Nocturnal convection initiation during pecan 2015

This article summarizes the different categories of the 49 NCI events that occurred during the PECAN field campaign. We have added to previous observational climatological studies (i.e., RB17) and model-based PECAN studies (i.e., SG17) of NCI by presenting conceptual models of the different categories of NCI. These PECAN NCI cases were primarily identified using the composite network of radar data. The five different NCI types are associated with (i) frontal overrunning (14% of the cases), (ii) the LLJ alone (10%), (iii) an MCS or preexisting convection (35%), (iv) a bore or density current (25%), or (v) a nocturnal atmosphere lacking a clearly observed forcing mechanism (pristine; 16%). We combined previous conceptual models with revised models and newly developed models to describe the primary environmental features and physical processes associated with our five broadly defined categories of NCI. Other potential NCI mechanisms were not examined here because they were not discernible using the PECAN radar network. These include lifting and horizontal advection associated with cyclonic potential vorticity anomalies, which have been shown to be an important factor in generation and maintenance of nocturnal convection (e.g., Jirak and Cotton 2007; RB18). Another NCI mechanism is quasigeostrophic-aided ascent (e.g., RB18). The mountains-plains solenoidal circulation has also been suggested to play a role in NCI (e.g., Carbone and Tuttle 2008). An additional mechanism that could contribute to NCI near a preexisting MCS is related to microphysical processes, including evaporation, sublimation, and melting, which may cool and moisten the air beneath preexisting anvils in such a way that may help initiate new convection (e.g., Knight et al. 2004; Parker and Johnson 2004). The contribution of these various processes to NCI during PECAN were not investigated because the focus of this paper was based on what could be observed with radar.