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Climate Variability, Model Prediction, Downscaling, and Forecast L imitations

Climate Variability, Model Prediction, Downscaling, and Forecast L imitations. Arlene Laing UCAR/COMET Boulder, Colorado, USA & St. Elizabeth, Jamaica. Learning Objectives. Describe dynamical and physical mechanisms for climate variability in the Caribbean

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Climate Variability, Model Prediction, Downscaling, and Forecast L imitations

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  1. Climate Variability, Model Prediction, Downscaling,and Forecast Limitations Arlene Laing UCAR/COMET Boulder, Colorado, USA & St. Elizabeth, Jamaica CARICOF Training Workshop, 22-25 May 2013 Port of Spain, Trinidad and Tobago

  2. Learning Objectives • Describe dynamical and physical mechanisms for climate variability in the Caribbean • Describe major climate oscillations critical to seasonal climate prediction in Caribbean • Understand strengths and limitations of Global Climate Models for climate prediction in the Caribbean • Describe methods of downscaling global models for regional climate prediction and their limitations Laing, 2013 CARICOF Training Workshop

  3. What influences Caribbean Precipitation? Caribbean precipitation affected by three major components: • Sea Surface Temperature (SST) • Wind directionand Shear • Strength of Caribbean Low Level Jet Laing, 2013 CARICOF Training Workshop

  4. SST Generally • Low SST => Dry anomalies • High SST => Wet anomalies Laing, 2013 CARICOF Training Workshop

  5. Wind Direction & Wind Shear Direction • Easterly flow from warm Atlantic = Wetter • Westerly flow blocked by Central American topography = Drier Shear (850-200 hPa) • Weak easterly shear = Wetter • Strong westerly shear = Drier • Strong zonal shear inhibits or weakens tropical cyclones (e.g., fewer during El Niño due to strong zonal shear) Laing, 2013 CARICOF Training Workshop

  6. Caribbean Low Level Jet (CLLJ) NARR • 925 hPa easterly wind maximum • Peaks in July and February Munoz et al. 2008 ECMWF Laing, 2013 CARICOF Training Workshop

  7. Correlation of 925 zonal wind & Precipitation Munoz et al. 2008 Correlation between 12-month seasonal cycle of precipitation and 12-month seasonal cycle of Caribbean 925-hPa zonal wind index. Laing, 2013 CARICOF Training Workshop

  8. July Precipitation CLLJ & Precipitation CLLJ July Peak • Associated with mid-summer dry period in Caribbean • Associated with mid-summer rain max along Central Americaeast coast July Vertical Velocity Munoz et al. 2008 July SST Whyte et al. 2007 Munoz et al. 2008 Laing, 2013 CARICOF Training Workshop

  9. CLLJvariations & Precipitation Convergence associated with jet exit region = Wetter Divergence with entrance jet region = Drier (Amador 1998, Whyte et al. 2007, Munoz et al. 2008) Laing, 2013 CARICOF Training Workshop

  10. CLLJ & SST Gradients • CLLJ seems to be maintained by positive ocean-atmosphere feedback • CLLJ produces wind stress => cools south and warms north => increases meridional SST gradient => increases pressure gradients and wind speed SST gradient SST gradient • CLLJ responds to zonal SST gradients between tropical Pacific and Atlantic Whyte et al. 2007 Laing, 2013 CARICOF Training Workshop

  11. Annual Cycle of CLLJ • Annual cycle also evident at surface • Max Mean Speed > 14 m/s in Jun-Jul • Secondary max in Jan-Feb • Minimum in Sep-Nov Munoz et al. 2008 Laing, 2013 CARICOF Training Workshop

  12. Strength of CLLJ Strength of CLLJ depends on pressure gradient between Subtropical High and Equatorial Trough Wind speed > 8 m/s contoured Wind speed > 8 m/s contoured Laing, 2013 CARICOF Training Workshop

  13. Variability of 925-zonal winds Whyte et al. 2007 Laing, 2013 CARICOF Training Workshop

  14. Major influences on Caribbean Precipitation • SST • Wind directionand Shear • Strength of CLLJ How do these components vary? Laing, 2013 CARICOF Training Workshop

  15. Modes of Tropical Variability Decadal Oscillations Adapted from Laing, 2013 CARICOF Training Workshop

  16. Major Climate Oscillations What do these have in common? • Centers of action generally over oceans • Close link to SST fluctuations Courtesy, NCAR Laing, 2013 CARICOF Training Workshop

  17. Teleconnection Strong correlation between meteorological parameters in distant parts of the globe, generally associated with large-scale atmospheric circulation patterns NCAR Jim Hurrell NCAR Laing, 2013 CARICOF Training Workshop

  18. Decadal Oscillations: Influence on the Caribbean AMO NAO (has dominant mode at decadal scale) AO/NAM Partners { Laing, 2013 CARICOF Training Workshop

  19. Atlantic Multidecadal Oscillation (AMO) Mean N. Atlantic SST Anomalies and vertical shear of horizontal winds over 20–40 year periods Correlates with NH Summer Rainfall Laing, 2013 CARICOF Training Workshop

  20. AMO & Hurricanes Negative AMO Index => Fewer Major Hurricanes in Caribbean Positive AMO Index => More Major Hurricanes in Caribbean Laing, 2013 CARICOF Training Workshop

