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Improving modeled momentum flux in the atmospheric boundary layer

Principal Investigator(s): Colin Zarzycki (Pennsylvania State University); Ming Zhao (NOAA/GFDL); Julio Bacmeister (NCAR); Vince Larson (University of Wisconsin–Milwaukee); Gunilla Svensson (Stockholm University); Leo Donner, (NOAA/GFDL); George Bryan (NCAR)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Climate Process Teams (CPTs) - Translating Ocean and/or Atmospheric Process Understanding to Improve Climate Models

Award Number: NA19OAR4310363, GC19-402 | View Publications on Google Scholar


Tropical cyclones (TCs), shallow cumuli, and low-level jets (LLJs) are all important phenomena in the climate system, but have been historically difficult to represent in climate models. For instance, even at higher resolution, simulated TCs often exhibit an incorrect relationship between minimum pressure and surface wind speed. Simulated shallow cumuli often exhibit a local maximum ("jet") in the wind profile that too broad and diffuse. Simulated LLJs often suffer from a weak diurnal cycle of surface winds. All three climate model deficiencies may be related in part to inadequate parameterization of subgrid momentum fluxes in the atmospheric boundary layer. The parameterizations of momentum flux in current-generation climate models are crude. Often momentum parameterization suites consists of downgradient diffusion plus a separate cumulus momentum transport scheme. However, the presence of a near-surface jet in the wind profile can sometimes lead to upgradient momentum flux at the top of the jet maximum, even when deep convection is not present. Furthermore, the need to model the complex diurnal evolution of winds in LLJs is difficult when the task of simulating momentum is divided between separate parameterizations. This project proposes to parameterize momentum transport by prognosing subgrid momentum fluxes directly. This approach is quite different from conventional approaches, but it adheres more closely the governing equations, and hence is more flexible and general. For instance, it is capable of predicting upgradient momentum fluxes. In this project, the process of momentum transport will be examined using a comprehensive hierarchy of observations and models. Based on these studies and improved understanding, prognostic equations for momentum fluxes will be refined and tested. The equations will be implemented into two leading climate models, one from GFDL and the other from NCAR. The resulting simulations will be evaluated against observations.

Ocean Transport and Eddy Energy

Principal Investigator(s): Laure Zanna (New York University), K. Shafer Smith (NYU); Sylvia Cole (WHOI); Alistair Adcroft (Princeton University); Ian Grooms (CU Boulder); Scott Bachman and Gokhan Danabasoglu (NCAR); Kyla Drushka (University of Washington APL); Baylor Fox-Kemper (Brown University); Ryan Abernathey (Columbia University); Malte Jansen (University of Chicago); Stephen Griffies and Robert Hallberg (NOAA/GFDL); Mark Petersen (Los Alamos National Lab)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Climate Process Teams (CPTs) - Translating Ocean and/or Atmospheric Process Understanding to Improve Climate Models

Award Number: NA19OAR4310364, NA19OAR4310365, NA19OAR4310366, GC19-403 | View Publications on Google Scholar


