COMPASS Friday - Archive

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Fridays at 11:00 am, RSMAS Auditorium / Virtual Auditorium


Jan 28: Dr. Akua Asa-Awuku
Department of Chemical & Biomolecular Engineering
A. James Clark School of Engineering, University of Maryland, College Park

When Is Fundamental Cloud Droplet Formation Not So Fundamental?

Aerosols, or particles, emitted into the air have adverse effects for regional air quality and health. In addition, aerosols significantly impact Earth's climate and the hydrological cycle. They can directly reflect the amount of incoming solar radiation into space; by acting as cloud condensation nuclei (CCN), they can indirectly impact climate by affecting cloud albedo. Our current assessment of the interactions of aerosols and clouds is uncertain, and parameters used to estimate cloud droplet formation in global climate models are not well constrained. Understanding the chemical and thermodynamic properties that control the ability of particles to form droplets, CCN activity, and droplet growth are necessary for constraining impacts on particle transport, particle inhalation, the hydrological cycle and uncertainties from the aerosol indirect effect. In this presentation, we discuss and identify fundamental parameters that affect aerosol formation and droplet growth from unique sources and diverse environments.


Feb 11: NO SEMINAR (Recruitment Weekend)

Feb 18: Chelsea Lopez
Department of Ocean Sciences, RSMAS
(one-hour OCE student seminar)

Gelatinous Zooplankton Blooms and Turbulent Fronts
Seasonally Stimulate Deep Carbon Export
Zoom Recording Available at COMPASS ON DEMAND

Marine organic carbon is arguably the crux of global biogeochemical cycling, therefore understanding its complex dynamics is essential as the world around us changes. This seminar focuses on two analyses that shed some light on organic carbon dynamics: 1) the seasonal and interannual variability of total organic carbon (TOC) in the deep northeastern Pacific, and 2) unique carbon export that releases dissolved organic carbon (DOC) beneath well-defined frontal zones that traverse the subarctic and subtropical Pacific. Deep TOC concentrations in the northeastern Pacific were highly variable across seasons as well as between the years 2017 and 2018. Such variability was logically attributed to fluctuating phytoplankton stocks (i.e. spring blooms), indicated by changes in upper-water fluorescence. In 2018, anomalous blooms of gelatinous zooplankton such as salps, larvaceans, and doliolids were linked to exceptionally high export of particles that released DOC during descent to the deep ocean. DOC concentrations are similarly enhanced by deep particle export stimulated instead by two turbulent fronts that zonally traverse the transitional region between the subarctic and subtropical gyres of the Pacific. Export of subjectivity small particles was apparent in the eutrophic subarctic as would be expected, but a unique signature of large particles and elevated DOC concentration was revealed directly beneath the Subarctic Front (∼42°N). A second DOC signature beneath the Northern Subtropical Front (∼34°N) did not coincide with the presence of large particles, but was inferred to be a residue of previous winter export. Both physical and biogeochemical factors such as frontal mixing, nutrient availability and mixed layer shoaling appeared to exert controls on carbon export dynamics within these unique locations.

Feb 25: Dr. Natalie Mahowald
Department of Earth and Atmospheric Sciences
Cornell University, Ithaca, New York

Constraining Atmospheric Microplastics
Zoom Recording Available at COMPASS ON DEMAND

Plastic pollution is one of the most pressing environmental and social issues of the 21st century. Recent work has highlighted the atmospheric role in transporting human-derived microplastics to remote location. Here we use in situ observations of microplastic deposition combined with an atmospheric transport model and optimal estimation techniques to test hypotheses of the most likely sources of atmospheric plastic. Results suggest that atmospheric microplastics are primarily derived from secondary re-emission sources including road, ocean, and soil sources. However, due to limited observations and understanding of the source processes, there are still large uncertainties in source attribution. In the western USA, the dominant sources of microplastic were from roads (84%), the ocean (11%) and agricultural dust (5%). Using our best estimate of plastic sources and modeled transport pathways, most continents were net importers of plastics from the marine environment, underscoring the cumulative role of legacy pollution in contributing to the atmospheric burden of plastic. This effort is the first to use high resolution spatial and temporal deposition data along with different hypothesized emission sources to constrain atmospheric plastic. Parallel to global biogeochemical cycles, plastics now spiral around the globe with distinct atmospheric, oceanic, cryospheric, and terrestrial lifetimes. Though advancements have been made on the manufacture of biodegradable polymers, our data suggest that the non-biodegradable polymers will continue to cycle through the surface Earth. Because of the limited observations and knowledge, there remain large uncertainties in the sources, transport and deposition of microplastics. Thus, we prioritize future research directions for understanding the plastic cycle.


