COMPASS Wednesday - Archive

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COMPASS Wednesday

Combined OCE MPO ATM Seminar Series

Wednesdays at 3:00 pm, Seminar Room SLAB 103 (unless stated otherwise)


Jan 23: Dr. Landolf Rhode-Barbarigos
Department of Civil, Architectural and Environmental Engineering, University of Miami

Structural Morphology and Dialectic Form Finding of Coastal Structures

Structural morphology refers to the study of form and shape in structures as well as the relations between form, forces, and material. Dialectic form finding reflects an extension of the traditional form-finding process integrating performance-related constraints and criteria in the exploration of a geometry in static equilibrium with a prescribed load. Although structural morphology and form finding have been investigated for civil and aerospace engineering applications resulting in materially and mechanically efficient structures, their potential in coastal engineering applications has yet to be accomplished. The talk will discuss structural morphology and form finding in civil and coastal engineering structures through a series of projects and examples.

Jan 30: Lisa Bucci
Department of Atmospheric Sciences, RSMAS
(one-hour ATM student seminar)

Using Observing System Simulation Experiments
to Explore Hurricane Predictability and the Potential Use
of Space-Based Doppler Wind Lidar Observations

The lack of vertical wind profiles in the tropical atmosphere, particularly over the oceans, suggests that there is room for improvement in initializing numerical forecasts of tropical cyclones (TCs). One instrument that could potentially measure detailed wind profiles in the environment of a TC is a space-based Doppler Wind Lidar (DWL). Observing System Simulation Experiments (OSSEs) provide a framework to test new observing systems and compare design trade-offs. The framework can also be used to explore the predictability limits of a forecast system and inform the user of the effectiveness of its data assimilation system.  Earlier OSSEs have shown the potential for improving TC track forecasts as a result of assimilating simulated DWL data. This study expands on those previous efforts by investigating how the assimilation of idealized simulated DWL wind observations modifies the environment near the TC. Synthetic DWL observations were simulated from a high-resolution regional “Nature Run” of a hurricane and assimilated using an Ensemble Square-Root Kalman Filter.  The study also establishes the predictability limits of this forecast system by exploring the results of several perfect initial condition experiments. Results from these analyses and subsequent forecasts using the Hurricane Weather and Research Forecast (HWRF) regional model will be presented.

Feb 06: Dr. Matthias Morzfeld
Department of Mathematics, University of Arizona

Should I Really Use a Localized Particle Filter?

I will first review particle filters (PF) as a tool for nonlinear / non-Gaussian data assimilation, describe how PFs fail when the dimension is large and how this can be fixed by localization. An interesting next question is: Are (localized) PFs really "better" than ensemble Kalman filters (EnKF) or variational methods? I will provide partial answers to this question by considering simplified data assimilation problems in which the degree of nonlinearity can be controlled to be mild, medium, or strong. My main conclusions are that PFs should only be used when nonlinearity is strong and that variational methods and smoothers can outperform EnKFs and PFs in the regime of mild nonlinearity. This is joint work with Daniel Hodyss, Marine Meteorology Division, Naval Research Laboratory, Monterey, California.

Feb 13: Dr. Joseph Prospero
Professor Emeritus, Department of Atmospheric Sciences, RSMAS

Sixty Years of African Dust Research at RSMAS:
A Personal History of Its Evolution and a Look to the Future
Recording Available at COMPASS ON DEMAND

Many scientists in RSMAS today are active in various aspects of research on windborne mineral dust and its link to climate and to marine and terrestrial biogeochemical processes. They continue a long history of dust research in the School, research that began in the 1960s when dust was more a topic of humor than of scientific interest. Over the following decades the School has played a pioneering role in dust studies, a field in which it continues to hold a prominent position. My presentation is mostly a personal history of this research and its evolution. From the beginning, the strategy of our program has been to develop a global view and to focus on large scale processes. This eventually led to a global ocean network of 20–30 island and coastal-based aerosol sampling stations which operated over the 1980s and 1990s. The marine aerosol data obtained from these sites continues to serve as the foundation for the testing of dust-climate models. However the reputation of my group's efforts rests largely on our research on African dust which is largely based on sampling programs in the Atlantic and especially the work on Barbados which began in 1965 and continues to this day. The Barbados data show great changes in dust transport which can be linked to climate variations in Africa and the Atlantic. These data serve as a unique test bed for the development of dust-climate models. Models have had a very difficult time in meeting that challenge. The understanding and the modeling of the dust-climate cycle requires that we bring together a broad spectrum of studies. I make the case that the location of RSMAS on the edge of the Caribbean Basin, the major receptor region of African dust, makes it an ideal place to serve as the center for such integrated studies. I will discuss some ways in which we can develop a strategy to this end. 

