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Characterization of the Variability of the South Pacific Convergence Zone Using Satellite and Reanalysis Wind Products

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JOURNAL OF CLIMATE 2016年第5期29卷 1717-1732页

作者： Kidwell, Autumn Lee, Tong Jo, Young-Heon Yan, Xiao-Hai Univ Delaware Coll Earth Ocean & Environm 215 Robinson Hall Newark DE 19716 USA CALTECH Jet Prop Lab Pasadena CA USA Pusan Natl Univ Dept Oceanog Busan South Korea Univ Delaware Xiamen Univ Joint Inst Coastal Res & Management Newark DE 19716 USA

The variability of the South Pacific convergence zone (SPCZ) is evaluated using ocean surface wind products derived from the atmospheric reanalysis ERA-Interim for the period of 1981-2014 and QuickSCAT for the period of 1999-2009. From these products, indices were developed to represent the SPCZ strength, area, and centroid location. Excellent agreement is found between the indices derived from the two wind products during the QuikSCAT period in terms of the spatiotemporal structures of the SPCZ. The longer ERA-Interim product is used to study the variations of SPCZ properties on intraseasonal, seasonal, interannual, and decadal time scales. The SPCZ strength, area, and centroid latitude have a dominant seasonal cycle. In contrast, the SPCZ centroid longitude is dominated by intraseasonal variability due to MJO influence. The SPCZ indices are all correlated with El Nino-Southern Oscillation indices. Interannual and intraseasonal variations of SPCZ strength during strong El Nino are approximately twice as large as the respective seasonal variations. SPCZ strength depends more on the intensity of El Nino rather than the central-Pacific versus eastern-Pacific type. The change from positive to negative Pacific decadal oscillation (PDO) around 1999 results in a westward shift of the SPCZ centroid longitude, a much smaller interannual swing in centroid latitude, and a decrease in SPCZ area. This study improves the understanding of the variations of the SPCZ on multiple time scales and reveals the variations of SPCZ strength not reported previously. The diagnostics analyses can be used to evaluate climate models to gauge their fidelity.

关键词： Variability Interannual variability Satellite observations Pacific decadal oscillation Circulation/ Dynamics observational techniques and algorithms Decadal variability ENSO Tropical variability

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Applying Automated Underway Ship Observations to Numerical Model Evaluation

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第3期33卷 409-428页

作者： Smith, Shawn R. Briggs, Kristen Lopez, Nicolas Kourafalou, Vassiliki Florida State Univ Ctr Ocean Atmospher Predict Studies POB 3062741 Tallahassee FL 32306 USA Univ Miami Rosenstiel Sch Marine & Atmospher Sci Dept Ocean Sci 4600 Rickenbacker Causeway Miami FL 33149 USA

Numerical models are used widely in the oceanic and atmospheric sciences to estimate and forecast conditions in the marine environment. Herein the application of in situ observations collected by automated instrumentation on ships at sampling rates <= 5 min is demonstrated as a means to evaluate numerical model analyses. Specific case studies use near-surface ocean observations collected by a merchant vessel, an ocean racing yacht, and select research vessels to evaluate various ocean analyses from the Hybrid Coordinate Ocean Model (HYCOM). Although some specific differences are identified between the observations and numerical model analyses, the purpose of these comparisons is to demonstrate the value of high-sampling-rate in situ observations collected on ships for numerical model evaluation.

关键词： Ship observations Automatic weather stations Ocean models Model evaluation/performance In situ atmospheric observations observational techniques and algorithms Models and modeling In situ oceanic observations

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Practical Approximations to Seasonal Fluctuation-Dissipation Operators Given a Limited Sample

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第6期73卷 2529-2545页

作者： Fuchs, David Sherwood, Steven Univ New S Wales ARC Ctr Excellence Climate Syst Sci Sydney NSW Australia Univ New S Wales Climate Change Res Ctr Sydney NSW Australia

This paper studies operators inspired by the fluctuation-dissipation theorem that consider the seasonality (nonstationarity) of the climate system under conditions of limited sample size relevant to application of the method to observational records. The approach is used to predict the steady-state response of an atmospheric general circulation model to localized temperature perturbations. A seasonal operator nominally requires a much larger data sample than a stationary operator;the authors study some strategies to overcome this. First, two methods for approximating the seasonality of the system are examined. Second, an alternative "transpose approach" to the standard dimension reduction is considered that is more efficient and accurate for small sample sizes and additionally enables the use of a kernel, which provides a convenient way to incorporate prior physical understanding into the operator. All operators show considerable skill in predicting seasonal responses for a variety of variables (temperature, winds, rainfall, and cloud cover) and better skill in predicting the annual-mean ones. A comparison of these predictions to ones done on the same system with temporally fixed boundary conditions shows unexpectedly that skill is, if anything, improved by the presence of a seasonal cycle. The authors suggest that the extra complexity due to a seasonal systemis outweighed by the added information due to the seasonal forcing and the effect of seasonality in smoothing out prediction errors.

