COMPASS Friday - Archive

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FALL 2021
Fridays at 11:00 am, RSMAS Auditorium / Virtual Auditorium (unless stated otherwise)


Sep 03: Brian McNoldy
Department of Atmospheric Sciences, RSMAS

Water Levels at Virginia Key: Past, Present, and Future
Zoom Recording Available at COMPASS ON DEMAND

Miami's character and history are intimately linked to both water and hurricanes. This seminar will begin with an introduction to the history of tide measurements taken at the Rosenstiel School campus on Virginia Key going back to 1994. Then we will take a look at how tide predictions are made and what natural cycles are important for understanding variability on timescales ranging from seasonal to multi-decadal. From there, we will examine sea level rise that has already occurred during the past 27 years of measurements and what to expect in the coming decades. King Tide season is upon us again, and the associated "nuisance flooding" is getting noticeably worse. Finally, no discussion of water levels in Miami would be complete without talking about hurricanes and storm surge. Hurricanes are low-frequency high-impact events that shape how we think and build here, and since the Rosenstiel School campus on Virginia Key was established in 1951, a handful of storms have left significant high water marks.

Sep 10: NO SEMINAR (COMPASS Committee Meeting)

Sep 17: NO SEMINAR (RSMAS Faculty Meeting)


Oct 01: Dr. David Ryglicki
National Hurricane Center, Miami

An Overview of the Atypical Rapid Intensification Process in Tropical Cyclones
Zoom Recording Available at COMPASS ON DEMAND

Classically, with regards to tropical cyclone (TC) intensification and, in particular, rapid intensification (RI), common wisdom dictates that TCs should intensify in favorable atmospheric conditions: warm oceans, sufficient low- and mid-level relative humidity, large upper-level divergence, and low values of deep-layer vertical wind shear. Recently, a new (RI) pathway has been identified that requires the presence of higher values of vertical wind shear for it to transpire. This talk will discuss the Atypical Rapid Intensification (ARI) theory. In brief, ARI is characterized by the modulation of convection by the tilt of the vortex; specifically, by nutations of the tilt of the vortex, where a "nutation" is defined as a higher-order wobble on the longer, larger, and slower precession. The convection modulated by nutations produces highly divergent outflow, not normal to classical TCs. If the depth of the strongest environmental winds is shallow enough, the outflow of this convection can re-route the environmental flow around the TC, reduce the shear, and permit realignment. This talk will discuss how this behavior can be identified in and abstracted from geostationary satellite imagery and will also discuss idealized modeling simulations of ARI, including a shallow-water facsimile of a divergent source in a background flow. Shortcomings of current shear calculations will be addressed.


Victoria Schoenwald (ATM)
Steps to Improve Prediction of Eastern U.S. Coastal Flooding Risk

Sea level variability along the U.S. East Coast occurs on a wide range of time scales (days to decades) and has led to increased coastal flooding in many heavily populated areas. Numerous mechanisms have been proposed attempting to diagnose why accelerations in sea level rise (SLR) or "SLR hot spots" up and down the coast are occurring. On shorter time scales the prevailing atmospheric state has been suggested to dominate coastal flooding risk. In contrast, on longer time scales (interannual - decadal) the oceanic state may control variability through the Atlantic-Meridional Overturning Circulation (AMOC). In this seminar, tide gauge measurements from across the East Coast as well as climate models will be used to separate signals from different aspects of the climate system relating to SLR. Here we begin to piece together how natural variability and climate change effects influence SLR in order to create a comprehensive flood risk system in the future.

