Clear Air Turbulence Indices Derived from U.S. Navy Numerical Model Data: A Verification Study.
NAVAL RESEARCH LAB MONTEREY CA DECISION AID SECTION
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Two clear air turbulence indices TI and CCAT are computed using data from the Navy Operational Global Atmospheric Prediction System NOGAPS model. The TI index is based on deformation and vertical wind shear the CCAT index is based on the advection of vertical stability and absolute vorticity. Verification of both indices is accomplished by comparing model-derived analyses and forecasts with pilot reports of turbulence intensity. Correlations between turbulence intensity and index value indicate that only the TI index has any ability viz., minimal in the forecasting of any arbitrary smooth through severe turbulence event. Verification statistics for both indices show high false alarm rates indicative of over- forecasting and only modest capability in correctly forecasting observed moderate or or greater turbulence. Comparisons among analysis, 12- and 24-hour statistics do not indicate degradation of turbulence forecasting skill with lead time for either index. A reduction in model resolution from 2.50 to 1.00 provides slightly improved forecasting capability to the CCAT index, noticeably less improvement for the TI index. Overall results indicate a slight preference for the TI index in operational forecasting of clear air turbulence when using the NOGAPS model output
- Statistics and Probability