An Investigation of Rawinsonde Ice Up during the Ontario Winter Lake-effect Systems (OWLeS) Project

The Ontario Winter Lake-effect Systems (OWLeS) Project took place during the winter of 2013-14 to gather data on lake-effect storms in the vicinity of Lake Ontario. This project incorporated many observing systems, including mobile Doppler radar, instrumented aircraft, ground-based remote sensing systems, and mobile soundings. During the project, 223 mobile soundings were launched. In post-analysis of these data, it was discovered that several of these soundings, particularly those launched directly into the bands of lake-effect precipitation, iced up during ascent. The purpose of this project is to determine the frequency of sounding ice up as a function of band-relative sounding launch location.

To determine whether a sounding suffered from ice up, the cloud top height was first determined qualitatively from the sounding.  We then compared these qualitative cloud-top temperatures to those obtained from Channel 4 (infrared) imagery from the Geostationary Operational Environmental Satellite (GOES-13). For cases in which soundings did not ice up, there was generally good agreement between the qualitatively-determined cloud-top temperatures and those determined from the satellite data. Exceptions were noted, however, particularly in cases of boundary-layer clouds or midlevel layered clouds. In cases of sounding ice-up, significant differences (> 19 K) were often present between the qualitatively-estimated and satellite-derived cloud-top temperatures. In many such instances, the mobile soundings revealed a deep cloud extending beyond the tropopause, which is clearly unlikely in regimes of lake-effect convection. In this work, we present detailed statistics and examples of sonde ice up and offer analysis of the exceptions to the general rule noted above.