A Rarely Witnessed Summertime Upwelling Event northwest off the Hainan Island

2020 ◽  
Author(s):  
Ai-Jun Pan ◽  
Fang-fang Kuang ◽  
Kai Li ◽  
Xu Dong
Keyword(s):  
Coastal Upwelling ◽  
Hainan Island ◽  
Heat Fluxes ◽  
Tidal Mixing ◽  
Coastal Current ◽  
Beibu Gulf ◽  
Surface Heat Fluxes ◽  
Upwelled Water ◽  
Basin Scale ◽  
Upwelling Event

<p>A field survey revealed a rare realization of upwelling event in the northwestern Hainan Island (UNWHI) on July 24, 2015. Model experiments suggest that the UNWHI is not locally generated, but can be treated as northward extension of the upwelling southwest off Hainan Island (USWHI) under favorable wind conditions. Therefore, presence of the USWHI is vital for the UNWHI occurrence. Tidal mixing is testified to be the primary driving force for the USWHI, whilst southerly winds plays an essential role in the induction of the UNWHI. Moreover, it is demonstrated that the UNWHI is not a stable, but intermittent coastal upwelling system. Shallow basin of the Beibu Gulf makes the interior circulation vulnerable to local monsoon changes. Given the favorable southerly winds, a cyclonic gyre northwest off Hainan Island will be induced and which, leads to northward coastal current and consequently, the UNWHI is to be formed due to the northward transport of the USWHI. Conversely, the UNWHI vanishes during northerly winds period, because the basin-scale anticyclonic gyre results in a southward current west off the Hainan Island and which, acts to push the upwelled water of the USWHI offshore and away from the northwestern Hainan Island. In addition, our diagnostics indicates that contributions from surface heat fluxes to the UNWHI occurrence is negligible. Besides, it also reminds us that application of a high-frequency, much closer to reality wind field is necessary for the coastal upwelling simulation. </p>

scholarly journals Low-Level Cool Air over the Midlatitude Oceans in Summer

2018 ◽  
Vol 31 (5) ◽  
pp. 2075-2090 ◽  
Author(s):  
Teruhisa Shimada ◽  
Yuki Kanno ◽  
Toshiki Iwasaki
Keyword(s):  
Southern Hemisphere ◽  
Coastal Upwelling ◽  
Heat Content ◽  
Warm Season ◽  
Heat Fluxes ◽  
Systematic Analysis ◽  
Surface Heat Fluxes ◽  
Low Level ◽  
Basin Scale ◽  
Subtropical Oceans

The climatology of low-level cool air over the midlatitude oceans in summer is presented based on an isentropic analysis. This study focuses on isentropic surfaces of 296 K to analyze an adiabatic invariant referred to as the negative heat content representing the coldness of the air layer below the threshold isentropic surface. This approach allows a systematic analysis and a quantitative comparison of the cool air distribution and a diagnosis of diabatic heating of the air mass. The cool air covers most of the subarctic oceans and extends equatorward over the coastal upwelling regions in the east of the ocean basins. In these regions, the genesis of the cool air is diagnosed. The loss of the cool air occurs over land and the subtropical oceans, particularly on the offshore side of the coastal upwelling regions. In the Pacific sector and the Indian Ocean sector of the Southern Ocean, another large loss of the cool air occurs along the oceanic frontal zone including the Agulhas Return Current. Over the zonally extended region where the cool air is generated in the Southern Hemisphere and the coastal upwelling regions, it is suggested that diabatic cooling associated with low-level clouds overcome heating by turbulent surface heat fluxes. The genesis of the cool air over the subarctic oceans in the Northern Hemisphere in the warm season switches into the loss of the cold air in the cool season on a basin scale. Meanwhile, over the oceans in the Southern Hemisphere, there is no basin-scale seasonal switch.

scholarly journals Shelf sea tidal currents and mixing fronts determined from ocean glider observations

2017 ◽  
Author(s):  
Peter M. F. Sheehan ◽  
Sarah L. Hughes ◽  
Barbara Berx ◽  
Alejandro Gallego ◽  
Rob A. Hall ◽  
...  
Keyword(s):  
Thermal Stratification ◽  
Thermohaline Circulation ◽  
Heat Fluxes ◽  
Tidal Mixing ◽  
Surface Heat Fluxes ◽  
Atlantic Origin ◽  
Shelf Seas ◽  
Shelf Sea ◽  
Northern North Sea ◽  
Ocean Observing

