The Second Phase of the Global Land-Atmosphere Coupling Experiment: Soil Moisture Contributions to Subseasonal Forecast Skill

The second phase of the Global Land-Atmosphere Coupling Experiment (GLACE-2) is a
multi-institutional numerical modeling experiment focused on quantifying the subseasonal (out
to two months) forecast skill for precipitation and air temperature derived from the realistic
initialization of land surface states, notably soil moisture. An overview of the experiment and
consensus model behavior at the global scale is described here. The models show modest but
significant skill in predicting air temperatures, especially where the rain gauge network is dense;
assuming rain gauge density is a reasonable proxy for the adequacy of the observational network
contributing to soil moisture initialization, this result indeed highlights the potential contribution
of enhanced observation to prediction. Precipitation forecast skill is much weaker than that for
air temperature. The skill for predicting air temperature, and to some extent precipitation,
increases with the magnitude of the initial soil moisture anomaly. GLACE-2 results are
examined further to provide insight into the asymmetric impacts of wet and dry soil moisture
initialization.