1. Detailed Dual-Doppler Structure of Kelvin–Helmholtz Waves from an Airborne Profiling Radar over Complex Terrain. Part II: Evidence for Precipitation Enhancement from Observations and Modeling.
- Author
-
Grasmick, Coltin, Geerts, Bart, Chu, Xia, French, Jeffrey R., and Rauber, Robert M.
- Subjects
- *
RADAR in aeronautics , *SPACE-based radar , *SNOWPACK augmentation , *DOPPLER radar , *STRATUS clouds , *LAMINAR flow , *STRATOCUMULUS clouds - Abstract
Kelvin–Helmholtz (KH) waves are a frequent source of turbulence in stratiform precipitation systems over mountainous terrain. KH waves introduce large eddies into otherwise laminar flow, with updrafts and downdrafts generating small-scale turbulence. When they occur in cloud, such dynamics influence microphysical processes that impact precipitation growth and fallout. Part I of this paper used dual-Doppler, 2D wind and reflectivity measurements from an airborne cloud radar to demonstrate the occurrence of KH waves in stratiform orographic precipitation systems and identified four mechanisms for triggering KH waves. In Part II, we use similar observations to explore the effects of KH wave updrafts and turbulence on cloud microphysics. Measurements within KH wave updrafts reveal the production of liquid water in otherwise ice-dominated clouds, which can contribute to snow generation or enhancement via depositional and accretional growth. Fallstreaks beneath KH waves contain higher ice water content, composed of larger and more numerous ice particles, suggesting that KH waves and associated turbulence may also increase ice nucleation. A large-eddy simulation (LES), designed to model the microphysical response to the KH wave eddies in mixed-phase cloud, shows that depositional and accretional growth can be enhanced in KH waves, resulting in more precipitation when compared to a baseline simulation. While sublimation and evaporation occur in KH downdrafts, persistent supersaturation with respect to ice allows for a net increase in ice mass. These modeling results and observations suggest that KH waves embedded in mixed-phase stratiform clouds may increase precipitation, although the quantitative impact remains uncertain. Significance Statement: This study investigates how the turbulence caused by Kelvin–Helmholtz (KH) waves embedded in deep clouds affect precipitation growth. To answer this question, we used a Doppler radar on board a research aircraft to locate KH waves inside of clouds. These waves often break, and produce fallstreaks, which may descend down to the surface. Aircraft measurements from within these fallstreaks confirmed that they contain larger, more numerous ice particles. This evidence of enhanced precipitation coincided with turbulence and supercooled liquid water produced by the KH waves. Modeled KH waves show that some of the precipitation enhancement is caused by accretion and deposition within updrafts, but further research is needed to understand the role of turbulence and ice initiation in KH waves. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF