The air-sea response during Hurricane Irma's (2017) rapid intensification over the Amazon-Orinoco River plume as measured by atmospheric and oceanic observations

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Atmospheres 125(18), (2020): e2019JD032368, doi:10.1029/2019JD032368.Hurricane Irma (2017) underwent rapid intensification (RI) while passing over the Amazon‐Orinoco River plume in the tropical Atlantic. The freshwater discharge from the plume creates a vertical salinity gradient that suppresses turbulent heat flux from the cool, ocean subsurface. The stability within the plume reduces sea surface temperature (SST) cooling and promotes energetic air‐sea fluxes. Hence, it is hypothesized that this ocean feature may have facilitated Irma's RI through favorable upper ocean conditions. This hypothesis is validated using a collection of atmospheric and oceanic observations to quantify how the ocean response influences surface flux and atmospheric boundary layer thermodynamics during Hurricane Irma's RI over the river plume. Novel aircraft‐deployed oceanic profiling floats highlight the detailed evolution of the ocean response during Irma's passage over the river plume. Analyses include quantifying the ocean response and identifying how it influenced atmospheric boundary layer temperature, moisture, and equivalent potential temperature (θE). An atmospheric boundary layer recovery analysis indicates that surface fluxes were sufficient to support the enhanced boundary layer θE (moist entropy) observed, which promotes inner‐core convection and facilitates TC intensification. The implicit influence of salinity stratification on Irma's intensity during RI is assessed using theoretical intensity frameworks. Overall, the findings suggest that the salinity stratification sustained SST during Irma's passage, which promoted energetic air‐sea fluxes that aided in boundary layer recovery and facilitated Irma's intensity during RI. Examination of the air‐sea coupling over this river plume, corresponding atmospheric boundary layer response, and feedback on TC intensity was previously absent in literature.This research was performed while the corresponding author held an NRC Research Associateship Award at the U.S. Naval Research Lab, Monterey. Chen is supported by Office of Naval Research (ONR) grant N0001416WX00470. Sanabia is sponsored by ONR grants N0001416WX01384 and N0001416WX01262. Jayne is supported by National Oceanic and Atmospheric Administration (NOAA) grant NA13OAR4830233.The authors gratefully acknowledge the HRD scientists, NOAA AOC crews, U.S. Air Force crews, and U.S. Navy crews who were involved in the collection of both atmospheric and oceanic data. This research would not be possible without your efforts. We are thankful for helpful discussion and pre‐RI AXBT data provided by Jun Zhang (NOAA/HRD).2020-12-1

Catalyzing Remote Collaboration During the COVID-19 Pandemic and Beyond: Early Career Oceanographers Adopt Hybrid Open Science Framework

The COVID-19 pandemic introduced many challenges for research scientists: reduction of lab and field observation collection and in-person meetings. These new constraints forced researchers to remote work and virtual networking, dramatically influencing scientific inquiry. Such challenges are compounded for those in early stages of their career, where data collection and networking are vital to be seen as productive. However, during this trying time of remote work, we, as a collective of early-career oceanographers, were actively developing and improving on an already-existent hybrid community of practice. Through our experiences, we believe this type of framework can enhance virtual collaboration to the point that it outlasts the pandemic and helps create new synergies that will diversify and enhance scientific inquiry within the ocean science community. We describe a hybrid community of practice and an example workflow that models effective collaboration. We have found that three components to this model are necessary for effective collaboration, inspiration, and communication: 1) openly accessible data, 2) software, computational, and professional-development resources, and 3) a team science approach. In our experience, both the in-person and remote aspects of the model are important. In person collaboration is key to expanding the community of practice and invigorating those already within the community. Remote collaboration has been critical for effective collaborations between in-person activities and has proven to maximize outputs during in-person collaborations. While the three components of this model are not new to the scientific community, we believe that utilizing them strategically post-pandemic will diversify and expand scientific collaboration in oceanography

On the hyperbolicity of the bulk air-sea heat flux functions: Insights into the efficiency of air-sea moisture disequilibrium for tropical cyclone intensification

