Development of JMA's new turbulence index

Japan Meteorological Agency (JMA) developed a new turbulence forecast index called TBindex which can predict various kinds of turbulences in a comprehensive manner. TBindex is constructed with multiple turbulence indices as with the Graphical Turbulence Guidance system. TBindex consists of independent five CAT indices and five non-CAT turbulence indices derived from JMA's meso scale model (MSM). These indices are compounded by the logistic regression technique with in-flight turbulence information of PIREPs, where effective indices are selected depending on the level by the stepwise method based on Akaike's information criterion. The regression equations are stratified and adjusted in every 2,000 ft from 1,000 ft to 41,000 ft so that TBindex can predict turbulences optimally over all height at the same threshold. Results of the verification show that the forecast accuracy of TBindex is significantly better than conventional turbulence indices. TBindex has been in operation since March 2011 and it has been used as one of basic data for issuance of SIGMET and domestic SIGWX prognostic charts in JMA.