Numerical Simulation Of The Three-dimensional Diffusion And Its Climate Effects Of Pinatubo Aerosols

Volcanic eruption is one kind of suddenly intensive natural phenomena and always brings large impacts to human society. Firstly, a large number of tephra injected into troposphere drift with regional circulation and threaten flight safety, social production and human health of the surrounding area. The removal processes with precipitation may form acid rain and other secondary disasters. Secondly, massive SO~2 injected into atmosphere converts into long-lived sulfate aerosol, which are removed from troposphere quickly by weather processes, but can stay for 3~5 years in stratosphere. The volcanic aerosols scatter visible solar radiation, reflect and absorb the near-infrared bands, and absorb thermal longwave radiation, perturbing radiation balance of atmosphere, influencing energy budget of earth system, and leading to a short-term climate change.Although there is no volcanic activity in modern China, but Taiwan and the southeast coast of China are located in the circum-Pacific volcanic belt. The neighboring countries such as the Philippines and Indonesia both experienced larger volcanic eruptions in the last century. June 1991 eruption of Mount Pinatubo in Luzon is the strongest volcanic eruption of the last century, which had a profound impact in China and global economy and climate. Therefore, studying migration, spread and impact of volcanic ash and aerosol on the climate system is very important.In this paper, the NCAR CAM3.0 model is used to simulate the migration and spread of volcanic ash and aerosol after the eruption of Mount Pinatubo. With the three-dimensional volcanic aerosol data we get from our experiments, we simulate the response of climate system. 3-D diffusion simulation results show that in the stratosphere volcanic aerosol cloud drift westward above 200hPa rapidly under the strong east wind, and surround the latitude circle in 23 days. Part of the aerosol cloud is caught by the cyclone in Eurasia and begin spreading to the Northern Hemisphere and in the center of the cyclone the aerosol move downward to 500hPa; Only little aerosol enter South Hemisphere. In the troposphere, aerosol first spread upward and downward along the vertical direction, then move in the horizontal level. In the first week the cloud above 300hPa move westward; One week later when aerosol arrive at 60°N, aerosols located at 300~500hPa move eastward along the western wind and spread in the North Hemisphere. From 200hPa the aerosol move into South Hemisphere and stay at 30°S above 500hPa; High concentration cloud is always along the low latitude.Using the three-dimensional diffusion simulation, we get a three-dimensional volcanic aerosol data and apply to CAM3.0 to study the response of climate. Volcanic aerosols in the troposphere quickly removed with the precipitation process, and can't cause significant climatic effects, so we just consider the stratospheric volcanic aerosols. Simulation results in this paper show that the stratospheric volcanic aerosol significantly reflect solar radiation (maximum 5.0W/ m~2), and absorb upward long-wave radiation (max 1.0W/ m~2), which cause net solar radiation anomalies of -4.5 W/m~2 in the earth surface, but no significant change in the long-wave radiation. Changes in surface radiation caused the maximum 0.8K summer cooling (global average), and the maximum 0.5K winter warming. The observed cooling and warming amplitude is smaller than the simulation; at the same time stratosphere appear 2.0K warming, which is a little larger than the observation (1.6K). We found that summer cooling and warming in Northern Hemisphere is mainly caused by radiation changes. Winter warming in high latitudes of the Northern Hemisphere is mainly caused by temperature advection anomalies (radiation changes cause the circulation changes), and winter cooling in the low-latitude is mainly caused by negative radiation anomalies. This study can help to verify the capacity of CAM3.0 to well simulate atmospheric circulation and tracer transport, deeply understand the three-dimensional diffusion of volcanic aerosol, and its climate impact after the eruption.