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Bofu Zheng, Andrew J. Lucas, Robert Pinkel, and Arnaud Le Boyer

Abstract

The Wirewalker (WW) ocean-wave-powered vertical profiling system allows the collection of high-resolution oceanographic data due to its rapid profiling, hydrodynamically quiet operation, and long endurance. We have assessed the potential for measuring fine-scale ocean velocities from the Wirewalker platform using commercially available acoustic velocimeters. Although the vertical profiling speed is relatively steady, platform motion affects the velocity measurements and requires correction. We present an algorithm to correct our velocity estimates using platform motion calculated from the inertial sensors – accelerometer, gyroscope, and magnetometer – on a Nortek Signature1000 Acoustic Doppler Current Profiler. This correction, carried out ping-by-ping, was effective in removing the vehicle motion from the measured velocities. The motion-corrected velocities contain contributions from surface wave orbital velocities, especially near the surface, and the background currents. To proceed, we use an averaging approach that leverages both the vertical platform profiling of the system and the ~15-20 m vertical profiling range resolution of the down-looking ADCP to separate the surface wave orbital velocities and the background flow. The former can provide information on the wave conditions. From the latter, we are able to estimate fine-scale velocity and shear with spectral wavenumber roll-off at vertical scales around 3 m, a vertical resolution several times finer than that possible from modern shipboard or fixed ADCPs with similar profiling range, and similar to recent glider measurements. When combined with a continuous time-series of buoy drift calculated from the onboard GPS, a highly-resolved total velocity field is obtained, with a unique combination of space and time resolution.

Open access
Christopher Daly, Matthew K. Doggett, Joseph I. Smith, Keith V. Olson, Michael D. Halbleib, Zlatko Dimcovic, Dylan Keon, Rebecca A. Loiselle, Ben Steinberg, Adam D. Ryan, Cherri M. Pancake, and Eileen M. Kaspar

Abstract

There is a great need for gridded daily precipitation datasets to support a wide variety of disciplines in science and industry. Production of such datasets faces many challenges, from station data ingest to gridded dataset distribution. The quality of the dataset is directly related to its information content, and each step in the production process provides an opportunity to maximize that content. The first opportunity is maximizing station density from a variety of sources and assuring high quality through intensive screening, including manual review. To accommodate varying data latency times, the Parameter-Elevation Regressions on Independent Slopes Model (PRISM) Climate Group releases eight versions of a day’s precipitation grid, from 24 h after day’s end to 6 months of elapsed time. The second opportunity is to distribute the station data to a grid using methods that add information and minimize the smoothing effect of interpolation. We use two competing methods, one that utilizes the information in long-term precipitation climatologies, and the other using weather radar return patterns. Last, maintaining consistency among different time scales (monthly vs daily) affords the opportunity to exploit information available at each scale. Maintaining temporal consistency over longer time scales is at cross purposes with maximizing information content. We therefore produce two datasets, one that maximizes data sources and a second that includes only networks with long-term stations and no radar (a short-term data source). Further work is under way to improve station metadata, refine interpolation methods by producing climatologies targeted to specific storm conditions, and employ higher-resolution radar products.

Open access
Julia W. Fiedler, Lauren Kim, Robert L. Grenzeback, Adam P. Young, and Mark A. Merrifield

Abstract

We demonstrate that a hovering, drone-mounted laser scanner (lidar) paired with a survey-grade satellite and inertial positioning system measures the wave transformation across the surf zone and the resulting runup with accuracy almost equal to a stationary truck-mounted terrestrial lidar. The drone, a multirotor small uncrewed aircraft system (sUAS), provides unobstructed measurements by hovering above the surf zone at 20-m elevation while scanning surfaces along a 150-m-wide cross-shore transect. The drone enables rapid data collection in remote locations where terrestrial scanning may not be possible. Allowing for battery changes, about 17 min of scanning data can be acquired every 25 min for several hours. Observations were collected with a wide (H s = 2.2 m) and narrow (H s = 0.8 m) surf zone, and are validated with traditional land-based survey techniques and an array of buried pressure sensors. Thorough postprocessing yields a stable (σ¯=1.7cm) back beach topography estimate comparable to the terrestrial lidar (σ¯=0.8cm). Statistical wave properties and runup values are calculated, as well as bathymetry inversions using a relatively simple nonlinear correction to wave crest phase speed in the surf zone, illustrating the utility of drone-based lidar observations for nearshore processes.

