Assessing the Variability and Accuracy of Vertical Profiles of Heating and Vertical Motion in the Tropical Eastern Pacific

Abstract:

Reanalyses are often used to describe the state of the atmosphere over the tropical Eastern Pacific (EP) because of the lack of in situ observations. Vertical profiles of vertical motion, which can be used as a proxy for latent heating profiles, have been shown to have large variability between reanalyses in the EP intertropical convergence zone (ITCZ), as well as a bottom heavy shape that contrasts with the top-heavy profile in the Western Pacific (WP) warm pool. At the same time, satellite-derived stratiform rain fractions are higher in convectively active portions of the EP than the WP, suggesting that a higher peak in latent heating (and thus vertical motion) should be seen in the EP. While the EP sees many more shallow precipitation systems than the WP, deep convection associated with synoptic waves still regularly occurs in the EP. The low-level peak in reanalysis vertical motion persists in the EP during El Niño, when precipitation systems become very similar to those in the WP. Additionally, comparison studies have shown a more top-heavy profile of heating derived from satellite retrieval algorithms than from reanalysis datasets, reinforcing the discrepancy.

The accuracy of vertical motion and heating profiles in the EP is important due to their relationship to large-scale circulations such as the Walker and Hadley cells, as well as the shallow meridional circulation that has been observed and modeled in the EP over the last decade and a half. Some implications for climate sensitivity have also been drawn from reanalysis vertical motion profiles in the EP, adding to the gravity of this issue. In order to determine why the variability in EP vertical motion and heating profiles is so large, as well as whether the bottom heavy profiles in reanalyses are accurate, we analyze and show results from a comparison of eight reanalysis datasets to ship borne radar observations from the Tropical Eastern Pacific Process Study (TEPPS) and satellite data from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) and the cloud profiling radar aboard CloudSat.