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Rapid-Scan, Polarimetric Observations of Central Oklahoma Severe Storms on 31 May 2013

WEATHER AND FORECASTING 2016年第1期31卷 19-42页

作者： Tanamachi, Robin L. Heinselman, Pamela L. Univ Oklahoma Cooperat Inst Mesoscale Meteorol Studies Norman OK 73019 USA NOAA OAR Natl Severe Storms Lab Norman OK 73069 USA Purdue Univ Dept Earth Atmospher & Planetary Sci 550 Stadium Mall Dr W Lafayette IN 47907 USA

On 31 May 2013, a polarimetric WSR-88D located in Norman, Oklahoma (KOUN), was used to collect sectorized volumetric observations in a tornadic supercell. Because only a fraction of the full azimuthal volume was observed, rapid volume update times of ~1-2 min were achieved. In addition, the number of pulses used in each radial was larger than is conventional, increasing the statistical robustness of the calculated polarimetric variables. These rapid observations serve as a proxy for those of a future dual-polarized phased-array radar. Through comparison with contemporaneous observations from two nearby dual-polarized WSR-88Ds [Twin Lakes, Oklahoma (KTLX), and near University of Oklahoma Westheimer Airport in Norman (KCRI)], a number of instances in which the rapidly scanned KOUN radar detected or better resolved (in a temporal sense) features of severe convective storms are highlighted. In particular, the polarimetric signatures of merging updrafts, a rapidly descending giant hail core, an anticyclonic tornado, and a dissipating storm cell are examined. These observations provided insights into the rapid evolution of severe convective storms that could not be made (or would have been made with much lower confidence) with current, operational WSR-88D scanning strategies. Possible implications of these rapid updates for the warning decision process are discussed.

关键词： Radars/Radar observations Hail Physical Meteorology and Climatology Tornadoes Convective storms Atm/Ocean Structure/ Phenomena Supercells observational techniques and algorithms Thunderstorms

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High-Speed Optical Disdrometer for Rainfall Microphysical Observations

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第2期33卷 231-243页

作者： Testik, F. Y. Rahman, M. K. Univ Texas San Antonio Dept Civil & Environm Engn BSE BldgRoom 1-3041 UTSA Circle San Antonio TX 78249 USA

A high-speed optical disdrometer (HOD) that was developed for measuring rainfall microphysical quantities, including raindrop shape, size distribution, and fall velocity/acceleration, is the subject of this paper. The main components of the HOD are a high-speed video camera, a light-emitting diode (LED) light, and a sensing unit to detect raindrops passing through the camera view frame. The high-speed video camera is directed at the LED light to capture the silhouettes of the backlit drops when triggered by a raindrop that is detected within a specified focal depth by the sensing unit. The use of a sensing unit enables the confinement of a measurement volume around the camera focal plane. This innovative operation principle ensures the capture of sharp images of raindrop silhouettes, which are then digitally processed to provide accurate information on various raindrop characteristics. The measurement capabilities of the HOD were evaluated through both laboratory and field tests. In the laboratory tests, high-precision spherical lenses with known diameters and water drops of different sizes generated for a known volume of water were used. In the field tests, the HOD was evaluated against a reference rain gauge in a number of rain events. These tests demonstrated the precise accuracy of HOD measurements and the HOD's technological readiness for field deployment for various applications. It is expected that the HOD will play an important role in generating new insights on raindrop dynamics and related research through its unique measurement capability of providing sequential high-speed images of raindrops.

