Ocean Sciences

COMPASS (Combined OCE MPO ATM Seminar Series) WEDNESDAY

FALL 2017 

(3:00 SLAB Seminar Room, unless stated otherwise)

 

Sep 06 --- Rodrigo Duran (Oregon State University) - CANCELED DUE TO HURRICANE IRMA

"Quasi-Steady Structures Organizing Lagrangian Transport"

Lagrangian transport is a difficult oceanographic problem for which solutions are frequently needed. Sensitivity to initial conditions, to the precision of the velocity field or to the intrinsic variability of a chaotic flow, requires more attention to detail than we are usually able to afford. In a quest to bypass these complications, we ask if it is possible to find structures that evolve slowly relative to Lagrangian timescales, while organizing transport. A relatively simple approach capitalizing on recent advances on the theory of Lagrangian Coherent Structures, is successful in finding such structures. This conclusion is reached by direct comparisons with a model and observations, and indirect comparisons with previous observational and numerical studies.

Work in collaboration with F.J. Beron-Vera and M.J. Olascoaga.

Sep 13 --- Xinfeng Liang (USF) - CANCELED DUE TO HURRICANE IRMA 

"Vertical Redistribution of the Global Oceanic Heat Content"

Observations show that the upper ocean has been warming since the 1970s, and it is usually attributed to global warming that is associated with the increasing concentration of greenhouse gases in the atmosphere. The global ocean is implicitly considered as a passive heat reservoir, and it is assumed that the ocean was in equilibrium with the atmosphere before the anthropogenic global warming had occurred. However, the global ocean is a dynamically active heat exchanger involving processes of various temporal and spatial scales and has a memory of thousands of years. Not only the heat exchange between ocean and atmosphere but the vertical heat flux passing the lower face of the upper ocean contribute to the changes in the observed upper ocean heat content. In this talk, I will present the mean and the bidecadal change of the ocean vertical heat flux as well as the related physical processes from a dynamically consistent and data-constrained ocean state estimate – ECCO (Estimating the Circulation & Climate of the Ocean). Implications of the vertical redistribution of ocean heat on the changes of the upper and deep ocean heat contents, particularly the recently much-debated global warming “hiatus”, will also be discussed.

Sep 25 --- Dr. Alexander Babanin (University of Melbourne), Monday, 1:00 pm

"Metocean Research at the University of Melbourne, Australia"

Metocean research at the University of Melbourne (Australia) will be described. This includes phase resolving and spectral modelling of the waves, wave influences in the atmospheric boundary layer and in the upper ocean ocean, remote sensing of waves and wave climate. As a specific example, role of the waves as a link between the ocean and atmosphere will be discussed. It is rapidly becoming clear that many large-scale geophysical processes are essentially coupled with the surface waves, and those include weather, tropical cyclones, climate and other phenomena in the atmosphere, at air/sea and sea/land interface, and many issues of the upper-ocean mixing below the surface. Besides, the wind-wave climate itself experiences large-scale trends and fluctuations, and can serve as an indicator for changes in the weather climate.  In the presentation, we will discuss wave influences at scales from oceanic turbulence to climate, on the atmospheric and oceanic sides.

Biography - Alexander V Babanin is Professor in Ocean Engineering at the Department of Infrastructure Engineering of The University of Melbourne, Australia. Qualifications: BSc (Physics), MSc (Physical Oceanography) (Lomonosov Moscow State University, Russia), PhD (Physical Oceanography) (Marine Hydrophysical Institute, Sebastopol, Russia). Worked as a Research Scientist in the Marine Hydrophysical Institute, as an academic at the Australian Defence Force Academy, Canberra, The University of Adelaide, South Australia, Swinburne University of Technology, Melbourne. Areas of expertise, research and teaching, are wind-generated waves, maritime and coastal engineering, air-sea interactions, ocean turbulence and ocean dynamics, climate, environmental instrumentation and remote sensing of the ocean. These include extreme Metocean conditions, from tropical cyclones to Arctic and Antarctic environments. ~250 career total publications.

Sep 27 --- Dr. Shane Elipot (RSMAS)

"Observed Agulhas Current Sensitivity to Interannual and Long-Term Trend Atmospheric Forcings"

It is found that 29% of the interannual variance of Agulhas transport can be linearly related to atmospheric patterns of variability over the southern hemisphere. The volume transport of the Agulhas Current is quantified by a 24-yr (1993-2016) proxy constructed using satellite altimetry and in situ data, and the atmospheric data are obtained from reanalysis products. The two leading modes of atmospheric variance, each explaining 5\% of the interannual variability of the Agulhas Current, can be likened to a tropical Indo-Pacific mode, strongly correlated to ENSO, and a subtropical-subpolar mode, strongly correlated with the SAM. ENSO alone can explain 11.5% of Agulhas transport variance, yet SAM alone has no significant correlation. The remaining four atmospheric modes are not related to common climate indices and together they explain 19% of Agulhas variability, describing a decadal mode of amplitude 10 Sv. Within the complex pattern of these modes, a region of positive wind stress curl directly over the larger Agulhas system is surmised to spin up a regional recirculation which strengthens the Agulhas transport. In previous studies using reanalyses and climate models it has been suggested that the Agulhas Current is intensifying in response to a strengthening and poleward shift of the Westerlies, expressed by a positive trend in the SAM. Here, we find that the Agulhas proxy has no significant trend, as previously shown, and that, assuming the same sensitivity as its interannual variability, the increase in SAM over the past 24 years does not lead to a significant trend in Agulhas Current transport.