Feb 20: Dr. Yana Bebieva
Geophysical Fluid Dynamics Institute, Florida State University

Double-Diffusive Layering in the Arctic Ocean:
An Explanation of Along-Layer Temperature and Salinity Gradients

A type of ocean mixing process, double-diffusive convection, gives rise to layers in the Arctic Ocean that may be characterized by their differing temperature and salinity properties. The properties and physics of these layers are key to understanding how heat is transported vertically and laterally in the Arctic Ocean. A theoretical formalism is put forward to explain distinct features of the layers that are characterized in the Ice-Tethered Profiler observations. The physical framework in context with observations brings new understanding to how the layers form, and how they relate to heat and salt transport in the Arctic Ocean.

Feb 27: Dr. Kathryn Gunn
Department of Ocean Sciences, RSMAS

Time-Lapse Acoustic Imaging of Oceanic Fronts and Eddies

Seismic reflection surveying is used to generate acoustic images of the water column whereby acoustic impedance contrasts are produced from variations in temperature and, to some extent, salinity. In this way, two- and three-dimensional images of thermohaline circulation can be generated. Critically, these images have equal vertical and horizontal resolutions of order 10 m and cover large areas. Here, I review oceanic seismic reflection profiling, namely seismic oceanography, and discuss how this technique can be used to overcome certain observational limitations. I present results from a three-dimensional seismic survey acquired across the Brazil-Malvinas Confluence in the southwest Atlantic Ocean. These observations reveal a deep-reaching front and rapidly changing sub-mesoscale and mesoscale thermohaline structures. The analysis of these data have significant implications for frontal dynamics.

Mar 06: Dr. Matthew Newman
CIRES / University of Colorado & NOAA / ESRL / PSD

Initialized Climate Forecasts Without Initialization

Seasonal forecasts are made by starting a climate model from an initial estimate of the latest global three-dimensional ocean, atmosphere, and land conditions, and then using supercomputers to run the model's equations forward in time. These extensive calculations are only feasible at a few national operational centers and large research institutions. However, many similar models are also used for long simulations of the Earth's pre-industrial climate, made freely available for climate change studies. We investigated whether seasonal forecasts might be drawn from the information already existing within these simulations, instead of by making new model computations. Within each simulation, we determine the best matches, or "model-analogs", to current observed tropical Indo-Pacific ocean surface conditions. How these analogs evolve over the next several months within each long simulation is then its seasonal forecast. We find this much less expensive model-analog technique is as skillful as the more traditional forecasting method. We then employed it to make forecasts during 1961-2015, using twenty-eight existing CMIP5 climate simulations, significantly expanding similar previous efforts. This study suggests that with little additional effort, sufficiently realistic and long existing climate model simulations can provide the basis for skillful seasonal forecasts. That is, anyone can be a climate forecaster.

Mar 13: NO SEMINAR (Spring Recess)

Mar 20: NO COMPASS SEMINAR (Rosenstiel Award Seminar on this day)

Mar 21 (Thursday, 1:30 pm): Dr. Tapio Schneider, 45th Rosenstiel Award Recipient
Division of Geological and Planetary Sciences, Caltech

Earth System Modeling 2.0:
Toward Accurate and Actionable Climate Predictions
with Quantified Uncertainties
Recording Available at COMPASS ON DEMAND

While climate change is certain, precisely how climate will change is less clear. But breakthroughs in the accuracy of climate projections and in the quantification of their uncertainties are now within reach, thanks to advances in the computational and data sciences and in the availability of Earth observations from space and from the ground. To achieve a leap in accuracy of climate projections, we are developing a new Earth system modeling platform. It will fuse an Earth system model (ESM) with global observations and targeted local high-resolution simulations of clouds and other elements of the Earth system. The ESM is being developed by the Climate Modeling Alliance (CliMA), which encompasses Caltech, MIT, and the Naval Postgraduate School. CliMA will capitalize on advances in data assimilation and machine learning to develop an ESM that automatically learns from diverse data sources, be they observations from space or data generated computationally in high-resolution simulations. It will also engineer the ESM from the outset to be performant on emerging computing architectures, including heterogeneous architectures that combine traditional CPUs with hardware accelerators such as graphical processing units (GPUs). This talk will cover key new concepts in the ESM, including turbulence, convection, and cloud parameterizations and fast and efficient algorithms for assimilating data and quantifying uncertainties.

