SPRING 2026
Wednesdays at 3:00 pm, Seminar Room SLAB 103 / Virtual SLAB 103
(unless stated otherwise)
Jan 14: Dr. Lauren Zamora
University of Maryland College Park / NASA Goddard Space Flight Center, Greenbelt, MD
Guest of Paquita Zuidema, Department of Atmospheric Sciences
To Arctic Clouds From Saharan Dust: An Alumnus Career Retrospective
Recording Available at COMPASS ON DEMAND
Aerosol-cloud interactions are one of the largest sources of uncertainty in climate projections for the rapidly warming Arctic, particularly through their influence on the radiative properties of mixed‑phase clouds containing both liquid water and ice. In this talk, I will present a retrospective of my research on aerosol impacts on the environment, tracing a trajectory from PhD work at Rosenstiel on Saharan dust and atmospheric nutrient deposition to the ocean to my current focus on Arctic aerosol-cloud interactions. I will talk about how my training in marine and atmospheric chemistry with Dennis Hansell and Joe Prospero continues to inform my research approach. The presentation will focus primarily on recent developments in understanding Arctic aerosol-cloud interactions, including new satellite observational methods, community scientific priorities identified at a recent QuIESCENT international workshop, and new observations from NASA's 2024 ARCSIX (Arctic Radiation-Cloud-Aerosol-Surface Interaction Experiment) field campaign. I will also discuss emerging satellite remote sensing approaches and recent work on polar mixed‑phase cloud thinning as a potential climate intervention strategy. I will conclude by briefly reflecting on career lessons learned that may be helpful for current graduate students, including managing research transitions, building diverse mentoring networks, and approaching complex scientific problems strategically.
Lauren Zamora is an Associate Research Scientist at the Earth System Science Interdisciplinary Center, University of Maryland, College Park. Since 2017, she has also been a cooperative agreement scientist partnering through the University of Maryland with NASA Goddard Space Flight Center. She obtained her PhD from the University of Miami Rosenstiel School in 2010 after studying atmospheric aerosol nutrient deposition to the ocean and its biogeochemical impacts. Her current work combines satellite observations, fieldwork, and modeling to investigate how aerosols affect cloud formation in polar regions. Dr. Zamora is on the leadership team for the NASA Arctic Radiation-Cloud-Aerosol-Surface Interaction EXperiment (ARCSIX) aircraft campaign and co-leads the QuIESCENT international scientific group, which coordinates global research efforts to quantify Arctic aerosol-cloud interactions.
Jan 21: SPECIAL ATM & OCE FACULTY PRESENTATION SERIES
Dr. Roland Romeiser
Department of Ocean Sciences, Rosenstiel School
SAR Remote Sensing of the Ocean
A General Overview and Update on Recent Projects
Recording Available at COMPASS ON DEMAND
The concept of synthetic aperture radar for high-resolution imaging of the Earth's surface was developed in the 1950s and tested on a first satellite in December 1964. Today, six decades later, we have about 100 operational SAR satellites available to acquire sub-meter-resolution images at almost any point on Earth within hours and to obtain repeated lower-resolution images of large land, coastal, and polar regions every few days. These capabilities, combined with advanced data processing and interpretation techniques and the fact that microwave radars can operate at day and night and see through clouds, have made the SAR satellites attractive and indispensable for a wide range of applications.
This seminar in the COMPASS Special ATM & OCE Faculty Presentation Series will begin with an overview of the history of SAR and of the presenter's own contributions to the field of ocean remote sensing in the last 40 years. The second part will be a sequel to the presentation from October 3, 2018. It was demonstrated how we can reprocess spotlight-mode SAR images into short video-like image sequences and use the theoretical dispersion relation of ocean waves as a filter to separate linear SAR signatures of moving waves from other contributions. The filtered wave signatures can then be inverted into waveheight spectra by applying a simple linear modulation transfer function. Now the latest version of our algorithm can account for changes of the dispersion relation in shallow water and in the presence of surface currents and estimate water depths and current vectors as byproducts of the filtering process. This technique has been used in the analysis of marine radar (ship radar) image sequences for many years, but the SAR-derived time series are too short for a full Fourier analysis in the time domain and required some new solutions, which will be discussed. Last but not least, examples of our team's contributions to the recent large collaborative project "NOPP Hurricane Coastal Impacts" will be shown.
