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FALL 2023
Fridays at 11:00 am, Rosenstiel School Auditorium / Virtual Auditorium
(unless stated otherwise)



Sep 08: NO SEMINAR (OCE Faculty Meeting)


Dr. Javier Beron-Vera1
with contributions from Dr. Josefina Olascoaga2 and Dr. Gage Bonner1
1Department of Atmospheric Sciences / 2Department of Ocean Sciences, Rosenstiel School

Nonlinear Dynamics Research at the Rosenstiel School

The Nonlinear Dynamics Group (NDG) investigates problems in geophysical fluid dynamics using methods from nonlinear dynamics, both geometric and probabilistic. Geometric tools include Lagrangian coherent structures methods, geometric singular perturbation theory, and geometric fluid mechanics techniques (e.g., Euler-Poincare variational principle, symmetry and conservation laws, Lie-Poisson Hamiltonian structure). Probabilistic tools include Markov chain models and transition path theory. Specific problems include those relating to transport and mixing in the ocean and planetary atmospheres (e.g., the detection of flow invariant objects such as long-lived vortices and barriers for transport such as Lagrangian jet axes), the motion of floating matter at the ocean surface (e.g., plastic debris, oil, and macroalgae such as Sargassum), and the dynamics in the upper ocean (e.g., the development and cascade of submesoscale circulations as a result of thermal instabilities). A new line of investigation is being developed dealing with the general problem of model reduction. Reduced order modeling is being investigated using geometric mechanics methods (which enable structure preservation), probabilistic techniques (e.g., transition manifold learning), and physics-informed machine learning of dynamics and related tools including data-driven algorithms for obtaining dynamical systems from data. In this talk, an overview will be presented of activities conducted by NDG members over the course of nearly 20 years. These activities spread over a period when the members' affiliation was AMP (Applied Marine Physics), rather than OCE and ATM, and NDG did not exist formally as such.


Dr. Brian Soden
Department of Atmospheric Sciences, Rosenstiel School

Radiative Feedbacks on Tropical Cyclone Development
Recording Available at COMPASS ON DEMAND

This talk will present an overview of recent and ongoing research by students and post-docs in my group. I will then go in more depth and review recent work that examines the role of radiative feedbacks on tropical cyclone (TC) development, focusing on new insights from a hierarchy of model simulations and observations. Model simulations indicate that the spatial gradient in radiative heating between areas of convection and large-scale environment induces a secondary circulation that generates an upgradient transport of moist static energy towards the convective center. A coordinate set of feedback suppression experiments under both realistic and idealized settings demonstrate the critical role of radiative heating on TC development, particularly at the earliest stages of formation. When radiative feedbacks are suppressed, TC frequency is reduced primarily due to a decrease in the number of pre-TC synoptic disturbances. Satellite analyses provide further observational support of this mechanism, with the spatial gradient in radiative heating providing an important indicator of subsequent TC intensification.


Dr. Kim Popendorf
Department of Ocean Sciences, Rosenstiel School

Marine Microbial Biogeochemistry: Measuring the Role of Microbes in
Ocean Phosphorus Cycling, Energy Dynamics, and Harmful Algal Blooms
Recording Available at COMPASS ON DEMAND

This talk will provide an overview of projects and progress from the P-Ocean lab group, where we investigate the role of microbes in ocean chemistry and quantify microbial chemical fluxes. We'll describe our projects on microbial energy dynamics, phosphorus cycling, and cyanobacterial harmful algal blooms. Our lab has developed new techniques for quantifying microbial energy flux by measuring the phosphorylation rate of adenosine triphosphate (ATP) in marine microbes, providing a way to quantify the energy used by microbes in different marine biomes and different environmental conditions. We are using this to study microbial growth efficiency across an upwelling zone, where efficiency is defined as the amount of biomass produced versus energy used, and plays an important role in defining the flow of carbon through the microbial system and the capacity of the surface ocean to be a carbon sink or source to the atmosphere. We've also measured microbial energy flux to investigate the expected impacts of climate change on coastal ecosystems, measuring the change in energy and nutrient fluxes under elevated ocean temperatures. We focus particularly on phosphorus cycling, as one of the two macronutrients required by all life for growth. We quantify the uptake rate and microbial utilization of phosphorus as an important driver for ecosystem productivity, and have collaborated on studies quantifying atmospheric deposition of phosphorus to the nutrient depleted North Atlantic subtropical gyre. Lastly, our lab spans from ocean systems to freshwater where we study cyanobacterial harmful algal blooms (HABs), again looking at the microbial role in chemical processes, here quantifying microbial toxin production as well as nutrient dynamics in HAB events. Our work on HABs focuses on the aerosolization of cyanobacterial toxins and the intersection of HABs and human health, with a project in its fifth year working with community partners across Florida to gather environmental samples and participant health data to study the health impacts of blue-green algal blooms.


