SPRING 2024
Wednesdays at 3:00 pm, Seminar Room SLAB 103 / Virtual SLAB 103
(unless stated otherwise)
Jan 17: NO SEMINAR
Jan 24: SPECIAL ATM & OCE FACULTY PRESENTATION SERIES
Dr. Sharanya Majumdar
Department of Atmospheric Sciences, Rosenstiel School
An Unpredictable Journey Into Hurricane Predictability Research
Recording Available at COMPASS ON DEMAND
In this talk, I will start out by discussing some chance occurrences that eventually led me into hurricane predictability research. Following the principles set out in Lorenz's legendary papers from the 1960s, I will first introduce my early research career phase on "targeted observations", which combined fieldwork, satellite and aircraft observations, data assimilation, and ensemble forecasting. In the second half of the talk, I will raise a series of research questions tackled by past and present group members on genesis, track, and intensity change, with an increasing emphasis on connecting predictability to physical processes on multiple scales.
Jan 31: SPECIAL ATM & OCE FACULTY PRESENTATION SERIES
Dr. Amy Clement
Department of Atmospheric Sciences, Rosenstiel School
From Slow Science to Usable Science:
The Challenge of Projecting Climate Hazards
Recording Available at COMPASS ON DEMAND
As climate scientists, we are increasingly being asked to weigh in on the question of 'what will climate change look like for me / my home / my community / my company, etc.?' What I will present is an in-progress story about how I have come to approach this question. I will focus on research from the last several decades of good old-fashioned climate dynamics, and what the challenges are that make this a difficult, thus 'slow' problem. The discussion of the scientific challenges will be informed by my experiences working with a range of applied researchers and decision makers working to adapt to a rapidly changing climate with increasingly costly and inequitable risks.
Feb 07: Dr. Alexander Soloviev
Nova Southeastern University, Dania Beach, Florida
Physical Oceanographic Aspects of Upwelling Events
on the Southeast Florida Shelf
Alexander Soloviev, Alfredo Quezada, Megan Miller, Bernhard Riegl, and Richard Dodge
Recording Available at COMPASS ON DEMAND
Coral reef benthic communities are acutely sensitive to changes in environmental parameters such as temperature and nutrient concentrations. Physical oceanographic processes that induce the coastal upwelling therefore act as drivers of community structure on tropical reefs. The cause and frequency of upwellings and how they impact coral communities on the Southeast Florida shelf, however, are not fully understood. The classical wind induced coastal upwelling is not typical for western boundary current regions like the Straits of Florida. We have nevertheless observed prominent upwelling events during hurricane conditions. For example, during Hurricane Wilma 2005 a 4°C drop of the bottom water temperature was registered at an 11 m isobath on the Broward County shelf. Upwelling events can also be caused by internal wave solitons breaking on the continental shelf; an example is the upwelling on Conch Reef that has been studied experimentally (Leichter et al. 1996) and modeled with computational fluid dynamics tools (Miller et al. 2023). Another potential upwelling mechanism is associated with the southward jet attached on the Southeast Florida shelf (Soloviev et al. 2017), which lifts the cold deeper water towards the coast due to the Coriolis effect. This process is being elucidated from a year-long series of glider transects on the shelf between Ft. Lauderdale and Jupiter, FL (Quezada et al. 2023). The upwelling events bringing cold and rich with nutrients water to the coral reef benthic communities may alter, suppress, or provide a natural buffer against climate impacts and could potentially enhance the efficacy of spatial management and reef conservation efforts (Zhu et al. 2022).