Natalie Mahowald is the Irving Porter Church Professor of Engineering in the Earth and Atmospheric Science Department at Cornell University, and the Co-Leader, Working Group on Reducing Climate Risk for Cornell Atkinson Center for Sustainability. Her research group is focused on understanding feedbacks in the earth system that impact climate change. This includes global and regional scale atmospheric transport of biogeochemically important species such as desert dust, as well as the carbon cycle. Her group look at these issues through a combination of 3-dimensional global transport and climate models, as well as analysis of satellite and in situ data. She received a PhD in Meteorology from MIT, MS in Natural Resource Policy from UMichigan, and she is a fellow of AMS, AGU, and AAAS and has been a lead author on two IPCC reports.


Mar 11: NO SEMINAR (RSMAS Faculty Meeting)

Mar 18: NO SEMINAR (Spring Recess)


Apr 01: Kayla Besong
Department of Atmospheric Sciences, RSMAS
(one-hour ATM student seminar)

Space-Time Blocking Sensitivity to the North Atlantic Oscillation
Zoom Recording Available at COMPASS ON DEMAND

A new perspective of atmospheric blocking is brought to light in this study that considers various analysis techniques and the implications of each on blocking statistics, impacts on weather variables due to blocking events, and the blocking-North Atlantic Oscillation (NAO) relationship. A PV-𝜃 blocking index is used alongside a direction of breaking metric to classify blocking as either cyclonic or anticyclonic based on the Rossby wave breaking occurring at onset. These results are compared against those found using an anomalous geopotential height (AGP) index. It can be seen throughout the study that differing results will be achieved based on which method is applied. Of the largest differences is in the wintertime correlation of blocking with the NAO, with AGP blocking results correlating much more strongly than those found with the PV-𝜃 index. Based on this analysis, it can be concluded that different blocking events are being measured between the two indices. Strengths and weaknesses of each index further suggest that the AGP index is more advantageous for correlation and extreme event analysis and the PV-𝜃, for detecting nosier signals such as a small, potential eastward shift in the NAO. The differences and similarities between blocking index selection, cyclonic or anticyclonic classification, relationship with the NAO, and breakdown into North Atlantic subregions were all considered in further investigation of blocking analysis sensitivity. Specifically, this was extended to impacts on weather variables via composites across all seasons and to blocking duration statistics where little consistency across all comparisons are found.


Lillian Henderson (OCE)
Investigating Photosynthetic and Degradative Effects on Carbon Isotope Ratios
of Particulate Organic Carbon in a Stratified Euphotic Zone

Particulate organic carbon (POC) is produced in the euphotic zone by photoautotrophs. Additionally, heterotrophs contribute to POC and also degrade it as it sinks to deeper depths. Our recent work showed that there is a widespread, significant difference in the stable carbon isotope ratios of POC (δ13CPOC) between the upper (high light) and lower (low light) portions of the euphotic zone in the open ocean. δ13C values of organic carbon can be used to determine food sources of consumers and to interpret changes in the carbon cycle that are preserved in the sedimentary record. Therefore, understanding what mechanisms cause variations in δ13CPOC values within the euphotic zone is vital to interpreting carbon isotopes in these other contexts. Hypotheses include mechanisms involving both photosynthesis and heterotrophs / degradative processes. We measured δ13C values of total POC, chlorophyll, and individual amino acids on particle samples from the open ocean water column at the Bermuda Atlantic Time Series site. Chlorophyll comes only from the photosynthetic community, while total POC and amino acids include material from photoautotrophs, heterotrophs, and degraded material. Thus, we isolated the δ13C signature of the in situ photosynthetic community from those of heterotrophs and degraded POC. The data suggest that differences in δ13CPOC values between the upper and lower euphotic zones are driven by photoautotrophs. However, the photosynthetic δ13C signal is partially hidden in the bulk POC and amino acid pools, likely due to dilution by heterotrophic processes and degraded POC. This is supported by δ15N values of individual amino acids, which show an increase in the trophic position of organic matter in the lower euphotic zone compared to the upper euphotic zone, indicating increasing heterotrophic contributions. We further discuss aspects of the low-light environment and the photosynthetic community living there that could cause differences in photosynthetic δ13CPOC values over depth.

