Sub-Seasonal to Seasonal Predictability and Prediction of Monsoon Climates

There is growing interest in the scientific, operational and applications communities in developing sub-seasonal to seasonal (S2S) forecasts (2 weeks to a season) to provide early warning of high-impact events such as floods, droughts, heat and cold waves. Monsoon climates present a vivid case for the potential of sub-seasonal to seasonal prediction. Monsoon precipitation varies profoundly on multiple time and space scales, from the immense seasonal cycle, down to intra-seasonal active and break phases, monsoon synoptic depressions, mesoscale convective clusters and large diurnal variations, as well as inter-annual changes where variations in the dates of onset and withdrawal have large impacts on agriculture and populations. Several sources of S2S predictability including ENSO, MJO and land-atmosphere interactions are particularly strong in some monsoonal regions. However, weather and climate models still have difficulty in simulation and forecasting of precipitation over tropical land regions, and large gaps in our understanding remain about the extent of its potential predictability on S2S scales, which societally-relevant aspects (eg monsoon onset, rainfall extremes, droughts, heat waves) are predictable and why they often vary so profoundly from one monsoon region to the other. The seriousness of these gaps is heightened by the very likely impacts of anthropogenic climate change on monsoonal climates. The predictability of more serious heat waves during the dry season is an important example. Several extensive data archives of weather and climate model ensemble forecasts have recently become available to the research community that provide a critical new resource for answering these unresolved scientific questions of S2S predictability, and developing forecast products designed for societal applications, with the potential to help build resiliency to weather and climate shocks of billions of people in countries across Africa, Asia and the Americas.
These include the TIGGE archive weather forecasts up to 15 days, available since 2007 from 10 operational forecasting centers, the CHFP and NMME archives of seasonal forecast model hind-casts, and the recently created WWRP/WCRP S2S archive of sub-seasonal forecasts and hind-casts out to ca. 30–45 days. These multi-model forecast ensemble archives enable, for example, probabilistic estimates of potential predictability to be obtained by analyzing the evolution of large ensembles of forecast trajectories. They also allow skill to be quantifies, forecast products and verification metrics to be developed and tested.

This Research Topic welcomes all contributions that harness these forecast ensembles data archives (CHFP, NMME, S2S, TIGGE), together with observational data that aim to further the scientific understanding of multi-scale weather and climate variability of monsoon climates on timescales ranging from daily to inter-annual, and/or develop weather and climate products on this time
scales from forecasts for societal applications. Case studies of the predictability of specific high-impact weather events (including but not limited to flood, drought, heat wave, sand storm etc.) on S2S scales as well as diagnostic and conceptual analyses focusing on these scales are encouraged.