Oct 04 --- Dr. Brian Mapes (RSMAS)

"Mesoscale Momentum Flux in a 7 km Atmosphere Model: Global Survey, Provenanced Cases, and new free Software for such Problems"

A two-year global nonhydrostatic atmosphere “nature run” simulation (G5NR) at 7km resolution is queried for one of its most unique strengths: What is the vertical momentum flux (u’w’ and v’w') by explicit air motions in the mesoscale (7-444 km) scale range? After motivating this classic question, especially in light of the hypothesis that organized convection can act as “negative viscosity” through upgradient flux, we address it comprehensively with the data. A global climatology indicates that these motions overall act as normal positive viscosity (damping the shear kinetic energy SKE), except perhaps for some grid points with steep topography and the associated gravity (internal) waves. However, many individual cases of positive SKE tendency are also seen. We drill down into space-time hyperslabs of full-resolution data for selected situations, to lay bare the nature of the calculation and the phenomena involved. Tropical cyclones are especially prodigious in producing convection-momentum interactions, of both signs. Finally, I will give a brief introduction to our semi-professional free scientific-visual software package for such "drilling down” activities (called DRILSDOWN), in hopes of inspiring some test users.

Oct 11 --- Dr. Lars Hole (Norwegian Meteorological Institute)

"Modeling and Observations of Oil Drift in the Northern Gulf of Mexico"

The presence of both shelf and open sea dynamics make the Northern Gulf of Mexico (NGoM) a topographically and dynamically complex study area, in the presence of intense oil exploration. Interactions of the Mississippi River plume and the Loop Current system were found important on the transport and fate of oil during the DeepWater Horizon (DWH) incident. An open source Lagrangian oil drift code, OpenDrift, has been used to simulate real oil spills in NGoM, such as the DWH in 2010 and ongoing leaks from the Taylor Energy platform. OpenDrift is developed at the Norwegian Meteorological Institute, is coded entirely in Python and is available at github.com. It is coupled to the NOAA oil chemistry database with more than 1000 oil types and is now the main model for oil spill preparedness and search and rescue operations in Norway. In the cases  presented here, high resolution HYCOM simulations (from Univ. of Miami) with daily river discharge is used as forcing, together with wind and wave forecasts from ECMWF (European Center for Medium-Weather Forecast). We focus on the DWH spill and observations around the Taylor platform from 2017 (including drifter data and drone surveillance). Simulations are initiated from NOAA shape files and point sources. The effect of using two different oil droplet spectra formulations is also discussed.

Oct 18 --- Dr. Viviane Menezes (WHOI) 

"Impacts of the Wintertime Westward Mountain-Gap Wind Jets on the Red Sea Eastern Boundary Current"

The Red Sea Overflow Water (RSOW) is one of the most saline water masses of the global oceans. It is formed in the northern Red Sea as part of the Red Sea Overturning Circulation. The RSOW is exported to the Indian Ocean and affects both adjacent and remote areas at intermediate depths. Its salty signal has been found as far as the southern tip of Africa and also off western Australia, and may even contribute to the Indo-Atlantic water exchange through Agulhas eddies, possibly being a component of the global overturning circulation. It is believed that maximum RSOW production occurs during the boreal winter as a result of intense evaporation and surface cooling, especially under extreme meteorological conditions. One of these conditions is the onset of the wintertime mountain-gap wind jets along the northern Red Sea eastern boundary. According to model simulations, this region is dominated by a surface poleward Eastern Boundary Current (EBC) that becomes cooler and saltier as it moves northward due to strong air-sea fluxes. In the present work, we characterize the wintertime mountain-gap wind jets and investigate their effects of on the EBC through analysis of in situ observations from a heavily instrumented WHOI air-sea interaction mooring deployed between 2008-2010, Satellite Sea Surface Temperature from the Multi-scale Ultra-high Resolution (MUR) product, QuikSCAT satellite data, and 1/12 HYCOM Reanalysis outputs. We show that during westward wind jet events the eastern boundary becomes cooler and saltier (denser) than usual, the mixed layer deepens and the EBC signature disappears from SST images. Analyses of terms in the mixed-layer temperature equation during these events indicate that the cooling is dominated by both heat loss and entrainment.

Oct 25 --- Joaquin Blanco (1-hour student seminar) TBA

Nov 01 ---  Graham Cook, TBA

Nov 02 --- Dr. Thomas Wahl (University of South Florida)

Nov 08 --- Rodrigo Duran (Oregon State University)

"Quasi-Steady Structures Organizing Lagrangian Transport"

Lagrangian transport is a difficult oceanographic problem for which solutions are frequently needed. Sensitivity to initial conditions, to the precision of the velocity field or to the intrinsic variability of a chaotic flow, requires more attention to detail than we are usually able to afford. In a quest to bypass these complications, we ask if it is possible to find structures that evolve slowly relative to Lagrangian timescales, while organizing transport. A relatively simple approach capitalizing on recent advances on the theory of Lagrangian Coherent Structures, is successful in finding such structures. This conclusion is reached by direct comparisons with a model and observations, and indirect comparisons with previous observational and numerical studies.

Work in collaboration with F.J. Beron-Vera and M.J. Olascoaga.

Nov 15 --- Ryan Kramer (1-hour student seminar) TBA

Nov 22 --- TBA

Dec 06 --- Rafael Goncalves (1-hour student seminar) TBA

Apr 11 --- Dr. Colwell