Yueyang Lu (MPO)
Isolating the Dynamical Effect of Mesoscale Eddies
From the Eddy-Induced Tracer Transport

Oceanic mesoscale eddies play a key role in the redistribution of climatically important tracers such as heat and carbon. However, in most ocean general circulation models, mesoscale eddies and associated tracer transport are not fully resolved. The eddy effects in these models, therefore, must be parameterized reliably predict tracer distributions on larger scales. Eddy parameterization involves a specific model of eddy effects and a closure for the model parameters. There are two direct eddy effects on tracers: 1) the isopycnal tracer transport resulting from the eddy (large-scale)-eddy interactions between mass (isopycnal thickness) flux and tracer, and 2) the advection of tracer by an eddy-induced velocity associated with eddy mass transport. An indirect effect is the dynamical effect of eddies on the large-scale flow, which requires a different consideration in momentum. To study the direct eddy effects separately, one needs a coarse-grid model with an accurate large-scale flow. However, this is difficult because the dynamics is distorted by the missing eddies. Here, we use an offline model where tracer is advected by precalculated velocities and introduce a novel way to define the large-scale flow that is consistent with the eddy-resolving solution. Such important features of the flow as the eastward Gulf Stream extension and the mass flux divergence are preserved. This allows us to better understand the eddy tracer transport with a realistic large-scale flow. Using this offline model, we apply and study a new approach to representing the eddy tracer transport. Preliminary results show potential for improving the traditional eddy parameterization.

Apr 15: Wei-Ming Tsai
Department of Atmospheric Sciences, RSMAS
(one-hour ATM student seminar)

Toward Better Understanding of Tropical Clustered Convection,
Mesoscale Patterns, and Large-Scale Dynamics
Recording Available at COMPASS ON DEMAND

Tropical deep convection exhibits a variety of organization with multi-scales, and Its interactions with large-scale dynamics, radiation, and vapor shape the tropical weather and climate. Relationships between spatial features of convective systems (e.g., size and pattern) and the surrounding environment, however, are limited or remained unclear. Efforts to untangle their connections encourage better representation of mesoscale, clustered convection in climate models where such information is missing. In this study, we endeavor to understand why the clustering of convection matters by asking (1) how deep clouds with different degrees of aggregation (how clustered they are) relate to the large-scale environments, (2) if we can quantify the role of convective aggregation in larger-scale weather and climate systems, and, appearance aside, (3) what makes clustered convection more "special" than isolated convection. By observing tropical convective events, more-aggregated events (with fewer and larger cloud objects) exhibit a drier area mean, greater horizontal gradient of moisture, more bottom-heavy ascent profile, and a greater prevalence of low-altitude cloud tops. Such bottom-heavy ascent and its lasting imply net energy import into the atmospheric column during the event composite. From reanalysis' assimilation budgets, more-aggregated scenes also have more drying by analysis, suggesting that parameterized convection (lacking any organization effect) is raining out less water than nature's real, aggregated convection in such scenes. Based on idealized cloud-permitting simulations, a uniformly forced domain reveals that more-agglomerated convection outcompetes isolated convection by inducing large-scale overturning circulations, with the upwelling branch encouraging the former. Greater precipitation gradients across two convective areas present as the organization gradient (how distinct two areas are) increases, suggesting a better role of more-agglomerated convection in stabilizing the forced large-scale domain. Such specialty of agglomerated convection may attribute to its wider and less-diluted updrafts embedded in the resulting large-scale circulations.


