COMPASS Wednesday - Archive

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COMPASS Wednesday

Combined OCE MPO ATM Seminar Series

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

Jan 27: Dr. Shane Elipot
Department of Ocean Sciences, RSMAS

A Proposal: Measuring Global Mean Sea Level Changes
With Surface Drifting Buoys
Zoom Recording Available at COMPASS ON DEMAND

Combining ocean model data and in situ Lagrangian data, I show that an array of surface drifting buoys tracked by a Global Navigation Satellite System (GNSS), such as the Global Drifter Program, could provide estimates of global mean sea level (GMSL) and its changes, including linear decadal trends. For a sustained array of 1,250 globally distributed buoys with a standardized design, I demonstrate that GMSL decadal linear trend estimates with an uncertainty less than 0.3 mm yr−1 could be achieved with GNSS daily random error of 1.6 m or less in the vertical direction. This demonstration assumes that controlled vertical position measurements could be acquired from drifting buoys, which is yet to be demonstrated. Development and implementation of such measurements could ultimately provide an independent and resilient observational system to infer natural and anthropogenic sea level changes, augmenting the ongoing tide gauge and satellites records.

Feb 03: Dr. Brian Mapes
Department of Atmospheric Sciences, RSMAS

Pattern and Meaning in Mesoscales
Zoom Recording Available at COMPASS ON DEMAND

Meso means middle, defined indirectly by two things it is not. In the realm of scale, the two poles are an inner scale, set by some foundational process, and an outer scale, set by the whole of the domain or playing field. In between may lie few or many decades of scale. Earth is the ultimate outer scale for Earth science, but sometimes geographical areas (like basins or flow-defined subsets) are a less-inclusive pseudo-closed whole that dominates or constrains its top few parts. Inner scales are a floor at which we discretize nature: a-tomic (uncuttable) atoms in the "mesoscopic" physics of chemistry and nanoscience; cells (from the latin for walled enclosure) in organismic biology; in-dividuals in ecology and social sciences. Discretization puts rungs on humanity's logarithmic ladder for climbing around the sky-high scale abyss, and truly new "fundamental" phenomena can emerge on each. Meteorology and physical oceanography are wonderful data-rich arenas for studying scale, ready to benefit from and contribute to how other sciences wrestle with complexity.

Meso-scales are a realm of pattern, which is harder to get a scientific handle on than the value of numbers or their elementary statistics. Two familiar aspects of pattern we measure are (1) components in orthogonal decompositions like into Fourier or empirical modes, and (2) objects composed of spatially-connected pixels or voxels. Sometimes patterns contain only-temporally contiguous things that still deserve to be called entities (Latin, a thing), such as trains or packets. But there may also be less-familiar "things" out there in the dark. New tools in informatics (under the heading of machine learning) are exploding our ability to seek and define new aspects of pattern. Those "less-familiar things" can be hunted agnostically, sought out by what they do rather than what they are, even if they are needles encrypted in a haystack of noise. Our visual cortex may not be the universe's best engine of pattern detection any more! There's a new diagnostic quantity in town: information. Our further measure of information's meaning is often its time coherence: the signature of causality, the gateway to prediction.

How can we better define and discern the meaning (or importance) of patterns and their aspects and features? Some meso-baubles may be just a kind of random noise, while some surely deserve Proper Names (like a hurricane). In general, the important and unimportant aspects of pattern are mixed up, and our fluid science's job is to decode the mess, for various purposes. I plan to start up a dialogue with all interested in these information-based ways of thinking and analyzing data, in a reading group to be organized on the new email listserv RSMAS-INFORMATICS... after finishing the writing of this seminar.

Feb 11 (Thursday): Dr. Philippe Miron
Department of Atmospheric Sciences, RSMAS

Transition Pathways of Marine Debris and the Stability of Garbage Patches
Zoom Recording Available at COMPASS ON DEMAND

Tons of plastic debris gets released into the ocean every day, and most of it accumulates within garbage patches in the center of each ocean. The most infamous one, known as the Great Pacific Garbage Patch, is in the North Pacific Ocean. In a recent publication, we explored debris pathways from the coasts to the garbage patches using transition path theory (TPT), as well as the relative strengths of different subtropical gyres in the ocean and how it influences long-term accumulation of debris. The TPT analysis was applied on a pollution-aware Markov chain model constructed from trajectories of satellite-tracked undrogued buoys from the NOAA Global Drifter Program. Directly connecting pollution sources along coastlines with garbage patches of varied strengths, the unveiled pollution routes represent alternative targets for ocean cleanup efforts. Among our specific findings we highlight: constraining a highly probable pollution source for the Great Pacific Garbage Patch; characterizing the weakness of the Indian Ocean gyre as a trap for plastic waste; and unveiling a tendency of the subtropical gyres to export garbage toward the coastlines rather than to other gyres in the event of anomalously intense winds.