Dr. Ben Kirtman
Department of Atmospheric Sciences
Frost Institute for Data Science and Computing
Cooperative Institute for Marine and Atmospheric Studies (CIMAS)
Rosenstiel School of Marine, Atmospheric, and Earth Science

Climate Predictability, Prediction, and Projection
Recording Available at COMPASS ON DEMAND

This informal talk describes five recently funded projects that include a range of climate predictability, prediction, and projection research projects. The motivation for each project is briefly summarized, some preliminary results are presented, and basic elements of the proposed research are discussed. The five projects briefly summarized are as follows:

(i) Title: "ENSO Predictability: Initial Condition Signal vs. Uncoupled Atmospheric Noise." Despite substantial progress in recent years in our ability to simulate and predict ENSO, a clear picture of what processes limit predictability remains elusive. Studies argue that predictability is determined by the strength of the buildup of heat content along the subsurface equatorial Pacific Ocean, whereas others assert that uncoupled atmospheric noise both ultimately determines the limit of predictability. This project seeks to diagnose the relative impact of both effects.

(ii) Title: "Predictability of Seasonal to Interannual Coastal Flood Risk." While sea level rise due to anthropogenically forced thermal expansion and land-ice melt increases flood risk overall, flood risk on seasonal to annual timescales is more directly connected to natural climate variability such as ENSO, NAO, and MJO. The primarily focus of the proposed research is to examine sources of predictability for coastal flood risk in the US, leveraging the output from existing NMME retrospective and real-time predictions.

(iii) Title: "Subseasonal Predictability of Fire Weather Metrics for Decision Support." The project is to determine the degree of success in predicting subseasonal fire weather metrics (HDWI, wind, humidity, soil moisture [as a proxy for fire fuel], precipitation, and temperature) by using forecasts from UFS S2S and SubX models.

(iv) Title: "Bridging Predictions and Projections: Understanding Predictability from Initialized Multi-Year to Decadal Predictions for High-Impact Climate Futures." The low frequency variability of North Atlantic SST can affect summer US precipitation, winds, and heat through its impact on the North Atlantic Subtropical High (NASH). We will test the hypothesis that the NASH is a source of decadal predictability, and that initialized multi-year to decadal predictions can better predict these high-impact climate futures than uninitialized projections.

(v) Title: "Developing Decadal Climate Projection Services Through Stakeholder Guidance and Foundational Science." We will develop the scientific understanding to underpin authoritative climate projection services. The research will be developed in collaboration with stakeholders and will be coordinated across five phenomenological themes: western water resources, heat waves, coastal flood risk, wildfire risk, and extreme wind events. Foundational climate projection research is focused on three areas: understanding and constraining uncertainty, identifying the large-scale drivers of projected changes, and developing hyper-local projection information.

Oct 13: Quinton Lawton
Department of Atmospheric Sciences, Rosenstiel School
(1-hour ATM student seminar)

Interactions Between Kelvin Waves and African Easterly Waves
and Their Representation in Global Simulations
Recording Available at COMPASS ON DEMAND