Mar 27: Dr. Brian Arbic
University of Michigan, Ann Arbor

Global Modeling of the Oceanic Internal Tide and Internal Gravity Wave
Continuum Spectrum

We discuss numerical simulations of oceanic internal gravity waves (IGWs) on a global scale, on US Navy, NASA, and European high performance computing platforms. IGWs are waves that exist on the interfaces between oceanic layers of different densities. IGWs of tidal frequency are known as internal tides. Beyond tidal frequencies, there is a spectrum of IGWs known as the IGW continuum. The rollover and breaking of IGWs controls most of the mixing in the open-ocean beneath the mixed layer. IGWs also impact the speed of sound, and yield a measurable sea surface height (SSH) signal. Therefore IGWs are important for satellite altimetry missions, including the upcoming Surface Water and Ocean Topography (SWOT) mission, and for operational oceanography in general. We describe our work with the US Navy HYbrid Coordinate Ocean Model (HYCOM), in which we pioneered high-resolution global ocean models simultaneously forced by atmospheric fields and the astronomical tidal potential. We also examine newer simulations performed under similar conditions, on NASA supercomputers, with the Massachusetts Institute of Technology general circulation model (MITgcm). Finally, we briefly describe related work done with the European ocean forecasting model, the Nucleus for European Modeling of the Oceans (NEMO). We summarize several papers on comparison of the modeled internal tides and the IGW continuum spectrum to altimetry and observations from moorings. We briefly discuss the generation of the continuum spectrum and the potential implications for a better understanding of ocean mixing.

Mar 28 (Thursday): Mariana Bernardi Bif
Department of Ocean Sciences, RSMAS
(one-hour OCE student seminar)

Understanding Resistant Organic Carbon in the Ocean:
From Microbes to Large-Scale Processes
Recording Available at COMPASS ON DEMAND

The cycling of elements on Earth and their allocation into major reservoirs is driven through their biogeochemical transformations. For example, carbon is transformed biologically with COconverted to organic carbon by photosynthesis, and then respired to the gaseous form by heterotrophs. Additionally, the cycling of elements such as nitrogen, phosphorus and iron is directly linked to carbon through the formation of organic matter resulting from production. A portion of organic carbon resists immediate degradation in the euphotic layer and can be exported to the deep to be respired far away from surface waters, thus contributing to the development of an oceanic sink for atmospheric CO2. However, controls on the production of a resistant organic carbon with potential for export are still unresolved and are the focus of my PhD thesis, as well as the subject of this talk. Using incubations of natural microbial populations, I demonstrate that the production of a resistant carbon fraction depends on the initial availability of nutrients to the microbial community. Then, I show how seasonality plays a role in organic carbon production in the Northeast Pacific Ocean due to vertical nutrient inputs during winter. For the same region, I present a novel applicability of BGC float data to estimate high-resolution organic carbon production, with the ability to differentiate total and dissolved carbon fractions. Finally, using BGC float and historical observational data from the North Pacific Ocean, I show how warm events driven by ocean-atmospheric oscillations, that happened between 2013 and 2016, restricted nutrient inputs to the euphotic zone and greatly reduced organic carbon production and, thus, its prospects for export to the deep ocean.

Apr 03: Dr. Margaret Leinen
SEEDS and RSMAS / DEIC 2019 Distinguished Lecturer
Scripps Institution of Oceanography

Oceanography in the Next Decade:
Where Will New Ways to Study the Ocean Lead Us?

The past few years have seen an explosion of new techniques for observing the ocean: new autonomous vehicles for seafloor mapping and ocean sampling; new acoustic, image and genomic sensors for biology that could be deployed long term at ocean sites to see changes in ecosystems. Both national and international organizations have realized that these new developments represent opportunities; but also challenges. For example, many of these sensors, platforms and systems are generating so much data that we need to develop new strategies for analyzing the data and making sense of what we see. Oceanographers have begun to work with data scientists and companies to apply artificial intelligence and machine learning to large data sets. This ocean of data is also causing scientists to embrace different paradigms for solving ocean science problems. In response, the UN begun planning for 2021-2030 as the International Decade of Ocean Science for Sustainable Development.

