MAPPING LOW-LEVEL WATER VAPOR WITH RADAR Weckwerth, Tammy M; Pettet, Crystalyne R; Fabry, Frédéric ...
Bulletin of the American Meteorological Society,
03/2005, Volume:
86, Issue:
3
Journal Article
Peer reviewed
Use of data from the International H2O Project has shown that radar refractivity can be used to map variations in low-level water vapor that cannot be resolved by conventional observing systems, such ...as radiosondes and surface nations. Adding this capability to the national network of operational radars might dramatically improve short-term forecasts of thunderstorm development. The refractivity signal is derived from an apparent change in the range of fixed ground targets from the radar caused by differences in the time taken for the radar waves to travel to the target and back.
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44.
The Lidars in Flat Terrain (LIFT) Experiment Cohn, Stephen A.; Mayor, Shane D.; Grund, Christian J. ...
Bulletin of the American Meteorological Society,
07/1998, Volume:
79, Issue:
7
Journal Article
Peer reviewed
The authors describe and present early results from the July–August 1996 Lidars in Flat Terrain (LIFT) experiment. LIFT was a boundary layer experiment that made use of recently developed Doppler, ...aerosol backscatter, and ozone lidars, along with radars and surface instrumentation, to study the structure and evolution of the convective boundary layer over the very flat terrain of central Illinois. Scientific goals include measurement of fluxes of heat, moisture, and momentum; vertical velocity statistics; study of entrainment and boundary layer height; and observation of organized coherent structures. The data collected will also be used to evaluate the performance of these new lidars and compare measurements of velocity and boundary layer height to those obtained from nearby radar wind profilers. LIFT was a companion to the Flatland96 experiment, described by Angevine et al.
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This study will validate the S-band dual-polarization Doppler radar (S-Pol) radar refractivity retrieval using measurements from the International H2O Project conducted in the southern Great Plains ...in May-June 2002. The range of refractivity measurements during this project extended out to 40-60 km from the radar. Comparisons between the radar refractivity field and fixed and mobile mesonet refractivity values within the S-Pol refractivity domain show a strong correlation. Comparisons between the radar refractivity field and low-flying aircraft also show high correlations. Thus, the radar refractivity retrieval provides a good representation of low-level atmospheric refractivity. Numerous instruments that profile the temperature and moisture arc also compared with the refractivity field. Radiosonde measurements. Atmospheric Emitted Radiance Interferometers, and a vertical-pointing Raman lidar show good agreement, especially at low levels. Under most daytime summertime conditions, radar refractivity measurements are representative of an ~250-m-deep layer. Analyses are also performed on the utility of refractivity for short-term forecasting applications. It is found that the refractivity field may detect low-level boundaries prior to the more traditional radar reflectivity and Doppler velocity fields showing their existence. Data from two days on which convection initiated within S-Pol refractivity range suggest that the refractivity field may exhibit some potential utility in forecasting convection initiation. This study suggests that unprecedented advances in mapping near-surface water vapor and subsequent improvements in predicting convective storms could result from implementing the radar refractivity retrieval on the national network of operational radars. PUBLICATION ABSTRACT
The three-dimensional kinematic structures of offshore and onshore flow sea-breeze fronts observed during the CaPE experiment are shown using high resolution dual-Doppler and aircraft data. The ...fronts interact with horizontal convective rolls (HCRs) that develop within the convective boundary layer. Nearly perpendicular intersections between the HCRs and sea-breeze front were observed during the offshore flow case. Close to the front, the HCR axes were tilted upward and lifted by the frontal updrafts. Consequently, a deeper updraft was created at the intersection points, providing additional impetus for cloud development. Furthermore, clouds forming at periodic intervals along the HCRs intensified as they propagated over the front. During the onshore flow case, the HCR orientation was nearly parallel to the front. Extended sections of the front ``merged'' with the HCRs. This process strengthened the front and is explained as the merger of like-sign vortices associated with both the front and HCRs. Clouds formed along the intensified portions of the front and at the locations of periodic enhancements on the HCR, which were present prior to the merger. Documentation of two distinct frontal boundaries is presented for the onshore flow case. The first is a kinematic sea-breeze front delineating the region of maximum near-surface convergence between the sea-breeze air and the warmer drier environmental air. The second is a thermodynamic sea-breeze front, which delineates the location where the mean thermodynamic properties differ from the ambient air mass. It is generated by the interaction of the HCRs with the sea breeze and extends a few kilometers ahead of the kinematic frontal position. The kinematic differences between the two cases are quantitatively illustrated. The offshore flow case exhibited stronger low-level convergence, larger vertical velocities, and larger radar reflectivity values. The source air for the clouds developing along the front originated from the ambient and moist sea-breeze air masses for the offshore and onshore flow cases, respectively.
This study will validate the S-band dual-polarization Doppler radar (S-Pol) radar refractivity retrieval using measurements from the International H₂O Project conducted in the southern Great Plains ...in May–June 2002. The range of refractivity measurements during this project extended out to 40–60 km from the radar. Comparisons between the radar refractivity field and fixed and mobile mesonet refractivity values within the S-Pol refractivity domain show a strong correlation. Comparisons between the radar refractivity field and low-flying aircraft also show high correlations. Thus, the radar refractivity retrieval provides a good representation of low-level atmospheric refractivity. Numerous instruments that profile the temperature and moisture are also compared with the refractivity field. Radiosonde measurements, Atmospheric Emitted Radiance Interferometers, and a vertical-pointing Raman lidar show good agreement, especially at low levels. Under most daytime summertime conditions, radar refractivity measurements are representative of an ∼250-m-deep layer. Analyses are also performed on the utility of refractivity for short-term forecasting applications. It is found that the refractivity field may detect low-level boundaries prior to the more traditional radar reflectivity and Doppler velocity fields showing their existence. Data from two days on which convection initiated within S-Pol refractivity range suggest that the refractivity field may exhibit some potential utility in forecasting convection initiation. This study suggests that unprecedented advances in mapping near-surface water vapor and subsequent improvements in predicting convective storms could result from implementing the radar refractivity retrieval on the national network of operational radars.
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The international field campaign called the Convective and Orographically-induced Precipitation Study (COPS) took place from June to August 2007 in southwestern Germany/eastern France. The ...overarching goal of COPS is to advance the quality of forecasts of orographically-induced convective precipitation by four-dimensional observations and modeling of its life cycle. COPS was endorsed as one of the Research and Development Projects of the World Weather Research Program (WWRP), and combines the efforts of institutions and scientists from eight countries. A strong collaboration between instrument principal investigators and experts on mesoscale modeling has been established within COPS. In order to study the relative importance of large-scale and small-scale forcing leading to convection initiation in low mountains, COPS is coordinated with a one-year General Observations Period in central Europe, the WWRP Forecast Demonstration Project MAP D-PHASE, and the first summertime European THORPEX Regional Campaign. Furthermore, the Atmospheric Radiation Measurement program Mobile Facility operated in the central COPS observing region for nine months in 2007. The article describes the scientific preparation of this project and the design of the observation systems. COPS will rest on three pillars: A unique synergy of observing systems, the next-generation high-resolution mesoscale models with improved model physics, and advanced data assimilation and ensemble prediction systems. These tools will be used to separate and to quantify errors in quantitative precipitation forecasting as well as to study the predictability of convective precipitation.
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