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Hurricane Ian rapidly intensified from Category 3 to 5 as it transited the wide West Florida Shelf (WFS). This is ascribed to heating by the anomalously warm shelf waters, despite the water depth being shallow when compared to the thicker, mixed layer areas of the deeper ocean. By examining temperature from long‐term moorings, we found that the sea surface and subsurface temperatures exceeded the climatologies by 1–2°C and 2–3°C, respectively. Additionally, these anomalously high temperatures in summer/fall of 2022 were related to the absence of Gulf of Mexico Loop Current interactions with the WFS slope at its “pressure point”. Without such offshore forcing to induce an upwelling circulation, the warmer waters on the shelf were not flushed and replaced by colder waters of deeper ocean origin. This work highlights the importance of subsurface temperature and ocean circulation monitoring on shallow continental shelves, which are largely overlooked in hurricane‐related ocean heat content observational programs. Plain Language Summary Rapid intensification of tropical cyclones can be fueled by upper ocean warm water. The favorable environment of high ocean heat potential is thought to be more likely during marine heatwaves. However, both the hurricane heat potential and marine heatwaves are primarily calculated from satellite‐derived sea surface data, with subsurface data largely overlooked due to lack of in situ measurements, particularly in coastal oceans where hurricanes may rapidly intensify before making landfall. Here we examine an unprecedented set of coastal ocean temperature records from long‐term (26 years) moorings on the wide West Florida Shelf for the cause of Hurricane Ian's rapid intensification to a Category 5 hurricane in 2022. We found that while sea surface temperatures exceeded their climatological mean values by 1–2°C in summer/fall of 2022, the subsurface temperature exceedances were even higher (2–3°C). These anomalously warm waters were further ascribed to a lack of a coastal ocean upwelling circulation due to the absence of offshore forcing by the Gulf of Mexico Loop Current. This work highlights the importance of subsurface temperature and current monitoring on shallow continental shelves, which are largely overlooked in hurricane‐related ocean heat content observing programs. Key Points Hurricane Ian (2022) rapidly intensified over a wide continental shelf with subsurface water 2–3°C warmer than climatology The anomalously warm water was related to the absence of Gulf of Mexico Loop Current interactions with the shelf slope Coastal ocean circulation and subsurface temperature monitoring is important for future hurricane intensification forecasts

One of the most significant, energetic, yet not well understood, oceanographic features in the Americas is the Gulf of Mexico Loop Current System (LCS), consisting of the Loop Current (LC) and the Loop Current Eddies (LCEs) it sheds. Understanding the dynamics of the LCS is fundamental to understanding the Gulf of Mexico's full oceanographic system, and vice versa. Hurricane intensity, offshore safety, harmful algal blooms, oil spill response, the entire Gulf food chain, shallow water nutrient supply, the fishing industry, tourism, and the Gulf Coast economy are all affected by the position, strength, and structure of the LC and associated eddies. This report recommends a strategy for addressing the key gaps in general understanding of LCS processes, in order to instigate a significant improvement in predicting LC/LCE position, evolving structure, extent, and speed, which will increase overall understanding of Gulf of Mexico circulation and to promote safe oil and gas operations and disaster response in the Gulf of Mexico. This strategy includes advice on how to design a long-term observational campaign and complementary data assimilation and numerical modeling efforts.

In the Gulf of Mexico (GoM), as the warm Loop Current (LC) extends into the southeastern Gulf, strong deep eddies are energized through LC interaction with topography and baroclinic instability. A 6-year free-running numerical simulation using a regional configuration of the Navy Coastal Ocean Model (NCOM) shows the importance of deep cyclones to Loop Current Eddy (LCE) formation, particularly in the deep region south of 25°N, circumscribed by the Yucatán Strait to the south and the steep lateral sidewalls of the Campeche Bank and the Florida Shelf to the west and east, respectively. Four eddy shedding events from this simulation illustrate ways that deep cyclones develop and strengthen jointly from baroclinic development as well as from lower-layer stretching when the LC moves away from the channel sidewalls. In all cases, the deep cyclone plays a key role: one event depicts the classic baroclinic joint-development process; two events demonstrate the influence of the steep bathymetry along the Campeche Bank and Florida Shelf in restricting lateral propagation; the fourth event emphasizes the role of a deep cyclone in preventing reattachment of a detached eddy. As deep cyclones are important in determining LCE separation, we advocate for more observation and modeling attention on the dynamics of the deep southeast channel.

