Second International Conference on Subseasonal to Seasonal Prediction (S2S) and
Second International Conference on Seasonal to Decadal Prediction (S2D)

Daily news

Day 1: Over 300 scientists gather to discuss subseasonal to decadal weather and climate predictions

Boulder, CO – Walter Orr, the first president of the University Corporation for Atmospheric Research (UCAR) and the founder of the National Center for Atmospheric Research (NCAR), was known for saying science in support of society, remarked Tony Busalacchi, the current president of UCAR. Busalacchi continued by saying that the subseasonal to seasonal (S2S) and seasonal to decadal (S2D) timescales are poised and ripe areas of research for the community to address the needs of society. This conference is aiming to do just that. Convening over 300 researchers from around the world, the conference will be used as a platform to discuss the latest science and exchange ideas to make advances to more seamless and skillful subseasonal to decadal predictions, which are useful to decision makers and stakeholders.

Gokhan Danabasoglu, NCAR, chaired the opening plenary, which included talks from many of the organizations working on the S2S and S2D topics, including the World Climate Research Programme (WCRP), World Meteorological Organization, World Weather Research Programme, NCAR, and the National Oceanographic and Atmospheric Administration (NOAA), among others. Additionally, specific projects were shown that emphasize some of the cutting edge research and collaboration being led by these organizations, including the S2S Prediction Project, the NOAA S2S Prediction Task Force and SubX projects, and the WCRP Decadal Climate Prediction Project and Working Group on Subseasonal to Interdecadal Prediction. 

Three invited speakers gave stage-setting talks. Tim Palmer, University of Oxford, reflected back on the past 40 years of the key successes across the range of initialized predictions on the subseasonal to decadal timescales. He noted that while process has been made, some current issues remain, including that some of the biases are an order of magnitude as that of the signals they are trying to predict. His hope for the future is the ability to look at model outputs and not be able to know if we are looking at a model or the real world. Arun Kumar, NOAA Climate Prediction Center, discussed the research needs for advancing operational S2D forecasting infrastructure. Current operational issues include the design of the configuration of operational S2D prediction systems and the science that provides the rational, development of products, communication of the forecasts, and the verification of the forecasts. While there is substantial diversity among operational systems, Kumar suggested that lagged ensembles have shown the potential for improving skill. Lisa Goddard, International Research Institute for Climate and Society at Columbia University, tied the research to applications by showing how prediction information has been used in real-world scenarios. For example, El Niño forecasts have been used to determine the seasonal flood potential in Somalia. They’ve also partnered with humanitarian organizations like the World Food Program to provide advance forecast information for emergency events (e.g., drought), so they can be more prepared, such as dispersing funds in advance. She noted that it is our job as a community to direct choices, particularly well-informed choices, that lead to appropriate and effective actions and decisions.

Over the week, two concurrent conferences will be taking place: the Second International Conference on Subseasonal to Seasonal Prediction and the Second International Conference on Seasonal to Decadal Prediction. Below are highlights from each of the conferences during the first day.

Subseasonal to Seasonal Conference Highlights

In the S2S portion, Andrew Robertson, IRI Columbia University, and Frédéric Vitart, ECMWF, chaired the opening session on “Mechanisms of S2S predictability.” Gilbert Brunet, Environment and Climate Change Canada, provided the keynote lecture on identifying wave processes associated with predictability across S2S timescales. Because S2S variability (such as the North Atlantic Oscillation (NAO), Madden-Julian Oscillation (MJO)) can influence high-impact weather, the community should characterize dynamical processes and predictability of S2S variability in reanalyses and reforecasting experiments, which is relevant for attribution studies. Brunet showed that it might be beneficial to see how well models can reproduce low-order adiabatic dynamics using Empirical Normal Mode analysis. 

Additional highlights include: 

