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Standing Internal Tides in the Tasman Sea Observed by Gliders

JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第11期45卷 2715-2737页

作者： Johnston, T. M. Shaun Rudnick, Daniel L. Kelly, Samuel M. Univ Calif San Diego Scripps Inst Oceanog La Jolla CA 92093 USA Univ Minnesota Large Lakes Observ Duluth MN 55812 USA Univ Minnesota Dept Phys Duluth MN 55812 USA

Low-mode internal tides are generated at tall submarine ridges, propagate across the open ocean with little attenuation, and reach distant continental slopes. A semidiurnal internal tide beam, identified in previous altimetric observations and modeling, emanates from the Macquarie Ridge, crosses the Tasman Sea, and impinges on the Tasmanian slope. Spatial surveys covering within 150 km of the slope by two autonomous underwater gliders with maximum profile depths of 500 and 1000 m show the steepest slope near 43 degrees S reflects almost all of the incident energy flux to form a standing wave. Starting from the slope and moving offshore by one wavelength (similar to 150 km), potential energy density displays an antinode-node-antinode-node structure, while kinetic energy density shows the opposite. Mission-mean mode-1 incident and reflected flux magnitudes are distinguished by treating each glider's survey as an internal wave antenna for measuring amplitude, wavelength, and direction. Incident fluxes are 1.4 and 2.3 kW m(-1) from the two missions, while reflected fluxes are 1.2 and 1.8 kW m(-1). From one glider surveying the region of highest energy at the steepest slope, the reflectivity estimates are 0.8 and 1, if one considers the kinetic and potential energy densities separately. These results are in agreement with mode-1 reflectivity of 0.7-1 from a model in one horizontal dimension with realistic topography and stratification. The direction of the incident internal tides is consistent with altimetry and modeling, while the reflected tide is consistent with specular reflection from a straight coastline.

关键词： Circulation/ Dynamics Internal waves Topographic effects Atm/Ocean Structure/ Phenomena Tides observational techniques and algorithms In situ oceanic observations Models and modeling Model comparison

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A Statistical Method for Correlating Paired Wave Spectra

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2015年第11期32卷 2130-2146页

作者： Collins, Clarence O., III Vincent, C. Linwood Graber, Hans C. Naval Res Lab Div Oceanog Stennis Space Ctr MS USA Naval Res Lab Marine Meteorol Div UCAR Visiting Scientist Programs Monterey CA USA Univ Miami Rosenstiel Sch Marine & Atmospher Sci Miami FL 33149 USA Univ Miami Dept Ocean Sci Miami FL 33149 USA

Ocean wave spectra are complex. Because of this complexity, no widely accepted method has been developed for the comparison between two sets of paired wave spectra. A method for intercomparing wave spectra is developed based on an example paradigm of the comparison of model spectra to observed spectra. Canonical correlation analysis (CCA) is used to investigate the correlation structure of the matrix of spectral correlations. The set of N ranked canonical correlations developed through CCA (here termed the r-sequence) is shown to be an effective method for understanding the degree of correlation between sets of paired spectral observation. A standard method for intercomparing sets of wave spectra based on CCA is then described. The method is elucidated through analyses of synthetic and real spectra that span a range of correlation from random to almost equal.

关键词： Atm Ocean Structure Phenomena Sea state observational techniques and algorithms Buoy observations Data processing Quality assurance control Mathematical and statistical techniques Principal components analysis Statistical techniques

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Proximity Soundings of Severe and Nonsevere Thunderstorms in Central Europe

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MONTHLY WEATHER REVIEW 2015年第12期143卷 4805-4821页

作者： Pucik, Tomas Groenemeijer, Pieter Ryva, David Kolar, Miroslav European Severe Storms Lab D-82234 Wessling Germany Masaryk Univ Brno Czech Republic Charles Univ Prague Prague Czech Republic Czech Hydrometeorol Inst Prague Czech Republic

