COMPASS Wednesday

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COMPASS Wednesday
COMPASS WEDNESDAY

Combined OCE MPO ATM Seminar Series

FALL 2019
Wednesdays at 3:00 pm, Seminar Room SLAB 103 (unless stated otherwise)

Aug 21: NO SEMINAR (room not available)

Aug 28: Dr. Harry DeFerrari
Professor Emeritus, Department of Ocean Sciences, RSMAS

Sixty Years of Ocean Acoustics Research and Academics at the University of Miami
Recording Available at COMPASS ON DEMAND

Throughout the cold war and for decades after, a top priority of the US Navy has been Anti-Submarine Warfare – ASW. The Sound Surveillance System – SOSUS, used for the underwater acoustic tracking of Soviet submarines over the world's deep ocean basins, and US submarine silencing programs were two vast classified undertakings with a cost of a significant fraction of the country's GNP. Both programs required continuing evolution in the understanding of underwater acoustics, especially sound transmission though a randomly fluctuating ocean. To that end, ONR sponsored research and academic programs at several universities and research labs around the country. Research was both basic and applied, and the academic programs produced MS and PhD degrees in ocean acoustics. One of these research program at the University of Miami, called project MIMI, led to the major discovery of phase coherent sound transmission and a direct observable relation between oceanographic and acoustic variations. It can be argued that these results set the course of research in underwater acoustics for the basic research community for the next fifty years. In this presentation, the ocean acoustics research and academic programs of RSMAS are reviewed, from the early days of project MIMI to the present. More than 60 graduate degrees have been awarded with research focus on ocean acoustics. While SOSUS has become obsolete, the basic research program lives on. The understanding of ocean acoustics continues to evolve. Concerns about the effects of manmade sounds on marine mammals and the geo-acoustic interaction of sound with the ocean bottom in shallow oceans are new drivers. The digital revolution has enabled new compact experimental instrumentation making possible experiments in most all of the world's oceans. Numerical methods and computational methods have advanced propagation modelling leading to new understanding.

Sep 04: NO SEMINAR (moved to Sep 11 because of Hurricane Dorian)

Sep 11: Dr. Milan Curcic
Department of Ocean Sciences, RSMAS

Revised Estimates of Ocean Surface Drag in Strong Winds
Recording Available at COMPASS ON DEMAND

We revisit the momentum budget approach to estimating the air-sea drag coefficient in hurricane-force winds. To bridge the gap between extremely young windsea in the laboratory and the well-developed sea state in the field, we measure the drag coefficient in strong winds with and without mechanically generated background waves. We identify an error in the analysis of previously published drag estimates, and present the corrected data. Drag estimates from new experiments, using momentum budget and eddy-covariance methods in wind-only conditions, agree with field measurements in low-to-moderate winds, and previous laboratory measurements in hurricane-force winds. We find drag coefficient saturation at 2.6∙10–3 and U10 ≈ 25 ms–1, in agreement with previous laboratory results. However, introducing a background wave field increases the drag coefficient beyond the previously established level of saturation, suggesting that the wind-only laboratory studies may be underestimating the drag coefficient. The drag saturation is correlated with the limit in the wave development. Our results suggest that the drag coefficient estimates in the laboratory are largely dependent on the level of wave development.

Sep 18: Dr. Josefina Olascoaga
Department of Ocean Sciences, RSMAS

Observation and Quantification of Inertial Effects on the Drift of
Floating Objects at the Ocean Surface
M.J. Olascoaga, F.J. Beron-Vera, P. Miron, J.Trinanes, R. Lumpkin, G.J. Goni, and N. Putman
Recording Available at COMPASS ON DEMAND

A series of field experiments consisting in deploying and satellite tracking buoys of varied sizes and buoyancies have been carried out in the North Atlantic to test the importance of inertial effects, i.e., those due to finite size and buoyancy, on their drift. We show that they indeed are important and that a recently proposed Maxey-Riley theory for surface ocean inertial particle dynamics describe them with accuracy.