Abstract. Tides and tidal mixing fronts are of fundamental importance to understanding shelf sea dynamics and ecosystems. We use dive-average currents from a two-month (12th October–2nd December 2013) glider deployment along a zonal hydrographic section in the northern North Sea to determine M2 and S2 tidal velocities, which agree well with tidal velocities measured by current meters and extracted from a tide model. The method enhances the utility of gliders as an ocean-observing platform, particularly in regions where tide models are known to be limited. We use the glider-derived tidal velocities to investigate tidal controls on the location of a tidal mixing front. During the deployment, the front moves offshore at a rate of 0.51 km day−1. During the first period of the deployment (i.e. until mid November), the front's position is explained by the local balance between tidal mixing and surface heat fluxes: as heat is lost to the atmosphere, full-depth tidal mixing is able to occur in progressively deeper water. In the latter half of the deployment, the output of a simple one-dimensional model suggests that the front should have decayed. By comparing this model output to hydrographic observations from the glider, we attribute the persistence of the front beyond this period to the advection of cold, saline Atlantic-origin water across the deeper portion of the section. The glider captures the transition of the front from being one controlled by the balance between tidal mixing and surface heating, to being one controlled by advection of buoyancy. Fronts in shelf regions with oceanic influence may be geographically fixed and persist during periods of little to no thermal stratification, with implications for the thermohaline circulation of shelf seas.

scholarly journals Physical and chemical aspects of transient stages of the upwelling at southwest of Cabo Frio (Lat. 23ºS - Long. 42ºW)

1979 ◽  
Vol 28 (2) ◽  
pp. 37-46 ◽  
Author(s):  
Argeo Magliocca ◽  
Luiz Bruner de Miranda ◽  
Sergio Romano Signorini
Keyword(s):  
Oxygen Concentration ◽  
Inorganic Phosphate ◽  
Coastal Region ◽  
Maximum Velocity ◽  
Phosphate Concentration ◽  
Coastal Current ◽  
Upwelled Water ◽  
Physical And Chemical ◽  
Upwelling Event ◽  
Cabo Frio

An upwelling event was observed during February 1971 in the coastal region between Cabo Frio and Saquarema Point. Isolated upwelled water observed on a first survey, with a temperature of 17ºC, oxygen concentration of 4.2 ml/liter and inorganic phosphate concentration of 0.6 µg-at/liter, cleanly indicating its subsurface origin, was replaced, after a period of four to seven days, by coastal water with a temperature of 22ºC, oxygen concentration of 5.0 ml/liter and inorganic phosphate concentration of less than 0.3 µg-at,/liter. The evidence indicates that this replacement took place due to an eastward coastal current with a maximum velocity of nearly 5.0 nautical miles per day. The subsurface distribution of the chemical and physical properties indicates that the upwelling occurred mostly in the narrowest portion of the continental shelf.

scholarly journals Interhemispheric SST Gradient Trends in the Indian Ocean prior to and during the Recent Global Warming Hiatusa

2016 ◽  
Vol 29 (24) ◽  
pp. 9077-9095 ◽  
Author(s):  
Lu Dong ◽  
Michael J. McPhaden
Keyword(s):  
Global Warming ◽  
Indian Ocean ◽  
Wind Stress ◽  
Coastal Upwelling ◽  
Surface Wind ◽  
Heat Fluxes ◽  
Thermocline Depth ◽  
Upwelled Water ◽  
The Indian Ocean ◽  
Sst Gradient

Abstract Sea surface temperatures (SSTs) have been rising for decades in the Indian Ocean in response to greenhouse gas forcing. However, this study shows that during the recent hiatus in global warming, a striking interhemispheric gradient in Indian Ocean SST trends developed around 2000, with relatively weak or little warming to the north of 10°S and accelerated warming to the south of 10°S. Evidence is presented from a wide variety of data sources showing that this interhemispheric gradient in SST trends is forced primarily by an increase of Indonesian Throughflow (ITF) transport from the Pacific into the Indian Ocean induced by stronger Pacific trade winds. This increased transport led to a depression of the thermocline that facilitated SST warming, presumably through a reduction in the vertical turbulent transport of heat in the southern Indian Ocean. Surface wind changes in the Indian Ocean linked to the enhanced Walker circulation also may have contributed to thermocline depth variations and associated SST changes, with downwelling-favorable wind stress curls between 10° and 20°S and upwelling-favorable wind stress curls between the equator and 10°S. In addition, the anomalous southwesterly wind stresses off the coast of Somalia favored intensified coastal upwelling and offshore advection of upwelled water, which would have led to reduced warming of the northern Indian Ocean. Although highly uncertain, lateral heat advection associated with the ITF and surface heat fluxes may also have played a role in forming the interhemispheric SST gradient change.