Convectively coupled Kelvin waves (CCKWs) are large atmospheric waves that propagate along Earth's equator and serve as one of the most important drivers of weather in the tropics. Recent work has indicated that CCKWs can interact with African Easterly waves (AEWs) and enhance the favorability of tropical cyclone (TC) formation. However, there is no existing framework permitting the direct attribution of AEW changes to CCKWs, and the accuracy of CCKW-AEW interactions in numerical simulations remains unknown. In this talk, I present a method for artificially modifying CCKWs in numerical simulations that can be used to better attribute their impacts and predictability. The Model for Prediction Across Scales – Atmosphere (MPAS-A) is used to simulate a strong CCKW-AEW interaction in 2021, and experiments are designed to either amplify or dampen the CCKW at model initialization. It is shown that this modification method is effective at changing the CCKW's structure and convective envelope, both at storm-permitting (3 km) and convection-parameterizing (30 km) resolutions. Nevertheless, parameterized experiments severely underpredict CCKW convective coupling in the Atlantic, even when the initial CCKW is amplified. It is hypothesized that this lack of convective coupling may be due to an inaccurate depiction of ITCZ convection in the parameterized MPAS runs. Attribution work using these experiments also suggests that CCKW dynamic fields (wind) may have less impact on AEW growth than previously anticipated. Taken together, these results highlight the need for additional research quantifying and improving the predictability of CCKW interactions in operational models.


Oct 27: NO SEMINAR (Rosenstiel School Faculty Meeting)

Nov 03: Dr. Xiaozhui Zhou
Guest of Peisen Tan, Department of Ocean Sciences
High Meadows Environmental Institute, Princeton University, Princeton, NJ

Surface Wave Impacts on Air-Sea Momentum Flux and Upper Ocean Turbulence
Under Tropical Cyclones
Recording Available at COMPASS ON DEMAND

Surface waves alternate the air-sea momentum and gas fluxes and upper ocean responses, especially under tropical cyclone conditions. The drag coefficient and upper ocean responses under tropical cyclones and their dependence on sea state are investigated by combining upper ocean current observations (using EM-APEX / Langragian floats deployed under five tropical cyclones) and a coupled ocean-wave model (Modular Ocean Model 6 - WAVEWATCH III). The estimated drag coefficient averaged over all storms is around 2–3×10–3 for wind speeds of 25–55 m/s, consistent with earlier observations and model parameterizations. The drag coefficient is significantly reduced by misaligned swell when the misalignment angle between the dominant wave direction and the wind direction exceeds about 45°. Even sea-state dependent Langmuir turbulence significantly modifies the three-dimensional ocean current response to tropical cyclones and enhances the upper ocean turbulence and mixed layer deepening. The sea-state dependent Langmuir turbulence parameterization is still not sufficient to reproduce upper ocean cooling under tropical cyclones, possibly due to missing dynamics such as wave breaking.


Sisam Shrestha (ATM)
Northward Shift of Tropical Precipitation Observed in Recent Years
Consistent With CMIP6 Models With Higher Aerosol-Cloud Interactions

A southward shift of the tropical precipitation band in the latter half of the twentieth century is attributed to the interhemispheric temperature gradient due to anthropogenic sulphate aerosols. More specifically, studies using CMIP3 and CMIP5 models linked this southward shift of the tropical precipitation to the indirect aerosol effect via aerosol-cloud interactions. Coupled models with a higher aerosol-mediated cloud radiative response were found to be in better agreement with the observed southward shift of the tropical precipitation. In recent years, however, satellite observations of precipitation, upper tropospheric relative humidity, and outgoing longwave radiations indicate a northward migration. This moistening of the Northern hemisphere along with a drying trend in the Southern tropics is primarily centered in the tropical Pacific. We find a comparable northward shift of precipitation in the coupled models belonging to CMIP6. The observed northward migration of tropical precipitation is consistent with models with a higher aerosol-cloud interaction. This work evaluates the intermodel spread in circulation shift and highlights the role of aerosol-cloud interactions.

Peisen Tan (OCE)
The Impact of Airflow Separation on the Wind-Wave Momentum Flux

When air blows over ocean waves, the waves' windward side shelters the leeward side, inducing a windward high pressure and a leeward low pressure, which result in momentum transfer from wind to waves. Previous research suggested the waves' amplitude, frequency, and the wind speed affect the structure of the airflow and wind stress above the waves, which in turn fuels the wave growth. However, systematic research on the synchronized measurement of airflow structure and pressure above waves with different amplitudes and frequency has been rare. Therefore, we conducted experiments under a wide range of wind and wave conditions in the SUSTAIN wave tank at the University of Miami. These experiments included high-frequency vertical air pressure profiling and wind speed measurement above the waves. Two distinct wave growth mechanisms have been found: Under low wind forcing, the sheltering effect is weak, and laminar viscous stress dominates the wave growth. Under strong wind forcing or with steeper waves, however, a high form stress caused by pressure dipoles at the waves' windward / leeward sides dominates the wave growth, accompanied by a strong airflow separation on the leeward side. In addition, the form stress to total stress ratio in our results matched well with previous research. Eventually, we will shed light on the wave growth regime under a range of wind and wave conditions and provide insights on future wave models' wind input parameterizations.

