Tuesday, 9 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
Precipitation-induced sensible heat (HPR) which is transferred between the ground/canopy and rainwater can be extremely large during a heavy precipitation event. Thus, the local land surface air temperature (LSAT) can be sharply altered on an hourly to daily timescale. When simulating land surface processes, although HPR is included in whether and synoptic models, it is commonly neglected in climate models because of its small magnitude on long timescales. As a consequence, the simulated LSAT may be biased in climate models. In this study, we use satellite and reanalysis datasets to estimate HPR on the decadal and global scale, and we use NCAR-CESM to investigate the effect of HPR on LSAT simulations over the second half of the 20th century. Our results show that the reanalysis-estimated HPR is largest over Intertropical Convergence Zone (ITCZ) regions, with the seasonal mean values of -0.22 W/m2 (-2.31 to 0.29 W/m2) in DJF and -0.28 W/m2 (-2.89 to 0.24 W/m2) in JJA. These values are consistent with the model-simulated HPR patterns. In DJF, the HPR leads to a weaker equator-pole surface heating difference and thus weakens northern stationary waves. The consequent changes of the heat and moisture advection likely result in noticeable LSAT warming effects (for example, 0.53 K over northern Eurasia and 0.46 K over central North America) and cooling effects (for example, -0.62 K over Alaska and -0.42 K over central Asia) at regional scales, which help significantly reduce the simulated LSAT biases in the model. In JJA, LSAT changes slightly due to probably the weak stationary wave responses during the northern summer. The impacts of HPR on regional LSAT patterns can be comparable to that of other factors such as changes in O3, aerosol concentrations and land use, and hence it is beneficial to include the HPR in the land-surface energy budget in current climate models.
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