Current Updates to the Graphical Turbulence Guidance Nowcast (GTGN) Algorithm

The Graphical Turbulence Guidance Nowcast (GTGN) algorithm has been developed as a tactical turbulence product to help dispatchers and pilots make short-term routing and operational decisions to avoid turbulence hazards and thus enhance safety in the National Airspace System (NAS). Currently, GTGN version 1 (GTGN1) output is being disseminated semi-operationally to aviation users by NCAR in real-time. GTGN provides information on the current state of atmospheric turbulent conditions that can impact aircraft across the continental US. The underlying basis for GTGN1 is a short term Graphical Turbulence Guidance (GTG) forecast based on the 13km RAP model. Recent turbulence observations, such as pilot reports (PIREPs), automated in situ eddy dissipation rate (EDR) reports from commercial aircraft, and EDR estimates from the NEXRAD turbulence detection algorithm (NTDA) are then used to nudge the short term forecast to most accurately represent the most current observed turbulence and to represent all sources of turbulence.

Development of a second generation, GTGN2, algorithm is currently underway with the goal to further improve nowcast accuracy. One major update involves increasing the resolution of GTGN to 3km. Transitioning from using the 13km GTG3 to using the 3km GTG4 as input and ingesting NTDA at 3km, which is closer to NTDA’s native resolution, should improve nowcasts of all forms of turbulence. GTGN2 will also include the addition of lighting data to infer turbulence. Current efforts have shown that a combined data set of space-based GLM satellite lightning data with ground-based lighting allows for GTGN to better identify turbulent regions in areas of spare or missing radar coverage such as the western US and over oceans. Also new this year, NCAR is developing an algorithm to derive EDR from ADS-B vertical rate data. Initial analysis of this new EDR dataset in GTGN shows potential to expand aircraft derived turbulence input in GTGN in areas most relevant to aircraft, along flight routes and where aircraft are flying. This paper will focus on showing these enhancements to GTGN, highlighting the impact of the higher resolution input data and additional data sources on nowcast accuracy.

This research is in response to requirements and funding by the Federal Aviation Administration (FAA). The views expressed are those of the authors and do not necessarily represent the official policy or position of the FAA.