US SOLAS Science Report

The article of record may be found at https://doi.org/10.1575/1912/27821The Surface Ocean – Lower Atmosphere Study (SOLAS) (http://www.solas-int.org/) is an international research initiative focused on understanding the key biogeochemical-physical interactions and feedbacks between the ocean and atmosphere that are critical elements of climate and global biogeochemical cycles. Following the release of the SOLAS Decadal Science Plan (2015-2025) (Brévière et al., 2016), the Ocean-Atmosphere Interaction Committee (OAIC) was formed as a subcommittee of the Ocean Carbon and Biogeochemistry (OCB) Scientific Steering Committee to coordinate US SOLAS efforts and activities, facilitate interactions among atmospheric and ocean scientists, and strengthen US contributions to international SOLAS. In October 2019, with support from OCB, the OAIC convened an open community workshop, Ocean-Atmosphere Interactions: Scoping directions for new research with the goal of fostering new collaborations and identifying knowledge gaps and high-priority science questions to formulate a US SOLAS Science Plan. Based on presentations and discussions at the workshop, the OAIC and workshop participants have developed this US SOLAS Science Plan. The first part of the workshop and this Science Plan were purposefully designed around the five themes of the SOLAS Decadal Science Plan (2015-2025) (Brévière et al., 2016) to provide a common set of research priorities and ensure a more cohesive US contribution to international SOLAS.This report was developed with federal support of NSF (OCE-1558412) and NASA (NNX17AB17G).This report was developed with federal support of NSF (OCE-1558412) and NASA (NNX17AB17G)

US SOLAS Science Report

The Surface Ocean – Lower Atmosphere Study (SOLAS) (http://www.solas-int.org/) is an international research initiative focused on understanding the key biogeochemical-physical interactions and feedbacks between the ocean and atmosphere that are critical elements of climate and global biogeochemical cycles. Following the release of the SOLAS Decadal Science Plan (2015-2025) (Brévière et al., 2016), the Ocean-Atmosphere Interaction Committee (OAIC) was formed as a subcommittee of the Ocean Carbon and Biogeochemistry (OCB) Scientific Steering Committee to coordinate US SOLAS efforts and activities, facilitate interactions among atmospheric and ocean scientists, and strengthen US contributions to international SOLAS. In October 2019, with support from OCB, the OAIC convened an open community workshop, Ocean-Atmosphere Interactions: Scoping directions for new research with the goal of fostering new collaborations and identifying knowledge gaps and high-priority science questions to formulate a US SOLAS Science Plan. Based on presentations and discussions at the workshop, the OAIC and workshop participants have developed this US SOLAS Science Plan. The first part of the workshop and this Science Plan were purposefully designed around the five themes of the SOLAS Decadal Science Plan (2015-2025) (Brévière et al., 2016) to provide a common set of research priorities and ensure a more cohesive US contribution to international SOLAS.This report was developed with federal support of NSF (OCE-1558412) and NASA (NNX17AB17G)

An Evaluation of Kolmogorov's −5/3 Power Law Observed Within the Turbulent Airflow Above the Ocean

The data used in this study are publicly available through an open access repository: https://nps.box.com/ shared/static/di5887nl4g3thgz 6bz67z3l44tj77qur.zip.The article of record as published may be found at https://doi.org/10.1029/ 2019GL085083In 1941, Kolmogorov postulated that the energy distribution of turbulence, across a particular range of eddy sizes cascading to dissipation, could be uniquely described as a universal −5/3 power law. This theory was readily accepted as the basis for conceptualizing the phenomenological characteristics of turbulence and remains central to continued experimental and theoretical developments in turbulence study. However, the theory's own validity lacks final certainty. Here we present the first observation‐based evaluation of Kolmogorov's power law within the atmospheric flow above the ocean. Using a unique platform and a novel analytical approach, we found that the expected power law varies systematically with height above the surface and the local environmental state. Our findings suggest that Kolmogorov's idealized value (−5/3) is approximately valid but, under certain conditions, may depend strongly on the unique processes and dynamics near the ocean surface. This discovery should motivate a reevaluation of how Kolmogorov'sU.S. Office of Naval ResearchDirected Energy Joint Technology Office (DEJTO)This work was supported through the Coupled Air‐Sea Processes and Electromagnetic ducting Research (CASPER) project funded by the U.S. Office of Naval Research grant N0001419WX01369 under its Multidisciplinary University Research Initiative (MURI). Q. W. is also supported by the Quantifying and Understanding Environmental Turbulence Affecting Lasers (QueTal) project funded by the Directed Energy Joint Technology Office (DEJTO) grant (F2KBAB8159G002)

