Search

Dr. Keith Thompson was a highly influential scientist in marine prediction and environmental statistics in Canada and abroad. He was also exceptionally successful for providing high-quality mentorship to graduate students and early-career scientists. In this article, we provide an overview of Dr. Thompson's career contributions to marine science programs and training for graduate students and other highly qualified personnel. [ABSTRACT FROM AUTHOR]

Among the documented consequences of anthropogenic global warming are the increased frequency and duration of marine heatwaves in the global ocean. The literature dedicated to Arctic marine heatwaves corroborates those results, but fails to identify the heat sources and sinks. Because of the numerous feedbacks impacting polar regions, understanding the processes triggering and dissipating those extreme events is particularly important to predict their occurrence in a fast changing ocean. A three‐dimensional regional ice‐ocean numerical model is used to calculate a surface mixed layer heat budget and to investigate mechanisms generating and dissipating marine heatwaves. The majority of the marine heatwaves are onset by surface heat fluxes and decayed by bottom and surface heat fluxes. The dominant processes are spatially and seasonally heterogeneous: lateral heat flux can become the primary process when advecting heat anomalies at the main Arctic gateways or by triggering temperature extremes in winter. Using a Reynolds decomposition, it can be determined that the shoaling of the surface mixed layer induced by ice melt can significantly lengthen and intensify Arctic marine heatwaves. In winter, the analysis of marine heatwaves poses unique challenges, with the long term freshening of the Arctic inducing a positive trend of 0.1°C per decade for the freezing point. Arctic marine heatwaves are expected to keep increasing in duration and intensity due to the increased trend of the primary process, the surface heat flux, and their dissipation by bottom heat flux provides a pathway for heat from the atmosphere to the Arctic subsurface water masses. Plain Language Summary: Extreme warm temperature anomalies in the ocean, called marine heatwaves are becoming more frequent, longer and more intense around the globe. In the Arctic Ocean, the complex links between sea ice, the atmosphere and the ocean could both amplify or hinder the impact of those events. Yet, understanding where the heat comes from and where it goes is critical to anticipate further changes in an already fast‐changing environment. To this aim, we calculate the sources and sinks of heat in a numerical model simulating the ocean and sea ice. Most marine heatwaves in the Arctic are generated by taking atmospheric heat up and disappear when this heat is transferred to the deeper ocean. In doing so, marine heatwaves provide a pathway for heat from the atmosphere to the subsurface ocean. Oceanic circulation can also propagate marine heatwaves along the continental shelf and toward the marginal ice zone. When ice melts, it shoals the upper layer of the ocean, concentrating the atmospheric heat and lengthening and intensifying marine heatwaves. The excess heat stored in the subsurface can be expected to resurface later in the season and will then delay the freezing of new sea ice. Key Points: A heat budget analysis is applied to a regional ice‐ocean model to determine the dominating drivers of marine heatwaves in the ArcticMarine heatwaves in the Arctic provide a pathway for heat from the atmosphere to the subsurface oceanSea ice melt shoals the surface mixed layer, and this prolongs and intensifies marine heatwaves [ABSTRACT FROM AUTHOR]

A three‐dimensional lake‐ice coupled model is used to investigate the space‐time variations of ice and underlying mechanisms in Lake Nam Co (LNC), the third largest lake over Tibetan Plateau (TP), during 2007–2017. The model reasonably reproduces the in situ measured ice thickness and water temperature profile, and satellite retrieved ice coverage and lake surface temperature. Seasonally, the lake ice first forms in the eastern basin during early January, expands from east to west during January and February, covers nearly the entire LNC in March, starts melting from west to east in April, and eventually disappears in May. The eastward drift of thin ice throughout the ice‐covered phase and the eastward water heat transport during the ice melting phase are key factors to determine the spatial variation of ice and freeze‐thaw processes. A multiple linear regression analysis confirms that the eastward drift of thin ice can be mostly attributed to the prevailing westerly. During 2007–2017, ice volume, duration, ice‐on and ice‐off dates show significant interannual variations, and they are highly correlated with the surface air temperature (T2m) averaged over January‐March, from the preceding December to May, in December and over March–May, respectively, suggesting the "cumulative effects" of T2m. Seasonal and interannual variations of ice drift are attributed to the combined effects of wind and ice volume variations. Sensitivity analysis further points out the important impacts of ice on the lake temperature and circulation structure in winter and spring, hence the necessity of hydrodynamic‐ice coupled models in large TP lakes. Plain Language Summary: The space‐time variations of ice play fundamental roles in controlling a wide range of physical and biogeochemical processes within lakes, as well as the regional climate, mainly by modulating the lake‐air interactions. In this study, we use a three‐dimensional lake‐ice coupled model to investigate the space‐time variations of ice and the underlying mechanisms in Lake Nam Co, the third largest lake over Tibetan Plateau. The numerical model reasonably reproduces the seasonal evolution of ice coverage from satellite remote sensing and ice thickness from in situ observations. Model results reveal that the eastward drift of thin ice throughout the ice‐covered phase and eastward water heat transport during the ice melting phase, which are related to the prevailing westerly, are key factors controlling the spatial variation of lake ice. The ice area, volume, duration, ice‐on date and ice‐off date all show large interannual variability, which can be mostly attributed to the "cumulative effects" of surface air temperature over different preceding months. Key Points: Analysis of hydrodynamic‐ice simulations gains insights on spatiotemporal variations in ice cover and underlying mechanisms in Lake Nam CoEastward drift of thin ice and water heat transport (related to westerly) are main factors determining the spatial variation of lake iceSignificant interannual variations of lake ice volume and phenology are closely related to "cumulative effects" of surface air temperature [ABSTRACT FROM AUTHOR]