scholarly journals Shelf sea tidal currents and mixing fronts determined from ocean glider observations

Ocean Science ◽  
2018 ◽  
Vol 14 (2) ◽  
pp. 225-236 ◽  
Author(s):  
Peter M. F. Sheehan ◽  
Barbara Berx ◽  
Alejandro Gallego ◽  
Rob A. Hall ◽  
Karen J. Heywood ◽  
...  
Keyword(s):  
North Sea ◽  
Thermohaline Circulation ◽  
Heat Fluxes ◽  
Water Masses ◽  
Tidal Mixing ◽  
Primary Control ◽  
Surface Heat Fluxes ◽  
The North ◽  
Shelf Sea ◽  
North Western

Abstract. Tides and tidal mixing fronts are of fundamental importance to understanding shelf sea dynamics and ecosystems. Ocean gliders enable the observation of fronts and tide-dominated flows at high resolution. We use dive-average currents from a 2-month (12 October–2 December 2013) glider deployment along a zonal hydrographic section in the north-western North Sea to accurately determine M2 and S2 tidal velocities. The results of the glider-based method agree well with tidal velocities measured by current meters and with velocities extracted from the TPXO tide model. The method enhances the utility of gliders as an ocean-observing platform, particularly in regions where tide models are known to be limited. We then use the glider-derived tidal velocities to investigate tidal controls on the location of a front repeatedly observed by the glider. The front moves offshore at a rate of 0.51 km day−1. During the first part of the deployment (from mid-October until mid-November), results of a one-dimensional model suggest that the balance between surface heat fluxes and tidal stirring is the primary control on frontal location: as heat is lost to the atmosphere, full-depth mixing is able to occur in progressively deeper water. In the latter half of the deployment (mid-November to early December), a front controlled solely by heat fluxes and tidal stirring is not predicted to exist, yet a front persists in the observations. We analyse hydrographic observations collected by the glider to attribute the persistence of the front to the boundary between different water masses, in particular to the presence of cold, saline, Atlantic-origin water in the deeper portion of the section. We combine these results to propose that the front is a hybrid front: one controlled in summer by the local balance between heat fluxes and mixing and which in winter exists as the boundary between water masses advected to the north-western North Sea from diverse source regions. The glider observations capture the period when the front makes the transition from its summertime to wintertime state. Fronts in other shelf sea regions with oceanic influence may exhibit similar behaviour, with controlling processes and locations changing over an annual cycle. These results have implications for the thermohaline circulation of shelf seas.

Numerical Simulation of Air–Sea Coupling during Coastal Upwelling

2007 ◽  
Vol 37 (8) ◽  
pp. 2081-2093 ◽  
Author(s):  
Natalie Perlin ◽  
Eric D. Skyllingstad ◽  
Roger M. Samelson ◽  
Philip L. Barbour
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Coastal Upwelling ◽  
Heat Fluxes ◽  
Lower Atmosphere ◽  
Ekman Transport ◽  
Internal Boundary ◽  
Surface Boundary ◽  
Oregon Coast ◽  
Upwelled Water

Abstract Air–sea coupling during coastal upwelling was examined through idealized three-dimensional numerical simulations with a coupled atmosphere–ocean mesoscale model. Geometry, topography, and initial and boundary conditions were chosen to be representative of summertime coastal conditions off the Oregon coast. Over the 72-h simulations, sea surface temperatures were reduced several degrees near the coast by a wind-driven upwelling of cold water that developed within 10–20 km off the coast. In this region, the interaction of the atmospheric boundary layer with the cold upwelled water resulted in the formation of an internal boundary layer below 100-m altitude in the inversion-capped boundary layer and a reduction of the wind stress in the coupled model to half the offshore value. Surface heat fluxes were also modified by the coupling. The simulated modification of the atmospheric boundary layer by ocean upwelling was consistent with recent moored and aircraft observations of the lower atmosphere off the Oregon coast during the upwelling season. For these 72-h simulations, comparisons of coupled and uncoupled model results showed that the coupling caused measurable differences in the upwelling circulation within 20 km off the coast. The coastal Ekman transport divergence was distributed over a wider offshore extent and a thinner ocean surface boundary layer, with consistently smaller offshore and depth-integrated alongshore transport formed in the upwelling region, in the coupled case relative to the uncoupled case. The results indicate that accurate models of coastal upwelling processes can require representations of ocean–atmosphere interactions on short temporal and horizontal scales.

scholarly journals Volume and Nutrient Transports Disturbed by the Typhoon Chebi (2013) in the Upwelling Zone East of Hainan Island, China

