The Correlation of Aircraft Reported Relative Humidity to Ceiling Heights at Selected Hub Airports in the United States

Measurements of atmospheric water vapor from commercial aircraft have slowly increased since their advent in the late 1990s. While a few studies have been conducted to compare aircraft water vapor measurements to radiosondes or numerical model first-guess fields, there have been no comparisons of aircraft reported relative humidity to measured ceiling heights at commercial airports. This study compared relative humidity measurements from approximately 120 aircraft equipped with WVSS-II sensors to measured ceilings at several airports in the continental United States during the late winter through early summer of 2015. The results suggest that the WVSS-II sensors report relative humidity of 95-100% at the measured ceilings more than 90 percent of the time. Due to insufficient reporting frequency of WVSS-II in the vertical, interpolation is required. This contributed to differences between the WVSS-II saturated layers and reported ceilings. Another challenge is that although WVSS-II equipped aircraft correctly report saturation (or near saturation) when flying through precipitation, the surface observation will typically report the visible cloud layer as the ceiling. The results of this study may help meteorologists better understand and utilize these soundings in their forecasts, and assist developers of numerical weather prediction models using WVSS-II data in the production of aviation related ceiling and visibility products.