Publications

Export 288 results:
Sort by: Author Title [ Year  (Desc)]
2018
Chen, Z, Bromirski PD, Gerstoft P, Stephen RA, Wiens DA, Aster RC, Nyblade AA.  2018.  Ocean-excited plate waves in the Ross and Pine Island Glacier ice shelves. Journal of Glaciology. 64:730-744.   10.1017/jog.2018.66   AbstractWebsite

Ice shelves play an important role in buttressing land ice from reaching the sea, thus restraining the rate of grounded ice loss. Long-period gravity-wave impacts excite vibrations in ice shelves that can expand pre-existing fractures and trigger iceberg calving. To investigate the spatial amplitude variability and propagation characteristics of these vibrations, a 34-station broadband seismic array was deployed on the Ross Ice Shelf (RIS) from November 2014 to November 2016. Two types of ice-shelf plate waves were identified with beamforming: flexural-gravity waves and extensional Lamb waves. Below 20 mHz, flexural-gravity waves dominate coherent signals across the array and propagate landward from the ice front at close to shallow-water gravity-wave speeds (similar to 70 m s(-1)). In the 20-100 mHz band, extensional Lamb waves dominate and propagate at phase speeds similar to 3 km s(-1). Flexural-gravity and extensional Lamb waves were also observed by a 5-station broadband seismic array deployed on the Pine Island Glacier (PIG) ice shelf from January 2012 to December 2013, with flexural wave energy, also detected at the PIG in the 20-100 mHz band. Considering the ubiquitous presence of storm activity in the Southern Ocean and the similar observations at both the RIS and the PIG ice shelves, it is likely that most, if not all, West Antarctic ice shelves are subjected to similar gravity-wave excitation.

Chen, Z, Bromirski PD, Gerstoft P, Stephen RA, Wiens DA, Aster RC, Nyblade AA.  2018.  Ocean-excited plate waves in the Ross and Pine Island Glacier ice shelves. Journal of Glaciology. 64:730-744.   10.1017/jog.2018.66   AbstractWebsite

Ice shelves play an important role in buttressing land ice from reaching the sea, thus restraining the rate of grounded ice loss. Long-period gravity-wave impacts excite vibrations in ice shelves that can expand pre-existing fractures and trigger iceberg calving. To investigate the spatial amplitude variability and propagation characteristics of these vibrations, a 34-station broadband seismic array was deployed on the Ross Ice Shelf (RIS) from November 2014 to November 2016. Two types of ice-shelf plate waves were identified with beamforming: flexural-gravity waves and extensional Lamb waves. Below 20 mHz, flexural-gravity waves dominate coherent signals across the array and propagate landward from the ice front at close to shallow-water gravity-wave speeds (similar to 70 m s(-1)). In the 20-100 mHz band, extensional Lamb waves dominate and propagate at phase speeds similar to 3 km s(-1). Flexural-gravity and extensional Lamb waves were also observed by a 5-station broadband seismic array deployed on the Pine Island Glacier (PIG) ice shelf from January 2012 to December 2013, with flexural wave energy, also detected at the PIG in the 20-100 mHz band. Considering the ubiquitous presence of storm activity in the Southern Ocean and the similar observations at both the RIS and the PIG ice shelves, it is likely that most, if not all, West Antarctic ice shelves are subjected to similar gravity-wave excitation.

Savelyev, I, Miller WD, Sletten M, Smith GB, Savidge DK, Frick G, Menk S, Moore T, de Paolo T, Terrill EJ, Wang Q, Shearman RK.  2018.  Airborne remote sensing of the upper ocean turbulence during CASPER-East. Remote Sensing. 10   10.3390/rs10081224   AbstractWebsite

This study takes on the challenge of resolving upper ocean surface currents with a suite of airborne remote sensing methodologies, simultaneously imaging the ocean surface in visible, infrared, and microwave bands. A series of flights were conducted over an air-sea interaction supersite established 63 km offshore by a large multi-platform CASPER-East experiment. The supersite was equipped with a range of in situ instruments resolving air-sea interface and underwater properties, of which a bottom-mounted acoustic Doppler current profiler was used extensively in this paper for the purposes of airborne current retrieval validation and interpretation. A series of water-tracing dye releases took place in coordination with aircraft overpasses, enabling dye plume velocimetry over 100 m to 10 km spatial scales. Similar scales were resolved by a Multichannel Synthetic Aperture Radar, which resolved a swath of instantaneous surface velocities (wave and current) with 10 m resolution and 5 cm/s accuracy. Details of the skin temperature variability imprinted by the upper ocean turbulence were revealed in 1-14,000 m range of spatial scales by a mid-wave infrared camera. Combined, these methodologies provide a unique insight into the complex spatial structure of the upper ocean turbulence on a previously under-resolved range of spatial scales from meters to kilometers. However, much attention in this paper is dedicated to quantifying and understanding uncertainties and ambiguities associated with these remote sensing methodologies, especially regarding the smallest resolvable turbulent scales and reference depths of retrieved currents.

