基于WRF的积云对流参数化方案对中国夏季降水预报的影响研究

Impacts of cumulus parameterization schemes on the summertime precipitation forecast in China based on the WRF model

中文关键词:  数值预报  积云对流参数化方案  尺度适应  夏季降水

英文关键词:Numerical weather prediction  Cumulus parameterization schemes  Scale-aware  Summertime precipitation

中文摘要:

      为了研究WRF（Weather Research and Forecasting）中尺度模式中积云对流参数化方案对夏季降水预报的影响，基于水平分辨率为9 km的WRF模式，采用Kain-Fritsch（KF）、尺度适应的KF、Tiedtke、new Tiedtke和尺度适应的new Tiedtke方案等5种积云对流参数化方案对中国2019年6—8月的降水进行了模拟。结果表明，两种尺度适应方案对夏季平均降水的量级和落区的预报比原方案（KF方案和new Tiedtke方案）更优，且能正确预报北方和南方的降水峰值时间。而Tiedtke方案、new Tiedtke方案和KF方案均提前了降水峰值时间。在降水的概率分布方面，相比原始的KF和new Tiedtke方案，其尺度适应方案降低（提高）了中小（大）量级降水的频率，模拟的50 mm/d量级以下的降水频次相对更接近观测，但高估了50 mm/d量级以上的降水频次。进一步对比5种方案的次网格积云降水与网格可分辨微物理降水对总降水的贡献，KF和new Tiedtke方案试验中总降水主要由积云降水主导，而Tiedtke方案和两种方案的尺度适应版本则由微物理过程降水主导。随着降水率的增大，尺度适应的KF方案和尺度适应的new Tiedtke方案中积云降水占比迅速减小到30%以下，对50 mm/d量级以上的降水，积云降水占比低于15%。而KF方案在25 mm/d量级以下的降水中，随着降水率的增大积云降水占比反而提高。统计评分表明，尺度适应KF方案和尺度适应new Tiedtke方案有助于减少小量级降水的空报和大量级降水的漏报，对0.1 mm到25 mm的24 h降水的TS评分均高于原始的KF和new Tiedtke方案。

英文摘要:

      This study analyzes impacts of cumulus parameterization schemes on summertime precipitation forecast in China using the WRF model. Five sets of simulations using the Kain-Fritsch, the multi-scale Kain-Fritsch, the Tiedtke, the new Tiedtke and the scale-aware new Tiedtke schemes were conducted. The horizontal resolution of the simulations is 9 km. The results show that the scale-aware schemes (multi-scale Kain-Fritsch and scale-aware new Tiedtke schemes) perform better in the forecast of the magnitude and location of precipitation as well as the diurnal variation. In regard to the probability density distribution of precipitation, compared to the Kain-Fritsch and the new Tiedtke schemes, the scale-aware schemes show lower (higher) frequency of small and middle (high) level of precipitation, leading to more comparable frequency of precipitation lower than 50 mm/d with observations and overestimation of frequency of precipitation higher than 50 mm/d. Further comparisons indicate that the precipitation simulated by the Kain-Fritsch and the new Tiedtke schemes (two scale-aware schemes and the Tiedtke schemes) are dominated by convective rain (microphysical rain). The percentage of convective rain dramatically decreases to 30% in the multi-scale Kain-Fritsch and the scale aware new Tiedtke schemes, and only accounts for 15% of total precipitation for precipitation higher than 50 mm/d. Statistical results show that the scale-aware schemes help to reduce the overestimation of light rain and the underestimation of heavy rain. The threat scores of 24 h accumulated precipitation are higher in the simulations using scale-aware schemes than those using the original schemes for precipitation within the range 0.1 mm to 25 mm.