1. Environmental Fluid Mechanics Laboratory, Civil and Environmental Engineering, Stanford University, Stanford, California
2. Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology, Zurich, Switzerland
3. Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology, and Swiss Federal Office for Meteorology and Climatology, MeteoSwiss, Zurich, Switzerland
4. School of Meteorology, and Center for Analysis and Prediction of Storms, University of Oklahoma, Norman, Oklahoma