COMPASS (Combined OCE MPO ATM Seminar Series) WEDNESDAY
(3:00 SLAB Seminar Room, unless stated otherwise)
Feb 01 --- Dr. Pierre Sochala (French Geological Survey (Bureau de Recherches Géologiques et Minières)
"Uncertainty Propagation Methods for Stochastic PDEs Outputs in Geoscience Applications"
The numerous advances in numerical methods and high-performance computing allowed the development of uncertainty quantification in several domains of applications. Many research efforts are motivated by the fact that the data of a large number of physical problems have uncertain components due to lack of knowledge. In uncertainty quantification, the polynomial chaos expansion is particularly efficient to represent smooth process but can fail for non-smooth quantity of interest. In this presentation, we focus on two methods designed to reconstruct stochastic fields for which the method of separation of variables (i.e. physical vs stochastic) is inappropriate. The first method targets solutions having steep gradients with random locations and is based on polynomial chaos expansions of the level sets. An adaptive choice of the level set can be used to control the approximation error, ensuring high accuracy at a significantly lower cost compared to classical non-intrusive approach. We apply and validate the method to reconstruct the pressure field in subsurface flows with uncertain hydrological properties. The second method concerns signals having random oscillations such as seismic time series due to wave propagation in uncertain medium. Our approach is based on a damped harmonic decomposition of the signal combined with a polynomial chaos expansion of the four coefficients of each harmonic term (amplitude, decay constant, pulsation, and phase). Computational tests show that the method is able to reproduce random seismic time series associated with layered soils having uncertainties in the geological data (geometry, wave velocities, damping factor). In both applications, a global sensitivity analysis is performed to investigate the relative impact of the random parameters.
Feb 08 --- Dr. Yoshiaki Miyamoto
"Global Atmospheric Simulation with Sub-Kilometer Grid Spacing"
This presentation introduces a global simulation for the atmosphere with a 0.87 km horizontal mesh size which has been conducted by one of the world’s fastest supercomputers.
We focus on the deep moist convection in the simulation. In particular, the global statistics and resolution dependence of convection were investigated. For this purpose, we developed a simple two step method to detect "convection core" grid points from discretized data set. It was shown that the averaged structure and number distribution of detected convection are reasonable. The convection core is resolved by multiple grids when the mesh size is smaller than 3 km.
Additionally, we analyzed the differences in structure and intensity of convection in various cloudy disturbances: Tropical Cyclones (TCs), Madden-Jullian Oscillation (MJO), Mid-latitudinal disturbances, and Fronts. It was found that the convection is stronger in MJO than in TCs. The former tends to be generated under the environment with high convective available potential energy (CAPE) and weak low-level mass convergence, whereas the convection in TC is accompanied by strong convergence, but less CAPE. In the presentation, the presenter would like to briefly introduce the computational challenge to conduct the global simulation on a massive parallel computer as well as the scientific results.
Feb 15 --- Dave Ortiz-Suslow (45-minute AMP student seminar)
"Observations and Modeling of Turbulent Air-Sea Coupling in Heterogeneous and Strongly Forced Conditions"
The turbulent fluxes of momentum, mass, and energy across the ocean-atmosphere boundary are fundamental to our understanding of a myriad of geophysical processes, such as wind-wave generation, oceanic circulation, and air-sea gas transfer. Therefore, empirical relationships were developed to quantify the interfacial exchange rates in terms of easily observed parameters (e.g., wind speed). However, mounting evidence suggests that these empirical formulae are only valid over the relatively narrow parametric space, i.e. open ocean conditions in light to moderate winds. Several near-surface processes have been observed to cause significant variance in the air-sea fluxes not predicted by the conventional functions, such as a heterogeneous surfaces, swell waves, and wave breaking. Further study is needed to fully characterize how these types of processes can modulate the interfacial exchange; in order to achieve this, a broad investigation into air-sea coupling was undertaken. The primary focus of this work was to use a combination of field and laboratory observations and numerical modeling in regimes where conventional theories would be expected to breakdown, namely: the nearshore and in very high winds. These seemingly disparate environments represent the marine atmospheric boundary layer (MABL) at its physical limit. In the nearshore, the convergence of land, air, and sea in a depth-limited domain marks the transition from a marine to a terrestrial boundary layer. Under extreme winds, the physical nature of the boundary layer remains unknown as an intermediate substrate layer, sea spray, develops between the atmosphere and ocean surface. At these ends of the MABL physical spectrum, direct measurements of the near-surface processes were made and directly related to local sources of variance. Our results suggest that the conventional treatment of air-sea fluxes in terms of empirical relationships developed from a relatively narrow set of environmental conditions do not generalize to the coastal and extreme wind environments.
