On the Nature of the Recent
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On the Nature of the Recent Southwestern Drought Philip Pegion 1 , Siegfried Schubert, Randy Koster, Max Suarez. NASA-GSFC Global Modeling and Assimilation Office. 1. SAIC. Characteristics of recent drought. Started with La Nina in 1999 5 years in a row of below normal precipitation

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On the Nature of the Recent Southwestern DroughtPhilip Pegion1, Siegfried Schubert, Randy Koster, Max Suarez.NASA-GSFC Global Modeling and Assimilation Office

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Characteristics of recent drought

  • Started with La Nina in 1999

  • 5 years in a row of below normal precipitation

  • 2002 was 4th driest year on record, the region received only 70% of normal precipitation, and in 2003, the region only received 83%.

  • Driest period since the 1950s.

  • Persisted past weak El-Nino in 2002

Motivation

We want to understand the cause of the recent drought, and can we

determine if it has ended?


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YEAR

Desert SW.

region


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Observed Precipitation Desert SW region.

25-month running mean anomaly (mm/day)

Anomaly

mm/month

YEAR


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Observed Precipitation Desert SW region.

25-month running mean anomaly (mm/day)

Anomaly

mm/month

YEAR


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Observed Precipitation: % of normal


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HADISST Sea Surface Temperature anomaly (K)


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Observed Precipitation Desert SW region.

25-month running mean anomaly (mm/day)

Anomaly

mm/month

ENSO

2nd EOF: HADISST

YEAR

Correlation: 0.51


Model description

Model Description

  • NASA Seasonal-to-Interannual Prediction Project (NSIPP-1) AGCM

    • 4th Order finite difference dynamical core (Suarez and Takacs, 1995).

    • Simple K-scheme boundary layer (Louis et al., 1982).

    • Relaxed Arakawa-Schubert (RAS) convection (Moorthi and Suarez, 1992).

    • Chou and Suarez (1994, 2000) radiation.

    • Mosaic land model (Koster and Suarez, 1996).

  • AMIP

    • 3.75o longitude, 3o latitude, 34 levels

    • 14 member ensemble (1902-present)

    • Additional AMIP runs at 2o and 1o degree.

  • DSP

    • 0.625o longitude, 0.5o latitude, 34 levels

    • Initialized December 1, 2001 with the NCEP Reanalysis.


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Precipitation Desert SW region.

25-month running mean anomaly (mm/day)


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Precipitation Desert SW region (1998-2004)

7-month running mean anomaly (% of normal)

CMAP

Model ensemble mean


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October 2001 -March 2002

Precipitation (% from normal)


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October 2001 -March 2002

Surface Air Temperature Anomaly (K)


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October 2001 -March 2002

200 mb Height Anomaly (m)


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October 2001 -March 2002

200 mb Height Anomaly (m)

Model La NINA Composite

NCEP La NINA Composite


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October 2001 -March 2002

850 mb v’q’ Anomaly (m s-1 g Kg-1)


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  • High Resolution GCM runs

  • Initialized 00z1DEC2001 with the NCEP/NCAR reanalysis.

  • Run through end of March.

  • 10 ensemble member run over Reynolds SST

  • 10 additional ensemble members with MODIS SST.


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DJFM 2002: SST anomaly (K)

MODIS

Reynolds

MODIS-Reynolds


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DJFM 2002: Precipitation Anomaly (mm/day)

0.5deg DSP w/ MODIS SST

0.5deg DSP w/ Reynolds SST

CMAP

MODIS - Reynolds


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DJFM 2002: Precipitation (% of normal)

0.5deg DSP w/ Reynolds SST

0.5deg DSP w/ MODIS SST

CMAP

MODIS - Reynolds


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DJFM 2002: 200 mb Height Anomaly (m)

0.5deg DSP w/ MODIS SST

0.5deg DSP w/ Reynolds SST

NCEP/NCAR Reanalysis

MODIS - Reynolds


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DJFM 2002: Precipitation (% of normal)

Ensemble 1 MODIS SST

Ensemble 2 MODIS SST

0.5deg DSP w/ Reynolds SST

Ensemble 2 Reynolds SST

NCEP/NCAR Reanalysis


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Has the long term drought ended, or is last winter just a bump in the time series?


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Annual Mean SST Anomaly (K)


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Annual Mean SST Anomaly (K)


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12 month coupled model forecast


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Lake Powell

Year

Conclusions

  • Recent drought was of the most severe and longest lasting in recent times.

  • Start of drought is linked with changes in Pacific Ocean SSTs

  • Most severe part of drought, 2002, lies outside of the envelope of response in the model.

  • Some hi-resolution runs do get the correct magnitude of the winter drought.

  • Last winter rains provided big relief to the drought, but the southwest hasn’t recovered yet.

Surface Elevation


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JFM 2002: 200 mb Height Anomaly (m)


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DJFM 2002: 200 mb Height Anomaly (m)


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DJFM 2002: 200 mb Height Anomaly (m)


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Precipitation Desert SW region (1998-2004)

7-month running mean anomaly (mm/day)

CMAP

Model ensemble mean


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Precipitation Desert SW region (1998-2004)

7-month running mean anomaly (normalized)

CMAP

Model ensemble mean


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