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Internal Waves and Mixing near the Kerguelen Plateau

JOURNAL OF PHYSICAL OCEANOGRAPHY 2016年第2期46卷 417-437页

作者： Meyer, Amelie Polzin, Kurt L. Sloyan, Bernadette M. Phillips, Helen E. CSIRO Ocean & Atmosphere Flagship Hobart Tas Australia Univ Tasmania Inst Marine & Antarctic Studies Hobart Tas Australia Woods Hole Oceanog Inst Woods Hole MA 02543 USA ARC Ctr Excellence Climate Syst Sci Hobart Tas Australia Norwegian Polar Res Inst N-9296 Tromso Norway

In the stratified ocean, turbulent mixing is primarily attributed to the breaking of internal waves. As such, internal waves provide a link between large-scale forcing and small-scale mixing. The internal wave field north of the Kerguelen Plateau is characterized using 914 high-resolution hydrographic profiles from novel Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats. Altogether, 46 coherent features are identified in the EM-APEX velocity profiles and interpreted in terms of internal wave kinematics. The large number of internal waves analyzed provides a quantitative framework for characterizing spatial variations in the internal wave field and for resolving generation versus propagation dynamics. Internal waves observed near the Kerguelen Plateau have a mean vertical wavelength of 200 m, a mean horizontal wavelength of 15 km, a mean period of 16 h, and a mean horizontal group velocity of 3 cm s(-1). The internal wave characteristics are dependent on regional dynamics, suggesting that different generation mechanisms of internal waves dominate in different dynamical zones. The wave fields in the Subantarctic/Subtropical Front and the Polar Front Zone are influenced by the local small-scale topography and flow strength. The eddy-wave field is influenced by the large-scale flow structure, while the internal wave field in the Subantarctic Zone is controlled by atmospheric forcing. More importantly, the local generation of internal waves not only drives large-scale dissipation in the frontal region but also downstream from the plateau. Some internal waves in the frontal region are advected away from the plateau, contributing to mixing and stratification budgets elsewhere.

关键词： Profilers, oceanic Wave properties Internal waves Circulation/ Dynamics Southern Ocean observational techniques and algorithms In situ oceanic observations Geographic location/entity Mixing

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Global Observations of Open-Ocean Mode-1 M₂ Internal Tides

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2016年第6期46卷 1657-1684页

作者： Zhao, Zhongxiang Alford, Matthew H. Girton, James B. Rainville, Luc Simmons, Harper L. Univ Washington Appl Phys Lab 1013 NE 40th St Seattle WA 98105 USA Univ Calif San Diego Scripps Inst Oceanog La Jolla CA 92093 USA Univ Alaska Fairbanks Fairbanks AK USA

A global map of open-ocean mode-1 M-2 internal tides is constructed using sea surface height (SSH) measurements from multiple satellite altimeters during 1992-2012, representing a 20-yr coherent internal tide field. A two-dimensional plane wave fit method is employed to 1) suppress mesoscale contamination by extracting internal tides with both spatial and temporal coherence and 2) separately resolve multiple internal tidal waves. Global maps of amplitude, phase, energy, and flux of mode-1 M-2 internal tides are presented. The M-2 internal tides are mainly generated over topographic features, including continental slopes, midocean ridges, and sea-mounts. Internal tidal beams of 100-300 km width are observed to propagate hundreds to thousands of kilometers. Multiwave interference of some degree is widespread because of the M-2 internal tide's numerous generation sites and long-range propagation. The M-2 internal tide propagates across the critical latitudes for parametric subharmonic instability (28.88S/N) with little energy loss, consistent with the 2006 Internal Waves across the Pacific (IWAP) field measurements. In the eastern Pacific Ocean, the M-2 internal tide loses significant energy in propagating across the equator;in contrast, little energy loss is observed in the equatorial zones of the Atlantic, Indian, and western Pacific Oceans. Global integration of the satellite observations yields a total energy of 36 PJ (1 PJ = 10(15) J) for all the coherent mode-1 M-2 internal tides. Finally, satellite observed M-2 internal tides compare favorably with field mooring measurements and a global eddy-resolving numerical model.

