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NOAA’s Global Ocean Monitoring and Observing Program (GOMO) funded six technology development projects in support NOAA’s contribution to TPOS 2020. Four projects were funded in 2016 to advance the readiness of in situ observing platforms (e.g. floats, gliders, moorings) and assess their potential to address observational requirements and gaps in the tropical Pacific Ocean region. Two additional projects were funded in 2019 by GOMO in partnership with NOAA CPO Climate Variability and Predictability Program and the NASA Ocean Biology and Biogeochemistry Program to advance use of Biogeochemical Argo floats. These projects will develop, calibrate, and demonstrate the efficacy of profiling ocean floats equipped with high-quality biogeochemical sensors for pH, oxygen, nitrate, and optical observations to observe biogeochemical properties in the upper 2000 meters with sufficient accuracy for climate studies.
1. Profiling Floats Equipped with Rainfall, Wind Speed, and Biogeochemical Sensors for Use in the Tropical Pacific Observing System.
Stephen Riser (University of Washington, School of Oceanography), Jie Yang (University of Washington, Applied Physics Laboratory)
Summary: We have been funded to deploy 15 Argo-type profiling floats in the Equatorial Pacific that measure the biogeochemical parameters dissolved oxygen, pH, chlorophyll fluorescence, and particulate backscatter; the surface parameters wind speed and rainfall; and the traditional parameters temperature and salinity as a function of pressure. We will analyze the data collected. This work is underway and going well.
Outcome: We have been funded to build and deploy 15 profiling floats to make these measurements. Eleven of these floats have been deployed to date, all in the Equatorial Pacific, and are working well aside from a few minor problems. The final 4 floats have been built for some time but their deployment was delayed due to the ongoing pandemic. These last floats are now aboard the vessel Bluefin and are scheduled for deployment in the western tropical Pacific (south of Guam) in early August of this year. The data provided by the floats has been added to the real-time Argo data stream and is publicly available. Strong regional and seasonal variability is present in all measured parameters, with several publications being prepared by the co-PIs that document these results.
Relevance to TPOS Strategy: A number of recommendations for future observations of the Tropical Pacific are made in the First Report of TPOS 2020, published in 2016. The report lays out a plan for future sampling of the Equatorial Pacific that includes enhanced sampling of the surface and subsurface ocean by profiling floats, increased sampling of biogeochemical parameters, and increased in situ sampling of rainfall and wind. In this project we have addressed the report recommendations by deploying profiling floats in the TPOS region that measure traditional quantities such as T and S, as well as observing biogeochemical variables such as dissolved oxygen, pH, and chlorophyll. Additionally, we measure rainfall and wind speed from the floats, addressing a third recommendation of the TPOS report. Measurements from a single float can thus be used to answer several recommendations relevant to TPOS planning.
2. Enhanced Ocean Boundary Layer Observations on NDBC TAO Moorings.
Karen Grissom (NOAA/NWS/NDBC), William Kessler (NOAA/PMEL), Meghan Cronin (NOAA/PMEL), and Jessica Masich (NRC, NOAA/PMEL)
Summary: The goal of this project was threefold: to develop the ability to measure near-surface horizontal current profiles on NDBC operational moorings; to develop the ability to telemeter these data to shore in near-realtime; and to determine where these enhanced boundary layer observations would be most beneficial. The developmental work was completed without interfering with operational measurements, successfully providing approximately one year of near-surface current profiles at nine mooring locations in near real-time. The project also produced the bonus capability to mount and telemeter multiple ADCPs on the NDBC mooring line, thus potentially extending the near-realtime current profiles down through the Equatorial Undercurrent. Combined with enhanced observations of meteorological conditions and near-surface temperature and salinity, the project has identified and characterized near-surface wind-forced warm water jets that can enable direct forcing from the atmosphere into the interior ocean on a diurnal timescale. These jets consistently form along the central and eastern equator, highlighting this region for potential long-term monitoring of enhanced atmosphere-ocean communication.
Outcome Each enhanced NDBC mooring included an upward-looking ADCP and 1-2 current meters; additional temperature and some salinity sensors in the upper 50 m to better resolve near-surface stratification and mixed layer depth; and a rain gauge, solar radiometer, and longwave radiometer to measure the full net-surface heat flux and moisture flux. NDBC safely mounted Nortek Aquadopp ADCPs on the NDBC mooring line and modified data loggers for real-time telemetry ahead of schedule, within the first year of the 4-year project. NDBC also employed pooled temperature-conductivity sensors so that additional profilers could be purchased. As a result, the project was able to test these systems on a total of nine sites over the course of four years. The enhanced moorings spanned a number of tropical Pacific regimes, including the cold tongue and cold tongue frontal region; the east edge of the warm pool; and the off-equatorial convergence zone regions in the north and south. Analysis of the enhanced observations revealed a diurnal enhancement of communication between the atmosphere and the ocean. This enhancement takes the form of a daytime stratified layer that captures heat and momentum at the ocean surface and mixes this surface forcing downward over the course of the night, reaching as deep as 60 m by local midnight. These layers consistently form along the equator, where a shallow EUC enhances the ability of the jets to form and mix downwards each day. The equatorial jets reach more deeply under higher wind conditions, and shallower short-term jets off the equator in the ITCZ region can also form in high-wind, high-insolation conditions.
