Water molecules comes in several varieties, of which H₂¹⁶O is the most common. These varieties behave differently enough under freezing to create strong changes in the ratio of heavy to light water molecules. Here we compare observations of these ratios from satellites and high-altitude airborne instruments. These observations provide information about how air reaches the upper parts of the atmosphere, so it is important to reconcile difference between different modes of observations.

The water molecule comes in several different varieties, which are nearly indistinguishable in daily life. However, slight differences between the water molecule types can be exploited to achieve better scientific understanding of parts of Earth's atmosphere. In this work we describe the design, construction, and operation of an instrument meant to measure these molecules aboard research aircraft up to altitudes of 20 km.

We studied water vapor in a critical region of the atmosphere, the Asian summer monsoon anticyclone, using rare in situ observations. Our study shows that extremely high water vapor values observed in the stratosphere within the Asian monsoon anticyclone still undergo significant freeze-drying and that water vapor concentrations set by the Lagrangian dry point are a better proxy for the stratospheric water vapor budget than rare observations of enhanced water mixing ratios.

This study investigates how ice grows directly from vapor in cirrus clouds by comparing observations of populations of ice crystals growing in a cloud chamber against models developed in the context of single-crystal laboratory studies. We demonstrate that previous discrepancies between different experimental measurements do not necessarily point to different physical interpretations but are rather due to assumptions that were made in terms of how experiments were modeled in previous studies.

In situ measurements of water vapor in the upper troposphere are necessary to study cloud formation and hydration of the stratosphere but challenging due to cold–dry conditions. We compare measurements from three water vapor instruments from the StratoClim campaign in 2017. In clear sky (clouds), point-by-point differences were <1.5±8 % (<1±8 %). This excellent agreement allows detection of fine-scale structures required to understand the impact of convection on stratospheric water vapor.