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2017
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.

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.

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.

Zhang, SJ, Sandwell DT, Jin TY, Li DW.  2017.  Inversion of marine gravity anomalies over southeastern China seas from multi-satellite altimeter vertical deflections. Journal of Applied Geophysics. 137:128-137.   10.1016/j.jappgeo.2016.12.014   AbstractWebsite

The accuracy and resolution of marine gravity field derived from satellite altimetry mainly depends on the range precision and dense spatial distribution. This paper aims at modeling a regional marine gravity field with improved accuracy and higher resolution (1' x V') over Southeastern China Seas using additional data from CryoSat-2 as well as new data from AltiKa. Three approaches are used to enhance the precision level of satellite-derived gravity anomalies. Firstly we evaluate a suite of published retracking algorithms and find the two-step retracker is optimal for open ocean waveforms. Secondly, we evaluate the filtering and resampling procedure used to reduce the full 20 or 40 Hz data to a lower rate having lower noise. We adopt a uniform low-pass filter for all altimeter missions and resample at 5 Hz and then perform a second editing based on sea surface slope estimates from previous models. Thirdly, we selected WHU12 model to update the corrections provided in geophysical data record. We finally calculated the 1' x 1' marine gravity field model by using EGM2008 model as reference field during the remove/restore procedure. The root mean squares of the discrepancies between the new result and DTU10, DTU13, V23.1, EGM2008 are within the range of 1.8-3.9 mGal, while the verification with respect to shipboard gravity data shows that the accuracy of the new result reached a comparable level with DTU13 and was slightly superior to V23.1, DTU10 and EGM2008 models. Moreover, the new result has a 2 mGal better accuracy over open seas than coastal areas with shallow water depth. (C) 2016 Elsevier B.V. All rights reserved.

2016
Barton, AD, Irwin AJ, Finkel ZV, Stock CA.  2016.  Anthropogenic climate change drives shift and shuffle in North Atlantic phytoplankton communities. Proceedings of the National Academy of Sciences of the United States of America. 113:2964-2969.   10.1073/pnas.1519080113   AbstractWebsite

Anthropogenic climate change has shifted the biogeography and phenology of many terrestrial and marine species. Marine phytoplankton communities appear sensitive to climate change, yet understanding of how individual species may respond to anthropogenic climate change remains limited. Here, using historical environmental and phytoplankton observations, we characterize the realized ecological niches for 87 North Atlantic diatom and dinoflagellate taxa and project changes in species biogeography between mean historical (1951-2000) and future (2051-2100) ocean conditions. We find that the central positions of the core range of 74% of taxa shift poleward at a median rate of 12.9 kmper decade (km.dec(-1)), and 90% of taxa shift eastward at a median rate of 42.7 km.dec(-1). The poleward shift is faster than previously reported for marine taxa, and the predominance of longitudinal shifts is driven by dynamic changes in multiple environmental drivers, rather than a strictly poleward, temperature-driven redistribution of ocean habitats. A century of climate change significantly shuffles community composition by a basin-wide median value of 16%, compared with seasonal variations of 46%. The North Atlantic phytoplankton community appears poised for marked shift and shuffle, which may have broad effects on food webs and biogeochemical cycles.

Jayarathne, T, Sultana CM, Lee C, Malfatti F, Cox JL, Pendergraft MA, Moore KA, Azam F, Tivanski AV, Cappa CD, Bertram TH, Grassian VH, Prather KA, Stone EA.  2016.  Enrichment of saccharides and divalent cations in sea spray aerosol during two phytoplankton blooms. Environmental Science & Technology. 50:11511-11520.   10.1021/acs.est.6b02988   AbstractWebsite

Sea spray aerosol (SSA) is a globally important source of particulate matter. A mesocosm study was performed to determine the relative enrichment of saccharides and inorganic ions in nascent fine (PM2.5) and coarse (PM102.5) SSA and the sea surface microlayer (SSML) relative to bulk seawater. Saccharides comprise a significant fraction of organic matter in fine and coarse SSA (11 and 27%, respectively). Relative to sodium, individual saccharides were enriched 141314-fold in fine SSA, 3138-fold in coarse SSA, but only up to 1.016.2-fold in SSML. Enrichments in SSML were attributed to rising bubbles that scavenge surface-active species from seawater, while further enrichment in fine SSA likely derives from bubble films. Mean enrichment factors for major ions demonstrated significant enrichment in fine SSA for potassium (1.3), magnesium (1.4), and calcium (1.7), likely because of their interactions with organic matter. Consequently, fine SSA develops a salt profile significantly different from that of seawater. Maximal enrichments of saccharides and ions coincided with the second of two phytoplankton blooms, signifying the influence of ocean biology on selective mass transfer across the oceanair interface.

