On the contribution of the Tropical Western Hemisphere Warm Pool source of moisture to the northern hemisphere precipitation through a Lagrangian approach

We herein investigate the role of the Tropical Western Hemisphere Warm Pool (WHWP) in providing moisture to the atmosphere throughout its annual cycle, and identify those regions that could be affected by precipitation whose origin lies in this source. We use data from the Lagrangian FLEXPART model for the period 2000-2004 to identify the contributions of humidity from a region, by determining changes in specific humidity along the forward trajectories over a 10-day period. An analysis was performed for all the air parcels that lay in the region of the WHWP (defined according to the 28.5ºC threshold applied in SST), and the monthly average conditions over the 5-year period were analysed for May to October, inclusive. Our results show that this source provides a higher contribution of moisture to North America from June onwards, when warmer waters may be observed over the Atlantic side of the warm pool and the transport of moisture may be increased by the Great Plains Low Level Jet. During the Boreal Summer, this contribution extends towards western Europe, probably as a result of the transport of moisture by the warm conveyor belts and the North Atlantic anticyclone. A qualitative similarity between the results of our Lagrangian analyses and the observed patterns of precipitation highlight the contribution of the source of moisture of the WHWP for the regimes of precipitation over eastern North America, the North Atlantic, and the Inter Tropical Convergence Zone.