S-band Weather Radar Research Articles

크리깅 방법을 기반으로 한 레이더 강우강도 오차 조정

정량적인 강수량 추정은 기상학 수문학적 연구와 활용에 가장 중요한 요소 중 하나이다. 본 논문에서는 정량적 강수량 추정을 위하여 레이더 강우의 지리통계적 오차 구조 함수를 공동크리깅에 적용하여 레이더 강우강도를 조정하였다. 레이더 강우강도의 오차는 공동크리깅의 주변수로서 지상 우량계와 레이더의 강우강도의 차이로 산출되었다. 지상 우량계 강우장은 공동크리깅의 이차변수로서 정규크리깅에 의해 산출되었다. 레이더 강우강도의 오차 분포는 실험적 베리오그램으로 결정된 이론적 베리오그램을 공동크리깅에 적용하여 생성되었고, 레이더 강우강도 조정을 위하여 레이더 강우강도의 오차 분포를 레이더 강우장에 적용하였다. 본 연구의 검증을 위하여 국지적으로 호우가 발생하였던 2009년 7월 6일에서 7일까지의 강우 사례를 선정하였다. 오차가 조정된 1시간 레이더 누적강우량과 지상 우량계 누적강우량의 상관성은 조정 전에 비하여 0.55에서 0.84로 향상되었고, 평균제곱근오차는 7.45에서 3.93 mm로 조정되었다. Quantitative precipitation estimation (QPE) is one of the most important elements in meteorological and hydrological applications. In this study, we adjusted the QPE from an S-band weather radar based on co-kriging method using the geostatistical structure function of error distribution of radar rainrate. In order to estimate the accurate quantitative precipitation, the error of radar rainrate which is a primary variable of co-kriging was determined by the difference of rain rates from rain gauge and radar. Also, the gauge rainfield, a secondary variable of co-kriging is derived from the ordinary kriging based on raingauge network. The error distribution of radar rain rate was produced by co-kriging with the derived theoretical variogram determined by experimental variogram. The error of radar rain rate was then applied to the radar estimated precipitation field. Locally heavy rainfall case during 6-7 July 2009 is chosen to verify this study. Correlation between adjusted one-hour radar rainfall accumulation and rain gauge rainfall accumulation improved from 0.55 to 0.84 when compared to prior adjustment of radar error with the adjustment of root mean square error from 7.45 to 3.93 mm.

Long-term impacts of aerosols on precipitation and lightning over the Pearl River Delta megacity area in China

Abstract. Seven-year measurements of precipitation, lightning flashes, and visibility from 2000 to 2006 have been analyzed in the Pearl River Delta (PRD) region, China, with a focus on the Guangzhou megacity area. Statistical analysis shows that the occurrence of heavy rainfall (>25 mm per day) and frequency of lightning strikes are reversely correlated to visibility during this period. To elucidate the effects of aerosols on cloud processes, precipitation, and lightning activity, a cloud resolving – Weather Research and Forecasting (CR-WRF) model with a two-moment bulk microphysical scheme is employed to simulate a mesoscale convective system occurring on 28 Match 2009 in the Guangzhou megacity area. The model predicted evolutions of composite radar reflectivity and accumulated precipitation are in agreement with measurements from S-band weather radars and automatic gauge stations. The calculated lightning potential index (LPI) exhibits temporal and spatial consistence with lightning flashes recorded by a local lightning detection network. Sensitivity experiments have been performed to reflect aerosol conditions representative of polluted and clean cases. The simulations suggest that precipitation and LPI are enhanced by about 16% and 50%, respectively, under the polluted aerosol condition. Our results suggest that elevated aerosol loading suppresses light and moderate precipitation (less than 25 mm per day), but enhances heavy precipitation. The responses of hydrometeors and latent heat release to different aerosol loadings reveal the physical mechanism for the precipitation and lightning enhancement in the Guangzhou megacity area, showing more efficient mixed phase processes and intensified convection under the polluted aerosol condition.

Consistent Clustering of Radar Reflectivities Using Strong Point Analysis: A Prelude to Storm Tracking

An image segmentation algorithm using an alternating erosion/dilation technique called strong point analysis (SPA) is introduced for general-purpose feature detection. The ability to associate and group pixels with the salient features of an image allows computers to consider images not as an array of values but as a collection of objects. This enables other algorithms to perform advanced tasks, such as tracking an object in a time series of images. The qualitative needs for proper tracking of storm cells in radar images are discussed. To test SPA for those qualities, radar reflectivity images from three S-band weather radars were used. The algorithm is demonstrated to identify features fairly consistently over a time series of images, as well as exhibiting well-behaved changes to its output with respect to changes to the algorithm's input parameters.

Hydrologic analysis of the Fort Collins, Colorado, flash flood of 1997

On 28 July 1997, an unusually moist air mass, driven westward towards the foothills of the Rocky Mountains near Fort Collins, Colorado, produced torrential rainfall. The nearly saturated atmospheric column in conjunction with light upper-level winds resulted in a “warm rain” process convective storm with little net motion. On the evening of 28 July over 200 mm of rain fell in western Fort Collins. This extreme rainstorm was observed by three S-band weather radars, including two National Weather Service WSR-88D radars and the dual-polarization CSU-CHILL radar. Fourteen recording rain gages in and near the affected area recorded the event. The US Geological Survey, Colorado District, performed indirect peak discharge measurements. In our analysis, the two-dimensional, physically-based hydrologic model CASC2D is applied to examine the influence of rainfall and land surface data uncertainty on runoff predictions in the 25 km 2 Spring Creek watershed. Soil saturated hydraulic conductivity values are calibrated in simulations of the rise in nearby Horsetooth Reservoir. Results of simulations driven by polarimetric and single-polarization radar-rainfall estimates and recording rain gage data show that for this extreme event in an urbanized watershed, rainfall estimation errors give rise to the most significant errors in runoff predictions. Hydrologic simulations with various levels of land-surface detail reveal that uncertainty in watershed characteristics has a considerably smaller effect on runoff predictions than uncertainty in the space/time distribution of rainfall. The soil saturated hydraulic conductivity, fraction of impervious area, and the retention depth are the most sensitive land-surface parameters.

A Variational Method for Real-Time Retrieval of Three-Dimensional Wind Field from Multiple-Doppler Bistatic Radar Network Data

Abstract A variational method for the retrieval of the 3D wind field from bistatic multiple-Doppler radar network data is developed, and its performance is evaluated. This bistatic network consists of one S-band weather radar and two passive low-gain receivers at remote sites. To allow for measurement error, the method uses the Doppler velocities of the three receivers as weak constraints and uses the continuity equation as a strong constraint in a cost function in which the two horizontal wind components are the control variables. Improvements are brought to the classical upward integration of the continuity equation, using a weighted combination of upward and downward integrations and its adjoint. A unique characteristic of a bistatic network is that all Doppler velocity measurements from individual resolution volumes are collected simultaneously, which minimizes the errors on the vertical wind component arising from the local evolution of the airflow. However, the time required to sample a complete wea...

Observations of sea clutter using an S‐band weather radar

AbstractIn this paper we review work undertaken on sea clutter illustrated by previously unpublished observations made with an S‐band radar during a research project in South Wales carried out during the winter of 1976/77. The implications for detection with C‐band Doppler radar are considered. Copyright © 1998 Royal Meteorological Society