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A Simple Method Based on Routine Observations to Nowcast Down-Valley Flows in Shallow, Narrow Valleys

JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2016年第7期55卷 1497-1511页

作者： Duine, Gert-Jan Hedde, Thierry Roubin, Pierre Durand, Pierre Univ Toulouse CNRS UPS Lab Aerol Toulouse France CEA Cadarache Lab Modelisat Transferts Environm St Paul Les Durance France Univ Virginia Dept Environm Sci Clark Hall Charlottesville VA 22903 USA

A simple relation to diagnose the existence of a thermally driven down-valley wind in a shallow (100 m deep) and narrow (1-2 km wide) valley based on routine weather measurements has been determined. The relation is based on a method that has been derived from a forecast verification principle. It consists of optimizing a threshold of permanently measured quantities to nowcast the thermally driven Cadarache (southeastern France) down-valley wind. Three parameters permanently observed at a 110-m-high tower have been examined: the potential temperature difference between the heights of 110 and 2 m, the wind speed at 110 m, and a bulk Richardson number. The thresholds are optimized using the wind observations obtained within the valley during the Katabatic Winds and Stability over Cadarache for the Dispersion of Effluents (KASCADE) field experiment, which was conducted in the winter of 2013. The highest predictability of the down-valley wind at the height of 10 m (correct nowcasting ratio of 0.90) was found for the potential temperature difference at a threshold value of 2.6 K. The applicability of the method to other heights of the down-valley wind (2 and 30 m) and to summer conditions is also demonstrated. This allowed a reconstruction of the climatology of the thermally driven down-valley wind that demonstrates that the wind exists throughout the year and is strongly linked to nighttime duration. This threshold technique will make it possible to forecast the subgrid-scale down-valley wind from operational numerical weather coarse-grid simulations by means of statistical downscaling.

关键词： Geographic location entity Complex terrain Circulation Dynamics Drainage flow observational techniques and algorithms In situ atmospheric observations Mathematical and statistical techniques Optimization Forecasting Nowcasting

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How Biased Is Aircraft Cloud Sampling?

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第1期33卷 185-189页

作者： Field, Paul R. Furtado, Kalli Met Off FitzRoy Rd Exeter EX1 3PB Devon England Univ Leeds Sch Earth & Environm Inst Climate & Atmospher Sci Leeds W Yorkshire England

Aircraft are the dominant method for in situ sampling of cloud properties. Resource limitations mean that aircraft tend to follow a sampling strategy when there is more than one cloud from which to choose. This can result in biased cloud statistics that are used for parameterization development and model testing. In this study, order statistics are used to estimate the potential magnitude of this bias when a strategy based on choosing the larger cloud is employed. It is found for cloud properties following gamma distributions that a typical bias of a factor of 1.5 can result when the larger of two clouds is repeatedly chosen for sampling.

关键词： observational techniques and algorithms Aircraft observations Sampling Mathematical and statistical techniques Bias Statistics

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An AIS-Based Site Planning Method to Help Minimize Collision Risk during Marine Autonomous Surface Craft Deployments

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第6期33卷 1251-1255页

作者： Filimon, Michael A. Codiga, Daniel L. Univ Rhode Isl Dept Ocean Engn Narragansett RI USA Univ Rhode Isl Grad Sch Oceanog 215 S Ferry Rd Narragansett RI 02882 USA

Marine autonomous surface crafts (MASCs), or unmanned surface vehicles as their precursors have traditionally been known, could cost effectively advance spatiotemporal coverage and resolution capabilities for oceanographic sampling in coastal and estuarine settings, if deployed for long durations (from days to weeks). Site planning for such deployments balances scientific goals against operational risk of collision avoidance (CA) maneuvers required by the MASC during encounters with other vessels. A method is developed and demonstrated in this paper, using archived Automatic Identification System (AIS) vessel tracking data, to quantify such potential encounters of a MASC on a repeat-transect survey. The demonstration site is Rhode Island Sound, where average vessel track frequencies are shown to range from about 8 to 0.01 or less per day, from inshore shipping lanes to areas farther offshore, respectively. Encounters per month ranged from 24 to 1 for increasingly offshore locations, based on a MASC repeatedly traversing an 18-km transect at an average speed of 2.5 m s(-1) (similar to 5 kt) over a one-month summer period and stopping at each of 10 equispaced stations in one direction to sample for 10 min. Crude estimates of non-AIS vessel traffic suggest total encounters (with vessels equipped by AIS or not) up to 3-4 times higher. The method can be applied anywhere AIS data are available and is generalizable to any survey configuration. It facilitates investigating sensitivity to choices of transect location and sampling configuration parameters, providing crucial information to guide deployment planning for a given level of confidence in CA capabilities of the MASC.

