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Global Wavenumber Spectrum with Corrections for Altimeter High-Frequency Noise

JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第2期45卷 495-503页

作者： Zhou, Xiao-Hui Wang, Dong-Ping Chen, Dake Second Inst Oceanog State Key Lab Satellite Ocean Environm Dynam Hangzhou Zhejiang Peoples R China SUNY Stony Brook Sch Marine & Atmospher Sci Stony Brook NY 11790 USA

The altimetry wavenumber spectra of sea surface height (SSH) provide a unique dataset for testing of geostrophic turbulence. While SSH spectral slopes of k(-11/3) and k(-5) are expected from theories and numerical simulations, the altimetry spectra from the original unfiltered and instrument noise-corrected data often are too shallow, falling between k(-2) and k(-3). In this study, the possibility that the flattened spectral slopes are partly due to contamination by unresolved high-frequency (<10 days) motions is tested. A spatiotemporal filter based on empirical orthogonal function expansion (EOF) is used to remove the temporally incoherent signals. The resulting spectral slopes are much steeper than in the previous studies. Over 70% of the revised global spectral estimates, excluding the tropics, are above k(-3). Moreover, in high energy regions like the Gulf Stream and Kuroshio, the spectral slopes are about k(-5), which is consistent with the classical quasigeostrophic (QG) turbulence. The spectral slopes are validated with the eddy kinetic energy (EKE) spectra from shipboard acoustic Doppler current profiler (ADCP) measurements in the high and low energy regions.

关键词： Circulation/ Dynamics Eddies Mesoscale processes observational techniques and algorithms Altimetry

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Nonstationary Internal Tides Observed Using Dual-Satellite Altimetry

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第9期45卷 2239-2246页

作者： Zaron, E. D. Portland State Univ Dept Civil & Environm Engn Portland OR 97207 USA

Dual-satellite crossover data from the Jason-2 and Cryosat-2 altimeter missions are used in a novel approach to quantify stationary and nonstationary tides from time-lagged mean square sea surface height (SSH) differences, computed for lags from 1 to 1440 h (60 days). The approach is made feasible by removing independent estimates of the stationary tide and mesoscale SSH variance, which greatly reduces the sampling error of the SSH statistics. For the semidiurnal tidal band, the stationary tidal variance is approximately 0.73 cm(2), and the nonstationary variance is about 0.33 cm(2), or 30% of the total. The temporal correlation of the nonstationary tide is examined by complex demodulation and found to be oscillatory with first 0 crossing at 400 h (17 days). Because a significant fraction of the time-variable mesoscale signal is resolved at time scales of roughly 150 h by the present constellation of satellite altimeters, the results suggest that it may be feasible to predict the nonstationary tide from modulations of the resolved mesoscale, thus enhancing the efficacy of tidal corrections for planned wide-swath altimeters such as the Surface Water and Ocean Topography (SWOT) mission.

关键词： Circulation/ Dynamics Internal waves Atm/Ocean Structure/ Phenomena Tides observational techniques and algorithms Satellite observations

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Automated Retrieval of Cloud and Aerosol Properties from the ARM Raman Lidar. Part II: Extinction

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2015年第11期32卷 1999-2023页

作者： Thorsen, Tyler J. Fu, Qiang Univ Washington Dept Atmospher Sci Seattle WA 98195 USA Lanzhou Univ Coll Atmospher Sci Lanzhou 730000 Peoples R China

A feature detection and extinction retrieval (FEX) algorithm for the Atmospheric Radiation Measurement Program's (ARM) Raman lidar (RL) has been developed. Presented here is Part II of the FEX algorithm: the retrieval of cloud and aerosol extinction profiles. The directly retrieved extinction profiles using the Raman method are supplemented by other retrieval methods developed for elastic backscatter lidars. Portions of features where the extinction-to-backscatter ratios (i.e., lidar ratios) can be obtained are used to infer the lidar ratios for the regions where no such estimate can be made. When neither directly retrieved nor an inferred value can be determined, a climatological lidar ratio is used. This best-estimate approach results in the need to use climatological lidar ratios for less than about 5% of features, except for thin cirrus at the ARM tropical western Pacific Darwin site, where above 12 km, about 20% of clouds use a climatological lidar ratio. A classification of feature type is made, guided by the atmosphere's thermodynamic state and the feature's scattering properties: lidar ratio, backscatter, and depolarization. The contribution of multiple scattering is explicitly considered for each of the ARM RL channels. A comparison between aerosol optical depth from FEX and that from collocated sun photometers over multiple years at two ARM sites shows an agreement (in terms of bias error) of about -0.3% to -4.3% (relative to the sun photometer).

