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Part II: Observed Multi-Time Scale Variability in the Tropical Atlantic Part I: Biases in the NCEP CFS in the Tropical Atlantic Diagnosing CGCM bias and.

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Presentation on theme: "Part II: Observed Multi-Time Scale Variability in the Tropical Atlantic Part I: Biases in the NCEP CFS in the Tropical Atlantic Diagnosing CGCM bias and."— Presentation transcript:

1 Part II: Observed Multi-Time Scale Variability in the Tropical Atlantic Part I: Biases in the NCEP CFS in the Tropical Atlantic Diagnosing CGCM bias and analyzing multi-time scale variability in the tropical Atlantic sector using satellite observations GEC-hri Project Meeting: COLA, Oct. 30, 2007

2 Part I: Biases in the NCEP CFS in the Tropical Atlantic Zeng-Zhen Hu (COLA) Bohua Huang (GMU & COLA) Kathy Pegion (COLA) Note: Since the GEOS5 is not running at COLA yet, here we have used CFS as an example. We plan to look into GEOS5 in the same way as we have done for CFS.

3 Data & CFS CFS Model& Simulations AGCM: NCEP T62&L64 OGCM: MOM3, 1/3 o (10 o S- 10 o N), 1 o (higher latitudes); 74 o S-64 o N, L40 Free run: Jan 1985-Dec 2036 Observations NCEP/NCAR reanalysis I (Kalnay et al. 1996); ERA40 (Uppala et al. 2005) Cloud coverage data by ISCCP on 2.5 o x2.5 o, Jul1983-Dec2004 (Rossow and Dueñas 2004); Corresponding radiation calculated by Zhang et al. (2004) The SST dataset is the extended reconstruction (ER-v2) on 2 o x2 o (Smith and Reynolds 2003)

4 CFS Well Simulates Leading Modes CFS ER-v2 1st 16% STA 2nd 15% NTA 3rd 10% SSA STA 3rd 10% NTA 2nd 11% SSA 1st 12%

5 CFS Systematic Biases MAM JJA SON DJF Low Clouds Short-WaveSST There are coherent biases in the southeastern Atlantic Ocean: (1) Too few low clouds (2) Too much short-wave radiation reaching the sea surface (3) Warm biases

6 JJA Low Clouds & Vertical T Gradient T700-T850 Low Clouds T850-T925 CFS: Region AOBS: Region B A B

7 Low Clouds & Vertical T Gradient CFS Region A OBS Region B T850-T925 T700-T850 Low Clouds Inversion layer NO inversion layer Quasi-inversion layer NO quasi-inversion layer

8 Also low clouds may be associated with different climate modes: CFS: Subtropical South Atlantic Mode (SSA) OBS: Atlantic Niño/Southern Tropical Atlantic Mode (STA) or Zonal Mode Regression: Low Clouds in region B &UV+SST CFSOBS

9 Summary of Part I: Biases in the NCEP CFS in the tropical Atlantic CFS: Deficit low-cloud and excessive SW radiation can cause the warm SST bias in the southeastern Atlantic. In return, the warm bias does not favor inversion layer and also low- cloud formation. CFS can not correctly simulate the vertical inversion layer of the temperature and the formation of low cloud. Low-cloud formation: Observed: (T850-T925); CFS: (T700-T850)

10 Publications (partly supported by this project and a NOAA project) Hu, Z.-Z., B. Huang, and K. Pegion, 2007: Leading patterns of the tropical Atlantic variability in a coupled GCM. Climate Dynamics, DOI /s x. Hu, Z.-Z., B. Huang, and K. Pegion, 2007: Low cloud errors over the southeastern Atlantic in the NCEP CFS and their association with lower- tropospheric stability and air-sea interaction. J. Geophys. Res. (atmosphere), (submitted).

11 Part II: Observed Multi-Time Scale Variability in the Tropical Atlantic Bohua Huang (GMU & COLA) Zeng-Zhen Hu (COLA)

12 Variance of Daily Precipitation in Different Time Scales

13 EOF1&2 of Daily Precipitation at Day Time Scales

14 The Oscillation of EOF1&EOF2 (Period about 60 days)

15 Connection of the Tropical Oceans at Day time Scales _ + +

16 Connection with SST Anomalies EOF1

17 Summary of Part II: Observed Multi-Time Scale Variability in the Tropical Atlantic There are multi-time scale variability in the tropical Atlantic Ocean. The variability at day time scales in the tropical Atlantic is a part of intra-seasonal variability of global tropical oceans. There is a clear connection between global tropics and tropical Atlantic: out-of-phase: the tropical western Pacific; in-phase: Indian Oceans. The variability in the atmosphere is weakly coupled with SST.

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19 Clouds in ISCCP & CFS ISCCP (Weare 1999; Rossow &Dueñas 2004) CFS (Xu& Randall 1996) BL (>900hPa) Middle ( hPa) Low ( hPa) High Middle ( hPa) High Low (680- surface) Unstable & convective clouds Stable & stratus clouds ISCCP CFS


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