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Weddell Sea Export Pathways from Surface Drifters

JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第4期45卷 1068-1085页

作者： Youngs, Madeleine K. Thompson, Andrew F. Flexas, M. Mar Heywood, Karen J. CALTECH Environm Sci & Engn Pasadena CA 91125 USA CALTECH Jet Prop Lab Pasadena CA 91125 USA Univ E Anglia Sch Environm Sci Norwich NR4 7TJ Norfolk England

The complex export pathways that connect the surface waters of the Weddell Sea with the Antarctic Circumpolar Current influence water mass modification, nutrient fluxes, and ecosystem dynamics. To study this exchange, 40 surface drifters, equipped with temperature sensors, were released into the northwestern Weddell Sea's continental shelf and slope frontal systemin late January 2012. Comparison of the drifter trajectories with a similar deployment in early February 2007 provides insight into the interannual variability of the surface circulation in this region. Observed differences in the 2007 and 2012 drifter trajectories are related to a variable surface circulation responding to changes in wind stress curl over the Weddell Gyre. Differences between northwestern Weddell Sea properties in 2007 and 2012 include 1) an enhanced cyclonic wind stress forcing over the Weddell Gyre in 2012;2) an acceleration of the Antarctic Slope Current (ASC) and an offshore shift of the primary drifter export pathway in 2012;and 3) a strengthening of the Coastal Current (CC) over the continental shelf in 2007. The relationship between wind stress forcing and surface circulation is reproduced over a longer time period in virtual drifter deployments advected by a remotely sensed surface velocity product. The mean offshore position and speed of the drifter trajectories are correlated with the wind stress curl over the Weddell Gyre, although with different temporal lags. The drifter observations are consistent with recent modeling studies suggesting that Weddell Sea boundary current variability can significantly impact the rate and source of exported surface waters to the Scotia Sea, a process that determines regional chlorophyll distributions.

关键词： Geographic location/entity Continental shelf/slope Southern Ocean Circulation/ Dynamics Boundary currents Trajectories observational techniques and algorithms Surface observations Variability Interannual variability

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The Observed State of the Water Cycle in the Early Twenty-First Century

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JOURNAL OF CLIMATE 2015年第21期28卷 8289-8318页

作者： Rodell, M. Beaudoing, H. K. L'Ecuyer, T. S. Olson, W. S. Famiglietti, J. S. Houser, P. R. Adler, R. Bosilovich, M. G. Clayson, C. A. Chambers, D. Clark, E. Fetzer, E. J. Gao, X. Gu, G. Hilburn, K. Huffman, G. J. Lettenmaier, D. P. Liu, W. T. Robertson, F. R. Schlosser, C. A. Sheffield, J. Wood, E. F. NASA Goddard Space Flight Ctr Greenbelt MD 20771 USA Univ Maryland Earth Syst Sci Interdisciplinary Ctr College Pk MD 20742 USA Univ Wisconsin Madison WI USA Univ Maryland Baltimore Cty Baltimore MD 21228 USA NASA Jet Prop Lab Pasadena CA USA George Mason Univ Fairfax VA 22030 USA Woods Hole Oceanog Inst Woods Hole MA 02543 USA Univ S Florida St Petersburg FL 33701 USA Univ Washington Seattle WA 98195 USA MIT Cambridge MA 02139 USA Remote Sensing Syst Santa Rosa CA USA NASA George C Marshall Space Flight Ctr Huntsville AL 35812 USA Princeton Univ Princeton NJ 08544 USA

This study quantifies mean annual and monthly fluxes of Earth's water cycle over continents and ocean basins during the first decade of the millennium. To the extent possible, the flux estimates are based on satellite measurements first and data-integrating models second. A careful accounting of uncertainty in the estimates is included. It is applied within a routine that enforces multiple water and energy budget constraints simultaneously in a variational framework in order to produce objectively determined optimized flux estimates. In the majority of cases, the observed annual surface and atmospheric water budgets over the continents and oceans close with much less than 10% residual. Observed residuals and optimized uncertainty estimates are considerably larger for monthly surface and atmospheric water budget closure, often nearing or exceeding 20% in North America, Eurasia, Australia and neighboring islands, and the Arctic and South Atlantic Oceans. The residuals in South America and Africa tend to be smaller, possibly because cold land processes are negligible. Fluxes were poorly observed over the Arctic Ocean, certain seas, Antarctica, and the Australasian and Indonesian islands, leading to reliance on atmospheric analysis estimates. Many of the satellite systems that contributed data have been or will soon be lost or replaced. Models that integrate ground-based and remote observations will be critical for ameliorating gaps and discontinuities in the data records caused by these transitions. Continued development of such models is essential for maximizing the value of the observations. Next-generation observing systems are the best hope for significantly improving global water budget accounting.