Mar 01 (Special time: 2:00 pm) --- Dr. Phil Klotzbach (Colorado State University)
"The impacts of El Nino Southern Oscillation and the Madden-Julian Oscilliation on global tropical cyclone activity"
Both El Nino-Southern Oscillation (ENSO) and the Madden-Julian oscillation (MJO) have been documented in previous studies to significantly impact tropical cyclone activity in most basins. For example, El Nino is well-known to significantly reduce Atlantic hurricane activity, while increasing hurricane activity in the Northeast Pacific. This presentation will investigate both the modulations of global tropical cyclone activity by ENSO as well as the large-scale features likely responsible for this modulation.
Most studies investigating the modulation of tropical cyclones by the MJO have used the Wheeler-Hendon index. This index is only available since 1974, the period over which remotely sensed outgoing longwave radiation data has been available. This presentation utilizes a long reconstructed MJO index, based on surface pressures, which extends back to 1905. Consistent modulation of tropical cyclone activity by the MJO in all basins over this time period are documented. These modulations are shown to be remarkably stable over the entire analysis period.
The combined impacts of ENSO and the MJO on tropical cyclone activity are also examined in each basin over multidecadal time scales.
Mar 02 (Special seminar: SLAB, 3:00 pm) --- Dr. Xiaofeng Li (NOAA-NESDIS)
"SAR Imaging of Oceanic and Atmospheric Features"
The interaction between ocean/atmosphere physical processes and the short Bragg and intermediate oceanic gravity waves will lead to a change in sea surface roughness, which is one of the key parameters that need to be measured from the space. Spaceborne synthetic aperture radar (SAR) can measure the ocean and ice surface roughness in the microwave band without being hampered by cloud cover and lack of Sun light during nighttime. Modern SAR’s are high-spatial-resolution (10 m) and wide-swath (up to 450 km) imaging radars that can “view” these sea surface roughness patterns associated oceanic and marine atmospheric boundary layer phenomena in great details. In this presentation, dynamical features associated with phenomena both in oceanic (surface waves, internal waves, tidal fronts, ocean bathymetric features, oil spills, coastal upwelling and atmospheric (tropical cyclones, atmospheric vortex streets, atmospheric gravity waves, fronts, katabatic winds) origins will be presented. SAR images of striking ocean and atmosphere features are presented along with the dynamical interpretations of these features using analytical/numerical models and observations from other in situ and satellite sensors.
Although many space agencies have been launching SAR satellites in the past few decades, SAR applications in ocean and atmosphere research have still not been fully explored due to the fact that these SAR data are commercially based. However, this fact has been changed as European Space Agency launched Sentinel-1A SAR satellite on April 3, 2013, and then its twin Sentinel-1B on April 22, 2016. The SAR data is now free and open and software tools developed by the international SAR community have made the use of the data straightforward. It’s anticipated there will be a fast growing applications of this data source in oceanography and marine meteorology studies.
