice pack and contrasts with previous estimates of yearlong downwelling; as a consequence, the yearly cumulative Ekman pumping over the gyre is significantly reduced. The spatial distribution of Ekman pumping is also modified, with the Beaufort Gyre region showing alternating, moderate upwelling and downwelling, while a more intense, yearlong downwelling averaging 18 m yr−1 is identified in the northern Chukchi Sea region. Implications of the results for understanding Arctic Ocean dynamics and change are discussed.
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Fan, Wei, Weicheng Bao, Yong Cai, Canbo Xiao, Zhujun Zhang, Yiwen Pan, Ying Chen e Shuo Liu. "Experimental Study on the Effects of a Vertical Jet Impinging on Soft Bottom Sediments". Sustainability 12, n. 9 (6 maggio 2020): 3775. http://dx.doi.org/10.3390/su12093775.
Testo completoAbstract (sommario):
Artificial downwelling, which is an ecological engineering method, potentially alleviates bottom hypoxia by bringing oxygen-rich surface water down below the pycnocline. However, the downward flow is likely to disturb sediments (or induce sediment resuspension) when reaching the bottom and then have unwanted side effects on the local ecosystem. To evaluate this, our paper presents a theoretical model and experimental data for the sediment resuspension caused by artificial downwelling. The theoretical model considers the critical conditions for sediment resuspension and the scour volume with the downwelling flow disturbing sediment. Experiments with altered downwelling flow speeds, discharge positions relative to the bottom, and particle sizes of sediment were conducted in a water tank, and the results were consistent with our theoretical model. The results show that the critical Froude number (hereinafter Fr) for sediment resuspension is 0.5. The prevention of sediment resuspension requires the downwelling flow speed and the discharge position to be adjusted so that Fr < 0.5; otherwise a portion of sediment is released into the water and its volume can be predicted by the derived formulation based on the Shields theory. Furthermore, sediment resuspension has side effects, such as a water turbidity increase and phosphorus release, the magnitudes of which are discussed with respect to engineering parameters. Further study will focus on field experiments of artificial downwelling and its environmental impacts.
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Liu, Shuo, Lige Zhao, Canbo Xiao, Wei Fan, Yong Cai, Yiwen Pan e Ying Chen. "Review of Artificial Downwelling for Mitigating Hypoxia in Coastal Waters". Water 12, n. 10 (13 ottobre 2020): 2846. http://dx.doi.org/10.3390/w12102846.
Testo completoAbstract (sommario):
Hypoxia is becoming a serious problem in coastal waters in many parts of the world. Artificial downwelling, which is one of the geoengineering-based adaptation options, was suggested as an effective means of mitigating hypoxia in coastal waters. Artificial downwelling powered by green energy, such as solar, wind, wave, or tidal energy, can develop a compensatory downward flow on a kilometer scale, which favors below-pycnocline ventilation and thus mitigates hypoxia in bottom water. In this paper, we review and assess the technical, numerical, and experimental aspects of artificial downwelling all over the world, as well as its potential environmental effects. Some basic principles are presented, and assessment and advice are provided for each category. Some suggestions for further field-based research on artificial downwelling, especially for long-term field research, are also given.
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Spurgin, J. M., e S. E. Allen. "Flow dynamics around downwelling submarine canyons". Ocean Science 10, n. 5 (14 ottobre 2014): 799–819. http://dx.doi.org/10.5194/os-10-799-2014.
Testo completoAbstract (sommario):
Abstract. Flow dynamics around a downwelling submarine canyon were analysed with the Massachusetts Institute of Technology general circulation model. Blanes Canyon (northwestern Mediterranean) was used for topographic and initial forcing conditions. Fourteen scenarios were modelled with varying forcing conditions. Rossby and Burger numbers were used to determine the significance of Coriolis acceleration and stratification (respectively) and their impacts on flow dynamics. A new non-dimensional parameter (χ) was introduced to determine the significance of vertical variations in stratification. Some simulations do see brief periods of upwards displacement of water during the 10-day model period; however, the presence of the submarine canyon is found to enhance downwards advection of density in all model scenarios. High Burger numbers lead to negative vorticity and a trapped anticyclonic eddy within the canyon, as well as an increased density anomaly. Low Burger numbers lead to positive vorticity, cyclonic circulation, and weaker density anomalies. Vertical variations in stratification affect zonal jet placement. Under the same forcing conditions, the zonal jet is pushed offshore in more uniformly stratified domains. The offshore jet location generates upwards density advection away from the canyon, while onshore jets generate downwards density advection everywhere within the model domain. Increasing Rossby values across the canyon axis, as well as decreasing Burger values, increase negative vertical flux at shelf break depth (150 m). Increasing Rossby numbers lead to stronger downwards advection of a passive tracer (nitrate), as well as stronger vorticity within the canyon. Results from previous studies are explained within this new dynamic framework.
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Spurgin, J. M., e S. E. Allen. "Flow dynamics around downwelling submarine canyons". Ocean Science Discussions 11, n. 3 (23 maggio 2014): 1301–56. http://dx.doi.org/10.5194/osd-11-1301-2014.
Testo completoAbstract (sommario):
Abstract. Flow dynamics around a downwelling submarine canyon were analysed with the Massachusetts Institute of Technology general circulation model. Blanes Canyon (Northwest Mediterranean) was used for topographic and initial forcing conditions. Fourteen scenarios were modelled with varying forcing conditions. Rossby number and Burger number were used to determine the significance of Coriolis acceleration and stratification (respectively) and their impacts on flow dynamics. A new non-dimensional parameter (χ) was introduced to determine the significance of vertical variations in stratification. Some simulations do see brief periods of upwards displacement of water during the 10 day model period, however, the presence of the submarine canyon is found to enhance downwards advection of density in all model scenarios. High Burger numbers lead to negative vorticity and a trapped anticyclonic eddy within the canyon, as well as an increased density anomaly. Low Burger numbers lead to positive vorticity, cyclonic circulation and weaker density anomalies. Vertical variations in stratification affect zonal jet placement. Under the same forcing conditions, the zonal jet is pushed offshore in more uniformly stratified domains. Offshore jet location generates upwards density advection away from the canyon, while onshore jets generate downwards density advection everywhere within the model domain. Increasing Rossby values across the canyon axis, as well as decreasing Burger values, increase negative vertical flux at shelf break depth (150 m). Increasing Rossby numbers lead to stronger downwards advection of a passive tracer (nitrate) as well as stronger vorticity within the canyon. Results from previous studies were explained within this new dynamic framework.
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Matano, Ricardo P., e Elbio D. Palma. "On the Upwelling of Downwelling Currents". Journal of Physical Oceanography 38, n. 11 (1 novembre 2008): 2482–500. http://dx.doi.org/10.1175/2008jpo3783.1.