Jayarathne, T, Sultana CM, Lee C, Malfatti F, Cox JL, Pendergraft MA, Moore KA, Azam F, Tivanski AV, Cappa CD, Bertram TH, Grassian VH, Prather KA, Stone EA.  2016.  Enrichment of saccharides and divalent cations in sea spray aerosol during two phytoplankton blooms. Environmental Science & Technology. 50:11511-11520.   10.1021/acs.est.6b02988   AbstractWebsite

Sea spray aerosol (SSA) is a globally important source of particulate matter. A mesocosm study was performed to determine the relative enrichment of saccharides and inorganic ions in nascent fine (PM2.5) and coarse (PM102.5) SSA and the sea surface microlayer (SSML) relative to bulk seawater. Saccharides comprise a significant fraction of organic matter in fine and coarse SSA (11 and 27%, respectively). Relative to sodium, individual saccharides were enriched 141314-fold in fine SSA, 3138-fold in coarse SSA, but only up to 1.016.2-fold in SSML. Enrichments in SSML were attributed to rising bubbles that scavenge surface-active species from seawater, while further enrichment in fine SSA likely derives from bubble films. Mean enrichment factors for major ions demonstrated significant enrichment in fine SSA for potassium (1.3), magnesium (1.4), and calcium (1.7), likely because of their interactions with organic matter. Consequently, fine SSA develops a salt profile significantly different from that of seawater. Maximal enrichments of saccharides and ions coincided with the second of two phytoplankton blooms, signifying the influence of ocean biology on selective mass transfer across the oceanair interface.

Brandon, J, Goldstein M, Ohman MD.  2016.  Long-term aging and degradation of microplastic particles: Comparing in situ oceanic and experimental weathering patterns. Marine Pollution Bulletin. 110:299-308.   10.1016/j.marpolbul.2016.06.048   AbstractWebsite

Polypropylene, low-density polyethylene, and high-density polyethylene pre-production plastic pellets were weathered for three years in three experimental treatments: dry/sunlight, seawater/sunlight, and seawater/darkness. Changes in chemical bond structures (hydroxyl, carbonyl groups and carbon-oxygen) with weathering were measured via Fourier Transform Infrared (FTIR) spectroscopy. These indices from experimentally weathered particles were compared to microplastic particles collected from oceanic surface waters in the California Current, the North Pacific Subtropical Gyre, and the transition region between the two, in order to estimate the exposure time of the oceanic plastics. Although chemical bonds exhibited some nonlinear changes with environmental exposure, they can potentially approximate the weathering time of some plastics, especially high-density polyethylene. The majority of the North Pacific Subtropical Gyre polyethylene particles we measured have inferred exposure times > 18 months, with some >30 months. Inferred particle weathering times are consistent with ocean circulation models suggesting a long residence time in the open ocean. (C) 2016 Elsevier Ltd. All rights reserved.

Stokes, MD, Deane G, Collins DB, Cappa C, Bertram T, Dommer A, Schill S, Forestieri S, Survilo M.  2016.  A miniature Marine Aerosol Reference Tank (miniMART) as a compact breaking wave analogue. Atmospheric Measurement Techniques. 9:4257-4267.   10.5194/amt-9-4257-2016   AbstractWebsite

In order to understand the processes governing the production of marine aerosols, repeatable, controlled methods for their generation are required. A new system, the miniature Marine Aerosol Reference Tank (miniMART), has been designed after the success of the original MART system, to approximate a small oceanic spilling breaker by producing an evolving bubble plume and surface foam patch. The smaller tank utilizes an intermittently plunging jet of water produced by a rotating water wheel, into an approximately 6 L reservoir to simulate bubble plume and foam formation and generate aerosols. This system produces bubble plumes characteristic of small whitecaps without the large external pump inherent in the original MART design. Without the pump it is possible to easily culture delicate planktonic and microbial communities in the bulk water during experiments while continuously producing aerosols for study. However, due to the reduced volume and smaller plunging jet, the absolute numbers of particles generated are approximately an order of magnitude less than in the original MART design.