关键词： Circulation/ Dynamics Internal waves Atm/Ocean Structure/ Phenomena Tides observational techniques and algorithms Altimetry Satellite observations Mathematical and statistical techniques Numerical analysis/modeling Applications Field experiments

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On-Orbit Absolute Calibration of the Global Precipitation Measurement Microwave Imager

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第7期33卷 1393-1412页

作者： Wentz, Frank J. Draper, David Remote Sensing Syst 444 Tenth St Santa Rosa CA 95401 USA Ball Aerosp & Technol Corp Boulder CO USA

The Global Precipitation Measurement (GPM) Core Observatory was launched on 27 February 2014. One of the principal instruments on the spacecraft is the GPM Microwave Imager (GMI). This paper describes the absolute calibration of the GMI antenna temperature (T-A) and the earth brightness temperature (T-B). The deep-space observations taken on 20 May 2014, supplemented by nadir-viewing data, are used for the T-A calibration. Data from two backlobe maneuvers are used to determine the primary reflector's cold-space spillover, which is required to convert the T-A into T-B. The calibrated GMI observations are compared to predictions from an ocean radiative transfer model (RTM) using collocated WindSat ocean retrievals as input. The mean difference when averaged globally over 13 months does not exceed 0.1 K for any of the nine channels from 11 to 89 GHz. The RTM comparisons also show that there are no significant solar intrusion errors in the GMI hot load. The absolute accuracy of the GMI instrument is defined as the average ocean-viewing error of the measured T-A or T-B relative to the true T-A or T-B. Based on the analyses herein, the GMI absolute accuracy for T-A is estimated to be about 0.1 K rms over all channels and 0.25 K rms over all channels for T-B.

关键词： Data processing Instrumentation/sensors Microwave observations observational techniques and algorithms Satellite observations

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Turbulence Estimation Using Fast-Response Thermistors Attached to a Free- Fall Vertical Microstructure Profiler

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第10期33卷 2065-2078页

作者： Goto, Yasutaka Yasuda, Ichiro Nagasawa, Maki Univ Tokyo Atmosphere & Ocean Res Inst 5-1-5 Kashiwanoha Kashiwa Chiba 2778564 Japan

Estimation of turbulence intensity with a fast-response thermistor is examined by comparing the energy dissipation rate epsilon(T) from a Fastip Probe, model 07 (FP07), thermistor with epsilon(S) from a shear probe, both of which are attached to a free-fall microstructure profiler with the fall rate of 0.6-0.7 ms(-1). Temperature gradient spectra corrected with previously introduced frequency response functions represented by a single-pole low-pass filter yields epsilon(T) with a bias that strongly depends on turbulence intensity. Meanwhile, the correction with the form of a double-pole low-pass filter derives less bias than of single-pole low-pass filter. The rate epsilon(T) is compatible with epsilon(S) when the double-pole correction with the time constant of 3 x 10(-3) s is applied, and 68% of epsilon(T) data are within a factor of 2.8 of epsilon(S) in the wide range of epsilon(S) = 10(-10) -3 x 10(-7) W kg(-1). The rate epsilon(T) is still compatible with epsilon(S) even in the anisotropy range, where the buoyancyReynolds number I = epsilon/(nu.N-2) is20-100. Turbulence estimation from the fast-response thermistor is thus confirmed to be valid in this range by applying the appropriate correction to temperature gradient spectra. Measurements with fast-response thermistors, which have not been common because of their poor frequency response, are less sensitive to the vibration of profilers than thosewith shear probes. Hence, measurements could be availablewhen a fast-response thermistor is attached to a CTD frame or a float, which extends the possibility of obtaining much more turbulence data in deep and wide oceans.