关键词： Instrumentation/sensors observational techniques and algorithms In situ atmospheric observations Drop size distribution Physical Meteorology and Climatology Hydrometeorology

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Water Surface Height Determination with a GPS Wave Glider: A Demonstration in Loch Ness, Scotland

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第6期33卷 1159-1168页

作者： Maqueda, M. A. Morales Penna, N. T. Williams, S. D. P. Foden, P. R. Martin, I. Pugh, J. Newcastle Univ Sch Marine Sci & Technol Armstrong Bldg Newcastle Upon Tyne NE1 7RU Tyne & Wear England Newcastle Univ Sch Civil Engn & Geosci Newcastle Upon Tyne NE1 7RU Tyne & Wear England NERC Natl Oceanog Ctr Liverpool Merseyside England

A geodetic GPS receiver has been installed on a Wave Glider, an unmanned water surface vehicle. Using kinematic precise point positioning (PPP) GPS, which operates globally without directly requiring reference stations, surface heights are measured with similar to 0.05-m precision. The GPS Wave Glider was tested in Loch Ness, Scotland, by measuring the gradient of the loch's surface height. The experiment took place under mild weather, with virtually no wind setup along the loch and a wave field made mostly of ripples and wavelets. Under these conditions, the loch's surface height gradient should be approximately equal to the geoid slope. The PPP surface height gradient and that of the Earth Gravitational Model 2008 geoid heights do indeed agree on average along the loch (0.03 m km(-1)). Also detected are 1) similar to 0.05-m-sized height changes due to daily water pumping for hydroelectricity generation and 2) high-frequency (0.25-0.5 Hz) oscillations caused by surface waves. The PPP heights compare favorably (similar to 0.02-m standard deviation) with relative carrier phase-based GPS processing. This suggests that GPS Wave Gliders have the potential to autonomously determine centimeter-precise water surface heights globally for lake modeling, and also for applications such as ocean modeling and geoid/mean dynamic topography determination, at least for benign surface states such as those encountered during the reported experiment.

关键词： Geographic location/entity Inland seas/lakes Atm/Ocean Structure/ Phenomena Sea level observational techniques and algorithms Global positioning systems (GPS) In situ oceanic observations

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Upwelling of Atlantic Water along the Canadian Beaufort Sea Continental Slope: Favorable Atmospheric Conditions and Seasonal and Interannual Variations

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JOURNAL OF CLIMATE 2016年第12期29卷 4509-4523页

作者： Kirillov, Sergei Dmitrenko, Igor Tremblay, Bruno Gratton, Yves Barber, David Rysgaard, Soren Univ Manitoba Ctr Earth Observat Sci Winnipeg MB R3T 2N2 Canada McGill Univ Montreal PQ Canada Inst Natl Rech Sci Quebec City PQ Canada

The role of wind forcing on the vertical displacement of the -1 degrees C isotherm and 33.8 isohaline depths was examined based on snapshots of historical (1950-2013) temperature and salinity profiles along the Mackenzie continental slope (Beaufort Sea). It is found that upwelling is correlated with along-slope northeast (T59 degrees) winds during both ice-free and ice-covered conditions, although the wind impact is more efficient during the ice-free season. One of the most important factors responsible for vertical displacements of isopycnals is sustained wind forcing that can last for several weeks and even longer. It accounts for 14%-55% of total variance in isotherm/isohaline depths, although these numbers might be underestimated. The upwelling and downwelling events are discussed in the context of the interplay between two regional centers of action-the Beaufort high and Aleutian low-that control the wind pattern over the southern Beaufort Sea. The probability of upwelling-favorable wind occurrence is closely related to the sea level pressure difference between these two centers, as well as their geographical positions. The combined effect of both centers expressed as the SLP differences is highly correlated (0.68/0.66 for summer/winter) with occurrences of extreme upwelling-favorable northeast (NE) winds over the Mackenzie slope, although the Beaufort high plays a more important role. The authors also diagnosed the predominant upwelling-favorable conditions over the Mackenzie slope in the recent decade associated with the summertime amplification of the Beaufort high. The upwelling-favorable NE wind occurrences also demonstrate the significant but low (-0.30) correlation with Arctic Oscillation (AO) during both summer and winter seasons, whereas the high correlation with North Pacific index (NPI;-0.52) is obtained only for the ice-covered period.

