面向四维变分资料同化的NSAS积云深对流参数化方案的简化及线性化研究

A study of simplification and linearization of the NSAS deep convection cumulus parameterization scheme for 4D-Var

中文关键词:  NSAS积云深对流参数化  雅可比矩阵评估  简化与线性化  GRAPES全球四维变分资料同化

英文关键词:NSAS deep convection cumulus parameterization  Jacob matrix assessment  Simplification and linearization  GRAPES global 4D-Var

中文摘要:

      GRAPES全球四维变分资料同化系统需要积云深对流参数化方案的线性化与伴随方案，直接采用原始复杂参数化方案进行线性化并不可行，需要发展简化光滑方案来减缓非线性与非连续性特征。GRAPES全球模式采用NSAS积云对流参数化方案，积云深对流对环境的反馈主要通过补偿下沉来实现，研究突出补偿下沉作用，忽略降水蒸发、动量反馈等贡献，形成简化方案。采用输入温、湿度廓线加入不同幅度小扰动方法，评估参数化方案计算的温度、比湿时间倾向对输入扰动的敏感性，检验非线性与非连续特征。提出避免或减缓非连续“开关”的方法，在简化方案的基础上发展了简化光滑方案。简化光滑方案与原始积云深对流方案相比，在对流触发上一致，在对流的位温与比湿倾向、降水的时序模拟等方面相似，而在减缓非线性、避免非连续性方面显著优于原始方案。基于简化光滑方案发展的线性化方案表明，对小于2倍分析增量幅度的扰动，线性化方案可以较好地模拟非线性方案的扰动发展。发展的简化光滑方案具有合理性和实用性。

英文摘要:

      The GRAPES global four-dimensional variational data assimilation system (4D-Var) requires tangent and adjoint schemes of deep convection cumulus parameterization scheme. It is not practical to directly linearize the original complicated deep convection cumulus parameterization scheme. Simplified smoothing scheme is needed to reduce the nonlinearity and discontinuity. The GRAPES global model adopts the New Simplified Arakawa-Schubert (NSAS) cumulus parameterization scheme developed in NCEP. Deep convection feedback to the environment is mainly achieved by compensating subsidence. In this paper, the contribution from compensating subsidence is addressed and the contributions of precipitation evaporation and momentum feedback are ignored to form a simplified scheme. By adding small amplitude perturbations to the input temperature and specific humidity profiles, the sensitivity of temperature and specific humidity tendencies calculated by the parameterization scheme to input perturbations is evaluated, and the non-linear and discontinuous characteristics of the scheme are tested. Based on the simplified scheme, a simplified smoothing scheme is proposed by using a method of avoiding or reducing discontinuous "switches". Compared with the original deep convection cumulus parameterization scheme, the simplified smoothing NSAS scheme is consistent in convection triggering, and the potential temperature and specific humidity tendencies are comparable with those from the original scheme, while the precipitation time series simulation is better. The simplified smoothing NSAS also has obvious advantages in reducing non-linearity and avoiding discontinuity. The tangent linear scheme based on the simplified smoothing scheme shows that when the perturbation amplitude is less than 2 times of the analysis increment, it can well simulate the difference of the nonlinear schemes. The above results clearly demonstrate the rationality and practicability of the simplified smoothing scheme developed in this paper.