The Western Hemisphere Warm Pool as a constrain to North American Monsoon activation moisture supply

With a well defined long term basis analysis of moisture supply to the North American Monsoon (NAM) domain based upon FLEXPART Lagrangian trajectories, the role of the Caribbean Sea and the Gulf of Mexico as the primary moisture source for the monsoon onset is analyzed. Regardless the NAM area requires the input from other sources, it is the eastern source which provides the required supply to activate the land moisture processes. The main control on the moisture supply is largely constrained by the transport mechanisms, being the Caribbean Low Level Jet the main modulator. However, it was found that the interannual variability and particularly the response of the moisture supply to ENSO is limited by the Western Hemisphere Warm Pool (WHWP). An alternative approach to the traditional area index based analysis of the WHWP allowed to identify the conditions that control the supply of moisture. Here we propose a hypothesis of the NAM onset activation considering the heat content of the WHWP and its dynamical link with the CLLJ as a limiting condition to moisture export from the Caribbean Sea and the Gulf of Mexico to the eastern Sierra Madre under the influence of ENSO.