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The heterogeneity in surface roughness caused by transient, nonlinear internal ocean waves is readily observed in coastal waters. However, the quantifiable impact this heterogeneity has on the marine atmospheric surface layer has not been documented. A comprehensive data set collected from a unique ocean platform provided a novel opportunity to investigate the interaction between this internal ocean process and the atmosphere. Relative to the background atmospheric flow, the presence of internal waves drove wind velocity and stress variance. Furthermore, it is shown that the wind gradient adjusts across individual wave fronts, setting up localized shear that enhanced the air‐sea momentum flux over the internal wave packet. This process was largely mechanical, though secondary impacts on the bulk humidity variance and gradient were observed. This study provides the first quantitative analysis of this phenomenon and provides insights into submesoscale air‐sea interactions over a transient, internal ocean feature. The ocean surface appears rough because the wind applies a tangential force to the water, which deforms the surface, generating short and steep waves. These small waves, in turn, increase the friction felt by the wind as it blows across the ocean surface, thereby setting up a feedback mechanism that physically links, or couples, the lower atmosphere to the upper ocean. However, our understanding of this interaction in the case of a heterogeneously rough ocean surface is limited. Using a unique ocean platform, we have collected a novel and complete data set demonstrating the impact internal ocean waves have on the near‐surface atmospheric variability, through their modulation of the ocean surface roughness. The surface currents associated with internal waves generate bands of smooth and rough water that travel coherently with the internal wave packet. Our analysis shows that these transient surface features have a distinct and profound impact on the physical characteristics and structure of the near‐surface atmosphere. In particular, internal waves enhance the wind forcing over the ocean and individual wave fronts significantly alter the vertical wind gradient. Our results provide the first documentation of the impact internal waves have on the atmosphere and suggest that these dynamics should be accounted for when studying fine‐scale atmosphere‐ocean interactions and the impact internal waves have on the marine environment. The first quantitative analysis detailing interactions between a nonlinear internal ocean wave packet and the atmosphere is presentedThe mean wind velocity and Reynolds stress components responded directly to internal wave‐induced roughness variabilityEvidence for responses in the humidity variance and gradient were found, but temperature was not directly impacted by the internal waves

In our era, the rapid increase of parallel programming coupled with high‐performance computing (HPC) facilities allows for the use of two‐dimensional shallow water equation (2D‐SWE) algorithms for simulating floods at the “hydrological” catchment scale, rather than just at the “hydraulic” fluvial scale. This approach paves the way for the development of new operational systems focused on impact‐based flash‐floods nowcasting, wherein hydrodynamic simulations directly model the spatial and temporal variability of measured or predicted rainfall on impacts even at a street scale. Specifically, the main goal of this research is to make a step to move toward the implementation of an effective flash flood nowcasting system in which timely and accurate impact warnings are provided by including weather radar products in the HPC 2D‐SWEs modelling framework able to integrate watershed hydrology, flow hydrodynamics, and river urban flooding in just one model. The timing, location, and intensity of the street‐level evolution of some key elements at risk (people, vehicles, and infrastructures) are also discussed considering both calibration issues and the role played by the spatial and temporal rainfall resolution. All these issues are analyzed and discussed having as a starting point the flood event which hit the Mandra town (Athens, Greece) on the 15 November 2017, highlighting the feasibility and the accuracy of the overall approach and providing new insights for the research in this field. In this study, we try to investigate if there is a potentiality for using a flood simulator, which usually requires a lot of time to give the final results, in order to predict, in real‐time, the flood hazard at the roads of a city. For this reason, we exploited the use of supercomputers, which significantly quickened the simulations and the meteorological forecasting given by a weather radar. According to our findings, there is merit for the proposed approach which can shift the flood awareness from generic instructions to more specific predictions, regarding the place and the time of the flood peak. The potential of radar data and high‐performance computing two‐dimensional shallow water equation solvers at the watershed scale for impact‐based flash‐flood nowcasting system is highlightedReliable prediction of water depths within the urban area, with run time 30 times faster than real‐time using a high‐resolution gridRain resolution can affect simulated arrival times, peak and time‐to‐peak values, and street‐level prediction of the effects on a specific target The potential of radar data and high‐performance computing two‐dimensional shallow water equation solvers at the watershed scale for impact‐based flash‐flood nowcasting system is highlighted Reliable prediction of water depths within the urban area, with run time 30 times faster than real‐time using a high‐resolution grid Rain resolution can affect simulated arrival times, peak and time‐to‐peak values, and street‐level prediction of the effects on a specific target