Jan 28: Dr. Alexander Soloviev
Dept of Marine and Environmental Sciences, Halmos College of Arts and Sciences
Nova Southeastern University's Oceanographic Center, Dania Beach, FL
"Hidden" Upwelling on the Southeast Florida Shelf
Recording Available at COMPASS ON DEMAND
Classical wind-driven coastal upwelling is predominantly observed along the eastern ocean boundaries, such as the California Shelf. Along western ocean boundaries, including the Southeast Florida Shelf (SFS), wind-driven upwelling typically occurs only during extreme wind events, such as hurricanes. However, an alternative and potentially powerful form of coastal upwelling exists along western boundaries. This upwelling does not generally penetrate the strong near-surface stratification of the summertime coastal ocean but can substantially modify temperature and nutrient conditions within the benthic boundary layer, with important ecological consequences. In recent literature, this phenomenon has been termed "hidden" upwelling. Evidence for hidden upwelling on the SFS is supported by numerous diver observations of episodic cooling events confined to reef depths, occurring in the absence of any detectable surface signature. While western boundary currents are known to generate upwelling through multiple physical mechanisms, the dominant processes underlying hidden upwelling on the SFS have not been fully resolved. Analysis of 25 years of coastal ocean observations from acoustic Doppler current profiler (ADCP) moorings, supplemented by recent measurements from a Wirewalker and a Slocum 3 Glider equipped with an ADCP, helps to identify the dominant mechanisms driving hidden upwelling along the SFS. Because coral reef benthic communities are highly sensitive to changes in temperature and nutrient supply associated with coastal upwelling, this work provides new insight into subsurface physical drivers of reef variability and has direct relevance for coral reef management on the SFS.
Feb 04: SPECIAL ATM & OCE FACULTY PRESENTATION SERIES
Dr. Joseph Prospero
Professor Emeritus, Department of Atmospheric Sciences, Rosenstiel School
My Life Chasing Dust Over the Global Oceans
Recording Available at COMPASS ON DEMAND
Most graduate students begin their studies with a hazy idea of where their studies might take them. Often, upon graduation, they find it necessary to adapt. That was true for me. I acquired a Ph.D. (Princeton, 1963) in nuclear chemistry and nuclear spectroscopy. In my fourth year I concluded that the field was approaching a dead-end and that I would have to switch to another field. By pure chance at a party, I learned of an opportunity to lead a project at the University of Miami "marine school". Despite knowing nothing about the school, I interviewed and was hired in 1963. Unfortunately, the project failed. Here I describe how my career evolved after that failure. In this presentation I review my journey and some of the science accomplished along the way.
I do not intend to present a survey of my research but rather to describe the context in which my program evolved. In 1965, I focused on aerosols in the ocean environment which at that time was relatively unexplored. My ultimate goal was to develop a global picture of marine aerosol concentrations and properties and their temporal and spatial distributions over the oceans. To this end and with a strong supporting group, I worked to create a global network of sampling stations on islands in the Atlantic, Pacific and Indian Oceans. Our primary interest was mineral dust because of its strong link to climate as a causative factor and also its role in ocean chemistry. However, we also measured many other species (e.g., nitrate, nss-sulfate, MSA, etc.) and also many important elements (e.g., Fe). These data were spatially integrated using a variety of remote sensing instruments, both ground-based and aboard satellites. These data are widely used to validate satellite aerosol retrieval algorithms. Participation in major field campaigns enabled synoptic observations and large-scale integration. Curiously, these data are now 25 to 50 years old but they remain the only synoptic ocean aerosol measurements. There is a clear need for the synoptic measurement of aerosols over the oceans because of the great variability in their concentrations and composition. Finally, as the result of this program, we (i.e., Cassie Gaston) have acquired an archive of over 60,000 filters that are available for study.