关键词： Geographic location/entity Estuaries Seas/gulfs/bays observational techniques and algorithms algorithms In situ oceanic observations Instrumentation/sensors Ship observations

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A Simple Algorithm to Discriminate between Meteorological and Nonmeteorological Radar Echoes

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第9期33卷 1875-1885页

作者： Krause, John M. Univ Oklahoma Cooperat Inst Mesoscale Meteorol Studies Norman OK 73019 USA NOAA OAR Natl Severe Storms Lab Norman OK USA

Discriminating between meteorological and nonmeteorological radar returns is necessary for a number of radar applications, including hydrometeor classification, quantitative precipitation estimation (QPE), and the computation of specific differential phase K-DP. The algorithm proposed, MetSignal, uses polarimetric radar data and is simple by design, allowing users to adjust its performance based on the location's specific needs. The MetSignal algorithm is a fuzzy logic technique with a few postprocessing rules and has been selected for implementation on the WSR-88D network in the United States.

关键词： observational techniques and algorithms algorithms Radars/Radar observations

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On Polarimetric Radar Signatures of Deep Convection for Model Evaluation: Columns of Specific Differential Phase Observed during MC3E

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MONTHLY WEATHER REVIEW 2016年第2期144卷 737-758页

作者： van Lier-Walqui, Marcus Fridlind, Ann M. Ackerman, Andrew S. Collis, Scott Helmus, Jonathan MacGorman, Donald R. North, Kirk Kollias, Pavlos Posselt, Derek J. Columbia Univ CCSR 2880 Broadway New York NY 10027 USA NASA Goddard Inst Space Studies New York NY 10025 USA Argonne Natl Lab Div Environm Sci 9700 S Cass Ave Argonne IL 60439 USA NOAA Natl Severe Storms Lab Norman OK 73069 USA Cooperat Inst Mesoscale Meteorol Studies Norman OK USA McGill Univ Montreal PQ Canada Univ Michigan Ann Arbor MI 48109 USA

The representation of deep convection in general circulation models is in part informed by cloud-resolving models (CRMs) that function at higher spatial and temporal resolution;however, recent studies have shown that CRMs often fail at capturing the details of deep convection updrafts. With the goal of providing constraint on CRM simulation of deep convection updrafts, ground-based remote sensing observations are analyzed and statistically correlated for four deep convection events observed during the Midlatitude Continental Convective Clouds Experiment (MC3E). Since positive values of specific differential phase observed above the melting level are associated with deep convection updraft cells, so-called columns are analyzed using two scanning polarimetric radars in Oklahoma: the National Weather Service Vance WSR-88D (KVNX) and the Department of Energy C-band Scanning Atmospheric Radiation Measurement (ARM) Precipitation Radar (C-SAPR). KVNX and C-SAPR volumes and columns are then statistically correlated with vertical winds retrieved via multi-Doppler wind analysis, lightning flash activity derived from the Oklahoma Lightning Mapping Array, and KVNX differential reflectivity . Results indicate strong correlations of volume above the melting level with updraft mass flux, lightning flash activity, and intense rainfall. Analysis of columns reveals signatures of changing updraft properties from one storm event to another as well as during event evolution. Comparison of to shows commonalities in information content of each, as well as potential problems with associated with observational artifacts.

关键词： Circulation Dynamics Convective storms Updrafts Atm Ocean Structure Phenomena Lightning Rainfall observational techniques and algorithms Radars Radar observations Mathematical and statistical techniques Pattern detection

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The GEWEX Water Vapor Assessment: Results from Intercomparison, Trend, and Homogeneity Analysis of Total Column Water Vapor

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JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2016年第7期55卷 1633-1649页

作者： Schroeder, Marc Lockhoff, Maarit Forsythe, John M. Cronk, Heather Q. Vonder Haar, Thomas H. Bennartz, Ralf Deutsch Wetterdienst Frankfurter Str 135 D-63067 Offenbach Germany Colorado State Univ Cooperat Inst Res Atmosphere Ft Collins CO 80523 USA Colorado State Univ Ft Collins CO 80523 USA Vanderbilt Univ 221 Kirkland Hall Nashville TN 37235 USA Univ Wisconsin Madison WI USA