Relevance to TPOS Strategy: As a joint effort between PMEL and NDBC, the project has bolstered the collaboration between the operational and research elements of NOAA’s efforts in the tropical Pacific. All mooring enhancements and near-realtime telemetry were implemented without interference with sampling on existing operational TAO moorings, demonstrating that boundary layer sampling can easily integrate into the existing array. The boundary layer observations have revealed direct, systematic communication between the atmosphere and the ocean interior on a diurnal timescale. Daytime layers of surface-forced heat and momentum can reach as deep as 60 m in the central and eastern equatorial region, highlighting this area for long term monitoring of enhanced ocean-atmosphere communication. Overall, the efficacy of the mooring enhancements has been proven, with observations across all nine sites that have provided important insights into the ‘blind spot’ of the near-surface ocean. Integration of these enhanced mooring observations into the TPOS strategy could provide myriad insights beyond the diurnal cycle analysis already completed, and would be an efficient way to gain key knowledge about the tropical Pacific ocean-atmosphere system.
3. Development and Testing of Direct Covariance Turbulent Flux Measurements for NDBC TAO Buoys.
James Edson and Tom Farrar (WHOI), Meghan Cronin (NOAA PMEL), Chris Fairall (NOAA PSL)
Summary: This is a project to transition recent advances in buoy-based air-sea flux measurements to operational TAO buoy array (R2X). In this project a low power direct covariance flux system (DCFS) developed at WHOI is being used as the technology base for future deployment on selected NDBC TAO buoys. It is designed to motion correct the 3-D sonic anemometer measurements; compute the fluxes, means and wave statistics onboard; and telemeter the data to shore in near real-time. During the course of the project, we joined forces with the Enhanced Ocean Boundary Layer Observations on NDBC TAO Moorings effort led by Karen Grissom (NOAA/NDBC) to build a stand-alone enhanced flux mooring.
Outcome: The DCFS and a TAO buoy were successfully built by WHOI and PMEL for the project. The DCFS was modified to measure all of the variables necessary for direct covariance and bulk flux estimates. The enhanced buoy was instrumented and deployed near a TAO mooring on the equator at 165oE on October 4, 2019. The DCFS successfully computed and telemetered fluxes, means and wave statistics every hour over the course of the deployment, which ended on April 21, 2020. The telemetered fluxes and means were used in an Ocean Sciences presentation in February before recovery. This is an obvious advantage of real-time delivery of research-quality data.
Relevance to TPOS Strategy: The enhanced mooring developed for this project can be considered a proto-type for the Tier-2 Enhanced moorings we expect to deploy for the TPOS array. The enhancements include directly measured momentum and buoyancy fluxes, surface waves, and all variables required to compute bulk fluxes including radiative fluxes and currents, which are available in near real-time. The fluxes and waves can be directly used in process studies to force the ocean as well as improve wind-speed and wave-based parameterization of the bulk flux algorithm used on other TPOS buoys.
4. Saildrone Missions
Meghan Cronin (NOAA PMEL), Dongxiao Zhang (UW JISAO), Adrienne Sutton (NOAA PMEL), Samantha Wills (UW JISAO), Chris Meinig (NOAA PMEL) see: https://www.pmel.noaa.gov/ocs/saildrone
Summary: With their ability to do repeat sections and adaptive sampling, Unmanned Surface Vehicles (USV), hold great potential for enhancing the observing capabilities of the TPOS. The Saildrone, in particular, measures a suite of surface ECV and EOVs similar to TPOS buoys (with the exception of rainfall). The objectives of the NOAA GOMO funded pilot study “Autonomous Surface Vessels as Low-Cost TPOS Platforms for Observing the Planetary Boundary Layer and Surface Biogeochemistry,” were to integrate the PMEL MAPCO2 system into an ASVCO2 system for deployment on the TPOS Saildrones, test these meteorological and BGC measurements against well-accepted flux moorings, and test the performance of this new platform in the variety of wind and current regimes found in the tropics – in regions of low winds and strong currents (e.g., cold tongue), steady winds with and without currents (e.g., trade wind regime), winds against the currents (e.g. North Equatorial Counter Current), and in regions of rapidly changing conditions (e.g., ITCZ). With supplemental funding from NOAA OMAO, three missions were carried out between September 2017 and December 2019: an eastern Pacific (~125W) mission launched and recovered from California, and two central Pacific (~140W) missions launched and recovered from Hawaii.