Tyler Fenske (ATM)
Separating Internal and External Variability in the North Pacific Ocean
and Its Relation to the North Atlantic

Separating internal and external variability is currently a significant challenge to better understanding of the global climate system. Here we focus on addressing this challenge in the North Pacific ocean basin, particularly regarding climate modes on decadal to multidecadal timescales in this region. Empirical Orthogonal Function (EOF) analysis shows the two traditional internal modes, the Pacific Decadal Oscillation (PDO) and Victoria Mode (VM). However, it also reveals another mode analogous to the regional non-linear aspects of external forcing, or global warming. This external mode appears to have grown in importance over time, with its variance explained increasing in the last two decades. With these modes now isolated (albeit not perfectly), we begin to analyze possible drivers of each mode's variability. Our primary focus here is on each mode's relationship with North Atlantic variability on similar timescales, namely the Atlantic Multidecadal Variability (AMV). Previous literature has suggested that the PDO and VM have internal connections to the AMV. Our analysis features a specialized statistical test and utilizes a modern dataset of large ensembles. Contrary to prior findings, we show that no internal connections between the two basins are significant. However, we do find that what we define as the forced responses in each basin are remarkably similar and may have caused a spurious relationship to appear in previous research. These findings pique more interest in other inter-basin connections and regional forced responses.

Amie Dobracki (ATM)
Characterizing the Evolution of Aged Biomass Burning Aerosol at Ascension Island

Ascension Island, located at the northwest corner of the southeast Atlantic Ocean stratocumulus deck (–7.95°N, –14.36°E), receives biomass burning aerosol at the surface during much of the year despite a semi-permanent deck of stratocumulus clouds guarding the island. The research presented here is motivated by understanding how aged biomass burning aerosol properties evolve as aerosol becomes transported from its source to Ascension, undergoing entrainment at times into the marine boundary layer. Much previous work examined the chemical evolution of biomass burning aerosol in the free troposphere over the southeast Atlantic region, however, I now turn my attention to the aerosol's chemical, physical, and optical properties in the boundary layer using data collected over 17 months from Ascension Island during the DOE's Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign. Based on monthly mean averages of black carbon and organic aerosol from 2017, August is the smokiest month, while October is the least. There is also considerable black carbon contribution during the early biomass burning season in June and July. This is remarkable as very few, if any previous studies have documented this. It has also been shown as the biomass burning season progresses, the aerosol becomes less absorbing, thus increasing the single scattering albedo (SSA). Results presented here will be the first steps to characterize the changes in the aerosol's chemical composition and physical properties in the boundary layer to help understand why SSA increases over the biomass burning season.

Oct 15: Dr. Cassandra Gaston
Department of Atmospheric Sciences, RSMAS
(Candidate for Promotion and Tenure)

Importance of Aerosol Composition for
Air Quality, Biogeochemical Cycles, and Climate
Zoom Recording Available at COMPASS ON DEMAND

Atmospheric particles, as known as aerosols, are critically important as a major source of uncertainty in global climate predictions and a leading cause of premature mortality worldwide. To address these outstanding issues, our research aims to elucidate direct links between the sources of aerosols and chemical transformations that they undergo during transport with their climate and health impacts. Our work has increased our understanding of (1) how aerosols affect the sequestration of carbon dioxide through the deposition of biologically necessary nutrients to the ocean and tropical forests that stimulates primary productivity and carbon uptake; (2) chemical reactions on dust that generate reactive halogens that lead to the formation of ozone, a criteria air pollutant and greenhouse gas; and (3) the aerosolization of algal toxins that negatively impact human health. This research is executed through laboratory studies as well as field measurements in South Florida, Barbados, and South America. In this talk, I will focus on major discoveries related to the first two research topics. Our work has challenged mainstream hypotheses regarding the origin of North African dust that is transported to South America and is thought to fertilize the Amazon Basin. We have also shown that climate and biogeochemical models have underestimated the importance of aerosols other than dust for the marine and terrestrial biogeochemical cycles that regulate carbon sequestration and the Earth’s climate. Finally, I will discuss connections between dust, air quality, and ozone pollution. Our recently published work shows, for the first time, that dry lakebed dust is reactive and facilitates chemistry that exacerbates ozone pollution suggesting that the desiccation of the Great Salt Lake and other water bodies due to water and land use practices will enhance urban air pollution.


