The relationship between moisture source, water isotopes, and the MJO in the GISS climate model.

Numerous studies have suggested the importance of lower tropospheric humidity and moisture in the development and propagation of the MJO [e.g. Berkelhammer et al., 2012]. Building a complete picture of the relationship between the MJO and atmospheric humidity requires process-level understanding of moisture sources and sinks throughout the life-cycle of the MJO. There are no direct observations of moisture source/sink, and thus the actual pathways of moisture and humidity in the atmosphere must be determined indirectly using meteorological observations, which adds uncertainty. Water isotope observations, though, can provide a secondary constraint on moisture source/sink estimates. Global Climate Models (GCMs) can also provide an opportunity to quantify moisture sources and sinks. However, examination of the moisture budget in GCM simulations is complicated by the impacts of clouds, precipitation, and convection, which are usually parameterized in global models and thus contain significant uncertainties. To help improve the understanding of the relationship between the MJO and the local atmospheric water cycle, unique modeling capabilities present in the GISS ModelE2.1 will be used to examine the relationship between the MJO, moisture source, and water isotopes in the model, and how that relationship compares to observations. Specifically, multiple simulations will be performed with the GISS model, both free-running and nudged, and the quality of the MJO in the simulations will be evaluated. Next, simulated water tracers will be used to determine where the evaporative moisture sources are for the MJO. Then water isotopes, also simulated by the GISS model, will be compared against satellite data to determine if the modeled water tracer results match what has been hypothesized in the literature using water isotope observations [Berkelhammer et al., 2012; Tuinenburg et al., 2015]. Finally, any significant errors in the simulated water isotope values compared to the observations in the MJO region will be more closely examined to determine what the root causes of the errors might be, and thus what future model developments should focus on in order to improve the simulation of the MJO and its hydrology in climate and earth system models.