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Abstract The term “downwelling currents” refers to currents with a downslope mass flux in the bottom boundary layer. Examples are the Malvinas and Southland Currents in the Southern Hemisphere and the Oyashio in the Northern Hemisphere. Although many of these currents generate the same type of highly productive ecosystems that is associated with upwelling regimes, the mechanism that may drive such upwelling remains unclear. In this article, it is postulated that the interaction between a downwelling current and the continental slope generates shelfbreak upwelling. The proposed mechanism is relatively simple. As a downwelling current flows along the continental slope, bottom friction and lateral diffusion spread it onto the neighboring shelf, thus generating along-shelf pressure gradients and a cross-shelf circulation pattern that leads to shelfbreak upwelling. At difference with previous studies of shelfbreak dynamics (e.g., Gawarkiewicz and Chapman, Chapman and Lentz, and Pickart), the shelfbreak upwelling in the proposed model is not controlled by the downslope buoyancy flux associated with the presence of a shelf current but by the along-shelf pressure gradient associated with the presence of a slope current. As these experiments demonstrate, shelfbreak upwelling will occur in flat-bottomed domains or even in the absence of a bottom boundary layer. The shelfbreak upwelling, moreover, is not evidence of the separation of the bottom boundary layer but of the downstream divergence of the slope currents, and its magnitude is proportional to the volume transport of that current. To prove this hypothesis, the results of a series of process-oriented numerical experiments are presented.
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Koweek, David A., Clara García-Sánchez, Philip G. Brodrick, Parker Gassett e Ken Caldeira. "Evaluating hypoxia alleviation through induced downwelling". Science of The Total Environment 719 (giugno 2020): 137334. http://dx.doi.org/10.1016/j.scitotenv.2020.137334.
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Hu, Dingzhu, Yipeng Guo, Feiyang Wang, Qi Xu, Yuanpu Li, Wenjun Sang, Xudong Wang e Meichen Liu. "Brewer–Dobson Circulation: Recent-Past and Near-Future Trends Simulated by Chemistry-Climate Models". Advances in Meteorology 2017 (2017): 1–13. http://dx.doi.org/10.1155/2017/2913895.
Testo completoAbstract (sommario):
Based on data from 16 chemistry-climate models (CCMs) and separate experimental results using a state-of-the-art CCM, the trends in the Brewer–Dobson circulation (BDC) during the second half of the 20th century (1960–2000) and the first half of the 21st century (2001–2050) are examined. From the ensemble mean of the CCMs, the BDC exhibits strengthening trends in both the 20th and 21st centuries; however, the acceleration rates of tropical upwelling and southern downwelling during 2001–2050 are smaller than those during 1960–2000, while the acceleration rate of the northern downward branch of the BDC during 2001–2050 is slightly larger than that during 1960–2000. The differences in the extratropical downwelling trends between the two periods are closely related to changes in planetary-wave propagation into the stratosphere caused by the combined effects of increases in the concentrations of greenhouse gases (GHGs) and changes in stratospheric ozone. Model simulations demonstrate that the response of southern downwelling to stratospheric ozone depletion is larger than that to the increase in GHGs, but that the latter plays a more important role in the strengthening of northern downwelling. This result suggests that, under the expected future climate, northern downwelling will play a more important role in balancing tropical upwelling.
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Lund-Hansen, Lars Chresten, Michael Bjerg-Nielsen, Tanja Stratmann, Ian Hawes e Brian K. Sorrell. "Upwelling Irradiance below Sea Ice—PAR Intensities and Spectral Distributions". Journal of Marine Science and Engineering 9, n. 8 (30 luglio 2021): 830. http://dx.doi.org/10.3390/jmse9080830.
Testo completoAbstract (sommario):
Upwelling and downwelling spectral (320–920 nm) distributions and photosynthetic active radiation (PAR) intensities were measured below a first-year land-fast sea ice in a western Greenland fjord with and without a snow cover. Time-series of surface upwelling PAR, downwelling PAR, and under-ice PAR were also obtained. Spectral distributions of upwelling and downwelling irradiances were similar except for reduced intensities in the UV, the red, and NIR parts of the spectrum when the ice was snow-covered. Upwelling PAR amounted to about 10% of downwelling intensities, giving 5.1 µmol photons m−2 s−1 at the bottom of the ice with a snow cover and 8.2 µmol photons m−2 s−1 without. PAR partitioning analyses showed that the upwelling was related to scattering by suspended particles in the water column. A snow melt increased under-ice daily maximum downwelling PAR from 50 to 180 µmol photons m−2 s−1 and overall under-ice PAR of 55 and 198 µmol photons m−2 s−1 with 10% upwelling. It is concluded that upwelling PAR below sea ice might be an important factor regarding sea ice algae photophysiology and performance with a 10% higher PAR; specifically when PAR > Ek the light saturation point of the sea ice algae.
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Jaimes, Benjamin, e Lynn K. Shay. "Enhanced Wind-Driven Downwelling Flow in Warm Oceanic Eddy Features during the Intensification of Tropical Cyclone Isaac (2012): Observations and Theory". Journal of Physical Oceanography 45, n. 6 (giugno 2015): 1667–89. http://dx.doi.org/10.1175/jpo-d-14-0176.1.
Testo completoAbstract (sommario):
AbstractTropical cyclones (TCs) typically produce intense oceanic upwelling underneath the storm’s center and weaker and broader downwelling outside upwelled regions. However, several cases of predominantly downwelling responses over warm, anticyclonic mesoscale oceanic features were recently reported, where the ensuing upper-ocean warming prevented significant cooling of the sea surface, and TCs rapidly attained and maintained major status. Elucidating downwelling responses is critical to better understanding TC intensification over warm mesoscale oceanic features. Airborne ocean profilers deployed over the Gulf of Mexico’s eddy features during the intensification of tropical storm Isaac into a hurricane measured isothermal downwelling of up to 60 m over a 12-h interval (5 m h−1) or twice the upwelling strength underneath the storm’s center. This displacement occurred over a warm-core eddy that extended underneath Isaac’s left side, where the ensuing upper-ocean warming was ~8 kW m−2; sea surface temperatures >28°C prevailed during Isaac’s intensification. Rather than with just Ekman pumping WE, these observed upwelling–downwelling responses were consistent with a vertical velocity Ws = WE − Rogδ(Uh + UOML); Ws is the TC-driven pumping velocity, derived from the dominant vorticity balance that considers geostrophic flow strength (measured by the eddy Rossby number Rog = ζg/f), geostrophic vorticity ζg, Coriolis frequency f, aspect ratio δ = h/Rmax, oceanic mixed layer thickness h, storm’s radius of maximum winds Rmax, total surface stresses from storm motion Uh, and oceanic mixed layer Ekman drift UOML. These results underscore the need for initializing coupled numerical models with realistic ocean states to correctly resolve the three-dimensional upwelling–downwelling responses and improve TC intensity forecasting.