Junfei Xia (MPO) Live from China at 9:00 am
Machine Learning Applications to Ocean Drifter Data Sets

Drifter observations provide high-resolution surface velocity data, with which researchers often use different methods to project the Eulerian velocity fields. Gaussian Process Regression (GPR) is a machine learning method based on Gaussian probability distribution used in projection. A Gaussian process is a collection of random variables, any finite number of which have a joint Gaussian distribution. Here we focus on the first step of the research, validation of the application of GPR. This study aims to answer 1) how accurate is the projected velocity field; 2) The relationship between the amount of training data and accuracy; 3) how it performs in convergence regions, divergence regions, and eddy regions. The idea of the test is to compare the velocity fields between the NCOM model and GPR produced. The training drifter data used in GPR are from the NCOM model through Lagrangian-Eulerian advection. The condition of the advection is set the same as CARTHE drifter, 15-minute time interval. The results show that the overall accuracy of projected velocity fields is high, and the error variance is sometimes high. The accuracy first increases with the increase of training data then reach a threshold. The threshold indicates the line of 'overfitting'. The method performs better in convergence and divergence regions than eddy regions.

Paul Wojtal (OCE) Regular time – 11:00 am
Importance of Fecal Pellets and Microbial Alteration of Organic Particles
in the Northeast Pacific

Particulate organic matter settling out of the euphotic zone is a major sink for atmospheric carbon dioxide (CO2) and serves as a primary food source to mesopelagic food webs. Organic matter degradation during sinking is an important mechanism of carbon flux attenuation, occurring mainly through heterotrophic metabolic processes of both microbes and metazoans. However, the relative contribution of microbial and metazoan heterotrophy to vertical carbon flux attenuation has been difficult to determine quantitatively, and biogeochemical models have lacked validation for the components contributing to carbon export. I present the results of compound specific isotope analysis of amino acids of sinking particles from sediment traps and four size classes of particles filtered through the water column at nine depths between the surface and 500 m at Ocean Station Papa (northeast Pacific), collected as part of the NASA EXPORTS program in summer 2018. I find variations over depth and size class in both the trophic position of particles, reflecting the input of zooplankton fecal pellets, and nitrogen isotope ratios of source amino acids, illustrating the imprint of microbial extracellular hydrolysis. I additionally present a preliminary quantitative particle composition mixing model. My results highlight the shifting interactions among microbes, zooplankton, and particle size classes as organic matter settles into mid-mesopelagic depths.

Lev Looney (MPO)
The Driving Forces of Hurricane-Induced Ocean Cooling

From 1980 until 2020, the US had 52 tropical cyclone related billion dollar disasters, totaling over $997 billion in damages. One of the best ways we can reduce the number of deaths and damages is to better prepare through accurate and timely forecasts. While the forecasts of tropical cyclone tracks have significantly improved through time, the intensity forecasts have not followed at nearly the same rate. It has been shown that oceanic conditions play a crucial role in the intensification of these storms. As hurricanes primarily get their energy from ocean heat, they can also cool the surface ocean through vertical mixing, acting as a limitation to their intensity. We aim to further understand the mechanisms that control the amount of ocean cooling under a storm and relate it back to intensity changes. To investigate this, we utilize a one-dimensional mixed layer model, initialized with a variety of oceanic profiles, forced with various cyclones to better forecast the amount of vertical mixing (and thus surface cooling). Temperature stratification has competing effects: stronger stratification leads to cooler water near the surface which can enhance SST cooling (thermodynamic effect), yet it also leads to resistance to vertical mixing due to the density gradient (mixing effect). In contrast, salinity stratification almost always acts to reduce mixing and cooling. Initial results show the thermodynamic effect is 2-3 times that of the mixing effect. Understanding the quantitative role of each of these is becoming even more imperative with the changing climate.