Cazenave, A, Meyssignac B, Ablain M, Balmaseda M, Bamber J, Barletta V, Beckley B, Benveniste J, Berthier E, Blazquez A, Boyer T, Caceres D, Chambers D, Champollion N, Chao B, Chen JL, Cheng LJ, Church JA, Chuter S, Cogley JG, Dangendorf S, Desbruyeres D, Doll P, Domingues C, Falk U, Famiglietti J, Fenoglio-Marc L, Forsberg R, Galassi G, Gardner A, Groh A, Hamlington B, Hogg A, Horwath M, Humphrey V, Husson L, Ishii M, Jaeggi A, Jevrejeva S, Johnson G, Kolodziejczyk N, Kusche J, Lambeck K, Landerer F, Leclercq P, Legresy B, Leuliette E, Llovel W, Longuevergne L, Loomis BD, Luthcke SB, Marcos M, Marzeion B, Merchant C, Merrifield M, Milne G, Mitchum G, Mohajerani Y, Monier M, Monselesan D, Nerem S, Palanisamy H, Paul F, Perez B, Piecuch CG, Ponte RM, Purkey SG, Reager JT, Rietbroek R, Rignot E, Riva R, Roemmich DH, Sorensen LS, Sasgen I, Schrama EJO, Seneviratne SI, Shum CK, Spada G, Stammer D, van de Wal R, Velicogna I, von Schuckmann K, Wada Y, Wang YG, Watson C, Wiese D, Wijffels S, Westaway R, Woppelmann G, Wouters B, Grp WGSLB.  2018.  Global sea-level budget 1993-present. Earth System Science Data. 10:1551-1590.   10.5194/essd-10-1551-2018   AbstractWebsite

Global mean sea level is an integral of changes occurring in the climate system in response to unforced climate variability as well as natural and anthropogenic forcing factors. Its temporal evolution allows changes (e.g.,acceleration) to be detected in one or more components. Study of the sea-level budget provides constraints on missing or poorly known contributions, such as the unsurveyed deep ocean or the still uncertain land water component. In the context of the World Climate Research Programme Grand Challenge entitled "Regional Sea Level and Coastal Impacts", an international effort involving the sea-level community worldwide has been recently initiated with the objective of assessing the various datasets used to estimate components of the sea-level budget during the altimetry era (1993 to present). These datasets are based on the combination of a broad range of space-based and in situ observations, model estimates, and algorithms. Evaluating their quality, quantifying uncertainties and identifying sources of discrepancies between component estimates is extremely useful for various applications in climate research. This effort involves several tens of scientists from about 50 research teams/institutions worldwide (www.wcrp-climate.org/grand-challenges/gc-sea-level, last access: 22 August 2018). The results presented in this paper are a synthesis of the first assessment performed during 2017-2018. We present estimates of the altimetry-based global mean sea level (average rate of 3.1 +/- 0.3mm yr(-1) and acceleration of 0.1 mm yr(-2) over 1993-present), as well as of the different components of the sea-level budget (http://doi.org/10.17882/54854, last access: 22 August 2018). We further examine closure of the sea-level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute 42%, 21%, 15% and 8% to the global mean sea level over the 1993-present period. We also study the sea-level budget over 2005-present, using GRACE-based ocean mass estimates instead of the sum of individual mass components. Our results demonstrate that the global mean sea level can be closed to within 0.3 mm yr(-1) (1 sigma). Substantial uncertainty remains for the land water storage component, as shown when examining individual mass contributions to sea level.

Cazenave, A, Meyssignac B, Ablain M, Balmaseda M, Bamber J, Barletta V, Beckley B, Benveniste J, Berthier E, Blazquez A, Boyer T, Caceres D, Chambers D, Champollion N, Chao B, Chen JL, Cheng LJ, Church JA, Chuter S, Cogley JG, Dangendorf S, Desbruyeres D, Doll P, Domingues C, Falk U, Famiglietti J, Fenoglio-Marc L, Forsberg R, Galassi G, Gardner A, Groh A, Hamlington B, Hogg A, Horwath M, Humphrey V, Husson L, Ishii M, Jaeggi A, Jevrejeva S, Johnson G, Kolodziejczyk N, Kusche J, Lambeck K, Landerer F, Leclercq P, Legresy B, Leuliette E, Llovel W, Longuevergne L, Loomis BD, Luthcke SB, Marcos M, Marzeion B, Merchant C, Merrifield M, Milne G, Mitchum G, Mohajerani Y, Monier M, Monselesan D, Nerem S, Palanisamy H, Paul F, Perez B, Piecuch CG, Ponte RM, Purkey SG, Reager JT, Rietbroek R, Rignot E, Riva R, Roemmich DH, Sorensen LS, Sasgen I, Schrama EJO, Seneviratne SI, Shum CK, Spada G, Stammer D, van de Wal R, Velicogna I, von Schuckmann K, Wada Y, Wang YG, Watson C, Wiese D, Wijffels S, Westaway R, Woppelmann G, Wouters B, Grp WGSLB.  2018.  Global sea-level budget 1993-present. Earth System Science Data. 10:1551-1590.   10.5194/essd-10-1551-2018   AbstractWebsite

Global mean sea level is an integral of changes occurring in the climate system in response to unforced climate variability as well as natural and anthropogenic forcing factors. Its temporal evolution allows changes (e.g.,acceleration) to be detected in one or more components. Study of the sea-level budget provides constraints on missing or poorly known contributions, such as the unsurveyed deep ocean or the still uncertain land water component. In the context of the World Climate Research Programme Grand Challenge entitled "Regional Sea Level and Coastal Impacts", an international effort involving the sea-level community worldwide has been recently initiated with the objective of assessing the various datasets used to estimate components of the sea-level budget during the altimetry era (1993 to present). These datasets are based on the combination of a broad range of space-based and in situ observations, model estimates, and algorithms. Evaluating their quality, quantifying uncertainties and identifying sources of discrepancies between component estimates is extremely useful for various applications in climate research. This effort involves several tens of scientists from about 50 research teams/institutions worldwide (www.wcrp-climate.org/grand-challenges/gc-sea-level, last access: 22 August 2018). The results presented in this paper are a synthesis of the first assessment performed during 2017-2018. We present estimates of the altimetry-based global mean sea level (average rate of 3.1 +/- 0.3mm yr(-1) and acceleration of 0.1 mm yr(-2) over 1993-present), as well as of the different components of the sea-level budget (http://doi.org/10.17882/54854, last access: 22 August 2018). We further examine closure of the sea-level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute 42%, 21%, 15% and 8% to the global mean sea level over the 1993-present period. We also study the sea-level budget over 2005-present, using GRACE-based ocean mass estimates instead of the sum of individual mass components. Our results demonstrate that the global mean sea level can be closed to within 0.3 mm yr(-1) (1 sigma). Substantial uncertainty remains for the land water storage component, as shown when examining individual mass contributions to sea level.

