SUNYA Regional Model Simulation of Radiative Forcing and Climate Impact due to Contrails over Regions around Taiwan

Abstract

The effects of contrails on the radiative forcing and climate impact around Taiwan are studied using the State University of New York at Albany (SUNYA) regional climate model. The effects are calculated based on the contrail coverage, radiative properties of particle effective radius, and solar and longwave optical thickness as simulated from the National Taiwan University (NTU) contrail mode (Chen et al. 2001). Both dissipating and persistent contrails are considered; for the latter, the diurnal variation of contrail coverage is also included.

For persistent contrails with diurnal variation, the daily mean solar and longwave radiative forcing at the top of the atmosphere are calculated to be 5.8 and 2.1 W m-2, respectively, while the corresponding values on the surface are 4.9 and 0.19 W m-2; the radiative forcing without diurnal cycle is about 2/3 of these estimates. For dissipating contrails, the radiative forcing is much smaller because of smaller optical thickness. The simulation results also indicate that the spatial pattern of the radiative forcing follows closely the spatial distribution of the contrail coverage. In addition to the radiation forcing, an ensemble of model simulations was also conducted to examine the climate impact. As expected, the presence of contrails leads to a warming of the contrail layer due to absorption of the solar radiation and trapping of the upwelling longwave radiation. However, the radiation-induced warming signal, although robust, is small when compared with the inherent temperature variability attributed to other dynamic factors. A small cooling of the surface is also simulated.

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