Summer Season Precipitation Biases in 4 km WRF Forecasts Over Southern China: Diagnoses of the Causes of Biases. Issue 23 (7th December 2021)

• Record Type: Journal Article
• Authors: Zhu, Kefeng; Yu, Biyu; Xue, Ming; Zhou, Bowen; Hu, Xiao‐Ming
• Is Part Of: Journal of geophysical research. Volume 126:Issue 23(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-07
• Subjects: Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2021JD035530
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: In a recent study, we evaluated the performance of real‐time convection‐permitting WRF model forecasting over China. Although the overall rainfall distribution and diurnal cycle are well simulated, the model greatly overestimates the rainfall intensity in southern China and the predicted rainfall shows a southeast location bias. In this study, possible factors contributing to the precipitation forecast bias are discussed. The precipitation over southern China is found to be greatly influenced by land‐sea circulations. While the model captures diurnal variations of winds well, the predicted amplitude and onset timing of the land/sea breezes differ from observations. Cold bias of land‐surface temperature is shown to partially cause wind bias. In the afternoon, the cold bias results in a weakened inland penetration of sea breeze, which in turn leads to more rain on the eastern south‐China coastline. During nighttime, excessive cooling over land results in a stronger land breeze, leading to location bias of early morning precipitation. While the observed coastal rain belt is mostly located over land during early morning, the predicted coastal rain belt is mostly located over ocean. In addition, the model overestimates moisture at low levels, especially over the southern slope of the coastal mountains and over ocean, which explains the excessive rainfall over southern China. This study emphasizes the importance of accurately simulating land‐surface‐related variables for precipitation forecast in coastal regions where land‐sea contrast plays an important role. Key Points: The initiation and propagation of convection over southern China are greatly influenced by land‐sea circulations Cold bias over land results in a weaker sea breeze during the afternoon and a stronger land breeze at night, causing rainfall location bias Overprediction of moisture along the coastal mountains and over the ocean is the primary cause of excessive rainfall