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Wang, Xi, Jian Liu, Bingyun Yang, Yansong Bao, George P. Petropoulos, Hui Liu e Bo Hu. "Seasonal Trends in Clouds and Radiation over the Arctic Seas from Satellite Observations during 1982 to 2019". Remote Sensing 13, n. 16 (12 agosto 2021): 3201. http://dx.doi.org/10.3390/rs13163201.
Testo completoAbstract (sommario):
A long-term dataset of 38 years (1982–2019) from the Advanced Very High Resolution Radiometer (AVHRR) satellite observations is applied to investigate the spatio-temporal seasonal trends in cloud fraction, surface downwelling longwave flux, and surface upwelling longwave flux over the Arctic seas (60~90° N) by the non-parametric methods. The results presented here provide a further contribution to understand the cloud cover and longwave surface radiation trends over the Arctic seas, and their correlations to the shrinking sea ice. Our results suggest that the cloud fraction shows a positive trend for all seasons since 2008. Both surface downwelling and upwelling longwave fluxes present significant positive trends since 1982 with higher magnitudes in autumn and winter. The spatial distribution of the trends is nearly consistent between the cloud fraction and the surface longwave radiation, except for spring over the Chukchi and Beaufort Seas. We further obtained a significant negative correlation between cloud fraction (surface downwelling/upwelling longwave fluxes) and sea-ice concentration during autumn, which is largest in magnitude for regions with substantial sea ice retreat. We found that the negative correlation between cloud fraction and sea-ice concentration is not as strong as that for the surface downwelling longwave flux. It indicates the increase in cloudiness may result in positive anomalies in surface downwelling longwave flux which is highly correlated with the sea-ice retreat in autumn.
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Whitney, Michael M., e J. S. Allen. "Coastal Wind-Driven Circulation in the Vicinity of a Bank. Part II: Modeling Flow over the Heceta Bank Complex on the Oregon Coast". Journal of Physical Oceanography 39, n. 6 (1 giugno 2009): 1298–316. http://dx.doi.org/10.1175/2008jpo3967.1.
Testo completoAbstract (sommario):
Abstract This study investigates wind-driven circulation in the vicinity of the Heceta Bank complex along the Oregon shelf. Numerical experiments forced with steady winds (0.1 Pa) are conducted; upwelling and downwelling cases are compared. The asymmetric bank bathymetry is the only configurational difference from the symmetric bank runs analyzed in Part I (Whitney and Allen). Upwelling-favorable winds generate an upwelling front and southward baroclinic jet. Model results indicate the upwelling jet is centered on the 100-m isobath along the straight shelf. The jet follows this isobath offshore around the northern part of the bank but separates from sharply turning isobaths in the southern half and flows over deeper waters. The jet turns back toward the coast farther downstream. Inshore of the main jet, currents reverse and flow back onto the bank. These reversed currents turn southward again (at the bank center) and join a secondary southward coastal upwelling jet. This secondary coastal jet converges with the stronger main jet farther downstream. Upwelling is intense at the northern bank edge near the coast, where a dense water tongue is advected over the bank. Upwelling also is strong on the southern bank half where the flow turns and reverses. Other areas of the bank have reduced upwelling or even downwelling during upwelling-favorable winds. Downwelling-favorable winds drive a near-bottom density front and a northward jet. The slower downwelling jet flows along the 130-m isobath over the straight shelf. The jet departs from isobaths over the southern bank half and follows a straighter path over shallower waters. There are no reversed currents over the bank. The bank is an area of reduced downwelling. Some of the differences in the evolution of the current and density fields are linked to fundamental differences between the upwelling and downwelling regimes; these are anticipated by the symmetric bank results of Part I. Other differences arise because of the bank asymmetry and opposite flow directions over the bank. The lowest-order depth-averaged across-stream momentum balance remains geostrophic over the bank. Advection, ageostrophic pressure gradients, wind stress, and bottom stress all are important in the depth-averaged alongstream momentum balance over the Heceta Bank complex. Both across-shelf and alongshelf density advection are important. Barotropic potential vorticity is not conserved over the bank, but the tendency for relative vorticity changes and depth changes to partially counter each other influences the different paths of the upwelling and downwelling jets. There are several regions of active upwelling and downwelling over the bank. In these areas, vertical velocities at the top of the bottom boundary layer are linked to topographic upwelling and downwelling and Ekman pumping. There is considerable spatial variability in the currents, densities, and dynamics over the Heceta Bank complex.
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Howard, Rosie, e Roland Stull. "Modeling the Downwelling Longwave Radiation over a Groomed Ski Run under Clear Skies". Journal of Applied Meteorology and Climatology 52, n. 7 (luglio 2013): 1540–53. http://dx.doi.org/10.1175/jamc-d-12-0245.1.
Testo completoAbstract (sommario):
AbstractThe surface radiation budget of a groomed ski run is important to ski racing. Variables such as snow-surface temperature and liquid water content depend upon the surface radiation budget and are crucial to preparing fast skis. This case study focuses on downwelling longwave radiation, measurements of which were made at a point on a ski run on Whistler Mountain, British Columbia, Canada, throughout a 5-day clear-sky intensive observation period. Tall trees often dominate the horizon of a point on a ski run, and so contributions to total downwelling longwave radiation from trees and sky were treated separately. The “LWRAD” longwave radiative flux model estimated the total downwelling longwave radiation by first calculating thermal contributions from the trees, incorporating regressions for tree temperature that use routine meteorological measurements. Contributions from each azimuth direction were determined with horizon-elevation angles from a theodolite survey. Thermal emissions were weighted accordingly and summed. Sky contributions were estimated using the “libRadtran” radiative transfer model with input of local atmospheric profiles of temperature and humidity and were added to tree emissions. Two clear-sky emissivity parameterizations using screen-height measurements were tested for comparison. LWRAD total downwelling longwave radiation varies between 235 and 265 W m−2 and compares well to measurements, with correlation coefficient squared (r2) of 0.96. These results can be used to improve estimates of downwelling longwave radiation for a groomed ski run.
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Toffolon, Marco. "Ekman circulation and downwelling in narrow lakes". Advances in Water Resources 53 (marzo 2013): 76–86. http://dx.doi.org/10.1016/j.advwatres.2012.10.003.