Sep 25: Dr. Natalie Perlin
Department of Atmospheric Sciences, RSMAS

A Regional Coupled Model for Studies of Mesoscale Air-Sea Interaction
in the Southern Ocean
Recording Available at COMPASS ON DEMAND

Our study presents a regional high-resolution atmosphere-ocean coupled model with a realistic atmospheric component and a semi-idealized oceanic model of a zonal flow, designed for studies of the atmosphere-ocean interactions at the scales from 10 to several hundreds of kilometers. The atmospheric model consisted of two nested domains: the inner domain fully coupled with the ocean model, and the outer domain one-way coupled with the observed SST. Two 2-year simulations are discussed here: one in which the oceanic isopycnals are steep and ocean currents are strong ("Strong Currents" or SC) and another with less steep isopycnals and weaker currents ("Weak Currents" or WC). Simulated mesoscale variability occurs on a wide range of spatial scales, and we distinguish large-mesoscale (hundreds of kilometers and shorter) and small-mesoscale (tens of kilometers and shorter) anomalies in these studies. Relationships between atmospheric variables and SST are studied using temporal correlations and coupling coefficients, and for both large-mesoscale and small-mesoscale anomalies. Consistent with the Vertical Mixing Mechanism (VMM), which implies an acceleration of winds over warm SST anomalies, we find significant positive correlation between large-mesoscale anomalies in the following pairs of variables: equivalent neutral stability (ENS) 10-meter winds and SST, wind stress and SST, wind stress divergence / curl, and SST along-wind / cross-wind gradients. The temporal correlations were smaller for the small-mesoscale anomalies. The correlation coefficients were also higher for the SC region, but the corresponding coupling coefficients were higher for the WC region. Among all pairs, the coupling coefficients for the ENS wind anomalies and SST anomalies were found to be most robust. Coupling coefficients for the wind stress also vary in time and show a nearly linear dependence on the ENS wind speed, whereas the coupling coefficients for the ENS wind and SST have a less obvious response to the ENS winds. The reported variability in these coupling coefficients indicates a complex, nonlinear relationship between the wind and SST anomalies. The relative importance of the Pressure Adjustment Mechanism was studied in both the WC and SC domains, using a correlation between the surface pressure Laplacian and ENS wind convergence.

Oct 02: Dr. John van Leer
Department of Ocean Sciences, RSMAS

Pathways to Negative Emissions
Recording Available at COMPASS ON DEMAND

After three decades of increasingly dire pronouncements by the IPCC and numerous national climate science bodies, which seem only to result in procrastination, disruptive movement toward significant emissions reduction has begun. The IPCC has set forth emissions reduction targets needed to limit global temperature increases to 1.5°C above preindustrial levels. Changes in international financial attitudes are beginning, exemplified by the global divestment movement. The DRAWDOWN project has given concrete estimates of carbon emission reductions, sequestrations and net costs, for each of 80 fast ramping solutions. Bi-partisan legislation has emerged on Capitol Hill this year, which prices carbon emissions aggressively enough to exceed the US Paris commitments, even in the event of complete US withdrawal from the accord. Additional motivation has recently been provided by Fridays For Future school strikes which totaled 4 million students globally this September 20th.

Oct 09: NO SEMINAR

Oct 16: Dr. Jörg Imberger
Adjunct Professor, Department of Ocean Sciences, RSMAS

The Health of the Swan River Estuary and the State of Water in Australia
Recording Available at COMPASS ON DEMAND