The Global Energy and Water Cycle Exchanges project (GEWEX) water vapor assessment's (G-VAP) main objective is to analyze and explain strengths and weaknesses of satellite-based data records of water vapor through intercomparisons and comparisons with ground-based data. G-VAP results from the intercomparison of six total column water vapor (TCWV) data records are presented. Prior to the intercomparison, the data records were regridded to a common regular grid of 2 degrees x 2 degrees longitude-latitude. All data records cover a common period from 1988 to 2008. The intercomparison is complemented by an analysis of trend estimates, which was applied as a tool to identify issues in the data records. It was observed that the trends over global ice-free oceans are generally different among the different data records. Most of these differences are statistically significant. Distinct spatial features are evident in maps of differences in trend estimates, which largely coincide with maxima in standard deviations from the ensemble mean. The penalized maximal F test has been applied to global ice-free ocean and selected land regional anomaly time series, revealing differences in trends to be largely caused by breakpoints in the different data records. The time, magnitude, and number of breakpoints typically differ from region to region and between data records. These breakpoints often coincide with changes in observing systems used for the different data records. The TCWV data records have also been compared with data from a radiosonde archive. For example, at Lindenberg, Germany, and at Yichang, China, such breakpoints are not observed, providing further evidence for the regional imprint of changes in the observing system.

关键词： Physical Meteorology and Climatology Climate variability Climatology Humidity Stability observational techniques and algorithms Climate records Satellite observations

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An Examination of Precipitation Using CSU-CHILL Dual-Wavelength, Dual-Polarization Radar Observations

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第2期33卷 313-329页

作者： Junyent, Francesc Chandrasekar, V. Colorado State Univ Dept Elect & Comp Engn 1373 Campus Delivery Ft Collins CO 80523 USA

The CSU-CHILL radar is a dual-wavelength, dual-polarization weather radar system operating at S and X bands with coaxial beams. One of the capabilities of this radar system is the possibility of developing and/or validating algorithms across dual wavelengths and dual polarizations. This paper presents one such instance, showing how the rainfall field can be estimated either from the S- and X-band reflectivities or from the differential propagation phase at X band. To do so, the paper first presents a dual-wavelength attenuation correction method that uses the reflectivity measured at S band, as the constraint for the correction of the reflectivity measured at X band, and it describes how Mie scattering regions at X band may be detected from the retrieved path-integrated attenuation field. Then, the paper describes how the resulting specific attenuation field relates to rainfall and specific phase at X band, which can be obtained from dual-polarization data at a single wavelength as well, and shows examples. Finally, the paper looks at the relation between attenuation and the differential phase as a function of elevation angle for a few cases, which may be related to the drop size distribution and mean diameter, as well as temperature.

关键词： Data processing Radars/Radar observations algorithms observational techniques and algorithms

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Measurements of Rainfall Velocity and Raindrop Size Distribution Using Coherent Doppler Lidar

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第9期33卷 1949-1966页

作者： Aoki, Makoto Iwai, Hironori Nakagawa, Katsuhiro Ishii, Shoken Mizutani, Kohei Natl Inst Informat & Commun Technol 4-2-1 Nukui Kitamachi Koganei Tokyo 1848795 Japan

Rainfall velocity, raindrop size distribution (DSD), and vertical wind velocity were simultaneously observed with 2.05- and 1.54-mm coherent Doppler lidars during convective and stratiform rain events. A retrieval method is based on identifying two separate spectra from the convolution of the aerosol and precipitation Doppler lidar spectra. The vertical wind velocity was retrieved from the aerosol spectrum peak and then the terminal rainfall velocity corrected by the vertical air motion from the precipitation spectrum peak was obtained. The DSD was derived from the precipitation spectrum using the relationship between the raindrop size and the terminal rainfall velocity. A comparison of the 1-min-averaged rainfall velocity from Doppler lidar measurements at a minimum range and that from a collocated ground-based optical dis-drometer revealed high correlation coefficients of over 0.89 for both convective and stratiform rain events. The 1-min-averaged DSDs retrieved from the Doppler lidar spectrum using parametric and nonparametric methods are also in good agreement with those measured with the optical disdrometer with a correlation coefficient of over 0.80 for all rain events. To retrieve the DSD, the parametric method assumes a mathematical function for the DSD and the nonparametric method computes the direct deconvolution of the measured Doppler lidar spectrum without assuming a DSD function. It is confirmed that the Doppler lidar can retrieve the rainfall velocity and DSD during relatively heavy rain, whereas the ratio of valid data significantly decreases in light rain events because it is extremely difficult to separate the overlapping rain and aerosol peaks in the Doppler spectrum.

