Boundary Layer Clear-Air Radar Echoes: Origin of Echoes and Accuracy of Derived Winds

Wilson, James W.; Weckwerth, Tammy M.; Vivekanandan, Jothiram; Wakimoto, Roger M.; Russell, Robert W.

doi:10.1175/1520-0426(1994)011<1184:blcare>2.0.co;2

Cited by 203 publications

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“…Boundary layer convergence along the sea breeze front causes sharp gradients of temperature, moisture and wind that can often be seen as a 'thin line' reflectivity signature on radar. The thin line is a region of enhanced radar reflectivity seen in the clear boundary layer (Atkins and Wakimoto, 1997) that is associated with boundary layer convergence and uplift along the sea breeze front or the gust front of thunderstorms (Wilson, Weckwerth, Vivekanandan, Wakimoto and Russell, 1994). While some debate over what causes these clear-air echoes still remains, it is widely accepted that the thin line is due to the presence of insects that are transported into the convergence zone and updraft (Wilson et al, 1994) or due to Bragg scattering from differences in refractive index along the air mass gradient separated by the SB (Atlas, 1960;Atkins and Wakimoto, 1997).…”

Section: Influence Of the North Atlantic Subtropical High On Wet And mentioning

confidence: 98%

Influence of the North Atlantic Subtropical High on wet and dry sea-breeze events in North Carolina, United States

Luchetti

Ferreira

Rickenbach

et al. 2017

Ingeo

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The sea-breeze (SB) is an important source of summertime precipitation in North Carolina (NC, southeast United States). However, not all SB events produce precipitation. A climatology of wet and dry SB events in NC is used to investigate the conditions that are conducive to precipitation associated with the sea breeze.Radar imagery was used to detect 88 SB events that occurred along the NC coast between MaySeptember of 2009-2012. The majority (85%) of SB events occurred during offshore flow (53%) or during flow that was parallel to the coast (22%). SB events were separated into dry (53%) and wet (47%) events and differences in the dynamic and thermodynamic parameters of the environment in which they formed were analyzed. Significant differences in dynamic and thermodynamic conditions were found. SB dry events occurred under stronger winds (6.00 ± 2.36 ms -1 ) than SB wet events (4.02 ± 2.16 ms -1 ). Moreover, during SB wet events larger values of convective available potential energy and lower values of convective inhibition were present, conditions that favor precipitation. Overall, the SB wet events accounted for 20-30% of the May-September precipitation along the NC coastal region. The position of the North Atlantic Subtropical High (NASH) controls both moisture availability and winds along the NC coast, thus providing a synoptic-scale control mechanism for SB precipitation. In particular, it was shown that when the NASH western ridge is located along the southeast coast of the United States, it causes a moist southwesterly flow along the NC coast that may favor the occurrence of SB wet events.Keywords: Sea breeze; precipitation; North Carolina; North Atlantic Subtropical High; wind direction; wind speed. Luchetti, N.T., Nieto Ferreira, R. Rickenbach, T.M., Nissenbaum, M.R. and McAuliffe J.D.Investigaciones Geográficas, nº 68, pp. 09 -25. ResumenLa brisa marina (BM) es una importante fuente de precipitación de verano en Carolina del Norte (NC en su sigla en inglés), sudeste de Estados Unidos. Sin embargo, no todos los eventos de BM producen precipitación. En este trabajo se utiliza una climatología de eventos de BM lluviosos y secos en NC para investigar las condiciones que conducen a la precipitación.Se utilizaron imágenes de radar para detectar 88 eventos de BM ocurridos a lo largo de la costa NC entre mayo y septiembre de 2009 a 2012. La mayoría (85%) de los eventos de BM ocurrieron durante períodos de viento hacia el mar (53%) o viento paralelo a la costa (22%). Los eventos BM se separaron en eventos secos (53%) y lluviosos (47%) y se analizaron las diferencias en los parámetros dinámicos y termodinámicos del entorno en el que se formaron. Se encontraron diferencias significativas en las condiciones dinámicas y termodinámicas. Eventos de BM secos ocurrieron bajo vientos más fuertes (6,00 ± 2,36 ms-1) que los eventos de BM lluviosos (4,02 ± 2,16 ms-1). Las BM lluviosas ocurrieron bajo valores de energía potencial convectiva disponible más altos y valores del parámetro de inhibición convectiva más ...