Chong Jia (MPO)
Emissivity Effects on MODIS Retrieved Sea Surface Temperatures at High Latitudes

Satellite remote sensing is the best way of deriving sea surface temperatures (SST) in the Arctic, but given the surface temperature retrieval algorithms in the infrared compensate for atmospheric effects mainly due to water vapor, satellite-derived SSTs have larger uncertainties at high latitudes, where the atmosphere is very dry and cold, an extreme of global conditions. We aim to improve the algorithms to obtain more accurate SSTs for climate change research and surface ocean processes in the Arctic. We use five years of collocated, simultaneous satellite brightness temperature (BT) from MODIS on Aqua and in-situ subsurface SST. Unlike elsewhere, the 11 and 12 μm BT differences are poorly related to the column water vapor at high latitudes, resulting in poor atmospheric water vapor correction. By conducting numerical simulations using RTTOV, a radiative transfer model, the sea surface emissivity difference between 11 and 12 μm have been shown to dominate the water vapor effect. This discrepancy is amplified by the effective atmosphere-sea temperature difference (ASTD). The emissivity effect is more significant during winter, when the atmosphere is very dry and the ASTD is large. Utilizing the matchups of satellite and buoy data, the characteristics of the emissivity effect on MODIS-derived SST have been demonstrated, as well as the development of an empirical formula for the emissivity correction. This study reveals the importance of emissivity effects on the infrared satellite SST retrievals at high latitudes. We anticipate that the correction can be further optimized and applied to future well-calibrated infrared satellite radiometers.

Oct 29: Dr. David Painemal
Science Systems and Applications, Inc. & NASA Langley Research Center, Hampton, Virginia

A Satellite Perspective on Aerosol-Cloud-Radiation Interactions
Zoom Recording Available at COMPASS ON DEMAND

The interactions between aerosols, clouds, precipitation, and radiation constitute one of the largest uncertainties in our current understanding of the anthropogenic radiative forcing. The fundamental mechanism in which an atmospheric aerosol enhancement can alter the cloud properties is by increasing the cloud droplet number concentration, thereby reflecting more solar radiation, and potentially giving rise to changes in precipitation and cloud water content. While the underlying physical foundations are reasonably well understood, the magnitude of changes in cloud properties and radiation is far from being settled. In-situ probes generally offer reliable information for quantifying the interactions between aerosol and clouds, however, only satellite sensors provide the required spatiotemporal coverage for regional and global scale assessments, which in turn can be applied to the validation of climate models. In this talk, I will review the role of NASA satellite sensors on monitoring aerosols, clouds, and radiation in boundary layers clouds. Current challenges and plans for the next satellite observatory will also be discussed.


Quinton Lawton (ATM)
A Comprehensive Study of the Influence of Convectively Coupled Kelvin Waves
on African Easterly Waves Using a Lagrangian Framework

While considerable attention has been given to how Convectively Coupled Kelvin Waves (CCKWs) influence the genesis of Tropical Cyclones (TCs) in the Atlantic Ocean, less attention has been given to their direct influence on African Easterly Waves (AEWs) themselves. This study builds a climatology of AEW and CCKW passages from 1981-2019 using an AEW-following framework. Vertical and horizontal composites of these passages are built and subset into categories based on AEW position and CCKW strength. Composites illustrate an increase in convective coverage and diabatic heating surrounding AEW centers in phase with convectively-active CCKW crests. Additionally, there is an enhancement in specific humidity and relative vorticity surrounding AEWs for up to 1.5 days following convectively-active CCKW crests, with anomalies building from middle to upper levels. CCKW-related modifications to specific humidity are more pronounced when AEWs are at lower latitudes and interacting with stronger CCKWs. While an attribution analysis suggests that most of these impacts come and go with passing CCKWs, we also provide evidence of CCKW-related modifications to AEW propagation speed and westward-filtered relative vorticity. This suggests that CCKWs may have long-term impacts on the AEW lifecycle, especially for stronger AEWs. Our analysis highlights that CCKWs have a significant influence on the characteristics of non-developing AEWs. It also provides indirect evidence that CCKW-related convection, specific humidity, and vorticity modify the favorability of AEWs to TC genesis over the Atlantic.