Feb 14: Daniel Melo Costa Santos
Guest of Tiago Bilo, CIMAS
Oceanographic Institute, University of Sao Paulo, Brazil
Abyssal Warming and Freshening Process Drives the
Contraction and Homogenization of the AABW in the Argentine Basin
Recording Available at COMPASS ON DEMAND
This study investigates changes in abyssal water properties, with a specific focus on the Antarctic Bottom Water (AABW), using data collected in the northwest Argentine Basin from 2009 to 2022, along 34.5°S, at a trans-basin mooring line known as the South Atlantic Meridional Overturning Circulation Basin-wide Array (SAMBA). The analysis centers at the three most frequently sampled locations: 48.5°W, 47.5°W, and 44.5°W, where pressure-equipped inverted echo sounders are installed and identified as Sites BB, C, and D, respectively. The results reveal an increase in the potential temperature and a simultaneous decrease in salinity at abyssal depths across all locations, except at Site BB. There, a positive change is observed near the bottom, followed by a negative change just above it. A decrease in the buoyancy frequency (N) is detected in the region commonly occupied by the AABW at Sites C and D, while at Site BB, the changes are positive along the profile. The temperature variations are predominantly influenced by vertical movements of isopycnals (heave) rather than changes along them (spiciness). As a result of these abyssal variations, the AABW contracted and freshened at Sites C and D, as its colder layer descended faster than its warmer layer, resulting in a downward expansion of the latter. At Site BB, the AABW also freshened, but with a smaller rate.
Feb 21: NO SEMINAR
Feb 28: NO SEMINAR
Mar 06 (MSC 365): POSTER SESSION
Mar 13: NO SEMINAR (Spring Recess)
Mar 20: Lev Looney
NOAA-AOML & Department of Atmospheric Sciences, Rosenstiel School
(one-hour MPO student seminar)
Observing and Modeling the Air-Sea Interface Beneath Tropical Cyclones
Recording Available at COMPASS ON DEMAND
Ocean conditions play a critical role in the intensification of tropical cyclones (TCs), and in most cases the feedback to the atmosphere from TC-induced sea surface temperature (SST) cooling cannot be ignored. It is known that stronger, more slowly moving TCs generate more SST cooling, as do stronger ocean temperature stratification and a thinner mixed layer. However, the relative importance of these factors, and the role of TC size, have not been quantified. Based on ocean mixed layer model experiments and global observational datasets, we show that the duration of wind forcing is the limiting factor for TC-induced SST cooling. Further, we find that the thermodynamic effect (changes in vertical temperature gradient with density gradient held constant) is 2-3 times that of the mixing effect (changes in density stratification with temperature stratification held constant). We also find that storm size has a greater influence on the amount of cooling than intensity. In efforts to expand our knowledge of TCs and their coupling with the ocean, several in-situ observational campaigns are carried out during the Atlantic hurricane season. The second part of the presentation will discuss the NOAA-Saildrone hurricane missions, focusing on data quality assessments and validation. Overall, the comparisons across numerous platforms, variables, and ocean-atmosphere conditions show the high quality and value of the saildrone measurements while also revealing unique challenges associated with multiplatform intercomparisons in extreme conditions. These observations are used in a variety of ways to improve our understanding of the air-sea interface beneath TCs.
Mar 25 (Monday, 11:00, Library Map & Chart Room): Dr. Mariana Bernardi Bif
Invited Speaker of the Department of Ocean Sciences
Research Specialist
Monterey Bay Aquarium Research Institute, Moss Landing, California
Constraining the Biogeochemistry of Marine Systems With BGC-Argo Floats
Recording Available at COMPASS ON DEMAND
The deployment of hundreds of robotic floats equipped with chemical sensors in the global oceans is revolutionizing the way we constrain the biogeochemical cycles. In addition to temperature and salinity found in Core Argo floats, BGC-Argo floats are equipped with up to six other sensors. To date, BGC-Argo floats have collected more profiles of nitrate, a key nutrient for ocean productivity, than all oceanographic cruises combined. A float's ability to sample at high spatio-temporal resolution is elucidating biogeochemical processes at remote locations and in areas affected by extreme climate events. In this talk I will provide an overview of BGC-Argo floats, the state of the global array, and the power behind a multi-platform approach to observe marine biogeochemical cycles. I will provide examples of float data used to constrain the biogeochemistry of marine systems that are sensitive to changes from heatwaves, ENSO conditions, and deoxygenation. I will wrap-up the talk with an overview of what's on the horizon for investigating the marine system with floats, and how to train the next generation of professionals to use BGC-Argo and other large ocean datasets.
Mar 27 (11:00, Library Map & Chart Room): Dr. Wokil Bam
Invited Speaker of the Department of Ocean Sciences
Postdoctoral Investigator
Woods Hole Oceanographic Institution, Massachusetts
Understanding Particle Export in the Western Arctic Ocean
and the Northern Gulf of Mexico
The ocean's biological carbon pump, driven by the production and transfers of particulate organic carbon (POC) from surface to the deeper ocean, is a key atmospheric CO2 sink. This pump has various components from physics to ecology that together control its efficiency in exporting particles. Hence, the influence of climate change on the functioning and magnitude of the pump is complex, non-linear, and heterogeneous on a spatial scale. This presentation assesses the pump's status and particle dynamics in two regions facing rapid climate shifts: the Arctic and the northern Gulf of Mexico (nGOM). In the Arctic, particle composition is rapidly changing due to increased primary productivity, sea ice loss, and more shelf-derived materials. The nGOM sees altered particle inputs from coastal erosion and rivers. Both represent the shallow shelf dominated by large river input and represent areas with major changes due to changes in freshwater inputs (nGOM and Arctic) and ice melting (Arctic). POC fluxes in these two contrasting continental shelves were estimated using naturally occurring 210Po-210Pb radioisotope tracers that provide flux estimates integrated over seasonal time scale. 210Po-210Pb radioisotope pair has been extensively used to study particle scavenging, cycling and transport in the ocean. However, the role of particle composition and concentration in the scavenging and sorption of 210Po-210Pb needs to be better understood to successfully utilize these radionuclides as oceanographic tracers. The first part of the talk will focus on the influence of particle composition and concentration on distribution of 210Po and 210Pb whereas the second part will focus on vertical fluxes of POC.
Mar 27: Paul Wojtal
Department of Ocean Sciences, Rosenstiel School
(one-hour OCE student seminar)
Uncovering the Importance of Heterotrophic Bacteria and Varying
Phytoplankton Communities for Particulate Carbon Export in the Northeast Pacific
Phytoplankton form the base of marine food webs in the epipelagic and contribute substantially to suspended and sinking particulate organic matter (POM) throughout the water column, thus sequestering carbon in the deep sea through the biological carbon pump. The biomass of bacterial consumers also may contribute significantly to these particle pools. The fate of POM – for instance, the depth at which it is remineralized – ultimately affects global climate and the carbon cycle. However, it has been difficult to link the biological origins of POM, such as proportional contributions of phytoplankton and bacteria, to its fate, due largely to significant alteration processes occurring as the POM sinks or is advected downward. To examine the origins of POM more closely, I will present the results of multiple geochemical and isotopic measurements of sinking particles from sediment traps and size-fractionated particles from in situ filtration between the surface and 500 m at Ocean Station Papa, collected during NASA EXPORTS (EXport Processes in the Ocean from RemoTe Sensing). From these particles, I examine the carbon isotope composition of amino acids from proteins, the relative concentration of D and L enantiomers of alanine, and the carbon isotope composition of phytol, cleaved from chlorophyll. In combination with my previous results of amino acid nitrogen isotope analysis, I use the D and L enantiomer ratios and the essential amino acid carbon isotope "fingerprints" to estimate the proportional contribution of bacteria to four different POM size fractions. I additionally use the d13C value of phytol to identify material of photosynthetic origin from the upper vs. lower euphotic zone. I will discuss how these results are helping me disentangle the sources of carbon that are the most important to POM in the mesopelagic, and thus are fueling midwater communities and contributing to carbon sequestration.