Mar 08 --- Dr. Howard Bluestein (George Lyn Cross Research Professor, University of Oklahoma)
“Probing Tornadoes and their Parent Supercells with Mobile, Rapid-Scan, Doppler Radars”
Rapid-scan Doppler radar measurements of tornadoes and their parent supercells have allowed us to view aspects of tornadogenesis that would otherwise be impossible to document because they take place on time scales too short to measure with conventional radars. During the past decade we have been using a mobile, phased array, X-band Doppler radar from the Naval Postgraduate School and a mobile, mechanically scanning, polarimetric, X-band, Doppler radar from the University of Oklahoma to make measurements during annual spring field experiments in the Plains of the U. S. In this talk I will summarize what we have learned about the following aspects of tornado behavior: (1) the origin of tornadogenesis in supercells from the perspective of the Tornadic Vortex Signature (TVS); (2) the behavior of sub-tornado-scale vortices in a violent, multiple-vortex tornado (El Reno, OK – 31 May 2013); and (3) the behavior of polarimetric signatures such as the Tornado Debris Signature (TDS) and the ZDR column. Experiments in retrieving the wind field in supercells by tracking reflectivity and other miscellany may also be discussed if time permits.
Mar 15 --- Dr. Susan Lozier (Duke University)
"A 21st Century Look at the Global Ocean Conveyor Belt"
In 1800 Count Rumford ascertained the ocean's meridional overturning circulation from a single profile of ocean temperature constructed with the use of a rope, a wooden bucket and a rudimentary thermometer. Over two centuries later, data from floats, gliders and moorings deployed across the North Atlantic has transformed our understanding of this overturning circulation, popularly termed the ocean 'conveyor belt'. While Rumford appreciated the role of the ocean's overturning in redistributing heat, today we understand the crucial role that this circulation plays in sequestering anthropogenic carbon dioxide in the deep ocean. In this talk I will discuss our current understanding of the ocean's overturning circulation and what we currently do and don't understand about the mechanisms controlling its temporal change.
Mar 22 --- Dr. Peter Hamilton (Leidos, Inc. (retired) / North Carolina State University)
"New Results from Observations of the Deep Gulf of Mexico Circulation"
A broad overview of the results from two recent major field studies in the Gulf of Mexico will be given. In the first, arrays of moorings and PIES were deployed for 2.5 years in the US and Mexican Loop Current (LC) regions of the eastern basin to observe LC mesoscale variability and LC eddy separations. The second study deployed 122, 1500-dbar and 37, 2500-dbar RAFOS floats, as well as 7, APEX CTD/Optical floats, profiling to 1500 m, over four years, in both eastern and western basins, to observe circulation processes throughout the deep Gulf. In the eastern basin, major results include the transfer of substantial eddy kinetic energy (EKE) to the lower layer (>1000 m) through baroclinic instability of the southward flowing limb of an extended LC. The deepening east-side troughs, caused by amplifying baroclinic instabilities, effect the LC eddy detachments and separations. Float trajectories showed the formation of a deep anticyclone under an actively extending LC. Observations also indicate that after a LC eddy separation, deep EKE dissipates rapidly in the eastern basin through westward propagating topographic Rossby waves (TRW) that feed a deep westward flowing boundary current along the escarpments of the northern continental slope. In the western basin, mean flows are more dominant portion of the total KE than in the east. The anticlockwise narrow boundary current hugs the deep escarpments, and is relatively continuous from south of the Mississippi delta, through the western Mexican slope, and around Campeche Bay, to the northern Campeche bank. Distinct from the boundary current is a large-scale cyclonic gyre in the deepest part of the western basin. Floats indicate that deep transfer between basins is limited in that few of the floats, deployed in the east, surfaced in the west after 630 days, and vice-versa. No RAFOS floats were observed to exit the Gulf through the Yucatan Channel.
