opening title page

1. opening title page On the Delayed Atmospheric Responseto ENSO SST Hui Su**, J. David Neelin** and Joyce E. Meyerson* Dept. of Atmospheric Sciences*, Inst. of Geophysics and Planetary Physics**, U.C.L.A. http://www.atmos.ucla.edu/~csi

2. On the Delayed Atmospheric Responseto ENSO SST ^ • Tropical Tropospheric Temperature Anomalies (<T>´) Lag ENSO SST Anomalies by 1-3 months • QTCM Experiments with Prescribed SST and Coupling with a Slab Mixed-layer Ocean Model. • Phase and Amplitude of <T>´Dependence on: • Mixed-layer Depth • ENSO SST Frequency • Fraction of Mixed-layer ocean Region • A Simple Analytical Atmospheric Model Coupled with a Mixed-layer Ocean Model • Various Damping Mechanisms Governing the Phase and Amplitude of <T>´ (Radiation, Surface Heat Fluxes, Advection of Temperature and Moisture from Tropics...) ^ ^ Hui Su**, J. David Neelin** and Joyce E. Meyerson* Dept. of Atmospheric Sciences*, Inst. of Geophysics and Planetary Physics**, U.C.L.A.

3. Tropospheric Temp. Anom. - NCEP, QTCM;SST Anom. Reynolds

4. Zonal Avg. of Tropospheric Temperature Anomaly Correlation with Niño3.4 SSTa

5. OBSPAC Mask Region

6. Lead/Lag Regression <T>´-Niño3.4 SSTa--comp ^ <T>´ lags Niño3.4 SSTa • OBS SST: • 3 Months • OBSPAC SST+ML: • 2 Months • CLIM+OBSPAC SST • 1 Month ^

7. Lead/Lag Regression <T>´-Niño3.4 SSTadepth ^ • Phase Lag is not a monotonic function of mixed-layer ocean depth • Amplitude of <T>´ decreases as mixed-layer ocean depth increases ^

8. Mask Regions

9. Lead/Lag RegressionTa-NINO34a-area <T>´-Niño3.4 SSTa-depth ^ • Lag reduces as area of mixed-layer ocean region decreases (CLIMSST in the Atlantic or the Indian Ocean)

10. ENSOCOMP Mask Region

11. QTCM Experiments with prescribedsinusoidal SST forcing • Phase lag of <T>´ is not a monotonic function of MLD • Phase lag increases as SST forcing period increases ^ ^ • Amplitude of <T>´ decreases as MLD increases • Amplitude increases as SST forcing period increases

12. A Simple Analytical Model

13. Approximate Linearization of Fluxes

14. Analytical Results • Modeled lag and amplitude are smaller than analytical results

15. Evolution of SST Forcing, <T>´ and Fluxes ^ • Tropical Mean Heat and Moisture Transports to Extratropics Comparable to Tropical Mean OLR Anomalies

16. Analytical Results without advection of T and q • Lag and amplitude increased when anomalous advection of T and q are suppressed

17. ^ Lead/Lag Regression <T>´-Niño3.4 SSTa with and without Advection Anomaly • Lag and amplitude increased when anomalous advection of T and q are suppressed

18. Summary ^ • The lag of <T>' relative to ENSO SST is simulated in an atmospheric model coupled with a slab mixed-layer ocean model, suggesting this phase lag is caused by ocean-atmosphere interaction resulting from teleconnection of atmospheric circulation.

19. Summary ^ • The lag of <T>' relative to ENSO SST is simulated in an atmospheric model coupled with a slab mixed-layer ocean model, suggesting this phase lag is caused by ocean-atmosphere interaction resulting from teleconnection of atmospheric circulation. • The lag and amplitude of <T>' depend on mixed-layer ocean depth, ENSO SST forcing period and areal fraction of mixed-layer ocean region. ^

20. Summary ^ • The lag of <T>' relative to ENSO SST is simulated in an atmospheric model coupled with a slab mixed-layer ocean model, suggesting this phase lag is caused by ocean-atmosphere interaction resulting from teleconnection of atmospheric circulation. • The lag and amplitude of <T>' depend on mixed-layer ocean depth, ENSO SST forcing period and areal fraction of mixed-layer ocean region. • The behavior of phase and amplitude variations of <T>' can be qualitatively explained by the simple analytical model, but quantitative disagreement exists, with modeled lags smaller than analytical results. ^ ^

21. Summary ^ • The lag of <T>' relative to ENSO SST is simulated in an atmospheric model coupled with a slab mixed-layer ocean model, suggesting this phase lag is caused by ocean-atmosphere interaction resulting from teleconnection of atmospheric circulation. • The lag and amplitude of <T>' depend on mixed-layer ocean depth, ENSO SST forcing period and areal fraction of mixed-layer ocean region. • The behavior of phase and amplitude variations of <T>' can be qualitatively explained by the simple analytical model, but quantitative disagreement exists, with modeled lags smaller than analytical results. • The phase and amplitude of <T>' are determined by the damping time scales of various physical processes, such as radiation and surface heat fluxes. However, transports of temperature and moisture from the tropics to extratropics may also contribute to reducing the phase lag. ^ ^ ^

22. Summary ^ • The lag of <T>' relative to ENSO SST is simulated in an atmospheric model coupled with a slab mixed-layer ocean model, suggesting this phase lag is caused by ocean-atmosphere interaction resulting from teleconnection of atmospheric circulation. • The lag and amplitude of <T>' depend on mixed-layer ocean depth, ENSO SST forcing period and areal fraction of mixed-layer ocean region. • The behavior of phase and amplitude variations of <T>' can be qualitatively explained by the simple analytical model, but quantitative disagreement exists, with modeled lags smaller than analytical results. • The phase and amplitude of <T>' are determined by the damping time scales of various physical processes, such as radiation and surface heat fluxes. However, transports of temperature and moisture from the tropics to extratropics may also contribute to reducing the phase lag. ^ ^ ^