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An Assessment of Diurnal and Seasonal Cloud Cover Changes over the Hawaiian Islands Using Terra and Aqua MODIS

JOURNAL OF CLIMATE 2016年第1期29卷 77-90页

作者： Barnes, Mallory L. Miura, Tomoaki Giambelluca, Thomas W. Univ Hawaii Manoa Dept Nat Resource & Environm Management Honolulu HI 96822 USA Univ Hawaii Manoa Dept Geog Honolulu HI 96822 USA

A comprehensive understanding of the spatial, seasonal, and diurnal patterns in cloud cover frequency over the Hawaiian Islands was developed using high-resolution image data from the National Aeronautics and Space Administration's Moderate Resolution Imaging Spectroradiometer (MODIS) sensors aboard the Terra and Aqua satellites. The Terra and Aqua MODIS cloud mask products, which provide the confidence that a given 1-km pixel is unobstructed by cloud, were obtained for the entire MODIS time series (10-plus years) over the main Hawaiian Islands. Monthly statistics were generated from the daily cloud mask data, including mean cloud cover frequency at the four daily overpass times. The derived mean cloud cover frequency showed patterns that were generally consistent with the known distribution of mean rainfall and with the results from previous studies. Cloud cover frequency was the highest over land areas with elevations between the lifting condensation level (similar to 600 m) and the mean height of the trade wind inversion (TWI) base (similar to 2200 m), especially for the windward (northeastern) mountain slopes. Above the TWI, cloud frequency decreased sharply with elevation. Irrespective of season, cloud cover frequency was generally higher in the afternoon than in the morning and higher in daytime than at nighttime although these trends varied spatially. The dry season months (May-October) were less cloudy than the wet season months (November-April) at nighttime. The analysis also revealed a local December-January minimum in the annual cycle of cloud cover frequency. The monthly time series produced in this study is the first high-spatial-resolution cloud cover dataset in Hawaii.

关键词： Geographic location entity Tropics Physical Meteorology and Climatology Climatology Cloud cover observational techniques and algorithms Remote sensing

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Improvements in Typhoon Intensity Change Classification by Incorporating an Ocean Coupling Potential Intensity Index into Decision Trees*^,+

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WEATHER AND FORECASTING 2016年第1期31卷 95-106页

作者： Gao, Si Zhang, Wei Liu, Jia Lin, I. -I. Chiu, Long S. Cao, Kai Nanjing Univ Informat Sci & Technol Minist Educ Int Joint Lab Climate & Environm Change Nanjing 210044 Jiangsu Peoples R China Nanjing Univ Informat Sci & Technol Minist Educ Key Lab Meteorol Disaster Nanjing 210044 Jiangsu Peoples R China Natl Taiwan Univ Dept Atmospher Sci Taipei 10764 Taiwan George Mason Univ Coll Sci Dept Atmospher Ocean & Earth Sci Fairfax VA 22030 USA Natl Univ Singapore Dept Geog Singapore 117548 Singapore

Tropical cyclone (TC) intensity prediction, especially in the warning time frame of 24-48 h and for the prediction of rapid intensification (RI), remains a major operational challenge. Sea surface temperature (SST) based empirical or theoretical maximum potential intensity (MPI) is the most important predictor in statistical intensity prediction schemes and rules derived by data mining techniques. Since the underlying SSTs during TCs usually cannot be observed well by satellites because of rain contamination and cannot be produced on a timely basis for operational statistical prediction, an ocean coupling potential intensity index (OC_PI), which is calculated based on pre-TC averaged ocean temperatures from the surface down to 100 m, is demonstrated to be important in building the decision tree for the classification of 24-h TC intensity change Delta V-24, that is, RI (Delta V-24 >= 25 kt, where 1 kt = 0.51 m s(-1)) and non-RI (Delta V-24 < 25 kt). Cross validations using 2000-10 data and independent verification using 2011 data are performed. The decision tree with the OC_PI shows a cross-validation accuracy of 83.5% and an independent verification accuracy of 89.6%, which outperforms the decision tree excluding the OC_PI with corresponding accuracies of 83.2% and 83.9%. Specifically for RI classification in independent verification, the former decision tree shows a much higher probability of detection and a lower false alarm ratio than the latter example. This study is of great significance for operational TC RI prediction as pre-TC OC_PI can skillfully reduce the overestimation of storm potential intensity by traditional SST-based MPI, especially for the non-RI TCs.