Western Australia as a whole is receiving about 40% more rain than at any time on record, however, in the South West, where Perth the State Capital is located, there has been an  observed 50% reduction of rainfall in the catchments servicing the City with scheme water. These rainfall shifts are attributed, by the governing decision makers, to Global Warming, and the political process has forced the Water Corporation to shift 70% of Perth's water supply to desalination, considerably increasing WA's GHG emissions. An extensive drilling program, by the same authorities, revealed that south of the City there was an additional huge deep groundwater aquifer water resource, conservatively containing about 1000 years of potable water at current usage rates. Further, a series of highly innovative technologies, by Perth inventors, will shortly go to market that will make it possible to service about 80% of household water needs from roof rainwater and storm water, greatly reducing the consumer's dependence on scheme water! Unfortunately, desalination will also do little for the health of the Swan River Estuary that has also been badly impacted by the rainfall reductions. This is because the health of the salt wedge estuary depends directly on being flushed once or twice a year. The water making up this rain originates from the moisture in the air that is swept in from the ocean and pumped inland by trees. Global climate changes account for about 30% of the observed 50% rainfall reduction in rainfall in the South West and vegetation clearing in the 1960's for the remaining 70%. On the east coast of Australia, a similar picture emergences when one examines the disastrous changes in the Murray Darling river basin, where huge fish kills have been observed recently. Clearly, there is an urgent need to carry out a detailed assessment of the water resources of Australia and then implement an appropriate engineering response and not just follow the masses and blame everything on the devil, Global Warming!

Oct 23: NO SEMINAR

Oct 30: Dr. Christine Wiedinmyer
Invited Speaker of the Department of Atmospheric Sciences
CIRES, University of Colorado Boulder

Fires and Their Impacts: From Household Burning to Wildfires
Recording Available at COMPASS ON DEMAND

Fires, including wildfires, prescribed burns, agricultural burning, or residential biomass burning, emit substantial amounts of particles, reactive trace gases, and longer lived species to the atmosphere on regional and global scales. These emissions and the products from downwind chemical processing degrade air quality, impact regional climate, and contribute to negative human health outcomes. There are many existing efforts to quantify emissions from biomass burning. These take advantage of laboratory and field measurements, remote sensing observations, and various modeling tools. Despite great advances in the ability to identify and quantify emissions from biomass burning, the techniques used to predict emissions and understand their fate and transport in the atmosphere remain uncertain, and the subsequent estimates of the impacts are difficult to assess. This presentation will detail efforts to identify and quantify biomass burning emissions across scales, and highlight their importance and confounding factors in air quality, health, and climate impact assessments. I will give an overview of my past and current biomass burning research, highlighting key uncertainties in our ability to predict biomass burning emissions and their impact and addressing needs for the future.

Nov 06: Samantha Kramer
Department of Atmospheric Sciences, RSMAS
(one-hour MPO student seminar)

Saharan Dust Variability at Miami, Florida
Recording Available at COMPASS ON DEMAND

Saharan dust can be harmful for human health, disrupt hurricane development, change cloud features, affect the atmospheric radiative balance, feed plants and sea life, and is the dominant aerosol in summertime South Florida. A 43-year record of daily dust mass concentrations measured at the Rosenstiel School of Marine and Atmospheric Science indicates large daily, seasonal, and interannual variations. While most of the dust arrives within 5-8 episodes each summer, there is at least trace concentrations of dust every day. Using the in-situ measurements, size-resolved dust measurements, and micropulse lidar-derived dust vertical profiles, we examine daily dust variability and its representation of dust in NASA's Modern-Era Retrospective analysis for Research and Application-Version 2 (MERRA2). After a deeper understanding of dust measurements is established, we shift focus to the transportation process which is driven by potentially predictable atmospheric dynamics. The daily dust mass concentrations from July and August are used to characterize the synoptic conditions most favorable for dust transport. Two key regions are linked with the highest daily dust mass concentrations above Miami: (i) easterly winds over the Tropical West Atlantic (15-25°N, 45-80°W) and (ii) southerly winds over the Florida Peninsula (20-30°N, 75-80°W). Winds within these two regions are enhanced when the North Atlantic subtropical high (NASH) is displaced south and zonally elongated, relocating the western edge over Florida. A dust transport efficiency (DTE), based on the maximum potential for dust to arrive above Miami with limited loss to deposition or mixing, identifies high dust loading cases on the sub seasonal scale. Monthly average DTE values agree well with the monthly dust extremes over the 43-year time span. While seasonal dust loadings have been decreasing over Florida in the past decade, the transport efficiency has been increasing, possibly due to trends in the NASH.

