SPRING 2025
Fridays at 11:00 am, Rosenstiel School Auditorium / Virtual Auditorium
Jan 17: NO SEMINAR
Jan 24: AVAILABLE
Jan 31: NO SEMINAR (Provost Search Committee Event)
Feb 07: NO SEMINAR (Recruitment Weekend)
Feb 14: STUDENT SEMINARS
Chanyoung Park (ATM)
Negligible Contribution from Aerosols to Recent Trends in Earth's Energy Imbalance
During the 21st century, Earth's energy imbalance (EEI) at the top of the atmosphere has markedly increased, mainly due to an increase in absorbed shortwave (SW) rather than a decrease in outgoing longwave (LW) radiation. While previous studies, based on single-forcing (aerosol-only) experiments, linked reductions in anthropogenic aerosols to this positive SW trend, we find that both aerosol-radiation interactions and aerosol-cloud interactions have had a negligible impact on recent increases in the EEI. We estimate recent trends in effective radiative forcing due to aerosols using observations and reanalysis data. While aerosol concentrations have declined in the Northern Hemisphere (NH), wildfires and volcanic activity in the Southern Hemisphere (SH) have resulted in larger aerosol loading. This contrast effectively cancels out the total aerosol forcing, resulting in a negligible global impact on the EEI trend (–0.012 ±0.04 W m–2 decade–1 for aerosol index and –0.0003 ±0.04 W m–2 decade–1 for sulfate mass concentration). Our findings also suggest that model-driven estimates may be overestimated (0.14 W m–2 decade–1 for the multi-model mean), as they overlook the compensating effects of SH aerosol emissions that balance out NH reductions.
Steven Akin (MPO)
Richardson Numbers Across Three Ocean Regimes
in the Path of Hurricane Michael (2018)
Barrier layers (BLs) form in the upper ocean between the base of the mixed layer and top of the thermocline. Their contribution to tropical cyclone intensification has been well-documented while the dynamics affecting their erosion or resilience have yet to be explored thoroughly. In 2018, the Upper Ocean Dynamics Lab deployed a robust suite of airborne expendables and three APEX-EM floats in the Gulf of Mexico ahead of Hurricane Michael. During its passage, Michael traversed a complex eddy field with three noteworthy ocean features: a detached Loop Current eddy (Eddy "Revelle"), a blocking eddy, and the "mid-field" between them. The mid-field was marked by low shear and moderately high buoyancy, resulting in a stable environment where BLs up to 24.4 m thick were recorded. The purpose of this talk will be to contrast the evolution of buoyancy frequency, horizontal shear, and Richardson numbers across the three different regimes and to discuss how these factors play a role in BL erosion or resiliency.
Michael Perez (ATM)
Airborne Remote Sensing Measurements of Super-Cooled Liquid
Above the Arctic Sea Ice
The Arctic is warming 2 to 4 times faster than the global average, with the role played by liquid-bearing clouds at sub-freezing temperatures still uncertain. The NASA Arctic Radiation-Cloud-Aerosol-Surface Interaction Experiment (ARCSIX) aircraft campaign, held during the summer of 2024, acquired unique measurements relevant to characterizing the cloud radiative effect upon the Arctic sea ice north of Greenland. Cloud liquid water path (LWP) and water vapor paths (WVP) are retrieved from brightness temperatures acquired by an upward-pointing airborne 183 GHz G-Band Vapor Radiometer (GVR). Two bands centered near the 183 GHz water vapor absorption band are primarily sensitive to WVP, while the 183 GHz ±7,14 GHz channels are more sensitive to LWP. An iterative method is developed to retrieve LWP values from the measured brightness temperatures and representative dropsonde thermodynamic profiles. A further initial task requires calibration against clear-sky dropsonde profiles. 'Cloud walls' executed during the campaign provide multiple repeat measurements of cloud decks, which can be assessed using in-situ liquid water content profiles. Our first case study, featuring multiple cloud layers with cloud top temperatures of –15°C, sampled on May 30, indicate GVR retrievals provide LWP values comparable to the in-situ measurements. The retrievals greatly expand the sampling of these thermodynamically-unstable clouds. A further comparison of the WVPs to those available from longer-term radiosondes at Alert, Canada, indicates more moisture is available over the central Arctic than at the northeast end of Ellesmere Island.