Ocean mesoscale eddies are energetic motions with lateral scales of tens to hundreds of kilometers. These eddies can significantly impact the transport of heat, freshwater, carbon, and nutrients throughout the oceans, and play an essential role in shaping the ocean's strongest mean currents and their variability. Energy exchanged between the ocean and atmosphere, and across reservoirs and scales in the ocean controls the impact of eddies on the circulation and transport, with most of the ocean kinetic energy contained in the mesoscale range. Mesoscale eddies are, at best, partially resolved in ocean climate models, and most of their momentum and tracer transport must be parameterized. Imperfections in these parameterizations lead to biases in modern climate models, including incorrect rates of exchange of heat and carbon with the atmosphere, errors in the position and strength of the ocean's strongest current systems, and incorrect stratification at high latitudes, among other things. Extant parameterizations fail to fully account for the exchanges of mesoscale energy with different scales, or conversions between eddy kinetic and potential energy reservoirs. Recent advances from theory, process studies and longer-term observational records of ocean energetics can now be leveraged to improve the current generation of climate models. Our Climate Process Team (CPT) proposes to vet, improve, and unify new advances in energy-, flow- and scale-aware eddy parameterizations in process studies and global models; constrain parameters and parameterized fluxes through a synthesis of up-to-date observations of ocean energetics and transport; and implement and assess schemes within IPCC-class models at NCAR, GFDL, and LANL. Modernized, energetically-consistent mesoscale eddy parameterizations are expected to significantly reduce model biases in ocean currents, stratification, and transport. Relevance to the CPT call & NOAA: The goals of our project are directly relevant to the CPT call in that they will provide improved representation of the ocean eddies and their role in the ocean energy cycle in climate models by combining recent advances in theory and observations. The CPT will focus on energy-related diagnostics of ocean eddies in order to constrain ocean eddy parameterization. The improvement in ocean and coupled model fidelity via the proper representation of eddy energy cycles is expected to lead to improvement of some of the most stubborn biases in climate models, primarily the strength and position of strong currents, and the ocean’s stratification. Our team includes three leading global coupled modeling centers (including NOAA’s GFDL) and will implement our parameterization within IPCC-class models. Our goals, results and methodology directly align with NOAA’s long-term goals and CPO program mission, which includes improving “understanding [...] and prediction of climate and its impacts”.

Air-Sea Surface Fluxes over Ocean Eddies during the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC)

Principal Investigator(s): Chidong Zhang (NOAA/PMEL); Dongxiao Zhang (UW-JISAO; NOAA/PMEL)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Upper - Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean

Award Number: GC19-301 | View Publications on Google Scholar


In the region of the northwest tropical Atlantic, there are energetic ocean eddies. They are anticyclonic warm core eddies and cyclonic cold core eddies generated in the interior ocean propagating to the western boundary, and deep reaching North Brazil Current (NBC) Rings generated by the NBC retroflection. These eddies can have strong signatures in sea surface temperature (SST) and surface currents, and thus modulate surface latent and sensible heat fluxes and momentum flux. Possible roles of these eddies on air-sea coupling and atmospheric shallow clouds in the region are unknown. In January-February 2020, U.S. and European scientists will jointly conduct field observations of Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) and EUREC4A-OA (Elucidating the role of clouds-circulation coupling in climate – Ocean and Atmosphere) in the northwest tropical Atlantic east of Barbados. The goal is to understand the air-sea interaction in the region, focusing on mesoscale ocean eddies and their influences on atmospheric shallow convection and formation of shallow cumulus clouds. This proposed research is to participate in this field campaign by deploying two Saildrones that cover the campaign period and beyond for 180 days. The objective of the Saildrone deployment is to advance understanding of air-sea coupling associated with ocean eddies in this region through measuring their signals in SST, SSS, upper-ocean current profiles, surface air temperature, humidity, pressure, wind direction and speed, short- and long-wave radiation, and possibly cloud images. These Saildrone measurements will complement in situ measurements to be made by ships, aircraft and other autonomous devices and remote measurement by satellites during the field campaign. The advantage of the Saildrones is their controllable mobility and long duration, which would allow them to be steered to follow individual ocean eddies and to sample a large number of eddies. The proposed Saildrone deployment during the ATOMIC-EUREC4A-OA campaign directly responds to the CVP solicitation for proposals that focuses on observing, understanding, and/or process modeling of upper ocean processes and air-sea interactions in the Northwest Tropical Atlantic. The proposed effort directly contributes to the first two objectives of NOAA’s long-term climate goals as described in NOAA’s Next-Generation Strategic Plan (NGSP): 1) Improved scientific understanding of the changing climate system and its impacts; 2) Assessment of current and future states of the climate system that identify potential impacts and inform science, service, and stewardship decisions.

