Easterly waves in the East Pacific during OTREC 2019 field campaign

Abstract:

Easterly waves (EWs) are synoptic (i.e., between 2 and 10 days) disturbances with a westward phase speed around 11.5 m/s. Over the East Pacific in boreal summer, the combination of EWs and other synoptic scale propagating disturbances (e.g., convectively coupled equatorial waves), plus local mechanisms such as sea surface temperature (SST) gradients, define the climatological structure of the ITCZ. The climatological East Pacific ITCZ has both deep and shallow convection that are linked to deep and shallow meridional circulations, respectively. The deep convection is located around 9°N over the East Pacific warm pool. The shallow convection is located around 6°N and is driven by the strong meridional SST gradient south of the ITCZ. This study aims to determine the interaction between EWs and the deep and shallow meridional circulations over the East Pacific during OTREC 2019 using field campaign observations, satellite precipitation, and ERA5 reanalysis. We identified three strong EWs during the OTREC 2019 period with similar vorticity and meridional winds. Composite fields suggest that the deep and shallow meridional circulations in the ITCZ are modified during the passage of EWs in the East Pacific. The convectively active part of the EW enhances the deep circulation at day 0 and is associated with the export of moist static energy (MSE). The suppressed part of the EW enhances the shallow circulation at day +2 and the shallow overturning flow at 850 hPa is linked to the anticyclonic circulation of the EW. The import of MSE is associated with the shallow convection over the southern part of the ITCZ.