Where ρ is the density and w is the vertical component of velocity. However, EPIC C-130 data were limited to the lower troposphere at a single longitude, which introduced significant limitations. Raymond ( 2017) studied the Eastern Pacific ITCZ based on EPIC2001 C-130 data by looking at thermodynamic parameters such as deep convective inhibition (DCIN), saturation fraction and instability index as a function of latitude. It also flew missions targeted at individual convective clusters. C-130 flew along 95 W to the equator at low altitude, but in its return leg dropped dropsondes from 6,300 m height. The P-3 was used to map the ITCZ by flying a grid pattern at 1,900 m. (For more details on EPIC, see Raymond et al. ( 2004).) During EPIC, two aircraft, NCAR C-130 and NOAA P-3, were deployed from Huatulco, Mexico. The program had a large oceanic component as well.
One of the goals was to determine variability, strength and location of deep convection, and the structure of the boundary layer. Previous to OTREC2019, the most recent field project to study East Pacific convection was East Pacific Investigation of Climate (EPIC2001), which took place from 1 September to 10 October 2001. This paper presents early results from the Organization of Tropical East Pacific Convection (OTREC2019) field program that cast light on this issue.
Alternatively, Raymond ( 2017) proposed that thermodynamic factors mainly in the free troposphere are sufficient to explain the latitudinal distribution of convection across the ITCZ in the tropical East Pacific.
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Riehl et al. ( 1951), Lindzen and Nigam ( 1987), Battisti et al. ( 1999), Tomas et al. ( 1999), Stevens et al. ( 2002), Back and Bretherton ( 2009) suggest that Ekman balance theory plus downward momentum transfer from above the boundary layer are responsible for the ITCZ. Understanding and describing the nature of convection in the East Pacific intertropical convergence zone (ITCZ) remains a challenge. In particular, the strongest convection in the former is to the south, while it is to the north in the latter, in spite of similar latitudinal sea surface temperature distributions. Finally, the characteristics of convection as a function of latitude differ greatly between the Southwest Caribbean and Colombian Pacific coast on one hand, and the intertropical convergence zone to the west. As in other regions that have been studied, a strong anti-correlation exists between the low to mid-level moist convective instability and the column relative humidity or saturation fraction. We found that active convection in this region has predominantly bottom-heavy vertical mass fluxes, while decaying systems exhibit top-heavy fluxes characteristic of stratiform rain regions. We present preliminary results from the field program Organization of Tropical East Pacific Convection (OTREC), with measurements during August and September of 2019 using the NSF/NCAR Gulfstream V over the tropical East Pacific and Southwest Caribbean.
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