Open access
Charles-Antoine Guérin, Dylan Dumas, Anne Molcard, Céline Quentin, Bruno Zakardjian, Anthony Gramoullé, and Maristella Berta

Abstract

We report on the installation and first results of one compact oceanographic radar in the region of Nice for a long-term observation of the coastal surface currents in the northwest Mediterranean Sea. We describe the specific processing and calibration techniques that were developed at the laboratory to produce high-quality radial surface current maps. In particular, we propose an original self-calibration technique of the antenna patterns, which is based on the sole analysis of the database and does not require any shipborne transponder or other external transmitters. The relevance of the self-calibration technique and the accuracy of inverted surface currents have been assessed with the launch of 40 drifters that remained under the radar coverage for about 10 days.

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Chung Taing, Katherine L. Ackerman, Alison D. Nugent, and Jorgen B. Jensen

Abstract

Sea salt aerosol (SSA) plays a significant role in the atmosphere through aerosol direct and indirect effects, and in atmospheric chemistry as a source of tropospheric bromine. In situ measurements of coarse-mode SSA particles are limited because of their low concentration and relatively large sizes (dry radius r d > 0.5 μm). With this in mind, a new, low-cost, easily usable method for sampling coarse-mode SSA particles in the marine boundary layer was developed. An SSA particle sampler that uses an impaction method was designed and built using 3D printing and Arduino microcontrollers and sensors. It exposes polycarbonate slides to ambient airflow remotely on a kite-based platform to capture coarse-mode SSA particles. Because it is a smaller version of the Giant Nucleus Impactor (GNI), designed for use on aircraft, it is named the miniature Giant Nucleus Impactor (miniGNI). After sample collection, the same optical microscope methodology utilized by the GNI was used to analyze the wetted salt particles that impacted onto the slides. In this proof-of-concept study, multiple miniGNIs were attached serially to a kite string, allowing for sampling at multiple altitudes simultaneously. The robustness of the results from this new instrument and methodology for sampling at ambient RH (~75%) the SSA particle size distribution with r d > 3.3 μm are compared with a similar study. We find that the SSA particle number concentration decreases weakly with altitude and shows no correlation to instantaneous U 10 wind speed along the windward coastline of Oʻahu in the Hawaiian Islands.

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Je-Yuan Hsu

Abstract

EM-APEX floats as autonomous vehicles have been used for profiling temperature, salinity, and current velocity for more than a decade. In the traditional method for processing horizontal current velocity from float measurements, signals of surface wave motion are removed as residuals. Here, a new data processing method is proposed for deriving the horizontal velocity of surface waves at the floats. Combined with the vertical acceleration measurements of waves, surface wave directional spectra E(f, θ) can be computed. This method is applied to the float measurements on the right of Typhoon Megi’s 2010 track. At 0.6 days before the passage of Megi’s eye to the floats, the fast-propagating swell may affect wind waves forced by the local storm wind. When the storm moves closer to the floats, the increasing wind speed and decreasing angle between wind and dominant wave direction may enhance the wind forcing and form a monomodal spectrum E(f). The peak frequency f p ~ 0.08 Hz and significant wave height > 10 m are found near the eyewall. After the passage of the eye to the floats, f p increases to >0.1 Hz. Although E(f) still has a single spectral peak at the rear-right quadrant of Megi, E(f, θ) at frequencies from 0.08 to 0.12 Hz has waves propagating in three different directions as a trimodal spectrum, partially due to the swell propagating from the rear-left quadrant. Enhancing the capability of EM-APEX floats to observe wave spectra is critical for exploring the roles of surface waves in the upper ocean dynamics in the future.

Open access
Ganesh Gopalakrishnan, Bruce D. Cornuelle, Matthew R. Mazloff, Peter F. Worcester, and Matthew A. Dzieciuch

Abstract

A strongly nonlinear eddy field is present in and around the subtropical countercurrent in the northern Philippine Sea (NPS). A regional implementation of the Massachusetts Institute of Technology General Circulation Model–Estimating the Circulation and Climate of the Ocean four-dimensional variational assimilation (MITgcm-ECCO 4DVAR) system is found to be able to produce a series of 2-month-long dynamically consistent optimized state estimates between April 2010 and April 2011 for the eddy-rich NPS region. The assimilation provides a stringent dynamical test of the model, showing that a free run of the model forced using adjusted controls remains consistent with the observations for 2 months. The 4DVAR iterative optimization reduced the total cost function for the observations and controls by 40%–50% from the reference solution, initialized using the Hybrid Coordinate Ocean Model 1/12° global daily analysis, achieving residuals approximately equal to the assumed uncertainties for the assimilated observations. The state estimates are assessed by comparing with assimilated and withheld observations and also by comparing 1-month model forecasts with future data. The state estimates and forecasts were more skillful than model persistence and the reference solutions. Finally, the continuous state estimates were used to detect and track the eddies, analyze their structure, and quantify their vertically integrated meridional heat and salt transports.