关键词： observational techniques and algorithms Geographic location/entity North Pacific Ocean Hurricanes/typhoons Statistical forecasting Classification Data mining Northern Hemisphere Forecasting Mathematical and statistical techniques Atm/Ocean Structure/ Phenomena

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Incorporating Diagnosed Intercept Parameters and the Graupel Category within the ARPS Cloud Analysis System for the Initialization of Double-Moment Microphysics: Testing with a Squall Line over South China

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MONTHLY WEATHER REVIEW 2016年第1期144卷 371-392页

作者： Pan, Yujie Xue, Ming Ge, Guoqing Nanjing Univ Informat Sci & Technol Collaborat Innovat Ctr Forecast & Evaluat Meteoro Key Lab Meteorol Disaster Minist Educ Nanjing Jiangsu Peoples R China Univ Oklahoma Ctr Anal & Predict Storms Norman OK 73019 USA Univ Oklahoma Sch Meteorol Norman OK 73019 USA Nanjing Univ Sch Atmospher Sci Nanjing 210008 Jiangsu Peoples R China

In this study, a new set of reflectivity equations are introduced into the Advanced Regional Prediction System (ARPS) cloud analysis system. This set of equations incorporates double-moment microphysics information in the analysis by adopting a set of diagnostic relationships between the intercept parameters and the corresponding mass mixing ratios. A reflectivity- and temperature-based graupel classification scheme is also implemented according to a hydrometeor identification (HID) diagram. A squall line that occurred on 23 April 2007 over southern China containing a pronounced trailing stratiform precipitation region is used as a test case to evaluate the impacts of the enhanced cloud analysis *** results show that using the enhanced cloud analysis scheme is able to better capture the characteristics of the squall line in the forecast. The predicted squall line exhibits a wider stratiform region and a more clearly defined transition zone between the leading convection and the trailing stratiform precipitation region agreeing better with observations in general, when using the enhanced cloud analysis together with the two-moment microphysics scheme. The quantitative precipitation forecast skill score is also improved.

关键词： Physical Meteorology and Climatology Cloud microphysics observational techniques and algorithms Cloud retrieval Models and modeling Data assimilation

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Volume and Freshwater Flux Observations from Nares Strait to the West of Greenland at Daily Time Scales from 2003 to 2009

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2016年第1期46卷 141-157页

作者： Muenchow, Andreas Univ Delaware Newark DE USA

Time series observations of velocity, salinity, pressure, and ice draft provide estimates of advective fluxes in Nares Strait from 2003 to 2009 at daily to interannual time scales. Velocity and salinity are integrated across the 36-km-wide and 350-m-deep channel for two distinct multiyear periods of sea ice cover. These observations indicate multiyear mean fluxes that range from 0.71 +/- 0.09 to 1.03 +/- 0.11 Sverdrups (Sv;1 Sv 10(6) m(3) s(-1) = 31 536 km(3) yr(-1)) for volume and from 32 +/- 5.7 to 54 +/- 9.3 mSv (1 mSv 10(3) m(3) s(-1)) for oceanic freshwater relative to a salinity of 34.8 for the first (2003-06) and second (2007-09) periods, respectively. Advection of ice adds another 8 +/- 2 mSv or 260 +/- 70 km(3) yr(-1) to the freshwater export. Flux values are larger when the sea ice is mobile all year. About 75% of the oceanic volume and freshwater flux variability is correlated at daily to interannual time scales. Flux variability peaks at a 20-day time scale and correlates strongly with along-channel pressure gradients (r(2) = 0.68). The along-channel pressure gradient peaks in early spring when the sea ice is often motionless with higher sea level in the Arctic that drives the generally southward ocean circulation. Local winds contribute only when the sea ice is mobile, when they explain 60% of its variance (r(2) = 0.60). Observed annual to interannual change in the duration of motionless sea ice conditions impacts ocean stratification and freshwater flux, while seasonal variations are small.

