Environmental fields of moderate clear air turbulence above 400 hPa around Japan

We analyzed environmental fields for moderate clear air turbulence (CAT) reported above 400 hPa over Japan between 2010 and 2017. We divided the year into five periods, with June separate from summer. In June, a stagnant front called the Baiu front is often present over Japan, making meteorological conditions different from summer. Using reanalysis data, we analyzed environmental fields for each period. It is shown that the environmental fields of aviation turbulence around Japan differ depending on altitude and period. In winter, CAT tends to occur on the west side of the trough of the jet stream axis. The jet stream is often weak when CAT occurred. CAT is likely to occur around trough in spring and fall, suggesting that the trough-enhanced deformation and strengthened vertical wind shear caused the CAT. CAT likely occurs in a field with cyclonic circulation and active convection in the lower levels in summer. In June, it is suggested that it tends to occur north of the Baiu front and around troughs associated with the jet stream. The jet stream to the north of the Baiu front suggests that the Baiu front is related to the onset of CAT.