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Sensitivity to precipitable water content and profile

Resolution dependence of sub-tropical westerlies. Introduction. Frequency of AR events.

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Sensitivity to precipitable water content and profile

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  1. Resolution dependence of sub-tropical westerlies. Introduction Frequency of AR events Atmospheric Rivers (ARs) are narrow bands of intense water vapor transport often found in the warm sectors of extratropical cyclones. They are responsible for more than 90% of water vapor transport to mid-latitudes and cause extreme precipitation in coastal mountainous regions such as the West Coast of the US. • As resolution increases, the sub-tropical westerlies shift poleward. • This effect has been observed in other dycores as well (Williamson 2008, Tellus). Resolution and Dynamical Core Dependence of the Statistics of Atmospheric River events in Community Atmospheric Model (CAM)Samson M. Hagos, L. Ruby Leung, Jian Lu, Qing Yang, Chun Zhao • In both real world and aquaplanet simulations AR frequency decreases with increasing model resolution. • HOMME dynamical core produces significantly more AR events than MPAS-A. An AR event simulated by the MPAS-A atmospheric model. Vertically integrated precipitable water content is shown. After accounting for the effects of this poleward shift of the westerlies by allowing the threshold latitude to depend on the latitude of 0m/s mean zonal wind at 800hPa, Sensitivity to precipitable water content and profile • This pole-ward shift explains most of the resolution dependence of the frequency of AR events. Objectives • The role of tropical diabatic heating variability As a step towards accurate modeling of the frequency of these extreme events and its response to climate variations including global warming, this study aims to; • examine the sensitivity of the frequency of these events to dynamical core and resolution of a global model in real world and aqua-planet frameworks. • estimate the relative contribution of tropical variability to circulations associated with AR events. Precipitation and stream function anomalies composite is constructed by shifting all the AR events to the same longitude (120oW), averaging, and then subtracting the 5-year climatology. • Increasing the model resolution decreases the vertically integrated PW but it increases the fraction below 800hPa. CT25K • Equatorially centered heating introduces a pair of cyclonic circulations to the northeast and southeast. Such heating is found to contribute about 30% of the stream function associated with AR events. After accounting for the effects of precipitable water content and its profile by adjusting the thresholds for vertically integrated PW and its fraction below 800hPa and recalculating the frequency of AR events; Definition of ARs • Summary • The latitudinal shift of sub-tropical explains the decrease in the frequency of AR events with the increase in model resolution. • Equatorially centered heating anomalies contribute significantly to circulations associated with AR events. • The resolution dependence of the frequency of AR events still exists, but dycore dependence is somewhat reduced. • Therefore, the dependence on resolution is primarily of dynamical origin. • samson.hagos@pnnl.gov, 509-375-7395 Regional and Global Climate Modeling Program

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