Dr. Margaret Leinen is the Director of Scripps Institution of Oceanography and Vice Chancellor for Marine Science of University of California at San Diego. Scripps Institution is one of the largest oceanographic research institutes. Dr. Leinen is an ocean biogeochemist and paleoceanographer whose research includes study of ocean carbon cycling and the role of the oceans in climate.  She is also the former President of the American Geophysical Union, the largest geoscience society in the world, and has also served as the President of The Oceanography Society and Chair of the AAAS Section on Atmospheric and Hydrospheric Science. She served as Assistant Director for Geosciences, U.S. National Science Foundation (NSF) from 2000-2007. She has been the Vice Chair of the International Geosphere Biosphere Programme, Chair of the US Global Change Research Program and Vice Chair of the U.S. Climate Change Science Program.

Apr 10: Rachel Zelinsky (Sodowsky)
Department of Ocean Sciences, RSMAS
(one-hour MPO student seminar)

Simulations of DYNAMO MJO Events in a
Coupled and Uncoupled Regional Model

The Madden-Julian oscillation (MJO) is the largest source of intraseasonal variability in the tropics and it is an important link between weather and climate. However, many general circulation models (GCMs) have a difficult time simulating realistic MJO-related variability. One possible way to improve simulations of the MJO is to use a regional model with high spatial resolution over the Indian Ocean. Also, air-sea coupling often improves the MJO in models. In the study, I compare a freely-coupled simulation of MJO events during the Dynamics of the MJO (DYNAMO) field campaign (October–November 2011) to an uncoupled simulation where the atmospheric model is forced with the sea surface temperature (SST) from the coupled simulation. I investigate the relationships between SST, latent heat flux, and rainfall. Observational estimates from DYNAMO, reanalysis products and satellite based data are used to validate model diagnosed relationships. I also examine whether anything is gained by using a regional model over GCMs, by comparing the DYNAMO MJO events in this regional model to the GCM from the Subseasonal Experiment (SubX) project.

Apr 11 (Thursday): Dr. Joellen Russell
Department of Geosciences, University of Arizona

Observation-Based Evaluation of the Southern Ocean
in Earth System Models

Global coupled climate models and earth system models vary widely in their simulations of the Southern Ocean and its role in, and response to, the ongoing anthropogenic forcing. The use of community-wide observationally-based metrics are essential for assessing relative strengths and weaknesses of the models, but sub-surface observations of the carbon system were rare before the deployment of biogeochemically-sensored floats by the SOCCOM mission. We now have the means to assess the air/sea exchange of carbon remotely and acidification at depth; an assessment of these and other fields in ESM simulations will be presented.

Apr 17: Jianhao Zhang
Department of Atmospheric Sciences, RSMAS
(one-hour MPO student seminar)

Understanding the Low Cloud Reduction and Its Diurnal Cycle
Within the Smoky Boundary Layer in the Remote SE Atlantic

Ground-based observational data from Ascension Island in the remote southeast Atlantic during August 2016 and 2017 of the DOE LASIC campaign reveal that smoke within the marine boundary layer (BL) modifies the thermodynamical structure as well as the low-cloud characteristics, through both radiative and microphysical processes. A strength of the data, which include 8x/day radiosondes, is its ability to document the full diurnal cycle, thereby complementing results from day-time-only aircraft campaigns. When smoke is present near the surface, the lowest 500 m of the boundary layer is warmed by 0.5 K, most notably in the mid-to-late afternoon, but persisting through the night. Satellite retrievals and surface-based remote sensing observations indicate a reduction in both day-time and nighttime low-cloud cover and LWP within smokier BLs. Boundary layer decoupling increases when smoke is present. Smokier boundary layers are characterized by the following diurnal cycle: increased warming of the sub-cloud layer reduces its relative humidity, raising the lifting condensation level, and thereby near-surface air must rise to form cloud. This coincides with a diurnal minimum in cloud cover and establishes decoupled conditions that are more clearly evident after sunset. Moisture accumulates within the near-surface layer during the night, increasing moisture stratification. A lack of nighttime recoupling is also evident in lower liquid water paths. A singular feature of smoky BLs is that at sunrise, the boundary layer becomes coupled again, with the BL deepening, cloud top heights rising, and LWPs increasing. Large-eddy-scale simulations are pursued to assess if the simulations can replicate the observations and provide insights into smoke-induced changes in thermodynamics, dynamics, and aerosol-cloud microphysical interactions. The diurnal composite of a smokier BL is illustrated with a case study of a multi-day 2017 mid-August smoke event using both observations and simulations. Associated meteorological conditions indicate that the cloud top inversion strength is reduced when BL biomass burning aerosol is present. This may help support increased entrainment that helps explain the observed persistence of smokier episodes. Although the direct aerosol radiative effect is a cooling, the reduction in cloud fraction from the BL semi-direct effect dominates the overall radiative impact during the month of August.