Sea-to-air heat fluxes are the energy source for tropical cyclone (TC) development and maintenance. In the bulk aerodynamic formulas, these fluxes are a function of surface wind speed U10 and air-sea temperature and moisture disequilibrium (ΔT and Δq, respectively). Although many studies have explained TC intensification through the mutual dependence between increasing U10 and increasing sea-to-air heat fluxes, recent studies have found that TC intensification can occur through deep convective vortex structures that obtain their local buoyancy from sea-to-air moisture fluxes, even under conditions of relatively low wind. Herein, a new perspective on the bulk aerodynamic formulas is introduced to evaluate the relative contribution of wind-driven (U10) and thermodynamically driven (ΔT and Δq) ocean heat uptake. Previously unnoticed salient properties of these formulas, reported here, are as follows: 1) these functions are hyperbolic and 2) increasing Δq is an efficient mechanism for enhancing the fluxes. This new perspective was used to investigate surface heat fluxes in six TCs during phases of steady-state intensity (SS), slow intensification (SI), and rapid intensification (RI). A capping of wind-driven heat uptake was found during periods of SS, SI, and RI. Compensation by larger values of Δq . 5 gkg-1 at moderate values of U10 led to intense inner-core moisture fluxes of greater than 600Wm22 during RI. Peak values in Δq preferentially occurred over oceanic regimes with higher sea surface temperature (SST) and upper-ocean heat content. Thus, increasing SST and Δq is a very effective way to increase surface heat fluxes-this can easily be achieved as a TC moves over deeper warm oceanic regimes

Open Data, Collaborative Working Platforms, and Interdisciplinary Collaboration: Building an Early Career Scientist Community of Practice to Leverage Ocean Observatories Initiative Data to Address Critical Questions in Marine Science

Ocean observing systems are well-recognized as platforms for long-term monitoring of near-shore and remote locations in the global ocean. High-quality observatory data is freely available and accessible to all members of the global oceanographic community—a democratization of data that is particularly useful for early career scientists (ECS), enabling ECS to conduct research independent of traditional funding models or access to laboratory and field equipment. The concurrent collection of distinct data types with relevance for oceanographic disciplines including physics, chemistry, biology, and geology yields a unique incubator for cutting-edge, timely, interdisciplinary research. These data are both an opportunity and an incentive for ECS to develop the computational skills and collaborative relationships necessary to interpret large data sets. Here, we use observatory data to demonstrate the potential for these interdisciplinary approaches by presenting a case study on the water-column response to anomalous atmospheric events (i.e., major storms) on the shelf of the Mid-Atlantic Bight southwest of Cape Cod, United States. Using data from the Ocean Observatories Initiative (OOI) Pioneer Array, we applied a simple data mining method to identify anomalous atmospheric events over a four-year period. Two closely occurring storm events in late 2018 were then selected to explore the dynamics of water-column response using mooring data from across the array. The comprehensive ECS knowledge base and computational skill sets allowed identification of data issues in the OOI data streams and technologically sound characterization of data from multiple sensor packages to broadly characterize ocean-atmosphere interactions. An ECS-driven approach that emphasizes collaborative and interdisciplinary working practices adds significant value to existing datasets and programs such as OOI and has the potential to produce meaningful scientific advances. Future success in utilizing ocean observatory data requires continued investment in ECS education, collaboration, and research; in turn, the ECS community provides feedback, develops knowledge, and builds new tools to enhance the value of ocean observing systems. These findings present an argument for building a community of practice to augment ECS ocean scientist skills and foster collaborations to extend the context, reach, and societal utility of ocean science

Ocean mixing during Hurricane Ida (2021): the impact of a freshwater barrier layer

