The Tropopause Folding Turbulence Detection(TFTD) algorithm which is originally developed for the Tropopause Folding Turbulence Product(TFTP) from the Geostationary Operational Environmental Satellite(GOES)?R is presented and discussed for the Korean Communication, Ocean, Meteorological Satellite(COMS) and the Japanese geostationary meteorological satellite(Himawari-8).
The TFTD algorithm assumes that the tropopause folding is linked to the Clear Air Turbulence(CAT). The tropopause folding areas are detected the rapid spatial gradients of the upper tropospheric specific humidity. The Layer Averaged Specific Humidity (LASH) is used to represent the upper tropospheric specific humidity, which is calculated using COMS 6.7㎛ and Himawari-8 6.2㎛ water vapor channel, and ERA-interim reanalysis temperature at 300, 400, and 500hPa. The comparison of LASH with the numerical model specific humidity shows a strong negative correlation of 80% or more. We apply the single threshold, which is determined from sensitivity analysis, for cloud-clearing to overcome strong gradient of LASH at the edge of clouds. The tropopause break lines are detected from the location of strong LASH-gradient using the Canny edge detection based on the image processing technique. The tropopause folding area is defined by expanding the break lines by 2-degree positive gradient direction.
The validations of COMS TFTD is performed with Pilot Reports(PIREPs) only filtered out Convective Induced Turbulence(CIT) from Dec 2013 to Nov 2014 over the South Korea. The score test shows 0.49 PODy(Probability of Detection ‘Yes’) and 0.64 PODn(Probability of Detection ‘No’) for COMS and 0.65 PODy and 0.47 PODn for Himawari-8. Low POD results from various kinds of CAT reported from PIREPs and the characteristics of high sensitivity in edge detection algorithm.