Feb 24: Dr. Anna-Lena Deppenmeier
Climate and Global Dynamics Laboratory, UCAR, Boulder, Colorado

Drivers of Water Mass Transformation in the Eastern Tropical Pacific
and Their Modulation With ENSO
Zoom Recording Available at COMPASS ON DEMAND

Variability of the cold pool of water in the eastern tropical Pacific (the cold tongue) plays a major role in the global climate system. The strength of the cold tongue sets the zonal temperature gradient in the Pacific, coupling the ocean with the atmospheric Walker circulation. This coupling is an essential component of the El Niño Southern Oscillation (ENSO). The cold tongue is supplied with cold water by the equatorial undercurrent that follows the thermocline to the east, transporting cold water towards the surface. As the thermocline shoals, its water is transformed through diabatic processes of water mass transformation (WMT) which allow water to cross mean isotherms. These WMT processes contribute to the maintenance and variability of the cold tongue. We examine WMT in the cold tongue region from a global high resolution ocean simulation with saved heat budget terms. We quantify each individual component of WMT (vertical mixing, horizontal mixing, eddy fluxes, solar penetration), and find that vertical mixing is the single most important contribution in the thermocline, while solar heating dominates close to the surface. We investigate how WMT changes on different time scales, (sub)-seasonal to interannual. During El Niño events vertical mixing, and hence cross-isothermal flow as a whole, is much reduced, while during La Niña periods strong vertical mixing leads to strong WMT, thereby cooling the surface. This analysis demonstrates the enhancement of diabatic processes during cold events, which in turn enhances cooling of the cold tongue from below the surface.


Mar 10: Dr. Isabel McCoy
Department of Atmospheric Sciences, RSMAS

The Power of Ocean Biology:
An Examination of Aerosol-Cloud Interactions in the Pristine,
Biologically Active Southern Ocean and What It Tells Us About Our Future
Zoom Recording Available at COMPASS ON DEMAND

The change in planetary albedo due to aerosol-cloud interactions (aci) during the industrial era is the leading source of uncertainty in inferring Earth's climate sensitivity to increased greenhouse gases from the historical record. Examining pristine environments such as the Southern Ocean helps us to understand the pre-industrial state and constrain the change in cloud brightness over the industrial period associated with aci. Two methods are presented for utilizing observations of Southern Ocean clouds and aerosols to constrain global climate models (GCMs) and advance our understanding of the pre-industrial state. Cloud droplet number concentration (Nd) is used as a direct measure of aci. The hemispheric Nd difference derived from MODIS satellite observations indicates pre-industrial Nd may have been higher and less cooling associated with aci has taken place than previously thought (e.g. radiative forcing associated with aci is constrained to between –1.2 and –0.6 Wm–2). Comparisons with MODIS Nhighlight significant GCM discrepancies in pristine, biologically active regions. Two potentially important aci mechanisms that occur in such regions are identified from recent Southern Ocean aircraft observations: i) production of new aerosol particles through synoptic uplift, and ii) buffering of Nd against precipitation removal by small, Aitken mode aerosols from the free troposphere. Observational comparisons with nudged CAM6 hindcasts show low-biased Southern Ocean Nd is linked to under-production of free-tropospheric Aitken aerosol, driving biases in cloud condensation nuclei number and likely also in composition. These results have important implications for the ability of current GCMs to capture aci in pristine environments and for estimating aci-associated cooling since the pre-industrial.

Mar 17: Shannon Doherty
Department of Ocean Sciences, RSMAS
(one-hour OCE student seminar)

Towards Quantifying Zooplankton Fecal Pellet Contributions
to the Biological Pump
Zoom Recording Available at COMPASS ON DEMAND

Zooplankton fecal pellets are a major contributor to the downward flux of particulate organic matter (POM) in the ocean; however, the contribution of fecal pellets to POM is difficult to quantify. Current estimates often rely on visual identification of fecal pellets to determine their relative input to POM pools. However, these methods only capture fecal pellets that are intact or recognizable and potentially underestimate the contribution of fragmented fecal pellets to POM. First, we define the zooplankton fecal pellet chemical end-member to POM using compound-specific stable isotope analysis of amino acids (CSIA-AA). The amino acids threonine and alanine showed distinct nitrogen isotope patterns that distinguished fecal pellets from zooplankton biomass, phytodetritus, and highly microbially reworked detritus. We then apply the threonine-alanine signature and carbon CSIA-AA tools to a water column profile of POM from Monterey Bay, spanning approximately 5 m to 500 m and three particle size classes: 0.7-20 micron, 20-100 micron, and >100 micron. Strong signatures of fecal pellets appear in the mesopelagic around 200 m, suggesting a flux of large fecal pellets from the surface at night into the mesopelagic during the day. Additionally, we examine the relationships between particle composition, microbial reworking, and diel vertical migration in the mesopelagic between 200 and 500 m. We demonstrate the unique potential for CSIA-AA to quantify fecal pellets in detrital POM pools in future studies and examine remaining questions about fecal pellet CSIA-AA signatures.

