Figure 9: Geopotential tendency (Φ/t; m day−1) at 500 hPa level at (a) 09:00 LST October 27, 2003, and (b) 21:00 LST. Triangle indicates Gangneung city. Shadow (white) area indicates negative (positive) geopotential tendency, which implies the shrunken (expansion) rate of geopotential height change at 500 hPa level for a day. As a positive tendency at 09:00 LST (21:00 LST) in Gangneung city was +83 m day−1 (+30 m day−1), the net one of −53 m for 12 hours implies a 53 m-shrunken atmospheric depth at 21:00 LST, causing a maximum PM10 at 17:00 LST.