1. Part II: Case Studies and Statistical Results
A New Direction in Clear-Air Turbulence Forecasting Based on Spontaneous Imbalance
Part II: Case Studies and Statistical Results
Donald McCann
McCann Aviation Weather Research, Inc.
Overland Park, Kansas
John A. Knox
Faculty of Engineering, University of Georgia
Athens, Georgia
Paul D. Williams
Department of Meteorology, University of Reading, Reading UK
CASE STUDY
STATISTICAL RESULTS
A major outbreak of upper level turbulence occurred during the morning on 24 October We counted 317 turbulence pilot reports between 1100 UTC and 1300 UTC.
We tested our method with 9542 text pilot reports carefully collected between 1500 UTC and 1700 UTC on each day from 3 November 2005 and 26 March PIREPs near convection, in mountain waves, or in the planetary boundary layer were not included. The maximum TKE dissipation in the layer with the PIREP FL computed from the corresponding 1-hour RUC2 forecast verifying at 1600 UTC within 50 km of the PIREP location validated the PIREP.
3-hr RUC2 300mb forecast from 0900 UTC.
3-hr RUC2 forecast verifying 1200 UTC
24 Oct 2007 of Lighthill-Ford Radiation (blue)
and Richardson number (pink) at FL290.
The Lighthill-Ford method’s Relative Operating Characteristic curve is much closer to the
upper right corner than Graphical Turbulence Guidance (GTG).
The highest score for the differentiation between no turbulence and positive
turbulence is for a zero threshold. In other words, when there is positive TKE
dissipation forecast, aircraft will likely feel some turbulence. At MODERATE and
SEVERE intensities the Heidke Skill Score peaks with higher TKE dissipation; this
indicates that the higher the forecast rate, the stronger the expected turbulence.
For turbulence at all flight levels our
application reaches the U.S. government
goal with a PODyes for MODERATE or
greater turbulence of .831 and a PODyes
of SMOOTH of .851.
3-hr RUC2 forecast of our TKE Dissipation, starting in the lower right clockwise, at FL170, FL230, FL290, and FL350 verifying 1200 UTC 24 Oct Color fills roughly correspond to LIGHT (blue), MODERATE (yellow), and SEVERE (red) turbulence. Pilot reports within 2000 ft and one hour of verifying altitude and time are plotted in standard notation.
Using Lighthill-Ford Radiation as a gravity wave trigger, we are able to skillfully forecast turbulence
at all flight levels.