Apr 01 (Monday, 11:00, Library Map & Chart Room): Dr. Mojtaba Fakhraee
Invited Speaker of the Department of Ocean Sciences
Postdoctoral Researcher
Department of Earth and Planetary Sciences & Yale Center for Natural Carbon Capture
Yale University, New Haven, Connecticut
Ocean's Carbon Cycle: Past, Present, and Future
Throughout Earth's history, atmospheric oxygen and carbon dioxide levels (pO2 and pCO2) have been the pivotal factors controlling the habitability of our planet. The ocean's carbon cycle plays a major role in regulating pO2 and pCO2. Despite its significance, the history of the ocean's carbon cycle and its response to shifts in global average temperature and biotic innovations remain poorly constrained. Moreover, there are still gaps in our knowledge about the potential role of the marine carbon cycle in mitigating the impact of anthropogenically-induced increases in global temperature. In the first part of my talk, I will present results that suggest shifts in temperature and oxygen play a larger role than shifts in ecosystem structure in driving changes in carbon export efficiency in the ocean. In the second part of my talk, I will present findings from a suite of biogeochemical models that underscore the substantial capacity of the modern marine carbon cycle to mitigate the impacts of climate change. Specifically, I will discuss that while there is considerable potential for marine enhanced silicate weathering in sequestering anthropogenic carbon, there are some potential environmental impacts on the marine organisms that need to be considered. Further, I will present results from time-varying reactive transport modeling that suggests a potentially important role of the restoration of the coastal blue carbon ecosystems (e.g., mangroves, seagrasses) in driving ocean alkalinity enhancement and capturing atmospheric CO2 with co-benefits on marine biodiversity and ecosystem services.
Apr 03: Lillian Henderson
Department of Ocean Sciences, Rosenstiel School
(one-hour OCE student seminar)
Vertical Variations in Organic Composition of Particulate Matter
in a Stratified Euphotic Zone
Marine particles are a critical contributor to carbon export, food webs, and the sedimentary record, but uncertainties remain in the origins and composition of this material. Variations in both the isotopic and chemical composition of organic particles have been observed latitudinally, but few studies have investigated variations over depth, especially within the euphotic zone. Here, using both isotopic and chemical measures, I have identified variations in the composition of POM between the upper and lower euphotic zones at the Bermuda Atlantic Time-Series study site. I will discuss how these variations reveal details of the different photosynthetic and degradative processes at these depths. First, unique carbon isotopic signatures of photosynthetic communities in the lower euphotic zone point to the impacts of variable sunlight intensity on photosynthetic communities and / or variations in phytoplankton community composition over depth. Second, I identified systematic variations C:N ratios of bulk (sinking & suspended) organic particles from the surface to the lower euphotic zone and across 3 particle size fractions (0.3 to >20 µm particles). I will discuss how this pattern is driven by the relative production of amino acids and carbohydrates. Finally, I identified patterns in the relative abundances of individual carbohydrate monomers over depth and particle size fraction that point to alteration during degradative processes. These observed variations in the chemical composition of organic material within the euphotic zone may be important for both carbon export and microbial communities, as particulate organic matter both transports carbon out of the euphotic zone and is used as a carbon and energy source by heterotrophic bacteria.
