Isotope meteorology of cold front passages: A case study combining observations and modeling

• Published in: Geophysical research letters Vol. 42; no. 13; pp. 5652 - 5660
• Main Authors: Aemisegger, F., Spiegel, J. K., Pfahl, S., Sodemann, H., Eugster, W., Wernli, H.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 16-07-2015; John Wiley & Sons, Inc
• Subjects: Atmospheric precipitations; below-cloud evaporation; Case studies; Climate Research; Climatology; Cold front; Cold fronts; Computer simulation; Depletion; Deuterium; Droplets; Earth and Related Environmental Sciences; Evaporation; Evapotranspiration; Fractionation; Fronts; Geovetenskap och miljövetenskap; Isotope fractionation; Isotopes; Klimatforskning; Mathematical models; Meteorology; Modelling; Natural Sciences; Naturvetenskap; Precipitation; Prediction models; Rain; Rainfall; Rainfall amount; Sensitivity; Soil; Stable isotopes; stable water isotopes; Surface water; Temporal resolution; Variability; Water vapor; Water vapour; Weather; Weather forecasting
• ISSN: 0094-8276; 1944-8007; 1944-8007
• DOI: 10.1002/2015GL063988

This study investigates the role of below‐cloud evaporation and evapotranspiration for the short‐term variability of stable isotopes in near‐surface water vapor and precipitation associated with central European cold fronts. To this end, a combination of observations with high temporal resolution and numerical sensitivity experiments with the isotope‐enabled regional weather prediction model COSMOiso is used. The representation of the interaction between rain droplets and ambient vapor below the cloud is fundamental for adequately simulating precipitation isotopes (δp) and total rainfall amount. Neglecting these effects leads to depletion biases of 20–40‰ in
δp2H and 5–10‰ in
δp18O and to an increase of 74% in rainfall amount. Isotope fractionation during soil evaporation is of primary importance for correctly simulating the variability of continental low‐level vapor
δv2H and
δv18O and particularly of the secondary isotope parameter deuterium excess (dv).
Key Points
Cold fronts leave characteristic imprint in water vapor and rain isotopes
Below‐cloud interaction affects rainfall amount and precipitation isotopes at short time scales
Soil evaporation fractionation is crucial for isotopes in low‐level water vapor