Observations and Modeling of Turbulent Air-Sea Coupling in Coastal and Strongly Forced Conditions

The turbulent fluxes of momentum, mass, and energy across the ocean-atmosphere boundary are fundamental to our understanding of a myriad of geophysical processes, such as wind-wave generation, oceanic circulation, and air-sea gas transfer. In order to better understand these fluxes, empirical relationships were developed to quantify the interfacial exchange rates in terms of easily observed parameters (e.g., wind speed). However, mounting evidence suggests that these empirical formulae are only valid over the relatively narrow parametric space, i.e. open ocean conditions in light to moderate winds. Several near-surface processes have been observed to cause significant variance in the air-sea fluxes not predicted by the conventional functions, such as a heterogeneous surfaces, swell waves, and wave breaking. Further study is needed to fully characterize how these types of processes can modulate the interfacial exchange; in order to achieve this, a broad investigation into air-sea coupling was undertaken. The primary focus of this work was to use a combination of field and laboratory observations and numerical modeling, in regimes where conventional theories would be expected to breakdown, namely: the nearshore and in very high winds. These seemingly disparate environments represent the marine atmospheric boundary layer at its physical limit. In the nearshore, the convergence of land, air, and sea in a depth-limited domain marks the transition from a marine to a terrestrial boundary layer. Under extreme winds, the physical nature of the boundary layer remains unknown as an intermediate substrate layer, sea spray, develops between the atmosphere and ocean surface. At these ends of the MABL physical spectrum, direct measurements of the near-surface processes were made and directly related to local sources of variance. Our results suggest that the conventional treatment of air-sea fluxes in terms of empirical relationships developed from a relatively narrow set of environmental conditions do not generalize to the coastal and extreme wind environments. This body of work represents a multi-faceted approach to understanding physical air-sea interactions in varied regimes and using a wide array of investigatory methods

Resume of David G. Ortiz-Suslow, 2018-01

Naval Postgraduate School Faculty Resum

Characterizing the Effects of Non-stationarity on the Marine Atmospheric Surface Layer during CASPER-West

