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Aoqi Zhang and Yunfei Fu

Abstract

We identified precipitating systems from May to August 2016 using data from the Global Precipitation Measurement mission Dual-frequency Precipitation Radar instrument. Then, using this set of cases, Himawari-8 10.4-μm brightness temperature data from before and after each precipitation event were used to identify three life stages of clouds: a developing stage, a mature stage, and a dissipating stage. Using statistical analysis and two case studies, we show that the precipitating systems at different life stages of the clouds have different systematic properties, including the area of precipitation, the convective ratio, the rain-top height, and the brightness temperature. The developing systems had the largest convective ratio, whereas the dissipating systems had the largest area of precipitation. The life stage of the cloud also influenced the vertical structure of the precipitation. The microphysical processes within each stage were unique, leading to various properties of the droplets in precipitation. The developing systems had large, but sparse, droplets; the mature systems had large and dense droplets; and the dissipating systems had small and sparse droplets. Our results suggest that the different properties of precipitating systems in each life cycle stage of clouds are linked to the cloud water content and the upward motion of air.

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Aoqi Zhang, Yilun Chen, Xiangdong Zhang, Qiong Zhang, and Yunfei Fu

Abstract

Despite the long existence of theoretical studies, few statistical studies of precipitation characteristics on the northern Pacific storm track have been reported due to lack of observation. Using data from GPM DPR and ERA-Interim, we examined the precipitation features of extratropical cyclones in the northern Pacific storm-track region. Extratropical cyclones were classified into four categories including developing, mature, dissipating, and short-term based on their life stages. Our results show that extratropical cyclones of all categories had a “comma” rainband and precipitation mostly occurred to the east of the cyclonic center. The extratropical cyclones promote precipitation to the east of their centers, but suppress precipitation to the west. Precipitation to the east of the extratropical cyclones had larger and more condensed droplets, a stronger intensity, and a higher rain top than the local seasonal average, while the opposite characteristics were seen to the west. Our results suggest that the different types of vertical air motion and moisture content in these two regions induced by the frontal structure of extratropical cyclones play important roles in the different impact of extratropical cyclones. Furthermore, the different life stages of extratropical cyclones had different degrees of impact on precipitation: the highest impact in the developing stage, followed by the mature stage, and the weakest impact in the dissipating stage.

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Shihe Ren, Xueming Zhu, Marie Drevillon, Hui Wang, Yunfei Zhang, Ziqing Zu, and Ang Li

Abstract

A frontal detection algorithm is developed with the capability of detecting significant frontal segments of sea surface temperature (SST) in the high-resolution South China Sea Operational Forecasting System (SCSOFS). To effectively obtain frontal information, a gradient-based Canny edge detection algorithm is improved with postprocessing designed for high-resolution numerical models, aiming at extracting primary ocean fronts while ensuring the balance of frontal continuity and positioning accuracy. Metrics of frontal probability and strength are used to measure the robustness of the results in terms of mean state and seasonal variability of frontal activities in the South China Sea (SCS). Most fronts are found in the nearshore and form a strip shape extending from the Taiwan Strait to the coast of Vietnam. The SCSOFS is found to reproduce strong seasonal signals dominating the variability of the frontal strength and occurrence probability in the SCS. We implement the algorithm on the daily averaged SST derived from two other SST analyses for intercomparison in the SCS.

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Weihua Yuan, Rucong Yu, Minghua Zhang, Wuyin Lin, Jian Li, and Yunfei Fu

Abstract

The simulations of summertime diurnal cycle of precipitation and low-level winds by the Community Atmosphere Model, version 5, are evaluated over subtropical East Asia. The evaluation reveals the physical cause of the observed diurnal rainfall variation in East Asia and points to the source of model strengths and weaknesses. Two model versions with horizontal resolutions of 2.8° and 0.5° are used.

The models can reproduce the diurnal phase of large-scale winds over East Asia, with an enhanced low-level southwesterly in early morning. Correspondingly, models successfully simulated the diurnal variation of stratiform rainfall with a maximum in early morning. However, the simulated convective rainfall occurs at local noontime, earlier than observations and with larger amplitude (normalized by the daily mean). As a result, models simulated a weaker diurnal cycle in total rainfall over the western plain of China due to an out-of-phase cancellation between convective and stratiform rainfalls and a noontime maximum of total rainfall over the eastern plain of China. Over the East China Sea, models simulated the early-morning maximum of convective precipitation and, together with the correct phase of the stratiform rainfall, they captured the diurnal cycle of total precipitation. The superposition of the stratiform and convective rainfalls also explains the observed diurnal cycle in total rainfall in East Asia. Relative to the coarse-resolution model, the high-resolution model simulated slight improvement in diurnal rainfall amplitudes, due to the larger amplitude of stratiform rainfall. The two models, however, suffer from the same major biases in rainfall diurnal cycles due to the convection parameterization.

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