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Foukal, Nicholas P., Robert S. Pickart, G. W. K. Moore e Peigen Lin. "Shelfbreak Downwelling in the Alaskan Beaufort Sea". Journal of Geophysical Research: Oceans 124, n. 10 (ottobre 2019): 7201–25. http://dx.doi.org/10.1029/2019jc015520.
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Lai, Zhigang, Ronghua Ma, Mingfen Huang, Changsheng Chen, Yong Chen, Congbin Xie e Robert C. Beardsley. "Downwelling wind, tides, and estuarine plume dynamics". Journal of Geophysical Research: Oceans 121, n. 6 (giugno 2016): 4245–63. http://dx.doi.org/10.1002/2015jc011475.
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Palmisano, Anna C., e George M. Simmons. "Spectral downwelling irradiance in an Antarctic lake". Polar Biology 7, n. 3 (maggio 1987): 145–51. http://dx.doi.org/10.1007/bf00259202.
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Zhou, S., e P. C. Flynn. "Geoengineering Downwelling Ocean Currents: A Cost Assessment". Climatic Change 71, n. 1-2 (luglio 2005): 203–20. http://dx.doi.org/10.1007/s10584-005-5933-0.
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Kämpf, Jochen. "Extreme bed shear stress during coastal downwelling". Ocean Dynamics 69, n. 5 (18 marzo 2019): 581–97. http://dx.doi.org/10.1007/s10236-019-01256-4.
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Spall, Michael A. "Dynamics of Downwelling in an Eddy-Resolving Convective Basin". Journal of Physical Oceanography 40, n. 10 (1 ottobre 2010): 2341–47. http://dx.doi.org/10.1175/2010jpo4465.1.
Testo completoAbstract (sommario):
Abstract The mean downwelling in an eddy-resolving model of a convective basin is concentrated near the boundary where eddies are shed from the cyclonic boundary current into the interior. It is suggested that the buoyancy-forced downwelling in the Labrador Sea and the Lofoten Basin is similarly concentrated in analogous eddy formation regions along their eastern boundaries. Use of a transformed Eulerian mean depiction of the density transport reveals the central role eddy fluxes play in maintaining the adiabatic nature of the flow in a nonperiodic region where heat is lost from the boundary current. The vorticity balance in the downwelling region is primarily between stretching of planetary vorticity and eddy flux divergence of relative vorticity, although a narrow viscous boundary layer is ultimately important in closing the regional vorticity budget. This overall balance is similar in some ways to the diffusive–viscous balance represented in previous boundary layer theories, and suggests that the downwelling in convective basins may be properly represented in low-resolution climate models if eddy flux parameterizations are adiabatic, identify localized regions of eddy formations, and allow density to be transported far from the region of eddy formations.
27
Chaudhuri, Ayan H., e Rui M. Ponte. "An Evaluation of Surface Atmospheric Changes over the Arctic Ocean for 2000–09 Using Recent Reanalyses". Earth Interactions 19, n. 2 (1 gennaio 2015): 1–18. http://dx.doi.org/10.1175/ei-d-14-0012.1.
Testo completoAbstract (sommario):
Abstract The authors examine five recent reanalysis products [NCEP Climate Forecast System Reanalysis (CFSR), Modern-Era Retrospective Analysis for Research and Applications (MERRA), Japanese 25-year Reanalysis Project (JRA-25), Interim ECMWF Re-Analysis (ERA-Interim), and Arctic System Reanalysis (ASR)] for 1) trends in near-surface radiation fluxes, air temperature, and humidity, which are important indicators of changes within the Arctic Ocean and also influence sea ice and ocean conditions, and 2) fidelity of these atmospheric fields and effects for an extreme event: namely, the 2007 ice retreat. An analysis of trends over the Arctic for the past decade (2000–09) shows that reanalysis solutions have large spreads, particularly for downwelling shortwave radiation. In many cases, the differences in significant trends between the five reanalysis products are comparable to the estimated trend within a particular product. These discrepancies make it difficult to establish a consensus on likely changes occurring in the Arctic solely based on results from reanalyses fields. Regarding the 2007 ice retreat event, comparisons with remotely sensed estimates of downwelling radiation observations against these reanalysis products present an ambiguity. Remotely sensed observations from a study cited herewith suggest a large increase in downwelling summertime shortwave radiation and decrease in downwelling summertime longwave radiation from 2006 and 2007. On the contrary, the reanalysis products show only small gains in summertime shortwave radiation, if any; however, all the products show increases in downwelling longwave radiation. Thus, agreement within reanalysis fields needs to be further checked against observations to assess possible biases common to all products.
28
Bell, Michael J. "Meridional Overturning Circulations Driven by Surface Wind and Buoyancy Forcing". Journal of Physical Oceanography 45, n. 11 (novembre 2015): 2701–14. http://dx.doi.org/10.1175/jpo-d-14-0255.1.
Testo completoAbstract (sommario):
AbstractThe meridional overturning circulation (MOC) can be considered to consist of a downwelling limb in the Northern Hemisphere (NH) and an upwelling limb in the Southern Hemisphere (SH) that are connected via western boundary currents. Steady-state analytical gyre-scale solutions of the planetary geostrophic equations are derived for a downwelling limb driven in the NH solely by surface heat loss. In these solutions the rates of the water mass transformations between layers driven by the surface heat loss determine the strength of the downwelling limb. Simple expressions are obtained for these transformation rates that depend on the most southerly latitudes where heat loss occurs and the depths of the isopycnals on the eastern boundary. Previously derived expressions for the water mass transformation rates in subpolar gyres driven by the Ekman upwelling characteristic of the SH are also summarized. Explicit expressions for the MOC transport and the depths of isopycnals on the eastern boundary are then derived by equating the water mass transformations in the upwelling and downwelling limbs. The MOC obtained for a “single-basin” two-layer model is shown to be generally consistent with that obtained by Gnanadesikan. The model’s energetics are derived and discussed. In a world without a circumpolar channel in the SH, it is suggested that the upwelling limb would feed downwelling limbs in both hemispheres. In a world with two basins in the NH, if one of them has a strong halocline the model suggests that the MOC would be very weak in that basin.
29
Stone, Peter H., e Yuriy P. Krasovskiy. "An Interhemispheric Four-Box Model of the Meridional Overturning Circulation". Journal of Physical Oceanography 41, n. 3 (1 marzo 2011): 516–30. http://dx.doi.org/10.1175/2009jpo4123.1.
