Measurements of relative humidity in a persistent contrail

Persistent contrails are a common feature of the upper troposphere. We describe two methods for intercomparing and evaluating RHi measurements in a persistent contrail with calculated or expected values. The methods were applied to measurements made in the upper troposphere on board an NASA WB-57F aircraft while sampling its own contrail. Included in the analysis are measurements of water vapor pressure, temperature, ice particle number and size, and nitric oxide (NO). The systematic use of these contrail-sampling methods in future studies will improve our understanding of contrail microphysics and the performance of fast-response water and temperature measurements.