Hope Elliott (OCE)
Comparison of Nutrient Solubility and Bioavailability in Volcanic Ash and Mineral Dust

The eruption of La Soufrière on St. Vincent Island in the southwestern Caribbean in April 2021 was this volcano's first major eruption in over forty years. Ash fallout had significant impacts on both human and ecosystem health on St. Vincent itself and in neighboring Barbados to the east. While there is a constant input of macronutrients (e.g. phosphorus) and micronutrients (e.g. iron) from aerosol sources like mineral dust into the tropical North Atlantic and the Caribbean Sea, far less is understood about nutrient inputs from large deposition fluxes that occur as a result of more rare, episodic events like volcanic eruptions. This study involves chemical analysis of volcanic ash from the La Soufrière eruption collected at Ragged Point in eastern Barbados between April 10 and April 18, 2021, coupled with seawater incubations. The analysis aims to characterize the elemental composition of the ash and identify major nutrient inputs due to the eruption, with a focus on iron and phosphorus. Incubations with radiolabeled phosphate are also used to quantify microbial phosphate uptake rates in the presence and absence of ash. Identical analyses are performed with background aerosol samples collected at the Ragged Point site in early April 2021 prior to the onset of the eruption to provide a basis for comparison to aerosols deposited due to the event. Acquiring information about nutrient inputs from deposition events like the La Soufrière eruption is a significant step towards achieving a better understanding of their impacts on primary productivity and, subsequently, carbon sequestration.

Haozhe He (ATM)
State Dependence of CO2 Forcing and Its Implications for Climate Sensitivity

Instantaneous radiative forcing (IRF) is a fundamental metric for measuring the extent to which anthropogenic activities and natural events perturb the Earth's energy balance. This perturbation initiates all other forced climate responses. Among all the anthropogenic forcing agents, CO2 is the dominant driver of warming over the past century and the defining forcing variable for quantifying climate sensitivity. When evaluating the effect of CO2 changes on the earth’s climate, it is universally assumed that the IRF from a doubling of a given CO2 concentration (IRF2×CO2) is constant and that variances in climate sensitivity arise from differences in radiative feedbacks, or a dependence of these feedbacks on the climatological base-state. In this paper, we show that the IRF2×CO2 is not constant, but also depends on the climatological base-state, increasing by ~25% for every doubling of CO2, and has increased by ~10% since the pre-industrial era, implying a proportionate increase in climate sensitivity. This base-state dependence also explains about half of the intermodel spread in IRF2×CO2, a problem that has persisted among climate models for nearly three decades. It may also have important implications for elucidating the causes and consequences of deep-time paleoclimates, where changes in the climatological base-state can strongly modulate the magnitude of the CO2 IRF.

Haozhe He (ATM)
An Easy and Effective Way to Diagnose Equilibrium Climate Sensitivity

It has been known that the most widely used Gregory method (Gregory et al. 2004; underestimates equilibrium climate sensitivity (ECS), which is defined as the change in global-mean surface air temperature required to restore radiative equilibrium in response to a doubling of CO2 concentration and is a prevalent metric to quantify the susceptibility of the climate to an externally forced change. Previous studies primarily attribute the underestimation to the time-dependent climate feedbacks (or the dependence of climate feedbacks on the degree of equilibration). However, our results suggest the underestimation truly results from the underestimation of effective radiative forcing (ERF) in Gregory method, as the ERF from Gregory method is on average 15% lower than the best ERF estimation from RFMIP while the effective net feedback from Gregory method is well matched with the best feedback estimation, calculated using land warming corrected RFMIP ERF and the best ECS estimation from LongRunMIP. In this case, we modify the Gregory method by adopting the ERF from first 20-yr coupled simulation and the effective net feedback from standard 150-yr coupled simulation. The modified method replicates the best ECS estimation from the millennia-long coupled simulation of LongRunMIP, providing an easy and effective way to diagnose the true ECS without any further computational expenses.