Testo completoAbstract (sommario):
Abstract The authors introduce a four-box interhemispheric model of the meridional overturning circulation. A single box represents high latitudes in each hemisphere, and in contrast to earlier interhemispheric box models, low latitudes are represented by two boxes—a surface box and a deep box—separated by a thermocline in which a balance is assumed between vertical advection and vertical diffusion. The behavior of the system is analyzed with two different closure assumptions for how the low-latitude upwelling depends on the density contrast between the surface and deep low-latitude boxes. The first is based on the conventional assumption that the diffusivity is a constant, and the second on the assumption that the energy input to the mixing is constant. There are three different stable equilibrium states that are closely analogous to the three found by Bryan in a single-basin interhemispheric ocean general circulation model. One is quasi-symmetric with downwelling in high latitudes of both hemispheres, and two are asymmetric solutions, with downwelling confined to high latitudes in one or the other of the two hemispheres. The quasi-symmetric solution becomes linearly unstable for strong global hydrological forcing, while the two asymmetric solutions do not. The qualitative nature of the solutions is generally similar for both the closure assumptions, in contrast to the solutions in hemispheric models. In particular, all the stable states can be destabilized by finite amplitude perturbations in the salinity or the hydrological forcing, and transitions are possible between any two states. For example, if the system is in an asymmetric state, and the moisture flux into the high-latitude region of downwelling is slowly increased, for both closure assumptions the high-latitude downwelling decreases until a critical forcing is reached where the system switches to the asymmetric state with downwelling in the opposite hemisphere. By contrast, in hemispheric models with the energy constraint, the downwelling increases and there is no loss of stability.
30
Key, Jeffrey R., Yong Liu e Robert S. Stone. "Development and evaluation of surface shortwave flux parameterizations for use in sea-ice models". Annals of Glaciology 25 (1997): 33–37. http://dx.doi.org/10.1017/s0260305500013756.
Testo completoAbstract (sommario):
The surface radiation budget of the polar regions strongly influences ice growth and melt. Thermodynamic sea-ice models therefore require accurate yet computationally efficient methods of computing radiative fluxes. In this paper a new parameterization of the downwelling shortwave radiation flux at the Arctic surface is developed and compared to a variety of existing schemes. Parameterized llnxes are compared to in situ measurements using data for one year at Barrow, Alaska. Our results show that the new parameterization can estimate the downwelling shortwave flux with mean and root mean square errors of 1 and 5%, respectively, for clear conditions and 5 and 20% for cloudy conditions. The new parameterization offers a unified approach to estimating downwelling shortwave fluxes under clear and cloudy conditions, and is more accurate than existing schemes.
31
Key, Jeffrey R., Yong Liu e Robert S. Stone. "Development and evaluation of surface shortwave flux parameterizations for use in sea-ice models". Annals of Glaciology 25 (1997): 33–37. http://dx.doi.org/10.3189/s0260305500013756.
Testo completoAbstract (sommario):
The surface radiation budget of the polar regions strongly influences ice growth and melt. Thermodynamic sea-ice models therefore require accurate yet computationally efficient methods of computing radiative fluxes. In this paper a new parameterization of the downwelling shortwave radiation flux at the Arctic surface is developed and compared to a variety of existing schemes. Parameterized llnxes are compared to in situ measurements using data for one year at Barrow, Alaska. Our results show that the new parameterization can estimate the downwelling shortwave flux with mean and root mean square errors of 1 and 5%, respectively, for clear conditions and 5 and 20% for cloudy conditions. The new parameterization offers a unified approach to estimating downwelling shortwave fluxes under clear and cloudy conditions, and is more accurate than existing schemes.
32
Tishchenko, Petr P., Pavel Ya Tishchenko, Vyacheslav B. Lobanov, Alexander F. Sergeev e Pavel Yu Semkin. "Role of downwelling/upwelling in formation/destruction of hypoxia in the bottom waters of the Amur Bay (Japan Sea)". Izvestiya TINRO 183, n. 4 (30 dicembre 2015): 156–65. http://dx.doi.org/10.26428/1606-9919-2015-183-156-165.
Testo completoAbstract (sommario):
Downwelling/upwelling influence on hypoxia at the bottom of the Amur Bay is determined on the data of oceanographic surveys conducted aboard RV Impulse in August 2012 and RV Malachite in August 2013 coupled with the data of monitoring oceanographic station in the bay. The hypoxia develops in the period of downwelling circulation driven by southern and southeastern winds and relaxes in conditions of upwelling induced by northern and northwestern winds.
33
Lentz, Steven J., e John Largier. "The Influence of Wind Forcing on the Chesapeake Bay Buoyant Coastal Current*". Journal of Physical Oceanography 36, n. 7 (1 luglio 2006): 1305–16. http://dx.doi.org/10.1175/jpo2909.1.
Testo completoAbstract (sommario):
Abstract Observations of the buoyant coastal current that flows southward from Chesapeake Bay are used to describe how the thickness, width, and propagation speed vary in response to changes in the along-shelf wind stress. Three basic regimes were observed depending on the strength of the wind. For weak wind stresses (from −0.02 to 0.02 Pa), the buoyant coastal current was relatively thin, the front slope was not steep, and the width was variable (1–20 km). For moderate downwelling (southward) wind stresses (0.02–0.07 Pa), wind-driven cross-shelf advection steepened the front, causing the plume to narrow and thicken. For stronger downwelling wind stresses (greater than 0.07 Pa), vertical mixing dominated, bulk Richardson numbers were approximately 0.25, isopycnals were nearly vertical, and the plume front widened but the plume width did not change. Plume thickness and width were normalized by the theoretical plume scales in the absence of wind forcing. Normalized plume thickness increased linearly from 1 to 2 as downwelling wind stresses increased from 0 to 0.2 Pa. Normalized plume widths were approximately 1 for downwelling wind stresses from 0.02 to 0.2 Pa. The observed along-shelf propagation speed of the plume was roughly equal to the sum of the theoretical propagation speed and the wind-driven along-shelf flow.
34
Long, Charles N., e Sally A. McFarlane. "Quantification of the Impact of Nauru Island on ARM Measurements". Journal of Applied Meteorology and Climatology 51, n. 3 (marzo 2012): 628–36. http://dx.doi.org/10.1175/jamc-d-11-0174.1.
Testo completoAbstract (sommario):
AbstractNauru Island at times generates low clouds that impact low-level cloud statistics and downwelling shortwave radiation measurements made at the Atmospheric Radiation Measurement Program (ARM) site. This study uses five years of Nauru data to quantify the island impact on the site measurements. The results indicate that the solar-heating-produced Nauru island effect occurs about 11% of the time during daylight hours. The island effect increases the 500–1000-m cloud base occurrence by 15%–20% when clouds occur, but because the island effect only occurs 11% of the time the overall increase in daylight low-cloud statistics is 2%, or 1% for 24-h statistics. In a similar way, the island effect produces a reduction of about 17% in the downwelling shortwave (SW) radiation across the daylight hours during the 11% of the time it occurs, an overall 2% daylight (or 1% for 24 h) average reduction. The island effect produces frequent positive downwelling SW cloud effects, in particular during the morning, which tend to somewhat mitigate the overall decrease in downwelling SW radiation that is due to clouds. This produces 17 W m−2 less daylight average SW cloud effect relative to non-island-effect times, in particular for the convectively suppressed regime that typifies island-effect-producing conditions. For long-term overall statistical studies such as model and satellite comparisons, the 2% daylight (or 1% per 24 h) average increase in low-level cloud occurrence and decrease in downwelling SW are not of large concern as long as researchers are aware of them. For shorter-term studies, however, or those that separate data by conditions such as convectively active/suppressed regimes, the Nauru island effect can have significant impacts.
