Laboratory measurements of falling velocity of individual ice columns

R. E. BÜRGESSER; N.E. CASTELLANO; E.E. ÁVILA

Congreso; 26th General Assembly of the International Union of Geodesy and Geophysics; 2015

Model studies of Earth´s climate typically represent ice particle fall velocities with theoretically derived power-law formulations. However, there is a significant lack of experimental data covering fall velocities of ice particles with maximum dimension less than 100 um. Therefore, the model studies may suffer from non-negligible error due to reliance on extrapolation of the representative equations for the smallest ice crystals.In the current work we directly determined the ice particle geometry, fall orientation and velocity of laboratory grown ice columns that form at temperatures ranging from -5 °C to - 10°C. The experimental apparatus consisted of an ice growth chamber for preparation of the ice crystals and a vertically oriented settling tube through which the ice crystals attain terminal velocity while being illuminated and recorded with a high-speed video camera.The fall velocities of pristine columns were determined as a function of the length (L) and width (W) of the columns. The measurements were performed for ice columns with L<150 um and W<40 um. A fitting function which depends on the capacity of the ice column is proposed to parameterize the fall velocities obtained in the present work.The fall orientation was characterized by the angle formed between the direction of fall and the direction of the major axes of the column. The observations do not show any preferential fall orientation of the columns. Besides, no drifts were observed from the vertical during fall.