  21. North Atlantic Oscillation (NAO) Oscillation between subtropical high (Azores) and polar low (Iceland) in North Atlantic Dominant mode of winter climate variability in North Atlantic region Affects trade winds but role in tropical forcing under active research and debate Less predictable on seasonal time scale than ENSO Stronger trade winds Weak trade winds University of New Hampshire Laing, 2013 CARICOF Training Workshop

  22. North Atlantic Oscillation (NAO) Laing, 2013 CARICOF Training Workshop

  23. NAO • No universally accepted index to describe temporal evolution of NAO (center of action moves around) • Simple pressure anomaly difference between locations • Principal Component time series of leading (usually regional) EOF of sea level pressure Laing, 2013 CARICOF Training Workshop

  24. Arctic Oscillation (AO) aka Northern Annular Mode (NAM) Closely related to NAO J. Wallace, University of Washington courtesy of National Snow and Ice Data Cente Laing, 2013 CARICOF Training Workshop

  25. NAO and AO/NAM NAO (Station Obs) NAO (Atlantic PC1) • Highly correlated AO/NAM (NH PC1) Jim Hurrell, NCAR Laing, 2013 CARICOF Training Workshop

  26. Pop Quiz • What are the major influences on precipitation in the Caribbean? • What time of year is the peak in the CLLJ? • How does CLLJ affect rainfall in Caribbean? • Name the decadal-scale climate oscillations that affect the Caribbean? Laing, 2013 CARICOF Training Workshop

  27. Interannual Variability influence on the Caribbean ENSO PNA (indirect, connected to ENSO) QBO Laing, 2013 CARICOF Training Workshop

  28. Zonal and SH Teleconnections • Cold-tongue/ITCZ complex (ENSO) • Eastern Pacific stratus regime • Tropical Atlantic variability region • South Atlantic Convergence Zone, • Inter-American Warm Pool • Arrows indicate hypothesized interactions with other regions http://eprints.soton.ac.uk/19188/1/vamos1_rep_p3.htm Laing, 2013 CARICOF Training Workshop

  29. Laing, 2013 CARICOF Training Workshop

  30. Walker Circulation Laing, 2013 CARICOF Training Workshop

  31. El Niño and La Niña Laing, 2013 CARICOF Training Workshop

  32. Strong El Niños and La Niñas Laing, 2013 CARICOF Training Workshop

  33. ENSO and Caribbean Summer Rains Laing, 2013 CARICOF Training Workshop

  34. ENSO and Hurricanes Hurricane Andrew Laing, 2013 CARICOF Training Workshop

  35. ENSO Monitoring NOAA Laing, 2013 CARICOF Training Workshop

  36. ENSO Prediction Laing, 2013 CARICOF Training Workshop

  37. SST Outlook: NCEP CFS.v2 ENSO Forecast Issued 12 May 2013 The CFS.v2 ensemble mean (black dashed line) predicts ENSO-neutral conditions through the end of 2013. Courtesy NCEP/CPC

  38. Pacific North American Pattern (PNA)& ENSO Laing, 2013 CARICOF Training Workshop

  39. Quasi-Biennal Oscillation (QBO) • Oscillations in zonal lower stratospheric winds (30-50 hPa) • 2-year cycle: easterly to westerly winds • Changes vertical wind shear at top of troposphere • Influences frequency of North Atlantic tropical cyclones Laing, 2013 CARICOF Training Workshop

  40. Sub-seasonal Climate Variability Madden Julian Oscillation (MJO) - 30-60 Tropical Oscillation Laing, 2013 CARICOF Training Workshop

  41. MJO Impacts on Caribbean • MJO can cause ½ a month or more of enhanced convection or suppression of convection • Should monitor its state and forecast and explain its impact to users Laing, 2013 CARICOF Training Workshop

  42. MJO & Hurricane Activity Laing, 2013 CARICOF Training Workshop

  43. Pop Quiz • What are the major interannual oscillations that influence Caribbean weather and climate? • To major climate components are interannual oscillations linked? Laing, 2013 CARICOF Training Workshop

  44. Global Climate Model Prediction How well do models capture climate variability of importance to the Caribbean? Laing, 2013 CARICOF Training Workshop

  45. Scales of Model Output: Forecast, Outlook, Projection How statistics of climate system will change in response to changing boundary conditions Use initial conditions to predict how the weather is going to evolve for some time going forward Laing, 2013 CARICOF Training Workshop

  46. GCM Biases in Model Means Example of bias in modeled SSTs Laing, 2013 CARICOF Training Workshop

  47. Modeled ITCZ & Precipitation Biases Laing, 2013 CARICOF Training Workshop

  48. GCMs & Caribbean Low-level Jet • GCMs can simulate location and height of CLLJ • However, observed semiannual cycle of CLLJ magnitude challengingfor models • Model means failed to capture strong July CLLJ peak; because did not predict westward and southward expansion of North Atlantic subtropical highbetween May and July Martinand Schumacher 2011 Laing, 2013 CARICOF Training Workshop

  49. Combining models reduces deficiencies of individual models Ranked Probability Skill Score (RPSS) for 2m TemperatureJan-Feb-Mar 1950-1995 Slide courtesy of Lisa Goddard, IRI

  50. Dynamical Models Statistical Forecast Tools Used independently or combined with GCMS • Canonical Correlation Analysis (CCA) • Screening Multiple Linear Regression (SMLR) • Constructed Analogue (CA) • Ensemble CCA (ECCA) Statistical Models Laing, 2013 CARICOF Training Workshop

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