Feb 11: STUDENT SEMINARS
Evan Wellmeyer (ATM)
Constraining Regional Projections of Precipitation Change With Machine Learning
Regional precipitation change remains a major source of uncertainty in climate projections. We develop a machine learning framework that learns a spatially structured mapping from historical precipitation climatology (PR) to precipitation change per degree of global warming (dPdK), enabling regional responses to be conditioned on present day mean state structure. We train a probabilistic neural network (NN) ensemble on three HadGEM perturbed-parameter ensembles (PPEs) and benchmark against ensemble mean, Gaussian-weighted model selection, and gridpoint regression baselines. In within-PPE tests, the NN reduces RMSE relative to the PPE mean by a median of 28%, with maximum reductions of 46% globally and 48% over land. To improve cross-model transfer, we use a prior–residual formulation in which the NN conditions on PR and a physically motivated prior dPdK (a weighted multi-model mean) and predicts the residual. Fine-tuning on CMIP6 response patterns improves performance for held-out models, though skill is constrained by the limited size of the training pool. Applied to 44 coupled CMIP6 models, this approach reduces RMSE by 7.5% on a held-out model (GFDL-ESM4) over the CMIP6 multi-model mean. Finally, we apply the fine-tuned ensemble to observations, producing observation-conditioned estimates of regional precipitation sensitivity with spatially resolved uncertainty.
Susan Harrison (OCE)
Spatial Variability of Coastal Air-Sea Drag and Its Departure From Standard Models
Operational weather prediction models struggle to reflect accurate dynamics within the coastal marine atmospheric boundary layer. This is typically due to the lack of representation of ocean wave effects, unresolved coastline topography, and insufficient measurements to inform the subgrid-scale parameterizations. As high-resolution coupled atmosphere-wave-ocean models become more popular, there is an increased need to reassess current wind- and wave-based parameterizations for air-sea drag. In this study, we analyze wind, wave, and eddy-covariance stress data from eight Air-Sea Interaction Spars (ASIS) deployed in the Northern Gulf of Mexico, with cross-shore distances between 5 and 40 km, as part of the Coastal Land Air-Sea Interaction (CLASI) project from January to March 2023. We analyze these data with those collected at Martha's Vineyard Coastal Observatory from 2020-2023 to compare coastal observations against the open ocean dataset used in Edson et al. [2013]. We find from both measurement sites that open-ocean momentum fluxes are consistently larger than values from the coastal transition zone. We use ASIS buoy data to initialize the sea-state dependent COARE3.5 parameterization and find that the parameterized momentum flux also deviates from the ground-truth coastal momentum flux. By classifying measurements by trajectory relative to the coastline, this study shows how coastal momentum fluxes differ systematically when compared with both open-ocean observations and the COARE3.5 model parameterization.
Feb 18: Dr. Andrew Dessler
Texas Center for Extreme Weather, Texas A&M University, College Station
Guest of the Department of Atmospheric Sciences
Climate Change, Renewables, and the Cost of Electricity
Recording Available at COMPASS ON DEMAND
Electricity is one of the most important enablers of our modern lifestyle. Many Americans live in regions where electricity markets set prices, and this talk explains why renewable energy and battery storage reduce costs in these regions. To do this, we analyze ERCOT and CAISO market data to quantify the growing cost burden from climate change as well as the savings due to renewable energy and batteries. We show that renewables and energy storage deliver measurable savings by lowering prices, but climate change is simultaneously driving both cost and demand upward.
Feb 25: Chanyoung Park
Department of Atmospheric Sciences, Rosenstiel School
(1-hour ATM student seminar)
Aerosols, Clouds, and Recent Trends in Earth's Energy Imbalance
Recording Available at COMPASS ON DEMAND
Earth's energy imbalance (EEI) – the difference between absorbed solar radiation and outgoing longwave emission – is a fundamental measure of the climate system and a key indicator of climate change. Over the past two decades, observations show a persistently positive EEI trend, driven primarily by increased absorption of shortwave (SW) radiation at the top of the atmosphere (TOA) and implying continued heat accumulation in the Earth system. Identifying the drivers of this SWTOA change is therefore essential for constraining climate sensitivity and for disentangling the roles of anthropogenic forcing and climate feedbacks.
Many radiative-kernel-based studies attribute much of the recent SWTOA increase to cloud-driven SW changes, denoted here as dSWcld. Some modeling studies further interpret these changes as resulting from declining anthropogenic aerosols through aerosol-cloud interactions. An observationally constrained framework is presented to quantify effective radiative forcing from aerosol-cloud interactions, explicitly accounting for aerosol activation efficiency under varying environmental conditions. Applied to recent EEI trends, the analysis indicates that increases in Southern Hemisphere aerosols associated with wildfires and a volcanic eruption offset reductions in Northern Hemisphere anthropogenic aerosols. This contrasts with model-based attributions that assign roughly half of the observed EEI increase to declining anthropogenic aerosol emissions. Overall, the results suggest that aerosols – through aerosol-cloud interactions – have made a negligible net contribution to the global EEI increase over the past two decades.