The environments of severe and nonsevere thunderstorms were analyzed using 16 421 proximity soundings from December 2007 to December 2013 taken at 32 central European stations. The soundings were assigned severity categories for the following hazards: hail, wind, tornado, and rain. For each of the soundings, parameters were calculated representing the instability, vertical wind profile, and moisture of the environment. The probability of the various hazards as a function of CAPE and 0-6-km bulk shear (DLS) is quite different for each of the hazards. Large hail is most likely for high CAPE and high DLS, a regime that also supports severe wind events. A second severe wind regime exists for low CAPE and very high DLS. These events are mostly cold season events. Storms with significant tornadoes occur with much higher DLS than storms with weak or no tornadoes, but with similar CAPE. The 0-1-km bulk shear (LLS) does not discriminate better than DLS between weak and significant tornadoes. Heavy rain events occur across a wide range of DLS, but with CAPE above the median for nonsevere thunderstorms and are most likely when both absolute humidity in the boundary layer and relative humidity in the low- to midtroposphere are high. LCL height does not discriminate well between the intensity categories of tornadoes, but higher LCL heights were associated with a higher probability of severe hail. Storm relative helicity shows similar results to DLS, but with more overlap among intensity categories.

关键词： Physical Meteorology and Climatology CAPE Convective storms Hail Storm environments observational techniques and algorithms Radiosonde observations

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Physical Mechanisms of Tropical Climate Feedbacks Investigated Using Temperature and Moisture Trends

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JOURNAL OF CLIMATE 2015年第22期28卷 8968-8987页

作者： Ferraro, A. J. Lambert, F. H. Collins, M. Miles, G. M. Univ Exeter Coll Engn Math & Phys Sci N Pk Rd Exeter EX4 4QF Devon England STFC Rutherford Appleton Lab Remote Sensing Grp Oxford England

Tropical climate feedback mechanisms are assessed using satellite-observed and model-simulated trends in tropical tropospheric temperature from the MSU/AMSU instruments and upper-tropospheric humidity from the HIRS instruments. Despite discrepancies in the rates of tropospheric warming between observations and models, both are consistent with constant relative humidity over the period 1979-2008. Because uncertainties in satellite-observed tropical-mean trends preclude a constraint on tropical-mean trends in models regional features of the feedbacks are also explored. The regional pattern of the lapse rate feedback is primarily determined by the regional pattern of surface temperature changes, as tropical atmospheric warming is relatively horizontally uniform. The regional pattern of the water vapor feedback is influenced by the regional pattern of precipitation changes, with variations of 1-2 W m(-2) K-1 across the tropics (compared to a tropical-mean feedback magnitude of 3.3-4 W m(-2) K-1). Thus the geographical patterns of water vapor and lapse rate feedbacks are not correlated, but when the feedbacks are calculated in precipitation percentiles rather than in geographical space they are anticorrelated, with strong positive water vapor feedback associated with strong negative lapse rate feedback. The regional structure of the feedbacks is not related to the strength of the tropical-mean feedback in a subset of the climate models from the CMIP5 archive. Nevertheless the approach constitutes a useful process-based test of climate models and has the potential to be extended to constrain regional climate projections.

关键词： Geographic location entity Tropics Physical Meteorology and Climatology Feedback Regional effects Water vapor observational techniques and algorithms Satellite observations Models and modeling Climate models

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An Initial Assessment of the Surface Reference Technique Applied to Data from the Dual-Frequency Precipitation Radar (DPR) on the GPM Satellite

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2015年第12期32卷 2281-2296页

作者： Meneghini, Robert Kim, Hyokyung Liao, Liang Jones, Jeffrey A. Kwiatkowski, John M. NASA Goddard Space Flight Ctr Greenbelt MD 20771 USA Goddard Earth Sci & Technol Ctr Greenbelt MD USA Morgan State Univ Baltimore MD 21239 USA Wyle Sci Technol & Engn Grp Greenbelt MD USA George Mason Univ Fairfax VA 22030 USA

