Deep Convection and Column Water Vapor over Tropical Land vs. Tropical Ocean: A comparison between the Amazon and the Tropical Western Pacific

Kathleen A. Schiro, J. David Neelin, David K. Adams, and Benjamin R. Lintner

J. Atmos. Sci., 73, 4023-4063, doi:10.1175/JAS-D-16-0119.1. Paper.

Abstract. The relationships between the onset of tropical deep convection, column water vapor (CWV), and other measures of conditional instability are analyzed with two years of data from the DOE Atmospheric Radiation Measurement (ARM) Mobile Facility in Manacapuru, Brazil as part of the GOAmazon campaign, and with 3.5 years of CWV derived from Global Positioning System meteorology at a nearby site in Manaus. Important features seen previously in observations over tropical oceans - precipitation conditionally averaged by CWV exhibiting a sharp pickup at high CWV, and the overall shape of the CWV distribution for both precipitating and non-precipitating points - are also found for this tropical continental region. The relationship between rainfall and CWV reflects the impact of lower free tropospheric moisture variability on convection. Specifically, CWV over land, as over ocean, is a proxy for the effect of free tropospheric moisture on conditional instability as indicated by entraining plume calculations from GOAmazon data. Given sufficient mixing in the lower troposphere, higher CWV generally results in progressively greater plume buoyancies through a deep convective layer. Although potentially greater sensitivity of buoyancy to boundary layer and microphysical processes is possible, the dependence on CWV is consistent with the observed onset of precipitation. Overall, leading aspects of the relationship between CWV and the transition to deep convection in the Amazon have close parallels over the tropical oceans. The relationship is robust to averaging on time and space scales appropriate for convective physics, but is strongly smoothed for averages greater than three hours or 2.5°.

Citation:
Schiro, K. A., J. D. Neelin, D. K. Adams, and B. R. Lintner: Deep Convection and Column Water Vapor over Tropical Land vs. Tropical Ocean: A comparison between the Amazon and the Tropical Western Pacific. J. Atmos. Sci., 73, 4023-4063, doi:10.1175/JAS-D-16-0119.1.

Acknowledgments. Department of Energy Atmospheric Radiation Measurement (ARM) Climate Research Facility GOAmazon and Tropical West Pacific field campaign data were essential to this work. This research was supported by the Office of Biological and Environmental Research of the U.S. Department of Energy grant DE-SC0011074, National Science Foundation Grant AGS-1102838, National Oceanic and Atmospheric Administration Grants NA14OAR4310274. We thank C. Holloway for providing analysis routines.

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