Stokes, MD, Deane G, Collins DB, Cappa C, Bertram T, Dommer A, Schill S, Forestieri S, Survilo M.  2016.  A miniature Marine Aerosol Reference Tank (miniMART) as a compact breaking wave analogue. Atmospheric Measurement Techniques. 9:4257-4267.   10.5194/amt-9-4257-2016   AbstractWebsite

In order to understand the processes governing the production of marine aerosols, repeatable, controlled methods for their generation are required. A new system, the miniature Marine Aerosol Reference Tank (miniMART), has been designed after the success of the original MART system, to approximate a small oceanic spilling breaker by producing an evolving bubble plume and surface foam patch. The smaller tank utilizes an intermittently plunging jet of water produced by a rotating water wheel, into an approximately 6 L reservoir to simulate bubble plume and foam formation and generate aerosols. This system produces bubble plumes characteristic of small whitecaps without the large external pump inherent in the original MART design. Without the pump it is possible to easily culture delicate planktonic and microbial communities in the bulk water during experiments while continuously producing aerosols for study. However, due to the reduced volume and smaller plunging jet, the absolute numbers of particles generated are approximately an order of magnitude less than in the original MART design.

Xu, L, Russell LM, Burrows SM.  2016.  Potential sea salt aerosol sources from frost flowers in the pan-Arctic region. Journal of Geophysical Research-Atmospheres. 121:10840-10856.   10.1002/2015jd024713   AbstractWebsite

In order to better represent observed wintertime aerosol mass and number concentrations in the pan-Arctic (60 degrees N-90 degrees N) region, we implemented an observationally based parameterization for estimating sea salt production from frost flowers in the Community Earth System Model (CESM, version 1.2.1). In this work, we evaluate the potential influence of this sea salt source on the pan-Arctic climate. Results show that frost flower salt emissions increase the modeled surface sea salt aerosol mass concentration by roughly 200% at Barrow and 100% at Alert and accumulation-mode number concentration by about a factor of 2 at Barrow and more than a factor of 10 at Alert in the winter months when new sea ice and frost flowers are present. The magnitude of sea salt aerosol mass and number concentrations at the surface in Barrow during winter simulated by the model configuration that includes this parameterization agrees better with observations by 48% and 12%, respectively, than the standard CESM simulation without a frost flower salt particle source. At Alert, the simulation with this parameterization overestimates observed sea salt aerosol mass concentration by 150% during winter in contrast to the underestimation of 63% in the simulation without this frost flower source, while it produces particle number concentration about 14% closer to observation than the standard CESM simulation. However, because the CESM version used here underestimates transported sulfate in winter, the reference accumulation-mode number concentrations at Alert are also underestimated. Adding these frost flower salt particle emissions increases sea salt aerosol optical depth by 10% in the pan-Arctic region and results in a small cooling at the surface. The increase in salt aerosol mass concentrations of a factor of 8 provides nearly two times the cloud condensation nuclei concentration at supersaturation of 0.1%, as well as 10% increases in cloud droplet number and 40% increases in liquid water content near coastal regions adjacent to continents. These cloud changes reduce longwave cloud forcing at the top of the atmosphere by 3% and cause a small surface warming, increasing the downward longwave flux at the surface by 1.8Wm(-2) in the pan-Arctic under the present-day climate. This regional average longwave warming due to the presence of clouds attributed to frost flower sea salts is roughly half of previous observed surface longwave fluxes and cloud-forcing estimates reported in Alaska, implying that the longwave enhancement due to frost flower salts may be comparable to those estimated for anthropogenic aerosol emissions. Since the potential frost flower area is parameterized as the maximum possible region on which frost flowers grow for the modeled atmospheric temperature and sea ice conditions and the model underestimates the number of accumulation-mode particles from midlatitude anthropogenic sources transported in winter, the calculated aerosol indirect effect of frost flower sea salts in this work can be regarded an upper bound.