Boundary layer fluxes into trade cumulus clouds

Principal Investigator(s): Simon de Szoeke (OSU); David Noone (OSU); Letter of Support: Chris Fairall (NOAA); Bjorn Stevens (MPI); Sandrine Bony (CNRS); Franziska Aemisegger (ETH)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Upper - Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean

Award Number: NA19OAR4310375 | View Publications on Google Scholar


Surface fluxes from the ocean moisten and warm the subcloud atmospheric boundary layer (SBL) as the surface winds approach the warm SST of the Intra-American Seas. The SBL supplies moisture that then enters the trade cumulus cloud base. Condensation of water in clouds generates buoyancy and stabilizes the trade inversion layer that surrounds the cumulus clouds. Cold pools generated by the evaporation of hydrometeors descend and cool the SBL. The representation of trade wind clouds in climate models has important implications for climate. Shallow cumulus clouds reflect sunlight from the climate system, shade the ocean surface, generate wind gusts that increase surface evaporation, and moisten the lower free troposphere, building the conditions for deeper convection. Widespread shallow clouds contribute more to planetary albedo than narrow cumulus towers. Despite the shallower clouds’ stronger radiative effect, models with shallower clouds have a more positive cloud climate feedback. That is because vertical mixing dries shallower clouds more in a warmer climate, reducing the cloud albedo, and thus enhancing the warming. The processes achieving this vertical mixing are not understood, either in models or in the observable atmosphere. Shallow cumulus clouds occur at the grey scales that are too small to resolve with weather models, and whose mesoscale circulations are too large to represent in large eddy simulations. Observations of turbulence, conserved thermodynamic variables (potential temperature, humidity, and stable isotope ratios of water vapor), and clouds from the US Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) will measure the turbulence hypothesized to affect the mixing and humidity of climatically important shallow cumulus clouds. This project is focused on analysis of measurements of the shallow cumulus clouds, and their related thermodynamic fluxes. These fluxes tie the cumulus clouds to the subcloud boundary layer and its moisture budget. We will observe the moisture transport by clouds, by clear air, and by turbulence, that are hypothesized to be responsible for the difference of shallow cumulus cloud feedbacks in models. We will make rawinsonde observations of the wind and thermodynamic structure of the atmosphere and stable isotope ratio observations to characterize surface fluxes and evaporative downdrafts. Vertical fluxes of moisture and heat from the surface through the cumulus layer will be estimated from thermodynamic budgets and from direct measurements of turbulent and cloud vertical velocities. We will integrate the sounding and isotope measurements with observations of the turbulence at the ocean surface, in the subcloud boundary layer, and in the shallow cumulus cloud layer. Relevance to the CVP competition “Observing and Understanding Upper-Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean”: Proposed soundings observations support the ATOMIC program on observing and understanding the interactions of upper ocean, atmospheric boundary layer, and shallow trade cumulus clouds. Stable isotope ratios combined with humidity data will place strong constraints on the transport of water between the ocean surface and the troposphere. The isotopic measurements contribute to the international effort with partners coordinated as the EUREC4A-iso project. Analysis of soundings and turbulent vertical velocity observations will be used to quantify mixing process in the atmosphere, differences of which have been used to explain differences in clouds and climate sensitivity among models.

Coupled ocean-atmosphere interaction mediated by ocean mesoscale eddies in the Northwest Tropical Atlantic Ocean

Principal Investigator(s): Hyodae Seo (WHOI); Carol Anne Clayson (WHOI)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Upper - Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean

Award Number: NA19OAR4310376 | View Publications on Google Scholar


The primary goal of the ATOMIC experiment is to improve understanding of ocean-atmosphere interaction in the presence of energetic ocean mesoscale variability in the northwest tropical Atlantic. A particular focus is on documenting the role of ocean mesoscale eddies and fronts in the surface fluxes of momentum, heat, and freshwater, and examining how the eddy-mediated air-sea fluxes relate to ocean boundary layer mixing, low-level clouds, and regional climate. We hypothesize that the mesoscale variations in the air-sea flux at sub-monthly and sub-100-200 km scales represent an essential part of the coupled boundary layer physics in the study region. However, spatially distributed measurements and dedicated high-resolution coupled model simulations do not coexist as yet to describe and quantify the eddy-mediated air-sea flux variability and its impacts. We propose a hierarchy of model simulations in tandem with other observational studies in support of the ATOMIC/EUREC4A to improve our process-level understanding of the physics of, and the factors influencing, the mesoscale variations in the air-sea fluxes. It will also provide a unique opportunity to explore their upscaling effects on the trade wind cumuli and large-scale regional climate. Our simulations will be based on the 3-D SCOAR regional coupled model (WRF-ROMS) and a 1-D implementation of the 3-D ocean model with various mixing schemes. The 1-D model simulations will primarily investigate the effects of background stratification modulated by mesoscale eddies and the resulting changes in the surface waves and air-sea fluxes on the ocean mixing and dissipation rate. The 3-D SCOAR model simulations will be run at 3 km resolutions both in the atmosphere and the ocean to explicitly resolve cumulus convection and ocean mesoscale variability. These fine-scale ocean and atmospheric fields will be coupled through the COARE bulk flux algorithm including any changes that may arise from other proposed ATOMIC research. The spatial-scale dependent effects of mesoscale eddies on the air-sea fluxes will be examined by our novel coupling technique, which filters out imprints of mesoscale eddies (SST and current) in surface fluxes. Finally, ensembles of 3-D coupled model simulations will be conducted with one-way and two-way nesting to explore the upscaling effects on the regional-scale ocean and atmospheric boundary layers. Coupled model simulations at the proposed fine spatial and temporal scales have not been conducted previously alongside observations with sufficient spatial and temporal detail to constrain and validate the model simulations. The proposed model simulations will allow for air-sea coupling at submonthly scales and sub-100-200 km scales to be quantified for the first time in the region. To guide the field experiments, various virtual sampling arrays with online budget calculations will be trialed to assess the efficacy for proposed sampling strategies. We expect that other science questions and new observational plans if they emerge can be addressed by our unique and flexible modeling plan. Improved physical understanding of mesoscale and frontal-scale ocean-atmosphere interactions is currently of significant interest to the science community. The proposed research will help improve climate model simulations at such scales and benefit the general public by helping to provide more reliable regional-scale predictions. The project will support a postdoc in physical oceanography and meteorology and offer various opportunities to mentor students from historically under-represented groups in the sciences through WHOI and other REU programs designed to promote diversity.

Interaction of the Lower Atmosphere and Upper Ocean

Principal Investigator(s): James C. McWilliams (UCLA); Peter P. Sullivan (NCAR), Lionel Renault (UCLA)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Upper - Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean

Award Number: NA19OAR4310377, NA19OAR4310378 | View Publications on Google Scholar


The proposed research is a joint project between UCLA and NCAR. The research is for process modeling of fine-scale circulations in the lower atmosphere and upper ocean in the northwest Tropical Atlantic as part of the U.S. Atlantic Trade-wind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) and the European EUERC4A-OA Projects. It is in response to NOAA's Climate Variability and Predictability (CVP) Program: Competition 2: CVP-Observing and Understanding Upper-Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean. The guiding hypothesis of the research is that surface heterogeneities in oceanic temperature (SST) and currents induce heterogeneities in the air-sea fluxes of heat, moisture, and momentum, which in turn modulate the mesoscale and submesoscale circulations in the oceanic surface layer and atmospheric boundary layer. The source of the heterogeneity is oceanic mesoscale eddies and submesoscale fronts. We will use two modeling approaches to elucidate the interaction between the lower atmosphere and the upper ocean: idealized flow configurations in a Large Eddy Simulations (LESs) that resolve the boundary-layer turbulence (led by NCAR) and “realistic” down-scaled coupled simulations using the Weather Research and Forecast (WRF) and the Regional Oceanic Modeling System (ROMS) with parameterized vertical fluxes due to boundary-layer turbulence (led by UCLA). The phenomena arising in these separate, different-scale simulations will be used to inform each other to develop, by bootstrapping, a better process understanding across the interacting range of scales from boundary-layer turbulence to the mesoscale winds and currents. We will design a sequence of studies that explore, in the context of Tropical Atlantic phenomena, how submeoscacle currents interact with the boundary layer turbulence in the ocean, how surface gradients in SST and currents interact with the boundary layer turbulence in the atmosphere, how the resulting secondary circulations extend vertically through the upper ocean and lower atmosphere, and how the Thermal and Current Feedbacks develop mesoscale and submesoscale correlations across the air-sea interface, even reaching into the shallow cloud layer above. The key methodologies are the massively parallel LES code developed over many years at NCAR, including surface wave dynamical influences in both the air and water, and the ROMS circulation model developed at UCLA that also includes surface wave interactions and allows multiple levels of grid nesting conveying larger scale influences down to finer scale circulations, in particular allowing very high resolution studies of submesoscale phenomena shaped by the encompassing mesoscale eddies and regional currents. Because of the extensive international field measurements planned, we would work closely with the observing groups, especially those that have fine-scale sampling in both time and at least one horizontal coordinate. The intent is to combine the relatively more complete information from model simulations with the measured reality, for the better interpretation of both, and to establish the importance of surface heterogeneity in climate outcomes. To this end we intend to work closely with both the European and American experimental teams. This research enhances our process-level understanding of the climate system through observation, modeling, analysis, and field studies. This vital knowledge is needed to improve climate models and predictions so that scientists and society can better anticipate the impacts of future climate variability and change.