Chenillat, F, Franks PJS, Capet X, Riviere P, Grima N, Blanke B, Combes V.  2018.  Eddy properties in the Southern California Current System. Ocean Dynamics. 68:761-777.   10.1007/s10236-018-1158-4   AbstractWebsite

The California Current System (CCS) is an eastern boundary upwelling system characterized by strong eddies that are often generated at the coast. These eddies contribute to intense, long-distance cross-shelf transport of upwelled water with enhanced biological activity. However, the mechanisms of formation of such coastal eddies, and more importantly their capacity to trap and transport tracers, are poorly understood. Their unpredictability and strong dynamics leave us with an incomplete picture of the physical and biological processes at work, their effects on coastal export, lateral water exchange among eddies and their surrounding waters, and how long and how far these eddies remain coherent structures. Focusing our analysis on the southern part of the CCS, we find a predominance of cyclonic eddies, with a 25-km radius and a SSH amplitude of 6 cm. They are formed near shore and travel slightly northwest offshore for similar to 190 days at similar to 2 km day(-1). We then study one particular, representative cyclonic eddy using a combined Lagrangian and Eulerian numerical approach to characterize its kinematics. Formed near shore, this eddy trapped a core made up of similar to 67% California Current waters and similar to 33% California Undercurrent waters. This core was surrounded by other waters while the eddy detached from the coast, leaving the oldest waters at the eddy's core and the younger waters toward the edge. The eddy traveled several months as a coherent structure, with only limited lateral exchange within the eddy.

Chao, Y, Farrara JD, Zhang HC, Armenta KJ, Centurioni L, Chavez F, Girton JB, Rudnick D, Walter RK.  2018.  Development, implementation, and validation of a California coastal ocean modeling, data assimilation, and forecasting system. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 151:49-63.   10.1016/j.dsr2.2017.04.013   AbstractWebsite

A three-dimensional, near real-time data-assimilative modeling system for the California coastal ocean is presented. The system consists of a Regional Ocean Modeling System (ROMS) forced by the North American Mesoscale Forecast System (NAM). The ocean model has a horizontal resolution of approximately three kilometers and utilizes a multi-scale three-dimensional variational (3DVAR) data assimilation methodology. The system is run in near real-time to produce a nowcast every six hours and a 72-hour forecast every day. The performance of this nowcast system is presented using results from a six-year period of 2009-2015. The ROMS results are first compared with the assimilated data as a consistency check. RMS differences in observed satellite infrared sea surface temperatures (SST) and vertical profiles of temperature between observations and ROMS nowcasts were found to be mostly less than 0.5 degrees C, while the RMS differences in vertical profiles of salinity between observations and ROMS nowcasts were found to be 0.09 or less. The RMS differences in SST show a distinct seasonal cycle that mirrors the number of observations available: the nowcast is less skillful with larger RMS differences during the summer months when there are less infrared SST observations due to the presence of low-level clouds. The larger differences during summer were found primarily along the northern and central coasts in upwelling regions where strong gradients exist between colder upwelled waters nearshore and warmer offshore waters. RMS differences between HF radar surface current observations and ROMS nowcasts were approximately 7-8 cm s-(1), which is about 30% of the time mean current speeds in this region. The RMS differences in sea surface height (SSH) between the AVISO (Archiving, Validation and Interpretation of Satellite Oceanographic) altimetric satellite observations and ROMS nowcasts were about 2 cm. In addition, the system realistically reproduces the interannual variability in temperatures at the M1 mooring (122.03 degrees W, 36.75 degrees N) in Monterey Bay, including the strong warming of the California coastal ocean during 2014. The ROMS nowcasts were then validated against independent observations. A comparison of the ROMS nowcast with independent profile observations of temperature and salinity shows RMS differences of 0.7 to 0.92 degrees C and 0.13 to 0.17, which are larger (by up to a factor of 2) than the differences found in the comparisons with assimilated data. Validation of the depth-averaged currents derived from Spray gliders shows that the flow patterns associated with California Current and California Undercurrent/Davidson current systems and their seasonal variations are qualitatively reproduced by the ROMS modeling system. Lastly, the impact of two recent upgrades to the system is quantified. Switching the lateral boundary conditions from a U.S. west coast regional model to the global HYCOM (HYbrid Coordinate Ocean Model) model results in an improvement in the simulation of the seasonal and interannual variations in the SSH, especially south of Pt. Conception (120.47 degrees W, 34.45 degrees N). The assimilation of altimetric satellite SSH data also results in an improvement in the model surface currents when compared to independent surface drifter observations.