Tropical cyclones are +ne of the costliest and deadliest natural disasters globally, and impacts are currently expected to worsen with a changing climate. Hurricane Ida (2021) made landfall as a category 4 storm on the US Gulf coast after intensifying over a Loop Current eddy and a freshwater barrier layer. This freshwater layer extended from the coast to the open ocean waters south of the shelf-break of the northern Gulf of Mexico (GoM). An autonomous underwater glider sampled this ocean feature ahead of Hurricane Ida operated through a partnership between NOAA, Navy, and academic institutions. In this study we evaluate hurricane upper ocean metrics ahead of and during the storm as well as carry out 1-D shear driven mixed layer model simulations to investigate the sensitivity of the upper ocean mixing to a barrier layer during Ida’s intensification period. In our simulations we find that the freshwater barrier layer inhibited cooling by as much as 57% and resulted in enhanced enthalpy flux to the atmosphere by as much as 11% and an increase in dynamic potential intensity (DPI) of 5 m s-1 (~9.72 knots) in the 16 hours leading up to landfall. This highlights the utility of new ocean observing systems in identifying localized ocean features that may impact storm intensity ahead of landfall. It also emphasizes the northern Gulf of Mexico and the associated Mississippi River plume as a region and feature where the details of upper ocean metrics need to be carefully considered ahead of landfalling storms

The Influence of the Barrier Layer on SST Response during Tropical Cyclone Wind Forcing Using Idealized Experiments

Abstract Multiple studies have shown that reduced sea surface temperature (SST) cooling occurs under tropical cyclones (TCs) where a fresh surface layer and subsurface halocline exist. Reduced SST cooling in these scenarios has been attributed to a barrier layer, an upper-ocean feature in the tropical global oceans in which a halocline resides within the isothermal mixed layer. Because upper-ocean stratification theoretically reduces ocean mixing induced by winds, the barrier layer is thought to reduce SST cooling during TC passage, sustaining heat and moisture fluxes into the storm. This research examines how both the inclusion of salinity and upper-ocean salinity stratification influences SST cooling for a variety of upper-ocean thermal regimes using one-dimensional (1D) ocean mixed layer (OML) models. The Kraus–Turner, Price–Weller–Pinkel, and Pollard–Rhines–Thompson 1D OML schemes are used to examine SST cooling and OML deepening during 30 m s−1 wind forcing (~category 1 TC) for both temperature-only and temperature–salinity stratification cases. Generally, the inclusion of salinity (a barrier layer) reduces SST cooling for all temperature regimes. However, results suggest that SST cooling sensitivities exist depending on thermal regime, salinity stratification, and the 1D OML model used. Upper-ocean thermal and haline characteristics are put into context of SST cooling with the creation of a barrier layer baroclinic wave speed to emphasize the influence of salinity stratification on upper-ocean response under TC wind forcing

The Impact of the Amazon–Orinoco River Plume on Enthalpy Flux and Air–Sea Interaction within Caribbean Sea Tropical Cyclones

Abstract The influence of the Amazon–Orinoco River plume in the Caribbean Sea on latent and sensible heat flux (enthalpy flux) and tropical cyclone (TC) intensity is investigated for Hurricanes Ivan (2004), Emily (2005), Dean (2007), and Felix (2007) using dropwindsonde data, satellite sea surface temperature (SST), and the SMARTS climatology. Relationships among enthalpy fluxes, ocean heat content relative to the 26°C isotherm depth (OHC), and SST during storm passage are diagnosed. Results indicate that sea surface cooling in the river plume, a low-OHC region, is comparable to that in the warm eddy region, which has high OHC. An isothermal layer heat budget shows that upper-ocean cooling in the river plume can be explained predominantly by sea-to-air heat flux, rather than by entrainment flux from the thermocline. The latter two findings suggest that relatively large upper-ocean stratification in the plume regime limited entrainment cooling, sustaining SST and enthalpy flux. Inspection of atmospheric variables indicates that deep moderate wind shear is prevalent, and equivalent potential temperature is enhanced over the river plume region for most of these storms. Thus, sustained surface fluxes in this region may have provided warm, moist boundary layer conditions, which may have helped these storms to rapidly intensify even over relatively low-OHC waters and moderate shear. These findings are important because several Caribbean Sea TCs, including these cases, have been underforecast with respect to intensity and/or rapid intensifications, yet minimal upper-ocean observations exist to understand air–sea interaction during TCs in the salinity-stratified Amazon–Orinoco plume regime