Validation of isotope-incorporated The Non-hydrostatic Icosahedral Atmospheric Model

Abstract:

The stable water isotopes (SWIs) (δ¹⁸O and δD) are used as an indicator of the intensity of the atmospheric hydrological cycle. SWIs are used for the validation of the hydrological cycle simulated by GCMs. Our research group aims to reduce uncertainty and improve the reproductivity of the deep convection process throughout data assimilation of SWI using a global cloud-resolving model, and further improve the accuracy of forecasting extreme weather events. In this presentation, we will introduce the results of experiments by low spatial resolution (about 200km) SWI-incorporated cloud-resolving model (iso-NICAM).

We incorporated the SWI tracer into the latest development version of NICAM (NICAM19) as a prognostic variable. The physical process of NICAM covers from low spatial resolution to high spatial resolution, and we focus on the physical process used at low horizontal resolution. Here, we mainly installed the SWI process into the Arakawa-Schubert (AS) scheme, a large-scale condensation scheme, and a land surface scheme. Using the iso-NICAM, we conducted an AMIP-type climate experiment with a start day as 1 July 2018.

In the results of July 2018, the simulated vapor δ¹⁸O was higher than -10‰ near the equator and lower than -60‰ in the polar region. Such a spatial distribution pattern is called the latitude effect and is also seen in observation of precipitation isotope and vapor isotope. The latitude effect was observed for the simulated precipitation isotope, however, the simulated δ¹⁸O in precipitation was higher than 0‰ in the low latitude region; this is higher than the observed value. This overestimation implies that it is necessary to further verify the tuning of the isotope process, in particular, the raindrop evaporation processes. The used parameters in its process will be optimized by data assimilation. In the future, we will continue to tune the SWI process and will extend the simulation period for the validation of the iso-NICAM.