Time Constant Estimates for Radiosonde Temperature Sensors

Abstract

Abstract To correct time lag errors in radiosonde temperatures the sensor time constant has to be known. Time constants are not published for some widely used sensors and, in some cases, available time constants disagree. This study focuses on ML-405, ML-419, VIZ/Sippican Mark II Microsonde and B2, Russian MMT-1, and Chinese GZZ-7 rod thermistors. It measures still air time constants and heat capacities and derives theoretical still air and aerated time constants based on heat transfer involving nonuniform cylinders. With low aeration, such as in the stratosphere, heat conduction by lead wires from the thermistor noticeably shortens the time constant. Some discrepancies in published time constants are explained by researchers not considering the temperature dependence of all relevant variables. Empirical formulas are derived to estimate the aerated time constant of cylindrical temperature sensors based on dimensions. The aerated time constant in soundings is found to be about 6 times as long at 10 hPa as near sea level.