High‐nitrogen stainless steel (HNSS) is prone to surface depression during continuous casting; however, its high‐temperature solidification characteristics and mold powder design have not been reported. Based on the analysis of mold thermocouple temperature variation, this study clarifies the high‐temperature solidification characteristics of HNSS and the cause of surface depression. It optimizes the mold powder for HNSS continuous casting according to factory and laboratory research. The factory trials indicate that the mold thermocouple temperature at the corresponding location decreases by 6.0–20.9 °C when the slab surface is depressed. The analysis shows that the high initial solidification strength of HNSS causes its slab surface depressions. Owing to this characteristic, the mold powder for HNSS should have a suitable melting rate, low basicity, and proper Al2O3. This low‐basicity Al2O3‐containing slag has a crystal slag film near the mold side and a thick liquid slag film near the slab. It can both provide good lubrication and control horizontal heat transfer. [ABSTRACT FROM AUTHOR]

The Arctic Ocean is generally undersaturated in CO 2 and acts as a net sink of atmospheric CO 2. This oceanic uptake is strongly modulated by sea ice, which can prevent air–sea gas exchange and has major impacts on stratification and primary production. Moreover, carbon is stored in sea ice with a ratio of alkalinity to dissolved inorganic carbon that is larger than in seawater. It has been suggested that this storage amplifies the seasonal cycle of seawater p CO 2 and leads to an increase in oceanic carbon uptake in seasonally ice-covered regions compared to those that are ice-free. Given the rapidly changing ice scape in the Arctic Ocean, a better understanding of the link between the seasonal cycle of sea ice and oceanic uptake of CO 2 is needed. Here, we investigate how the storage of carbon in sea ice affects the air–sea CO 2 flux and quantify its dependence on the ratio of alkalinity to inorganic carbon in ice. To this end, we present two independent approaches: a theoretical framework that provides an analytical expression of the amplification of carbon uptake in seasonally ice-covered oceans and a simple parameterization of carbon storage in sea ice implemented in a 1D physical–biogeochemical ocean model. Sensitivity simulations show a linear relation between ice melt and the amplification of seasonal carbon uptake. A 30 % increase in carbon uptake in the Arctic Ocean is estimated compared to ice melt without amplification. Applying this relationship to different future scenarios from an earth system model that does not account for the effect of carbon storage in sea ice suggests that Arctic Ocean carbon uptake is underestimated by 5 % to 15 % in these simulations. [ABSTRACT FROM AUTHOR]

The lower deep branch of the Pacific Meridional Overturning Circulation (L‐PMOC) is a crucial element of the ocean's climate and biogeochemical systems through carrying the Lower Circumpolar Water (LCPW). For the first time, the pathway and volume transport of L‐PMOC from the Yap‐Mariana Junction (YMJ) to the Northern Philippine Basin (NPB) are revealed by a six‐mooring array measurement over 2019–2021. The L‐PMOC seasonally intrudes into the western Pacific at the YMJ. Then, it is directed into the West Mariana Basin (WMB) through YMJ‐Northern Channel with 1.41 ± 1.43/0.26 (mean ± standard deviation/total rms error) Sv, and further into the NPB through Kyushu‐Palau Ridge (KPR) Channel with 0.75 ± 0.53/0.18 Sv. Their difference 0.65 ± 1.35/0.28 Sv is the net lateral flux of LCPW into the WMB over the 2.5 yr. Analyses of a data‐assimilative ocean model solution suggest that the L‐PMOC transports through the deep channels are consistent with deep pressure gradients forced mainly by upper ocean processes. Plain Language Summary: The North Pacific bottom water cannot be locally formed due to the shallow connection to the Arctic. It originates from the Antarctic and is transported northward by the lower deep branch of the Pacific Meridional Overturning Circulation (L‐PMOC). We deployed a six‐mooring array over 2019–2021 to measure the L‐PMOC from the Yap‐Mariana Junction (YMJ) to the Northern Philippine Basin (NPB). The new data extend our previous observations about the pathway and volume transport of L‐PMOC intruding into the western Pacific at the YMJ, and for the first time depicts the abyssal flow from the West Mariana Basin (WMB) into the NPB through the Kyushu‐Palau Ridge (KPR) Channel. Because the YMJ‐Northern and KPR Channels are effectively the only two channels allowing the Lower Circumpolar Water (LCPW) in/out of the WMB, the positive difference of transport through them is the net lateral flux of LCPW into the WMB over the 2.5 yr. A high‐resolution data assimilative ocean model is analyzed to link the variations of the transports through deep channels to the deep pressure gradient. Key Points: A six‐mooring array captured hitherto unknown abyssal flow from Yap‐Mariana Junction to Northern Philippine Basin (NPB) during 2019–2021A single mooring in a deep channel at Kyushu‐Palau Ridge provides an exploratory transport estimate of Lower Circumpolar Water into NPBModel data reveal that lower deep branch of the Pacific Meridional Overturning Circulation transport variations through channels correspond to deep pressure gradients mainly forced by upper ocean [ABSTRACT FROM AUTHOR]

High-frequency measurements of tides, waves, and turbulence were made using the bottom-mounted tripod equipped with the Nortek 6-MHz acoustic Doppler velocimetry during 20–23 February 2016 (winter) and 12–26 June 2017 (summer) in Heini Bay, Yellow Sea. The synchro-squeezed wavelet transform was applied for wave-turbulence decomposition, and an iterative procedure was developed to identify the turbulence inertial subrange in the bottom boundary layer. The analysis results reveal the dependency of the inertial subrange on the tidal current and turbulence intensities. The flood-ebb tidal flows are different between the summer and winter seasons, without and with the presence of dense raft aquaculture for kelp, respectively. In summer, the turbulent kinetic energy (TKE), turbulent Reynolds stress (TRS), and dissipation rate (ε) of TKE increase smoothly with the increasing tidal flow magnitude, and ε is approximately in balance with TKE production related to the vertical shear. The presence of heavy kelp aquaculture in winter causes the reduction in flow speeds and TRS, while keeping TKE and ε at high levels. [ABSTRACT FROM AUTHOR]

This paper describes the Coastal Ice Ocean Prediction System for the East Coast of Canada (CIOPS-E) running operationally at Environment and Climate Change Canada (ECCC). CIOPS-E uses a one-way downscaling technique on a 1/36° horizontal grid (~2 km) to simulate high-resolution ice and ocean conditions over the northwest Atlantic Ocean and the Gulf of St. Lawrence (GSL). CIOPS-E is forced at its lateral boundaries with ECCC's Regional Ice-Ocean Prediction System (RIOPS) and tidal conditions from the Oregon State University TPXO model. The three-dimensional temperature and salinity fields are spectrally nudged towards the RIOPS solution offshore of the 1500 m isobath to, effectively constrain mesoscale features in the Gulf Stream area. Over the continental shelf and the GSL, the CIOPS-E solution is free to develop fully according to model dynamics. CIOPS-E is evaluated over one year from March 2019 to February 2020. Overall, the CIOPS-E improves the representation of tides compared to ECCC's lower resolution systems: RIOPS (1/12°) and the Regional Marine Prediction System – Gulf of St. Lawrence (RMPS-GSL, 5 km). The accuracy of the tides are comparable to the TPXO at most coastal tide gauges. Sub-tidal water levels from CIOPS-E agree well with the observed seasonal variability and show improved errors statistics at all stations compared to RIOPS and RMPS-GSL. Improvements are especially noted for the GSL. Sea surface temperatures (SSTs) from CIOPS-E are lower (higher) in spring (fall) over most of the GSL compared to satellite-derived analyses and RIOPS. Comparison with in-situ observations of SST show significant improvement in CIOPS-E with respect to the RMPS-GSL. Lastly, sea ice conditions in the GSL are compared with the Canadian Ice Service (CIS) charts and the RMPS-GSL model. The sea ice cover and thickness from the pseudo-analysis component (without data assimilation) shows an overestimation compared to the CIS estimates, which is subsequently corrected in the forecast phase through the direct insertion of a Radarsat image analysis product. [ABSTRACT FROM AUTHOR]