35
Sliva, Lucie, e D. Dudley Williams. "Exploration of riffle-scale interactions between abiotic variables and microbial assemblages in the hyporheic zone". Canadian Journal of Fisheries and Aquatic Sciences 62, n. 2 (1 febbraio 2005): 276–90. http://dx.doi.org/10.1139/f04-190.
Testo completoAbstract (sommario):
Molecular methods were applied to explore the composition of hyporheic bacterial assemblages and their possible interaction with interstitial physicochemical variables. Hyporheic flows on a riffle were manipulated (a downwelling zone was converted to an upwelling zone and vice versa) in order to examine the influence of vertical flow patterns on microbial assemblages. Bacterial assemblages were heterogeneously distributed throughout the riffle, the greatest similarity among them occurring at similar depths rather than in areas of similar flow regimes (upwelling versus downwelling). There was no correlation between the measured physicochemical variables and the microbial assemblages, with the exception of depth and sediment particle size. The flow manipulation in the original downwelling zone appeared to have had an effect on the microbial assemblages, although this influence may have been primarily due to a change in temperature in the manipulated region rather than an alteration of the vertical-flow direction per se.
36
Shi, C., D. Guo, J. Xu, A. M. Powell e T. Xu. "The latitudinal structure of recent changes in the boreal Brewer–Dobson circulation". Atmospheric Chemistry and Physics Discussions 15, n. 17 (8 settembre 2015): 24403–17. http://dx.doi.org/10.5194/acpd-15-24403-2015.
Testo completoAbstract (sommario):
Abstract. Upwelling branch of the Brewer–Dobson circulation (BDC) controls the tropical lower stratospheric water vapor (WV) through dynamic cooling near the tropopause. Downwelling branch of BDC dominates the extratropical middle-lower stratospheric Hydrogen Chloride (HCl) by dynamic transport. Climatologically, a symmetric weakening BDC indicates increasing tropical lower stratospheric WV and decreasing extratropical middle-lower stratospheric HCl. However, the global ozone chemistry and related trace gas data records for the stratosphere data (GOZCARDS) show that the tropical lowermost stratospheric WV increased by 18 % decade−1 during 2001–2011 and the boreal mid-latitude lower stratospheric HCl rose 25 % decade−1 after 2006. We interpret this as resulting from a slowdown of the tropical upwelling and a speedup of the mid-latitude downwelling. This interpretation is supported by composite analysis of Eliasen–Palm Flux (EPF), zonal wind and regression of temperature on the EPF from the ERA-Interim data. Results present that the enhancing polar vortex and weakening planetary wave activity leads to a downwelling branch narrowing equatorward and a local speedup of 24 % at 20 hPa in the mid-latitudes. Moreover, there are regressive temperature increase of 1.5 K near the tropical tropopause and that of 0.5 K in the mid-latitude middle stratosphere, which also indicates the tropical upwelling slowdown and the mid-latitude downwelling speedup during 2001–2011.
37
Rydbeck, Adam V., Tommy G. Jensen e Matthew R. Igel. "Idealized Modeling of the Atmospheric Boundary Layer Response to SST Forcing in the Western Indian Ocean". Journal of the Atmospheric Sciences 76, n. 7 (26 giugno 2019): 2023–42. http://dx.doi.org/10.1175/jas-d-18-0303.1.
Testo completoAbstract (sommario):
Abstract The atmospheric response to sea surface temperature (SST) variations forced by oceanic downwelling equatorial Rossby waves is investigated using an idealized convection-resolving model. Downwelling equatorial Rossby waves sharpen SST gradients in the western Indian Ocean. Changes in SST cause the atmosphere to hydrostatically adjust, subsequently modulating the low-level wind field. In an idealized cloud model, surface wind speeds, surface moisture fluxes, and low-level precipitable water maximize near regions of strongest SST gradients, not necessarily in regions of warmest SST. Simulations utilizing the steepened SST gradient representative of periods with oceanic downwelling equatorial Rossby waves show enhanced patterns of surface convergence and precipitation that are linked to a strengthened zonally overturning circulation. During these conditions, convection is highly organized, clustering near the maximum SST gradient and ascending branch of the SST-induced overturning circulation. When the SST gradient is reduced, as occurs during periods of weak or absent oceanic equatorial Rossby waves, convection is much less organized and total rainfall is decreased. This demonstrates the previously observed upscale organization of convection and rainfall associated with oceanic downwelling equatorial Rossby waves in the western Indian Ocean. These results suggest that the enhancement of surface fluxes that results from a steepening of the SST gradient is the leading mechanism by which oceanic equatorial Rossby waves prime the atmospheric boundary layer for rapid convective development.
38
Bakun, Andrew, e Vera Natalie Agostini. "Seasonal patterns of wind-induced upwelling/downwelling in the Mediterranean Sea". Scientia Marina 65, n. 3 (30 settembre 2001): 243–57. http://dx.doi.org/10.3989/scimar.2001.65n3243.
Testo completo
39
Longuet-Higgins, Michael S. "Surface manifestations of turbulent flow". Journal of Fluid Mechanics 308 (10 febbraio 1996): 15–29. http://dx.doi.org/10.1017/s0022112096001371.
Testo completoAbstract (sommario):
The surface of a turbulent, open-channel flow is often characterized by smooth areas of upwelling, each surrounded by a zone of downwelling marked by short steep waves. The dynamics of short waves on such a downwelling region are investigated and some laboratory experiments are proposed. Assuming that the horizontal strain rate Ω is locally constant, a simple expression is derived for the amplitude a of the short capillary–gravity waves, and hence also for the spectrum of the surface slopes.
40
Williams, William J., Thomas J. Weingartner e Albert J. Hermann. "Idealized Two-Dimensional Modeling of a Coastal Buoyancy Front, or River Plume, under Downwelling-Favorable Wind Forcing with Application to the Alaska Coastal Current". Journal of Physical Oceanography 40, n. 2 (1 febbraio 2010): 279–94. http://dx.doi.org/10.1175/2009jpo4206.1.
