A New Airborne Thermometer for Atmospheric and Cloud Physics Research. Part I: Design and Preliminary Flight Tests

Abstract

A new airborne thermometer has been designed using results from numerical simulators of airflow and particle (drop) trajectories. Initial flight tests with the NCAR King Air show that the new thermometer, which uses a fine-wire thermocouple for the sensor and lacks a probe housing, has a response time that is significantly faster than thermometers currently in use. An example of heat-flux calculations in a convective boundary layer shows that, compared to measurements using the Rosemount thermometer and NCAR K probes, the turbulent heat flux is greater by about 20% when using measurements from the new thermometer. Theoretical calculations of time response support the claim that the improved response is due to the absence of a probe housing. The new thermometer was designed to inertially separate cloud drops from the airflow, and flights in warm clouds suggest that the thermocouple sensor stays dry except in clouds that contain high concentrations of drizzle-size drops. In small cumulus clouds with approximately 1 g m?3 of liquid water that contained low concentrations (?10 l?1) of drizzle drops, the new thermocouple probe consistently measured warmer temperatures than the reverse-flow and Rosemount thermometers, suggesting that in these clouds the thermocouple probe may not have been affected by errors from sensor wetting. Thus, static temperature measured by the new thermometer in clouds with continental drop spectra should be reliable. An example of data collected in a mixed region of a small cumulus cloud shows that there may be more temperature structure at scales of 2?50 m than previously observed.