关键词： Physical Meteorology and Climatology Aerosols observational techniques and algorithms Cloud retrieval Lidars Lidar observations Remote sensing

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Cyclones and Anticyclones in Seismic Imaging

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第9期45卷 2436-2443页

作者： Barbosa Aguiar, A. C. Menesguen, C. Le Gentil, S. Schopp, R. Carton, X. IFREMER Lab Phys Oceans Brest France UBO UEB Lab Phys Oceans Brest France

Nearly all the subsurface eddies detected in seismic imaging of sections in the northeast Atlantic have been assumed to be anticyclones containing Mediterranean Water (MW). Fewer MW cyclones have been observed and studied. In this study, the work of previous numerical studies is extended to investigate some characteristics of layering surrounding MW cyclones, using a primitive equation model with equal diffusivities for salinity and temperature to suppress the effects of double diffusion. It is shown that, after a stable state is reached, both anticyclones and cyclones display similar patterns of layering: stacked thin layers of high acoustic reflectivity located above and below the core of each vortex, which do not match isopycnals. The authors conclude that it should not be possible to distinguish between MW cyclones and anticyclones based on their signature in seismic imaging alone. Complementary information is needed to determine the sense of rotation.

关键词： Geographic location/entity North Atlantic Ocean Circulation/ Dynamics Small scale processes Atm/Ocean Structure/ Phenomena Eddies Vortices observational techniques and algorithms Acoustic measurements/effects Models and modeling Primitive equations model

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An In-Depth Evaluation of Heritage algorithms for Snow Cover and Snow Depth Using AMSR-E and AMSR2 Measurements

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2015年第12期32卷 2319-2336页

作者： Lee, Yong-Keun Kongoli, Cezar Key, Jeffrey Univ Wisconsin CIMSS Madison WI 53706 USA Univ Maryland Cooperat Inst Climate & Satellites College Pk MD 20742 USA NOAA NESDIS Ctr Satellite Applicat & Res Madison WI USA

The Advanced Microwave Scanning Radiometer 2 (AMSR2) was launched in 2012 on board the Global Change Observation Mission 1st-Water (GCOM-W1) satellite. This study presents a robust evaluation of AMSR2 algorithms for the retrieval of snow-covered area (SCA) and snow depth (SD) that will be used operationally by the National Oceanic and Atmospheric Administration (NOAA). Quantitative assessment of the algorithms was performed for a 10-yr period with AMSR-E and a 2-yr period with AMSR2 data using the NOAA Interactive Multisensor Snow and Ice Mapping System (IMS) snow cover and in situ SD data as references. AMSR-E SCA showed a monthly overall accuracy rate of about 80% except in May. Accuracy improves significantly to over 90% when wet snow cases are excluded, and accuracy differences between ascending and descending portions of orbits also decrease. Microwave-derived SCA over dry snow areas can therefore be obtained with accuracy close to optically derived SCA. An evaluation of the results for AMSR-E SD showed a low overall bias of 1 cm and a root-mean-square error of 20 cm. Results for AMSR2-based SCA and SD are similar to those from AMSR-E. Biases and root-mean-square errors show dependencies on elevation, forest fraction, the magnitude of snow depth, and snow cover class.

关键词： Atm/Ocean Structure/ Phenomena Snow Physical Meteorology and Climatology Snow cover observational techniques and algorithms Microwave observations Remote sensing Satellite observations

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Aircraft Observations and Numerical Simulations of the Developing Stage of a Southerly Surge near Southern California

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MONTHLY WEATHER REVIEW 2015年第12期143卷 4883-4903页

作者： Parish, Thomas R. Rahn, David A. Leon, Dave Univ Wyoming Dept Atmospher Sci Laramie WY 82071 USA Univ Kansas Dept Geog & Atmospher Sci Lawrence KS 66045 USA

