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Summer Precipitation Regimes over North America and Prediction. Kingtse C. Mo & Jae Schemm Climate Prediction Center NCEP/NWS. Purposes. 1. Identify Summer Precipitation Regimes over Mexico and the United States 2 Determine P regimes are related to Tropical convection - PowerPoint PPT Presentation
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Summer Precipitation Regimes over North America and Prediction
Kingtse C. Mo & Jae SchemmClimate Prediction Center
NCEP/NWS
Purposes
• 1. Identify Summer Precipitation Regimes over Mexico and the United States
• 2 Determine P regimes are related to Tropical convection
• 3. Influence of soil moisture on P regimes
• 4 Week2 to Seasonal Forecasts
Data sets
*Precipitation over Mexico and the United States
(1968-2002)
* Circulation anomalies: CDAS/reanalysis R1
1968-2002
* OLRA : 1979-2002 ( Total & IS 10-90 day filtered)
* Qfluxes (vertically integrated moisture flux)
from CDAS 1968-1996, RSM 1991-2000
* Soil moisture and E from an off line NAOH model
1968-1998 (Huug van Den Dool et al. 2003)
Methods
Pentad precipitation data from June-September
1979-2002 Square root transformation to make rainfall
close to a normal distribution Perform EOF analysis Rotated EOF 5 day running mean of P and take square root take out the mean and project onto REOF to get RPCs.
Northern Great plains Southern Mexico
NW Mexico & SW Southern Plains
Weak Tropical linkage ,Zonal pattern
RPC 1 Southern Mexico
Both ENSO & MJO can influence REOF 3
Meridional modeREOF 2 REOF 5
MJO
When suppressed convection shifts to the central Pacific, Central America is likely to be wet (REPF 3), more rainfall over northwestern Mexico & less rainfall over southern Great Plains (REOF 2)
OLRA
REOF 5
Submonthly mode
Four REOF patterns related to the NAMs
REOF 1- Continental Zonal pattern, weak tropical influence
REOF 3- Southern Mexico Both ENSO and MJO influence
REOF 2 & REOF 5- Phase reserval Northwestern Mexico & southern Plains – Intraseasonal oscillations influence
Northern & Southern Great Plains
• They belong to two REOFs (REOF 1 & 5)
• They both are controlled by the Great Plains LLJ
• REOF 1 rainfall is influenced by soil moisture at the entrance region of the GPLLJ,but not REOF 5
Northern Plains GPLLJ
Southern Plains
RPC 1 Continental P pattern
• Zonal pattern (Cavazos et al2002)• Strong GPLLJ & weak GCLLJ• Associated with strong upper level wind over the
west region. (Beryle & Paegle2003)• Weak tropical convection• Wet soil moisture anomalies near the entrance of
the GPLLJ 10 days before positive events
REOF 3 – Southern Mexico
• Strong influence from tropical convection in the tropical Pacific. Both the MJO and ENSO can influence rainfall over Central America and REOF 3
REOF 2 & REOF 5 Northwestern Mexico, the
Southwest & southern Plains• Phase reversal between the GPLLJ and the
GCLLJ
• Meridional pattern
• No precursor of soil moisture influence
• Influenced by tropical intraseasonal oscillations
Monthly ForecastsCase studies
• July 1999 – A very wet Southwest
• August 2000- A dry Southwest
• Four members in the ensemble
• T62L28 forecasts– 50 km RSM downscaling
1999July 2000Aug
Seasonal Forecasts (July-September)
• GFS model 92 day forecasts
• 8- member ensemble ICs 6 h apart
• T62L28, T62L64 and T126L28
• Observed SSTs
• 1999 summer
Seasonal Forecasts
• High resolution model is needed to capture rainfall over the Southwest
• Future Plans
a) Systematically test the impact of model resolution (T126L64, T170L28)
b) Radiation & diurnal cycle
c) Test of convection
d) T62L28 downscaling with RSM & T170L28
30 day forecasts (calibration run)Jae Schemm
• JJAS from 1998-2002
• T126L28 for 7 days T62L28 to 30 days
• Errors for T126L28 and T62L28 are very different
REOF 1 black
REOF 2
Green
REOF 3
Red
REOF 5
blue