Impacts of Multi-Timescale Circulations on Meridional Moisture Transport

Abstract

AbstractRelative impacts of the climatological annual mean, the climatological annual variation, the synoptic, the intra-seasonal and the inter-annual flows on meridional moisture transport were investigated based on reanalysis data. Due to an in-phase relationship between the poleward wind and specific humidity, the synoptic and intra-seasonal motions contribute about 50% and 30% of the maximum zonal and annual mean poleward moisture transport in the middle latitudes, respectively. The preferred latitudinal location (40°N or S) of the maximum zonal mean moisture transport by the synoptic motion is attributed to the combined effect of the maximum wind variability poleward of 40°N or S in association with atmospheric baroclinic instability and the maximum moisture variability equatorward of 40°N or S in association with the anomalous advection of the mean moisture. While the MJO and ENSO have a small contribution to the long-term mean transport, they may strongly affect regional moisture transport through interaction with the mean moisture and through the modulation to higher-frequency modes. A statistical relationship between tropical cyclone (TC) moisture and intensity was constructed based on a large number of high-resolution Weather Research and Forecasting (WRF) model simulations, and the so-derived relationship was further applied to estimate TC moisture transport. It is found that TC transport accounts for about 30% (53%) of the climatological seasonal mean total moisture transport over key northern (southern) hemispheric TC track regions in the northern (southern) hemispheric TC season.