The Arctic Ocean is generally undersaturated in CO2 and acts as a net sink of atmospheric CO2. This oceanic uptake is strongly modulated by sea ice, which can prevent air-sea gas exchange and has major impacts on stratification and primary production. Moreover, carbon is stored in sea ice with a ratio of alkalinity to dissolved inorganic carbon that is larger than in seawater. It has been suggested that this storage amplifies the seasonal cycle of seawater p CO2 and leads to an increase in oceanic carbon uptake in seasonally ice-covered regions compared to those that are ice-free. Given the rapidly changing ice-scape in the Arctic Ocean, a better understanding of the link between the seasonal cycle of sea ice and oceanic uptake of CO2 is needed. Here, we investigate how the storage of carbon in sea ice affects the air-sea CO2 flux and quantify its dependence on the ratio of alkalinity to inorganic carbon in ice. To this end, we present two independent approaches: a theoretical framework that provides an analytical expression of the amplification of carbon uptake in seasonally ice-covered oceans, and a simple parameterization of carbon storage in sea ice implemented in a 1D physical-biogeochemical ocean model. Sensitivity simulations show a linear relation between ice melt and the amplification of seasonal carbon uptake. A 30 % increase in carbon uptake in the Arctic Ocean is estimated compared to ice melt without amplification. Applying this relationship to different future scenarios from an Earth System Model that does not account for the effect of carbon storage in sea ice suggests that Arctic Ocean carbon uptake is underestimated by 5 to 15 % in these simulations. [ABSTRACT FROM AUTHOR]

A series of laboratory experiments are carried out to demonstrate the impacts of instrumented bottom frame legs on flow and turbulence. The magnitudes of vertical velocity, turbulent kinetic energy, dissipation, and shear stress induced by the frame legs depend on several factors, including the diameter and number of the frame legs, distances between the legs and the observational location, and the magnitude of the incoming flow and its direction with respect to the layout of the frame. In situ observations were carried out near the mouth of the Yellow River using two acoustic Doppler velocimeters mounted on a bottom frame. The estimated vertical velocity and turbulent kinetic energy dissipation rate show a significant asymmetry with flood and ebb tidal flows. This asymmetry can be partly explained by the influences of the bottom frame legs. Finally, the design and deployment principles of bottom frames are discussed for the purpose of reducing the impacts of the frame legs. Significance Statement: Instrumented bottom frames are widely used for observations in the oceanic bottom boundary layer and above. However, the impacts of frame legs on the observed flow and turbulence have rarely been investigated. A series of laboratory experiments demonstrate that frame legs can induce vertical flow and enhanced turbulence, and the magnitudes of these influences vary with the size and layout of the frame legs and the magnitude and direction of the background flow. The results of the laboratory experiments can partially explain an "asymmetry" behavior of the vertical flow and turbulent kinetic energy with the flood and ebb tidal flows, derived from in situ observations near the mouth of the Yellow River. [ABSTRACT FROM AUTHOR]

The synoptic variability in adjusted sea level at coastal tide gauge stations around the North Atlantic can be studied by use of a barotropic shallow-water model, using time scales of a few days or months. The resolution of the model is 1/3 degree latitude and 0.4 degree longitude. A comparison of the model results with coastal tide gauge data indicates that coherence squared is in the range 0.5-0.75 over a 3-10 day period. The model-computed variability inside the ocean is also discussed.