关键词： Abyssal circulation Atm/Ocean Structure/ Phenomena Circulation/ Dynamics Diapycnal mixing In situ oceanic observations observational techniques and algorithms Ship observations Thermocline circulation Turbulence

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Homogenized Variability of Radiosonde-Derived Atmospheric Boundary Layer Height over the Global Land Surface from 1973 to 2014

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JOURNAL OF CLIMATE 2016年第19期29卷 6893-6908页

作者： Wang, Xiaoyan Wang, Kaicun Beijing Normal Univ Coll Global Change & Earth Syst Sci 19 Xinjiekouwai St Beijing 100875 Peoples R China Joint Ctr Global Change Studies Beijing Peoples R China Univ Texas Austin Jackson Sch Geosci Dept Geol Sci Austin TX 78712 USA

Boundary layer height (BLH) significantly impacts near-surface air quality, and its determination is important for climate change studies. Integrated Global Radiosonde Archive data from 1973 to 2014 were used to estimate the long-term variability of the BLH based on profiles of potential temperature, relative humidity, and atmospheric refractivity. However, this study found that there was an obvious inhomogeneity in the radiosonde-derived BLH time series because of the presence of discontinuities in the raw radiosonde dataset. The penalized maximal F test and quantile-matching adjustment were used to detect the changepoints and to adjust the raw BLH series. The most significant inhomogeneity of the BLH time series was found over the United States from 1986 to 1992, which was mainly due to progress made in sonde models and processing procedures. The homogenization did not obviously change the magnitude of the daytime convective BLH(CBLH) tendency, but it improved the statistical significance of its linear trend. The trend of nighttime stable BLH (SBLH) is more dependent on the homogenization because the magnitude of SBLH is small, and SBLH is sensitive to the observational biases. The global daytime CBLH increased by about 1.6% decade(-1) before and after homogenization from 1973 to 2014, and the nighttime homogenized SBLH decreased by -4.2% decade(-1) compared to a decrease of -7.1% decade(-1) based on the raw series. Regionally, the daytime CBLH increased by 2.8%, 0.9%, 1.6%, and 2.7% decade(-1) and the nighttime SBLH decreased significantly by -2.7%, -6.9%, -7.7%, and -3.5% decade(-1) over Europe, the United States, Japan, and Australia, respectively.

关键词： Atm/Ocean Structure/ Phenomena Boundary layer Mixed layer observational techniques and algorithms Radiosonde observations Variability Climate variability Decadal variability Applications Air pollution

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Brightness Temperature Simulation of Observed Precipitation Using a Three-Dimensional Radiative Transfer Model

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第10期33卷 2053-2064页

作者： Adams, Ian S. Bettenhausen, Michael H. Naval Res Lab Remote Sensing Div Code 72334555 Overlook Ave SW Washington DC 20375 USA

This study demonstrates the capabilities of a three-dimensional radiative transfer model coupled to a polarized microwave surface emissivity model. Simulations are performed at 10, 19, and 37 GHz for TMI and WindSat using three-dimensional fields of rain, snow, and graupel derived from Tropical Rainfall Measuring Mission observations of moderate Tropical Storm Asma in conjunction with atmospheric profiles and surface fields from ECMWF. Simulations are well behaved and compare well with measured brightness temperatures. Comparisons are made between simulations with a wind-roughened surface and simulations assuming a specular surface. This theoretical study, which is supported with WindSat retrievals, shows the frequencies and conditions under which surface emissions may be detected in the presence of rain.

关键词： Atm/Ocean Structure/ Phenomena Microwave observations observational techniques and algorithms Precipitation Remote sensing Satellite observations Tropical cyclones Wind

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Evaluation of Thermosalinograph and VIIRS Data for the Characterization of Near-Surface Temperature Fields

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第9期33卷 1843-1858页

作者： Schloesser, Fabian Cornillon, Peter Donohue, Kathleen Boussidi, Brahim Iskin, Emily Univ Rhode Isl Grad Sch Oceanog 215 S Ferry Rd Narragansett RI 02882 USA Inst Mines Telecom Telecom Bretagne UMR Lab STICC Brest France Univ Calif Davis Davis CA 95616 USA