关键词： algorithms Atm/Ocean Structure/ Phenomena Drop size distribution Lidars/Lidar observations observational techniques and algorithms Physical Meteorology and Climatology Rainfall Wind

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A Consistent Treatment of Microwave Emissivity and Radar Backscatter for Retrieval of Precipitation over Water Surfaces

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第2期33卷 215-229页

作者： Munchak, S. Joseph Meneghini, Robert Grecu, Mircea Olson, William S. Univ Maryland Earth Syst Sci Interdisciplinary Ctr College Pk MD 20742 USA NASA Goddard Space Flight Ctr Greenbelt MD 20771 USA Morgan State Univ Baltimore MD 21239 USA Univ Maryland Baltimore Cty Joint Ctr Earth Syst Technol Baltimore MD 21228 USA

The Global Precipitation Measurement (GPM) Microwave Imager (GMI) and dual-frequency precipitation radar (DPR) are designed to provide the most accurate instantaneous precipitation estimates currently available from space. The GPM Combined Radar-Radiometer Algorithm (CORRA) plays a key role in this process by retrieving precipitation profiles that are consistent with GMI and DPR measurements;therefore, it is desirable that the forward models in CORRA use the same geophysical input parameters. This study explores the feasibility of using internally consistent emissivity and surface backscatter cross-sectional ( [GRAPHICS] ) models for water surfaces in CORRA. An empirical model for DPR Ku- and Ka-band [GRAPHICS] as a function of 10-m wind speed and incidence angle is derived from GMI-only wind retrievals under clear-sky conditions. This allows for the [GRAPHICS] measurements, which are also influenced by path-integrated attenuation (PIA) from precipitation, to be used as input to CORRA and for wind speed to be retrieved as output. Comparisons to buoy data give a wind rmse of 3.7 m s(-1) for Ku+GMI retrievals and 3.2 m s(-1) for Ku+Ka+GMI retrievals under precipitation (compared to 1.3 m s(-1) for clear-sky GMI-only retrievals), and there is a reduction in bias from the global analysis (GANAL) background data (-10%) to the Ku+GMI (-3%) and Ku+Ka+GMI (-5%) retrievals. Ku+GMI retrievals of precipitation increase slightly in light (<1 mm h(-1)) and decrease in moderate to heavy precipitation (>1 mm h(-1)). The Ku+Ka+GMI retrievals, being additionally constrained by the Ka reflectivity, increase only slightly in moderate and heavy precipitation at low wind speeds (<5 m s(-1)) relative to retrievals using the surface reference estimate of PIA as input.

关键词： Satellite observations Filtering techniques Mathematical and statistical techniques observational techniques and algorithms Radars/Radar observations Microwave observations

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Aerial Damage Survey of the 2013 El Reno Tornado Combined with Mobile Radar Data

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MONTHLY WEATHER REVIEW 2016年第5期144卷 1749-1776页

作者： Wakimoto, Roger M. Atkins, Nolan T. Butler, Kelly M. Bluestein, Howard B. Thiem, Kyle Snyder, Jeffrey C. Houser, Jana Kosiba, Karen Wurman, Joshua Univ Colorado Dept Atmospher & Ocean Sci Boulder CO 80309 USA Lyndon State Coll Dept Atmospher Sci Lyndonville VT USA Ohio Univ Dept Geog Athens OH 45701 USA Univ Oklahoma Sch Meteorol Norman OK 73019 USA Univ Oklahoma Cooperat Inst Mesoscale Meteorol Studies Norman OK 73019 USA NOAA Natl Severe Storms Lab OAR Norman OK 73069 USA Ctr Severe Weather Res Boulder CO USA

A detailed damage survey of the El Reno, Oklahoma, tornado of 31 May 2013 combined with rapid-scanning data recorded from two mobile radars is presented. One of the radars was equipped with polarimetric capability. The relationship between several suction vortices visually identified in pictures with the high-resolution Doppler velocity data and swath marks in fields is discussed. The suction vortices were associated with small shear features in Doppler velocity and a partial ringlike feature of high spectral width. For the first time, a suction vortex that created a swath mark in a field was visually identified in photographs and high-definition video while the rotational couplet was tracked by radar. A dual-Doppler wind synthesis of the tornadic circulation at low levels near the location of several storm chaser fatalities resolved ground-relative wind speeds in excess of 90 m s(-1), greater than the minimum speed for EF5 damage. The vertical vorticity analysis revealed a rapid transition from a single tornadic vortex centered on the weak-echo hole (WEH) to suction vortices surrounding the WEH and collocated with the ring of enhanced radar reflectivities. Several bands/zones of enhanced convergence were resolved in the wind syntheses. One of the bands was associated with an internal or secondary rear-flank gust front. An inner band of convergence appeared to be a result of the positive bias in tornado-relative radial velocity owing to centrifuging of large lofted debris swirling within the tornado. An outer band of convergence formed at the northern edge of a region of strong inflow that was lofting small debris and dust into the storm.

关键词： Circulation/ Dynamics Tornadogenesis observational techniques and algorithms Radars/Radar observations Applications Damage assessment

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