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Ganesh Gopalakrishnan, Bruce D. Cornuelle, Matthew R. Mazloff, Peter F. Worcester, and Matthew A. Dzieciuch

Abstract

The 2010–11 North Pacific Acoustic Laboratory (NPAL) Philippine Sea experiment measured travel times between six acoustic transceiver moorings in a 660-km diameter ocean acoustic tomography array in the northern Philippine Sea (NPS). The travel-time series compare favorably with travel times computed for a yearlong series of state estimates produced for this region using the Massachusetts Institute of Technology General Circulation Model–Estimating the Circulation and Climate of the Ocean four-dimensional variational (MITgcm-ECCO 4DVAR) assimilation system constrained by satellite sea surface height and sea surface temperature observations and by Argo temperature and salinity profiles. Fluctuations in the computed travel times largely match the fluctuations in the measurements caused by the intense mesoscale eddy field in the NPS, providing a powerful test of the observations and state estimates. The computed travel times tend to be shorter than the measured travel times, however, reflecting a warm bias in the state estimates. After processing the travel times to remove tidal signals and extract the low-frequency variability, the differences between the measured and computed travel times were used in addition to SSH, SST, and Argo temperature and salinity observations to further constrain the model and generate improved state estimates. The assimilation of the travel times reduced the misfit between the measured and computed travel times, while not increasing the misfits with the other assimilated observations. The state estimates that used the travel times are more consistent with temperature measurements from an independent oceanographic mooring than the state estimates that did not incorporate the travel times.

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Douglas Mach and Katrina Virts

Abstract

We have developed a technique to estimate the three-dimensional (3D) location of lightning optical pulses based on the stereo view of common lightning pulses from two different orbital instruments. The technique only requires the satellite position and the look vector to the lightning optical source. An example dataset of the Geostationary Lightning Mappers (GLMs) on GOES-16 and GOES-17 from 10 June 2019 is used to illustrate the technique. For this dataset, we find that the values for the stereo determination of cloud-top altitudes are on average lower by 740 m than the ones calculated from the lightning ellipsoid that is currently applied during geolocation. When we compare the locations to the Advanced Baseline Imager (ABI) Cloud Height Algorithm (ACHA), we find that our technique also produces slightly lower altitude values by 240 m. There is greater spread in our technique than either the lightning ellipsoid or the ABI cloud-top height that is likely due to the incorrect pairing of groups between the two GLMs and the 8–14-km resolution in the group locations. Based on GLM location errors derived from comparisons to ground truth sources, the uncertainty in the radial location determined by the stereo location technique is 5.2 km, while the altitude uncertainty is 4.0 km. The technique can be used to 3D map lightning or other optical sources such as bolides and other upper-atmospheric optical phenomena from any two orbital sensors with overlapping fields of view.

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Agustinus Ribal, Ali Tamizi, and Ian R. Young

Abstract

Four scatterometers, namely, MetOp-A, MetOp-B, ERS-2, and OceanSat-2 were recalibrated against combined National Data Buoy Center (NDBC) data and aircraft Stepped Frequency Microwave Radiometer (SFMR) data from hurricanes. As a result, continuous calibration relations over the wind speed range from 0 to 45 m s−1 were developed. The calibration process uses matchup criteria of 50 km and 30 min for the buoy data. However, due to the strong spatiotemporal wind speed gradients in hurricanes, a method that considers both scatterometer and SFMR data in a storm-centered translating frame of reference is adopted. The results show that although the scatterometer radar cross section is degraded at high wind speeds, it is still possible to recover wind speed data using the recalibration process. Data validation between the scatterometers shows that the calibration relations produce consistent results across all scatterometers and reduce the bias and root-mean-square error compared to previous calibrations. In addition, the results extend the useful range of scatterometer measurements to as high as 45 m s−1.

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