Nov 13: Breanna Zavadoff
Department of Atmospheric Sciences, RSMAS
(one-hour MPO student seminar)

North Atlantic Rossby Wave Breaking and Its Relationship
to European Atmospheric Rivers
Recording Available at COMPASS ON DEMAND

Anticyclonic Rossby wave breaking (RWB) is characterized by the rapid and irreversible deformation of potential vorticity (PV) contours on isentropic surfaces. Despite being the season in which anticyclonic RWB events are most prevalent, no work has focused solely on the variability of these events during the North Atlantic summertime. Using 58 years (1960-2017) of NCEP-NCAR reanalysis data, a climatology of boreal North Atlantic anticyclonic RWB is developed and a multidecadal pattern of intra-basin RWB frequency is observed. Analysis of the large scale dynamics suggest this variability is driven by convectively forced atmospheric responses to Pacific decadal oscillation (PDO) sea surface temperature (SST) anomalies, such that anticyclonic RWB events are favored in the East (West) North Atlantic during PDO+(–). To test this hypothesized relationship, an idealized modeling study is performed using the NCAR Community Earth System Model. Eleven 15-year simulations are run, each using a unique set of prescribed SSTs corresponding to different configurations and phases of the PDO. Preliminary results show that, as hypothesized, more anticyclonic RWB events are recorded in the eastern (western) half of the North Atlantic during PDO+(–). Further analysis is performed to determine how the different PDO+/– signals alter the large scale circulation to drive these frequency changes. Recent studies have found that US West Coast atmospheric rivers (ARs), narrow filaments of high water vapor content that extend thousands of kilometers, are dynamically related to anticyclonic RWB. While ARs occur all over the world, this connection has not been made elsewhere. To determine if this AR-RWB relationship exists over western Europe, 38 years (1980-2017) of MERRA-2 reanalysis data is employed to develop an AR climatology. Of the 578 ARs identified, 73% are related to anticyclonic RWB. Additionally, AR variability is shown to be closely tied to jet stream latitude modulation by the North Atlantic Oscillation (NAO), such that during NAO+(–), the North Atlantic jet is shifted north (south), creating an environment more (less) favorable for anticyclonic RWB and AR landfalls at higher (lower) latitudes.

Nov 20: Kay McMonigal
Department of Ocean Sciences, RSMAS
(one-hour MPO student seminar)

Estimating a Time Series of South Indian Ocean Meridional Heat Transport

The meridional heat transport of the South Indian Ocean is climatically important, with potential impacts to the Atlantic Meridional Overturning Circulation and the Southern Ocean. Historically, ocean heat transport has been calculated using data from cross basin hydrographic sections, which have only been conducted three times in the South Indian Ocean. To assess seasonal variability in meridional heat transport, we are estimating a 25 month time series of heat transport of the South Indian Ocean by connecting high spatial and temporal resolution mooring data at the western boundary (the Agulhas Current) to lower resolution Argo and satellite data across the basin interior. First, we focus on the interior of the South Indian Ocean. Previously observed changes between hydrographic crossings in 1987 and 2002 imply that the gyre has strengthened. However, seasonal variability may be aliased in the inference of multidecadal circulation changes. We use 10 years of data from Argo, satellite altimetry, and an Agulhas Current volume transport proxy to quantify the seasonal variability of the upper 2000 m volume transport. A semi-annual cycle is revealed, with peak-to-peak amplitude of 6.4±3.1 Sv (1 Sv = 106 m3 s1). Seasonal aliasing cannot account for the previously observed gyre strengthening. Next, we quantify the temperature variability and transport of the Agulhas Current at 34°S over a 25 month mooring deployment. Variability in the temperature field is dominated by the core of the current meandering offshore, which increases temperature offshore and decreases temperature near the coast. However, this effect is largely local. The full current temperature transport varies more closely with a broadening and deepening of the current without meandering. In the mean, the current transports 3.6 PW (1 PW = 1015 Watts) southward, confirming that the Agulhas Current plays a dominant role in the full basin heat budget. Assuming a linear relationship between temperature transport and volume transport yields an error of 0.25 PW. 

We are currently combining the methods to estimate a 25 month time series of the heat transport of the South Indian Ocean at 34°S.

