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March 2005VAMOS/MESA Evaluation of a Nested Model Ensemble Climatology for South America: Annual Cycle, Interannual Variability and Rainy Season Onset.

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Presentation on theme: "March 2005VAMOS/MESA Evaluation of a Nested Model Ensemble Climatology for South America: Annual Cycle, Interannual Variability and Rainy Season Onset."— Presentation transcript:

1 March 2005VAMOS/MESA Evaluation of a Nested Model Ensemble Climatology for South America: Annual Cycle, Interannual Variability and Rainy Season Onset Anji Seth (Sara Rauscher and Brant Liebmann) International Research Institute for Climate Prediction

2 March 2005VAMOS/MESA Testing a nested model for variability/predictability Hindcasts ( ‘ perfect forcing ’ ) 1.Extreme Seasons [Seth and Rojas (2003); Rojas and Seth (2003); Seth et al. (2004)] RegCM2 / CCM3 2.Sensitivity Studies [Seth and Rojas (2003); Rauscher et al. (2005)] Surface & Domain RegCM2 / CCM3; Domain RegCM3 / ECHAM4.5 3.Nested Model Ensemble Climatology [Seth et al. (2005)] Convection Grell / Emanuel RegCM Simulations Reanalyses GCM Observed SST

3 March 2005VAMOS/MESA Outline Experiments Results from Reanalyses and ECHAM driven RegCM/Grell Annual cycle Interannual variability Rainy season onset Reanalyses driven RegCM/Emanuel Grell - Emanuel differences ECHAM driven RegCM/Emanuel Preliminary Conclusions

4 March 2005VAMOS/MESA Models and Experiments 1. RegCM3/Grell (Giorgi et al., 2005) Convection (Grell 1993) A-S (stability) closure Ocean (Zeng et al., 1998) BATS (Dickinson et al, 1993) Domain: 111x138x18 Resolution: 80 km Period: Jan Dec 1998 Boundary Conditions: NCEP/NCAR ECHAM4.5 (ensemble) 2. RegCM3/Emanuel Emanuel (1991, 1999) Jan Dec 1998 AmazonNordeste Monsoon Southeast

5 March 2005VAMOS/MESA Annual Cycle: Lat-Pentad Precipitation: 65W-40W CMAP NN-RegCMECHAMEC-RegCM

6 March 2005VAMOS/MESA Precipitation (mm/day Amazon MonsoonSoutheast Nordeste

7 March 2005VAMOS/MESA Precipitation CMAP RegCM GRELL JFMJAS

8 March 2005VAMOS/MESA FMAM Nordeste Preca vs. SSTa CMAP ECHAM NN-RegCM EC-RegCM

9 March 2005VAMOS/MESA NDJ Southeast Preca vs. SSTa CMAP ECHAM NN-RegCMEC-RegCM

10 March 2005VAMOS/MESA Calculation of Onset and Withdrawal (Liebmann and Marengo, 2001) R(n) = daily climatological rainfall R = annual mean daily rain rate day 0 = starting day of summation (within dry season - Jul 1) Objective method This definition is local because it depends on the climatology of each region of interest. The onset date can change depending on the start date of the summation. ONSETWITHDRAWAL Daily Precipitation Anomaly Sum of Daily Precipitation Anomalies

11 March 2005VAMOS/MESA Mean Date of Onset, Withdrawal, and Length of Rainy Season: July June 1996

12 March 2005VAMOS/MESA Northeast Onset, Withdrawal, and Length of Rainy Season: July June 1996

13 March 2005VAMOS/MESA Precipitation CMAP JFM JAS RegCM/EMANUEL RegCM/GRELL

14 March 2005VAMOS/MESA Precipitation (mm/day) Amazon Monsoon Nordeste Southeast

15 March 2005VAMOS/MESA Amazon Precipitation (mm/day)Surface Air Temperature (°C) Evapotranspiration (mm/day)Surface Sensible Heat Flux (W/m^2)

16 March 2005VAMOS/MESA Specific Humidity and Temp: Amazon

17 March 2005VAMOS/MESA JFM SLP GRELL, EMANUEL Reanalyses

18 March 2005VAMOS/MESA JFM Vertically Integrated Moisture tranport GRELL EMANUEL

19 March 2005VAMOS/MESA Nordeste: Prec, Ts, ET, H

20 March 2005VAMOS/MESA Precipitation CMAP JFM JAS ECHAMECHAM-RegCM/EMANUEL

21 March 2005VAMOS/MESA Precipitation (mm/day) AmazonNordeste MonsoonSoutheast

22 March 2005VAMOS/MESA Discussion Annual Cycle - RegCM/Grell captures the seasonal cycle in Northeast, Monsoon and Southeast, but exhibits a substantial dry bias in Amazon. Interannual Variability - Northeast variability is well captures by the model versions. The Southeast relationship to ENSO is weak at best in RegCM/Grell. Rainy season onset - Onset is well simulated in Northeast and Southeast (better than GCM). Monsoon region onset not as good. Emanuel Scheme - improves the large scale circulation (SLP, winds, moisture transport) and precipitation in Amazon. Improves annual cycle in Northeast, Amazon, Southeast. Too wet in Monsoon.

23 March 2005VAMOS/MESA

24 March 2005VAMOS/MESA GrellEmanuel closure Destabilization ratePrognostic quasi- equilibrium Modifies by Mass flux Downdrafts? yes comment Simple cloud modelBouyancy sorting and mixing hypothesis

25 March 2005VAMOS/MESA Rainfall anomalies in Nordeste, Rainfall, SLP, Surface wind anomalies SST and Surface wind anomalies Wallace et al., 1998

26 March 2005VAMOS/MESA CLIVAR/VAMOS, Kousky/Halpert Features of South American Warm Season Rains

27 March 2005VAMOS/MESA

28 March 2005VAMOS/MESA South America: Population Density coastal populations ecosystem diversity arid Nordeste: 60% rural Southeast: population And economic center, agricultural breadbasket

29 March 2005VAMOS/MESA JanJul (Nicolini et al. 2002)

30 March 2005VAMOS/MESA FMAM 1983 (Rojas and Seth 2003) FMAM CMAPCCM3CCM3>RegCM2

31 March 2005VAMOS/MESA Southeast: Prec,Ts, ET, SH

32 March 2005VAMOS/MESA Monsoon: Prec,Ts,ET,H

33 March 2005VAMOS/MESA Temperature (ºC): Amazon, Nordeste Monsoon, Southeast

34 March 2005VAMOS/MESA Specific Humidity: Amazon, Nordeste Monsoon, Southeast

35 March 2005VAMOS/MESA Monthly Evolution of the 6 mm/day Isohyet (Onset Period) Monthly Climatology

36 March 2005VAMOS/MESA Monthly Evolution of the 6 mm/day Isohyet (Withdrawal Period) Monthly Climatology

37 March 2005VAMOS/MESA Precipitation Onset and Withdrawal: Definitions in Monsoon Regions Wind-based Amount or accumulation of precipitation (or OLR as a precipitation proxy) –e.g., Kousky (1988) Onset occurs when: –climatological OLR falls below 240 W m -2 in a given pentad AND –10 of 12 previous pentads have OLR > 240 W m -2 –10 of 12 subsequent pentads have OLR < 240 W m -2 Non-local Sensitive to threshold criteria

38 March 2005VAMOS/MESA Monsoon Region Onset, Withdrawal, and Length of Rainy Season: July June 1996

39 March 2005VAMOS/MESA Southeast Region Onset, Withdrawal, and Length of Rainy Season: July June 1996


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