Spurious mountain-wave features have been reported as false alarms of light-or-stronger numerical weather prediction (NWP)-based cruise level turbulence forecasts especially over the western mountainous region of North America. To reduce this problem, a hybrid sigma-pressure vertical coordinate system was implemented in NOAA's operational Rapid Refresh model, version 4 (RAPv4), which has been running in parallel with the conventional terrain-following coordinate system of RAP version 3 (RAPv3). Direct comparison of vertical velocity |w| fields from the RAPv4 and RAPv3 models shows that the new RAPv4 model significantly reduces small-scale spurious vertical velocities induced by the conventional terrainfollowing coordinate system in the RAPv3. For aircraft-scale turbulence forecasts, |w| and |w|/Richardson number (|w|/Ri) derived from both the RAPv4 and RAPv3 models are converted into energy dissipation rate (EDR) estimates. Then, those EDR-scaled indices are evaluated using more than 1.2 million in situ EDR turbulence reports from commercial aircraft for 4 months (September-December 2017). Scores of the area under receiver operating characteristic curves for the |w|- and |w|/Ri-based EDR forecasts from the RAPv4 are 0.69 and 0.83, which is statistically significantly improved over the RAPv3 of 0.63 and 0.77, respectively. The new RAPv4 became operational on 12 July 2018 and provides better guidance for operational turbulence forecasting over North America.
Bibliographical noteFunding Information:
Acknowledgments. The authors thank Dr. Joshua W. Scheck at the NOAA/Aviation Weather Center (AWC) for his thorough review on the original manuscript. The authors also thank another anonymous reviewer for his/her comments and suggestions on the paper. This research was funded in part by the Federal Aviation Administration (FAA) Grant DTFACT-17-X-80002. The views expressed are those of the authors and do not necessarily represent the official policy or position of the FAA. Jung-Hoon Kim (JHK) used to work at the NOAA/ (AWC) as an affiliated research scientist from the Colorado State University/Cooperative Institute for Research in Atmosphere (CSU/CIRA). He appreciates all of the support from the NOAA/AWC and CSU/CIRA for this work. JHK was supported by the Research Resettlement Fund for the new faculty of Seoul National University. JHK was also supported by the Research and Development for the Korean Meteorological Administration (KMA) Weather, Climate, and Earth System Services. Sang-Hun Park (SHP) was supported by the Yonsei University Future-leading Research Initiative of 2018-22-0021.
All Science Journal Classification (ASJC) codes
- Atmospheric Science