Testo completoAbstract (sommario):
Abstract The cross-shelf structure of a buoyancy-driven coastal current, such as produced by a river plume, is modeled in a two-dimensional cross-shelf slice as a “wide” geostrophically balanced buoyancy front. Downwelling-favorable wind stress applied to this front leads to advection in the surface and bottom boundary layers that causes the front to become steeper so that it eventually reaches a steep quasi-steady state. This final state is either convecting, stable and steady, or stable and oscillatory depending on D/δ* and by /f 2, where D is bottom depth, δ* is an Ekman depth, by is the cross-shelf buoyancy gradient, and f is the Coriolis parameter. Descriptions of the cross-shelf circulation patterns are given and a scaling is presented for the isopycnal slope. The results potentially apply to the Alaska Coastal Current, which experiences strong, persistent downwelling-favorable wind stress during winter, but also likely have application to river plumes subjected to downwelling-favorable wind stress.
41
Pavlakis, K. G., D. Hatzidimitriou, C. Matsoukas, E. Drakakis, N. Hatzianastassiou e I. Vardavas. "Ten-year global distribution of downwelling longwave radiation". Atmospheric Chemistry and Physics 4, n. 1 (30 gennaio 2004): 127–42. http://dx.doi.org/10.5194/acp-4-127-2004.
Testo completoAbstract (sommario):
Abstract. Downwelling longwave fluxes, DLFs, have been derived for each month over a ten year period (1984-1993), on a global scale with a spatial resolution of 2.5x2.5 degrees and a monthly temporal resolution. The fluxes were computed using a deterministic model for atmospheric radiation transfer, along with satellite and reanalysis data for the key atmospheric input parameters, i.e. cloud properties, and specific humidity and temperature profiles. The cloud climatologies were taken from the latest released and improved International Satellite Climatology Project D2 series. Specific humidity and temperature vertical profiles were taken from three different reanalysis datasets; NCEP/NCAR, GEOS, and ECMWF (acronyms explained in main text). DLFs were computed for each reanalysis dataset, with differences reaching values as high as 30 Wm-2 in specific regions, particularly over high altitude areas and deserts. However, globally, the agreement is good, with the rms of the difference between the DLFs derived from the different reanalysis datasets ranging from 5 to 7 Wm-2. The results are presented as geographical distributions and as time series of hemispheric and global averages. The DLF time series based on the different reanalysis datasets show similar seasonal and inter-annual variations, and similar anomalies related to the 86/87 El Niño and 89/90 La Niña events. The global ten-year average of the DLF was found to be between 342.2 Wm-2 and 344.3 Wm-2, depending on the dataset. We also conducted a detailed sensitivity analysis of the calculated DLFs to the key input data. Plots are given that can be used to obtain a quick assessment of the sensitivity of the DLF to each of the three key climatic quantities, for specific climatic conditions corresponding to different regions of the globe. Our model downwelling fluxes are validated against available data from ground-based stations distributed over the globe, as given by the Baseline Surface Radiation Network. There is a negative bias of the model fluxes when compared against BSRN fluxes, ranging from -7 to -9 Wm-2, mostly caused by low cloud amount differences between the station and satellite measurements, particularly in cold climates. Finally, we compare our model results with those of other deterministic models and general circulation models.
42
Pavlakis, K. G., D. Hatzidimitriou, C. Matsoukas, E. Drakakis, N. Hatzianastassiou e I. Vardavas. "Ten-year global distribution of downwelling longwave radiation". Atmospheric Chemistry and Physics Discussions 3, n. 5 (13 ottobre 2003): 5099–137. http://dx.doi.org/10.5194/acpd-3-5099-2003.
Testo completoAbstract (sommario):
Abstract. Downwelling longwave fluxes, DLFs, have been derived for each month over a ten year period (1984–1993), on a global scale with a resolution of 2.5° × 2.5°. The fluxes were computed using a deterministic model for atmospheric radiation transfer, along with satellite and reanalysis data for the key atmospheric input parameters, i.e. cloud properties, and specific humidity and temperature profiles. The cloud climatologies were taken from the latest released and improved International Satellite Climatology Project D2 series. Specific humidity and temperature vertical profiles were taken from three different reanalysis datasets; NCEP/NCAR, GEOS, and ECMWF (acronyms explained in main text). DLFs were computed for each reanalysis dataset, with differences reaching values as high as 30 Wm−2 in specific regions, particularly over high altitude areas and deserts. However, globally, the agreement is good, with the rms of the difference between the DLFs derived from the different reanalysis datasets ranging from 5 to 7 Wm−2. The results are presented as geographical distributions and as time series of hemispheric and global averages. The DLF time series based on the different reanalysis datasets show similar seasonal and inter-annual variations, and similar anomalies related to the 86/87 El Niño and 89/90 La Niña events. The global ten-year average of the DLF was found to be between 342.2 Wm−2 and 344.3 Wm−2, depending on the dataset. We also conducted a detailed sensitivity analysis of the calculated DLFs to the key input data. Plots are given that can be used to obtain a quick assessment of the sensitivity of the DLF to each of the three key climatic quantities, for specific climatic conditions corresponding to different regions of the globe. Our model downwelling fluxes are validated against available data from ground-based stations distributed over the globe, as given by the Baseline Surface Radiation Network. There is a negative bias of the model fluxes when compared against BSRN fluxes, ranging from −7 to −9 Wm−2, mostly caused by low cloud amount differences between the station and satellite measurements, particularly in cold climates. Finally, we compare our model results with those of other deterministic models and general circulation models.
43
O’Donnell, James, George O. Marmorino e Clifford L. Trump. "Convergence and Downwelling at a River Plume Front". Journal of Physical Oceanography 28, n. 7 (luglio 1998): 1481–95. http://dx.doi.org/10.1175/1520-0485(1998)028<1481:cadaar>2.0.co;2.
Testo completo
44
Middleton, John F., e Mauro Cirano. "Wind-Forced Downwelling Slope Currents: A Numerical Study". Journal of Physical Oceanography 29, n. 8 (agosto 1999): 1723–43. http://dx.doi.org/10.1175/1520-0485(1999)029<1723:wfdsca>2.0.co;2.
Testo completo
45
Gege, Peter, e Nicole Pinnel. "Sources of variance of downwelling irradiance in water". Applied Optics 50, n. 15 (16 maggio 2011): 2192. http://dx.doi.org/10.1364/ao.50.002192.
Testo completo
46
Osychny, V. I., e N. B. Shapiro. "Modelling of upwelling and downwelling in the ocean". Physical Oceanography 5, n. 6 (novembre 1994): 401–12. http://dx.doi.org/10.1007/bf02198506.