Outcome: The first mission included a 3-week intercomparison against a WHOI surface flux mooring, deployed at 10N, 125W as part of the NASA-funded Salinity Process in the Upper Ocean Study-2 (SPURS-2). As described by Zhang et al. (2019), the Saildrone and moored buoy showed excellent agreement for all physical measurements, including for wind speed, sea surface temperature (SST), air-temperature, humidity, solar and long-wave radiation.
After departing the 10°N, 125°W study region, the two Mission 1 Saildrones transited to the equator, crossing an abrupt front on the northern edge of the equatorial cold tongue. These observations have led to a study, currently underway, of the nature of these abrupt fronts and their influence on the atmosphere. Unfortunately, once the Saildrones entered the equatorial cold tongue’s low wind, strong current environment the drones lost navigational control and were swept to the west. The Saildrones were subsequently redesigned with a larger wing and increased antifoulant. For Mission 2, a pair of these new Gen5 and a pair of Gen4 were deployed from Hawaii for tests at 0, 140W. Unfortunately, again, all 4 drones had trouble with navigational control on the equator, where winds were weak and currents were strong. Away from the equator, there was better navigational control and the cluster of Saildrones were able to provide novel observations of convective downdrafts and cold pools. For the final 6-month GOMO/OMAO-funded Saildrone Mission (Mission 3), Gen5 Saildrones were modified again, returning to the smaller wing for added stability, changing navigation firmware to gain control in swell conditions, and adding antifoulant to the hull and keel. This cluster of four modified Gen5’s had the best success navigating on the equator at 140°W.
Relevance to TPOS Strategy: In summary, lessons learned from the GOMO/OMAO TPOS Saildrone pilot study’s three missions are: (1) Precise navigation is very challenging in the tropics, and particularly in the low wind/high current equatorial cold tongue region. (2) Saildrone’s surface observations are comparable in quality to surface buoy observations used with the TPOS. (3) Saildrone is an excellent platform for observing fast processes such as convective downdrafts, surface atmospheric cold pools, and sharp oceanic fronts. We suspect that abrupt ocean fronts are much more prevalent than previously known. (4) The carbon footprint of these measurements was very low — the sensors were solar powered, the platform used wind-power for propulsion and were deployed from shore (HI and CA). In the future, Palmyra Atoll (~162W, 6N) might be used as a servicing base for efficient access to the TPOS array. (5) The present cost structure for Saildrone is appropriate for a process study, but would need to be reduced if a fleet were used operationally within the TPOS. We believe that economies of scale, as well as automated sampling schemes (including for adaptive sampling) could reduce the costs for sustained observations in comparison to process study missions. (6) Pilot studies for emerging technologies, like Saildrone, are absolutely critical: Each mission led to new understanding of both the climate system and improvements to the platform and its use. Further work is needed to develop and test the Saildrone as an operational platform within the TPOS.
Zhang et.al, 2019; https://doi.org/10.5670/oceanog.2019.220
5. Improvements to Profiling Float Technology in Support of Equatorial Pacific
Biogeochemical Studies Stephen C. Riser (University of Washington), Ken Johnson (MBARI), Brendan Carter, (JISAO/UW), Thomas Mitchell (Seabird)
Summary: The goal of this project is to develop, build, and deploy 8-16 prototype Seabird biogeochemical (BGC) Argo profiling floats in the tropical Pacific. The project will evaluate a new design of a full suite (6-parameter) BGC Argo float with a potential pathway for commercialization. The proposed 6-parameter BGC Argo will build from the existing design of the Sea-Bird BGC Navis float, which at present includes oxygen, chlorophyll, backscatter, nitrate, and pH. To meet the requirements of the BGC Argo program for a 6-parameter float with sufficient longevity, the team will modify the current float design to: increase the buoyancy capacity and longevity of the Navis buoyancy engine; change the location of the optode O2 sensor for in-situ air calibration; add a downwelling irradiance (Ed) sensor; and experiment with a new version of the pH sensor to address pressure compensation issues. In addition to the float development, the team will implement a new region specific, multiple linear regression (MLR) model for the tropical Pacific leveraging the new GLODAPV2 data. The regional MLR will allow for the estimation of other parameters of the inorganic carbon system (pCO2, alkalinity, DIC) from the standard suite of Argo physical and biogeochemical measurements. Estimates of pCO2 from the MLR applied to the new float data will be compared with pCO2 directly measured during Saildrone missions in the same region.
