Speaker
Description
Water vapor (H$_2$O) is a key trace gas in the upper troposphere (UT) and lowermost stratosphere (LMS), as it significantly influences the Earth's climate system through its roles in radiative forcing and cloud formation. However, accurate knowledge of the amount of H$_2$O in this atmospheric region is still insufficient due to the difficulty and lack of precise in-situ and space-borne measurements. This study presents a new methodology to derive adjusted H$_2$O climatologies for the extra-tropical UT/LMS from regular measurements aboard passenger aircraft between 1994 and 2022 within the IAGOS (In-service Aircraft for a Global Observing System) research infrastructure.
To this end, a synthesis of mean H$_2$O is performed by sampling air mass bins of similar origin and thermodynamic conditions relative to the tropopause between a dataset from ~60.000 flights applying the IAGOS-MOZAIC and -CORE compact hygrometer(ICH) and a data set of ~500 flights using the more sophisticated IAGOS-CARIBIC hygrometer. % Maybe clarify that JULIA was also use: First, campaign measurements summarized in the JULIA dataset are compared to CARIBIC to varifiy the measurement quality of CARIBIC. Even for low LMS H$_2$O, CARIBIC and JULIA are in good agreement within the known uncertainties.
The analysis is, in combination with ECMWF ERA5 meteorological data, accomplished for the extra-tropical northern hemisphere, where the datasets have the largest common coverage. We find very good agreement in the UT, but a systematic positive humidity bias in the ICH measurements for the LMS. To account for this bias, mean H$_2$O of the ICH are adjusted to the IAGOS-CARIBIC measurements based on a new mapping and adjustment approach. After applying this new method, the LMS H$_2$O measurements are in good agreement between all investigated platforms. The extensive H$_2$O data set from the compact IAGOS sensor can now be used to produce highly resolved H$_2$O climatologies for the climatically sensitive LMS region.
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