关键词： Physical Meteorology and Climatology Water budget observational techniques and algorithms Remote sensing Mathematical and statistical techniques Numerical analysis modeling

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Tropical Cyclogenesis Detection in the North Pacific Using the Deviation Angle Variance Technique

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WEATHER AND FORECASTING 2015年第6期30卷 1663-1672页

作者： Wood, Kimberly M. Rodriguez-Herrera, Oscar G. Ritchie, Elizabeth A. Pineros, Miguel F. Hernandez, Ivan Arias Tyo, J. Scott Univ Arizona Dept Atmospher Sci Tucson AZ USA Univ Arizona Coll Opt Sci Tucson AZ USA Univ Norte Dept Elect & Elect Engn Barranquilla Colombia

The deviation angle variance technique (DAV-T) for genesis detection is applied in the western and eastern North Pacific basins. The DAV-T quantifies the axisymmetric organization of cloud clusters using infrared brightness temperature. Since axisymmetry is typically correlated with intensity, the technique can be used to identify relatively high levels of organization at early stages of storm life cycles associated with tropical cyclogenesis. In addition, the technique can be used to automatically track cloud clusters that exhibit signs of organization. In the western North Pacific, automated tracking results for the 2009-11 typhoon seasons show that for a false alarm rate of 25.6%, 96.8% of developing tropical cyclones are detected with a median time of 18.5 h before the cluster reaches an intensity of 30 knots (kt;1 kt = 0.51 m s(-1)) in the Joint Typhoon Warning Center best track at a DAV threshold of 1750 degrees(2). In the eastern North Pacific, for a false alarm rate of 38.0%, the system detects 92.9% of developing tropical cyclones with a median time of 1.25 h before the cluster reaches an intensity of 30 kt in the National Hurricane Center best track during the 2009-11 hurricane seasons at a DAV threshold of 1650 degrees(2). A significant decrease in tracked nondeveloping clusters occurs when a second organization threshold is introduced, particularly in the western North Pacific.

关键词： Geographic location/entity Pacific Ocean Atm/Ocean Structure/ Phenomena Tropical cyclones observational techniques and algorithms Remote sensing Satellite observations

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Linear Trends and Closures of 10-yr Observations of AIRS Stratospheric Channels

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JOURNAL OF CLIMATE 2015年第22期28卷 8939-8950页

作者： Pan, Fang Huang, Xianglei Strow, L. Larabbe Guo, Huan Univ Michigan Dept Climate & Space Sci & Engn Ann Arbor MI 48109 USA Univ Maryland Baltimore Cty Dept Phys Baltimore MD 21228 USA NOAA Geophys Fluid Dynam Lab UCAR Visiting Scientist Programs Princeton NJ USA

The Atmospheric Infrared Sounder (AIRS) level-1b radiances have been shown to be well calibrated (similar to 0.3 K or higher) and have little secular drift (similar to 4 mK yr(-1)) since operation started in September 2002. This paper investigates the linear trends of 10 years (2003-12) of AIRS global-mean radiances in the CO(2)v(2) band that are sensitive to emissions from the stratosphere (stratospheric channels). AIRS lower-stratospheric channels have a cooling trend of no more than 0.23 K decade(-1) whereas the midstratospheric channels consistently show a statistically significant cooling trend as large as 0.58 K decade(-1). The 95% confidence interval for the trend is similar to +/- 0.20 K decade(-1). Two sets of synthetic AIRS radiances are computed using the principal component-based radiative transfer model (PCRTM), one based on a free-running GFDL Atmospheric Model, version 3 (AM3), over the same period and one based on ERA-Interim. The GFDL AM3 simulations overestimate the cooling trends in the mid- to upper-stratospheric channels but slightly underestimate them in the lower-stratospheric channels. The synthetic radiances based on ERA-Interim, however, have statistically significant positive trends at virtually all stratospheric channels. This confirms the challenge to the GCM modeling and reanalysis community to create a better simulation or assimilation of the stratospheric climate. It is shown that the linear trends in AIRS radiances can be reproduced to a large extent by the spectral radiative kernel technique and the trends from the AIRS L2 temperature retrievals and from the change of CO2. This suggests a closure between AIRS L1 radiances and L2 retrievals and the potential merit of AIRS data in studies of stratosphere changes.