Summertime low-level winds in the marine boundary layer off the California coast are predominantly from the north. This pattern is interrupted periodically by southerly winds and low stratus that can propagate for hundreds of kilometers northward along the coast. These events have been termed coastally trapped disturbances, coastally trapped wind reversals, and southerly surges;their forcing has been the subject of extensive study and debate. Southerly surges remain difficult to forecast, yet have a significant impact on coastal *** beginning stage of a southerly surge on 16 June 2012 was explored during the Precision Atmospheric Marine Boundary Layer Experiment. Measurements of the horizontal wind and pressure field in the marine layer offshore from Cape Arguello hours prior to the onset of the surge were made using the University of Wyoming King Air research aircraft. Airborne measurements show that a horizontal pressure field is established with higher pressure to the south just prior to the surge, supporting southerly ageostrophic winds and a south-to-north movement of marine stratus. Aircraft soundings and lidar returns confirm the existence of offshore flow of warm, continental air north of Point Arguello that alters the pressure field adjacent to the coast. The southerly surge originates near Point Arguello and propagates northward past San Francisco during the early morning hours on 17 June 2012. Results from the Weather Research and Forecasting Model are consistent with the King Air observations. Analyses and model output presented here confirm that the large-scale environment is critical to the initiation of these wind reversals.

关键词： Circulation Dynamics Coastal flows Atm Ocean Structure Phenomena Marine boundary layer Physical Meteorology and Climatology Coastal meteorology observational techniques and algorithms Aircraft observations

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Inherent Bounds on Forecast Accuracy due to Observation Uncertainty Caused by Temporal Sampling

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MONTHLY WEATHER REVIEW 2015年第10期143卷 4236-4243页

作者： Mittermaier, Marion P. Stephenson, David B. Met Off Numer Modelling Weather Sci Exeter EX1 3PB Devon England Univ Exeter Dept Math & Comp Sci Exeter Climate Syst Exeter Devon England

Synoptic observations are often treated as error-free representations of the true state of the real world. For example, when observations are used to verify numerical weather prediction (NWP) forecasts, forecast-observation differences (the total error) are often entirely attributed to forecast inaccuracy. Such simplification is no longer justifiable for short-lead forecasts made with increasingly accurate higher-resolution models. For example, at least 25% of t + 6 h individual Met Office site-specific (postprocessed) temperature forecasts now typically have total errors of less than 0.2 K, which are comparable to typical instrument measurement errors of around 0.1 K. In addition to instrument errors, uncertainty is introduced by measurements not being taken concurrently with the forecasts. For example, synoptic temperature observations in the United Kingdom are typically taken 10 min before the hour, whereas forecasts are generally extracted as instantaneous values on the hour. This study develops a simple yet robust statistical modeling procedure for assessing how serially correlated subhourly variations limit the forecast accuracy that can be achieved. The methodology is demonstrated by application to synoptic temperature observations sampled every minute at several locations around the United Kingdom. Results show that subhourly variations lead to sizeable forecast errors of 0.16-0.44 K for observations taken 10 min before the forecast issue time. The magnitude of this error depends on spatial location and the annual cycle, with the greater errors occurring in the warmer seasons and at inland sites. This important source of uncertainty consists of a bias due to the diurnal cycle, plus irreducible uncertainty due to unpredictable subhourly variations that fundamentally limit forecast accuracy.

关键词： observational techniques and algorithms Sampling Surface observations Mathematical and statistical techniques Numerical analysis modeling Statistical techniques Forecasting Forecast verification skill

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Wave-Induced Boundary Layer Separation in the Lee of the Medicine Bow Mountains. Part I: Observations

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2015年第12期72卷 4845-4863页

作者： French, Jeffrey R. Haimov, Samuel J. Oolman, Larry D. Grubisic, Vanda Serafin, Stefano Strauss, Lukas Univ Wyoming Dept Atmospher Sci Laramie WY 82071 USA Natl Ctr Atmospher Res Boulder CO USA Univ Vienna Dept Meteorol & Geophys Vienna Austria

Two cases of mountain waves, rotors, and the associated turbulence in the lee of the Medicine Bow Mountains in southeastern Wyoming are investigated in a two-part study using aircraft observations and numerical simulations. In Part I, observations from in situ instruments and high-resolution cloud radar on board the University of Wyoming King Air aircraft are presented and analyzed. Measurements from the radar compose the first direct observations of wave-induced boundary layer *** data from these two events show some striking similarities but also significant differences. In both cases, rotors were observed;yet one looks like a classical lee-wave rotor, while the other resembles an atmospheric hydraulic jump with midtropospheric gravity wave breaking aloft. High-resolution (30 x 30 m(2)) dual-Doppler syntheses of the two-dimensional velocity fields in the vertical plane beneath the aircraft reveal the boundary layer separation, the scale and structure of the attendant rotors, and downslope windstorms. In the stronger of the two events, near-surface winds upwind of the boundary layer separation reached 35 m s(-1), and vertical winds were in excess of 10 m s(-1). Moderate to strong turbulence was observed within and downstream of these regions. In both cases, the rotor extended horizontally 5-10 km and vertically 2-2.5 km. Horizontal vorticity within the rotor zone reached 0.2 s(-1). Several subrotors from 500 to 1000 m in diameter were identified inside the main rotor in one of the *** II presents a modeling study and investigates the kinematic structure and the dynamic evolution of these two events.