关键词： Geographic location entity Arctic Circulation Dynamics Baroclinic flows Channel flows Fluxes observational techniques and algorithms In situ oceanic observations Mathematical and statistical techniques Time series

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Assimilation of TRMM Multisatellite Precipitation Analysis with a Low-Resolution NCEP Global Forecast System

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MONTHLY WEATHER REVIEW 2016年第2期144卷 643-661页

作者： Lien, Guo-Yuan Miyoshi, Takemasa Kalnay, Eugenia 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

Current methods of assimilation of precipitation into numerical weather prediction models are able to make the model precipitation become similar to the observed precipitation during the assimilation, but the model forecasts tend to return to their original solution after a few hours. To facilitate the precipitation assimilation, a logarithm transformation has been used in several past studies. Lien et al. proposed instead to assimilate precipitation using the local ensemble transform Kalman filter (LETKF) with a Gaussian transformation technique and succeeded in improving the model forecasts in perfect-model observing system simulation experiments (OSSEs).In this study, the method of Lien et al. is tested within a more realistic configuration: the TRMM Multisatellite Precipitation Analysis (TMPA) data are assimilated into a low-resolution version of the NCEP Global Forecast System (GFS). With guidance from a statistical study comparing the GFS model background precipitation and the TMPA data, some modifications of the assimilation methods proposed in Lien et al. are made, including 1) applying separate Gaussian transformations to model and to observational precipitation based on their own cumulative distribution functions;2) adopting a quality control criterion based on the correlation between the long-term model and observed precipitation data at the observation location;and 3) proposing a new method to define the transformation of zero precipitation that takes into account the zero precipitation probability in the background ensemble rather than the climatology. With these modifications, the assimilation of the TMPA precipitation data improves both the analysis and 5-day model forecasts when compared with a control experiment assimilating only rawinsonde data.

关键词： Atm Ocean Structure Phenomena Precipitation observational techniques and algorithms Data quality control Satellite observations Models and modeling Data assimilation

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Daytime Cirrus Cloud Top-of-the-Atmosphere Radiative Forcing Properties at a Midlatitude Site and Their Global Consequences

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JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2016年第8期55卷 1667-1679页

作者： Campbell, James R. Lolli, Simone Lewis, Jasper R. Gu, Yu Welton, Ellsworth J. Naval Res Lab Monterey CA USA Univ Maryland Baltimore Cty Joint Ctr Earth Syst Technol Baltimore MD 21228 USA Univ Calif Los Angeles Los Angeles CA USA NASA Goddard Space Flight Ctr Greenbelt MD USA

One year of continuous ground-based lidar observations (2012) is analyzed for single-layer cirrus clouds at the NASA Micro Pulse Lidar Network site at the Goddard Space Flight Center to investigate top-of-the-atmosphere (TOA) annual net daytime radiative forcing properties. A slight positive net daytime forcing is estimated (i.e., warming): 0.07-0.67 Wm(-2) in sample-relative terms, which reduces to 0.03-0.27 W m(-2) in absolute terms after normalising to unity based on a 40% midlatitude occurrence frequency rate estimated from satellite data. Results are based on bookend solutions for lidar extinction-to-backscatter (20 and 30 sr) and corresponding retrievals of the 532-nm cloud extinction coefficient. Uncertainties due to cloud undersampling, attenuation effects, sample selection, and lidar multiple scattering are described. A net daytime cooling effect is found from the very thinnest clouds (cloud optical depth <= 0.01), which is attributed to relatively high solar zenith angles. A relationship involving positive/negative daytime cloud forcing is demonstrated as a function of solar zenith angle and cloud-top temperature. These properties, combined with the influence of varying surface albedos, are used to conceptualise how daytime cloud forcing likely varies with latitude and season, with cirrus clouds exerting less positive forcing and potentially net TOA cooling approaching the summer poles (not ice and snow covered) versus greater warming at the equator. The existence of such a gradient would lead cirrus to induce varying daytime TOA forcing annually and seasonally, making it a far greater challenge than presently believed to constrain the daytime and diurnal cirrus contributions to global radiation budgets.