Calorimetric biochemical measurements offer various advantages such as low waste, low cost, low sample consumption, short operating time, and labor-savings. Multichannel calorimeters can enhance the possibility of performing higher-throughput biochemical measurements. An enthalpy sensor (ES) array is a key device in multichannel calorimeters. Most ES arrays use Wheatstone bridge amplifiers to condition the sensor signals, but such an approach is only suitable for null detection and low resistance sensors. To overcome these limitations, we have developed a multichannel calorimetric simultaneous assay (MCSA) platform. An adjustable microampere constant-current (AMCC) source was designed for exciting the ES array using a microampere current loop measurement circuit topology. The MCSA platform comprises a measurement unit, which contains a multichannel calorimeter and an automatic simultaneous injector, and a signal processing unit, which contains multiple ES signal conditioners and a data processor. This study focused on the construction of the MCSA platform; in particular, construction of the measurement circuit and calorimeter array in a single block. The performance of the platform, including current stability, temperature sensitivity and heat sensitivity, was evaluated. The sensor response time and calorimeter constants were given. The capability of the platform to detect relative enzyme activity was also demonstrated. The experimental results show that the proposed MCSA is a flexible and powerful biochemical measurement device with higher throughput than existing alternatives.

This study proposes an analysis and specification of current loop tracking error in the grid-connected voltage source converter with direct current control. In practical applications, it is a common phenomenon that the current control loop sees a quite significant command-tracking error while the actual output current of the converter is still satisfactory, for example, for static var generators or parallel active power filters, it is exactly the reactive current and/or the harmonic current that are needed to compensate the load current. In this study, a detailed analysis is presented to investigate this confusing issue. Based on the obtained current loop transfer function, analytical expressions of the current tracking error are derived. The reasons why a significant current tracking error exists together with satisfactory compensation result are revealed subsequently. The current tracking error has a relationship with the source voltage. An over-shoot start current appears because of the current tracking error. Two new methods used to suppress the over-shoot current are also presented. Finally, the hardware experimental results verify the analysis and the methods of suppressing the over-shoot current.

Sheddings of Kuroshio Loop Current (KLC) eddies in the northeastern South China Sea (SCS) are investigated using mooring arrays, multiple satellite data, and data-assimilative HYCOM products. Based on altimeter sea surface heights between 1992 and 2014, a total of 19 prominent KLC eddy shedding (KLCES) events were identified, among which four events were confirmed by the concurrent moored and satellite observations. Compared to the leaping behavior of Kuroshio, KLCES is a relatively short-duration phenomenon that primarily occurs in boreal autumn and winter. The KLC and its shedding anticyclonic eddy (AE) trap a large amount of Pacific water with high temperature–salinity and low chlorophyll concentration in the upper layer. The corresponding annual-mean transport caused by KLCES reaches 0.24–0.38 Sv (1 Sv ≡ 10 6 m 3 s −1 ), accounting for 6.8%–10.8% of the upper-layer Luzon Strait transport. Altimeter-based statistics show that among ~90% of the historical KLCES events, a cyclonic eddy (CE) is immediately generated behind the AE southwest of Taiwan. Both energetics and stability analyses reveal that because of its large horizontal velocity shear southwest of Taiwan, the northern branch of KLC is strongly unstable and the barotropic instability of KLC constitutes the primary generation mechanism for the CE. After CE is generated, it quickly grows and gradually migrates southward, which in turn facilitates the detachment of AE from KLC. The intrinsic relationship between KLC and CE explains well why eddy pairs are commonly observed in the region southwest of Taiwan.

