The USCLIVAR Working Group on Drought: A Multi-Model Assessment of the Impact of SST Anomalies on Regional Drought

The US CLIVAR Drought Working Group U.S. Membership Tom Delworth NOAA GFDL Rong Fu Georgia Institute of Technology Dave Gutzler (co-chair) University of New Mexico Wayne HigginsNOAA/CPC Marty HoerlingNOAA/CDC Randy KosterNASA/GSFC Arun KumarNOAA/CPC Dennis LettenmaierUniversity of Washington Kingtse MoNOAA CPC Sumant NigamUniversity of Maryland Roger Pulwarty NOAA- NIDIS Director David Rind NASA - GISS Siegfried Schubert (co-chair) NASA GSFC Richard Seager Columbia University/LDEO Mingfang Ting Columbia University/LDEO Ning Zeng University of Maryland International Membership: Ex Officio Bradfield Lyon International Research Institute for Climate Victor O. Magana Mexico Tim Palmer ECMWF Ronald Stewart Canada Jozef Syktus Australia

Other interested participants Lisa Goddard Alex Hall Jerry Meehl Jin Huang John Marshall Adam Sobel Max Suarez Phil Pegion Tim Palmer Entin, Jared K. Donald Anderson Rong Fu Doug Lecomte Hailan Wang Junye Chen Eric Wood Aiguo Dai Alfredo Ruiz-Barradas Jae Kyung E Schemm Clara Deser Kirsten Findell Mark Helfand Scott J. Weaver Kit K. Szeto Chunzai Wang Adam Phillips Matias Mendez Hugo Berbery

Terms of Reference propose a working definition of drought and related model predictands of drought coordinate evaluations of existing relevant model simulations suggest new model experiments designed to address some of the outstanding uncertainties concerning the roles of the ocean and land in long term drought coordinate and encourage the analysis of observational data sets to reveal antecedent linkages of multi-year drought organize a community workshop in 2008 to present and discuss results

Model Experiments Force global models with idealized SST anomalies –Address physical mechanisms, model dependence Participating groups/models: NASA (NSIPP1), Lamont(CCM3), NCEP(GFS), GFDL (AM2.1), NCAR (CAM3.5), and COLA/Univ. of Miami/ (CCSM3.0) Web site with access to monthly data ftp://gmaoftp.gsfc.nasa.gov/pub/data/clivar_drought_wg/README/www/index.html

Focus Here on Two Leading Patterns of Annual SST Variability Pacific Pattern Atlantic Pattern CC

Main Experiments Warm Atlantic Neutral Atlantic Cold Atlantic Warm Pacific PwAwPwAnPwAc Neutral Pacific PnAwPnAn Control PnAc Cold Pacific PcAwPcAnPcAc - REOF patterns superimposed on mean seasonal cycle with +/- 2 std amplitude - e.g., PwAc is the combined pattern of warm Pacific and cold Atlantic - all runs 50 years (35 for GFS)

Global Spatial Correlations of Annual Mean Responses Precipitation z 200mb     Agreement among models for response to Pacific is high Agreement among models for response to Atlantic is lower Agreement is higher for z200 than it is for precipitation

Warm Pacific Annual Mean Precip (mm/day) and z200 (5 meter CI) Response

Warm Atlantic Annual Mean Precip (mm/day) and z200 (5 meter CI) Response

Annual Precipitation (mm/day) Pacific Cold+Atlantic WarmPacific Warm+Atlantic Cold US Drought! US Pluvials!

Some Basic Results: Over US Mean Responses –Models tend to agree that Cold Pacific+Warm Atlantic => drought/warm Warm Pacific+Cold Atlantic => pluvial conditions/cold –There are substantial differences in details of anomaly patterns –There is a large seasonality in responses Potential Predictability (Pacific signal to noise) –Largest in spring –Models appear to agree more on precipitation than surface temperature responses!

Special issue highlighting results is now being put together for J. Climate

End

The model results are from AMIP- style runs from each model (runs forced by observed SSTs for the period ). Contour interval for the height field is 20m (negative values are dashed and the zero line is the first solid contour). Precipitation is in mm/day. Annual Mean Precipitation and 200mb Eddy Height Climatologies

Annual Mean Tsfc Response (°C) Pacific WarmPacific Cold

Annual Mean Tsfc Response (°C) Atlantic WarmAtlantic Cold

Great Plains (Annual Mean Response) Tsfc Precip warm Pacific cold Pacific

Cold Pacific Annual Mean Precip (mm/day) and z200 (5 meter CI) Response

Cold Atlantic Annual Mean Precip (mm/day) and z200 (5 meter CI) Response

Annual Precipitation (mm/day) Pacific ColdAtlantic Warm Tendency for US Drought!

Annual Precipitation (mm/day) Pacific WarmAtlantic Cold Tendency for US Pluvials!

Annual Precipitation (mm/day) Pacific Cold+Atlantic WarmPacific Warm+Atlantic Cold US Drought! US Pluvials!

Seasonal Evolution of Response

DJF - Cold Weak and shifted anti-cyclonic anomalies Contours: 200mb height anomalies Vectors: 850mb wind anomalies Colors: precipitation anomalies

MAM - Cold General consistency in height anomalies but CFS again shifted south

JJA - Cold Cyclonic anomalies in IAS

SON - Cold Cyclonic anomalies in IAS

DJFMAM JJASON Great Plains (Seasonality of Response) warm Pacific cold Pacific Tsfc Precip

Predictability Measures Signal to Noise Ratio

R= ( x-y )/s xy ( ): 50 yr mean x : seasonal mean from experiment y : seasonal mean from control (climatological SST) s 2 xy = ( s 2 X + s 2 Y )/2 s 2 X variance of seasonal mean from experiment s 2 Y : variance of seasonal mean from control Signal to Noise Ratio ( R)

GP SE SW NW  Focus U.S. Response to Pacific Forcing

Precipitation Response to Warm and Cold Pacific (signal/noise) R R

Tsfc Response to Warm/Cold Pacific (signal/noise) R R