关键词： Atmospheric circulation Circulation/ Dynamics Climate variability observational techniques and algorithms Sensitivity studies Variability

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An Impact Study of GPS Radio Occultation Observations on Frontal Rainfall Prediction with a Local Bending Angle Operator

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WEATHER AND FORECASTING 2016年第1期31卷 129-150页

作者： Huang, Ching-Yuang Chen, Shu-Ya Anisetty, S. K. A. V. Prasad Rao Yang, Shu-Chih Hsiao, Ling-Feng Natl Cent Univ Dept Atmospher Sci Jhongli Taiwan Natl Cent Univ GPS Sci & Applicat Res Ctr Jhongli Taiwan Univ Corp Atmospheric Res Boulder CO USA Taiwan Typhoon & Flood Res Inst Taipei Taiwan

The impact of global positioning system (GPS) radio occultation (RO) soundings on the prediction of severe mei-yu frontal rainfall near Taiwan in June 2012 was investigated in this study using a developed local bending angle (LBA) operator. Two operators for local refractivity (REF) and nonlocal refractivity [excess phase (EPH)] were also used for comparisons. The devised LBA simplifies the calculation of the Abel transform in inverting model local refractivity without a loss of accuracy. These operators have been implemented into the three-dimensional variational data assimilation system of the Weather Research and Forecasting (WRF) Model to assimilate GPS RO soundings available from the Formosa Satellite Mission 3/Constellation Observing Systems for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC). The RO data are found to be beneficial to the WRF forecast of local severe rainfall in Taiwan. Characteristics of assimilation performance and innovation for the three operators are discussed. Both of the local operators performing assimilation at observation levels appear to produce mostly larger positive moisture increments than do the current nonlocal operators performing assimilation on the mean height of each model vertical level. As the information of the initial increments has propagated farther south with the frontal flow, the simulation for LBA shows better prediction of rainfall peaks in Taiwan on the second day than both REF and EPH, with a maximum improvement of about 25%. The positive impact of the RO data results partially from several RO observations near Mongolia and north China. This study provides an intercomparison among the three RO operators, and shows the feasibility of regional assimilation with LBA.

关键词： observational techniques and algorithms Numerical weather prediction/forecasting Forecasting Occultation

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Global Water Vapor Trend from 1988 to 2011 and Its Diurnal Asymmetry Based on GPS, Radiosonde, and Microwave Satellite Measurements

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JOURNAL OF CLIMATE 2016年第14期29卷 5205-5222页

作者： Wang, Junhong Dai, Aiguo Mears, Carl SUNY Albany Dept Atmospher & Environm Sci 1400 Washington Ave Albany NY 12222 USA Natl Ctr Atmospher Res POB 3000 Boulder CO 80307 USA Remote Sensing Syst Santa Rosa CA USA

This study analyzes trends in precipitable water (PW) over land and ocean from 1988 to 2011, the PW-surface temperature T-s relationship, and their diurnal asymmetry using homogenized radiosonde data, microwave satellite observations, and ground-based global positioning system (GPS) measurements. It is found that positive PW trends predominate over the globe, with larger magnitudes over ocean than over land. The PW trend is correlated with surface warming spatially over ocean with a pattern correlation coefficient of 0.51. The PW percentage increase rate normalized by T-s expressed as d lnPW/dT(s) is larger and closer to the rate implied by the Clausius-Clapeyron (C-C) equation over ocean than over land. The 2-hourly GPS PW data show that the PW trend from 1995 to 2011 is larger at night than during daytime. Nighttime PW monthly anomalies correlate positively and significantly with nighttime minimum temperature T-min at all stations, but this is not true for daytime PW and maximum temperature T-max. The ratio of relative PW changes with T-min (dlnPW/dT(min)) is larger and closer to the C-C equation's implied value of similar to 7% K (1)than d lnPW/dT(max). This suggests that the relationship between PW and T-s at night is a better indicator of the water vapor feedback than that during daytime, when clouds and other factors also influence T-s.