Victoria Pizzini (ATM)
Exploring CYGNSS and Its Role in Advancing Hurricane Research and Predictability

The National Oceanographic Partnership Program (NOPP) project Hurricane Coastal Impacts (NHCI) unites teams from more than 10 institutions in the U.S. and the Netherlands to enhance the predictability of damages from landfalling hurricanes. This includes advancements in satellite remote sensing. Our team at the Rosenstiel School and its Center for Southeastern Tropical Advanced Remote Sensing (CSTARS) focuses on a rapid mapping of topographic changes and flooded areas on land and improvements of wind and wave field products for the ocean. In this context we explore the utilization of NASA's Cyclone Global Navigation Satellite System (CYGNSS), consisting of eight microsatellites employing Global Navigation Satellite Systems Reflectometry (GNSS-R) for wind retrievals. CYGNSS measures wind speed and direction over the ocean, utilizing reflected signals from the Global Positioning System (GPS). A key promise of using GNSS-R is that it can provide measurements of ocean surface winds even in adverse weather conditions which can interfere with other types of remote sensing technologies. This sets it apart from the more commonly used Advanced Scatterometer (ASCAT) on the European MetOp satellites, which face complications like signal attenuation by heavy precipitation and saturation effects at high wind speeds. My first student seminar introduces the NHCI project and compares the wind retrieval methods of CYGNSS and ASCAT. Next steps will include comparisons between CYGNSS and ASCAT products and high-resolution wind fields derived from synthetic aperture radar (SAR) images, as well as an attempt to enhance the quality of SAR-derived wind fields by combining them with CYGNSS data.


Nov 24: NO SEMINAR (Thanksgiving Recess)

Dec 01 (10:50 am): STUDENT SEMINARS

Karen Papazian (ATM)
Understanding the Dynamical Mechanisms for Large-Scale Cold Air Outbreaks

Cold air outbreaks (CAOs) have large societal and environmental impacts, such as agricultural losses, infrastructure damage, changes in atmospheric circulation, etc.  This study advances the understanding of CAOs through an idealized modeling framework by exploring the use of aquaplanet (AP) simulations. AP simulations, in which the Earth's surface is simplified to a uniform water-covered planet, provide a unique platform to dissect and understand the fundamental aspects of climate dynamics without the complexities of land-sea contrasts and topography. In our approach, we conduct three AP simulations, each characterized by varying pole-to-equator surface temperature gradients. These variations allow for an in-depth exploration of how different thermal structures influence CAO patterns and their influence on the dynamics of the atmosphere, regionally and globally. The differing pole-to-equator surface temperature gradients were chosen to resemble potential global climate change scenarios and extreme climate change scenarios. We find that when there is no pole-to-equator surface temperature gradient, there are still CAOs present. Additionally, we juxtaposed the findings from these idealized simulations with reanalysis data from the NCEP-NCAR Reanalysis 1 project. This comparison begins to bridge the gap between simplified modeling and real-world atmospheric conditions, enhancing the validity and applicability of our results. With these differing AP simulations and their connection to reanalysis data this study aims to further understand the physical mechanisms of CAOs, and the role dynamics plays in their frequency and intensity.