关键词： Circulation/ Dynamics Arctic Oscillation Atmosphere-ocean interaction Ekman pumping/transport Upwelling/downwelling observational techniques and algorithms Ship observations

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Limb Correction of MODIS and VIIRS Infrared Channels for the Improved Interpretation of RGB Composites

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第5期33卷 1073-1087页

作者： Elmer, Nicholas J. Berndt, Emily Jedlovec, Gary J. Univ Alabama Dept Atmospher Sci 320 Sparkman Dr Huntsville AL 35805 USA NASA Short Term Predict Res & Transit SPoRT Ctr Huntsville AL USA Univ Alabama Ctr Earth Syst Sci Huntsville AL 35805 USA NASA Marshall Space Flight Ctr Earth Sci Off Huntsville AL USA

Red-green-blue (RGB) composite imagery combines information from several spectral channels into one image to aid in the operational analysis of atmospheric processes. However, infrared channels are adversely affected by the limb effect, the result of an increase in optical pathlength of the absorbing atmosphere between the satellite and the earth as viewing zenith angle increases. This study develops a technique to quickly correct for limb effects in both clear and cloudy regions using latitudinally and seasonally varying limb correction coefficients for real-time applications. These limb correction coefficients account for the increase in optical pathlength in order to produce limb-corrected RGB composites. The improved functionality of limb-corrected RGB composites is demonstrated by multiple case studies of Air Mass and Dust RGB composites using Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) and Suomi-National Polar-Orbiting Partnership (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) imagery. However, the limb correction can be applied to any polar-orbiting sensor infrared channels, provided the proper limb correction coefficients are calculated. Corrected RGB composites provide multiple advantages over uncorrected RGB composites, including increased confidence in the interpretation of RGB features, improved situational awareness for operational forecasters, and the ability to use RGB composites from multiple sensors jointly to increase the temporal frequency of observations.

关键词： Forecasting observational techniques and algorithms Operational forecasting Remote sensing Satellite observations

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Radar Observation of Evaporation and Implications for Quantitative Precipitation and Cooling Rate Estimation

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第8期33卷 1779-1792页

作者： Xie, Xinxin Evaristo, Raquel Troemel, Silke Saavedra, Pablo Simmer, Clemens Ryzhkov, Alexander Univ Bonn Inst Meteorol Huegel 20 D-53121 Bonn Germany Univ Oklahoma Cooperat Inst Mesoscale Meteorol Studies Norman OK 73019 USA NOAA OAR Natl Severe Storms Lab Norman OK 73069 USA

This study analyzes radar observations of evaporation in rain and investigates its impact on surface rainfall and atmospheric cooling rates. A 1D model is used to examine the impact of raindrop evaporation on the evolution of the initial raindrop size distribution (DSD), the resulting reflectivity (Z), and differential reflectivity (ZDR) and surface rain rates. Raindrop evaporation leads to a decrease of Z and an increase of Z(DR) toward the surface because of the depletion of small raindrops that evaporate first and thus enhance the mean raindrop size. The latter effect, however, can be reduced because of the increasing temperature toward the surface and may even lead to a decrease of Z(DR) toward the surface. Two events with significant rain evaporation, observed simultaneously by a polarimetric X-band radar and a K-band Micro Rain Radar (MRR), offer quite detailed insight into the evaporation process. During the first event, which exhibits an initial Z(DR) > 1.5 dB in the upper rain column, raindrops undergo relatively weak evaporation as deduced from the decrease of the small raindrop fraction observed by the MRR. The second event is characterized by a lower initial Z(DR) < 0.5 dB with all raindrops evaporating before reaching the ground. A retrieval scheme for estimating the evaporation-related cooling rate and surface precipitation from polarimetric radar observations below the bright band is derived based on MRR observations. The algorithm is then used to simulate polarimetric X-band radar observations, which might mitigate uncertainties in the surface rainfall retrievals due to evaporation at far distances from the radars and in the case of beam blocking.

