Numerical simulations vs

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Numerical simulations vs. physical experiments

 

Climate change could have a large impact on precipitation (rain and snow), with consequences for drinking water, farming, etc.  Clouds are obviously important to precipitation (and to climate change more broadly), and their formation is dependent on aerosols, tiny particles in the atmosphere, which occur naturally but are also products of industry and other human activities.  Cloud-formation processes are difficult to model: Boucher et al. wrote in the 2013 Intergovernmental Panel on Climate Change that "[c]louds and aerosols continue to contribute the largest uncertainty to estimates and interpretations of the Earth's changing energy budget."

 

In a study of the effect of temperature and aerosols on precipitation, Teller and Levin (2008) carried out a numerical simulation using a computer model.  They investigated the effect of temperature change by varying ground temperature at 5 levels (15, 16, 17, 18, and 19°C).  They also varied aerosol concentration at 4 levels (225, 600, 900, and 1530 cm^-3), representing clean to polluted clouds.  The output of the simulation is the result of a computer solution of equations representing the physical processes of cloud formation and precipitation over time. 

 

The numerical model was run under conditions typical of the eastern Mediterranean in winter.  Running the model requires the initial atmospheric conditions to be specified.  It appears that these conditions were fixed for all runs in the simulation, except for the changes in temperature and aerosol concentration mentioned above.  In contrast, in a real atmosphere, the conditions would vary over space for any one rainfall event and would vary from day to day.

 

Questions

 

1. Speculate on how a physical experiment could be run in a laboratory to investigate the same temperature and aerosol factors.  What are some advantages and disadvantages of a physical experiment relative to a numerical simulation here?

2. In the numerical simulation, cloud-formation processes were modelled by a computer code called TAU-2D, the Tel Aviv University 2-dimensional cloud model to simulate a single cloud.  What are some advantages and disadvantages of a numerical simulation using TAU-2D relative to a physical experiment here