Apr 08 (Monday, Auditorium): Dr. Agustinus Ribal
Guest of Brian Haus, Department of Ocean Sciences
Department of Mathematics, Hasanuddin University, Makassar, Indonesia
Global Wave Model Performance in the Vicinity of the Monterey Bay, California
Recording Available at COMPASS ON DEMAND
Agustinus Ribal1,2, Brian K. Haus1, Stefan Zieger3, and Milan Curcic1
1Department of Ocean Sciences, Rosenstiel School
2Department of Mathematics, Faculty of Mathematics and Natural Sciences,
Hasanuddin University, Makassar, Indonesia
3Research Program, Bureau of Meteorology, Melbourne, Victoria, Australia
We investigated the performance of a global wave model, specifically the third-generation WAVEWATCH III model, downscaled to Monterey Bay, California, over a two-year period. We employed two different source term packages, namely ST4 and ST6, for wind input. Four distinct grids were generated, with three of them being regular grids and one being unstructured. A two-way nesting approach was applied for three grids, with resolutions in latitude of 0.5°, 0.2°, and 0.05°, respectively. The fourth grid is unstructured, with maximum and minimum resolutions of 2 km and 0.2 km, respectively. Boundary conditions for the unstructured grids were obtained from the two-way nesting grids. Additionally, the model was forced by CFSv2 wind data with resolutions of 0.2°. This study focuses on the highest resolution model, which utilizes an unstructured grid. Significant wave heights were validated using data from five NDBC buoys, six CDIP buoys, 22 CLASI buoy locations, and eight spotter buoys. Across all 41 locations, the measurements exhibited excellent agreement with the model in terms of statistical properties. Furthermore, we observed that ST4 outperformed ST6 in terms of scatter index and Pearson's correlation coefficient, while ST6 exhibited lower RMSE and bias. Regarding computational time, it was found that ST4 runs 25% slower than ST6. In addition to significant wave height, wind sea and swell were also compared based on one-dimensional wave spectra. Eleven buoys were used to validate the swell, with both ST4 and ST6 showing similar statistical performance.
Apr 10 (11:00, Library Map & Chart Room): Dr. Bo Yang
Invited Speaker of the Department of Ocean Sciences
Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami
The Ocean Carbon Cycle:
From Biological Carbon Pump to Seawater Carbonate System
The biological carbon pump and the seawater carbonate system are two important components of the ocean carbon cycle. The ocean's biological carbon pump is the process in which marine producers sequence carbon from the atmosphere and land runoff to the ocean interior. It supports the marine ecosystem and regulates atmospheric CO2 and oxygen distributions in the ocean. However, its magnitude and distribution have not been well quantified due to the limitations of traditional approaches. In the opening section of the presentation, I will go through my research on primary production, net community production, and carbon export efficiency, utilizing the chemical tracer and bio-optical data from autonomous platforms (e.g. Argo profiling float and mooring), satellite remote sensing, and model outputs. The results revealed the spatial and temporal distributions of carbon production and export in the under-studied regions and provided insights into the factors that control the carbon production and export in these regions. The seawater carbonate system controls the acidity of seawater and acts as a governor for the ocean carbon cycle. For the second part of the presentation, several examples will be presented for my work on seawater carbonate system, including lab-based physical chemistry studies, time-series field observations, and related instrumentation. The presentation will conclude by outlining the roadmap for future research and funding acquisition.
Apr 10: Leah Chomiak
Department of Ocean Sciences, Rosenstiel School
(one-hour MPO student seminar)
The Advection of Subpolar Climate Signals From a Subtropical Atlantic Viewpoint
Recording Available at COMPASS ON DEMAND
The Subpolar North Atlantic plays a critical role in the formation of the deep-water masses that drive the Atlantic Meridional Overturning Circulation (AMOC), such as Labrador Sea Water (LSW). LSW is formed in the Labrador Sea and advected equatorward out of the Subpolar North Atlantic via the Deep Western Boundary Current (DWBC) among other pathways. The DWBC is an essential component of the AMOC carrying these deep waters southward, flowing at depth along the continental shelf of the western Atlantic. The unique convective anomalies of LSW can be used as advective tracers when assessing equatorward propagation of LSW. In this collective study, we explore advective pathways and timescales of two distinct LSW classes formed in the 1990s and early 2000s from the Labrador Sea to 26.5°N via DWBC advection and Atlantic-interior propagation. LSW anomalies are found to propagate on varying time scales, supporting a linkage between the Subpolar and Subtropical North Atlantic via interior propagation pathways. Findings continue to highlight the abundance of LSW within the Atlantic interior, not just along the western boundary, suggesting that interior pathways may play an influential role on the export and timescale of these subpolar climate signals. In addition to the investigation of LSW across the Atlantic, we also turn attention to 40 years of unprecedented, significant deep ocean (>2000 m) cooling and freshening at 26.5°N and summarize a deep link between subpolar climate signals and their connection to the subtropics, discussing what this could mean for future AMOC projections.