Chao, Y, Farrara JD, Zhang HC, Armenta KJ, Centurioni L, Chavez F, Girton JB, Rudnick D, Walter RK.  2018.  Development, implementation, and validation of a California coastal ocean modeling, data assimilation, and forecasting system. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 151:49-63.   10.1016/j.dsr2.2017.04.013   AbstractWebsite

A three-dimensional, near real-time data-assimilative modeling system for the California coastal ocean is presented. The system consists of a Regional Ocean Modeling System (ROMS) forced by the North American Mesoscale Forecast System (NAM). The ocean model has a horizontal resolution of approximately three kilometers and utilizes a multi-scale three-dimensional variational (3DVAR) data assimilation methodology. The system is run in near real-time to produce a nowcast every six hours and a 72-hour forecast every day. The performance of this nowcast system is presented using results from a six-year period of 2009-2015. The ROMS results are first compared with the assimilated data as a consistency check. RMS differences in observed satellite infrared sea surface temperatures (SST) and vertical profiles of temperature between observations and ROMS nowcasts were found to be mostly less than 0.5 degrees C, while the RMS differences in vertical profiles of salinity between observations and ROMS nowcasts were found to be 0.09 or less. The RMS differences in SST show a distinct seasonal cycle that mirrors the number of observations available: the nowcast is less skillful with larger RMS differences during the summer months when there are less infrared SST observations due to the presence of low-level clouds. The larger differences during summer were found primarily along the northern and central coasts in upwelling regions where strong gradients exist between colder upwelled waters nearshore and warmer offshore waters. RMS differences between HF radar surface current observations and ROMS nowcasts were approximately 7-8 cm s-(1), which is about 30% of the time mean current speeds in this region. The RMS differences in sea surface height (SSH) between the AVISO (Archiving, Validation and Interpretation of Satellite Oceanographic) altimetric satellite observations and ROMS nowcasts were about 2 cm. In addition, the system realistically reproduces the interannual variability in temperatures at the M1 mooring (122.03 degrees W, 36.75 degrees N) in Monterey Bay, including the strong warming of the California coastal ocean during 2014. The ROMS nowcasts were then validated against independent observations. A comparison of the ROMS nowcast with independent profile observations of temperature and salinity shows RMS differences of 0.7 to 0.92 degrees C and 0.13 to 0.17, which are larger (by up to a factor of 2) than the differences found in the comparisons with assimilated data. Validation of the depth-averaged currents derived from Spray gliders shows that the flow patterns associated with California Current and California Undercurrent/Davidson current systems and their seasonal variations are qualitatively reproduced by the ROMS modeling system. Lastly, the impact of two recent upgrades to the system is quantified. Switching the lateral boundary conditions from a U.S. west coast regional model to the global HYCOM (HYbrid Coordinate Ocean Model) model results in an improvement in the simulation of the seasonal and interannual variations in the SSH, especially south of Pt. Conception (120.47 degrees W, 34.45 degrees N). The assimilation of altimetric satellite SSH data also results in an improvement in the model surface currents when compared to independent surface drifter observations.

Buehler, JS, Mancinelli NJ, Shearer PM.  2018.  S-to-Rayleigh wave scattering from the continental margin observed at USArray. Geophysical Research Letters. 45:4719-4724.   10.1029/2017gl076812   AbstractWebsite

We show examples of teleseismic S waves from western Pacific earthquakes converting to surface waves near the western U.S. coastline. Many of these events originate in the Tonga-Samoa region. We observe these surface wave conversions at USArray stations at relatively long periods (>10s). The amplitudes vary considerably from station to station and appear highly amplified in the Yellowstone region. Two-dimensional spectral element simulations successfully generate scattered Rayleigh waves from incident SV waves and models with surface topography at the coastline and crustal thickness variations across the margin, although simple models cannot explain the large Rayleigh wave amplitudes (greater than the direct S wave amplitude) observed in some regions, suggesting that the wave train is amplified by local structure or 3-D focusing effects. Plain Language Summary We show new observations of body-to-surface wave conversions at the U.S. continental margin observed with USArray. Simulation results show how simple surface topography at the coastline can successfully generate scattered Rayleigh waves from incident SV waves. These converted surface waves may be an important source of signal-generated noise in continental seismology, in particular in studies of seismic phases and parts of the wavefield between direct S and later-arriving surface waves from the source.

Michaud, JM, Thompson LR, Kaul D, Espinoza JL, Richter RA, Xu ZZ, Lee C, Pham KM, Beall CM, Malfatti F, Azam F, Knight R, Burkart MD, Dupont CL, Prather KA.  2018.  Taxon-specific aerosolization of bacteria and viruses in an experimental ocean-atmosphere mesocosm. Nature Communications. 9   10.1038/s41467-018-04409-z   AbstractWebsite

Ocean-derived, airborne microbes play important roles in Earth's climate system and human health, yet little is known about factors controlling their transfer from the ocean to the atmosphere. Here, we study microbiomes of isolated sea spray aerosol (SSA) collected in a unique ocean-atmosphere facility and demonstrate taxon-specific aerosolization of bacteria and viruses. These trends are conserved within taxonomic orders and classes, and temporal variation in aerosolization is similarly shared by related taxa. We observe enhanced transfer into SSA of Actinobacteria, certain Gammaproteobacteria, and lipid-enveloped viruses; conversely, Flavobacteriia, some Alphaproteobacteria, and Caudovirales are generally underrepresented in SSA. Viruses do not transfer to SSA as efficiently as bacteria. The enrichment of mycolic acid-coated Corynebacteriales and lipid-enveloped viruses (inferred from genomic comparisons) suggests that hydrophobic properties increase transport to the sea surface and SSA. Our results identify taxa relevant to atmospheric processes and a framework to further elucidate aerosolization mechanisms influencing microbial and viral transport pathways.