23rd Symposium on Boundary Layers and Turbulence/21st Conference on Air-Sea InteractionThe Monin-Obukhov similarity theory (MOST) proposed that: given a logarithmic boundary layer, the gradients of the mean wind velocity, temperature, and water vapor within the surface layer are self-similar and universal functions of stability, respectively. While MOST is empirically supported, under certain conditions it has been demonstrated that the complex dynamics at the air-sea interface can erode the validity of the theory’s fundamental assumptions of homogeneity, stationarity, and no flux divergence. These limitations present a significant challenge to developing a general understanding of the MASL and therefore, further investigation is needed to address this critical gap. As part of this effort, the large-scale and field-based project, Coupled Air-Sea Processes and Electromagnetic ducting Research (CASPER), was specifically under-taken to provide new insights into the dynamics within the MASL combining the state-of-the-art measurement abilities of research vessels, platforms, and autonomous vehicles. This presentation will focus on the atmospheric and wave measurements made from an air-sea interaction mast mounted on the R/P FLIP during the second CASPER field campaign, which took place offshore of Southern CA during September and October of 2017. FLIP is an ideal platform for making undisturbed near-surface observations and reduces the operational challenges associated with making detailed measurements at sea from conventional research vessels. The platform was moored at 33° 41'20.40" N, 118° 59'24.00" W, which is 58 km southwest of Santa Monica and east of the Pt. Mugu Naval Sea Range, and was oriented into the seasonally-adjusted wind direction (~290°). The mast was installed on the port-side and comprised of 17 measurement levels representing overlapping bulk and flux profiles spanning from 3 m to 16 m above mean sea level. The 10 bulk-levels included two-dimensional wind and temperature/humidity probes. Six of the flux levels simultaneously measured the turbulent wind, temperature, and water vapor content, while the lowest level was only outfitted with a three-dimensional sonic anemometer. This recent FLIP data set represents one of the few extensive measurements of the near-surface water vapor gradient within the marine environment. The objective of this study is to investigate the effect non-stationarity and local heterogeneity has on the air-sea fluxes and mean profiles of wind velocity, temperature, and humidity. Preliminary examination of the data revealed 17 non-stationary cases, which were visually identified as strong, coherent deviations from the nominal condition. These events were found to be transient, but long-lived enough (typically 1-3 hours) to justify not classifying them as spurious measurements. Additionally, a review of the imagery acquired from a high-resolution camera mounted on FLIP’s face boom, showed the occasional presence of distinct short-wave anomalies (i.e. rough and smooth patches) advecting passed FLIP. During the campaign, some evidence indicated that these may be internal wave-driven surface expressions. The effects these surface discontinuities have on the fluxes and/or profiles within the MASL will be evaluated. The implications these non- stationary and locally heterogenic features have on the general dynamics and thermodynamics within the MASL will be discussed

An Evaluation of the Constant Flux Layer in the Atmospheric Flow above the Wavy Air-Sea Interface

The article of record as published may be found at https://doi.org/10.1029/2020JD032834The constant flux layer assumption simplifies the problem of atmospheric surface layer (ASL) dynamics and is an underlying assumption of Monin‐Obukhov Similarity Theory, 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 FLIP was 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 findings of a study assessing the prevalence of the constant flux layer within the ASL, using an approach that accounts for wave‐coherent turbulence, defines the wave boundary layer height, and empirically quantifies the observed flux divergence. Our analysis revealed that only 30‐40% of momentum flux gradients were approximately constant; for the heat fluxes, this increased to 50‐60%. 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. Swell‐wind alignment was associated with momentum flux profile divergence under moderate wind speeds. In conjunction, our findings suggest that the constant flux layer, as it is conventionally defined, is not generally valid within the marine ASL. This holds significant implications for measuring air‐sea fluxes from single point sources and the application of Monin‐Obukhov similarity theory over the ocean.Office of Naval Research (ONR)This research was funded by the Office of Naval Research (ONR) Grant N0001418WX01087 under its Multidisciplinary University Research Initiative (MURI)

Windowed Inspection of Stationarity & Quality (WISQ): An Algorithm For Eddy Covariance Sample Quality Control and Assessment

Approved for public release; distribution is unlimitedMeasuring atmospheric fluxes requires various steps of measurement quality control, in addition to experimental design and post-processing corrections, in order to provide robust and high-fidelity data for wider use. However, within the measurement community, methods for these control steps are still applied ad hoc. Regardless of the availability of several comprehensive references texts available in the literature and licensed software programs.The theoretical and technical design of an algorithm for eddy covariance flux sample quality control and assessment is presented. This algorithm, WISQ, is robust and efficient and can be readily incorporated into existing processing experimental software packages. The goal of this algorithm is to output a flagging system that can be used to judge the quality of individual flux samples, with the option for outputting more detailed information. WISQ is unique in that it directly and automatically assess the sample flux accumulation and convergence. WISQ is also a general method that can be utilized for flux measurement outside of the realm of meteorology and is open-sourced for ease in development and innovation

A New Method for Identifying Kolmogorov’s Inertial Subrange and Analyzing the Variability of the -5/3 Power Law Using Observations from FLIP