A three‐dimensional (3‐D) hydrodynamic model based on the Princeton Ocean Model (POM) was applied to simulate the thermal structure and circulation of Lake Nam Co (LNC), the third largest lake over the Tibetan Plateau (TP), during May–December 2013. Compared with a spatially distributed set of one‐dimensional thermal diffusion lake models, POM better reproduced the observed seasonal evolution of the horizontal distribution of lake surface temperature and the vertical thermal structure. A heat budget analysis confirmed that the lateral heat exchange made significant contributions to the horizontal variability of lake temperature. The model results showed that LNC was thermally stratified in summer, had a weak inverse stratification since mid‐December, and was fully turned over during late spring and autumn. During both overturning phases, the modeled "thermal bar" was developed as a result of the density‐driven convection in response to the radiative heating (surface cooling) during spring (autumn). The 3‐D model results showed that the monthly mean circulation featured a predominant mid‐lake cyclonic gyre throughout the ice‐free period; upwelling along the western coast and strong coastal currents occurred in all months except in July–August. Model sensitivity experiments confirmed that the lake circulation was primarily driven by the barotropic dynamics of the prevailing southwesterly wind, while the baroclinic process made a secondary contribution. The results pointed out the necessity to resolve lateral processes when modeling large TP lakes. Plain Language Summary: The Tibetan Plateau has the highest alpine lake concentration in the world and Lake Nam Co is the third largest lake in the region. This study showed that a three‐dimensional (3‐D) hydrodynamic model performed better than a spatially distributed set of one‐dimensional thermal diffusion lake models in reproducing the observed spatial and temporal variations of the lake temperature, and depicted the existence of lake gyre circulation, coastal currents, and upwelling. Model sensitivity experiments revealed that the lake circulation during the ice‐free season was primarily driven by the prevailing southwesterly wind, while the thermal structure made a secondary contribution. The improved simulation of the thermal structure and circulation with 3‐D models is important to understand the variations of the ecosystem in large lakes and the impacts of lakes on the regional weather and climate. Key Points: Three‐dimensional modeling of Lake Nam Co reveals the spatial‐temporal variations of thermal structure and circulationsHeat budget analysis indicates the importance of both the lake‐air heat flux and lateral heat redistribution for the thermodynamicsLake circulation is primarily determined by the wind‐driven barotropic dynamics and baroclinic process makes a secondary contribution [ABSTRACT FROM AUTHOR]

This study reveals that the yearday of open‐water onset (topen) in Bering Strait can be predicted with a lead time of about 4 months using a regression equation topen = 37.45CCN + 125.2 (in Julian days), with an averaged absolute error of 5 days and the maximum error of 12 days, where CCN is the ice concentration averaged from 16th January to 15th February near Cape Navarin. This "predictor" is revealed through analyzing the solution of a regional ocean and sea‐ice model. A key factor contribution to the prediction is that the prior winter ice concentration is controlled by the sea surface temperature, and persists into the start of the melting phase near the marginal ice zone in the Cape Navarin area. As ice melts near Cape Navarin, successive melting due to solar heat absorption and lateral heat transport occurs rapidly downstream along Anadyr Current. Plain Language Summary: Open‐water onset in Bering Strait has significant impacts on hydrological, ecological, and human activities in the Pacific‐Arctic region. There are scientific and practical interests if the onset dates (topen) can be predicted with a lead time as long as possible. This study reveals that topen can be predicted with ice concentration near Cape Navarin with a lead time of about 4 months. The Cape Navarin area is located on the Siberia coast of the Bering Sea, about 750 km southwest of Bering Strait. This "predictor" and underlying mechanism are revealed by analyzing the solution of a regional ocean and sea‐ice model. Key Points: Bering Strait open‐water onset can be predicted with ice concentration near Cape Navarin with a lead time of ~4 monthsThe Cape Navarin area is located near the marginal ice zone where the ice coverage during freeze up affects melt onsetDownstream Cape Navarin, successive melting due to solar heat absorption, and lateral heat transport occurs rapidly along Anadyr Current [ABSTRACT FROM AUTHOR]