This paper reports upper ocean thermohaline structure and variability observed during the life cycle of an intense Madden Julian Oscillation (MJO) event occurred in the southern tropical Indian Ocean (14°S–Eq, 70°E–81°E). Water column measurements for this study were collected using airborne expendable probes deployed from NOAA's WP‐3D Orion aircraft operated as a part of Dynamics of MJO field experiment conducted during November–December 2011. Purpose of the study is twofold; (1) to provide a statistical analysis of the upper ocean properties observed during different phases of MJO and, (2) to investigate how the upper ocean thermohaline structure evolved in the study region in response to the MJO induced perturbation. During the active phase of MJO, mixed layer depth (MLD) had a characteristic bimodal distribution. Primary and secondary modes were at ∼34 m and ∼65 m, respectively. Spatial heterogeneity of the upper ocean response to the MJO forcing was the plausible reason for bimodal distribution. Thermocline and isothermal layer depth deepened, respectively, by 13 and 19 m from the suppressed through the restoring phase of MJO. Thicker (>30 m) barrier layers were found to occur more frequently in the active phase of MJO, associated with convective rainfalls. Additionally, the water mass analysis indicated that, in the active phase of this MJO event the subsurface was dominated by Indonesian throughflow, nonetheless intrusion of Arabian Sea high saline water was also noted near the equator. In situ observations are made from the tropical Indian Ocean using airborne expendable probes deployed from P‐3 Orion aircraftResponse of mixed layer, isothermal layer, and thermocline is analyzed with respect to the different phases of MJO in the Indian OceanIn the active phase of MJO, the mixed layer depth showed a bimodal distribution

The constant flux layer assumption simplifies the problem of atmospheric surface layer (ASL) dynamics and is an underlying assumption of Monin‐Obukhov similarity theory (MOST), which is ubiquitously applied to model interfacial exchange and atmospheric turbulence. Within the marine environment, the measurements necessary to confirm the local ASL as a constant flux layer are rarely available, namely: direct observations of the near‐surface flux gradients. Recently, the Research Platform FLIPwas deployed with a meteorological mast that resolved the momentum and heat flux gradients from 3 to 16 m above the ocean surface. Here, we present an assessment of the prevalence of the constant flux layer within the ASL, using an approach that accounted for the role of wave‐coherent motion in air and evaluated each observed flux gradien. Our analysis revealed that only 30%–40% of momentum flux gradients were approximately constant; for the heat fluxes, this increased to 50%–60%. For low winds, the stationarity of local turbulence was critical to the constant flux layer's validity, but resulted in excising a large proportion of the observed profiles. Under moderate wind speeds, swell‐wind alignment was associated with momentum flux divergence. Our findings suggest that the constant flux layer, as it is conventionally defined, is not generally valid over the ocean. This holds significant implications for measuring air‐sea fluxes from single point sources and marine applications of MOST. Our ability to quantify the exchange of energy and material (e.g., gas) between the atmosphere and ocean has greatly improved over the second half 20th and into the beginning of the 21st centuries. While there have been significant technological and methodological advancements within the community of researchers studying this problem, a central theory to the physical framework we use to conduct the majority of studies has not been adequately validated or assessed using observations over the ocean. The constant flux layer model (or assumption) greatly simplifies the physical problem of studying the atmosphere near the ocean surface, but the data necessary to validate this theory are rarely collected. A recent field campaign deployed a unique ocean‐going platform that enabled us to conduct this much needed evaluation. We found strong evidence suggesting that the constant flux layer model is only valid within the general marine environment at most 50%–60% of the time. We also found that the prevalence of this theory's validity differed between the exchange (i.e., flux) of kinetic energy and heat, two critical parameters controlling the atmosphere‐ocean system. Our findings suggest that the simplified physics we rely on to study air‐sea exchange needs to be critically re‐evaluated. Profiles of eddy covariance fluxes were used to evaluate the prevalence of the constant flux layer above ocean wavesOnly one third of momentum flux gradients were deemed "constant"; non‐divergence was substatially higher for the heat fluxesFlux divergence was strongly linked with turbulence non‐stationarity, swell‐wind alignment, and moderate‐strong stability conditions Profiles of eddy covariance fluxes were used to evaluate the prevalence of the constant flux layer above ocean waves Only one third of momentum flux gradients were deemed "constant"; non‐divergence was substatially higher for the heat fluxes Flux divergence was strongly linked with turbulence non‐stationarity, swell‐wind alignment, and moderate‐strong stability conditions