Samantha Furtney (OCE)
Automated Retrieval of Internal Wave Phase Speed and Direction
From Pairs of Synthetic Aperture Radar Images

Synthetic Aperture Radar (SAR) is the premier sensor for the detection of oceanic internal waves due to its sensitivity to changes in small-scale ocean surface roughness and large spatial coverage. The satellite constellation COSMO-SkyMed offers the unique capability to acquire pairs of images of the same scene within 24 minutes, which is ideal for making internal wave motions visible and extracting phase speeds. Other researchers have done this with pairs of airborne SAR images or images from two different satellite systems, but none have developed an automated method or applied standard feature tracking techniques due to the challenges SAR data pose. Unlike optical images, SAR images suffer from speckle noise making it difficult to apply feature tracking algorithms for detecting and quantifying motions. We propose a multistep approach building on a feature tracking algorithm from the literature to overcome this issue and successfully estimate the phase speed and direction of SAR detected internal waves. The steps include image preprocessing, application of a feature tracking algorithm (Oriented FAST and Rotated BRIEF a.k.a. ORB), internal wave parameter match filtering, and machine learning density-based clustering. Our technique is tested on three pairs of COSMO-SkyMed SAR images containing internal wave signatures. The estimated internal wave speeds are comparable to results based on in-situ measurements and Korteweg-de Vries (KdV) theory. This new technique paves the way for a more automated approach to derive internal wave parameters from SAR images.

Samantha Nebylitsa (ATM)
Revisiting Environmental Wind and Moisture Computations in Tropical Cyclones

The environmental wind and moisture fields around tropical cyclones are widely acknowledged as being important for tropical cyclone intensity forecasting and research. The wind field is usually summarized most simply by the vertical wind shear, conventionally calculated as the vector difference between the 200 hPa and 850 hPa wind. The moisture field is typically represented by a mid-tropospheric average of relative humidity. Both calculations are performed in a 200-800 km annulus around the center of the storm. However, these single values of wind shear and moisture may be overly simplistic and not representative of the complex environmental interactions around tropical cyclones. We therefore aim to investigate more sophisticated representations of the environment around these storms by expanding beyond these conventional definitions. Using ERA5 reanalysis data in the Atlantic basin between 1980 and 2021 together with Weather Research and Forecasting (WRF) model output, we vary the annuli around the storm center and use different combinations of vertical levels to identify relationships between the environment and intensification rates. This allows us to understand the variability of these variables across storms that rapidly intensify, defined as an increase in winds of 30 knots over 24 hours, versus those that do not. Distributions of wind shear and moisture indicate differences across intensification rates. Additionally, in the time leading up to rapid intensification, there are distinctions by annulus of these variables, prompting a new metric that includes both the inner core and environmental wind and moisture in future intensity forecasts.

Samantha Medina (OCE)
Wave and Current Variability and Their Effect on Air-Sea Momentum Fluxes
in Coastal Zones

Current operational forecast models for air-sea exchanges rely on drag coefficient parameterizations derived from open water observations and Monin-Obukhov similarity theory (MOST). In the case for coastal zones, the transition from marine to terrestrial boundary atmospheric layers can see the development of spatially heterogenous wind and wave fields where previous parameterizations may fail to account for nearshore spatial variability as well as the breakdown of MOST. Therefore, local wave field observations can assist in the development of new parameterizations for coastal wind models. Under the Coastal Land-Air-Sea Interaction (CLASI) project, 'coast aware' parameterizations of air-sea fluxes are being developed through direct measurements of near-shore and onshore conditions in Monterey Bay, California. CLASI measurements include Air-Sea Interaction Spar (ASIS) buoys, Inner-shelf Spar (I-Spar) buoys, and land towers. This research will use observations from Acoustic Doppler Current Profilers and wave wires mounted on the ASIS buoys. Vertical current profile observations will be compared to current, wind, and wave fields extracted from spotter buoys, shore-based X-band radars, and satellite surface observations. We will also assess the effect of upper ocean currents, turbulence, and directional wave spectra on air-sea momentum fluxes in the coastal zone.