Detailed understanding of submesoscale processes and their role in global ocean circulation is constrained, in part, by the lack of global observational datasets of sufficiently high resolution. Here, the potential of thermosalinograph (TSG) and Visible Infrared Imager Radiometer Suite (VIIRS) data is evaluated, to characterize the submesoscale structure of the near-surface temperature fields in the Gulf Stream and Sargasso Sea. In addition to spectral density, the structure function is considered, a statistical measure less susceptible to data gaps, which are common in the satellite-derived fields. The structure function is found to be an unreliable estimator, especially for steep spectral slopes, nominally between 2 and 3, typical of the Gulf Stream and Sargasso regions. A quality-control threshold is developed based on the number and size of gaps to ensure reliable spectral density estimates. Analysis of the impact of gaps in the VIIRS data on the spectra shows that both the number of missing values and the size of gaps affect the results, and that the steeper the spectral slope the more significant the impact. Furthermore, the TSG, with a nominal resolution of 75m, captures the spectral characteristics of the fields in both regions down to scales substantially smaller than 1 km, while the VIIRS fields, with a nominal resolution of 750m, reproduce the spectra well down to scales of about 20 kmin the Sargasso Sea and 5 km in the Gulf Stream. The scales at which the VIIRS and TSG spectra diverge are thought to be determined by sensor and retrieval noise.

关键词： Circulation/Dynamics Error analysis Fourier analysis In situ oceanic observations Mathematical and statistical techniques observational techniques and algorithms Satellite observations Ship observations Subgrid-scale processes

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High-Resolution Measurements of Turbulent Flow Close to the Sediment-Water Interface Using a Bistatic Acoustic Profiler

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第4期33卷 769-788页

作者： Brand, Andreas Noss, Christian Dinkel, Christian Holzner, Markus Swiss Fed Inst Aquat Sci & Technol Surface Waters Res & Management Seestr 79 CH-6047 Kastanienbaum Switzerland Swiss Fed Inst Technol Inst Biogeochem & Pollutant Dynam Zurich Switzerland Univ Koblenz Landau Inst Environm Sci Landau Germany Swiss Fed Inst Technol Environm Fluid Mech Zurich Switzerland

Velocity profile measurements at high spatial and temporal resolution are required for the detailed study of solute and momentum transfer close to the sediment water interface. Still, not many devices allow such measurements in natural systems. Recently, a bistatic acoustic current profiler has become commercially available that allows the recording of profiles at down to 1-mm resolution with a maximum frequency of 100 Hz and a profile length of 3.5 cm. This study tested the ability to characterize the turbulent flow of this profiler in a laboratory flume and in a run of the river reservoir. The tests showed that average velocities were reliably measured in the upper 2.5 cm, while the flow statistics were affected by Doppler noise and signal decorrelation. The latter is caused by the decreasing overlap between the individual beam signals. Doppler noise can be estimated and accounted for by established correction procedures, but currently there is no method to quantify the influence of signal decorrelation. Both error sources mainly affect the measured variances of the velocities, while the Reynolds stresses are reliable as long as there is no interference with the solid bottom. In the field application, most problems arise because of the necessity of coordinate system rotation, since a perfect alignment of the profiler with the current is not possible. Also, because of the coordinate system rotation, the Reynolds stresses become contaminated by noise, which can be removed by low-pass filtering. Still, this filtering results in loss of the turbulent signal, which was estimated in this study to be between 2% and 10%.

关键词： Acoustic measurements/effects Atm/Ocean Structure/ Phenomena Bottom currents/bottom water Data processing In situ oceanic observations Instrumentation/sensors observational techniques and algorithms Profilers, oceanic

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A Multisensor Investigation of Rime Splintering in Tropical Maritime Cumuli

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第6期73卷 2547-2564页

作者： Lasher-Trapp, Sonia Leon, David C. DeMott, Paul J. Villanueva-Birriel, Cecille M. Johnson, Alexandria V. Moser, Daniel H. Tully, Colin S. Wu, Wei Purdue Univ Dept Earth Atmospher & Planetary Sci W Lafayette IN 47907 USA Univ Illinois Dept Atmospher Sci 105 S Gregory St Urbana IL 61801 USA Univ Wyoming Dept Atmospher Sci Laramie WY 82071 USA Colorado State Univ Dept Atmospher Sci Ft Collins CO 80523 USA

