Climatological Study of the Short-Term Variation of the 0, -10, and -20 Degree Celsius Altitude Levels over the Florida Spaceport

For evaluation of the potential of cloud electrification, it is necessary to know the altitude of the 0, -10 and -20 degree Celsius levels.  Cape Canaveral Air Force Station has recorded balloon launch data back to 1989.  In support of rocket launches, often multiple balloons are launched within minutes of each other in the 4-6 hours leading up to launch. In the past, temperature data from sondes was typically available every hour or so through the launch countdown, allowing for frequent updates of these critical temperature thresholds. Recently, launch customers are relying on jimsphere and wind profiler data that do not have a thermodynamic component in the latter 4-6 hours of a countdown.  This study compares the altitude differences of the 0, -10 and -20 degree Celsius levels from consecutive balloon pairs not to exceed 6 hours apart.  The analysis uses 9685 soundings from 1989 to 2013.  Approximately 5% of the time the altitude of the temperature level in question (0, -10, -20 degrees C), varies by more than 500 feet (operationally significant threshold) within 6 hours. This study analyzes the altitude variability as a function of several meteorological parameters, such as change in sonde type, dew point depression, and solar zenith angle.  Additionally, the study concludes with impacts to launch operations.