Lundquist, JD, Roche JW, Forrester H, Moore C, Keenan E, Perry G, Cristea N, Henn B, Lapo K, McGurk B, Cayan DR, Dettinger MD.  2016.  Yosemite Hydroclimate Network: Distributed stream and atmospheric data for the Tuolumne River watershed and surroundings. Water Resources Research. 52:7478-7489.   10.1002/2016wr019261   AbstractWebsite

Regions of complex topography and remote wilderness terrain have spatially varying patterns of temperature and streamflow, but due to inherent difficulties of access, are often very poorly sampled. Here we present a data set of distributed stream stage, streamflow, stream temperature, barometric pressure, and air temperature from the Tuolumne River Watershed in Yosemite National Park, Sierra Nevada, California, USA, for water years 2002-2015, as well as a quality-controlled hourly meteorological forcing time series for use in hydrologic modeling. We also provide snow data and daily inflow to the Hetch Hetchy Reservoir for 1970-2015. This paper describes data collected using low-visibility and low-impact installations for wilderness locations and can be used alone or as a critical supplement to ancillary data sets collected by cooperating agencies, referenced herein. This data set provides a unique opportunity to understand spatial patterns and scaling of hydroclimatic processes in complex terrain and can be used to evaluate downscaling techniques or distributed modeling. The paper also provides an example methodology and lessons learned in conducting hydroclimatic monitoring in remote wilderness.

Chenillat, F, Franks PJS, Combes V.  2016.  Biogeochemical properties of eddies in the California Current System. Geophysical Research Letters. 43:5812-5820.   10.1002/2016gl068945   AbstractWebsite

The California Current System (CCS) has intense mesoscale activity that modulates and exports biological production from the coastal upwelling system. To characterize and quantify the ability of mesoscale eddies to affect the local and regional planktonic ecosystem of the CCS, we analyzed a 10 year-long physical-biological model simulation, using eddy detection and tracking to isolate the dynamics of cyclonic and anticyclonic eddies. As they propagate westward across the shelf, cyclonic eddies efficiently transport coastal planktonic organisms and maintain locally elevated production for up to 1year (800km offshore). Anticyclonic eddies, on the other hand, have a limited impact on local production over their similar to 6month lifetime as they propagate 400km offshore. At any given time similar to 8% of the model domain was covered by eddy cores. Though the eddies cover a small area, they explain similar to 50 and 20% of the transport of nitrate and plankton, respectively.

Liu, JW, Xie SP, Yang S, Zhang SP.  2016.  Low-cloud transitions across the Kuroshio Front in the East China Sea. Journal of Climate. 29:4429-4443.   10.1175/jcli-d-15-0589.1   AbstractWebsite

The East China Sea Kuroshio (ECSK) flows in the East Asian monsoon region where the background atmospheric circulation varies significantly with season. A sea surface temperature (SST) front associated with the ECSK becomes narrower and sharper from winter to spring. The present study investigates how low clouds respond to the ECSK front in different seasons by synthesizing spaceborne lidar and surface visual observations. The results reveal prominent cross-frontal transitions in low clouds, which exhibit distinct behavior between winter and spring. In winter, cloud responses are generally confined below 4 km by the strong background descending motion and feature a gradual cloud-top elevation from the cold to the warm flank of the front. The ice clouds on the cold flank of the ECSK front transform into liquid water clouds and rain on the warm flank. The springtime clouds, by contrast, are characterized by a sharp cross-frontal transition with deep clouds reaching up to 7 km over the ECSK. In both winter and spring, the low-cloud morphology exhibits a large transformation from the cold to the warm flank of the ECSK front, including increases in cloud-top height, a decline in smoothness of cloud top, and the transition from stratiform to convective clouds. All this along with the atmospheric soundings indicates that the decoupling of the marine atmospheric boundary layer (MABL) is more prevalent on the warm flank of the front. Thus, long-term observations reveal prominent cross-frontal low-cloud transitions in morphology associated with MABL decoupling that resemble a large-scale cloud-regime transition over the eastern subtropical Pacific.