Ivenis Pita (MPO)
South Atlantic Meridional Overturning Circulation
and Meridional Heat Transport Variability Estimates
From Optimal Mapping and Machine Learning

The Atlantic Meridional Overturning Circulation (AMOC) drives northward Meridional Heat Transport (MHT) and affects climate and weather patterns, regional sea levels, and ecosystems. AMOC monitoring arrays in the South Atlantic are limited, mainly at 11°S (TRACOS) and 34.5°S (SAMBA). In a recent study, the AMOC and MHT were estimated at 22.5°S (AXMOC) from in-situ data using an optimized mapping methodology. This study expands on the previous study by estimating the AMOC and MHT at 34.5°S. For this, in-situ temperature (T) and salinity (S) from XBT, ARGO, and CTD data, as well as the WOA18 climatology, satellite and reanalysis products are used to obtain monthly AMOC and MHT estimates since 2005. Two mapping methods are used and compared at the reference section: (i) a mapping method that consists of an optimal weighted average of the T-S profiles considering an ensemble of temporal and spatial ranges by minimizing the root mean square error between in-situ and satellite sea level data, and (ii) a two-layers feed-forward neural network using various input parameters (latitude, longitude, year, sine and cosine of day of the year, pressure, sea surface temperature and sea level anomaly) and T and S sections as outputs. The sensitivity of the AMOC / MHT estimates to these mapping methods are analyzed. Both methods present a good agreement with SAMBA array. The AMOC timeseries presented here represent the longest in-situ-based AMOC estimate at 34.5°S.

Victoria Schoenwald (ATM)
Gulf Stream Variability and East Coast Sea Level Rise

Across the East Coast of the United States there are approximately 1.4 million houses located less than 1 meter above the local mean high-water value. These houses are already experiencing environmental and economic damage which is predicted to only worsen due to migrating "hot spots" of sea level rise (SLR). Therefore, the prediction of coastal flooding for these communities in the coming decades will become extremely important. Due to the proximity to the East Coast, the Gulf Stream (GS) has been looked at as a potential source of predictability of SLR in this region. Changes in the sea level slope across the GS are proportional to the GS flow intensity. A weaker GS will raise the water on the shoreside and lower the water on the open ocean side. Whether or not these changes are part of a long-term trend or part of a natural cycle are still being debated. To investigate the role of the GS on "hot spots" of SLR, an index of strength and position was created both with observational datasets and with high resolution (HR) CESM data with a record of more than 100 years. The GS strength and position were then compared with sea surface height from two tide gauge stations from the mid-Atlantic bight (MAB) and two from the south-Atlantic bight (SAB). From our results, we propose that wind driven oceanic changes are influencing periods of East Coast SLR acceleration on interannual-to-decadal timescales. We also explore how GS flow will change in a warming climate and how that will affect sea level at coastal locations by utilizing the RCP 8.5 climate simulation from the HR CESM experiment. These studies attempt to improve coastal flooding projections by understanding how large-scale oceanic circulation affects coastal sea level variability.

Katrina Simi (OCE)
Wave Energy Dissipation Induced by Gyroid Structures
to Be Used as a Base for Coral Outplanting

Naturally occurring coral reefs are the pinnacle of breakwaters in the ocean as they shield shorelines from erosion and flooding. As a result, a Defense Advanced Research Projects Agency (DARPA) program titled "Reefense" aims to protect coastal infrastructure using hybrid artificial and living coral reefs. As a part of this effort, different reef component structures and materials have been tested in the University of Miami's SUSTAIN laboratory for wave dissipation performance. One of these hybrid coral reef designs include stacked gyroid lattice structures developed by the Applied Research Laboratory (ARL) at the Pennsylvania State University. The lattice structures are a 1/4.2 scaled model made from concrete and can be nested in various geometries and arranged in consecutive rows. The wave energy dissipation was measured by placing the lattice structures inside of a 15 meter long wind-wave tank called Air-Sea Interaction Saltwater Tank (ASIST). Wave probe sensors were placed before and after the stacked lattice structure. The lattices were arranged in a pyramid shape, extending across the entire flume, and dissipating wave energy between 11-81%. Long term objectives of this project include implementation of scaled-up lattice structures in combination with nature based components (outplanted corals) off of coastlines, serving as a living reef to attenuate wave action. Observations on the range of energy dissipation under varying conditions of frequency and amplitude and water level over the structure were examined.



Jan 19: Dr. Allison Wing
Invited Speaker of the Department of Atmospheric Sciences
Werner A. and Shirley B. Baum Professor and Associate Professor,
Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee

Mar 29: Jamie Meacham
Imperial College London