Michaud, JM, Thompson LR, Kaul D, Espinoza JL, Richter RA, Xu ZZ, Lee C, Pham KM, Beall CM, Malfatti F, Azam F, Knight R, Burkart MD, Dupont CL, Prather KA.  2018.  Taxon-specific aerosolization of bacteria and viruses in an experimental ocean-atmosphere mesocosm. Nature Communications. 9   10.1038/s41467-018-04409-z   AbstractWebsite

Ocean-derived, airborne microbes play important roles in Earth's climate system and human health, yet little is known about factors controlling their transfer from the ocean to the atmosphere. Here, we study microbiomes of isolated sea spray aerosol (SSA) collected in a unique ocean-atmosphere facility and demonstrate taxon-specific aerosolization of bacteria and viruses. These trends are conserved within taxonomic orders and classes, and temporal variation in aerosolization is similarly shared by related taxa. We observe enhanced transfer into SSA of Actinobacteria, certain Gammaproteobacteria, and lipid-enveloped viruses; conversely, Flavobacteriia, some Alphaproteobacteria, and Caudovirales are generally underrepresented in SSA. Viruses do not transfer to SSA as efficiently as bacteria. The enrichment of mycolic acid-coated Corynebacteriales and lipid-enveloped viruses (inferred from genomic comparisons) suggests that hydrophobic properties increase transport to the sea surface and SSA. Our results identify taxa relevant to atmospheric processes and a framework to further elucidate aerosolization mechanisms influencing microbial and viral transport pathways.

Bresnahan, PJ, Martz TR.  2018.  Gas diffusion cell geometry for a microfluidic dissolved inorganic carbon analyzer. Ieee Sensors Journal. 18:2211-2217.   10.1109/jsen.2018.2794882   AbstractWebsite

Variable gas diffusion cell geometries were tested for the extraction of dissolved inorganic carbon (DIC) from a microfluidic (tens to hundreds of microliters) seawater sample. With a focus on optimization of diffusion cell geometry, we compare five unique diffusion cell designs. Using 3-D printing technology to streamline the prototyping and testing process, we were able to conceive, design, fabricate, and thoroughly evaluate each design over the course of about one month. In total, 1043 DIC measurements were carried out in 109 experiments for the five working manifolds. We find that a small diameter, cylindrical diffusion cell design offers several advantages over its planar counterparts and a larger diameter cylindrical cell, most notably the ability to increase the ratio of the exchange membrane's contact surface area to solution volume (the "aspect ratio") without sacrificing channel integrity. Multiple designs approached short-term repeatability of <1%, but only the cylindrical diffusion cell design allowed for <0.2% repeatability using less than 200 mu L of sample.

Thorpe, SA, Malarkey J, Voet G, Alford MH, Girton JB, Carter GS.  2018.  Application of a model of internal hydraulic jumps. Journal of Fluid Mechanics. 834:125-148.   10.1017/jfm.2017.646   AbstractWebsite

A model devised by Thorpe & Li (J. Fluid Mech., vol. 758, 2014, pp. 94-120) that predicts the conditions in which stationary turbulent hydraulic jumps can occur in the flow of a continuously stratified layer over a horizontal rigid bottom is applied to, and its results compared with, observations made at several locations in the ocean. The model identifies two positions in the Samoan Passage at which hydraulic jumps should occur and where changes in the structure of the flow are indeed observed. The model predicts the amplitude of changes and the observed mode 2 form of the transitions. The predicted dissipation of turbulent kinetic energy is also consistent with observations. One location provides a particularly well-defined example of a persistent hydraulic jump. It takes the form of a 390 m thick and 3.7 km long mixing layer with frequent density inversions separated from the seabed by some 200 m of relatively rapidly moving dense water, thus revealing the previously unknown structure of an internal hydraulic jump in the deep ocean. Predictions in the Red Sea Outflow in the Gulf of Aden are relatively uncertain. Available data, and the model predictions, do not provide strong support for the existence of hydraulic jumps. In the Mediterranean Outflow, however, both model and data indicate the presence of a hydraulic jump.

2017
Sun, XL, Abshire JB, Borsa AA, Fricker HA, Yi DH, DiMarzio JP, Paolo FS, Brunt KM, Harding DJ, Neumann GA.  2017.  ICESAT/GLAS Altimetry Measurements: Received Signal Dynamic Range and Saturation Correction. Ieee Transactions on Geoscience and Remote Sensing. 55:5440-5454.   10.1109/tgrs.2017.2702126   AbstractWebsite

NASA's Ice, Cloud, and land Elevation Satellite (ICESat), which operated between 2003 and 2009, made the first satellite-based global lidar measurement of earth's ice sheet elevations, sea-ice thickness, and vegetation canopy structure. The primary instrument on ICESat was the Geoscience Laser Altimeter System (GLAS), which measured the distance from the spacecraft to the earth's surface via the roundtrip travel time of individual laser pulses. GLAS utilized pulsed lasers and a direct detection receiver consisting of a silicon avalanche photodiode and a waveform digitizer. Early in the mission, the peak power of the received signal from snow and ice surfaces was found to span a wider dynamic range than anticipated, often exceeding the linear dynamic range of the GLAS 1064-nm detector assembly. The resulting saturation of the receiver distorted the recorded signal and resulted in range biases as large as similar to 50 cm for ice-and snow-covered surfaces. We developed a correction for this "saturation range bias" based on laboratory tests using a spare flight detector, and refined the correction by comparing GLAS elevation estimates with those derived from Global Positioning System surveys over the calibration site at the salar de Uyuni, Bolivia. Applying the saturation correction largely eliminated the range bias due to receiver saturation for affected ICESat measurements over Uyuni and significantly reduced the discrepancies at orbit crossovers located on flat regions of the Antarctic ice sheet.