关键词： Physical Meteorology and Climatology Climate change Water vapor observational techniques and algorithms Radiosonde observations Satellite observations Variability Diurnal effects Trends

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Comparison of Direct Covariance Flux Measurements from an Offshore Tower and a Buoy

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第5期33卷 873-890页

作者： Flugge, Martin Paskyabi, Mostafa Bakhoday Reuder, Joachim Edson, James B. Plueddemann, Albert J. Univ Bergen N-5020 Bergen Norway Bjerknes Ctr Climate Res Bergen Norway Univ Connecticut Groton CT USA Woods Hole Oceanog Inst Woods Hole MA 02543 USA Christian Michelsen Res AS Bergen Norway

Direct covariance flux (DCF) measurements taken from floating platforms are contaminated by wave-induced platform motions that need to be removed before computation of the turbulent fluxes. Several correction algorithms have been developed and successfully applied in earlier studies from research vessels and, most recently, by the use of moored buoys. The validation of those correction algorithms has so far been limited to short-duration comparisons against other floating platforms. Although these comparisons show in general a good agreement, there is still a lack of a rigorous validation of the method, required to understand the strengths and weaknesses of the existing motion-correction algorithms. This paper attempts to provide such a validation by a comparison of flux estimates from two DCF systems, one mounted on a moored buoy and one on the Air-Sea Interaction Tower (ASIT) at the Martha's Vineyard Coastal Observatory, Massachusetts. The ASIT was specifically designed to minimize flow distortion over a wide range of wind directions from the open ocean for flux measurements. The flow measurements from the buoy system are corrected for wave-induced platform motions before computation of the turbulent heat and momentum fluxes. Flux estimates and cospectra of the corrected buoy data are found to be in very good agreement with those obtained from the ASIT. The comparison is also used to optimize the filter constants used in the motion-correction algorithm. The quantitative agreement between the buoy data and the ASIT demonstrates that the DCF method is applicable for turbulence measurements from small moving platforms, such as buoys.

关键词： Circulation/ Dynamics Turbulence Atm/Ocean Structure/ Phenomena Boundary layer Physical Meteorology and Climatology Air-sea interaction observational techniques and algorithms Buoy observations Quality assurance/control

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A Case Study on the Far-Field Properties of Propagating Tropospheric Gravity Waves

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MONTHLY WEATHER REVIEW 2016年第8期144卷 2947-2961页

作者： Stephan, Claudia C. Alexander, M. Joan Hedlin, Michael de Groot-Hedlin, Catherine D. Hoffmann, Lars Univ Colorado Dept Atmospher & Ocean Sci Boulder CO 80309 USA Northwest Res Associates Inc CoRA Off Boulder CO USA Univ Calif San Diego Lab Atmospher Acoust San Diego CA 92103 USA Forschungszentrum Julich Julich Supercomp Ctr Julich Germany Univ Reading Dept Meteorol Natl Ctr Atmospher Sci Climate Reading Berks England

Mesoscale gravity waves were observed by barometers deployed as part of the USArray Transportable Array on 29 June 2011 near two mesoscale convective systems in the Great Plains region of the United States. Simultaneously, AIRS satellite data indicated stratospheric gravity waves propagating away from the location of active convection. Peak perturbation pressure values associated with waves propagating outside of regions where there was precipitation reached amplitudes close to 400 Pa at the surface. Here the origins of the waves and their relationship to observed precipitation are investigated with a specialized model study. Simulations with a 4-km resolution dry numerical model reproduce the propagation characteristics and amplitudes of the observed waves with a high degree of quantitative similarity despite the absence of any boundary layer processes, surface topography, or moist physics in the model. The model is forced with a three-dimensional, time-dependent latent heating/cooling field that mimics the latent heating inside the precipitation systems. The heating is derived from the network of weather radar precipitation observations. This shows that deep, intense latent heat release within the precipitation systems is the key forcing mechanism for the waves observed at ground level by the USArray. Furthermore, the model simulations allow for a more detailed investigation of the vertical structure and propagation characteristics of the waves. It is found that the stratospheric and tropospheric waves are triggered by the same sources, but have different spectral properties. Results also suggest that the propagating tropospheric waves may potentially remotely interact with and enhance active precipitation.

关键词： Atm/Ocean Structure/ Phenomena Storm environments Synoptic-scale processes observational techniques and algorithms Radars/Radar observations Satellite observations Surface observations Models and modeling Numerical analysis/modeling

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Shortwave Radiative Fluxes on Slopes

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JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2016年第7期55卷 1513-1532页

作者： Ma, Yingtao Pinker, Rachel T. Wonsick, Margaret M. Li, Chuan Hinkelman, Laura M. Univ Maryland Dept Atmospher & Ocean Sci Comp & Space Sci Bldg College Pk MD 20742 USA Univ Washington Joint Inst Study Atmosphere & Ocean Seattle WA 98195 USA