Melville, WK, Lenain L, Cayan DR, Kahru M, Kleissl JP, Linden PF, Statom NM.  2016.  The Modular Aerial Sensing System. Journal of Atmospheric and Oceanic Technology. 33:1169-1184.   10.1175/jtech-d-15-0067.1   AbstractWebsite

Satellite remote sensing has enabled remarkable progress in the ocean, earth, atmospheric, and environmental sciences through its ability to provide global coverage with ever-increasing spatial resolution. While exceptions exist for geostationary ocean color satellites, the temporal coverage of low-Earth-orbiting satellites is not optimal for oceanographic processes that evolve over time scales of hours to days. In hydrology, time scales can range from hours for flash floods, to days for snowfall, to months for the snowmelt into river systems. On even smaller scales, remote sensing of the built environment requires a building-resolving resolution of a few meters or better. For this broad range of phenomena, satellite data need to be supplemented with higher-resolution airborne data that are not tied to the strict schedule of a satellite orbit. To address some of these needs, a novel, portable, high-resolution airborne topographic lidar with video, infrared, and hyperspectral imaging systems was integrated. The system is coupled to a highly accurate GPS-aided inertial measurement unit (GPS IMU), permitting airborne measurements of the sea surface displacement, temperature, and kinematics with swath widths of up to 800 m under the aircraft, and horizontal spatial resolution as low as 0.2 m. These data are used to measure ocean waves, currents, Stokes drift, sea surface height (SSH), ocean transport and dispersion, and biological activity. Hydrological and terrestrial applications include measurements of snow cover and the built environment. This paper describes the system, its performance, and present results from recent oceanographic, hydrological, and terrestrial measurements.

Melville, WK, Lenain L, Cayan DR, Kahru M, Kleissl JP, Linden PF, Statom NM.  2016.  The Modular Aerial Sensing System. Journal of Atmospheric and Oceanic Technology. 33:1169-1184.   10.1175/jtech-d-15-0067.1   AbstractWebsite

Satellite remote sensing has enabled remarkable progress in the ocean, earth, atmospheric, and environmental sciences through its ability to provide global coverage with ever-increasing spatial resolution. While exceptions exist for geostationary ocean color satellites, the temporal coverage of low-Earth-orbiting satellites is not optimal for oceanographic processes that evolve over time scales of hours to days. In hydrology, time scales can range from hours for flash floods, to days for snowfall, to months for the snowmelt into river systems. On even smaller scales, remote sensing of the built environment requires a building-resolving resolution of a few meters or better. For this broad range of phenomena, satellite data need to be supplemented with higher-resolution airborne data that are not tied to the strict schedule of a satellite orbit. To address some of these needs, a novel, portable, high-resolution airborne topographic lidar with video, infrared, and hyperspectral imaging systems was integrated. The system is coupled to a highly accurate GPS-aided inertial measurement unit (GPS IMU), permitting airborne measurements of the sea surface displacement, temperature, and kinematics with swath widths of up to 800 m under the aircraft, and horizontal spatial resolution as low as 0.2 m. These data are used to measure ocean waves, currents, Stokes drift, sea surface height (SSH), ocean transport and dispersion, and biological activity. Hydrological and terrestrial applications include measurements of snow cover and the built environment. This paper describes the system, its performance, and present results from recent oceanographic, hydrological, and terrestrial measurements.

Melville, WK, Lenain L, Cayan DR, Kahru M, Kleissl JP, Linden PF, Statom NM.  2016.  The Modular Aerial Sensing System. Journal of Atmospheric and Oceanic Technology. 33:1169-1184.   10.1175/jtech-d-15-0067.1   AbstractWebsite