AGU Fall Meeting, 2019Kolmogorov’s hypothesis for the presence of an inertial subrange exhibiting a power law scaling of -5/3 is one of the most widely recognized concepts in the fluid dynamics and remains an integral component of our general understanding of the turbulent cascade from energy-containing eddies to dissipation scales. While his theories have been debated since their proposal, its practical application to an observed turbulent field remains hampered by the lack of a systematic approach for identifying the bandwidth of this critical subrange. Within the atmospheric boundary layer literature, decades of studied has not yielded a standardized approach and the various methods reported appear ad hoc. This creates a significant hurdle to the applications of Kolmogorov’s theory to atmospheric boundary layer turbulence and the inter-comparison between disparate data sets. As part of a recent major field campaign conducted from the unique ocean- going platform the R/P FLIP, we developed the algorithm for robust identification of the inertial subrange (ARIIS) to study the inertial subrange characteristics within the atmospheric surface layer. ARIIS is a novel approach that explicitly uses the isotropic relationship between transverse velocity components to identify the onset and extent of the inertial subrange in the variance spectrum. After identifying the most plausible subrange bandwidth, ARIIS uses a robust, iterative fitting algorithm to derive an empirical estimate of the spectral slope, which can be compared to Kolmogorov’s expected -5/3 value. This presentation will discuss the implementation of ARIIS and describe the results of using this new method to conduct a systematic evaluation of Kolmogorov’s inertial subrange theory within the marine atmospheric surface layer using the FLIP data. Our findings provide compelling evidence for conditions where the inertial subrange slope diverges from -5/3, indicating that some other process(es), e.g. surface gravity waves, may play an integral role in the turbulence cascade near the air-sea interface

Observations of the Marine Atmospheric Surface Layer Gradients during the CASPER-West Field Experiment

99th American Meteorological Society Annual MeetingThe bulk of our knowledge of air-sea exchange coefficients for momentum and heat derives from single-point measurements made at some height within the marine atmospheric surface layer (MASL). These point measurements rely on assumptions regarding the vertical structure of the MASL. Foremost among these assumptions, is the validity of Monin- Obukhov Similarity Theory (MOST), which postulates that the gradient-flux relationship is a universal function of surface layer stability. Under neutral conditions, this simplifies to the familiar logarithmic profile. While MOST has been validated over land, observations of the actual gradients within the MASL remain scarce, in part due to the challenges of making near-surface profile measurements over the ocean. The Research Platform FLIP was recently deployed on the west coast for the Coupled Air-Sea Processes and Electromagnetic ducting Research field campaign (CASPER-West), a large-scale air-sea interaction study that took place offshore of Pt. Mugu, CA. FLIP remains an ideal platform for making measurements in proximity to the air-sea interface, with minimal contamination from the platform. During CASPER, a meteorological mast was installed on FLIP that resolved both the bulk and flux profiles of momentum and heat, from 3 to 16 m above the surface. This mast included 7 flux levels, 10 mean wind measurements, and over 20 temperature and humidity probes. This presentation will focus on the vertical gradients measured from FLIP’s mast, with the specific aim of using these high-resolution measurements to test the variability predicted by MOST. As a preliminary step, linear regression was used to determine the natural prevalence of the logarithmic profile. For the mean wind profiles, only 10.2% of the profiles were strongly logarithmic (r2 > 0.9). For specific humidity, this increased to 40.9% of profiles, with no temperature profiles exhibiting a strong logarithmic relationship. Mean r2 was 0.624, 0.265, and 0.853 for wind, temperature, and specific humidity respectively, which increased to 0.761, 0.362, and 0.950 for wind speeds > 6 ms-1 (12.3% of the total data set). Wind speed exhibited positive, and temperature demonstrated negative, relationships with bulk air-sea temperature difference; for example, in stable conditions the mean r2 increased to 0.783 for wind speed, and decreased to 0.145 for temperature. Further analysis will focus on comparing strongly-logarithmic profiles to the empirical gradient-flux relationships available in the literature as well as, determining environmental factors driving the majority of profiles away from the expected logarithmic behavior. This unique dataset provides an opportunity to directly evaluate the prevalence and validity of the MASL vertical structure predicted by MOST, which is assumed to be generally valid over the ocean