Humidity Measurements in the Tropical Tropopause Layer from Pre-AVE

Upper tropospheric and lower stratospheric relative humidity and temperature were characterized by instruments on the NASA WB-57F high-altitude aircraft during the NASA Pre-Aura Validation Experiment (Pre-AVE). On three flights in late January 2004, the aircraft made extensive measurements in the Tropical Tropopause Layer (TTL) near the Galapagos Islands. Humidity in the TTL is important to climate through its direct radiative impact, its role in ice cloud formation, and its role in determining stratospheric-entry water mixing ratios. Ultimately, this research is directed toward answering the following question: What are the physical mechanisms that control (and cause) long-term changes in the humidity of the upper troposphere and lower stratosphere in the tropics and subtropics? We report here relative humidity calculated from water vapor measurements by the JPL Laser Hygrometer (JLH) and temperature measurements by the NOAA Pressure-Temperature (PT) instrument. The distribution of humidity and accuracy of the water measurements will be discussed. We will also discuss previous tropical humidity measurements from the NASA CRYSTAL-FACE mission.