关键词： Atm Ocean Structure Phenomena Stratosphere Physical Meteorology and Climatology Longwave radiation observational techniques and algorithms Remote sensing Models and modeling Climate models Variability Trends

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Midshelf to Surfzone Coupled ROMS-SWAN Model Data Comparison of Waves, Currents, and Temperature: Diagnosis of Subtidal Forcings and Response

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第6期45卷 1464-1490页

作者： Kumar, Nirnimesh Feddersen, Falk Uchiyama, Yusuke McWilliams, James O'Reilly, William Scripps Inst Oceanog La Jolla CA 92093 USA Kobe Univ Dept Civil Engn Kobe Hyogo 657 Japan Univ Calif Los Angeles Inst Geophys & Planetary Phys Los Angeles CA 90024 USA

A coupled wave and circulation model that includes tide, wind, buoyancy, and wave processes is necessary to investigate tracer exchange in the shelf region. Here, a coupled Regional Ocean Model System (ROMS)-Simulating Waves Nearshore (SWAN) model, resolving midshelf to the surfzone region of the San Pedro Bay, California, is compared to observations from the 2006 Huntington Beach experiment. Waves are well modeled, and surfzone cross- and alongshore velocities are reasonably well modeled. Modeled and observed rotary velocity spectra compare well in subtidal and tidal bands, and temperature spectra compare well in the subtidal band. Observed and modeled mid- and inner-shelf subtidal velocity ellipses and temperature variability determined from the first vertical complex EOF (cEOF) mode have similar vertical structure. Although the modeled subtidal velocity vertical shear and stratification are weaker than observed, the ratio of stratification to shear is similar, suggesting model vertical mixing is consistent with observations. On fortnightly and longer time scales, the surface heat flux and advective heat flux divergence largely balance on the inner shelf and surfzone. The surfzone and inner-shelf alongshore currents separated by 220 m are unrelated. Both modeled and observed subtidal alongshelf current and temperature are cross-shelf coherent seaward of the surfzone. Wind forcing explains 50% of the observed and modeled inner-shelf alongshore current variability. The observed and modeled inner-shelf alongshelf nonuniformities in depth-averaged alongshore velocities are similar. Inferred, inner-shelf, wave-induced, cross-shore exchange is more important than on the U.S. East Coast. Overall, the coupled ROMS-SWAN model represents well the waves and subtidal circulation dynamics from the midshelf to the surfzone.

关键词： observational techniques and algorithms Buoy observations Profilers oceanic Mathematical and statistical techniques Empirical orthogonal functions Numerical analysis modeling Models and modeling Coupled models Model comparison

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Forcing Mechanisms for an Internal Rear-Flank Downdraft Momentum Surge in the 18 May 2010 Dumas, Texas, Supercell

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MONTHLY WEATHER REVIEW 2015年第11期143卷 4305-4330页

作者： Skinner, Patrick S. Weiss, Christopher C. Wicker, Louis J. Potvin, Corey K. Dowell, David C. NOAA Natl Severe Storms Lab Norman OK 73072 USA Texas Tech Univ Lubbock TX 79409 USA Univ Oklahoma Cooperat Inst Mesoscale Meteorol Studies Norman OK 73019 USA NOAA Earth Syst Res Lab Boulder CO USA

The forcing and origins of an internal rear-flank downdraft (RFD) momentum surge observed by the second Verification of the Origin of Rotation in Tornadoes Experiment (VORTEX2) within a supercell occurring near Dumas, Texas, on 18 May 2010 is assessed through ensemble Kalman filter (EnKF) storm-scale analyses. EnKF analyses are produced every 2 min from mobile Doppler velocity data collected by the Doppler on Wheels and Shared Mobile Atmospheric Research and Teaching radars, as well as radial velocity and reflectivity data from the KAMA (Amarillo, Texas) WSR-88D. EnKF analyses are found to reproduce the structure and evolution of an internal RFD momentum surge observed in independent mobile Doppler radar *** retrievals of EnKF analyses reveal that the low-level RFD outflow structure is primarily determined through nonlinear dynamic perturbation pressure gradient forcing. Horizontal acceleration into a trough of low perturbation pressure between the low-level mesocyclone and mesoanticyclone and trailing the primary RFD gust front is followed by an abrupt deceleration of air parcels crossing the trough axis. This deceleration and associated strong convergence downstream of the pressure trough and horizontal velocity maximum are indicative of an internal RFD momentum surge. Backward trajectory analyses reveal that air parcels within the RFD surge originate from two source regions: near the surface to the north of the low-level mesocyclone, and in the ambient flow outside of the storm environment at a height of approximately 2 km.