关键词： Atm/Ocean Structure/ Phenomena Evaporation observational techniques and algorithms Physical Meteorology and Climatology Precipitation Radars/Radar observations Rainfall

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Estimating Lightning from Microwave Remote Sensing Data

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JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2016年第9期55卷 2021-2036页

作者： Magi, Brian I. Winesett, Thomas Cecil, Daniel. J. Univ North Carolina Charlotte Dept Geog & Earth Sci 9201 Univ City Blvd Charlotte NC 28223 USA NASA Marshall Space Flight Ctr Huntsville AL USA

This study evaluates a method for estimating the cloud-to-ground (CG) lightning flash rate from microwave remote sensing data. Defense Meteorological Satellite Program satellites have been in operation since 1987 and include global-viewing microwave sensors that capture thunderstorms as brightness temperature depressions. The National Lightning Detection Network (NLDN) has monitored CG lightning in the United States since 1997. This study investigates the relationship between CG lightning and microwave brightness temperature fields for the contiguous United States from April to September for the years 2005-12. The findings suggest that an exponential function, empirically fit to the NLDN and SSM/I data, provides lightning count measurements that agree to within 60%-70% with NLDN lightning, but with substantial misses and false alarms in the predictions. The discrepancies seem to be attributable to regional differences in thunderstorm characteristics that require a detailed study at smaller spatial scales to truly resolve, but snow at higher elevations also produces some anomalous microwave temperature depressions similar to those of thunderstorms. The results for the contiguous United States in this study are a step toward potentially using SSM/I data to estimate CG lightning around the world, although the sensitivity of the results to regional differences related to meteorological regimes would need further study.

关键词： Geographic location/entity North America Atm/Ocean Structure/ Phenomena Lightning Physical Meteorology and Climatology Atmospheric electricity observational techniques and algorithms Microwave observations Satellite observations Surface observations

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The Implementation of the Ice-Phase Microphysical Process into a Four-Dimensional Variational Doppler Radar Analysis System (VDRAS) and Its Impact on Parameter Retrieval and Quantitative Precipitation Nowcasting

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第3期73卷 1015-1038页

作者： Chang, Shao-Fan Liou, Yu-Chieng Sun, Juanzhen Tai, Sheng-Lun Natl Cent Univ Dept Atmospher Sci 300 Jhongda Rd Taoyuan 320 Taiwan Taiwan Typhoon & Flood Res Inst Taipei Taiwan Natl Ctr Atmospher Res POB 3000 Boulder CO 80307 USA

The microphysical process of a cloud-scale model used by a four-dimensional Variational Doppler Radar Analysis System (VDRAS) is extended from its original warm rain parameterization scheme to a cold rain process containing ice and snow. The development of the adjoint equations for the additional control variables related to ice physics is accomplished by utilizing the existing four-dimensional variational (4DVar) minimization framework employed by VDRAS. Experiments are conducted to examine the accuracy of the new 4DVar system with the ice physics scheme implemented and to explore the impact of the ice-phase process on numerical simulations, parameter retrievals, and the model's quantitative precipitation nowcasting (QPN) capability. It is shown that the ice-phase microphysical process can significantly alter the kinematic and thermodynamic structure of deep convection and provide a better description of the contents of the hydrometeors. During the 4DVar minimization, using the VDRAS-predicted freezing level after the previous assimilation cycle to replace the true but unknown 0 degrees C line is found to be a feasible approach for separating the rain and snow and, at the same time, allowing the 4DVar minimization algorithm to converge to an optimal solution. A real case study from intensive observation period 8 of the 2008 Southwest Monsoon Experiment shows that, with the added ice-phase process, VDRAS is more capable of capturing the actual evolution of the reflectivity field than the original scheme. The model's QPN skill is also improved significantly. Thus, the benefits of adding the ice-phase process into a 4DVar radar data assimilation system on the convective-scale weather analysis and forecast are demonstrated.

