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 http://www.usclivar.org/Organization/drought-wg.html

U.S. Membership• Tom Delworth NOAA GFDL • Rong Fu Georgia Institute of Technology • Dave Gutzler (co-chair) University of New Mexico• Wayne Higgins NOAA/CPC• Marty Hoerling NOAA/CDC • Randy Koster NASA/GSFC• Arun Kumar NOAA/CPC• Dennis Lettenmaier University of Washington• Kingtse Mo NOAA CPC• Sumant Nigam University 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 <goddard@iri.columbia.edu> • Alex Hall <alexhall@atmos.ucla.edu> • Jerry Meehl <meehl@ucar.edu>• Jin Huang <Jin.Huang@noaa.gov>• John Marshall <jmarsh@MIT.EDU> • Adam Sobel <ahs129@columbia.edu>• Max Suarez <Max.J.Suarez@nasa.gov>• Phil Pegion <pegion@gmao.gsfc.nasa.gov>• Tim Palmer <Tim.Palmer@ecmwf.int>• Entin, Jared K. <jared.k.entin@nasa.gov>• Donald Anderson <donald.anderson-1@nasa.gov> • Rong Fu <rf66@mail.gatech.edu>• Doug Lecomte <Douglas.Lecomte@noaa.gov>• Hailan Wang <hwang@climate.gsfc.nasa.gov>• Junye Chen <jchen@gmao.gsfc.nasa.gov>• Eric Wood <efwood@princeton.edu>• Aiguo Dai <adai@ucar.edu>• Alfredo Ruiz-Barradas <alfredo@atmos.umd.edu>• Jae Kyung E Schemm <Jae.Schemm@noaa.gov>• Clara Deser cdeser@cgd.ucar.edu• Kirsten Findell <Kirsten.Findell@noaa.gov>• Mark Helfand Mark.Helfand@nasa.gov• Scott J. Weaver <sweaver@gmao.gsfc.nasa.gov>• Kit K. Szeto <Kit.Szeto@ec.gc.ca>• Chunzai Wang <Chunzai.Wang@noaa.gov>• Adam Phillips <asphilli@cgd.ucar.edu>• Matias Mendez <matias@atmosfera.unam.mx>• Hugo Berbery <berbery@atmos.umd.edu>

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

Main Experiments

Warm Atlantic

Neutral Atlantic

Cold Atlantic

Warm Pacific

PwAw PwAn PwAc

Neutral Pacific

PnAw PnAn

Control

PnAc

Cold Pacific

PcAw PcAn PcAc

- 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 Warm Pacific 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 1980-1998). 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 Warm Pacific Cold

Annual Mean Tsfc Response (°C)

Atlantic Warm Atlantic 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 Cold Atlantic Warm

Tendency for US Drought!

Annual Precipitation (mm/day)

Pacific Warm

Atlantic Cold

Tendency for US Pluvials!

Annual Precipitation (mm/day)

Pacific Cold+Atlantic Warm Pacific 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

DJF MAM

JJA SON

Great Plains(Seasonality of Response)

warm Pacificcold Pacific

Tsfc

Precip

Predictability Measures

Signal to Noise Ratio

R = ( x-y )/sxy

( ): 50 yr mean

x: seasonal mean from experiment

y: seasonal mean from control (climatological SST)

s2xy = (s2

X+s2Y)/2

s2X variance of seasonal mean from experiment

s2Y : variance of seasonal mean from control

Signal to Noise Ratio ( R)

GP SESW

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