Apr 11 (Thursday, 2:30): Dr. Siyuan Wang
Invited Speaker of the Department of Atmospheric Sciences
Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder,
and NOAA Earth System Research Laboratory (ESRL), Boulder, Colorado
Advancing the Representation of Marine Aerosols and Wildfire Smoke in Models
Recording Available at COMPASS ON DEMAND
The ocean is a large source of trace gases and aerosols, with major impacts on the self-cleansing capacity of the atmosphere and the radiative balance of the climate system. Many of the marine emitted trace gases undergo chemical and physical processes in the atmosphere, contributing to the formation and growth of aerosols. In the first half of this presentation, I will discuss some of my recent work on marine emissions of volatile organic compounds and their interactions with aerosols, focusing on aqueous-phase chemistry on wet aerosols and cloud droplets and their impacts on air quality and climate system. Given the growing concern of wildfires in recent years, I will explore wildfire smoke in the second half of the presentation. Wildfires are very challenging to represent in models, with plume injection height being one major source of uncertainty. Plumes with low injection often lead to worsening air quality in nearby regions, while plumes with high injection can affect the weather/climate system in broader areas. I will discuss the development of a machine learning-based wildfire plume rise emulator, trained by using a high-resolution, turbulence-resolving Large Eddy Simulation (LES) model. This work also leverages multiple satellite products, aiming at improving the representation of wildfire smoke in air quality models.
Apr 17: Chong Jia
Department of Ocean Sciences, Rosenstiel School
(one-hour MPO student seminar)
Characteristics of the Sea-Surface Temperatures in the Arctic
Derived From Measurements From Saildrones and Satellites
Recording Available at COMPASS ON DEMAND
Sea-surface temperature (SST) is one of the most important variables in the global ocean-atmosphere system. The accuracy of SST retrievals from infrared satellite remote sensing is generally lower at northern high latitudes than elsewhere, and the density of in-situ SST measurements needed to refine and test algorithms for the correction of atmospheric effects on the infrared radiative transfer is relatively sparse as well. From May 15 to October 11, 2019, two Saildrone uncrewed surface vehicles (USVs) funded by NASA were deployed for 150-day cruises from Dutch Harbor, Alaska, transiting the Bering Strait into the Chukchi Sea and the Arctic Ocean, carrying infrared (IR) radiation pyrometers on the deck for the determination of the sea-surface skin temperature (SSTskin). This study produced an algorithm to derive SSTskin and an estimate of the sources of inaccuracies. After stringent quality control of data by restricting the acceptable tilt angles of the USV determined using radiative transfer simulations, SSTskin can be derived to an accuracy of ~0.12 K. Thus, Saildrones can provide sufficiently accurate SSTskin retrievals for scientific research. Our study has demonstrated how the Saildrone-derived SSTskin along with the subsurface temperature measurements and meteorological data has improved our understanding of upper ocean thermal structure (including cool / warm skin effects and diurnal warming events) and benefit the validation of IR satellite SSTskin retrievals, to alleviate the challenges in deriving SST at high latitudes.
