Modelling work during SNOWPACE
The SNOWPACE project developed a hierarchical suite of models to support the interpretation of stable water isotope measurements. Different aspects of the field data can be addressed with each model, and thus the models supplement each other and provide an multifaceted analytical framework.
The Craig-Gordon model, and Rayleigh-type models provide idealised, first-order information of either evaporation or condensation during adiabatic ascent. Single-column isotope fractionation models provide a vertically resolved analysis of warm-phase and mixed-phase microphysics driven by vertical ascent due to winds or topography, and support the interpretation of isotope evolution during cloud formation and precipitation. Application of the Below-Cloud Interaction Model (BCIM) and the 4D-framework for post-condensational exchange (Graf et al., 2019) to high-resolution precipitation measurements during SNOWPACE showed that different parts of frontal weather systems provide information that is dominated by either source information, transport characteristics, or cloud processes (Weng et al., 2021). The vapour isotope composition during precipitation events thereby followed the precipitation characteristics, suggesting that vapour and precipitation can replace each other during warm rain periods.
A conceptual 2-D model for orographic drying simulates the isotope fractionation connected to orographic water extraction from airmasses (X and Barstad, 2018). Simultaneous measurements of the vapour isotope composition in Bergen and at Finse during field campaign periods will enable constraints on the theoretical, computational, and actual drying of airmasses due to the orography of southern Norway.
The 3-D numerical weather prediction model COSMOiso is a full-fledged isotope-enabled, non-hydrostatic model that provides the detailed forecast at high resolution. COSMOiso was used for model simulations covering the time period of the IGP field campaign (Golid, 2019). Simulation of a large cold-air outbreak with the atmospheric tracer model COSMOtag showed the rapid turnover of water vapour in the Norwegian sea, emphasizing the importance of local processes during certain weather events (Papritz and Sodemann, 2018).
The Lagrangian particle dispersion model FLEXPART with the WaterSip moisture source diagnostic (Sodemann 2020) provides access to the source and transport properties of airmasses and water vapour, based on either reanalysis of COSMO forecast data. A climatology of the moisture sources of Norway and Scandinavia obtained from the WaterSip method reveals the dominance of nearby seas for precipitation in Scandinavia (Lanzky et al., in prep.). Seasonal variation, with an increase in contributions from land evaporation, and distinct spatial gradients are futher important climatological characteristics.
An exporatory study to relate moisture sources of Norway to river runoff modelling was conducted for a small catchment in Western Norway. Further case studies in different and larger catchments will be needed to obtain more robust conclusions, and in particular to further investigate the relation between runoff and moisture source variation.
References
Sodemann 2020
Gimeno et al., 2021
Lanzky et al., in prep.
Graf et al., 2019
Papritz and Sodemann, 2018
Duran and Barstad, 2018
Golid, 2019
Weng et al., 2021