An Analysis of the Environmental Moisture Impacts of Western North Pacific Tropical Cyclones

Abstract

Abstract The present study examines the environmental moisture anomalies present during western North Pacific tropical cyclone (TC) passage using storm-relative composites. Composited precipitable water anomalies reveal asymmetric anomalies with dry anomalies to the northwest and southwest of the TC and moist anomalies to the east of the TC. Precipitable water anomalies filtered in space and time suggest that the moisture anomalies in the northwest, southwest, and east regions (NWR, SWR, and ER, respectively) are partially due to the TC, while the anomalies in the SWR are also forced by a convectively suppressed Madden–Julian oscillation (MJO) and equatorial Rossby wave (ERW). Composited vertically integrated moisture budgets and backward parcel trajectories reveal that the moisture anomalies in the NWR, SWR, and ER are primarily due to the convergence of climatological mean moisture by the anomalous meridional wind. This convergence is induced by the secondary circulation of the TC in the NWR and ER and by inertial instability induced by the TC, MJO, and ERW in the SWR and ER as also suggested by prior work. Dry anomalies in the NWR are also forced by the advection of moisture by lower-tropospheric northerly wind anomalies associated with the primary circulation of the TC. Together with prior work, these results suggest that TCs can have significant impacts on their large-scale atmospheric environment extending well beyond the spatiotemporal scales of the lower-tropospheric cyclonic circulation of the TC.