关键词： Physical Meteorology and Climatology Cirrus clouds Cloud forcing Cloud radiative effects Energy budget/balance observational techniques and algorithms Lidars/Lidar observations

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Fast Playback Framework for Analysis of Ground-Based Doppler Radar Observations Using MapReduce Technology

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第4期33卷 621-634页

作者： Tang, Jingyin Matyas, Corene J. Univ Florida Dept Geog 3141 Turlington HallPOB 117315 Gainesville FL 32611 USA

The creation of a 3D mosaic is often the first step when using the high-spatial- and temporal-resolution data produced by ground-based radars. Efficient yet accurate methods are needed to mosaic data from dozens of radar to better understand the precipitation processes in synoptic-scale systems such as tropical cyclones. Research-grade radar mosaic methods of analyzing historical weather events should utilize data from both sides of a moving temporal window and process them in a flexible data architecture that is not available in most stand-alone software tools or real-time systems. Thus, these historical analyses require a different strategy for optimizing flexibility and scalability by removing time constraints from the design. This paper presents a MapReduce-based playback framework using Apache Spark's computational engine to interpolate large volumes of radar reflectivity and velocity data onto 3D grids. Designed as being friendly to use on a high-performance computing cluster, these methods may also be executed on a low-end configured machine. A protocol is designed to enable interoperability with GIS and spatial analysis functions in this framework. Open source software is utilized to enhance radar usability in the nonspecialist community. Case studies during a tropical cyclone landfall shows this framework's capability of efficiently creating a large-scale high-resolution 3D radar mosaic with the integration of GIS functions for spatial analysis.

关键词： observational techniques and algorithms Radars/Radar observations

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An Airborne and Ground-Based Study of a Long-Lived and Intense Atmospheric River with Mesoscale Frontal Waves Impacting California during CalWater-2014

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MONTHLY WEATHER REVIEW 2016年第3期144卷 1115-1144页

作者： Neiman, Paul J. Moore, Benjamin J. White, Allen B. Wick, Gary A. Aikins, Joshua Jackson, Darren L. Spackman, J. Ryan Ralph, F. Martin NOAA Earth Syst Res Lab Div Phys Sci Mail Code R-PSD2325 Broadway Boulder CO 80305 USA SUNY Albany Dept Atmospher & Environm Sci Albany NY 12222 USA Univ Colorado NOAA Cooperat Inst Res Environm Sci Boulder CO 80309 USA NOAA Earth Syst Res Lab Boulder CO 80305 USA NOAA Sci & Technol Corp Earth Syst Res Lab Boulder CO 80305 USA Univ Calif San Diego Scripps Inst Oceanog La Jolla CA 92093 USA

