Thursday, 12 July 2018: 8:45 AM
Regency D (Hyatt Regency Vancouver)
As a step towards better understanding how direct atmospheric heating by greenhouse gases or absorbing aerosols affects moist convection and tropical circulation, we reduce the specified radiative cooling by half in a radiative-convective equilibrium (RCE) simulation with the Weather Research and Forecasting (WRF) Model. It is found that the total rainfall reduces approximately by half as well, as dictated by the balance between radiative cooling and latent heating. Yet, this reduction is realized almost entirely through low-intensity events (rain rate less than 400 mm day-1), while the contribution from heavy events is largely unaffected. The latter is attributed to increased boundary-layer moisture content, which is necessary for reducing evaporation. Rain re-evaporation is identified as a main mechanism for free-tropospheric heating to alter boundary-layer energy balance. A series of sensitivity experiments with rain re-evaporation turned off highlight its importance for regulating surface air temperature and humidity responses, and convective organization.
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