Kohler Curves

Swarn Gill, California University of Pennsylvania
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In this assignment students investigate the process of cloud droplet nucleation by analyzing the importance of supersaturation, radius of curvature, CCN solute mass and temperature. Students will be produce 3 plots using the spreadsheet program of their choice. The first plot is used to test their understanding of the reading. The second plot is used to help them determine the importance of supersaturation and solute mass, and the third to help them determine the importance of supersaturation and temperature. The final questions let them apply calculus skills to the problem. Questions are a mixture of short and long answer questions.

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Learning Goals

  • review kohler curve concepts
  • construct a family of Kohler curves
  • discuss the relative importance of temperature and solute mass to cloud drop nucleation
  • helps them understand the first part of the precipitation growth process
  • interpreting graphs
  • applying calculus concepts to meteorology
  • developing skills for using graphing software

Context for Use

This assignment is designed for use in a cloud physics/physical meteorology course. Within cloud physics it belongs to the area of drop nucleation.
  • The assignment can be presented between a discussion of heterogenous nucleation and growth by diffusion.
  • The assignment is designed to take about 10 hrs to complete and thus a due date 7-10 days after it is given is appropriate
  • Excel or another graphing program needs to be available for the students

Description and Teaching Materials

Assignment (Microsoft Word 30kB Jul17 04)
Partial Solution (Microsoft Word 344kB Jul17 04)

Teaching Notes and Tips

This is assignment could easily include a part that asks them to draw the solute and curvature terms seperately so that they can perhaps better see how the Kohler curve is a combination of these two. I have left it out here because it is covered in the reading and the assignment is quite lengthy already.

More information on reading material that is useful for the professor and possibly the students, as well as information on the background knowledge and context for this assignment in a course and curriculum can be found in the following file: Instructor notes - context (Microsoft Word 25kB Jul17 04)

Some information on the common problems I have seen students have with this assignment can be found in the following file: Instructor notes - problems (Microsoft Word 21kB Jul17 04)


The assignment should be handed in either electronically or on paper (I prefer paper) to the instructor with just the figures attached to their answers to the questions. I also ask students to send me their excel file by e-mail. This is a way in which I can give partial credit by possibly seeing where they went wrong if their graphs are incorrect. The weight given to the graphs and the conceptual answers are at the teachers discretion. Since it is a quantitative assignment and since most of the time will be spent on the excel program I like to give greater rewards to the graphs created, although ultimately the concepts are the most important.

References and Resources

Rogers, R. R., M. K. Yau, 1989. A Short Course in Cloud Physics, 3rd Ed. Pergamon Press. 293 pp.

Young, K. C., 1993. Microphysical Processes in Clouds. Oxford Press. 427 pp.

Wallace, J. M., P.V. Hobbs, 1977. Atmospheric Science: An Introductory Survey. Academic Press. 467 pp.