Nov 27: NO SEMINAR (Thanksgiving Recess)

Dec 04: Dr. Eric S. Cramer
Florida Institute of Technology, Melbourne, 2008-2015
Center for Space Plasma and Aeronomic Research, University of Alabama, Huntsville, 2015-2017
(Now at Northrop Grumman Aerospace Systems, Melbourne, Florida)

High Energy Atmospheric Physics and the Mysteries of Lightning
over Land and Water

Although lightning is one of the most commonly known and destructive natural phenomena on Earth, it remains poorly understood in terms of the most basic physics. Adding to the mystery has been the discovery that lightning emits X-rays and gamma rays. Terrestrial Gamma-ray Flashes (TGFs) are sub millisecond intense bursts of gamma-ray radiation (up to 40 MeV) associated with thunderstorms and lightning. TGFs have been observed from ground instrumentation, aircraft, and satellites, such as the Gamma-ray Burst Monitor (GBM) onboard NASA Fermi. In addition, I will discuss how TGFs have been observed with the strengthening phase of tropical storm systems and hurricanes. The fact that these lightning related events can affect the upper atmosphere and lower ionosphere has reshaped the scientific field to the study of high energy atmospheric physics. The research done on lightning has thus fused many areas of physics including plasma physics, atmospheric physics, and quantum electrodynamics. This talk will give a review of the field, including my graduate (FIT) and postdoctoral (UAH) theoretical research pertaining to the generation and propagation of TGFs through the atmosphere, as well as current and future satellite missions to study their physical properties. In addition, I will give a summary of rocket triggered lightning and the experimental data that was collected over several summer campaigns in conjunction with Florida Institute of Technology and the University of Florida.

 

Future Semester Preview:

Jan 22 (4:00 pm): Dr. Rana Fine
Department of Ocean Sciences, RSMAS

Jan 29 (Auditorium): Dr. Pavel Berloff
Imperial College London, UK

Some Novel Approaches for Parameterizing Mesoscale Eddies

This talk focuses on some new approaches for parameterizing oceanic mesoscale eddy effects for use in non-eddy-resolving and eddy-permitting general circulation models. The context is provided in terms of discussing the existing ideas and problems with their realizations. A specific example of eddy-rich eastward jet extensions of western boundary currents and their adjacent recirculation zones is considered in the classical multi-layer quasigeostrophic model of the wind-driven midlatitude circulation. First, the key dynamical mechanism operating in the eddy-resolving model and maintaining the eastward jet is identified as the "eddy backscatter", which is based on persistent and positive time-lag correlations between the transient part of the nonlinear eddy forcing and the large-scale flow response. Second, this mechanism has to be ultimately parameterized, and discussing how this can be done is the main part of the talk. We will systematically (but not too technically) discuss four different, novel parameterization approaches, which are complimentary to the existing ones: (1) direct stochastic forcing (DSF); (2) implicit stochastic footprints (ISF); (3) data-driven eddy emulations (DEE); and (4) local eddy amplification (LEA). The DSF approach explicitly adds statistically constrained stochastic forcing to the coarse model. The ISF approach imposes statistically constrained stochastic forcing on an intermediate-complexity eddy-resolving model, obtains its nonlinear response in terms of the coarse-grained footprint, and then imposes local footprints on the coarse model. The DEE approach emulates eddies via multi-layer nonlinear regression, then feeds them to the deterministic eddy forcing operator coupled to the large-scale flow fields, and adds the resulting forcing to the coarse model. The LEA approach interactively identifies eddies and amplifies them locally and in a simple way – this is the simplest and also most practical approach for the present state of modelling. Relative strengths and weaknesses of these approaches, as well as some future developments will be also discussed.

Feb 12: Dr. Levi Cowan
Invited Speaker of the Department of Atmospheric Sciences
Florida State University, Tallahassee

Mar 04 (Auditorium): Dr. Everette Joseph
SEEDS and RSMAS / DEIC 2020 Distinguished Lecturer
National Center for Atmospheric Research, Boulder, Colorado