Properties of Convectively Induced Turbulence over Developing Oceanic Convection

Abstract

Convectively induced turbulence (CIT) is an aviation hazard that continues to be a forecasting challenge as operational forecast models are too coarse to resolve turbulence affecting aircraft. In particular, little is known about tropical maritime CIT. In this study, a numerical simulation of a tropical oceanic CIT case where severe turbulence was encountered by a commercial aircraft is performed. The Richardson number (Ri), subgrid-scale eddy dissipation rate (EDR), and second-order structure functions (SF) are used as diagnostics to determine which may be used for CIT related to developing and mature convection. Model-derived subgrid-scale EDR in past studies of midlatitude continental CIT was shown to be a good diagnostic of turbulence but underpredicted turbulence intensity and areal coverage in this tropical simulation. SF diagnosed turbulence with moderate to severe intensity near convection and agreed most with observations. Further, SF were used to diagnose turbulence for developing convection. Results show that the areal coverage of turbulence associated with developing convection is less than mature convection. However, the intensity of turbulence in the vicinity of developing convection is greater than the turbulence intensity in the vicinity of mature convection highlighting developing convection as an additional concern to aviation.

The Importance of Convective Stage on Out-of-Cloud Convectively Induced Turbulence from High-Resolution Simulations

“…Otherwise, the parameterizations were kept consistent for the midlatitude and tropical simulations in order to reduce uncertainty in the turbulence response due to differences in physics schemes. While a full investigation of the sensitivity to parameterizations is beyond the scope of this study, we are confident that the comparative results presented in this study (e.g., tropical versus midlatitude and developing stage versus mature stage) are robust based on prior simulations of CIT conducted (Barber 2015, Barber et al 2018, Barber 2019. Simulation output is saved every 10 min during periods of convective activity to examine convective development, maturity, and dissipation of individual convective cells (Table 1).…”

“…Simulation output is saved every 10 min during periods of convective activity to examine convective development, maturity, and dissipation of individual convective cells (Table 1). Turbulence is identified in this study using second-order structure functions following the methodology implemented in Barber et al (2019). Structure functions are an estimation method for eddy dissipation rate (EDR, «) in the inertial range (Kolmogorov 1941;Frehlich and Sharman 2004a,b;Sharman et al 2006) and have had success for turbulence identification in many studies (Barber et al 2019;Sharman and Pearson 2017;Pearson and Sharman 2017;Frehlich and Sharman 2010).…”

“…The hazards to aviation caused by convection are also dependent on the type and stage of convection (Barber et al 2019;Barber et al 2018;Lane et al 2003). However, variations in turbulence probability relative to convective type of stage are not addressed by current FAA guidelines; only the classification ''severe convection'' is mentioned.…”

“…High-resolution modeling is commonly used to examine small-scale processes that operational forecasting systems cannot resolve. CIT occurs across multiple scales from 10 to 1000 m (Lester 1994) and can impact aviation over 100 km away from the source of convection (Barber et al 2018;Lane et al 2012), well past the FAA lateral avoidance distance of 20 miles (;32 km). CIT is generally expressed as an empirical diagnostic or ensemble of diagnostics in operational forecasts (e.g., GTG-2, Ellrod index; Ellrod and Knapp 1992).…”

“…These small-scale and temporally limited processes include the generation of convective gravity waves, enhancement of deformation zones along cloud boundaries, and enhancement of shear as convection penetrates the tropopause (Lane et al 2003). An additional benefit of highresolution simulations is the more representative depiction of turbulence intensity (Barber et al 2018). While high-resolution simulations of convection allow for further examination of the characteristics of turbulence and the relationship of convective intensity to turbulence, the majority of these simulations have been designed for midlatitude CIT (Barber et al 2018; Zovko-Rajak and Lane 2014; Kim and Chun 2012;Lane and Sharman 2008;Lane et al 2003).…”