深对流系统中初始误差增长和传播的热动力机制

利用WRF模式模拟一个典型的超级单体风暴,揭示了深对流系统中初始误差增长和传播的热动力机制,讨论了系统的高度非线性作用和可预报性等问题。结果表明:影响深对流系统发展强度的不稳定能量和潜热释放是影响误差增长和空间分布的主要因素;误差增长主要集中在对流区,对流区域外的初始扰动有向对流区域传播的趋势,并可在对流区域内迅速增长。随着对流系统的强烈发展,量级为O(10^-2)的初始扰动在210 min时即可达到量级O(10⁰),反映了系统高度的非线性作用和单一确定性预报显著的局限性。另外还发现,初始扰动对的相关性迅速增加,这将导致集合离散度偏低,给集合预报捕获极端天气的能力设置了障碍。误差的传播主要以声波和重力波两种波动形式传播。声波主要表现在积分初期,能量较小。重力波则能够在对流系统以外的区域激发新的对流中心(目前这种误差是不可预报的),进而限制了系统的可预报性。

Thermal dynamics mechanism for growth and propagation of initial perturbation in deep convective system

A supercell storm is simulated by using WRF model to study the growth and propagation of initial perturbation in deep convective system and discuss the predictability of convective system. Results suggest that the instability energy and latent heat release of deep convective system affect the growth and spatial distribution of perturbation which tends to spread towards the moist convection area. The convection system is highly nonlinear and the weather prediction is subject to limitations in term of initial perturbations, which grow rapidly up to O(10⁰) from O(10^-2) in 210 minutes with the development of convection. The correlation of initial perturbations increases sharply as well which is responsible for the low ensemble spread and reduces the ability to predict extreme weather. In addition, it''s been found that the error propagation is related to sound wave and gravity wave which are dominating at the initial and medium-term, respectively. The energy of sound wave is negligible in magnitude. However, gravity wave is able to bring about new convection in other areas. The triggered convection is unpredictable which limits the predictability of the system.