It has long been recognized that path-integrated attenuation (PIA) can be used to improve precipitation estimates from high-frequency weather radar data. One approach that provides an estimate of this quantity from airborne or spaceborne radar data is the surface reference technique (SRT), which uses measurements of the surface cross section in the presence and absence of precipitation. Measurements from the dual-frequency precipitation radar (DPR) on the Global Precipitation Measurement (GPM) satellite afford the first opportunity to test the method for spaceborne radar data at Ka band as well as for the Ku-band-Ka-band combination. The study begins by reviewing the basis of the single- and dual-frequency SRT. As the performance of the method is closely tied to the behavior of the normalized radar cross section (NRCS or sigma(0)) of the surface, the statistics of sigma(0) derived from DPR measurements are given as a function of incidence angle and frequency for ocean and land backgrounds over a 1-month period. Several independent estimates of the PIA, formed by means of different surface reference datasets, can be used to test the consistency of the method since, in the absence of error, the estimates should be identical. Along with theoretical considerations, the comparisons provide an initial assessment of the performance of the single- and dual-frequency SRT for the DPR. The study finds that the dual-frequency SRT can provide improvement in the accuracy of path attenuation estimates relative to the single-frequency method, particularly at Ku band.

关键词： observational techniques and algorithms Radars/Radar observations Remote sensing Satellite observations

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Three Cases of a New Multichannel Threshold Technique to Detect Fog/Low Stratus during Nighttime Using SNPP Data

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WEATHER AND FORECASTING 2015年第6期30卷 1763-1780页

作者： Jiang, Jun Yan, Wei Ma, Shuo Jie, Yangyang Zhang, Xiarong Hu, Shensen Fan, Lei Xia, Linyu PLA Univ Sci & Technol Coll Meteorol & Oceanog Nanjing 211101 Jiangsu Peoples R China Peoples Liberat Army Beijing Peoples R China Zhengzhou Univ Hist Inst Zhengzhou 450052 Peoples R China

The day-night band (DNB) low-light-level visible sensor, mounted on the Suomi-National Polar-Orbiting Partnership (SNPP) satellite, can measure visible radiances from the earth and atmosphere (solar/lunar reflection, and natural/anthropogenic nighttime light emissions) during both day and night and can achieve unprecedented nighttime low-light-level imaging with its accurate radiometric calibration and fine spatiotemporal resolution. Based on the good characteristics of DNB, a multichannel threshold (MCT) algorithm combining DNB with other Visible-Infrared Imager-Radiometer Suite (VIIRS) channels is proposed to monitor nighttime fog/low stratus. Through a gradual separation of the underlying surface (land, vegetation, water bodies, and city lights), snow, and high/medium clouds, a fog/low-stratus region can ultimately be extracted by the algorithm. Then, the algorithmic feasibility is verified by three typical cases of heavy fog/low stratus in China. The experimental results demonstrate that the outcomes of the MCT algorithm approximately coincide with the ground-measured results. Furthermore, the MCT algorithm shows promise for nighttime fog/low-stratus detection in some example cases with about a 0.84 average probability of detection (POD), a 0.73 average critical success index (CSI), and a 0.15 average false alarm ratio (FAR), which reveals some improvement over the conventional dual-channel difference (DCD) algorithm.