A separate – and critical – question is whether current observational methods robustly quantify long-term trends themselves. An independent cloud radiative kernel (CRK) framework is used to diagnose the cloud contribution to SW trends. The CRK estimates reproduce the observed spatial pattern of trends but explain only about one third of the global-mean trend over 2003-2022, leaving a substantial residual with a near-uniform positive signal. Three lines of evidence suggest this residual may reflect observational or methodological uncertainties rather than a physical cloud response: (i) the SWCRK exhibits a small positive drift that is large enough to project onto multi-decadal SW cloud radiative effect trends, (ii) climate model results showing close agreement between radiative-kernel-based and CRK-based trends with no uniform residual, and (iii) deep convective cloud albedo diagnostics indicating subtle negative reflectance drifts. These findings motivate further work to quantify observational and methodological uncertainties in long-term SW cloud trend estimates and to clarify their implications for EEI attribution.
Mar 04 (MSC 365): POSTER SESSION
Mar 11: NO SEMINAR (Spring Recess)
Mar 18: STUDENT SEMINARS
Theresia Phoa (ATM)
Extreme Rainfall in South Florida: Insights From Statistically Downscaled Climate Data
Extreme rainfall events put significant pressure on infrastructure and pose serious risks to communities through flooding and structural damage. Improving resilience requires reliable regional projections of these events. However, widely used infrastructure planning resources such as NOAA's Atlas 14, rely on historical stationarity assumptions that may underestimate future risk under a changing climate. While current Global Climate Models (GCMs) provide valuable insight into potential changes in precipitation extremes, their coarse spatial resolution limits their usefulness for regional impact assessments. To bridge this gap, statistically downscaling method such as LOCA (Localized Constructed Analogs) often utilized to help translating large-scale climate model projections into higher-resolution data that better capture regional variability in extreme rainfall. This study evaluates the ability of LOCA to represent seasonal extreme rainfall in South Florida using outputs from the Community Earth System Model (CESM), CMIP5 (CCSM4) and CMIP6 (CESM2-LENS), in comparison to NOAA's nClimGrid as gridded observation estimates. The evaluation focuses on key metrics of daily rainfall extremes, including intensity and frequency, to determine how well downscaled climate data capture observed patterns of extreme rainfall in South Florida.
Lily Johnston (ATM)
Assessment of Subseasonal Predictability in the North American Multi-Model Ensemble
Subseasonal prediction occupies a critical transition between weather and climate prediction. At these timescales, forecast skill typically declines rapidly after about 10 days as deterministic atmospheric predictability is lost due to chaotic error growth. However, predictive skill can still arise from slower-evolving components of the climate system, including large-scale circulation patterns and boundary conditions. Quantifying predictability in this regime is therefore important for improving forecast systems and guiding confidence in extended-range forecasts. Multimodel ensemble systems provide a useful framework for examining these limits. The North American Multi-Model Ensemble (NMME) combines forecasts from multiple coupled climate models, increasing ensemble size while incorporating diversity in model physics and initialization strategies. In this study we analyze four NMME models – CCSM4, CFSv2, CESM1, and GEOS-5 – to assess subseasonal predictability across models with differing representations of physical processes. Predictability is evaluated using homogeneous and heterogeneous frameworks following Becker et al. [2014]. Homogeneous predictability assesses how well an ensemble mean forecast represents an individual realization from the same model using a leave-one-out approach. Heterogeneous predictability compares the ensemble mean from one model against a member from another model treated as "truth". Forecast skill and predictability are quantified using gridpoint-based root-mean-squared error (RMSE) and anomaly correlation (AC), with additional verification against ERA5 reanalysis. Results show that precipitation forecasts are largely under dispersive, with RMSE often exceeding ensemble spread, while surface temperature forecasts exhibit better spread-skill consistency. Homogeneous predictability consistently exceeds heterogeneous predictability, suggesting heterogeneous predictability provides only limited guidance as a proxy for real-world forecast skill.