Apr 24: Dr. Michael Spall
2019 Invited Speaker of the OCE Faculty

Woods Hole Oceanographic Institution

Dynamics and Thermodynamics of the Transpolar Drift and Mean Ice Thickness
in the Arctic Ocean
Recording Available at COMPASS ON DEMAND

The goal of this study is to develop a simple model for the Transpolar Drift and mean ice thickness in the Arctic Ocean. The approach makes use of asymptotic solutions to the governing ice momentum and thickness equations and idealized configurations of a coupled ocean / ice general circulation model of the Arctic Ocean. Two distinct dynamic / thermodynamic regimes are identified, an eastern region with thin ice and a western region with thick ice. The influences of wind, ice parameters (strength, conductivity), basin size, and atmospheric cooling on the ice distribution, ice-atmosphere heat flux, and ice export from the Arctic are discussed.

Michael Spall is a Senior Scientist at the Woods Hole Oceanographic Institution, where he has been working since 1990. Dr. Spall earned his PhD from Harvard University in 1988 in Applied Mathematics, and worked at NCAR and Institut für Meerskunde, Kiel, Germany. Dr. Spall has a wide range of research interests, including dynamics of large-scale and mesoscale currents, wind-driven and thermohaline circulations, marginal seas and ocean gyres, as well as wave processes, convection, mixing, and atmosphere / ocean interactions. Dr. Spall is an author on more than 100 peer-reviewed publications, and has had several editorial appointments, including Chief Editor of JPO. Dr. Spall was awarded the Henry Bryant Bigelow Chair for Excellence in Oceanography in 2017.

May 01: Lisa Nyman
Department of Ocean Sciences, RSMAS
(one-hour AMP student seminar)

Using Advanced Doppler Marine Radar Techniques
to Measure Surface Currents and Study Internal Waves
Recording Available at COMPASS ON DEMAND

During three research cruises in the Pacific in 2016 and 2017, a Helmholtz-Zentrum Geesthacht rotating vertically-polarized (VV) X-band Doppler Marine Radar (DMR) was installed onboard the R/V Roger Revelle and the R/V Oceanus. Ocean currents with marine radar are typically acquired with the use of the three-dimensional fast Fourier transform (3D FFT) on a radar image sequence in order to measure the velocity of the ocean waves in comparison to the theoretical wave velocity in the absence of a current. However, dispersion shell currents cannot resolve very fine-scale current variations, such as at the interface of a current front or an internal wave. To fill this gap, the marine radar data were used in a different way. The raw data include the phase of the backscattered signal of each radar pulse, which can be converted to radial Doppler velocities. The Doppler velocity itself includes contributions from a multitude of ocean surface processes.  A linear regression was set up to determine a functional relationship between Doppler velocity and surface current. The Doppler Velocity Synthesis algorithm (DoVeS) was developed to synthesize radial Doppler velocity information from a moving ship in order to obtain a two-dimensional vector surface current field around the ship track. To showcase the fine-scale capabilities of this method and of the DMR itself, the surface current convergence and divergence above internal waves off the coast of California is compared with echo sounder data, which show the shape of the internal wave beneath the ship. The convergent and divergent Doppler zones are phase shifted with respect to the internal wave itself. Different radar signatures correspond to varying water depths and wind speeds. It is hypothesized that these signatures correspond to different stages of the internal wave’s shoaling process, which is also discussed.