The wettest period during the CalWater-2014 winter field campaign occurred with a long-lived, intense atmospheric river (AR) that impacted California on 7-10 February. The AR was maintained in conjunction with the development and propagation of three successive mesoscale frontal waves. Based on Lagrangian trajectory analysis, moist air of tropical origin was tapped by the AR and was subsequently transported into California. Widespread heavy precipitation (200-400 mm) fell across the coastal mountain ranges northwest of San Francisco and across the northern Sierra Nevada, although only modest flooding ensued due to anomalously dry antecedent conditions. A NOAA G-IV aircraft flew through two of the frontal waves in the AR environment offshore during a ~24-h period. Parallel dropsonde curtains documented key three-dimensional thermodynamic and kinematic characteristics across the AR and the frontal waves prior to landfall. The AR characteristics varied, depending on the location of the cross section through the frontal waves. A newly implemented tail-mounted Doppler radar on the G-IV simultaneously captured coherent precipitation features. Along the coast, a 449-MHz wind profiler and collocated global positioning system (GPS) receiver documented prolonged AR conditions linked to the propagation of the three frontal waves and highlighted the orographic character of the coastal-mountain rainfall with the waves' landfall. A vertically pointing S-PROF radar in the coastal mountains provided detailed information on the bulk microphysical characteristics of the rainfall. Farther inland, a pair of 915-MHz wind profilers and GPS receivers quantified the orographic precipitation forcing as the AR ascended the Sierra Nevada, and as the terrain-induced Sierra barrier jet ascended the northern terminus of California's Central Valley.

关键词： Mesoscale processes Precipitation Orographic effects Atm/Ocean Structure/ Phenomena Dropsondes Physical Meteorology and Climatology Coastal meteorology Radars/Radar observations observational techniques and algorithms Circulation/ Dynamics

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Antenna Pattern Measurements of Weather Radars Using the Sun and a Point Source

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第5期33卷 891-898页

作者： Reimann, Jens Hagen, Martin Deutsch Zentrum Luft & Raumfahrt Inst Phys Atmosphare Wessling Germany

The sun is known to be a good target for weather radar calibration. In this paper high-resolution raster scans of the sun at high elevations will be used to derive the antenna pattern of weather radar, without being affected by beam propagation effects and reflections close to the earth's surface. It is shown that this pattern matches well to pattern measurements using a point source. Hence, a good estimation of the real antenna pattern can be derived using the sun. Furthermore, formulas to extract undistorted antenna patterns from the sun, even at high-elevation angles, are derived. The signal processing required to achieve high sensitivity for the antenna pattern measurements will be described. Important parts of the antenna pattern-for example, sidelobes-become visible when using long integration times. The polarimetric receiver channel cross-correlation coefficient is proposed as a figure of merit of the cross-polar isolation of the antenna and hence the cross-polar pattern. The results are also compared to point source measurements. This illustrates how an unpolarized signal source like the sun can be used to derive polarimetric variables.

关键词： observational techniques and algorithms Radars/Radar observations

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Assessment and Implications of NCEP Stage IV Quantitative Precipitation Estimates for Product Intercomparisons

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WEATHER AND FORECASTING 2016年第2期31卷 371-394页

作者： Nelson, Brian R. Prat, Olivier P. Seo, D. -J. Habib, Emad NOAA Natl Ctr Environm Informat 151 Patton Ave Asheville NC 28801 USA N Carolina State Univ Cooperat Inst Climate & Satellites Asheville NC USA Univ Texas Arlington Arlington TX 76019 USA Univ Louisiana Lafayette Lafayette LA 70504 USA

The National Centers for Environmental Prediction (NCEP) stage IV quantitative precipitation estimates (QPEs) are used in many studies for intercomparisons including those for satellite QPEs. An overview of the National Weather Service precipitation processing system is provided here so as to set the stage IV product in context and to provide users with some knowledge as to how it is developed. Then, an assessment of the stage IV product over the period 2002-12 is provided. The assessment shows that the stage IV product can be useful for conditional comparisons of moderate-to-heavy rainfall for select seasons and locations. When evaluating the product at the daily scale, there are many discontinuities due to the operational processing at the radar site as well as discontinuities due to the merging of data from different River Forecast Centers (RFCs) that use much different processing algorithms for generating their precipitation estimates. An assessment of the daily precipitation estimates is provided based on the cumulative distribution function for all of the daily estimates for each RFC by season. In addition it is found that the hourly estimates at certain RFCs suffer from lack of manual quality control and caution should be used.

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

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