Satellite remote sensing has enabled remarkable progress in the ocean, earth, atmospheric, and environmental sciences through its ability to provide global coverage with ever-increasing spatial resolution. While exceptions exist for geostationary ocean color satellites, the temporal coverage of low-Earth-orbiting satellites is not optimal for oceanographic processes that evolve over time scales of hours to days. In hydrology, time scales can range from hours for flash floods, to days for snowfall, to months for the snowmelt into river systems. On even smaller scales, remote sensing of the built environment requires a building-resolving resolution of a few meters or better. For this broad range of phenomena, satellite data need to be supplemented with higher-resolution airborne data that are not tied to the strict schedule of a satellite orbit. To address some of these needs, a novel, portable, high-resolution airborne topographic lidar with video, infrared, and hyperspectral imaging systems was integrated. The system is coupled to a highly accurate GPS-aided inertial measurement unit (GPS IMU), permitting airborne measurements of the sea surface displacement, temperature, and kinematics with swath widths of up to 800 m under the aircraft, and horizontal spatial resolution as low as 0.2 m. These data are used to measure ocean waves, currents, Stokes drift, sea surface height (SSH), ocean transport and dispersion, and biological activity. Hydrological and terrestrial applications include measurements of snow cover and the built environment. This paper describes the system, its performance, and present results from recent oceanographic, hydrological, and terrestrial measurements.

Lin, JF, Lee Z, Ondrusek M, Kahru M.  2016.  Attenuation coefficient of usable solar radiation of the global oceans. Journal of Geophysical Research-Oceans. 121:3228-3236.   10.1002/2015jc011528   AbstractWebsite

Usable solar radiation (USR) represents spectrally integrated solar energy in the spectral range of 400-560 nm, a domain where photons penetrate the most in oceanic waters and thus contribute to photosynthesis and heating at deeper depths. Through purely numerical simulations, it was found that the diffuse attenuation coefficient of downwelling USR (K-d(USR), m(-1)) is nearly a constant vertically in the upper water column for clear waters and most turbid waters. Subsequently an empirical model was developed to estimate Kd(USR) based on the diffuse attenuation coefficient at 490 nm (Kd(490), m(-1)). We here evaluate this relationship using data collected from a wide range of oceanic and coastal environments and found that the relationship between Kd(490) and Kd(USR) developed via the numerical simulation is quite robust. We further refined this relationship to extend the applicability to "clearest" natural waters. This refined relationship was then used to produce sample distribution of Kd(USR) of global oceans. As expected, extremely low Kd(USR) (similar to 0.02 m(-1)) was observed in ocean gyres, while significantly higher Kd(USR) (similar to 5.2 m(-1)) was found in very turbid coastal regions. A useful application of Kd(USR) is to easily and accurately propagate surface USR to deeper depths, potentially to significantly improve the estimation of basin scale primary production and heat fluxes in the upper water column.

Diez, A, Bromirski PD, Gerstoft P, Stephen RA, Anthony RE, Aster RC, Cai C, Nyblade A, Wiens DA.  2016.  Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica. Geophysical Journal International. 205:785-795.   10.1093/gji/ggw036   AbstractWebsite

An L-configured, three-component short period seismic array was deployed on the Ross Ice Shelf, Antarctica during November 2014. Polarization analysis of ambient noise data from these stations shows linearly polarized waves for frequency bands between 0.2 and 2 Hz. A spectral peak at about 1.6 Hz is interpreted as the resonance frequency of the water column and is used to estimate the water layer thickness below the ice shelf. The frequency band from 4 to 18 Hz is dominated by Rayleigh and Love waves propagating from the north that, based on daily temporal variations, we conclude were generated by field camp activity. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile within the firn and ice to similar to 150 m depth. The derived density profile allows estimation of the pore close-off depth and the firn-air content thickness. Separate inversions of Rayleigh and Love wave dispersion curves give different shear wave velocity profiles within the firn. We attribute this difference to an effective anisotropy due to fine layering. The layered structure of firn, ice, water and the seafloor results in a characteristic dispersion curve below 7 Hz. Forward modelling the observed Rayleigh wave dispersion curves using representative firn, ice, water and sediment structures indicates that Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. The forward modelling shows that analysis of seismic data from an ice shelf provides the possibility of resolving ice shelf thickness, water column thickness and the physical properties of the ice shelf and underlying seafloor using passive-source seismic data.

