climatologic "India-Burma Trough Index" defined by hgt_dif. Unit: gpm. Jan~Dec
-7.33124
-8.63026
-6.23523
-3.71848
-7.78747
-18.8073
-20.6408
-15.8447
-12.4078
-11.0705
-10.2668
-7.49814