The transport of oil droplets following a surface oil spill was investigated using a uniform vertical eddy diffusivity model and the K‐profile parameterization model, which assumes a maximum K value at 1/3 depth of the mixed layer. The initial droplet size distribution was obtained based on the Delvigne and Sweeney (1988, https://doi.org/10.1007/s13131‐013‐0364‐7) model. Using a uniform eddy diffusivity Kave, an exact analytical solution was used to produce the transient and steady state profile of the concentration of droplets of all sizes. It was found that the concentration at the surface is proportional to the droplet rise velocity and inversely proportional to Kave. Thus, small droplets (smaller than 100 μm) do not persist at the water surface. It was found that K‐profile parameterization produces smaller concentrations at the water surface than the uniform K model. The impact of waves was introduced into the K‐profile parameterization model through a roughness height, zo, that is comparable to the wave height. The investigation herein reveals that the Delvigne and Sweeney approach, commonly used in oil spill modeling, is not sufficient to predict the oil droplet size distribution, and that one needs to use a vertical eddy diffusivity to accurately predict the transport in the following hours and days. A new dimensionless formulation was provided to generalize the results, and showed that transport depends on three major parameters, the water friction speed, the mixed layer depth, and the droplet diameter. Plain Language Summary: Oil slicks at sea form oil droplets that get transported into the water column based on their size (buoyancy) and the vertical mixing at sea, as governed by the eddy diffusivity (K) profile. We explored using a uniform K and the well‐known K‐profile parameterization model. The uniform K profile provided fundamental relations between the size of each droplet and the level of turbulence. It was found that the concentration of a given oil droplet size is proportional to the rise velocity and inversely proportional to K. Based on the Stokes' laws, the concentration at the sea surface is proportional to the square of the droplet diameter. Therefore, the concentration of 5‐μm droplets (for example) is 100 times smaller than the concentration of 50‐μm droplets. The K‐profile parameterization model was found incapable of transporting droplets below the surface due to turbulence, which is not realistic; hence, a parameter is applied to the amended model to account for the impact of waves. A dimensionless formulation was introduced and it shows that two sea systems of various wind speeds, mixed layer depth, and droplet size could be equivalent. Therefore, one could use it to design experiments and/or to interpret sea observations. Key Points: The oil droplet distribution at the ocean surface is proportional to the rise velocity and inversely proportional to the eddy diffusivityThe KPP model provides smaller concentrations at the water surface compared to uniform K. The impact of wave roughness was consideredA dimensionless formulation was provided to generalize the results [ABSTRACT FROM AUTHOR]

High‐frequency measurements of waves, currents, and turbulence were made using the bottom‐mounted tripod equipped with the Nortek 6‐MHz acoustic Doppler velocimetry at eight mooring stations in the East China Shelf Seas. The observational data are analyzed to estimate the bottom drag coefficient and also the contributions from currents and waves. Variations of bottom drag coefficient caused by currents show no obvious relationship with water depth. Generally, the current‐induced drag coefficient decreases with the strengthening currents, and the wave‐induced drag coefficient increases with the enhancing waves. Synthesis analyses of the observational data reveal a scale relationship between the current‐induced drag coefficient and the turbulent Reynolds number and that between the wave‐induced drag coefficient and the bottom wave orbital velocity. The analyses show no significant impacts of waves on turbulent Reynolds stress, and the total bottom drag coefficient is the sum of that due to currents and waves. The empirical formula for bottom drag coefficient derived from this study may help to improve the simulation of tides, storm surges, and sediment transport in coastal seas. Plain Language Summary: Ocean floor exerts a frictional force on ocean currents, and this force is particularly important in coastal oceans. This force is difficult to measure directly and is usually parameterized using the near‐bottom currents and a bottom drag coefficient. In this study, we derive estimates of bottom drag coefficient from observed currents and turbulence at eight mooring stations in the East China Shelf Seas. The estimated bottom drag coefficient is not a constant. Empirical relationships are established to link the impacts of currents and waves on bottom drag coefficient to separate dynamic parameters, that is, the turbulent Reynolds number and the bottom wave orbital velocity. The total bottom drag coefficient can be taken as the sum of the two components. The empirical formula for bottom drag coefficient derived from this study may help to improve the simulation of tides, storm surges, and sediment transport in coastal seas. Key Points: Near‐bottom currents, waves, and turbulence were measured at eight mooring stations in the East China Shelf SeasThe estimated bottom drag coefficient shows significant variationsScale relationships are established to represent the impacts of currents and waves on bottom drag [ABSTRACT FROM AUTHOR]

