Identification of forcing mechanisms of convective initiation over mountains through high-resolution numerical simulations

Abstract

Convection and its ensuing severe weather, such as heavy rainfall, hail, tornado, and high wind, have significant impacts on our society and economy (e.g., Cao et al., 2004; Fritsch and Carbone, 2004; Verbout et al., 2006; Ashley and Black, 2008; Cao, 2008; Cao and Ma, 2009; Zhang et al., 2014). Due to its localized and transient nature, the initiation of convection or convective initiation remains one of the least understood aspects of convection in the scientific communities, and it is a significant challenge to accurately predict the exact timing and location of convective initiation (e.g., Cai et al., 2006; Wilson and Roberts, 2006; Xue and Martin, 2006; Cao and Zhang, 2016). Convective initiation can be attributed to various forcing mechanisms, including, but not limited to, upper-level forcing, boundary-layer forcing, and a combination of them (e.g., Bennett et al., 2006; Lopez, 2007; Marsham et al., 2011). For surface-based convective initiation, boundary-layer forcing often determines the precise location where convection is triggered within large areas of potential instability (e.g., Pielke, 2001). The most common boundary-layer triggering mechanisms include surface fronts, drylines, gust fronts, sea/lake land breezes, orographic circulations, and boundary layer horizontal convective rolls. In addition, inhomogeneity in land surface characteristics can also produce sufficient vertical motion to force convection, particularly under strong surface heating conditions (Trier et al., 2004). Various possible mechanisms for convective initiation are generally recognized, but the exact forcings responsible for a specific case are often difficult to ascertain, especially when multiple physical processes and their interactions are involved. In this issue (Page 1120–1136), Wang et al. (2016) devote themselves to the understanding of the physical mechanisms responsible for convective initiation over the Dabie Mountains located in eastern China. By performing numerical simulations and sensitivity experiments for a real case associated with weak synoptic flows of Meiyu front, the