Three flights from the Ice in Clouds Experiment-Tropical (ICE-T) field campaign examined the onset of ice near the ascending cloud tops of tropical maritime cumuli as they cooled from 0 degrees to -14 degrees C. Careful quantitative analysis of ice number concentrations included manual scrutiny of particle images and corrections for possible particle-shattering artifacts. The novel use of the Wyoming Cloud Radar documented the stage of cloud development and tops relative to the aircraft sampling, complemented the manual estimates of graupel concentrations, and provided new clear evidence of graupel movement through the rime-splintering zone. Measurements of ice-nucleating particles (INPs) provided an estimate of primary initiated ice. The data portray a dynamically complex picture of hydrometeor transport contributing to, and likely resulting from, the rime-splintering process. Hundreds per liter of supercooled raindrops ascended within the updrafts as the cloud tops reached 0 degrees C and contributed in part to the 0.1 L-1 graupel detected soon after the cloud tops cooled to -5 degrees C. Rime splintering could thus be initiated upon first ascent of the cloud top through that zone and arguably contributed to the 1 L-1 ormore graupel observed above it. Graupel ascending/descending into, or balancedwithin, the rime-splintering zone were found. In wider, less isolated clouds with dying updrafts and tops near -14 degrees C, ice particle concentrations sometimes reached 100 L-1. Future 3D numerical modeling will be required to evaluate if rime splintering alone can explain the difference of three to four orders of magnitude in the observed INPs and the graupel observed at -5 degrees C and colder.

关键词： Aircraft observations Cloud microphysics Cumulus clouds Ice crystals Ice particles observational techniques and algorithms Physical Meteorology and Climatology Radars/Radar observations

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Statistical Properties of Global Precipitation in the NCEP GFS Model and TMPA Observations for Data Assimilation

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MONTHLY WEATHER REVIEW 2016年第2期144卷 663-679页

作者： Lien, Guo-Yuan Kalnay, Eugenia Miyoshi, Takemasa Huffman, George J. Univ Maryland Dept Atmospher & Ocean Sci College Pk MD 20742 USA RIKEN Adv Inst Computat Sci Kobe Hyogo Japan Japan Agcy Marine Earth Sci & Technol Yokohama Kanagawa Japan NASA Goddard Space Flight Ctr Mesoscale Atmospher Proc Lab Greenbelt MD USA

Assimilation of satellite precipitation data into numerical models presents several difficulties, with two of the most important being the non-Gaussian error distributions associated with precipitation, and large model and observation errors. As a result, improving the model forecast beyond a few hours by assimilating precipitation has been found to be difficult. To identify the challenges and propose practical solutions to assimilation of precipitation, statistics are calculated for global precipitation in a low-resolution NCEP Global Forecast System (GFS) model and the TRMM Multisatellite Precipitation Analysis (TMPA). The samples are constructed using the same model with the same forecast period, observation variables, and resolution as in the follow-on GFS/TMPA precipitation assimilation experiments presented in the companion *** statistical results indicate that the T62 and T126 GFS models generally have positive bias in precipitation compared to the TMPA observations, and that the simulation of the marine stratocumulus precipitation is not realistic in the T62 GFS model. It is necessary to apply to precipitation either the commonly used logarithm transformation or the newly proposed Gaussian transformation to obtain a better relationship between the model and observational precipitation. When the Gaussian transformations are separately applied to the model and observational precipitation, they serve as a bias correction that corrects the amplitude-dependent biases. In addition, using a spatially and/or temporally averaged precipitation variable, such as the 6-h accumulated precipitation, should be advantageous for precipitation assimilation.

关键词： Atm Ocean Structure Phenomena Precipitation observational techniques and algorithms Satellite observations Mathematical and statistical techniques Bias Models and modeling Data assimilation

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