Snow-covered mountain ranges are a major source of water supply for runoff and groundwater recharge. Snowmelt supplies as much as 75% of the surface water in basins of the western United States. Net radiative fluxes make up about 80% of the energy balance over snow-covered surfaces. Because of the large extent of snow cover and the scarcity of ground observations, use of remotely sensed data is an attractive option for estimating radiative fluxes. Most of the available methods have been applied to low-spatial-resolution satellite observations that do not capture the spatial variability of snow cover, clouds, or aerosols, all of which need to be accounted for to achieve accurate estimates of surface radiative fluxes. The objective of this study is to use high-spatial-resolution observations that are available from the Moderate Resolution Imaging Spectroradiometer (MODIS) to derive surface shortwave (0.2-4.0 mm) downward radiative fluxes in complex terrain, with attention on the effect of topography (e.g., shadowing or limited sky view) on the amount of radiation received. The developed method has been applied to several typical melt seasons (January-July during 2003, 2004, 2005, and 2009) over the western part of the United States, and the available information was used to derive metrics on spatial and temporal variability of shortwave fluxes. Issues of scale in both the satellite and ground observations are also addressed to illuminate difficulties in the validation process of satellite-derived quantities. It is planned to apply the findings from this study to test improvements in estimation of snow water equivalent.

关键词： Physical Meteorology and Climatology Budgets Radiation budgets Radiative fluxes Shortwave radiation observational techniques and algorithms algorithms Remote sensing

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Toward an Algorithm for Estimating Latent Heat Release in Warm Rain Systems

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第6期33卷 1309-1329页

作者： Nelson, Ethan L. L'Ecuyer, Tristan S. Saleeby, Stephen M. Berg, Wesley Herbener, Stephen R. van den Heever, Susan C. Univ Wisconsin Dept Atmospher & Ocean Sci 1225 W Dayton St Madison WI 53706 USA Colorado State Univ Ft Collins CO 80523 USA

This paper outlines an approach for estimating latent heating, surface rainfall rate, and liquid water path in warm rain from downward-viewing W-band radar observations using a Bayesian Monte Carlo algorithm. The algorithm utilizes observed vertical and path-integrated characteristics of precipitating liquid clouds to identify the most appropriate hydrometeor and latent heating structures in a large database of profiles generated using a cloud-resolving model. These characteristics are selected by applying multiple performance metrics to synthetic retrievals. Analysis of the retrievals suggests that a combination of cloud-top, rain-top, and maximum reflectivity heights;vertically integrated reflectivity and attenuation;and a measure of near-surface intensity is sufficient to constrain bulk properties and the vertical structure of warm rain systems. When applied to observations at CloudSat resolution, biases in retrieved liquid water path and surface rainfall rate are small (less than 10%). The algorithm also captures the vertical structure of latent heating, although the magnitudes of integrated heating and cooling exhibit nearly compensating low biases. Random errors are larger owing to the limitations of single-frequency radar observations in constraining drop size distributions. Uncertainties in the altitudes of peak heating and cooling at the pixel scale are typically less than one vertical level, while uncertainties in vertically resolved estimates of heating and cooling rates are on the order of a factor of 2. The utility of the technique is illustrated through application to case studies from airborne radar data from the VAMOS Ocean-Cloud-Atmosphere-Land Study field campaign and satellite observations from CloudSat.

关键词： Latent heating/cooling observational techniques and algorithms Physical Meteorology and Climatology Radars/Radar observations Satellite observations

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A Probabilistic Multispectral Pattern Recognition Method for Detection of Overshooting Cloud Tops Using Passive Satellite Imager Observations

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JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2016年第9期55卷 1983-2005页

作者： Bedka, Kristopher M. Khlopenkov, Konstantin NASA Langley Res Ctr Mail Stop 420 Hampton VA 23681 USA Sci Syst & Applicat Inc Hampton VA USA

Deep convective updrafts often penetrate through the surrounding cirrus anvil and into the lower stratosphere. Cross-tropopause transport of ice, water vapor, and chemicals occurs within these "overshooting tops'' (OTs) along with a variety of hazardous weather conditions. OTs are readily apparent in satellite imagery, and, given the importance of OTs for weather and climate, a number of automated satellite-based detection methods have been developed. Some of these methods have proven to be relatively reliable, and their products are used in diverse Earth science applications. Nevertheless, analysis of these methods and feedback from product users indicate that use of fixed infrared temperature-based detection criteria often induces biases that can limit their utility for weather and climate analysis. This paper describes a new multispectral OT detection approach that improves upon those previously developed by minimizing use of fixed criteria and incorporating pattern recognition analyses to arrive at an OT probability product. The product is developed and validated using OT and non-OT anvil regions identified by a human within MODIS imagery. The product offered high skill for discriminating between OTs and anvils and matched 69% of human OT identifications for a particular probability threshold with a false-detection rate of 18%, outperforming previously existing methods. The false-detection rate drops to 1% when OT-induced texture detected within visible imagery is used to constrain the IR-based OT probability product. The OT probability product is also shown to improve severe-storm detection over the United States by 20% relative to the best existing method.

关键词： Circulation/ Dynamics Deep convection Atm/Ocean Structure/ Phenomena Severe storms observational techniques and algorithms Satellite observations Mathematical and statistical techniques Pattern detection Forecasting Mesoscale forecasting

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