A set of numerical simulations (with horizontal resolutions of 1/4° and 1/12°) is conducted to study the Pacific Water pathway in the Arctic Ocean and the freshwater content in Beaufort Gyre. Passive tracer tags the Pacific Water entering through Bering Strait into the Arctic Ocean and further reveals its circulation routes and spatial distribution. Both the 1/4° and 1/12° simulations show Pacific Water mainly follows the Transpolar Drift over the integration period of 2002–2016, with a limited amount being able to flow eastward along the Alaskan coast to enter the Canadian Arctic Archipelago. However, the circulation pattern of Pacific Water within the Beaufort Gyre is quite different with a stronger and tighter anticyclonic circulation in the 1/12° simulation corresponding to the difference in freshwater content. The 1/12° simulation successfully reproduces the overall recent increasing trend in the freshwater content in the Beaufort Gyre, while the 1/4° simulation fails to maintain the high freshwater content state after 2007. Budget analysis suggests that this difference in Beaufort Gyre freshwater storage is mainly caused by lateral advection. The lateral freshwater flux is decomposed into two components due to the slow‐varying circulation and mesoscale eddies. The difference in the capability to resolve eddies in the two simulations causes the difference in the temporal evolution of both components of the lateral flux. Key Points: Passive tracer reveals Pacific Water mainly circulates along the transpolar route in the Arctic OceanModel resolution plays a big role in simulating liquid freshwater storage within Beaufort GyreDifference in simulated Beaufort Gyre freshwater content is caused by the lateral advection processes [ABSTRACT FROM AUTHOR]

The sea surface temperature and surface currents during 1993–2016 based on satellite remote sensing, along with the ocean temperature and currents during 1993–2013 from a data assimilative ocean simulation product, are analyzed to investigate the influence of the Galápagos Islands (GI) in the eastern tropical Pacific on the sea surface temperature. Variations of the cold core west of the GI are quantified by TC − TW, TC − TE, and the cold core area (CCA), where TW, TC, and TE are the sea surface temperature to the west of the cold core, in the cold core, and to the east of the GI, respectively. TC − TE and the CCA show a stronger influence of the GI in boreal fall than in spring, in contrast to TC − TW, which shows a stronger influence in spring than in fall. All three indices show weaker (stronger) GI's influence during El Niño (La Niña) years, but only CCA and TC − TE have significant correlations of −0.66 and 0.61 with the Niño3 index. Variations of TC − TW are related to that of upwelling immediately the west of the GI. Variations of TC − TE and CCA are related to that of the spatial distributions of the upper ocean temperature, the advection of temperature by the horizontal currents, specifically the north branch of the South Equatorial Current, and upwelling in the eastern tropical Pacific. Key Points: Two new indices are defined to quantify the influence of Galápagos Islands on SST in Eastern Tropic PacificNew indices show stronger (weaker) Islands' influence in boreal fall (spring) and during La Niña (El Niño) yearsVariations of the Islands' influence are related to distributions of background temperature, upwelling, and surface currents [ABSTRACT FROM AUTHOR]

Signals prior to tropical cyclone (TC) intensification are important for improving TC intensity forecasts. The existence of such signals has been noted in previous studies of satellite‐borne observations and lightning. Vertical motions can enhance TCs via the transportation of heat to the warm core; thus, we hypothesized they might signal TC intensification. This study separately examined the processes of updrafts and downdrafts, which are both concentrated within the eyewall surrounding the warm core. The analysis focused on the intensification of Typhoon Hagupit (2008). Numerical experiments were conducted using the Weather Research and Forecasting model to elucidate the changing structure of the vertical motions and their effects on the timing of TC intensification. A control (CTL) simulation and an idealized No‐Land experiment both reproduced the storm structure well, whereas a Half‐Bogus (Half‐Moisture) experiment generated less‐organized TC core structures (weakened moisture convection). Upward motions were found to signal TC intensification with lead times of 1.67–4.50 hr in all experiments. Downward motions apparently signaled TC intensification with lead times of 0.67–4.50 hr in the Half‐Bogus and Half‐Moisture experiments. However, the lead‐lag relationship between downward motion and TC intensification was unclear in the CTL and No‐Land experiments because of the large amount of water vapor in the enhanced eyewall. Thermodynamic analysis showed the latent heat consumed in the downdrafts in the CTL and No‐Land experiments was much greater than in the two other experiments, which resulted in the smallest heating contribution in the downdrafts and a weak relationship with TC intensification. Plain Language Summary: We believe that everyone can forecast the intensification of a tropical cyclone (TC) by the help of some prior signals, thus we tried to find these signals in this study. Vertical motions are the winds that moving upward or downward. They are able to become such prior signals, because they can strengthen the TC through transporting energy to the TC center. We found that the intensification of upward motions occurs <5 hr before the intensification of a TC. This proves the existence of such prior signals and might help to improve the forecast skill of TCs in future. Key Points: Control and No‐Land simulations reproduce the well‐organized TC well, while Half‐Bogus and Half‐Moisture experiments generate weaker TCsLead‐lag relationship with TC intensification is obvious in updrafts of all experiments but weak in downdrafts of the well‐organized TCThe thermal structure of the well‐organized TC weakens the downdraft leading to TC intensification via the consumption of more latent heat [ABSTRACT FROM AUTHOR]

