NASA/TM_2002-104606, Vol. 23 Techmcal Report Series• on Global Modehn_,• _J and Data Assimilation Volume 23 Prospects for Improved Forecasts of Weather and Short-Term Climate Variability on Subseasonal (2-Week to 2-Month) Time Scales S. Schubert, R. Dole, H. van den DooL MI Suarez, and D. Waliser Ptvceedings flvm a _fbrkshop Sponsored hy the Earth Sciences Directorate at NASA's Goddard Space Flight Centez Co-sponsored by 2v_dSA Seasonal-to-bm_rannual Prediction Project and NAS_d Data Assimilation OJfice April 16-18, 2002 Nc_vember__ 2002 The NASA STI Program Office ... m Profile Since its founding, NASA has been dedicated to CONFERENCE PUBLICATION. Collected the advancement of aeronautics and space papers from scientific and technical science. The NASA Scientific and Technical conferences, symposia, seminars, or other hlf()rmation (STI) Program Office plays a key meetings sponsored or cosponsored by NASA. part in helping NASA maintain this important role. SPECIAL PUBLICATION. 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NASA/TM_2002-104606, VoL 23 Technical Report Series on Global Modeling and Data Assimilation Volume 23 Prospects for Improved Forecasts of Weather and Short-Term Climate Variability on Subseasonal (2-Week to 2-Month) Time Scales Siegfried Schubert, Goddard Space Flight Centez Greenbelt, AID Randall Dole, NOAA- Coopelvtive hzstitute /br Research in Envh_mmenml Sciences Climate Di_gnostics Centez Boulder, CO Huug van den Dool, NOAA- Climate Prediction Center, Camp 5_rings, MD Mcc¢ Suarez, Goddard Space Flight Centel; Greenbelt, MD 1-)uane t4_liser, lnstitute fi_r Terrestrial and Planetaty A tmo_pheres State University of New York. Stony Brook, NY National Aeronautics and Space Administration Goddard Space Hight Center Greenbelt, Maryland 20771 November 2002 Available from: NASA Center for AeroSpace Inlk_rmation National Technical In[i)rmation Service 7121 Standard Drive 5285 Port Royal Road Hanover, MD 21076-1320 Springfield, VA 22161 Price Code: A17 Price Code: A10 Table of Contents Abstract .............................................................................................................................. 5 I. Introduction .................................................................................................................... 7 II. Summary of Sessions ...................................................................................................... 9 i. Current operational methods and their skill ............................................................ 9 ii. Predictability of extra-tropical "modes". .............................................................. 11 iii-iv) Predictability of the ISO/MJO and tropical/extra-tropical interactions .............. 14 v. Role of land surface processes ............................................................................ 17 vi. Link between low frequency and weather/regional phenomena ............................ 19 Ill. Discussion and Summary .............................................................................................. 22 i. Role of tropical heating and the MJO ................................................................... 23 ii. Extra- tropical modes of variability ....................................................................... 24 iii. Soil moistuxe and snow ...................................................................................... 25 iv. Links with weather and other regional phenomena .............................................. 26 v. Methodology and data ........................................................................................ 27 1V. Recommendations ........................................................................................................ 28 i. High priority research and development ................................................................ 28 ii. High priority action items ..................................................................................... 29 Acknowledgments .............................................................................................................. 31 References ......................................................................................................................... 31 Appendix - List of participants ........................................................................................... 33 Agenda .............................................................................................................................. 37 Extended Abstracts ............................................................................................................ 43 3 Abstract A workshop was held in April of 2002 that brought together various experts in the Earth Sciences to focus on the subseasonal prediction problem. While substantial advances have occurred over the last few decades in both weather and seasonal prediction, progress in improving predictions on these intermediate time scales (time scales ranging from about two weeks to two months) has been slow. The goals of the workshop were to get an assessment of the "state of the art" in predictive skill on these time scales, to determine the potential sources of "untapped" predictive skill, and to make recommendations for a course of action that will accelerate progress in this area. A remarkable aspect of the workshop was the multi-disciplinary natuxe of the attendees, consisting of about 100 scientists with specialties in areas that included stratospheric dynamics, hydrology and land surface modeling, the monsoons, the Madden-Julian Oscillation (MJO) and other tropical variability, extratropical variability including extratropical-tropical interactions, coupled atmosphere- ocean-land modeling, weather prediction, seasonal prediction, and various aspects of statistical modeling, analysis, and prediction. This broad range of expertise reflected the wide array of physical processes that are deemed potentially important sources of predictive skill on subseasonal time scales. One of the key conclusions of the workshop was that there is compelling evidence for predictability at forecast lead times substantially longer than two weeks. Tropical diabatic heating and soil wetness were singled out as particularly important processes affecting predictability on these time scales. Predictability was also linked to various low-frequency atmospheric phenomena such as the annular modes in high latitudes (including their connections to the stratosphere), the Pacific/North American pattern (PNA), and the MJO. The latter, in particular, was highlighted as a key source of untapped predictability in the tropics and subtropics, including the Asian and Australian monsoon regions. The key recommendations of the workshop are: a) That a coordinated and systematic analysis of current subseasonal forecast sldll be conducted by generating ensembles of 30-day hindcasts for the past 30-50 years with several "frozen" AGCMs. Specific goals include, sampling all seasons, and generating sufficiently large ensembles to estimate the evolution of the probability density function. 5 b) Thataseriesof workshopsbeconvenedfocusedonmodelingtheMJO,andthatacoordinated multi-nation/multi-modelexperimentalpredictionprogrambedevelopedfocusedontheMJO. e) That new satellite