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Section: Influence Of the North Atlantic Subtropical High On Wet And mentioning

confidence: 98%

Influence of the North Atlantic Subtropical High on wet and dry sea-breeze events in North Carolina, United States

Luchetti

Ferreira

Rickenbach

et al. 2017

Ingeo

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“…Insects and aerosol are also ignored in this derivation. Scattering from insects can be significant in the boundary layer (Wilson et al, 1994). Knight and Miller (1998) discuss insects as sources of radar backscatter in Florida, concluding that, while they probably do contribute to radar signals in the SCMS data in some circumstances, they are not responsible for the main features of concern to us here.…”

Section: B Appendix: Estimating the Radar Signal From In Situ Aircramentioning

confidence: 99%

Radar and in situ observations of small cumulus: physical interpretations of radar Bragg scatter

Baker

Brenguier

2007

Quart J Royal Meteoro Soc

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Radar observations of small cumulus clouds are compared to predictions of radar measurements based on in situ measurements and the theory of radar back-scatter. At the wavelengths used, both Rayleigh and Bragg scatter can be important in small cumulus. A theoretical derivation of radar back-scatter from small cumulus clouds, in which both terms are succinctly derived using a common mathematical model, is presented.For the earliest stages of cumulus clouds, the predictions of Bragg scatter, based on in situ measurements of water-vapour fluctuations, are in close agreement with radar-measured Bragg scatter. This suggests that the theory is adequate and our interpretations of the radar observations are correct. These interpretations include identifying regions where entrainment and mixing are ongoing, identifying adiabatic cores, and estimating the Kolmogorov microscale of turbulence.As the small cumulus develop and enter the early collision and coalescence stages, another source of Bragg scatter can become significant. It is argued, via observations, that the additional Bragg scatter comes from anomalous liquid-water fluctuations. These liquid-water fluctuations are called 'anomalous' because they exceed what would result if liquid water mixed as a passive scalar. The Bragg scatter caused by liquid water may reach effective values of 5-10 dBZ, for a 3 cm-wavelength (X-band) radar, and thus confounds attempts to derive Rayleigh-scatter values below this level using a dual-wavelength (X-and S-band) radar system.

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“…However, after applying those filters, residual echoes of ground clutter and other non-meteorological targets, such as insects, exist on the radar measurements. Some of these are useful, e.g., Doppler velocities in clear air and regions with insects for data assimilation into weather prediction models [14], but for many applications including quantitative rainfall estimation, clutter should be recognized, classified and removed.…”

Section: Introductionmentioning

confidence: 99%

An Objective Prototype-Based Method for Dual-Polarization Radar Clutter Identification

2017

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A prototype-based method is developed to discriminate different types of clutter (ground clutter, sea clutter, and insects) from weather echoes using polarimetric measurements and their textures. This method employs a clustering algorithm to generate data groups from the training dataset, each of which is modeled as a weighted Gaussian distribution called a "prototype." Two classification algorithms are proposed based on the prototypes, namely maximum prototype likelihood classifier (MPLC) and Bayesian classifier (BC). In the MPLC, the probability of a data point with respect to each prototype is estimated to retrieve the final class label under the maximum likelihood criterion. The BC models the probability density function as a Gaussian mixture composed by the prototypes. The class label is obtained under the maximum a posterior criterion. The two algorithms are applied to S-band dual-polarization CP-2 weather radar data in Southeast Queensland, Australia. The classification results for the test dataset are compared with the NCAR fuzzy-logic particle identification algorithm. Generally good agreement is found for weather echo and ground clutter; however, the confusion matrix indicates that the techniques tend to differ from each other on the recognition of insects.

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Boundary Layer Clear-Air Radar Echoes: Origin of Echoes and Accuracy of Derived Winds

Cited by 203 publications

References 0 publications

Influence of the North Atlantic Subtropical High on wet and dry sea-breeze events in North Carolina, United States

Influence of the North Atlantic Subtropical High on wet and dry sea-breeze events in North Carolina, United States

Radar and in situ observations of small cumulus: physical interpretations of radar Bragg scatter

An Objective Prototype-Based Method for Dual-Polarization Radar Clutter Identification

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