Karen Papazian (ATM)
Using an Idealized Model Towards Understanding How
Pole to Equator Temperature Gradients Affect Cold Air Outbreaks

Cold air outbreaks (CAOs) have large societal and environmental impacts, such as agricultural losses, infrastructure damage, changes in atmospheric circulation, etc. As the Earth experiences a climate crisis, the focus on CAOs has been diminishing, but we still see extreme CAOs occurring that society is gravely underprepared for. We look to explore where and how CAOs originate and how they change in a changing climate. We analyze CAOs using observations and model simulations to aid us in better predicting their future. Observational data from the Twentieth Century Reanalysis (V2) product is used in addition to model simulations from the Community Atmospheric Model version 5 (CAM5), of the NCAR Community Earth System Model 1 (CESM1). In the model simulations, we prescribe ocean data to a fully ocean-covered planet, an aquaplanet simulation, to create different pole to equator temperature gradients. These temperature gradients create an idealized space to analyze CAOs. We see in the model simulations that CAOs still occur as we expand the tropics. Therefore, understanding the sources of CAOs will help in the understanding of how their frequency and intensity may change as a result of climate change.

Peisen Tan (OCE)
Effect of Aerodynamic Sheltering on Wave Growth in Very Strong Winds

Understanding wave growth under extreme wind forcing is vital for improving wave models and hurricane prediction. In strong winds, air flow detaches from the surface in the lee of wave crests and modulates the momentum input from wind to waves. This "sheltering" effect can be parameterized in wave models. However, such parameterization relies on the so-called sheltering coefficient, whose value and dependence on wind and wave state is not well understood. In this study, we conduct wind-wave laboratory experiments in up to Category 4 hurricane-force (65.9 m/s) winds blown over various initial wave conditions and measure wind, waves, and stress at high frequency. We find two regimes: 1. In tropical storm conditions (18 m/s < U10 < 33 m/s), the sheltering effect is similar between different background wave configurations; 2. In hurricane conditions (U10 > 33 m/s), the sheltering coefficient's values increase at a different rate depending on the type of background waves. Local steepness, obtained using the wavelet transform method, reveals hydrodynamic and aerodynamic modulation of short wind wave growth, the latter being due to the aerodynamic sheltering by long waves. The sheltering coefficient decreases with the increase of wave steepness, and asymptotes in high values of wave steepness and wind speed.

Nov 12: Dr. Michael Haigh
Faculty of Natural SciencesDepartment of Mathematics, Imperial College London, UK

A Full-Tensor Approach to Parameterising Oceanic Eddy Tracer Transport
Zoom Recording Available at COMPASS ON DEMAND

In numerical ocean models the effects of unresolved mesoscale eddies on large-scale tracer distributions are typically represented by a turbulent diffusion closure. Such a closure is characterised by a diffusivity coefficient for which scalars, diagonal tensors and full tensors have been proposed. We opt for the most general full-tensor approach applied to an eddy-resolving tracer simulation with no additional averaging or simplifications. The resulting 'transport tensor' exhibits new levels of spatio-temporal complexity and its properties – such as negative eigenvalues, non-uniqueness and its relationship with the large-scale flow – contrast those of eddy diffusion closures currently implemented in numerical ocean models. This work suggests a rethink of the role of mesoscale eddies and their representation in numerical models may be required in order to improve simulations of large-scale tracer distributions.


Leah Chomiak (MPO)
Tracking Labrador Sea Water From the Source Region to the Tropical Atlantic
Reveals New Overturning Pathways

The Subpolar North Atlantic plays a critical role in the formation of the cold, dense deep-water masses that drive the Meridional Overturning Circulation (MOC). Labrador Sea Water (LSW) is formed in the Subpolar North Atlantic and advected out of the Labrador Sea predominantly via the Deep Western Boundary Current (DWBC). The DWBC is an essential component of the MOC carrying cold and dense deep waters southward, flowing at depth along the continental shelf of the western Atlantic. Hydrographic observations in the Labrador Sea for nearly eight and a half decades have revealed considerable changes in the temperature, salinity, and density of LSW through extreme wintertime convective and freshening events. Here, we combine sustained hydrographic observations from the Labrador Sea, 39°N, Bermuda basin, and 26.5°N to investigate the signal propagation and transit time of LSW via the DWBC from its source region to the Tropical Atlantic. The onset of LSW1987-1994 and LSW2000-2003 classes with distinguishable cold, fresh pulses are observed to pass through all monitored locations, advecting at timescales that support a new plausible route of the DWBC – one that ventures into the central Atlantic via a recirculation pathway on time scales of approximately ten years prior to arriving at 26.5°N four years later. Using these LSW convective signals as advective tracers along the DWBC permits the estimation of transit times from the Subpolar North Atlantic to the lower latitudes, shedding new light to multiple deep water advection pathways across the North Atlantic and the lower-limb of AMOC as a whole.