Mar 29 --- Naresh Kumar (UM Medical School)
"Personal Real-time Exposure Using Cellphone Integrated SEnsor (PRECISE)"
Naresh Kumar, Sung Jin Kim, Diego Palacios, Joshua Krstic, and Allen D. Chu
One-quarter of the disease/disability burden can be attributed to environmental conditions (WHO 2006). While we have made great strides in characterizing an individual’s genotypes and phenotypes, it has been difficult to characterize and quantify an individual’s personal exposure due to the lack of location- and time-specific environmental measurement. A long-term mission of the University of Miami PRECISE (Personal Real-time Environmental Exposure using Cellphone Integrated SEnosors) is to provide patients (researchers, decision-makers and healthcare providers) with the concentrations of multiple gaseous, particulate and organic air pollutants and their associated personalized (or individual specific) risks in real time. Testing and validation of a portable sensor and a hybrid approach that can quantity time- and location-resolved exposure to gaseous and particulate air pollution is first critical step. To address this gap, we have developed a portable sampler that records gaseous and particulate air pollution and stream these data to a secure server in real-time through cellphones or WiFi. The manufacturing cost of the instrument is < $750/unit. This sampler can also be mounted inside home, on a car and can be carried by study participants.
We have also developed a hybrid approach to estimate location specific concentration of fine particulate on a given day anywhere in the global cities. This approach capitalizes on satellite remote sensing, local time-space Kriging (an optimal interpolation technique) and in-situ monitored data to develop region-specific empirical model to quantify ambient PM2.5 estimates at 2 km spatial resolution, and then employ local-time space Kriging to impute estimates at any given location and day. Our portable sensor and hybrid approach together offer an unprecedented opportunity to quantify personal exposure to air pollution in real time and also changes in exposure due to changing meteorological conditions. Not only does this formulate bases for identifying personal health risk (including asthma, COPD, and other cardiopulmonary diseases) associated with the short- and long-term exposure to the mixture of air pollutants, needed to engage individuals in avoidance behavior but also quantify the burden of disease associated with extreme-weather mediated changes in personal and regional air pollution exposure.
Reference: WHO, Preventing disease through healthy environments - towards an estimate of the environmental burden of disease, 2006, World Health Organization: Geneva, Switzerland.
Mar 30 (Special seminar: SLAB, 3:00 pm) --- Dr. Kristofer Döös (Stockholm University)
"The Hydrothermohaline Circulation and the Water Mass Transformations in the Atlantic Ocean in a Lagrangian Framework"
The thermohaline circulation of the ocean is compared to the hydrothermal circulation of the atmosphere. The oceanic thermohaline circulation is expressed in potential temperature–absolute salinity space and comprises a tropical cell, a conveyor belt cell, and a polar cell, whereas the atmospheric hydrothermal circulation is expressed in potential temperature–specific humidity space and unifies the tropical Hadley and Walker cells as well as the midlatitude eddies into a single, global circulation. The oceanic thermohaline streamfunction makes it possible to analyse and quantify the entire World Ocean conversion rate between cold–warm and fresh–saline waters in one single representation. Its atmospheric analog, the hydrothermal streamfunction, instead captures the conversion rate between cold–warm and dry–humid air in one single representation. It is shown that the ocean thermohaline and the atmospheric hydrothermal cells are connected by the exchange of heat and freshwater through the sea surface. The two circulations are compared on the same diagram by scaling the axes such that the latent heat energy required to move an air parcel on the moisture axis is equivalent to that needed to move a water parcel on the salinity axis. Such a comparison leads the authors to propose that the Clausius–Clapeyron relationship guides both the moist branch of the atmospheric hydrothermal circulation and the warming branches of the tropical and conveyor belt cells of the oceanic thermohaline circulation.