Sun, XL, Abshire JB, Borsa AA, Fricker HA, Yi DH, DiMarzio JP, Paolo FS, Brunt KM, Harding DJ, Neumann GA.  2017.  ICESAT/GLAS Altimetry Measurements: Received Signal Dynamic Range and Saturation Correction. Ieee Transactions on Geoscience and Remote Sensing. 55:5440-5454.   10.1109/tgrs.2017.2702126   AbstractWebsite

NASA's Ice, Cloud, and land Elevation Satellite (ICESat), which operated between 2003 and 2009, made the first satellite-based global lidar measurement of earth's ice sheet elevations, sea-ice thickness, and vegetation canopy structure. The primary instrument on ICESat was the Geoscience Laser Altimeter System (GLAS), which measured the distance from the spacecraft to the earth's surface via the roundtrip travel time of individual laser pulses. GLAS utilized pulsed lasers and a direct detection receiver consisting of a silicon avalanche photodiode and a waveform digitizer. Early in the mission, the peak power of the received signal from snow and ice surfaces was found to span a wider dynamic range than anticipated, often exceeding the linear dynamic range of the GLAS 1064-nm detector assembly. The resulting saturation of the receiver distorted the recorded signal and resulted in range biases as large as similar to 50 cm for ice-and snow-covered surfaces. We developed a correction for this "saturation range bias" based on laboratory tests using a spare flight detector, and refined the correction by comparing GLAS elevation estimates with those derived from Global Positioning System surveys over the calibration site at the salar de Uyuni, Bolivia. Applying the saturation correction largely eliminated the range bias due to receiver saturation for affected ICESat measurements over Uyuni and significantly reduced the discrepancies at orbit crossovers located on flat regions of the Antarctic ice sheet.

Alford, MH, MacKinnon JA, Pinkel R, Klymak JM.  2017.  Space-time scales of shear in the North Pacific. Journal of Physical Oceanography. 47:2455-2478.   10.1175/jpo-d-17-0087.1   AbstractWebsite

The spatial, temporal, and directional characteristics of shear are examined in the upper 1400m of the North Pacific during late spring with an array of five profiling moorings deployed from 25 degrees to 37 degrees N (1330 km) and simultaneous shipboard transects past them. The array extended from a regime of moderate wind generation at the north to south of the critical latitude 28.8 degrees N, where parametric subharmonic instability (PSI) can transfer energy from semidiurnal tides to near-inertial motions. Analyses are done in an isopycnal-following frame to minimize contamination by Doppler shifting. Approximately 60% of RMS shear at vertical scales >20m (and 80% for vertical scales >80 m) is contained in near-inertial motions. An inertial back-rotation technique is used to index shipboard observations to a common time and to compute integral time scales of the shear layers. Persistence times are O(7) days at most moorings but O(25) days at the critical latitude. Simultaneous shipboard transects show that these shear layers can have lateral scales >= 100 km. Layers tend to slope downward toward the equator north of the critical latitude and are more flat to its south. Phase between shear and strain is used to infer lateral propagation direction. Upgoing waves are everywhere laterally isotropic. Downgoing waves propagate predominantly equatorward north and south of the critical latitude but are isotropic near it. Broadly, results are consistent with wind generation north of the critical latitude and PSI near it-and suggest a more persistent and laterally coherent near-inertial wave field than previously thought.

Alford, MH, MacKinnon JA, Pinkel R, Klymak JM.  2017.  Space-time scales of shear in the North Pacific. Journal of Physical Oceanography. 47:2455-2478.   10.1175/jpo-d-17-0087.1   AbstractWebsite

The spatial, temporal, and directional characteristics of shear are examined in the upper 1400m of the North Pacific during late spring with an array of five profiling moorings deployed from 25 degrees to 37 degrees N (1330 km) and simultaneous shipboard transects past them. The array extended from a regime of moderate wind generation at the north to south of the critical latitude 28.8 degrees N, where parametric subharmonic instability (PSI) can transfer energy from semidiurnal tides to near-inertial motions. Analyses are done in an isopycnal-following frame to minimize contamination by Doppler shifting. Approximately 60% of RMS shear at vertical scales >20m (and 80% for vertical scales >80 m) is contained in near-inertial motions. An inertial back-rotation technique is used to index shipboard observations to a common time and to compute integral time scales of the shear layers. Persistence times are O(7) days at most moorings but O(25) days at the critical latitude. Simultaneous shipboard transects show that these shear layers can have lateral scales >= 100 km. Layers tend to slope downward toward the equator north of the critical latitude and are more flat to its south. Phase between shear and strain is used to infer lateral propagation direction. Upgoing waves are everywhere laterally isotropic. Downgoing waves propagate predominantly equatorward north and south of the critical latitude but are isotropic near it. Broadly, results are consistent with wind generation north of the critical latitude and PSI near it-and suggest a more persistent and laterally coherent near-inertial wave field than previously thought.

Alford, MH, MacKinnon JA, Pinkel R, Klymak JM.  2017.  Space-time scales of shear in the North Pacific. Journal of Physical Oceanography. 47:2455-2478.   10.1175/jpo-d-17-0087.1   AbstractWebsite

The spatial, temporal, and directional characteristics of shear are examined in the upper 1400m of the North Pacific during late spring with an array of five profiling moorings deployed from 25 degrees to 37 degrees N (1330 km) and simultaneous shipboard transects past them. The array extended from a regime of moderate wind generation at the north to south of the critical latitude 28.8 degrees N, where parametric subharmonic instability (PSI) can transfer energy from semidiurnal tides to near-inertial motions. Analyses are done in an isopycnal-following frame to minimize contamination by Doppler shifting. Approximately 60% of RMS shear at vertical scales >20m (and 80% for vertical scales >80 m) is contained in near-inertial motions. An inertial back-rotation technique is used to index shipboard observations to a common time and to compute integral time scales of the shear layers. Persistence times are O(7) days at most moorings but O(25) days at the critical latitude. Simultaneous shipboard transects show that these shear layers can have lateral scales >= 100 km. Layers tend to slope downward toward the equator north of the critical latitude and are more flat to its south. Phase between shear and strain is used to infer lateral propagation direction. Upgoing waves are everywhere laterally isotropic. Downgoing waves propagate predominantly equatorward north and south of the critical latitude but are isotropic near it. Broadly, results are consistent with wind generation north of the critical latitude and PSI near it-and suggest a more persistent and laterally coherent near-inertial wave field than previously thought.

