The isotopic composition of precipitation from a winter storm – a case study with the limited-area model COSMO<sub>iso</sub>

Abstract

Abstract. Stable water isotopes are valuable tracers of the atmospheric water cycle, and potentially provide useful information also on weather-related processes. In order to further explore this potential, the water isotopes H 18 2 O and HDO are incorporated into the limited-area model COSMO. In a first case study, the new COSMO iso model is used for simulating a winter storm event in January 1986 over the eastern United States associated with intense frontal precipitation. The modelled isotope ratios in precipitation and water vapour are compared to spatially distributed δ 18 O observations. COSMO iso very accurately reproduces the statistical distribution of δ 18 O in precipitation, and also the synopticscale spatial pattern and temporal evolution agree well with the measurements. Perpendicular to the front that triggers most of the rainfall during the event, the model simulates a gradient in the isotopic composition of the precipitation, with high δ 18 O values in the warm air and lower values in the cold sector behind the front. This spatial pattern is created through an interplay of large scale air mass advection, removal of heavy isotopes by precipitation at the front and microphysical interactions between rain drops and water vapour beneath the cloud base. This investigation illustrates the usefulness of high resolution, event-based model simulations for understanding the complex processes that cause synoptic-scale variability of the isotopic composition of atmospheric waters. In future research, this will be particularly beneficial in combination with laser spectrometric isotope observations with high temporal resolution.

Accomplishments of the MUSICA project to provide accurate, long-term, global and high-resolution observations of tropospheric {H<sub>2</sub>O,<i>δ</i>D} pairs – a review

“…In the next step, concrete research opportunities should be identified and evaluated. For this purpose, atmospheric models (like COSMOiso, Pfahl et al, 2012) will be essential. Sensitivity tests with the models are needed in order to reveal the links between different moisture processes and distinct {H 2 O,δD} pair distributions and in order to estimate whether the characteristics of the remote sensing data (e.g.…”

Comparison of Eulerian and Lagrangian moisture source diagnostics – the flood event in eastern Europe in May 2010

“…For the simulation of moisture tracers a secondary water cycle has been introduced in the COSMO model, similar to the implementation of water isotopes by Pfahl et al (2012). As this method is entirely diagnostic, the secondary moisture cycle does not interact with the primary moisture cycle nor affect any other model component.…”

Synoptic scale controls on the δ18O in precipitation across Beringia

“…These storms carry warm 18 O-enriched vapor to Adak from as south as 29°N (48 h prior) (Figure 2c and Figure S3 in the supporting information). Precipitation has relatively high δ 18 O values, and these are likely amplified by postcondensational exchange with the ambient moisture as it falls to the ground [e.g., Dansgaard, 1964;Pfahl et al, 2012].…”