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The structure and nature of warm-season interannual variability of the Great Plains hydroclimate

The structure and nature of warm-season interannual variability of the Great Plains hydroclimate. Alfredo Ruiz-Barradas, and Sumant Nigam. Department of Atmospheric and Oceanic Science University of Maryland. Predicting Drought on Seasonal to Decadal Time Scales Adelphi, MD.

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The structure and nature of warm-season interannual variability of the Great Plains hydroclimate

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  1. The structure and nature of warm-season interannual variability of the Great Plains hydroclimate Alfredo Ruiz-Barradas, and Sumant Nigam Department of Atmospheric and Oceanic Science University of Maryland Predicting Drought on Seasonal to Decadal Time Scales Adelphi, MD. May 17-19, 2005

  2. Outline • Precipitation variability over the Great Plains. • Structure of hydroclimate fields and their relative contributions associated with precipitation anomalies. • Pacific and Atlantic connections • Conclusions • References

  3. Standard Deviation of monthly precipitation during summer (J,J,A) in NARR (1979-1998). Great Plains Precipitation index in the warm-season (J,J,A) in NARR and US-Mexico data sets. 1993 1998 1958 1998 1950s 1970s 1983-84

  4. Warm-season regressions of the GPP index show: • Precip anomalies are not linked • with precip anomalies over other continental regions • Significant moisture fluxes from the Gulf of Mexicoand associated convergence • Weak connection with the Pacific • Low evaporation Precipitation Precipitation Total Moisture Flux & MF Convergence St. Moisture Flux & MF Convergence This suggests the dominance of remote water sources over local recycling of precipitation for precipitation variability over the Great Plains. Evaporation Tr. Moisture Flux & MF Convergence

  5. Correlation between July’s precipitation and previous months’ precipitation Low dependence of precipitation anomalies on preceding precipitation anomalies suggests a weak local recycling of precipitation

  6. SST-leading Correlations with July GPP index (1950-1998) • Links to both Pacific and Atlantic • basins • - From ENSO-like pattern • to PDO-like structure • - Atlantic forcing too?

  7. Pacific Mode (7th) Rotated EOFs of extratropical (155°E-15°W,25°N-60°N) Φ(700mb) & SST show linkages to North American summer hydroclimate variability • PNA-like pattern • Moisture transport at • mid-troposphere levels • Not moisture fluxes to/ • from the Gulf of Mexico • Correlates with the GPP • index at -0.43. 1970s 1988

  8. Atlantic Mode (1st) • NAO-like pattern • Moisture transports at • low-troposphere levels • Moisture fluxes to/from • the Gulf of Mexico • Correlates with the GPP • index at -0.33. 1976 1983-84 1955 1993 1958 1998

  9. Conclusions • Remote water sources dominate over local water sources (precipitation recycling) in the generation of precipitation variability. • Pacific’s link with the Great Plains hydroclimate is through northeastward moisture transports across the Gulf of California, at mid- troposphere levels. • The Atlantic connection, on the other hand, is through NAO’s influence on the Bermuda High, and the resulting interaction of circulation with North American orography; all of which serve to modulate the low-level moisture transports from the Gulf of Mexico

  10. References • Nigam, S., and A. Ruiz-Barradas, 2005: Seasonal hydroclimate variability over North America in ERA-40, Regional Reanalysis and AMIP simulations. Submitted to J. Climate. • Ruiz-Barradas, A., and S. Nigam, 2005a: Warm-season Precipitation Variability over the US Great Plains in Observations, NCEP and ERA-40 Reanalyses, and NCAR and NASA Atmospheric Simulations. To appear in the 1 June issue of the J. Climate. • ______, ______, 2005b: Great Plains Hydroclimate Variability: The View from the North American Regional Reanalysis. Submitted, J. Climate.

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