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. Here we study how the warm SSTs of the WHWP enclosed region increase the moisture content, modulate the depth of the boundary layer and to which extent the CLLJ is able to advect the moist air towards the eastern Sierra Madre region. The analysis focuses on how different these processes are for warm and cold ENSO events and the relevance of this variability mode as a control of the meridional rainfall distribution across tropical north America under ENSO forcing. For this analysis, a different approach for the WHWP characterization is implemented as a new volume heat content definition is used for the WHWP instead of the traditional area defined index.
I think it sure does, still the moisture export signature contains a lot of noise which makes hard to underpin only the Gulf evaporation contribution, looking for such relationship has been normally conducted by performing EOF analysis or projecting the pattern onto the SST fields, in those cases some correlations can be found but the signal is not that good. This changes when you repeat the analysis using other variables that have a direct physic link to evaporation such as the heat release (we aim to shown this result in the full manuscript of this contribution for WATER).
You can think of a bunch of nice experiments to check on how large the forcing could be by imposing the pattern as a temperature gradient for example in an aquaplanet simulation.
There are some suggestion on the mechanisms that connect the Intra Americas Seas (moisture fluxes) to the NAM region. For instance, Adams and Stensrud (2007) suggested that Tropical Easterly Waves may be playing an important role in forcing convective activity over the NAM region. Have you included how TEW activity changes might result in forcing moisture fluxes and the onset of the NAM over northwestern Mexico? My point is that we should consider a dynamical mechanism to connect to distant regions
Not directly for this work but we have checked on the low system as a possible precursor of instabilities during the first rainy season in southern Central America and the intensification of rainfall in the Caribbean slope (our question there was how that low pressure could be related with the CLLJ and its associated transport). My feeling on that is that it might result from the influence of the exit region of the CLLJ and the subsidence associated with the descending branch ITCZ that is 'pivoted' in northern South America. If that suggestion is true you should at least observe a marked intensification and a zonal displacement of the low during warm ENSO compared to cold ENSO and neutral years. We did some compositing and the relationship was certainly there but we think we are missing to incorporate in the picture a few thing namely the SST gradients, the boundary layer height which should be tilted when the low intensifies and also filter out the days with heavy rain for which deep convection was influencing the area (but we have not done that yet...).