Ana Tavares
School of Geography and the Environment, University of Oxford, UK
Guest of the Kirtman Group, Department of Atmospheric Sciences
Can Extratropical Interactions Create a Favourable Environment
for Tropical Cyclone Activity on the Subseasonal Timescale?
Tropical cyclone (TC) activity in the Atlantic varies significantly on subseasonal timescales, yet the factors modulating this variability beyond the Madden-Julian Oscillation (MJO) remain poorly understood. Recent studies have found that extratropical interactions also play a critical role, suppressing TC activity by increasing wind shear and reducing relative humidity through wave breaking. Additionally, Hansen et al. [2020] identified wind shear as the most important indicator of enhanced subseasonal TC activity, and their results implied that the MJO does not explain all the observed shear variability. We hypothesise that mid-latitude interactions may also create a favourable TC environment on this timescale. Our study quantifies how upper-tropospheric PV spatially and temporally influences Atlantic Accumulated Cyclone Energy (ACE), a proxy for TC activity. We use composite analyses to explore this relationship across the peak of the hurricane season (July-September) over the North Atlantic basin. Daily PV and geopotential height fields are obtained from ERA5, and ACE data is computed from the IBTrACS dataset. Anomalies are calculated relative to the 1980-2024 climatology, and ACE is filtered to isolate subseasonal signals. We construct both instantaneous and lagged composites of high and low subseasonal TC activity and assess the associated patterns in upper-level PV anomalies, along with precursor geopotential height anomalies in the upper, middle, and lower troposphere. Our results reveal that the tropical upper tropospheric trough region is an important indicator of abnormal subseasonal TC activity in the basin. Furthermore, we find a wave train forming 15 to 10 days prior to active TC activity periods, travelling from Northeast North America into the subtropical North Atlantic. Overall, this work suggests a potentially untapped source of predictability of TC activity on subseasonal timescales and advances our understanding of the influence of midlatitude interactions on TC activity.
Mar 25: STUDENT SEMINARS
Phoebe Scharle (OCE)
Organic Matter Coats Most Sea Spray Aerosols Over the Tropical Atlantic Ocean
Near Barbados
Phoebe Scharle1, Haley M. Royer2, Sujan Shrestha1, Edmund Blades1, Nurun Nahar Lata3, Zezhen Cheng3,
Swarup China3, Zihua Zhu3, Jefferey Reid4, Rebecca Parham5, Andrew P. Ault5, Cassandra J. Gaston1
1Department of Atmospheric Sciences, Rosenstiel School
2Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill
3Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA
4US Naval Research Laboratory, Monterey, CA
5Department of Chemistry, University of Michigan, Ann Arbor
Marine aerosols are shown to be dominated by mass by sea salt. The prevalence of organic aerosol coatings on sea spray is poorly characterized but important for marine aerosol-cloud-climate interactions and reactivity with trace gases. To evaluate organic enrichment of the surface of sea spray aerosols, we collected aerosols at the Ragged Point site in Barbados on silicon substrates and TEM grids using a three-stage microanalysis particle sampler (MPS) during both summer and winter field campaigns. Aerosol composition and morphology were measured across all three stages using time-of-flight secondary ion mass spectrometry (TOF-SIMS), a surface-sensitive technique. Organic coatings were observed on most sea spray particles. This coating was removed after sputtering the top 10 to 100 nm of the particles, revealing an inorganic salt core. Further, single particle analysis with computer-controlled scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (CCSEM-EDX) revealed the prevalence of this core-shell morphology with the shell enriched in organics coupled with divalent cations such as magnesium. Single-particle infrared and Raman spectroscopy (OPTIR-RAMAN) analysis provides further confirmation of organic matter enrichment in sea spray aerosol. Utilizing single-particle techniques to identify the inorganic and organic fractions of sea spray aerosol is critical for understanding aerosol morphology, composition, and phase state within the marine boundary layer.