Abstract: A high‐resolution baroclinic coastal ocean model is applied to study seasonal circulation and upwelling off South West Nova Scotia (SWNS) based on 1 year simulations for 2010. The model reasonably reproduces tidal currents, seasonal hydrography, and circulation from multiyear observations, in consistence with the observed strong seasonal variations of these properties in the study area. The main physical processes affecting circulation are analyzed using numerical experiments, with focus on the effect of tidal and density induced currents on topographic upwelling. It is confirmed that the shoreward near‐bottom currents and associated upwelling are tidally induced and persistent throughout the year. It is revealed that these currents have seasonal variability, with cross‐isobath component being strong in summer throughout a large area, but weaker and confined to deeper regions in winter. The seasonal variability of Scotian Current is the dominant forcing affecting the variability of onshore bottom currents. Lagrangian particle tracking identifies two major pathways of source waters arriving at the SWNS upwelling region. A large proportion of particles come from the east with the Scotian Current, mostly from the surface layer; and a small portion of water parcels come from a mean depth exceeding 100 m from the Gulf of Maine and Northeast Channel. [ABSTRACT FROM AUTHOR]

As part of a broader study of ocean downscaling, the seasonal and tidal variability of the Gulf of Maine and Scotian shelf, and their dynamical interaction, are investigated using a high-resolution (1/36°) circulation model. The model's seasonal hydrography and circulation, and its tidal elevations and currents, are compared with an observed seasonal climatology, local observations, and results from previous studies. Numerical experiments with and without density stratification demonstrate the influence of stratification on the tides. The model is then used to interpret the physical mechanisms responsible for the largest seasonal variations in the M2 surface current that occur over, and to the north of, Georges Bank. The model generates a striation pattern of alternating highs and lows, aligned with Georges Bank, in the M2 surface summer maximum speed in the Gulf of Maine. The striations are consistent with observations by a high-frequency coastal radar system and can be explained in terms of a linear superposition of the barotropic tide and the first-mode baroclinic tide, generated on the north side of Georges Bank, as it propagates into the Gulf of Maine. The seasonal changes in tidal currents in the well-mixed area on Georges Bank are due to a combination of increased sea level gradients, and lower vertical viscosity, in summer. [ABSTRACT FROM AUTHOR]

The movement of oil droplets due to waves and buoyancy was investigated by assuming an irregular sea state following a JONSWAP spectrum and four buoyancy values. A technique known as Wheeler stretching was used to model the movement of particles under the moving water surface. In each simulation, 500 particles were released and were tracked for a real time of 4.0 h. A Monte Carlo approach was used to obtain ensemble properties. It was found that small eddy diffusivities that decrease rapidly with depth generated the largest horizontal spreading of the plume. It was also found that large eddy diffusivities that decrease slowly with depth generated the smallest horizontal spreading coefficient of the plume. The increase in buoyancy resulted in a decrease in the horizontal spreading coefficient, which suggests that two-dimensional (horizontal) models that predict the transport of surface oil could be overestimating the spreading of oil. [ABSTRACT FROM AUTHOR]

Copyright of Atmosphere -- Ocean (Taylor & Francis Ltd) is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Results from a high-resolution ice-ocean model are analyzed to understand the physical processes responsible for the interannual variability of ocean convection over the Irminger Sea. The modeled convection in the open Irminger Sea for the winters of 2007/08 and 2008/09 is in good agreement with observations. Deep convection is caused by strong atmospheric forcing that increases the ocean heat loss through latent and sensible heat fluxes. Greenland tip jets are found to be the only strong wind events that directly affect the deep convection area and explain up to 53% of the total turbulent heat loss during active convection years. Deep convection is modeled where there is favorable preconditioning of the water column due to isopycnal doming inside the semienclosed Irminger Gyre. The region of deep convection is also characterized by weak eddy kinetic energy. Finally, an estimation of the surface-forced water mass transformation confirms the Irminger Sea as a region of intermittent production of Labrador Sea Water, with annual averages between 0.9 and 1.9 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) of water denser than 27.7 kg m−3 for years of active convection. [ABSTRACT FROM AUTHOR]