Apr 19 (Friday, 2:30): Dr. Zichong Chen
Invited Speaker of the Department of Atmospheric Sciences
Harvard University, Cambridge, Massachusetts
Understanding Methane Emissions With Satellite Observations:
Sources, Trends, and Implications for Climate Action
Recording Available at COMPASS ON DEMAND
Methane (CH4) is a potent greenhouse gas with a relatively short atmospheric lifetime. Decreasing methane is a powerful lever to mitigate near-term warming and thereby give the world time to "bend the curve" on carbon dioxide (CO2) emissions and adapt to climate change. Current methane emission inventories are highly uncertain, difficult to be used as basis for mitigation strategies. I seek to better understand methane emissions at various scales by utilizing satellite observations and chemical transport models. My talk covers three topics driven by three questions. First, how can we use satellite observations of atmospheric methane to quantify regional methane emissions? Using the Middle East and North Africa region as an illustration, we utilize 2019 TROPOMI satellite observations in a high-resolution inversion to infer methane emissions from this region at up to 25 km × 25 km resolution, with an emphasis on the contributions from individual countries and from the oil and gas sector. Second, how well can we explain the recent rise in atmospheric methane mixing ratios? Interestingly, we find that rapidly increasing rice emissions in sub-Saharan Africa, driven by a widespread rice farming revolution, is a substantial but previously unrecognized contributor to the global methane trend. Third, can Earth observing (EO) satellites, which do not measure atmospheric methane, be used to better understand methane emissions? We use Landsat satellite imagery to develop a global high-resolution methane inventory from rice paddies with resolved seasonality. Compared to existing inventories, our rice methane emission inventory shows large improvements in both seasonality and spatial patterns in major rice-producing regions.
Apr 24: Ivenis Pita
Department of Atmospheric Sciences, Rosenstiel School
(one-hour MPO student seminar)
South Atlantic Meridional Overturning Circulation and Associated
Heat and Freshwater Transports From Sustained In-Situ Observations
Recording Available at COMPASS ON DEMAND
The Atlantic Meridional Overturning Circulation (AMOC) is a part of the global circulation and controls the meridional transport of heat (MHT), freshwater (FWT), carbon, and other properties across the basin and links the timescales of heat uptake and carbon storage. AMOC has been estimated in the South Atlantic by some observing arrays, at 11°S (TRACOS) and 34.5°S (SAMBA), and other latitudes by synthetic products. Models suggest that the stability of the AMOC is dependent on the oceanic freshwater budget in the South Atlantic. In addition, the overturning contribution to the freshwater transport at 34.5°S has been described as an AMOC stability indicator. This study aims to leverage sustained in-situ observations to estimate the overturning circulation. We perform an optimized mapping strategy to estimate the AMOC, MHT, and FWT since 2005 at 22.5°S and 34.5°S and compare our estimates to other products available (e.g., reanalysis, in-situ transects, observing systems, and synthetic products). An alternative machine learning mapping method is also used to validate our estimates. Water masses are identified and compared to previous results. Findings highlight the importance of the boundary currents on total variability and the contributions of Ekman and geostrophic components. In addition, the overturning and gyre contributions for MHT and FWT at 34.5°S are assessed in terms of z levels and integrated across the basin. Almost two decades of data allow us to observe significant long-term trends for some estimates.
May 01: Dr. Milan Curcic
Department of Ocean Sciences, Rosenstiel School
Dispersion of Short Waves Riding on Longer Waves
Hydrodynamic modulation of short waves by ambient longer waves has long been a known process in ocean wave physics. This modulation is important for at least: remote sensing; numerical wave forecasting; and interpretation of in situ wave measurements. However, it's not yet fully understood due to many processes occurring at once. One possible way to study it is through the linear wave theory, which provides us with elegant solutions, but also allows for interesting, non-linear, emerging properties. In this talk, we’ll revisit the classic Longuet-Higgins & Stewart (1960) result that short waves are modulated proportionally with the steepness of the long wave. By combining the linear dispersion, wave conservation laws, and high-order variations in gravity of the short waves, we can obtain solutions for the short-wave wavenumber and wave action that are different from the original solution in a non-negligible way. The exact analytical solution deviates by 18-38% relative to the Longuet-Higgins & Stewart (1960) solution in the long-wave steepness range of 0.1-0.2, making it a significant departure from their classical modulation result. Further, numerical solutions of the full (non-linear) equation set show negligible differences from the analytical solutions in long-wave steepness less than 0.2, indicating that the non-linear terms begin to significantly contribute only in very steep waves.