Yang, JC, Lin XP, Xie SP.  2017.  A Transbasin Mode of Interannual Variability of the Central American Gap Winds: Seasonality and Large-Scale Forcing. Journal of Climate. 30:8223-8235.   10.1175/jcli-d-17-0021.1   AbstractWebsite

A transbasin mode (TBM) is identified as the leading mode of interannual surface wind variability over the Intra-Americas Seas across Central America based on empirical orthogonal function analysis. The TBM is associated with variability in Central American gap winds, most closely with the Papagayo jet but with considerable signals over the Gulfs of Tehuantepec and Panama. Although El Nino-Southern Oscillation (ENSO) is the main large-scale forcing, the TBM features a distinct seasonality due to sea level pressure (SLP) adjustments across the Pacific and Atlantic. During July-September, ENSO causes meridional SLP gradient anomalies across Central America, intensifying anomalous geostrophic winds funneling through Papagayo to form the TBM. During wintertime, ENSO peaks but imparts little anomalous SLP gradient across Central America with a weak projection on the TBM because of the competing effects of the Pacific-North American teleconnection and tropospheric Kelvin waves. Besides ENSO, tropical Atlantic sea surface temperature anomalies make a weak contribution to the TBM in boreal summer by strengthening the cross-basin gradient. ENSO and the Atlantic forcing constitute a cross-basin seesaw pattern in SLP, manifested as an anomalous Walker circulation across the tropical Americas. The TBM appears to be part of the low-level branch of the anomalous Walker circulation, which modulates Central American wind jets by orographic effect. This study highlights the seasonality of gap wind variability, and calls for further research into its influence on regional climate.

Zheng, ZW, Zheng QA, Gopalakrishnan G, Kuo YC, Yeh TK.  2017.  Response of upper ocean cooling off northeastern Taiwan to typhoon passages. Ocean Modelling. 115:105-118.   10.1016/j.ocemod.2017.05.008   AbstractWebsite

A comprehensive investigation of the typhoon induced upper ocean processes and responses off northeastern Taiwan was conducted. Using the Regional Ocean Modeling System, the upper ocean responses of all typhoons striking Taiwan between 2005 and 2013 were simulated. In addition to Kuroshio intrusion, the present study demonstrates another important mechanism of typhoon induced near-inertial currents over the continental shelf of East China Sea, which can also trigger a distinct cooling (through entrainment mixing) within this region. Results indicate that the processes of typhoon inducing distinct cooling off northeastern Taiwan are conditional phenomena (only similar to 12% of typhoons passing Taiwan triggered extreme cooling there). Subsequently, by executing a series of sensitivity experiments and systematic analyses on the behaviors and background conditions of all those typhoon cases, key criteria determining the occurrences of cooling through both mechanisms were elucidated. Occurrences of cooling through the Kuroshio intrusion mechanism are determined mainly by the strength of the local wind over northeastern Taiwan. A distinct cooling triggered by enhanced near-inertial currents is shown to be associated with the process of wind-current resonance. Both processes of Kuroshio intrusion and enhanced near-inertial currents are dominated by wind forcing rather than upper oceanic conditions. Based on the recent findings on the possible dynamic linkage between sea surface temperature near northeast Taiwan and local weather systems, the results elucidated in this study lay the foundation for further improvement in the regional weather prediction surrounding northeast Taiwan. (C) 2017 Elsevier Ltd. All rights reserved.

Chen, R, Gille ST, McClean JL.  2017.  Isopycnal eddy mixing across the Kuroshio Extension: Stable versus unstable states in an eddying model. Journal of Geophysical Research-Oceans. 122:4329-4345.   10.1002/2016jc012164   AbstractWebsite

The Kuroshio Extension (KE) jet transitions between stable and unstable states on interannual time scales. Cross-jet eddy mixing in the two states is contrasted in the KE region ( 28 degrees-40 degrees N,125 degrees-165 degrees E), using a global eddying 0.1 degrees configuration of the Parallel Ocean Program with online numerical particles. The 4 year period chosen (June 1994 to May 1998) covers a full cycle of the stable state, unstable state and the transition period. Large values of cross-jet eddy diffusivities within the KE jet are concentrated in the upper 1000 m. In the upper ocean, elevated cross-jet mixing within the KE jet is mainly concentrated in the downstream part of the KE jet, where the jet is weak but eddy activity is strong. The simulated time-mean KE jet is more intense and extends further east in the stable state than in the unstable state. Consequently, strong cross-jet mixing within the KE jet is located west of 150 degrees E during June 1996 to May 1997 (a typical unstable state), but east of 150 degrees E during June 1995 to May 1996 (a typical stable state). However, average mixing within the KE jet is indistinguishable in the typical stable and unstable states. In the deep ocean, mixing is strongly influenced by topography, and thus their horizontal structures have less inter-annual variability than in the upper ocean. One caveat is that results here cover one representative cycle of the two states. To obtain the climate mean mixing structures for the stable or unstable state, one would need numerical output covering a period much longer than 4 years.

