Search Results
Abstract
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 (1σ) to ±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.
Abstract
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 (1σ) to ±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.
Abstract
Satellite measurements using the backscattered ultraviolet technique provide a powerful method for the observation of stratospheric ozone. However, rapid input signal variations over three to four orders of magnitude in several minutes can lead to problems with instrument response. Inflight data have recently been used to characterize a “hysteresis” problem on the NOAA-9 SBUV/2 instrument, which affects measurements made shortly after emerging from darkness. Radiance values observed under these conditions can be up to 2%–3% lower than expected. A correction has been derived for NOAA-9 data that is solar zenith angle dependent and varies in amplitude and time. Typical changes to affected polar total ozone values are on the order of 1% but can reach 5% in some cases. Profile ozone changes are altitude dependent, with maximum values of 4%–5% at 1 hPa. The NOAA-11 and NOAA-14 SBUV/2 instruments have a much smaller hysteresis effect than that observed for NOAA-9 SBUV/2 due to a change in photomultiplier tubes. The Nimbus-7 SBUV instrument also shows a hysteresis effect, which has not been fully characterized at this time.
Abstract
Satellite measurements using the backscattered ultraviolet technique provide a powerful method for the observation of stratospheric ozone. However, rapid input signal variations over three to four orders of magnitude in several minutes can lead to problems with instrument response. Inflight data have recently been used to characterize a “hysteresis” problem on the NOAA-9 SBUV/2 instrument, which affects measurements made shortly after emerging from darkness. Radiance values observed under these conditions can be up to 2%–3% lower than expected. A correction has been derived for NOAA-9 data that is solar zenith angle dependent and varies in amplitude and time. Typical changes to affected polar total ozone values are on the order of 1% but can reach 5% in some cases. Profile ozone changes are altitude dependent, with maximum values of 4%–5% at 1 hPa. The NOAA-11 and NOAA-14 SBUV/2 instruments have a much smaller hysteresis effect than that observed for NOAA-9 SBUV/2 due to a change in photomultiplier tubes. The Nimbus-7 SBUV instrument also shows a hysteresis effect, which has not been fully characterized at this time.
