Comparison of In Situ Humidity Data from Aircraft, Dropsonde, and Radiosonde.

Results are presented from the Measurement of Tropospheric Humidity (MOTH) Tropic and MOTH Arctic airborne field experiments, comparing a number of in situ humidity measurements. Good agreement is shown between the Total Water Content probe on board the C-130 aircraft, and the Vaisala RS90 and "new" Vaisala RS80 radiosondes; "old" Vaisala RS80 radiosondes and Vaisala RD93 dropsondes show the dry bias noted by others. An empirical correction for RD93 dry bias is presented and is shown to produce good results with both MOTH and non-MOTH data. It was concluded that the aircraft and corrected dropsonde data agree (1delta) to (plus-minus)1 g kg^-1; these limits are due to atmospheric variability. The possibility of temperature measurement errors producing errors in RD93 relative humidities is not significant compared to atmospheric variability. Meteolabor Snow White radiosondes are shown to exhibit a wet bias at high and low mixing ratios and possible reasons are discussed. Intercomparisons between the RS90s and other instruments, partitioned by day–night and by experiment, suggest deficiencies in RS90 daytime radiation corrections.