Observing and Understanding Upper-Ocean Processes and Shallow Atmospheric Convection in the Tropical Atlantic Ocean

Principal Investigator(s): Christopher Fairall (NOAA/ESRL/PSD); Gijs de Boer (CU-CIRES); Alan Brewer (NOAA/ESRL/CSD); Partner: Phillip Hall (NOAA/UAS)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Upper - Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean

Award Number: GC19-302 | View Publications on Google Scholar


Above most of the oceans, liquid clouds of a few thousand meters or less drive mixing in a process called shallow convection in the atmospheric boundary layer (ABL). The warm clouds dominate the ocean’s area coverage and may strongly influence weather on seasonal to sub-seasonal time scales. Shallow convection exerts an important influence on sea surface temperatures (SSTs) and salinity by moderating the air-sea exchanges of energy and moisture and represent a ‘major source of uncertainty in projections of future climate’. The interaction between shallow convection and the ocean’s surface layers is a two-way street: though shallow convection influences SSTs, shallow convection is itself controlled to a large extent by SST and air-sea fluxes, which are mediated by processes within the ocean, especially Oceanic Barrier Layers (OBL) and mesoscale ocean eddies. OBL are near-surface layers created by low salinity waters and embedded in the ocean mixed layer. OBLs tend to decouple the ocean mixed layer from surface momentum fluxes, which facilitates subsurface warming as short wave radiation penetrates to the base of the OBL. Both eddies and OBL can influence weather and climate patterns. In this project we propose to investigate the structure and dynamics of shallow convective boundary layers and their coupling to oceanic variability and mixing via ship-based surface flux and atmospheric boundary layer observations during the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC). We propose continuous sampling aboard a research vessel that operates east of Barbados during the ATOMIC field program. The observing systems will be similar to those deployed in NOAA’s recent DYNAMO and PISTON studies. The ship will sample the atmosphere and ocean in the context of a larger array of ships and aircraft in cooperation with the Elucidating the role of cloud-circulation coupling in climate (EUREC4A) field program. Using in situ sensors, unmanned aircraft (UAS), and vertically-pointing Doppler remote sensing, we will measure and characterize mesoscale and synoptic variability in the surface fluxes, ABL and cloud turbulence as convective systems pass over the ship. The large-scale forcing will be determined by a combination of ship-launched balloon soundings and aircraft dropsondes associated with the larger ATOMIC/EUREC4A programs. We expect to work closely with P. Zuidema (U. Miami), S. de Szoeke (OSU), G. Feingold (NOAA/CSD) and P. Sullivan (NCAR) on LES modeling of the oceanic and atmospheric boundary layer and ABL-cloud interactions. The combination of LES and UAS plus radar-lidar velocity profiles will allow us to examine local gradient vs non-local (mass flux) boundary-layer flux profile parameterizations. We will coordinate with PMEL (Quinn) on UAS and aerosols observations. We will work with E. Thompson (APL-US) and J. edson (WHOI) on connecting atmospheric forcing with oceanic response. We will coordinate with the NOAA P-3 aircraft to set the mesoscale context of the ship observations. The P-3 will deploy dropsondes and AXBT (S. Chen NRL) and it will host the PSD Airborne Doppler W-band radar and the WSRA ocean surface wave radar.