Sisam Shrestha (ATM)
Use of Upper-Tropospheric Relative Humidity to Investigate Changes in Tropical Circulations

Climate models suggest an overall weakening of large-scale tropical circulations with warming. This weakening primarily manifests as a weakening of the Walker Cell – the zonally asymmetric component of the tropical circulation. Unfortunately, a lack of observational record for the mid-tropospheric vertical velocity (ω500) – a measure of tropical circulation, forces heavy reliance on reanalysis products which introduce error due to incorporation of heterogeneous datasets. In this work, we use upper-tropospheric relative humidity (UTH) as a proxy to investigate trends and variability in the tropical circulation. UTH is the vertical integration of weighted-relative humidity from around 200 to 500 hPa of the atmosphere. We employ an intercalibrated climate record of UTH from the High‐Resolution Infrared Radiation Sounder (HIRS) instrument onboard the National Oceanic and Atmospheric Administration (NOAA) operational polar-orbiting satellites that goes back to 1979, providing us with a 40+ year of record. We also incorporate climate models belonging to Coupled Model Intercomparison Project Phase 6 (CMIP6) to derive a relation between UTH and ω500. Preliminary results suggest both the observed UTH and model-derived UTH can be used as a good estimation for changes in ω500. For recent decades, the ensemble mean of amip simulations lack a discernible trend in WC strength. However, we find a decrease in the ensemble mean spatial variance of ω500 over the 21st century for different forcing scenarios of CMIP6 (ScenarioMIPs) that suggests a weakening of the tropical circulation in a warming climate.

Haley Royer (ATM)
Transported African Wildfire Smoke Influences Cloud Formation in the Tropical Atlantic

Shallow cumulus clouds are among the most geographically pervasive clouds on Earth. In the tropical Atlantic, the presence of these clouds plays an especially important role in Earth's radiative budget by reflecting incoming solar radiation and obscuring the low-albedo ocean surface. Despite the importance of these clouds in the tropical Atlantic, the aerosol-cloud interactions that influence the formation of shallow cumulus clouds are still not fully understood. In this study, we attempt to gain a better understanding of aerosol-cloud interactions in the tropical Atlantic by linking aerosol size-resolved chemical composition from single particle microscopy coupled with elemental analysis to size-resolved cloud condensation nuclei (CCN) activity from a CCN counter (CCNC). Data were collected for approximately 1 month during the winter of 2020 at the University of Miami's Barbados Atmospheric Chemistry Observatory, which is research site situated on the east coast of Barbados. Results of CCSEM/EDX analysis reveal that smoke particles from biomass burning in the African Sahel were transported to Barbados during the sampling period, indicating a greater geographic influence of Sahelian smoke than previously thought. Results form CCNC analysis show that these smoke particles are also viable CCN and can potentially affect the radiative properties of shallow cumulus clouds via the Twomey Effect. The findings from this research suggest that current climate and aerosol models must be updated to account for the role of smoke particles on cloud formation and cloud properties in the tropical Atlantic.