Diez, A, Bromirski PD, Gerstoft P, Stephen RA, Anthony RE, Aster RC, Cai C, Nyblade A, Wiens DA.  2016.  Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica. Geophysical Journal International. 205:785-795.   10.1093/gji/ggw036   AbstractWebsite

An L-configured, three-component short period seismic array was deployed on the Ross Ice Shelf, Antarctica during November 2014. Polarization analysis of ambient noise data from these stations shows linearly polarized waves for frequency bands between 0.2 and 2 Hz. A spectral peak at about 1.6 Hz is interpreted as the resonance frequency of the water column and is used to estimate the water layer thickness below the ice shelf. The frequency band from 4 to 18 Hz is dominated by Rayleigh and Love waves propagating from the north that, based on daily temporal variations, we conclude were generated by field camp activity. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile within the firn and ice to similar to 150 m depth. The derived density profile allows estimation of the pore close-off depth and the firn-air content thickness. Separate inversions of Rayleigh and Love wave dispersion curves give different shear wave velocity profiles within the firn. We attribute this difference to an effective anisotropy due to fine layering. The layered structure of firn, ice, water and the seafloor results in a characteristic dispersion curve below 7 Hz. Forward modelling the observed Rayleigh wave dispersion curves using representative firn, ice, water and sediment structures indicates that Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. The forward modelling shows that analysis of seismic data from an ice shelf provides the possibility of resolving ice shelf thickness, water column thickness and the physical properties of the ice shelf and underlying seafloor using passive-source seismic data.

2015
Cape, MR, Vernet M, Skvarca P, Marinsek S, Scambos T, Domack E.  2015.  Foehn winds link climate-driven warming to ice shelf evolution in Antarctica. Journal of Geophysical Research-Atmospheres. 120(21):11037-11057.   10.1002/2015JD023465   Abstract

Rapid warming of the Antarctic Peninsula over the past several decades has led to extensive surface melting on its eastern side, and the disintegration of the Prince Gustav, Larsen A, and Larsen B ice shelves. The warming trend has been attributed to strengthening of circumpolar westerlies resulting from a positive trend in the Southern Annular Mode (SAM), which is thought to promote more frequent warm, dry, downsloping foehn winds along the lee, or eastern side, of the peninsula. We examined variability in foehn frequency and its relationship to temperature and patterns of synoptic-scale circulation using a multidecadal meteorological record from the Argentine station Matienzo, located between the Larsen A and B embayments. This record was further augmented with a network of six weather stations installed under the U.S. NSF LARsen Ice Shelf System, Antarctica, project. Significant warming was observed in all seasons at Matienzo, with the largest seasonal increase occurring in austral winter (+3.71 degrees C between 1962-1972 and 1999-2010). Frequency and duration of foehn events were found to strongly influence regional temperature variability over hourly to seasonal time scales. Surface temperature and foehn winds were also sensitive to climate variability, with both variables exhibiting strong, positive correlations with the SAM index. Concomitant positive trends in foehn frequency, temperature, and SAM are present during austral summer, with sustained foehn events consistently associated with surface melting across the ice sheet and ice shelves. These observations support the notion that increased foehn frequency played a critical role in precipitating the collapse of the Larsen B ice shelf.

Reuveni, Y, Bock Y, Tong XP, Moore AW.  2015.  Calibrating interferometric synthetic aperture radar (InSAR) images with regional GPS network atmosphere models. Geophysical Journal International. 202:2106-2119.   10.1093/gji/ggv253   AbstractWebsite

Interferometric synthetic aperture radar (InSAR) technology provides a valuable tool for obtaining Earth surface deformation and topography at high spatial resolution for crustal deformation studies. Similar to global positioning system (GPS), InSAR measurements are affected by the Earth's ionospheric and tropospheric layers as the electromagnetic signals significantly refract while propagating through the different layers. While GPS signals propagating through the neutral atmosphere are affected primarily by the distribution, pressure and temperature of atmospheric gases, including water vapour, the propagation through the ionosphere is mainly affected by the number of free electrons along the signal path. Here, we present the use of dense regional GPS networks for extracting tropospheric zenith delays and ionospheric total electron content (TEC) maps in order to reduce the noise levels in InSAR images. The results show significant reduction in the root mean square (RMS) values when simultaneously combining the two corrections, both at short time periods where no surface deformation is expected, and at longer periods, where imaging of localized subsidence and fault creep is enhanced.