Testo completo
47
Whitney, Michael M., e J. S. Allen. "Coastal Wind-Driven Circulation in the Vicinity of a Bank. Part I: Modeling Flow over Idealized Symmetric Banks". Journal of Physical Oceanography 39, n. 6 (1 giugno 2009): 1273–97. http://dx.doi.org/10.1175/2008jpo3966.1.
Testo completoAbstract (sommario):
Abstract This study examines how coastal banks influence wind-driven circulation along stratified continental shelves. Numerical experiments are conducted for idealized symmetric banks; the standard bank (200 km long and 50 km wide) has dimensions similar to the Heceta Bank complex along the Oregon shelf. Model runs are forced with 10 days of steady winds (0.1 Pa); upwelling and downwelling cases are compared. The bank introduces significant alongshelf variability in the currents and density fields. Upwelling-favorable winds create an upwelling front and a baroclinic jet (flowing opposite coastal-trapped wave propagation) that bend around the standard bank, approximately centered on the 90-m isobath. The upwelling jet is strongest over the upstream bank half, where it advects a tongue of dense water over the bank. There is a current reversal shoreward of the main jet at the bank center. Upwelling is most intense over the upstream part of the bank, while there is reduced upwelling and even downwelling over other bank sections. Downwelling-favorable winds create a near-bottom density front and a baroclinic jet (flowing in the direction of coastal-trapped wave propagation) that bend around the standard bank; the jet core moves from the 150-m isobath to the 100-m isobath and back over the bank. The downwelling jet is slowest and widest over the bank; there are no current reversals. Results over the bank are more similar to 2D results (that preclude alongshelf variability) than in the upwelling case. Downwelling is weakened over the bank. The density field evolution over the bank is fundamentally different from the upwelling case. Most model results for banks with different dimensions are qualitatively similar to the standard run. The exceptions are banks having a radius of curvature smaller than the inertial radius; the main jet remains detached from the coast far downstream from these banks. The lowest-order across-stream momentum balance indicates that the depth-averaged flow is geostrophic. Advection, ageostrophic pressure gradients, wind stress, and bottom stress are all important in the depth-averaged alongstream momentum balance over the bank. There is considerable variability in alongstream momentum balances over different bank sections. Across-shelf and alongshelf advection both change the density field over the bank. Barotropic potential vorticity is not conserved, but the tendency for relative vorticity changes and depth changes to partially counter each other results in differences between the upwelling and downwelling jet paths over the bank. Only certain areas of the bank have significant vertical velocities. In these areas of active upwelling and downwelling, vertical velocities at the top of the bottom boundary layer are due to either the jet crossing isobaths or bottom Ekman pumping.
48
Ruddick, Kevin G., Kenneth Voss, Andrew C. Banks, Emmanuel Boss, Alexandre Castagna, Robert Frouin, Martin Hieronymi et al. "A Review of Protocols for Fiducial Reference Measurements of Downwelling Irradiance for the Validation of Satellite Remote Sensing Data over Water". Remote Sensing 11, n. 15 (24 luglio 2019): 1742. http://dx.doi.org/10.3390/rs11151742.
Testo completoAbstract (sommario):
This paper reviews the state of the art of protocols for the measurement of downwelling irradiance in the context of Fiducial Reference Measurements (FRM) of water reflectance for satellite validation. The measurement of water reflectance requires the measurement of water-leaving radiance and downwelling irradiance just above water. For the latter, there are four generic families of method, using: (1) an above-water upward-pointing irradiance sensor; (2) an above-water downward-pointing radiance sensor and a reflective plaque; (3) a Sun-pointing radiance sensor (sunphotometer); or (4) an underwater upward-pointing irradiance sensor deployed at different depths. Each method—except for the fourth, which is considered obsolete for the measurement of above-water downwelling irradiance—is described generically in the FRM context with reference to the measurement equation, documented implementations, and the intra-method diversity of deployment platform and practice. Ideal measurement conditions are stated, practical recommendations are provided on best practice, and guidelines for estimating the measurement uncertainty are provided for each protocol-related component of the measurement uncertainty budget. The state of the art for the measurement of downwelling irradiance is summarized, future perspectives are outlined, and key debates such as the use of reflectance plaques with calibrated or uncalibrated radiometers are presented. This review is based on the practice and studies of the aquatic optics community and the validation of water reflectance, but is also relevant to land radiation monitoring and the validation of satellite-derived land surface reflectance.
49
Gjermundsen, Ada, Joseph H. LaCasce e Liv Denstad. "The Thermally Driven Ocean Circulation with Realistic Bathymetry". Journal of Physical Oceanography 48, n. 3 (marzo 2018): 647–65. http://dx.doi.org/10.1175/jpo-d-17-0147.1.
Testo completoAbstract (sommario):
AbstractThe global circulation driven solely by relaxation to an idealized surface temperature profile and to interior mixing is examined. Forcing by winds and evaporation/precipitation is excluded. The resulting circulation resembles the observed in many ways, and the overturning is of similar magnitude. The overturning is driven by large-scale upwelling in the interior (which is relatively large, because of the use of a constant mixing coefficient). The compensating downwelling occurs in the northern North Atlantic and in the Ross and Weddell Seas, with an additional, smaller contribution from the northern North Pacific. The latter is weaker because the Bering Strait limits the northward extent of the flow. The downwelling occurs in frictional layers near the boundaries and depends on the lateral shear in the horizontal flow. The shear, in turn, is linked to the imposed surface temperature gradient via thermal wind, and as such, the downwelling can be reduced or eliminated in selected regions by removing the surface gradient. Doing so in the northern North Atlantic causes the (thermally driven) Antarctic Circumpolar Current to intensify, increasing the sinking along Antarctica. Eliminating the surface gradient in the Southern Ocean increases the sinking in the North Atlantic and Pacific. As there is upwelling also in the western boundary currents, the flow must increase even more to accomplish the necessary downwelling. The implications of the results are then considered, particularly with respect to Arctic intensification of global warming, which will reduce the surface temperature gradient.
50
Moscadelli, Matteo, Nicola Acito, Marco Diani e Giovanni Corsini. "A Novel Method for LWIR Hyperspectral Target Detection by Means of a Subspace-Based Approach". Proceedings 27, n. 1 (16 ottobre 2019): 47. http://dx.doi.org/10.3390/proceedings2019027047.
Testo completoAbstract (sommario):
In this work, we present a new approach to detect materials with known spectral emissivity, in data acquired by thermal infrared hyperspectral systems. The method takes into account the spectral variability of the downwelling radiance, commonly neglected in most target detection techniques. We address such variability supposing that the downwelling radiance spans a low-rank subspace, whose basis matrix is learned off-line by means of MODTRAN. We evaluate the performance of the method with simulated data, and present results that show the effectiveness of the proposed algorithm.