Nov 26: NO SEMINAR (Thanksgiving Recess)


Manish Devana (MPO)
Boundary Layer Dynamics in Bottom Intensified Flow Along the Reykjanes Ridge

The Iceland Scotland Overflow, a key component of Atlantic Overturning Circulation, forms a bottom intensified current along the Reykjanes Ridge in the Iceland Basin and generates a several hundred-meter-thick boundary layer. Numerous hydrographic sections and newly available mooring observations consistently display the thick bottom boundary layer, a phenomenon that is typically linked with bottom intensified mixing processes. Mooring observations also show frequent boundary layer collapses where isopycnals are flattened for 2-3 days. We explore the dynamics that drive such a thick boundary layer and the processes that drive the periodic growth and collapse of the layers. Preliminary results indicate that the large boundary layer is linked to both the roughness of the ridge topography and the structure of the ISOW flow. The development of the layer is suspected to be a combination of small-scale mixing from topographic interactions, development of an arrested Ekman layer, and internal tides. Estimates of mixing rates from hydrographic sections suggest strong mixing near the top of the ridge axis. Composite analysis of moored temperature, salinity, and current records are used to analyze periods of boundary layer growth and collapse. These results show elevated tidal energy during boundary layer collapses and characteristics of arrested Ekman layer growth during boundary layer growth. The boundary layer dynamics likely play a critical role in setting the final water mass characteristics and density of the ISOW layer which can lead to downstream impacts on the AMOC.

Ivenis Pita (MPO)
Transbasin Temperature and Salinity Section at 22°S
for Atlantic Meridional Overturning Circulation Estimations

The Atlantic Meridional Overturning Circulation (AMOC) causes a northward Meridional Heat Transport and affects climate and weather patterns, regional sea levels, and ecosystems. Therefore, continued monitoring, hindcast prediction, and future projections of the AMOC variability are crucial for a better understanding of the Earth system dynamics. A suite of efforts are geared towards estimating the AMOC transport at several latitudes using specific methodologies subject to the type of instrumentation used, data availability, and operational constraints. Currently, two observational arrays monitor the AMOC in the South Atlantic at 11°S and 34.5°S, and synthetic temperature (T) and salinity (S) profiles are used for estimating the AMOC at 20, 25, 30 and 35°S. In this work, we estimate the AMOC transport at 22°S from 2004 to present using XBT transect and ARGO profile data. Given the sparse data coverage within the region, the use of weighted average methods is considered here to provide a potentially more robust technique to estimate the AMOC. Regionally varying spatial and temporal average ranges are tested and optimized for the entire transbasin section. The understanding of local dynamics on both of the boundaries is important to evaluate the T and S sections elaborated. The optimized T and S sections improve the dynamic height (DH) representation relative to the gridded Argo product. AMOC estimations are analyzed and compared to different AMOC products (e.g. model, synthetic and in situ observations). Future steps involve exploring the relationship between AMOC, the boundary currents, and coastal sea level.

Ryder Fox (MPO)
Sensitivity of WRF-Modeled Surface Rainfall Accumulation to Subkilometer Grid Spacing
and Microphysical Parameterizations for Landfalling Hurricane Florence (2018)

We focus on the case study of Hurricane Florence (2018), conducting an intercomparison study of the Weather Research and Forecasting (WRF) model to analyze sensitivities to horizontal grid spacing and microphysics parameterizations. Slow-moving Florence broke records upon making landfall in North Carolina, flooding the area with over 35 inches of rain. Hurricanes are typically modeled using O(1 km) resolution; here we explore the impacts to modelled surface flooding using subkilometer resolution. In particular, we analyze 0.2- and 0.6-km horizontal grid spacing using three different bulk cloud microphysics schemes: WRF Double Moment 6-Class (WDM6), Morrison, and Predicted Particle Properties (P3). We show that increasing resolution and varying microphysics make only nominal impacts to hurricane track and intensity, but larger impacts to surface rain rate, accumulated surface rainfall, and hydrometeor distributions. All simulations produce more rainfall in finer resolutions, with P3 generating more convective-designated rainfall while WDM6 and Morrison generate more stratiform-designated rainfall. Differing ice assumptions lead to varied spatial distributions of hydrometeors in our simulations, with WDM6 generating larger ice and snow mixing ratios and smaller graupel mixing ratios in finer resolution. Morrison and P3 both vary in time, with the finer resolution simulations producing larger ice mixing ratios during the second period of heavy precipitation. Dynamics also affect rainfall partitioning, lending to greater sensitivities for WDM6 simulations and suggesting that future work might consider partitioning algorithms for tropical cyclones modeled in subkilometer grid spacing.