Convective transition statistics over tropical oceans for climate model diagnostics: Observational baseline.

Yi-Hung Kuo, Kathleen A. Schiro, and J. David Neelin

J. Atmos. Sci., , accepted 02/2018.
Preprint (1.3 MB), Supplemental Info (3.2 MB)

Abstract:
Convective transition statistics, which describe the relation between column-integrated water vapor (CWV) and precipitation, are compiled over tropical oceans using satellite and ARM site measurements to quantify the temperature and resolution dependence of the precipitation-CWV relation at fast timescales relevant to convection. At these timescales, and for precipitation especially, uncertainties associated with observational systems must be addressed by examining features with a variety of instrumentation, and identifying robust behaviors versus instrument sensitivity at high rain rates. Here the sharp pickup in precipitation as CWV exceeds a certain critical threshold is found to be insensitive to spatial resolution, with convective onset occurring at higher CWV but at lower column relative humidity as bulk tropospheric temperature increases. Mean tropospheric temperature profiles conditioned on precipitation show vertically coherent structure across a wide range of temperature, reaffirming the use of a bulk temperature measure in defining the convective transition statistics. The joint probability distribution of CWV and precipitation develops a peak probability at low precipitation for CWV above critical, with rapid decreasing probability of high precipitation below and near critical, and exhibits systematic changes under spatial-averaging. The precipitation pickup with CWV is reasonably insensitive to time-averaging up to several hours but is smoothed at daily timescales. This work demonstrates that CWV relative to critical serves as an effective predictor of precipitation with only minor geographic variations in the tropics, quantifies precipitation-related statistics subject to different spatial-temporal resolution, and provides a baseline for model comparison to apply these statistics as observational constraints on precipitation processes.

Citation: Kuo, Y.-H., K. A. Schiro, and J. D. Neelin, 2018: Convective transition statistics over tropical oceans for climate model diagnostics: Observational baseline. J. Atmos. Sci., accepted 02/2018.

This research was supported by National Oceanic and Atmospheric Administration Grants NA15OAR4310097 and NA14OAR4310274, the Office of Biological and Environmental Research of the U.S. Department of Energy Grant DE-SC0011074, and National Science Foundation Grant AGS-1540518. U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Climate Research Facility GOAmazon and tropical western Pacific field campaign data are acknowledged. We thank J. Meyerson for graphical assistance. A portion of this work has previously been presented at an American Geophysical Union meeting (Kuo et al. 2016). The authors thank Dr. M. W. Moncrieff and an anonymous reviewer for insightful review comments.