State Variables

Because of the importance of the static pressure and temperature measurements, these variables are measured redundantly. The static pressure instrument, the Rosemount 1301-A-4-B, has a basic accuracy of 0.1% and response time of a few tens of milliseconds. Two of these units are now carried on the aircraft. The resolution of the 16-bit analog-to-digital converter in the data recording system is 0.0000152, so the realized resolution of incremental pressure measurements with the Rosemount instrument is about 0.0015 kPa.

Reliable temperature measurements outside the clouds are obtained from both a Rosemount and an NCAR reverse-flow sensor ( Rodi and Spyers-Duran , 1972). In-cloud temperatures cannot be measured as reliably because of wetting of the sensing elements ( Heymsfield et al. , 1979; Lawson and Cooper, 1990). The NCAR reverse-flow thermometer has a basic accuracy similar to that of the Rosemount device (+- 0.5 d C) but a slower response, with the Rosemount time constant being ~1 s and the reverse-flow time constant ~3 s. Usually the NCAR device is relied upon for in-cloud measurements because of its superior wetting resistance, but it may not be possible to provide reliable in-cloud temperature measurements under all conditions, particularly at above-freezing temperatures ( Lawson and Cooper , 1990).

The T-28 system does not include a humidity sensor. The emphasis of research involving T-28 observations is usually on the interior characteristics of storms, and we have yet to find a robust, generally suitable instrument for measuring humidity in clouds.