Global scale remote sensing of water isotopologues in the troposphere: representation of first-order isotope effects

Abstract

Abstract. Over the last-decade, global scale datasets of atmospheric water vapor isotopologues (HDO) have become available from different remote-sensing instruments. Due to the observational geometry and the spectral ranges that are used, only few satellites sample water isotopologues in the lower troposphere, where the bulk of hydrological processes within the atmosphere take place. Here, we compare three satellite HDO datasets, two from the Tropospheric Emission Spectrometer (TES retrieval version 4 and 5) and one from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY), with results from the atmospheric global circulation model ECHAM4 (European Center HAMburg 4). We examine a list of known isotopologue effects to qualitatively benchmark the various observational datasets. TES version 5 (TESV5), TES version 4 (TESV4), SCIAMACHY, ECHAM, and ECHAM convoluted with averaging kernel of TES version 5 (ECHAMAK5) successfully reproduced a number of established isotopologue effects such as the latitude effect, the amount effect, and the continental effect, but to different extent. The improvement of TES version 5 over version 4 was confirmed by the steeper latitudinal gradient at higher latitudes in agreement with SCIAMACHY. Other features of the water isotopologue cycle such as the seasonally varying signal in the tropics due to the movement of the Inter Tropical Convergence Zone (ICTZ) are captured in TESV5 and SCIAMACHY. We suggest that the qualitative and quantitative tests carried out in this study could become benchmark tests for evaluation of future satellite isotopologue datasets.