关键词： Circulation Dynamics Mountain waves Turbulence Wave breaking observational techniques and algorithms Aircraft observations Radars Radar observations

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Precipitation Properties Observed during Tropical Cyclone Intensity Change

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MONTHLY WEATHER REVIEW 2015年第11期143卷 4476-4492页

作者： Alvey, George R., III Zawislak, Jonathan Zipser, Edward Univ Utah Dept Atmospher Sci Salt Lake City UT USA Florida Int Univ Dept Earth & Environm Miami FL 33199 USA

Using a 15-yr (1998-2012) multiplatform dataset of passive microwave satellite data [tropical cyclone-passive microwave (TC-PMW)] for Atlantic and east Pacific storms, this study examines the relative importance of various precipitation properties, specifically convective intensity, symmetry, and area, to the spectrum of intensity changes observed in tropical cyclones. Analyses are presented not only spatially in shear-relative quadrants around the center, but also every 6 h during a 42-h period encompassing 18 h prior to onset of intensification to 24 h after. Compared to those with slower intensification rates, storms with higher intensification rates (including rapid intensification) have more symmetric distributions of precipitation prior to onset of intensification, as well as a greater overall areal coverage of precipitation. The rate of symmetrization prior to, and during, intensification increases with increasing intensity change as rapidly intensifying storms are more symmetric than slowly intensifying storms. While results also clearly show important contributions from strong convection, it is concluded that intensification is more closely related to the evolution of the areal, radial, and symmetric distribution of precipitation that is not necessarily intense.

关键词： Geographic location entity Atlantic Ocean North Pacific Ocean Atm Ocean Structure Phenomena Tropical cyclones observational techniques and algorithms Microwave observations Satellite observations Forecasting Short-range prediction

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Analysis and Interpretation of Frequency-Wavenumber Spectra of Young Wind Waves

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第10期45卷 2484-2496页

作者： Leckler, Fabien Ardhuin, Fabrice Peureux, Charles Benetazzo, Alvise Bergamasco, Filippo Dulov, Vladimir Serv Hydrog & Oceanog Marine Brest France IFREMER Ctr Brest Lab Oceanog Spatiale Plouzane France UMR 6523 CNRS IFREMER IRD UBO Lab Phys Oceans Plouzane France Natl Res Council CNR ISMAR Inst Marine Sci Venice Italy Univ Ca Foscari Venezia Venice Italy Inst Marine Hydrophys Sebastopol Russia

The energy level and its directional distribution are key observations for understanding the energy balance in the wind-wave spectrum between wind-wave generation, nonlinear interactions, and dissipation. Here, properties of gravity waves are investigated from a fixed platform in the Black Sea, equipped with a stereo video system that resolves waves with frequency f up to 1.4 Hz and wavelengths from 0.6 to 11 m. One representative record is analyzed, corresponding to young wind waves with a peak frequency f(p) = 0.33 Hz and a wind speed of 13 m s(-1). These measurements allow for a separation of the linear waves from the bound second-order harmonics. These harmonics are negligible for frequencies f up to 3 times f(p) but account for most of the energy at higher frequencies. The full spectrum is well described by a combination of linear components and the second-order spectrum. In the range 2f(p) to 4f(p), the full frequency spectrum decays like f(-5), which means a steeper decay of the linear spectrum. The directional spectrum exhibits a very pronounced bimodal distribution, with two peaks on either side of the wind direction, separated by 150 degrees at 4f(p). This large separation is associated with a significant amount of energy traveling in opposite directions and thus sources of underwater acoustic and seismic noise. The magnitude of these sources can be quantified by the overlap integral I(f), which is found to increase sharply from less than 0.01 at f = 2f(p) to 0.11 at f = 4f(p) and possibly up to 0.2 at f = 5f(p), close to the 0.5 value proposed in previous studies.

关键词： Circulation Dynamics Waves oceanic observational techniques and algorithms Remote sensing

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