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Rosemary Auld Miller and William M. Frank

Abstract

A number of field experiments and subsequent studies in the 1970s and 1980s have led to the belief that radiative processes play a more significant role in the evolution of tropical mesoscale convective systems (MCSS) than was once thought. In this study, an interactive radiative transfer scheme is incorporated into a two-dimensional version of the Pennsylvania State University-NCAR Mesoscale Model to simulate the evolution of these systems within a large-scale environment under a diurnally varying radiative influence. The radiative effects are examined in terms of the net rainfall, diurnal phasing, and the vertical distribution of diabatic heating within the systems. In addition, three current radiative forcing hypotheses are addressed.

Simulations of individual MCSs with radiation produced more rainfall than those without it. While runs with forced background meant all peaked after the same elapsed time regardless of diurnal initialization time, the peak rainfall rates that occurred at night were greater than those occurring during daytime hours. Without the imposed destabilizing influence of an initialized intertropical convergence zone, rainfall rates peaked near midnight in spite of significantly different model-run start times, and a distinct diurnal cycle was established.

Initialized deep stratiform and cirriform clouds developed mesoscale, edge-oriented convective organization due to the lateral gradients of radiative forcing at the cloud edges. Convective overturning within these mesoscale systems' own trailing anvil clouds was insignificant, and there was no evidence of active latent heating in the clouds great distances away from the convection. A simulation of an MCS with imposed horizontally uniform radiative cooling throughout the domain showed no significant differences in 12-h, domain-averaged rainfall from the control case. Cloud-cloud-free radiative differences tended to modulate the life cycles of the mesoscale circulations within the simulated MCSs, and to concentrate a slightly larger fraction of the total domain rainfall within the MCSs, but they did not significantly alter the MCS structures or net domain rainfall production.

Radiative processes in this study modulate the evolution of tropical mesoscale systems, and hence, tropical rainfall, primarily through large, domainwide destabilization. These simulations indicate that mesoscale radiative forcing through cloud-cloud-free radiative differences and direct destabilization of stratiform clouds is of lesser importance. Although horizontally varying radiative processes appear to play some role in determining the location of convection, they do not appear to have major effects upon either the total amount of or the diurnal variations in tropical rainfall.

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Brian A. Colle, Rosemary Auld, Kenneth Johnson, Christine O’Connell, Temis G. Taylor, and Joshua Rice

Abstract

It is challenging to communicate uncertainty for high-impact weather events to the public and decision makers. As a result, there is an increased emphasis and training within the National Weather Service (NWS) for “impact-based decision support.” A Collaborative Science, Technology, And Research (CSTAR) project led by Stony Brook University (SBU) in collaboration with the Alan Alda Center for Communicating Science, several NWS forecast offices, and NWS operational centers held two workshops at SBU on effective forecast communication of probabilistic information for high-impact weather. Trainers in two 1.5-day workshops helped 15-20 forecasters learn to distill their messages, engage audiences, and more effectively communicate risk and uncertainty to decision makers, media, and the general public. The novel aspect of the first workshop focused on using improvisational techniques to connect with audiences along with exercises to improve communication skills using short, clear, conversational statements. The same forecasters participated in the second workshop, which focused on matching messages to intended audiences and stakeholder interaction. Using a recent high-impact weather event, representatives in emergency management, TV media, departments of transportation, and emergency services provided feedback on the forecaster oral presentations (2-3 minute) and a visual slide. This article describes our innovative workshop approach, illustrates some of the techniques used, and highlights participant feedback.

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