Quality assessment of MOZAIC and IAGOS capacitive hygrometers: insights from airborne field studies

Abstract

A B S T R A C TIn 2011, the MOZAIC (Measurement of Ozone by AIRBUS In-Service Aircraft) successor programme IAGOS (In-service Aircraft for a Global Observing System) started to equip their long-haul passenger aircraft with the modified capacitive hygrometer Vaisala HUMICAP † of type H. The assurance of the data quality and the consistency of the data set during the transition from MOZAIC Capacitive Hygrometers to IAGOS Capacitive Hygrometers were evaluated within the CIRRUS-III and AIRTOSS-ICE field studies. During these performance tests, the capacitive hygrometers were operated aboard a Learjet 35A aircraft together with a closedcell Lyman-a fluorescence hygrometer, an open-path tunable diode laser (TDL) system and a closed-cell, direct TDL absorption hygrometer for water vapour measurement. For MOZAIC-typical operation conditions, the comparison of relative humidity (RH) data from the capacitive hygrometers and reference instruments yielded remarkably good agreement with an uncertainty of 5% RH. The temperature dependence of the sensor's response time was derived from the cross-correlation of capacitive hygrometer data and smoothed data from the fast-responding reference instruments. The resulting exponential moving average function could explain the major part of the observed deviations between the capacitive hygrometers and the reference instruments.

In situ temperature measurements in the upper troposphere and lowermost stratosphere from 2 decades of IAGOS long-term routine observation

“…The median ozone mixing ratio in the UT is 60 ppb, median CO mixing ratio is 90 ppb, and median PV is 0.5 PVU. Within the LMS, the median values for O 3 (310 ppb), for CO (40 ppb), and for PV (7 PVU) are consistent with previous studies (Pan et al, 2004;Kunz et al, 2008;Brioude et al, 2009;Schmidt et al, 2010). …”

“…To ensure the reliability of the IAGOS temperature observations, we make use of temperature measurements from the AIRTOSS-ICE aircraft campaign (Aircraft Towed Sensor Shuttle -Inhomogeneous Cirrus Experiment), which focused on midlatitude cirrus clouds (Neis et al, 2015). During this campaign, the IAGOS temperature instrument was installed on the research aircraft (Learjet 35A) and provides the opportunity to compare both temperature measurements.…”

“…The temperature is measured with an uncertainty of ±0.25 K by a microprocessor-controlled transmitter unit (model HMT333,Vaisala,Finland), which passes the signal to the data acquisition system of the IAGOS Package 1 instrument, in which it is recorded with a time resolution of 4 s Petzold et al, 2015). Pre-and post-deployment calibrations from the laboratory are used to evaluate the temperature signal and to ensure the quality of the temperature measurement Neis et al, 2015). Typical deployment phases are in the range of 2-3 months.…”

Global-scale atmosphere monitoring by in-service aircraft – current achievements and future prospects of the European Research Infrastructure IAGOS

“…MOZAIC-IAGOS provides 20 yr of continuous measurements of UTH, using capacitive hygrometers which have been subject to careful evaluation in airborne field studies (Neis et al, 2015a(Neis et al, , 2015b) and reanalysis of the calibration procedure (Smit et al, 2014).…”

The IAGOS NO<sub><i>x</i></sub> instrument – design, operation and first results from deployment aboard passenger aircraft

“…from the avionics system of the aircraft . The uncertainty of ozone is given with 2 ppbv ± 2 %, and the uncertainty of water vapor is 5 % over liquid water Neis et al, 2015). Figure 2 shows the schematic flow and position of the major components of the IAGOS NO x instrument.…”