Feb 21: STUDENT SEMINARS
Rachel Sampson (MPO)
From Rings to Water Masses: Agulhas Leakage's Influence in the Cape Basin
Agulhas Leakage is the inter-ocean exchange of warm, salty Indian Ocean waters into the cooler, fresher South Atlantic. The result is a northward flux of heat and salt which may contribute to the Atlantic Meridional Overturning Circulation's strength, stability, and variability. These fluxes are challenging to quantify because of the turbulent nature of the leakage, a background hotspot of eddy kinetic energy, and fluctuations in air-sea fluxes. For the first time, we present a climatological view of water mass transformation along the Leakage Corridor – utilizing 33,563 ARGO profiles collected over 20 years – to emphasize Agulhas leakage's influence in driving water mass changes. Water masses are characterized by their properties and gradients in the Cape Basin, with transformations quantified by a combination of property variations and water mass thickness. Two key sites for water mass transformations have been found, the Agulhas Retroflection Front and the center of the Leakage Corridor. At the Retroflection, the South Atlantic Mode Waters (SASTMW) and the South Indian Central Waters (Agulhas Leakage Mode waters, SICW) are cooling and freshening due to the intrusion of cooler, fresher South Atlantic waters. These layers are thinning as isopycnals are pushed up by the front and subsurface topography. At the second site, heat and salt are transferred into the South Atlantic Mode Waters as they thicken along the corridor. In contrast, the leakage mode waters (SICW) are cooling and thinning, losing some of their warm, salty signature. Our next step is to quantify heat and salt transports in these water masses, confirming the exchange of Agulhas Leakage waters and its role in water mass transformations.
Samuel Ephraim (ATM)
A New Neural Network Retrieval of Liquid Water Path
Optimized for Mixed-Phase Cold Air Outbreaks
Using Radiometer and Radar Observations
Cold-air outbreaks over high latitude oceans typically include mixed-phase clouds and precipitation, in particular liquid clouds that support snow and graupel through ice growth processes. The partitioning of the total water into the liquid and ice phases impacts both weather and climate prediction, but accurate measurements on the phase partitioning remain difficult to acquire, especially near-real-time. Here we present a neural network approach to retrieve liquid water path (LWP) using passive microwave measurements combined with vertically-integrated radar reflectivities. The approach is an extension of Cadeddu et al. (2009), with the novel addition of radar reflectivity. The neural network is trained using the Passive and Active Microwave radiative TRAnsfer (PAMTRA) code applied to output from numerical simulations of three independent cold-air outbreaks sampled during the Cold-Air Outbreaks in the Marine Boundary Layer Experiment (COMBLE) campaign. Brightness temperatures corresponding to the four sidebands of an upward-looking G-band (183 GHz) Vapor Radiometer, along with the vertically-integrated reflectivity from a zenith-pointing 95 GHz Wyoming Cloud Radar, are simulated from the perspective of a near-surface aircraft track. The radar reflectivity helps discriminate the snow contribution to the brightness temperatures. The neural network regression is thereafter tested on a simulation of an independent cold-air outbreak during COMBLE, and against measurements from the US Department of Energy Atmospheric Radiation Measurement North Slope of Alaska observatory. This neural network approach is shown to provide robust, computationally-efficient, near-real-time measurements of LWP and water vapor path during the Cold Air Outbreak Experiment in the Sub-Arctic Region (CAESAR) campaign in February-April 2024.