Outcome: At this time (near the end of the first year of the project) the redesign of the oxygen sensor is nearly complete. The first deployment of a prototype will likely occur off the coast of Monterey, California in August of this year. This float will have 3 different O2 sensors: a traditional Aanderaa Optode, that is widely used in biogeochemical applications; a SeaBird 63, that has been used for some time on SeaBird floats (but is unable to collect in-air observations for in situ calibration); and a new version of the SeaBird 63 that can be calibrated in-air. A second prototype (based on design revisions discerned from the first) will be deployed in the fall of this year. It is hoped that a commercial version of the new sensor will be available in the first quarter of 2021. A redesign of SBE float hull is also underway in order to be able to increase the battery payload and float lifetime. A test deployment early in 2021 is planned. The MLR work and downwelling irradiance sensor work are just beginning and will be a new focus of the work in the coming year.
Relevance to TPOS Strategy: The First Report of TPOS 2020, published in 2016, calls for making profiling float measurements in the Equatorial Pacific using a variety of sensors and measurements. It is desirable to have commercial versions of such floats so that they might be readily available to multiple groups of investigators. At the present time the commercially-available versions are inferior to those produced by hand in a few research laboratories. As there is a limit to the number of that can be produced by these labs, a viable commercial product is required. This project aims to help to develop and improve this commercial expertise, based on the experience gained in the past 2 decades by UW.
6. Developing an autonomous biogeochemical profiling float to monitor biological productivity, ocean-atmosphere CO2 fluxes, and hypoxia in the Tropical Pacific Ocean
Sarah Purkey, Todd Martz, Lynne Talley, Dean Roemmich, Matthew Mazloff, Daniel Rudnick, Ariane Verdy (SIO-UCSD); Neil Bogue (MRV Systems LLC); Ken Johnson (MBARI)
Summary: The Tropical Pacific is the largest natural oceanic source of CO2 to the climate system and houses one of the world’s most productive ecosystems. However, the drivers and consequences of the interannual-to-decadal variability associated with ENSO on biogeochemical processes in the region still have high uncertainty. This award is to advance US’s technical and commercial readiness to support the new TPOS and the larger global BGC Argo array. The award is to design, test, and commercialize a new model of float that can measure temperature, salinity, oxygen, pH, nitrate, chlorophyll-a, backscatter, and downwelling irradiance. This award will support the design and building of 5 BGC floats to be deployed in the Tropical Pacific as part of the TPOS in 2022. In addition, this award supports the development of a biogeochemical ocean model of the Tropical Pacific. The model developed through this award uses physical dynamics constrained by ocean and atmospheric data between 2010-2019 to produce a high-resolution reconstruction of the interior ocean’s biogeochemistry over the time period. This product is a powerful tool for observing system design and for advancing our understanding of the chemistry and biology of the Tropical Pacific.
Expected Outcome: The major outcomes of this project will be: (1) A new model of biogeochemical (BGC) Argo profiling float based on SIO’s SOLO-II core Argo model. The new model will utilize the reliable, robust SOLOII body and add 6 BGC sensors and be Commercialize through MRV systems. A total of 5 test floats (4 built by SIO and 1 by MRV systems) will be built, tested and then deployed along the equator of the Tropical Pacific, capable of monitoring the biogeochemical variability in the upper 2000m as part of the TPOS 2020. (2) The development of a coupled BGC model to the Tropical Pacific Ocean State Estimate (TPOSE) to assess temporal and spatial length scales of the climate variability. The model will be used to better plan an optimize the monitoring system of the biogeochemistry of the Tropical Pacific in line with TPOS 2020’s requirements, and to provide a major BGC analysis tool.
Relevance to TPOS Strategy: The profiling BGC Argo floats will contributes to the requirements of TPOS by (1) accurately measuring subsurface chlorophyll concentration, particulate backscatter, oxygen, nitrate and pH to monitor the seasonal to interannual variability in the biogeochemistry in order to assess the rates of ocean productivity and ecosystem health, including subsurface oxygen budgets and the expansion of oxygen minimum zones, (2) add a new platform to the current proposed pCO2 monitoring system to quantify seasonal-to-interannual variability in ocean-atmosphere carbon exchange, and (3) provide in-situ chlorophyll estimates for calibration of the broad scale surface ocean color satellite observations. The floats will also support many of the TPOS 2020 key backbone functions, which require doubling the Argo float concentration between 10°S and 10°N to enhance coverage of subsurface temperature and salinity profiles.
In addition, analysis of TPOSE will inform the future Tropical Pacific BGC observing system as a whole by evaluating the magnitude and relative spatial scales of the large seasonal to interannual variability in tropical BGC properties and fluxes. These results will provide a concrete assessment of the value of the BGC Argo array to TPOS 2020 and provide guidance on the needed future size and distribution of the array.