Sophia DiPietro (ATM)
Seasonally Varying Drivers of Chronic Heat in South Florida
Studies of heat hazards have traditionally used a heat wave definition, which generally excludes much of the tropics and subtropics. The tropics and subtropics typically experience chronic heat, defined by extended periods of time at high heat thresholds. While extreme heat is an increasingly deadly and damaging disaster, the mechanisms of its interannual variability and long-term trends are poorly understood in chronically hot regions. Therefore, it is essential to establish an understanding of the drivers of heat hazard in these regions in order to provide more accurate future projections for adaptation and planning. This study identifies seasonally varying drivers of chronic heat in the South Florida region using high-resolution reanalysis data products. We find that temperatures are increasing more rapidly during the dry season than during the wet season due to an increase in summertime precipitation. Increasing precipitation limits temperature increases through cloud cover and evaporation cooling. We also find that different physiologically based metrics for evaluating heat hazard result in different seasonal trends for the region due to non-linearities in heat index at high temperature and humidity thresholds. Overall, our results demonstrate that the chronic heat hazard in South Florida is governed by seasonally distinct mechanisms and metric-dependent responses, with important implications for projections of the heat hazard in chronically hot regions.
Claire Fandel (OCE)
Influences of Dissolved Organic Carbon Quantity and Substrate Quality
on Bacterial Growth Efficiency
Claire Fandel1, Sabrina Glynn1, Mellisa Brock2, Allison Cook3, Alee Winkler1, Kayla Ellerbe1, Katrina Rosing1,
Tiffany Mastrovito4, Noah Schuhmann5, Miguel Desmarais2, Ewa Merz2, Jeff S. Bowman2, Kimberly J. Popendorf1
1Rosenstiel School
2Scripps Institution of Oceanography, La Jolla, CA
3College of Arts & Sciences, Texas A&M University, College Station
4California State University, Northridge
5California State Polytechnic University, Arcata
Dissolved Organic Carbon (DOC) comprises a complex pool of molecules central to global nutrient cycling. Marine heterotrophic bacteria utilize DOC as a primary energy source for respiration and to sustain or build biomass. The balance between these pathways determines the efficiency of the microbial loop, thus the magnitude of DOC available for export. This balance by heterotrophic bacteria is captured by bacterial growth efficiency (BGE), yet the extent to which DOC quantity and substrate quality regulate BGE remains unclear. DOC concentration represents substrate quantity, while deviations from Redfield stoichiometry reflect nutrient imbalances that may limit microbial metabolism through substrate quality. This study investigates how BGE varies with DOC quantity and substrate quality across diverse biogeochemical provinces of the California Current Ecosystem, spanning upwelling and offshore oligotrophic zones, sampled in the summer of 2025. Traditional BGE estimates rely on bacterial production rates (3H-leucine incorporation) and respiration rates (oxygen consumption). However, these methods may fail to capture the diversity of microbial energy use and are often limited by logistical constraints in the field. Therefore, we apply a recently developed method that quantifies energy turnover rates, measured via adenosine triphosphate (ATP) turnover rates using brief incubations with radiolabeled 32P-phosphate. This ATP-based approach provides a more direct and rapid way to measure the energetic denominator underlying BGE. By examining the links between DOC quantity and substrate quality and BGE in this manner, this work highlights the diversity in microbial dynamics across key environments reflective of the global ocean.
Apr 01: James Christie
Department of Atmospheric Sciences, Rosenstiel School
(1-hour ATM student seminar)
From the Lab to the Field:
Understanding how Atmospheric N2O5-Aerosol Chemical Reactions
Facilitate Wintertime Pollution in the Salt Lake Valley
Salt Lake City (SLC) frequently experiences severe wintertime pollution due to the accumulation of ammonium nitrate (AN) during inversion events. Recent measurements in SLC have suggested that the reaction between dinitrogen pentoxide (N2O5) and ambient aerosol drives most AN accumulation in the city. However, we lack quantitative information on which ambient aerosol sources are present, and how efficiently they react with N2O5 (with the rate of reaction denoted as γN2O5) to form AN. To understand how γN2O5 controls AN accumulation under polluted conditions in the SLC, thus improving our ability to predict wintertime pollution in SLC, measurements of γN2O5 for aerosol sources relevant to SLC are required.