Madeleine Dawson (OCE)
Advancing Island Wake Characterization
With Multi-Sensor Synthetic Aperture Radar Imagery
Island wakes arise from the interaction between incoming flow and island topography, typically developing on the leeward side as regions of reduced wind speed. However, their structure and extent are influenced by factors such as island size and topographic features, leading to significant variability in wake characteristics. This underscores the need to complement existing theoretical and experimental studies with direct observational approaches to accurately capture the complexities of island wake dynamics. Synthetic Aperture Radar (SAR) is a powerful tool for studying island wakes, providing cloud-penetrating observations of ocean surface roughness independent of sunlight illumination. SAR's ability to detect spatial variations in wake structure at high resolution makes it particularly valuable for analyzing wind-induced island wakes. It captures changes in backscatter intensity, which correspond to variations in surface roughness. These backscatter changes can be directly related to ocean surface wind speed using the CMOD5 Geophysical Model Function (GMF), enabling a quantitative assessment of wake structure and wind speed distribution. This study utilizes C-band Sentinel-1 SAR imagery from the European Space Agency to investigate wake dynamics using CMOD5. During the Office of Naval Research-funded Island Arc Turbulent Eddy Regional Exchange (ARCTERX) cruise in January 2025, additional SAR imagery was collected across multiple sensors focused on the Western Pacific over Guam, Saipan, and Tinian. This data was collected primarily in X band to extend upon the initial investigation, as its higher frequency enables finer-scale detection of surface roughness variations compared to C band. Future work will focus on integrating this X-band SAR data collected by the University of Miami's Center for Southeastern Tropical Advanced Remote Sensing (CSTARS) into the existing analysis.
Feb 28: NO SEMINAR (Rosenstiel School Faculty Meeting)
Mar 07: Dr. Kosuke Ito
Kyoto University, Japan
Guest of David Nolan, Department of Atmospheric Sciences
Three-Dimensional Fujiwhara Effect
It has been widely believed that binary tropical cyclones (TCs) rotate cyclonically and get closer to each other with respect to the center of the circulations (known as "Fujiwhara effect"). In fact, binary TCs (initially separated by 1000 km or more) move away from each other in the quiescent environment on an f-plane, based on an idealized simulation with a three-dimensional model. To investigate this phenomenon, we calculated the potential vorticity (PV) budget and found that the horizontal advection term was largely compensated by the asymmetric diabatic heating. The asymmetric diabatic heating served to resist the cyclonic rotation and help the motion moving away from each other. This asymmetric diabatic heating was associated with the vertical wind shear (VWS) consisting of the upper-level anticyclonic circulation and lower-level cyclonic circulation, both of which were originally from the binary TCs. These three-dimensional Fujiwhara effects were verified in the western North Pacific using the best track and ERA5 reanalysis data. The TC motion was found to deviate systematically from the steering flow. The direction of deviation is clockwise and repelling with respect to the midpoint of the binary TCs with a separation distance of more than 1000 km. The large-scale upper-level anticyclonic and lower-level cyclonic circulations serve as the VWS for each TC in a manner consistent with the idealized simulations. The VWS of a TC tends to be directed to the rear-left quadrant from the direction of the counterpart TC, where the maxima of rainfall and diabatic heating are observed. The PV budget analysis supports that the actual TC motion is modulated by the diabatic heating asymmetry that offsets the counterclockwise and approaching motion owing to horizontal advection when the separation distance of the binary TCs is 1000–2000 km. With a small separation distance (<1000 km), horizontal advection becomes significant, but the impact of diabatic heating asymmetry is not negligible. These features are robust, while there are some dependencies on the TC intensities, size, circulation, duration, and geographical location. This research sheds light on the motion of binary TCs that has not been previously explained by a two-dimensional barotropic framework.
Mar 14: NO SEMINAR (Spring Recess)
Mar 21: Dr. Shafer Smith
Department of Mathematics, New York University
Guest of Lisa Beal, Department of Ocean Sciences
Mar 28: STUDENT SEMINARS
Katie Simi (OCE)
Gabby Ricche (OCE)
Sabrina Glynn (OCE)
Apr 04: STUDENT SEMINARS
Cam Pine (ATM)
Will Downs (ATM)
Paloma Cartwright (OCE)
Apr 11: STUDENT SEMINARS
Alexis Wilson (ATM)
Snigdha Samantaray (MPO)
Claire Fandel (OCE)
Apr 18: STUDENT SEMINARS
Jo Kaiser (ATM)
Christina Schuler (ATM)
Ian Gifford (MPO)
Apr 25: AVAILABLE
FALL 2025 OUTLOOK:
Oct 10: Dr. Claudia Benitez-Nelson
School of the Earth, Ocean & Environment, University of South Carolina, Columbia
Invited Speaker of the Department of Ocean Sciences