关键词： Circulation Dynamics Pressure Tornadogenesis Atm Ocean Structure Phenomena Supercells Tornadoes observational techniques and algorithms Radars Radar observations Mathematical and statistical techniques Kalman filters

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Estimating a Submesoscale Diffusivity Using a Roughness Measure Applied to a Tracer Release Experiment in the Southern Ocean

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第6期45卷 1610-1631页

作者： Boland, Emma J. D. Shuckburgh, Emily Haynes, Peter H. Ledwell, James R. Messias, Marie-Jose Watson, Andrew J. British Antarctic Survey Cambridge CB3 0ET England Univ Cambridge Dept Appl Math & Theoret Phys Cambridge CB3 9EW England Woods Hole Oceanog Inst Woods Hole MA 02543 USA Univ E Anglia Sch Environm Sci Norwich NR4 7TJ Norfolk England Univ Exeter Coll Life & Environm Sci Exeter Devon England

The use of a measure to diagnose submesoscale isopycnal diffusivity by determining the best match between observations of a tracer and simulations with varying small-scale diffusivities is tested. Specifically, the robustness of a roughness measure to discriminate between tracer fields experiencing different submesoscale isopycnal diffusivities and advected by scaled altimetric velocity fields is investigated. This measure is used to compare numerical simulations of the tracer released at a depth of about 1.5 km in the Pacific sector of the Southern Ocean during the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) field campaign with observations of the tracer taken on DIMES cruises. The authors find that simulations with an isopycnal diffusivity of similar to 20 m(2) s(-1) best match observations in the Pacific sector of the Antarctic Circumpolar Current (ACC), rising to similar to 20-50 m(2) s(-1) through Drake Passage, representing submesoscale processes and any mesoscale processes unresolved by the advecting altimetry fields. The roughness measure is demonstrated to be a statistically robust way to estimate a small-scale diffusivity when measurements are relatively sparse in space and time, although it does not work if there are too few measurements overall. The planning of tracer measurements during a cruise in order to maximize the robustness of the roughness measure is also considered. It is found that the robustness is increased if the spatial resolution of tracer measurements is increased with the time since tracer release.

关键词： Geographic location entity Southern Ocean Circulation Dynamics Diffusion Physical Meteorology and Climatology Isopycnal mixing observational techniques and algorithms Tracers Models and modeling Model comparison Tracers

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Cyclonic Eddies in the Gulf of Mexico: Observations by Underwater Gliders and Simulations by Numerical Model

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第1期45卷 313-326页

作者： Rudnick, Daniel L. Gopalakrishnan, Ganesh Cornuelle, Bruce D. Univ Calif San Diego Scripps Inst Oceanog La Jolla CA 92093 USA

Circulation in the Gulf of Mexico (GoM) is dominated by the Loop Current (LC) and by Loop Current eddies (LCEs) that form at irregular multimonth intervals by separation from the LC. Comparatively small cyclonic eddies (CEs) are thought to have a controlling influence on the LCE, including its separation from the LC. Because the CEs are so dynamic and short-lived, lasting only a few weeks, they have proved a challenge to observe. This study addresses that challenge using underwater gliders. These gliders' data and satellite sea surface height (SSH) are used in a four-dimensional variational (4DVAR) assimilation in the Massachusetts Institute of Technology (MIT) general circulation model (MITgcm). The model serves two purposes: first, the model's estimate of ocean state allows the analysis of four-dimensional fields, and second, the model forecasts are examined to determine the value of glider data. CEs have a Rossby number of about 0.2, implying that the effects of flow curvature, cyclostrophy, to modify the geostrophic momentum balance are slight. The velocity field in CEs is nearly depth independent, while LCEs are more baroclinic, consistent with the CEs origin on the less stratified, dense side of the LCE. CEs are formed from water in the GoM, rather than the Atlantic water that distinguishes the LCE. Model forecasts are improved by glider data, using a quality metric based on satellite SSH, with the best 2-month GoM forecast rivaling the accuracy of a global hindcast.