Mar 24: Dr. Anthony Didlake
Penn State College of Earth and Mineral Sciences, University Park, Pennsylvania

The Role of Asymmetric Features During Secondary Eyewall Formation
in Tropical Cyclones
Zoom Recording Available at COMPASS ON DEMAND

Secondary eyewall formation is often associated with intensity and structural changes during a tropical cyclone’s evolution. These changes are generally difficult to predict given that the underlying dynamical mechanisms for secondary eyewall formation remain uncertain. Many current hypotheses focus on the axisymmetric projection (or azimuthal mean) of inner core features, but they do not fully explain the role of asymmetric features, such as inner core spiral rainbands. Observations show that these rainbands spiral inward and often coalesce to form the axisymmetric secondary eyewall, but the exact processes of this evolution are not yet fully understood. Here we examine several aspects of rainbands and secondary eyewalls, including their detailed structures and their impact on the overall storm. We investigate airborne observations of inner core convection from several case studies and a composite study, and we also investigate these features using model simulations. These results provide a better understanding of the evolution of inner core convection which can help improve forecasts of intensity and structure in future storms.

Mar 31: Houraa Daher
Department of Ocean Sciences, RSMAS
(one-hour OCE student seminar)

The Southern Hemispheric Response to Ozone Recovery
Zoom Recording Available at COMPASS ON DEMAND

The stratospheric ozone is expected to recover by mid-century with the implementation of the Montreal Protocol and the banning of ozone depleting substances. Previously, the combination of stratospheric ozone depletion over Antarctica and an increase in greenhouse gas emissions led to changes in the Southern Hemisphere climate, such as a poleward shift and intensification of the westerly jet, a poleward expansion of the Hadley cell, a poleward shift of the storm tracks, an increase in sea surface temperatures, and an increase in sea ice melting. As the ozone recovers, however, it is expected that these changes will be weakened or reversed with the ozone and greenhouse gas forces opposing each other. Here, the role of stratospheric ozone recovery in the Southern Hemisphere is analyzed using Community Climate System Model, version 4 (CCSM4) for the Coupled Model Intercomparison Project phase 5 (CMIP5). Multi-member ensembles for three different greenhouse gas emission scenarios are examined to identify the ozone fingerprint in each simulation and to forecast a range of post-ozone recovery climate storylines. It is shown that the westerly jet, Hadley cell, sea surface temperature, and precipitation trends are weakened as the ozone recovers but that these trends heavily depend on the emission levels moving forward into the post-ozone recovery time period. South Africa, a region prone to droughts and precipitation changes, is considered in this study, with a strong east-west rainfall pattern found over the continent. Lastly, the ozone and greenhouse gases are specified independently to determine which forcing has a greater impact on the Southern Hemisphere climate system.




Apr 28: Marybeth Arcodia
Department of Atmospheric Sciences, RSMAS
(one-hour ATM student seminar)

Regional Weather and Climate Impacts from Subseasonal Variability
of Tropical-Extratropical Teleconnections
Zoom Recording Available at COMPASS ON DEMAND

Despite the vast distance between the tropical Indo-Pacific region and the U.S., tropical variability affects Northern Hemisphere weather patterns via teleconnections on many time scales. This talk will discuss the remote impacts from the two dominant sources of subseasonal (2 week to 2 month) and interannual tropical variability: the Madden-Julian Oscillation (MJO) and El Nino Southern Oscillation (ENSO), respectively. The MJO is shown to impact North American rainfall through perturbations in both the upper-tropospheric flow and regional low-level moisture availability. A composite analysis shows that during a particular phase of an active MJO, the extratropical response can considerably enhance or mask the interannual ENSO signal in the U.S., potentially resulting in anomalies of the opposite sign than that expected during a specific ENSO phase. The mechanistic hypotheses of these teleconnections are tested via a dry linear baroclinic model (LBM) to quantify the linearity of MJO and ENSO remote patterns. The use of a dry LBM is motivated by the ability to investigate complex atmospheric phenomena simply by stripping away all nonlinear feedbacks and moisture terms. The role of the background state and its modulation of the extratropical teleconnections are explored based on month, MJO phase, and ENSO phase, revealing that at least part of the subseasonal variability can be captured linearly. To address a higher localized impact factor, statistical techniques are applied to regionalized NOAA flood projections to predict when a particular U.S. coastal city will have a 70% chance of flooding for at least one hour on at least 70 days of the year. We extend the results to analyze six hours of flooding per day, increasing the risk severity of the coastal flooding. This study focuses on flooding events prone to causing property damage and hazardous conditions to make flooding forecasts that are the most impactful.