We estimate ocean heat content (OHC) change in the upper 2000 m in the Gulf of Mexico (GOM) from 1950 to 2020 to improve understanding of regional warming. Our estimates are based on 192 890 temperature profiles from the World Ocean Database. Warming occurs at all depths and in most regions except for a small region at northeastern GOM between 200 and 600 m. GOM OHC in the upper 2000 m increases at a rate of 0.38 ± 0.13 ZJ decade-1 between 1970 and 2020, which is equivalent to 1.21 ± 0.41 terawatts (TW). The GOM sea surface temperature (SST) increased ~1.0° ± 0.25°C between 1970 and 2020, equivalent to a warming rate of 0.19° ± 0.05°C decade-1. Although SST in the GOM increases at a rate approximately twice that for the global ocean, the full-depth ocean heat storage rate in the GOM (0.86 ± 0.26 W m-2) applied to the entire GOM surface is comparable to that for the global ocean (0.82–1.11 W m-2). The upper-1000-m layer accounts for approximately 80%–90% of the total warming and variations in the upper 2000 m in the GOM. The Loop Current advective net heat flux is estimated to be 40.7 ± 6.3 TW through the GOM. A heat budget analysis shows the difference between the advective heat flux and the ocean heat storage rate (1.76 ± 1.36 TW, 1992–2017) can be roughly balanced with the annual net surface heat flux from ECCO (-37.9 TW).

A recently developed tool, the multiscale window transform, along with the theory of canonical energy transfer is used to investigate the roles of multiscale interactions and instabilities in the Gulf of Mexico Loop Current (LC) eddy shedding. A three-scale energetics framework is employed, in which the LC system is reconstructed onto a background flow window, a mesoscale eddy window, and a high-frequency eddy window. The canonical energy transfer between the background flow and the mesoscale windows plays an important role in LC eddy shedding. Barotropic instability contributes to the generation/intensification of the mesoscale eddies over the eastern continental slope of the Campeche Bank. Baroclinic instability favors the growth of the mesoscale eddies that propagate downstream to the northeastern portion of the well-extended LC, eventually causing the shedding by cutting through the neck of the LC. These upper-layer mesoscale eddies lose their kinetic energy back to the background LC through inverse cascade processes in the neck region. The deep eddies obtain energy primarily from the upper layer through vertical pressure work and secondarily from baroclinic instability in the deep layer. In contrast, the canonical energy transfer between the mesoscale and the high-frequency frontal eddy windows accounts for only a small fraction in the mesoscale eddy energy balance, and this generally acts as a damping mechanism for the mesoscale eddies. A budget analysis reveals that the mesoscale eddy energy gained through the instabilities is balanced by horizontal advection, pressure work, and dissipation.

The Gulf of Mexico (GoM) is home to some of the most energetic eddies in the ocean. Warm‐core rings detach from the Loop‐Current and drift through the basin, transporting large amounts of heat and salt. These eddies, known as Loop Current rings (LCRs) have a crucial role in the GoM's dynamics and in the weather of the eastern US, and this role is largely conditioned by their longevity and decay properties. Here, we use an empirical method to estimate the energy evolution of all LCRs detached since 1993. We found that, contrary to the commonly accepted idea that LCRs conserve their energy as they drift through the GoM and decay suddenly against the western platform, LCRs' energy decay is faster in the eastern basin, and they typically lose three‐quarter of their energy before encountering the continental shelf. We also show that wind‐current feedback contributes to the energy decay and conversion. Plain Language Summary Ocean eddies can be long‐lived and carry large amounts of heat and salt across ocean basins and marginal seas. This is the case of Loop Current rings (LCRs), which are large warm‐core eddies drifting through the Gulf of Mexico (GoM). Understanding how these eddies lose their energy is key to understand their longevity and transport properties. Here, we use a previously validated empirical method based on in situ observations to estimate the time evolution of LCRs energy using satellite observations. We show that LCRs decay continuously during their life cycle, contrary to the previously accepted idea that they decay when collapsing against the western GoM's continental shelf. LCRs typically lose three‐quarter of their energy before reaching any topographic obstacle. Using wind observations, we also show that wind‐current interactions are key to the energy loss of these eddies. Key Points Time evolution of the energy of warm‐core rings in the Gulf of Mexico is assessed using empirical methods and satellite altimetry The vast majority of mechanical energy (kinetic plus available potential) is lost early in the eddies’ life cycles, far from the western boundary Wind‐current feed back effects play an important role in energy conversion and decay