关键词： Circulation/ Dynamics Currents Eddies Mesoscale processes observational techniques and algorithms In situ oceanic observations Models and modeling Data assimilation Ocean models

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An Inductive Charging and Real-Time Communications System for Profiling Moorings

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2015年第12期32卷 2243-2252页

作者： Alford, Matthew H. McGinnis, Tim Howe, Bruce M. Univ Calif San Diego Scripps Inst Oceanog La Jolla CA 92093 USA Univ Washington Appl Phys Lab Seattle WA 98105 USA Univ Washington Sch Oceanog Seattle WA 98105 USA Univ Hawaii Manoa Honolulu HI 96822 USA

This paper describes a system for providing power and communications to moored profiling vehicles. A McLane Moored Profiler (MP) was equipped with a rechargeable battery pack and an inductive charging system to allow it to move periodically to a charging dock at the top of a subsurface mooring. Power was provided from a large bank of alkaline batteries housed in two 0.94-m steel spheres. Data were transferred inductively from the profiler to a mooring controller, and from there back to shore via radio and Iridium satellite modems housed in a small surface communications float on an L tether. An acoustic modem provided backup communications to a nearby ship in the event of loss or damage to the surface float. The system was tested in a 180-m-deep fjord (Puget Sound, Washington) and at Station ALOHA (A Long-Term Oligotrophic Habitat Assessment), a 4748-m-deep open-ocean location north of Hawaii. Basic functionality of the system was demonstrated, with the profiler repeatedly recharging at about 225 W (with an overall efficiency of about 70%). Data were relayed back to shore via Iridium and to a nearby ship via the radio and acoustic modems. The system profiled flawlessly for the entire 6-week test in Puget Sound, but charging at the deep site stopped after only 9 days in the deep-ocean deployment owing to damage to the charging station, possibly by surface wave action.

关键词： observational techniques and algorithms Profilers oceanic

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Seasonal Variability of Salinity and Salt Transport in the Northern Indian Ocean

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第7期45卷 1947-1966页

作者： D'Addezio, Joseph M. Subrahmanyam, Bulusu Nyadjro, Ebenezer S. Murty, V. S. N. Univ S Carolina Marine Sci Program Columbia SC 29208 USA Univ S Carolina Dept Earth & Ocean Sci Columbia SC 29208 USA Univ New Orleans Dept Phys New Orleans LA 70148 USA CSIR Natl Inst Oceanog Reg Ctr Visakhapatnam Andhra Pradesh India

Analyses using a suite of observational datasets (Aquarius and Argo) and model simulations are carried out to examine the seasonal variability of salinity in the northern Indian Ocean (NIO). The model simulations include Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2), the European Centre for Medium-Range Weather Forecasts-Ocean Reanalysis System 4 (ECMWF-ORAS4), Simple Ocean Data Assimilation (SODA) reanalysis, and the Hybrid Coordinate Ocean Model (HYCOM). The analyses of salinity at the surface and at depths up to 200 m, surface salt transport in the top 5-m layer, and depth-integrated salt transports revealed different salinity processes in the NIO that are dominantly related to the semiannual monsoons. Aquarius proves a useful tool for observing this dynamic region and reveals some aspects of sea surface salinity (SSS) variability that Argo cannot resolve. The study revealed large disagreement between surface salt transports derived from observed- and analysis-derived salinity fields. Although differences in SSS between the observations and the model solutions are small, model simulations provide much greater spatial variability of surface salt transports due to finer detailed current structure. Meridional depth-integrated salt transports along 6 degrees N revealed dominant advective processes from the surface toward near-bottom depths. In the Arabian Sea (Bay of Bengal), the net monthly mean maximum northward (southward) salt transport of similar to 50 x 10(6) kg s (-1) occurs in July, and annual-mean salt transports across this section are about -2.5 x 10(6) kg s (-1) (3 x 10(6) kg s (-1)).

关键词： Geographic location entity Indian Ocean Circulation Dynamics Advection Ocean dynamics Transport observational techniques and algorithms Satellite observations Models and modeling General circulation models

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