关键词： Nowcasting Forecasting Models and modeling Radars/Radar observations observational techniques and algorithms Data assimilation Numerical weather prediction/forecasting

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A Comparison of ASOS Near-Surface Winds and WSR-88D-Derived Wind Speed Profiles Measured in Landfalling Tropical Cyclones

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WEATHER AND FORECASTING 2016年第4期31卷 1343-1361页

作者： Krupar, Richard J., III Schroeder, John L. Smith, Douglas A. Kang, Song-Lak Lorsolo, Sylvie Univ Queensland Sch Civil Engn 49 Adv Engn BldgStaff House Rd St Lucia Qld 4072 Australia Texas Tech Univ Atmospher Sci Grp Lubbock TX 79409 USA Texas Tech Univ Dept Civil Engn Lubbock TX 79409 USA AIR Worldwide Boston MA USA

A set of velocity azimuth display (VAD) wind speed profiles derived from coastal Weather Surveillance Radar-1988 Doppler (WSR-88D) systems was paired with Automated Surface Observing System (AS OS) 10-m standardized mean and nonstandardized gust wind speeds measured within 10 km of nearby WSR-88Ds. The goal was to formulate an appropriate methodology and empirical relationships to estimate overland near-surface wind conditions in landfalling tropical cyclones (TCs) using VAD tropical cyclone boundary layer (TCBL) lower-tropospheric wind measurements. A total of 17 TCs and seven ASOS/WSR-88D sites were used to construct a unique comparative dataset. Four estimation methods including the log and power laws, mean and gust wind speed ratio (WSR) methods, and curve fitting with linear regression and polynomial fits were evaluated. Results from the evaluation show that WSR-88D site-specific linear regression equations using a VAD 0-200-m layer average wind speed and nonzero intercepts provided the most accurate predictions of the ASOS 10-m standardized mean wind speed. Results also show that a non-site-specific linear regression model using a VAD 0-500-m mean boundary layer (MBL) wind speed and nonzero intercept is 1.07% more accurate than using a single-gust WSR to predict ASOS 10-m nonstandardized gust wind speeds. Only 2.15% of the ASOS 10-m nonstandardized maximum 3-s gust wind speeds were found to exceed the VAD 0-500-m MBL wind speed, indicating that the VAD 0-500-m MBL wind speed represents a viable source of momentum available for transport to the surface in the form of a gust.

关键词： Atm/Ocean Structure/ Phenomena Tropical cyclones observational techniques and algorithms Radars/Radar observations Surface observations Mathematical and statistical techniques Regression analysis Statistical techniques

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Automated Underway Eddy Covariance System for Air-Sea Momentum, Heat, and CO₂ Fluxes in the Southern Ocean

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第4期33卷 635-652页

作者： Butterworth, Brian J. Miller, Scott D. SUNY Albany Atmospher Sci Res Ctr 251 Fuller Rd Albany NY 12203 USA

A ruggedized closed-path eddy covariance (EC) system was designed for unattended direct measurements of air sea momentum, heat, and CO2 flux, and was deployed on the Research Vessel Icebreaker (RV/IB) Nathaniel B. Palmer (NBP), an Antarctic research and supply vessel. The system operated for nine cruises during 18 months from January 2013 to June 2014 in the Southern Ocean and coastal Antarctica, sampling a wide variety of wind, wave, biological productivity, and ice conditions. The methods are described and the results are shown for two cruises chosen for their latitudinal range, inclusion of both open water and sea ice cover, and relatively large air water CO2 concentration differences (Delta pCO(2)). Ship flow distortion was addressed by comparing mean winds, fluxes, and cospectra from an array of 3D anemometers at the NBP bow, comparing measured fluxes with bulk formulas, and implementing and evaluating several recently published data processing techniques. Quality-controlled momentum, heat, and CO2 flux data were obtained for 25% of the periods when NBP was at sea, with most (86%) of the rejected periods due to wind directions relative to the ship >+/- 30 degrees from the bow. In contrast to previous studies, no bias was apparent in measured CO2 fluxes for low vertical bar Delta pCO(2)vertical bar. The relationship between momentum flux and wind speed showed a clear dependence on the degree of sea ice cover, a result facilitated by the geographical coverage possible with a ship-based approach. These results indicate that ship-based unattended EC in high latitudes is feasible, and recommendations for deployments of underway systems in such environments are provided.

关键词： Geographic location/entity Southern Ocean Physical Meteorology and Climatology Air-sea interaction Atmosphere-ocean interaction Carbon dioxide observational techniques and algorithms In situ atmospheric observations Ship observations

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