Shallow cumulus convection in the Tropical Atlantic Ocean: Controls, responses, and mechanisms

Principal Investigator(s): Graham Feingold (NOAA/ESRL/CSD); Jan Kazil (CU-CIRES); Takanobu Yamaguchi (CU-CIRES)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Upper - Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean

Award Number: GC19-303 | View Publications on Google Scholar


Differences in the representation of shallow cumulus convection and cloudiness are a leading contribution to diversity in climate model sensitivity and climate projections. We propose to use numerical modeling of trade-wind cumulus from large eddy simulations to regional modeling, analysis of field observations, satellite data, and of reanalysis products to address the coupling between convective mixing, surface turbulent fluxes, and low-cloud radiative effects in largescale subsidence regimes. The modeling will be tightly integrated with the Atlantic Trade-wind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC, US) and the Elucidating the Role of Clouds-Circulation Coupling in Climate (EUREC4A, Europe) Ocean-Atmosphere field campaigns. We will examine the controls on the properties, statistics, and organization of shallow cumulus convection and cloudiness, and its response to ocean and atmosphere mean state and variability. Emphasis will be placed on processes that are unresolved or unrepresented in climate models and which contribute to diversity and biases in climate simulations and model-derived climate sensitivity. The objectives are: • Quantification of the mean state and statistical properties of shallow cumulus convection in response to atmospheric and oceanic mean state, and atmospheric and oceanic spatiotemporal variability • Quantification and characterization of mesoscale organization, its response to oceanic and atmospheric mean state and variability, and its role for the properties of trade cumulus convection and cloudiness • Characterization of feedback mechanisms between the atmosphere and the ocean that codetermine ocean-atmosphere interactions and the properties of trade cumulus convection and cloudiness Modeling will be carried out in close concert with the European and US assets to be brought to the field: aircraft observations (the NOAA P-3 and NOAA G-IV, the French ATR-42 and the German HALO), shipborne measurements (the NOAA R/V Ronald H. Brown and up to three European ships), and satellite remote sensing. The proposed work will further NOAA's long-term climate research goals and the goals of the NOAA CVP program by enhancing the understanding of the climate system and its predictability in a number of ways. First, it will elucidate our fundamental understanding of the trade-wind cumulus system by focusing on the meteorological/ocean surface factors that control cloud field properties (e.g. cloud fraction, condensate, and precipitation) through comprehensive modeling and observations at a broad range of scales (10s to 100s of km). Second, the extent to which variance in these factors at the sub GCM grid-scale affects these cloud field properties will reveal the model grid mesh required to adequately resolve them. Third, the model output and analysis of observations will together provide a wealth of data to inform development of GCM subgrid cloud and precipitation schemes for years to come.

Shipboard and Unmanned Aerial System (UAS) measurements of aerosol properties in the Coupled Ocean-Atmosphere System of the Northwest Tropical Atlantic

Principal Investigator(s): Patricia K. Quinn (NOAA/PMEL); Tim Bates (UW-JISAO; NOAA/PMEL); Partner: Phillip Hall (NOAA/UAS)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Upper - Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean

Award Number: GC19-305 | View Publications on Google Scholar


We propose to participate in the ATOMIC field campaign aboard the RV Ronald H. Brown in January/February 2020. Our objective is to improve the understanding of the effects of aerosol particles on clouds and radiation transfer over the Northwest Tropical Atlantic and the related impacts on the upper ocean. Aerosols in this region have both ocean-derived (sea spray and dimethylsulfide) and continental sources (European pollution, African dust, and biomass burning). Our hypothesis is that the temporal variability of atmospheric aerosols, through aerosol-cloud interactions and direct aerosol light scattering and absorption, influence the temporal variability in net radiation reaching the ocean surface and sea surface temperature. We will test this hypothesis with measurements of aerosol properties in the marine boundary layer on the ship and vertically and regionally with a UAS. This proposal directly addresses the call for proposals to study lower atmospheric boundary layer processes and their influence on the ocean. This work contributes to NOAA’s long term climate goal to strengthen scientific understanding of climate. We will be using the shipboard measurements that have been deployed on many field campaigns (VOCALS, DYNAMO, NEAQS, TexAQS, CalNex) and the UAS aerosol payload that has been deployed in Svalbard, Norway. The shipboard measurements will include aerosol number-size distributions, chemical analysis, cloud condensation nuclei (CCN) potential at supersaturations in the range of 0.1% to 2%, aerosol light scattering and absorption coefficients, and aerosol optical depth. The UAS measurements will include particle number concentration, aerosol absorption coefficient, filter collection for aerosol chemistry (Bates et al., 2013), aerosol size distributions from 130 to 3000 nm (Gao et al., 2016), optical depth measurements from a miniature scanning sun photometer (Murphy et al., 2016), cloud droplet number size distributions (CDP, DMT, Boulder, CO), temperature, and RH. The UAS will also be equipped with a flux measurement system (miniFLux) for the measurement of atmospheric thermodynamic state, turbulence, three dimensional winds, and surface and sky infra-red temperature (Fairall et al., in a separate proposal to this announcement). The measured aerosol and cloud properties will be regressed against net radiation and SST measured on the ship to test our hypothesis. The time series of these parameters will be analyzed in the context of the larger set of meteorological, oceanographic, and satellite data to investigate the processes and cause-effect relationships between aerosols, radiative transfer, cloud physics, precipitation, and surface ocean properties. Multivariate statistical analysis will be used to determine relationships between aerosol parameters (e.g., concentration, size distribution, composition) and cloud physics parameters, (e.g., thermodynamic profiles, cloud albedo and effective radius, vertical mixing, cloud base, cloud top, and precipitation rate). The products, time series of aerosol parameters and derived empirical relationships, will provide input to the ATOMIC/EUREC4A-OA and EUREC4A modeling communities. The final data sets will be archived on the PMEL Atmospheric Chemistry data server (http://saga.pmel.noaa.gov/data/) and NOAA PMEL’s ERDDAP Data Server.

Spatial structure of air-sea interaction in the tropical Atlantic Ocean

Principal Investigator(s): Elizabeth Thompson (U Wash/APL); Jim Thomson (UW/APL)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Upper - Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean

Award Number: NA19OAR4310374 | View Publications on Google Scholar


The proposed study will investigate the spatial structure of surface fluxes and waves due to organized patterns of low clouds along with ocean mesoscale eddies and fronts. These processes are known to coexist in all tropical oceans, but the details of their spatial variations have not been captured in any available datasets. Waves, trade winds, shallow clouds, and ocean eddies frequently coexist in the tropical northwestern Atlantic, where the ATOMIC field campaign has been planned. We propose an observation-based project as part of ATOMIC, in which we will investigate the spatial structure in the atmospheric and oceanic mixed layers when cloud patterns and ocean mesoscale eddies are present. We will use a distributed array of ten autonomous platforms called SWIFTs, a NOAA research vessel, and the NOAA P3 aircraft to make these observations. The Surface Wave Instrumented Floats with Tracking (SWIFTs) will offer a Lagrangian, distributed view of ocean features as they evolve and clouds as they develop overhead. The specific scientific questions raised about clouds and waves are: 1. How are surface energy fluxes influenced by organized cloud patterns within the trade winds and spatial gradients in SST across eddies? 2. How are surface waves, and in particular wave breaking, modified by ocean mesoscale variations in currents? 3. How are surface fluxes and turbulence in the oceanic and atmospheric mixed layers impacted by coinciding perturbations of cloud and wave conditions? 1-D air-sea interaction has been well-studied with decades of point-measurements collected from ships. That these measurements only cover a single point in space produces the largest gap in our understanding of air-sea interaction as well as the largest limitation of these datasets for use by numerical models. Research is needed on waves and air-sea fluxes, particularly in the tropics where ocean mesoscale features, persistent trade winds, and organized patterns of low-clouds coexist. The overarching theme of this work is to understand how fine-scale patterns in the oceanic and atmospheric mixed layers co-evolve so that, in the future, these processes can be represented in satellite data and predicted in numerical models with greater fidelity. Our project involves multiple observational datasets in the ocean, atmosphere, and at the sea surface. The project methodology systematically sifts through these data with objective analysis focused on physical processes. These steps will efficiently translate data into research results about coupled air-sea interaction that are actionable and relevant for operational environmental monitoring and numerical prediction.



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