• Due to the how fast the Earth system responds to initial conditions in models and how the definition of prediction inherently depends on the timescale, probabilistic/statistical prediction may, at times, be more beneficial than deterministic prediction at S2S timescales. (Zoltan Toth, NOAA Earth System Research Lab)
• Using the linear inverse model, after about three weeks the increased skill should be attributed to the El Niño-Southern Oscillation (ENSO) instead of the MJO, due to the longer term dynamics of ENSO in comparison to the MJO. This is because larger scale phenomena take longer to be affected by initial condition errors that amplify via instabilities. (Matt Newman, University of Colorado/CIRES & NOAA Earth System Research Lab)
• The strength of the Holton-Tan (H-T) relationship – a phenomenon in which the strength of northern stratospheric winter polar vortex synchronizes with the equatorial quasi-biennial oscillation – may not be robust based on the reanalysis ensemble. The members produce different flavors of the H-T relationship that are particularly sensitive to stratospheric sudden warmings during the quasi-biennial oscillation easterly phase. (Judith    Perlwitz, University of Colorado/CIRES & NOAA Earth System Research Lab)
• Statistically predicted sea ice improves S2S prediction over the Arctic in early winter and over East Asia and North America in late winter. (Baek-Min Kim, Korea Polar Research Institute)
• Wave properties can be partitioned into slow, basic state variations and fast perturbations. Analyzing the perturbations, it appears that adiabatic dynamics are just common resonant (Rossby-like) modes under varying basic states. (Gilbert Brunet, Environment and Climate Change Canada)
• The subseasonal forecast skill of many extratropical phenomena is dependent on the amplitude and/or phase of the MJO. (multiple speakers)
• Conditional skill (i.e., skill of extratropical forecasts as a function of skill in the tropics) is a useful diagnostic tool for characterizing the propagation of forecast errors from the tropics to the mid-latitudes. (Juliana Dias, University of Colorado/CIRES & NOAA Earth System Research Lab)
• Subseasonal prediction requires a good representation of the basic state for teleconnections between the MJO and the North Atlantic to be correct. (Robert Lee, NCAR/U. Reading)

Seasonal to Decadal Conference Highlights

The S2D track also opened with a session on “Mechanisms of S2D predictability,” chaired by Doug Smith, UK Met Office, and Steve Yeager, NCAR. The session’s keynote speaker, Jon Robson, University of Reading, dedicated his talk to mechanisms that give rise to predictive skill on interannual to decadal timescales, stressing that increasing skill must go hand-in-hand with increased insight by the community into underlying mechanisms of predictability. Robson highlighted that initialization of the Labrador Sea density leads to skillful predictions for the North Atlantic and a number of climate impacts such as hurricanes, Sahel rainfall, and temperature in China via circumglobal teleconnection. However, predicting the Labrador Sea density remains a challenge that will likely require multi-year predictability of the NAO, which in turn suffers from the signal-to-noise paradox.

Later in the afternoon, Thomas Delworth, NOAA Geophysical Fluid Dynamics Laboratory, presented on decadal variability and predictability in the Southern Ocean. He noted that recent observed trends in the Southern Ocean (i.e., surface ocean cooling and sea ice growth from 1979 to the present) are similar to transitions associated with an internal mode of Southern Ocean variability seen in long coupled control simulations, namely one characterized by long (multidecadal) predictability. Experiments starting from periods of active Southern Ocean convection exhibit highly predictable transitions to inactive Southern Ocean convection with trends of ocean cooling and sea ice growth, which closely match those observed, whereas experiments started from neutral or inactive states do not show matching trends.

Additional highlights include:

• The Interdecadal Pacific Oscillation (IPO) phase transitions are preceded by anomalies in off-equatorial western Pacific Ocean heat content and wind stress and can be triggered by El Niño/La Niña events, if the anomalies are sufficiently large. (Gerald Meehl, NCAR)
• Sub-decadal variability in the tropical Pacific had different characteristics in the 2000s compared to previous decades, likely caused by tropical Atlantic anomalies. (Takashi Mochizuki, JAMSTEC)
• Wildfire occurrence in the Southwest US is predictable on multi-year timescales, with skill arising from trans-basin variability and integrated soil moisture anomalies. (June-Yi Lee, Pusan National University)
• Recently revealed, the Pacific Decadal Precession is a robust mode of variability characterized by approximately 10-year counterclockwise progression of an atmospheric pressure dipole, with potential influence on precipitation in the Northwest US. (Bruce Anderson, Boston University)
• Model bias in the tropics greatly inhibits predictability of tropical cyclones otherwise expected from interannual (El Niño) to decadal (Atlantic Multidecadal Variability (AMV)) ocean modes. (Yohan Ruprich-Robert, Barcelona Supercomputing Center, Princeton University, GFDL; Christina Patricola, Lawrence Berkeley National Laboratory)
• AMV ensemble pacemaker experiments reveal substantial impacts on European winter climate given sufficiently strong SST forcing. This implies a potential predictability of European winter climate that has been overlooked because of low signal-to-noise in models. (Rym Msadek, NOAA GFDL, presenting work by Christophe Cassou, CECI/Université de Toulouse/CNRS/CERFACS)
• Suppression of African easterly wave variability in a high-resolution tropical channel model does not diminish mean cyclone activity, despite their hypothesized role in Atlantic cyclogenesis. (Christina Patricola, Lawrence Berkeley National Laboratory)

The meetings are being live streamed all week.