Apr 05 (Special location: MSC343) --- Yu Cheng (1-hour MPO student seminar)
"Agulhas Leakage Variability in a Coupled Climate System: Controls and Responses"
Apr 12 --- Lucas Laurindo (1-hour MPO student seminar)
"On the Air-Sea Exchange of Mechanical Power: A Multi-Scale Assessment Using Satellite and Drifter Observations"
There is increasing evidence in support of the key role of air-sea coupling at the ocean mesoscales in regulating the air-sea exchange of mechanical power, as well as affecting the evolution and propagation of ocean eddies. The coupling arises from the dependence of wind stress on surface ocean currents and on sea surface temperature (SST), and while recent regional modeling studies are converging on the conclusion that the current-driven coupling reduces the wind work rate on the general ocean circulation and have a net damping effect on the oceanic eddy field, they diverge on the role of SST on ocean energetics. Furthermore, currently available observational assessments, based on regularly-gridded altimeter-derived geostrophic velocity fields, indicate that time-dependent fluctuations in the ocean and the atmosphere respond for only about 5% of the globally-integrated mechanical power flux; a result at odds with the strong feedbacks of air-sea coupling to ocean dynamics implied by numerical experiments.
The general objective of this study is to estimate the relative contribution of the current and SST-driven coupling to the air-sea exchange of mechanical power at global scales, using observational data. The proposed investigation strategy is two-fold, first involving a spectral analysis of the coupling between SST and 10-m wind speed (w), resolved by satellite radiometers and scatterometers, in terms of their magnitude squared coherence and cross-spectral phase angle along the frequency and zonal wavenumber domains. After removing large-scale fluctuations in SST and w via high-pass filtering, the coherence in frequency domain is used to calculate transfer functions for the spectral linear response of w to mesoscale SST fluctuations, which are evaluated in physical space using SST data. In a second phase, to circumvent the caveats of altimeter data, concurrent observations from ocean drifters and scatterometers are used to estimate the contribution of time-mean, seasonal, and time-dependent components of oceanic and atmospheric motions to the air-sea flux of mechanical power. Near-surface velocities from ocean drifters and the estimated SST-induced anomalies in w are used to isolate the influence of currents and SST effects in the wind stress bulk formulation, allowing evaluating their impacts to the diagnosed components of the power flux.
Preliminary results reveal that SST-induced modifications in w occur along a broadband continuum in both frequency and zonal wavenumber domains, with dispersion characteristics compatible with either 1st mode baroclinic oceanic Rossby waves or propagating nonlinear ocean eddies, and can explain up to 30% of the wind speed variance at wavelengths between 100 and 1000 km at the latitudes of high eddy kinetic energy (EKE) ocean systems. Regarding the effects of mesoscale air-sea coupling to the mechanical power flux, estimates using drifter and scatterometer data indicate that time-dependent fluctuations in the ocean and the atmosphere have a net negative contribution of about 0.07 terawatts, or about 12% of the globally-integrated wind power input to ocean general circulation, thus constituting a non-negligible sink of oceanic kinetic energy. Explicitly removing the dependence of wind stress on ocean currents, however, produces a positive power input of 0.10 terawatts via the time-dependent components, suggesting that other mechanisms can also regulate the air-sea power flux. The next steps of this research will determine if the SST-driven air-sea coupling is one of those mechanisms, and quantify its contribution.
Apr 13 (Special seminar: SLAB, 3:00 pm) --- Dr. Susanne Lehner (German Aerospace Center DLR)
"Measurement of Sea Surface Parameters Using the TerraSAR-X Satellite"
High resolution Synthetic Aperture Radar (SAR) images of the TerraSAR-X satellite are used in order to investigate the spatial characteristics of the sea surface. With a SAR the roughness of the sea surface can be determined and used to measure parameters like the wind field, sea state and currents over an area of up to 100 km x 100km. This can information be used to derive related parameters like underwater bathymetry and parameters of internal waves. The high resolution data TS-X are of particular interest in areas of high wind field and ocean wave variability, like hurricanes or local storm systems, in coastal areas with rapidly changing bathymetry or currents and near the sea ice boundary. We investigate coastal ocean wave fields and analyse the variability of sea state parameters derived from images acquired by the TerraSAR-X satellite (TS-X). A new empirical algorithm to derive the sea state parameters is discussed. We analyse the SAR derived sea state parameters including significant wave height to investigate shoaling , refraction and local variability of the parameters due to wind gusts and can thus give an assessment of model performance in coastal areas. Examples from typhoon Megi and hurricane Sandy are shown. We further present examples of spatial wave field parameters obtained from a TerraSAR-X StripMap swath in the southern Beaufort Sea near the ice edge. The results are compared to current state-of-the-art implementation of spectral wave prediction models. Overall, good agreement is observed, and limitations of the remote sensing algorithm and the wave model are highlighted. Examples from d the fall 2016 cruise of the research vessel Sikuliaq the interaction between ocean waves and sea ice is analysed.