关键词： Physical Meteorology and Climatology Cloud cover observational techniques and algorithms algorithms Remote sensing Mathematical and statistical techniques Statistical techniques Forecasting Nowcasting Applications Transportation meteorology

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Horizontal Transition of Turbulent Cascade in the Near-Surface Layer of Tropical Cyclones

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2015年第12期72卷 4915-4925页

作者： Tang, Jie Byrne, David Zhang, Jun A. Wang, Yuan Lei, Xiao-tu Wu, Dan Fang, Ping-zhi Zhao, Bing-ke China Meteorol Adm Shanghai Typhoon Inst Shanghai Peoples R China Nanjing Univ Minist Educ Key Lab Mesoscale Severe Weather Nanjing 210093 Jiangsu Peoples R China Nanjing Univ Sch Atmospher Sci Nanjing 210093 Jiangsu Peoples R China ETH Inst Biogeochem & Pollutant Dynam Environm Phys Grp Zurich Switzerland NOAA Atlantic Oceanog & Meteorol Lab Hurricane Res Div Miami FL 33149 USA

Tropical cyclones (TC) consist of a large range of interacting scales from hundreds of kilometers to a few meters. The energy transportation among these different scalesthat is, from smaller to larger scales (upscale) or vice versa (downscale)may have profound impacts on TC energy dynamics as a result of the associated changes in available energy sources and sinks. From multilayer tower measurements in the low-level (<120 m) boundary layer of several landing TCs, the authors found there are two distinct regions where the energy flux changes from upscale to downscale as a function of distance to the storm center. The boundary between these two regions is approximately 1.5 times the radius of maximum wind. Two-dimensional turbulence (upscale cascade) occurs more typically at regions close to the inner-core region of TCs, while 3D turbulence (downscale cascade) mostly occurs at the outer-core region in the surface layer.

关键词： Circulation Dynamics Nonlinear dynamics Turbulence Atm Ocean Structure Phenomena Boundary layer Tropical cyclones observational techniques and algorithms In situ atmospheric observations In situ oceanic observations

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The M₂ Internal Tide Simulated by a 1/10° OGCM

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第12期45卷 3119-3135页

作者： Li, Zhuhua von Storch, Jin-Song Muller, Malte Max Planck Inst Meteorol D-20146 Hamburg Germany Int Max Planck Res Sch Earth Syst Modelling Hamburg Germany Norwegian Meteorol Inst Oslo Norway

Using a concurrent simulation of the ocean general circulation and tides with the 1/10 degrees Max Planck Institute Ocean Model (MPI-OM), known as STORMTIDE, this study provides a near-global quantification of the low-mode M-2 internal tides. The quantification is based on wavelengths and their near-global distributions obtained by applying spectral analysis to STORMTIDE velocities and on comparisons of the distributions with those derived by solving the Sturm-Liouville eigenvalue problem. The simulated wavelengths, with respect to both their magnitudes and their geographical distributions, compare well with those obtained by solving the eigenvalue problem, suggesting that the STORMTIDE internal waves are, to a first approximation, linear internal waves satisfying local dispersion relations. The simulated wavelengths of modes 1 and 2 range within 100-160 and 45-80 km, respectively. Their distributions reveal, to different degrees for both modes, a zonal asymmetry and a tendency of a poleward increase with stratification N and the Coriolis parameter f being responsible for these two features, respectively. Distributions of mode 1 wavelengths are found to be determined by both N and f, but those of mode 2 are mainly controlled by variations in N. Larger differences between the STORMTIDE wavelengths and those of the eigenvalue problem occur, particularly for mode 2, primarily in high-latitude oceans and the Kuroshio and Gulf Stream and their extensions.

关键词： Circulation Dynamics Internal waves Waves oceanic Atm Ocean Structure Phenomena Tides observational techniques and algorithms Satellite observations Mathematical and statistical techniques Spectral analysis models distribution Models and modeling Ocean models

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Analysis of Thundersnow Storms over Northern Colorado

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WEATHER AND FORECASTING 2015年第6期30卷 1469-1490页

作者： Kumjian, Matthew R. Deierling, Wiebke Penn State Univ Dept Meteorol University Pk PA 16802 USA Natl Ctr Atmospher Res Res Applicat Lab Boulder CO 80307 USA

