The Physical Structures And Evolution Characteristics Of Perturbation In Ensemble Prediction

One of the key issues in the development of ensemble forecasting is how to construct the initial perturbation,so we can accurately describe atmospheric uncertainty.A reasonable initial perturbation can correctly describe the forecast error structure,and the quality of the initial perturbation can directly affect the overall performance of the ensemble forecast.According to the uncertainty of the initial value of the model and based on a comprehensive assessment of the quality of the ensemble forecasting,this paper studies and reveals the physical structure and evolution characteristics of the initial perturbation of the ensemble forecast,and provides a theoretical basis for the rational construction of the initial perturbation of the ensemble forecast.Firstly,the quality of European medium-term global ensemble forecasting system,the T639 global ensemble forecasting system and GRAPES regional ensemble forecasting system are evaluated and assessed.Secondly,from different angles,such as the physical structure of the initial perturbation,the evolution characteristics of the ensemble spread,and the temporal and spatial distribution of the perturbation energy,to analyze the characteristics of the initial perturbation of wind field and mass field.Finally,the ensemble perturbation is filtered to study the development characteristics of the initial perturbation of each physical quantity under the influence of different scale weather systems,to explore the possible connection between the two,and to reveal the law of reasonable evolution of large-scale and medium-scale perturbation.The main conclusions are as follows:(1)The initial perturbation is distributed near the main weather system and has flowdependent characteristics that can evolve with the weather.The evolution of perturbation at different scales is related to the scale of the weather system.Under the influence of the weather scale system,the disturbance will rise to higher scale and spread widely;The small perturbation is mainly dominated by the meso and micro scale weather system,and its development can be consistent with the precipitation intensity and the distribution is relatively local.(2)The evolution of ensemble spread is also consistent with the changes of weather conditions.For different latitude zones,the ensemble spread in the mid-high latitudes develops rapidly but lack in the low latitudes.Reasonable growth ensemble spread can reflect the ability to capture the forecast error.In contrast,the global central ensemble forecast in Europe has a more reasonable perturbation structure,but it is not as good as the other two in China.(3)The perturbation energy can also grow with the forecasting time.The internal perturbation energy develops faster in the lower troposphere,while the upper layer is dominated by the development of kinetic perturbation energy,and kinetic perturbation energy plays a leading role in the whole evolution process.The large false perturbation that appear in the early stage of the regional ensemble forecast are caused by the false internal perturbation energy and its exist in the upper troposphere.In addition,the development of perturbation energy in the high-level troposphere is faster than that in the lower layer,which means that it is more difficult to increase the ensemble spread of low-level physical quantities than the upper layers.