Apr 19 --- Johna Rudzin (1-hour MPO student seminar)
"An Assessment of the Caribbean Sea's Upper Ocean Influence on Air-Sea Interaction During Tropical Cyclone Passage"
The unique characteristics of the Caribbean Sea’s upper ocean are investigated to understand its influence on air-sea processes during tropical cyclones (TC). The three-dimensional temperature, salinity, and velocity structure of both the Caribbean Sea and a large anticyclonic eddy are measured via aircraft expandable instruments during an aircraft ocean survey over the eastern Caribbean Sea. The observations focus on the differences between the upper ocean in the eddy and the background flow, and compare them with the near-by Gulf of Mexico. This includes analyses of the barrier layer, upper ocean stratification, temperature and salinity anomalies, and eddy origin. Secondly, air-sea fluxes during Caribbean Sea TC events are estimated and compared with respect to upper ocean thermal and haline variability. Moisture and heat fluxes are compared to ocean heat content and sea surface temperature (SST) to understand if ocean variability plays a role in enhancing air-sea flux, independent of wind speed. Additionally, an isothermal layer heat budget is estimated in attempt to quantify the dominant upper ocean processes that affect air-sea exchanges during TCs. Upper ocean and atmospheric parameters along the TCs track are compared to understand their temporal relationship with each other. Finally, idealized temperature and salinity profiles that are representative of the Caribbean Sea ocean regimes are used to understand how thermal structure, the inclusion of salinity, and vertical salinity gradient play a role in the upper ocean response during TCs. Preliminary results of one-dimensional mixed layer model experiments will be presented that highlight how upper ocean vertical structure in each scenario dictates SST response.
Future work consists of investigating the interactions between Hurricane Ivan (2004), the upper ocean, and the atmospheric boundary layer during the storm’s passage through the Caribbean Sea using the Weather Research and Forecasting model (WRF) with a simple ocean mixed layer and a fully coupled ocean-atmospheric model. Several numerical simulations using WRF and the Coupled-Ocean-Atmospheric-Wave-Sediment Transport (COAWST) model will be conducted to understand the Caribbean Sea’s upper-ocean response during Hurricane Ivan (2004).
Apr 20 (Special seminar: Auditorium, 3:00 pm) --- Dr. George Haller (Institute for Mechanical Systems, ETH Zürich)
"Objective Eulerian Coherent Structures in Fluids"
Short-term variability in coherent features of unsteady fluid flows is of prime interest in fields ranging from flow control through environmental assessment to search and rescue operations. Available methods for the identification of the instantaneously most influential flow structures, however, are generally frame-dependent and heuristic, which limits the reliability of the results they provide. In this talk, we discuss a rigorous global variational theory of objective Eulerian Coherent Structures (OECSs), which uncovers the correct instantaneous material skeleton of an unsteady fluid flow in a frame-invariant fashion. We show applications to detecting unsteady flow structures objectively in satellite-based and radar-inferred ocean surface velocity fields. We find that these structures remain generally hidden to traditional, non-objective Eulerian flow analysis.
Apr 26 --- Dr. Eileen Hofmann (Old Dominion University)
May 17 (Special time: 3:30 pm) --- I-Kuan Hu (1-hour MPO student seminar)
September 13 --- Xinfeng Liang (USF)
October 11 --- Dr. Lars Hole (Norwegian Meteorological Institute)