Lightning flashes during snowstorms occur infrequently compared to warm-season convection. The rarity of such thundersnow events poses an additional hazard because the lightning is unexpected. Because cloud electrification in thundersnow storms leads to relatively few lightning discharges, studying thundersnow events may offer insights into mechanisms for charging and possible thresholds required for lightning discharges. Observations of four northern Colorado thundersnow events that occurred during the 2012/13 winter are presented. Four thundersnow events in one season strongly disagrees with previous climatologies that used surface reports, implying thundersnow may be more common than previously thought. Total lightning information from the Colorado Lightning Mapping Array and data from conterminous United States lightning detection networks are examined to investigate the snowstorms' electrical properties and to compare them to typical warm-season thunderstorms. Data from polarimetric WSR-88Ds near Denver, Colorado, and Cheyenne, Wyoming, are used to reveal the storms' microphysical structure and determine operationally relevant signatures related to storm electrification. Most lightning occurred within convective cells containing graupel and pristine ice. However, one flash occurred in a stratiform snowband, apparently triggered by a tower. Depolarization streaks were observed in the radar data prior to the flash, indicating electric fields strong enough to orient pristine ice crystals. Direct comparisons of similar lightning- and nonlightning-producing convective cells reveal that though both cells likely produced graupel, the lightning-producing cell had larger values of specific differential phase K-DP and polarimetric radar-derived ice mass. Compared to warm-season thunderstorms, the analyzed thundersnow storms had similar electrical properties but lower flash rates and smaller vertical depths, suggesting they are weaker, ordinary thunderstorms lacking any w

关键词： Atm/Ocean Structure/ Phenomena Lightning Snow observational techniques and algorithms Radars/Radar observations

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Biases in Thorpe-Scale Estimates of Turbulence Dissipation. Part I: Assessments from Large-Scale Overturns in Oceanographic Data

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第10期45卷 2497-2521页

作者： Mater, Benjamin D. Venayagamoorthy, Subhas K. St Laurent, Louis Moum, James N. Colorado State Univ Dept Civil & Environm Engn Ft Collins CO 80523 USA Woods Hole Oceanog Inst Woods Hole MA 02543 USA Oregon State Univ Coll Earth Ocean & Atmospher Sci Corvallis OR 97331 USA

Oceanic density overturns are commonly used to parameterize the dissipation rate of turbulent kinetic energy. This method assumes a linear scaling between the Thorpe length scale L-T and the Ozmidov length scale L-O. Historic evidence supporting L-T similar to L-O has been shown for relatively weak shear-driven turbulence of the thermocline;however, little support for the method exists in regions of turbulence driven by the convective collapse of topographically influenced overturns that are large by open-ocean standards. This study presents a direct comparison of L-T and L-O, using vertical profiles of temperature and microstructure shear collected in the Luzon Straita site characterized by topographically influenced overturns up to O(100) m in scale. The comparison is also done for open-ocean sites in the Brazil basin and North Atlantic where overturns are generally smaller and due to different processes. A key result is that L-T/L-O increases with overturn size in a fashion similar to that observed in numerical studies of Kelvin-Helmholtz (K-H) instabilities for all sites but is most clear in data from the Luzon Strait. Resultant bias in parameterized dissipation is mitigated by ensemble averaging;however, a positive bias appears when instantaneous observations are depth and time integrated. For a series of profiles taken during a spring tidal period in the Luzon Strait, the integrated value is nearly an order of magnitude larger than that based on the microstructure observations. Physical arguments supporting L-T similar to L-O are revisited, and conceptual regimes explaining the relationship between L-T/L-O and a nondimensional overturn size (L-T) over cap are proposed. In a companion paper, Scotti obtains similar conclusions from energetics arguments and simulations.

关键词： Circulation Dynamics Diapycnal mixing Small scale processes Turbulence Atm Ocean Structure Phenomena Mixing observational techniques and algorithms Profilers oceanic Models and modeling Parameterization

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