A spatial shift of precipitation from the sea to the land caused by introducing submicron soluble aerosols: Numerical modeling

摘要

Precipitation in the eastern Mediterranean takes place during the cold season, when sea surface temperature is higher than the land surface temperature by 5℃-10℃. This temperature difference leads to the formation of the land breeze-like circulation, which interacts with dominating westerlies and leads to an intense cloud formation over the sea ～10-20 km from the coastal line. As a result, most of the precipitation falls on the sea without reaching the land. At the same time the eastern Mediterranean region experiences a lack of freshwater. For investigating a possibility to shift the release of precipitation from sea to land, numerical simulations were performed using the Hebrew University 2-D cloud model and the 3-D Weather Research and Forecasting model, both operating with spectral bin microphysics, and the 3-D COSMO model of the German Weather Service applying a two-moment bulk parameterization for cloud physics. The respective results indicate that an increase in concentration of small aerosols leads to a delay in raindrop formation and fosters the formation of extra ice particles with low settling velocity. This ice is advected inland by the background wind. As a result, precipitation over land increases at the expense of precipitation over sea by 15-20. The spatial shift of precipitation from sea to land can be as large as 50-70 km depending on the wind speed of the background flow. These results suggest a new possibility to enhance precipitation in a particular region by cloud seeding with small aerosols.