Sumargo, E, Cayan DR.  2017.  Variability of cloudiness over mountain terrain in the western United States. Journal of Hydrometeorology. 18:1227-1245.   10.1175/jhm-d-16-0194.1   AbstractWebsite

This study investigates the spatial and temporal variability of cloudiness across mountain zones in the western United States. Daily average cloud albedo is derived from a 19-yr series (1996-2014) of half-hourly Geostationary Operational Environmental Satellite (GOES) images. During springtime when incident radiation is active in driving snowmelt-runoff processes, the magnitude of daily cloud variations can exceed 50% of long-term averages. Even when aggregated over 3-month periods, cloud albedo varies by +/- 10% of long-term averages in many locations. Rotated empirical orthogonal functions (REOFs) of daily cloud albedo anomalies over high-elevation regions of the western conterminous United States identify distinct regional patterns, wherein the first five REOFs account for; similar to 67% of the total variance. REOF1 is centered over Northern California and Oregon and is pronounced between November and March. REOF2 is centered over the interior northwest and is accentuated between March and July. Each of the REOF/rotated principal components (RPC) modes associates with anomalous large-scale atmospheric circulation patterns and one or more large-scale teleconnection indices (Arctic Oscillation, Nino-3.4, and Pacific-North American), which helps to explain why anomalous cloudiness patterns take on regional spatial scales and contain substantial variability over seasonal time scales.

Farrokhrooz, M, Wage KE, Dzieciuch MA, Worcester PF.  2017.  Vertical line array measurements of ambient noise in the North Pacific. Journal of the Acoustical Society of America. 141:1571-1581.   10.1121/1.4976706   AbstractWebsite

Shipping noise and wind are the dominant sources of ocean noise in the frequency band between 20 and 500 Hz. This paper analyzes noise in that band using data from the SPICEX experiment, which took place in the North Pacific in 2004-2005, and compares the results with other North Pacific experiments. SPICEX included vertical arrays with sensors above and below the surface conjugate depth, facilitating an analysis of the depth dependence of ambient noise. The paper includes several key results. First, the 2004-05 noise levels at 50 Hz measured in SPICEX had not increased relative to levels measured by Morris [(1978). J. Acoust. Soc. Am. 64, 581-590] at a nearby North Pacific site three decades earlier, but rather were comparable to those levels. Second, at 50Hz the noise below the conjugate depth decreases at a rate of -9.9 dB/km, which is similar to the rate measured by Morris and much less than the rate measured by Gaul, Knobles, Shooter, and Wittenborn [(2007). IEEE J. Ocean. Eng. 32, 497-512] for the CHURCH OPAL experiment. Finally, the paper describes the seasonal trends in noise over the year-long time series of the measurements. (C) 2017 Acoustical Society of America.

Farrokhrooz, M, Wage KE, Dzieciuch MA, Worcester PF.  2017.  Vertical line array measurements of ambient noise in the North Pacific. Journal of the Acoustical Society of America. 141:1571-1581.   10.1121/1.4976706   AbstractWebsite

Shipping noise and wind are the dominant sources of ocean noise in the frequency band between 20 and 500 Hz. This paper analyzes noise in that band using data from the SPICEX experiment, which took place in the North Pacific in 2004-2005, and compares the results with other North Pacific experiments. SPICEX included vertical arrays with sensors above and below the surface conjugate depth, facilitating an analysis of the depth dependence of ambient noise. The paper includes several key results. First, the 2004-05 noise levels at 50 Hz measured in SPICEX had not increased relative to levels measured by Morris [(1978). J. Acoust. Soc. Am. 64, 581-590] at a nearby North Pacific site three decades earlier, but rather were comparable to those levels. Second, at 50Hz the noise below the conjugate depth decreases at a rate of -9.9 dB/km, which is similar to the rate measured by Morris and much less than the rate measured by Gaul, Knobles, Shooter, and Wittenborn [(2007). IEEE J. Ocean. Eng. 32, 497-512] for the CHURCH OPAL experiment. Finally, the paper describes the seasonal trends in noise over the year-long time series of the measurements. (C) 2017 Acoustical Society of America.

Stuart, RK, Bundy R, Buck K, Ghassemain M, Barbeau K, Palenik B.  2017.  Copper toxicity response influences mesotrophic Synechococcus community structure. Environmental Microbiology. 19:756-769.   10.1111/1462-2920.13630   AbstractWebsite

Picocyanobacteria from the genus Synechococcus are ubiquitous in ocean waters. Their phylogenetic and genomic diversity suggests ecological niche differentiation, but the selective forces influencing this are not well defined. Marine picocyanobacteria are sensitive to Cu toxicity, so adaptations to this stress could represent a selective force within, and between, species', also known as clades. Here, we compared Cu stress responses in cultures and natural populations of marine Synechococcus from two co-occurring major mesotrophic clades (I and IV). Using custom microarrays and proteomics to characterize expression responses to Cu in the lab and field, we found evidence for a general stress regulon in marine Synechococcus. However, the two clades also exhibited distinct responses to copper. The Clade I representative induced expression of genomic island genes in cultures and Southern California Bight populations, while the Clade IV representative downregulated Fe-limitation proteins. Copper incubation experiments suggest that Clade IV populations may harbour stress-tolerant subgroups, and thus fitness tradeoffs may govern Cu-tolerant strain distributions. This work demonstrates that Synechococcus has distinct adaptive strategies to deal with Cu toxicity at both the clade and subclade level, implying that metal toxicity and stress response adaptations represent an important selective force for influencing diversity within marine Synechococcus populations.