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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 - PowerPoint PPT Presentation
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On the Nature of the Recent Southwestern Drought
Philip Pegion1, Siegfried Schubert, Randy Koster, Max Suarez.
NASA-GSFC Global Modeling and Assimilation Office
1. SAIC
Characteristics of recent drought
MotivationWe want to understand the cause of the recent drought, and can we
determine if it has ended?
•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
YEAR
Desert SW. region
25-month running mean anomaly (mm/day)
YEAR
Ano
mal
ym
m/m
onth
Observed Precipitation Desert SW region.
YEAR
Ano
mal
ym
m/m
onth
Observed Precipitation Desert SW region.
25-month running mean anomaly (mm/day)
Observed Precipitation: % of normal
HADISST Sea Surface Temperature anomaly (K)
YEAR
Ano
mal
ym
m/m
onth
ENSO
2nd EOF: HADISST
Correlation: 0.51
Observed Precipitation Desert SW region.
25-month running mean anomaly (mm/day)
• 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.
Model Description
Precipitation Desert SW region.
25-month running mean anomaly (mm/day)
Precipitation Desert SW region (1998-2004)
7-month running mean anomaly (% of normal)
CMAP
Model ensemble mean
October 2001 -March 2002Precipitation (% from normal)
Surface Air Temperature Anomaly (K)
October 2001 -March 2002
200 mb Height Anomaly (m)
October 2001 -March 2002
200 mb Height Anomaly (m)
October 2001 -March 2002
Model La NINA Composite
NCEP La NINA Composite
850 mb v’q’ Anomaly (m s-1 g Kg-1)
October 2001 -March 2002
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.
DJFM 2002: SST anomaly (K)MODIS
MODIS-Reynolds
Reynolds
DJFM 2002: Precipitation Anomaly (mm/day)
0.5deg DSP w/ MODIS SST
CMAP
0.5deg DSP w/ Reynolds SST
MODIS - Reynolds
DJFM 2002: Precipitation (% of normal)
0.5deg DSP w/ MODIS SST
CMAP
0.5deg DSP w/ Reynolds SST
MODIS - Reynolds
DJFM 2002: 200 mb Height Anomaly (m)
0.5deg DSP w/ MODIS SST
NCEP/NCAR Reanalysis
0.5deg DSP w/ Reynolds SST
MODIS - Reynolds
DJFM 2002: Precipitation (% of normal)
NCEP/NCAR Reanalysis
0.5deg DSP w/ Reynolds SST
Ensemble 1 MODIS SST Ensemble 2 MODIS SST
Ensemble 2 Reynolds SST
Has the long term drought ended, or is last winter just a bump in the time series?
Annual Mean SST Anomaly (K)
Annual Mean SST Anomaly (K)
12 month coupled model forecast
Lake PowellConclusions
•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.
Surf
ace
Elev
atio
n
Year
JFM 2002: 200 mb Height Anomaly (m)
DJFM 2002: 200 mb Height Anomaly (m)
DJFM 2002: 200 mb Height Anomaly (m)
Precipitation Desert SW region (1998-2004)
7-month running mean anomaly (mm/day)
CMAP
Model ensemble mean
Precipitation Desert SW region (1998-2004)
7-month running mean anomaly (normalized)
CMAP
Model ensemble mean