In this seminar, I will discuss the impacts of several aerosol sources relevant to SLC on N2O5-aerosol reactivity, including the effects of changing single particle and bulk aerosol chemical composition on γN2O5, and how variability in aerosol chemical composition broadly affects secondary AN accumulation. Values of γN2O5 were informed through idealized laboratory studies using an aerosol-kinetic flow tube (AFT), particle sizing, and advanced mass spectroscopic techniques. Ambient values of γN2O5 were observed during a field campaign in SLC, where a custom-built ambient-AFT was deployed for several weeks to study the effects of inversion layer chemistry on γN2O5. The results of both laboratory and field studies suggest that γN2O5 is enhanced by an increased presence of mineral dust, road salt, and ammonium sulfate. We also find that γN2O5 is reduced by an increase in aerosol organic content and nitrate, suggesting increases in AN during inversion events limits secondary pollutant formation.
Apr 08: Dr. Xianglin Ren
Department of Ocean Sciences, Rosenstiel School
Driving Mechanisms of Global Marine Heatwaves in a Warming Climate
Marine heatwaves (MHWs), defined as prolonged periods of anomalously warm sea surface temperatures (SST), have occurred frequently in recent decades, posing increasing threats to marine ecosystems and coastal societies, necessitating a better understanding of their mechanism and predictability.
In the Northeast Pacific, the Pacific Decadal Oscillation (PDO) plays a dominant role in modulating coastal MHWs through changes in the mean state. During PDO positive phase, reduced coastal upwelling together with enhanced downward surface heat flux leads to warmer coastal SSTs, resulting in longer, stronger, and more frequent MHWs. Relative to the background warming trend, the positive PDO during 2013–2022 increases MHW duration by up to 43% and annual frequency by up to 32%. In the Atlantic, the Atlantic Meridional Overturning Circulation (AMOC) exerts a distinct and evolving influence. While its impact on MHWs has been limited in recent decades, continued weakening over the 21st century induces a bipolar see-saw response, with more frequent MHWs in the Southern Hemisphere and fewer in the Northern Hemisphere.
Beyond these regional modes, ocean dynamics also play a critical role in MHW evolution and predictability. Comparisons between dynamic and slab ocean simulations reveal that ocean dynamics significantly enhance MHW intensity and duration in mid-to-high latitude oceans and the eastern tropical Pacific, where MHWs are inherently tied to extreme El Niño events. Mixed-layer heat budget analysis further shows that vertical mixing and lateral heat transport strongly regulate heat accumulation during MHW episodes, yielding substantial differences in both the magnitude and temporal evolution of warm SST extremes between the two configurations. These processes also support multi-year MHW predictability in the North Atlantic, where AMOC variability provides an intrinsic source of long-term oceanic memory.
Apr 15 (11:00 am): Dr. Adam Sobel
Columbia University, New York
Guest of the Department of Atmospheric Sciences
Apr 15: Alexis Wilson
Department of Atmospheric Sciences, Rosenstiel School
(1-hour ATM student seminar)
Apr 22: Dr. Milan Curcic
Department of Ocean Sciences, Rosenstiel School
Wave Action Balance in Strongly Varying Currents
Wave action balance is the fundamental equation behind spectral wave models that are used for global wave forecasting. Originated in Whitham's [1965] variational method and generalized by Bretherton & Garrett [1968] to propagation over slowly-varying currents, wave action conservation has since been taken as accurate within the first order of the relative variation in the current field. Slow variation of currents has been assumed by most wave models to date. In this work, we analyze an expanded form of the wave action balance that includes 1st-order effects of current gradients within the wavetrain (this term was presented by Bretherton & Garrett but neglected as small). First, based on a month-long submesoscale (150-m resolution) simulation of ocean circulation, we demonstrate that the contribution of unresolved current gradients to the wave action tendency, at the 1st order, is ~6 times larger than the wave strain / convergence by wave grid-resolved currents, and ~1.2 times larger than the propagation term itself. Second, we perform numerical simulations of wave propagation over the 150-m resolution surface currents and quantify the adjustment of the wave field to the circulation. Not suprisingly, strong current gradients act to boost wave action gradients such that the propagation term becomes as dominant as the current strain terms. Although there has been increasing evidence in the past decade of strong impacts of the resolved currents on the wave fields, we believe that this is the first quantitative assessment of subgrid-scale current gradients on the wave field. We expect this effect to be important for the accuracy of swell propagation over large basins, as well as for wave amplification when crossing strong boundary currents.
Apr 29: Dr. Jane Baldwin
Department of Earth System Science, University of California Irvine
Guest of Amy Clement, Department of Atmospheric Sciences