2021 ◽  
Vol 9 (3) ◽  
pp. 324
Author(s):  
Manli Zheng ◽  
Lingling Xie ◽  
Quanan Zheng ◽  
Mingming Li ◽  
Fajin Chen ◽  
...  
Keyword(s):  
South China Sea ◽  
Coastal Upwelling ◽  
Unit Area ◽  
Hainan Island ◽  
Volume Transport ◽  
Coastal Ocean ◽  
Offshore Water ◽  
Nutrient Distribution ◽  
Before And After ◽  
Ekman Flow

Using cruise observations before and after the typhoon Chebi in August 2013 and those without the typhoon in July 2012, this study investigates variations in current structure, nutrient distribution, and transports disturbed by a typhoon in a typical coastal upwelling zone east of Hainan Island in the northwestern South China Sea. The results show that along-shore northeastward flow dominates the coastal ocean with a volume transport of 0.64 × 106 m3/s in the case without the typhoon. The flow reversed southwestward, with its volume transport halved before the typhoon passage. After the typhoon passage, the flow returned back northeastward except the upper layer in waters deeper than 50 m and the total volume transport decreased to 0.10 × 106 m3/s. For the cross-shelf component, the flow kept shoreward, while transports crossing the 50 m isobath decreased from 0.25, 0.12 to 0.06 × 106 m3/s in the case without the typhoon as well as before and after typhoon passage, respectively. For the along-shore/cross-shelf nutrient transports, SiO32− has the largest value of 866.13/632.74 μmol/s per unit area, NO3− half of that, and PO43− and NO2− one order smaller in the offshore water without the typhoon. The values dramatically decreased to about one-third for SiO32−, NO3−, and PO43− after the typhoon, but changed little for NO2−. The disturbed wind field and associated Ekman flow and upwelling process may explain the variations in the current and nutrient transports after the typhoon.

Trends of land surface heat fluxes on the Tibetan Plateau from 2001 to 2012

2017 ◽  
Vol 37 (14) ◽  
pp. 4757-4767 ◽  
Author(s):  
Cunbo Han ◽  
Yaoming Ma ◽  
Xuelong Chen ◽  
Zhongbo Su
Keyword(s):  
Tibetan Plateau ◽  
Land Surface ◽  
Surface Heat ◽  
Heat Fluxes ◽  
The Tibetan Plateau ◽  
Surface Heat Fluxes ◽  
Land Surface Heat Fluxes

scholarly journals Diagnosis of 3D Vertical Circulation in the Upwelling and Frontal Zones East of Hainan Island, China

2017 ◽  
Vol 47 (4) ◽  
pp. 755-774 ◽  
Author(s):  
Lingling Xie ◽  
Enric Pallàs-Sanz ◽  
Quanan Zheng ◽  
Shuwen Zhang ◽  
Xiaolong Zong ◽  
...  
Keyword(s):  
Coastal Upwelling ◽  
Frontal Zone ◽  
Dominant Role ◽  
Subsurface Layer ◽  
Vertical Mixing ◽  
Hainan Island ◽  
Eddy Diffusivity ◽  
Vertical Circulation ◽  
Forcing Term ◽  
Advection Term

AbstractUsing the generalized omega equation and cruise observations in July 2012, this study analyzes the 3D vertical circulation in the upwelling region and frontal zone east of Hainan Island, China. The results show that there is a strong frontal zone in subsurface layer along the 100-m isobath, which is characterized by density gradient of O(10−4) kg m−4 and vertical eddy diffusivity of O(10−5–10−4) m2 s−1. The kinematic deformation term SDEF, ageostrophic advection term SADV, and vertical mixing forcing term SMIX are calculated from the observations. Their distribution patterns are featured by banded structure, that is, alternating positive–negative alongshore bands distributed in the cross-shelf direction. Correspondingly, alternating upwelling and downwelling bands appear from the coast to the deep waters. The maximum downward velocity reaches −5 × 10−5 m s−1 within the frontal zone, accompanied by the maximum upward velocity of 7 × 10−5 m s−1 on two sides. The dynamic diagnosis indicates that SADV contributes most to the coastal upwelling, while term SDEF, which is dominated by the ageostrophic component SDEFa, plays a dominant role in the frontal zone. The vertical mixing forcing term SMIX, which includes the momentum and buoyancy flux terms SMOM and SBUO, is comparable to SDEF and SADV in the upper ocean, but negligible below the thermocline. The effect of the vertical mixing on the vertical velocity is mainly concentrated at depths with relatively large eddy diffusivity and eddy diffusivity gradient in the frontal zone.

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