opening title page On the Delayed Atmospheric Response to 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. ~ csi

On the Delayed Atmospheric Response to 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. Tropical Tropospheric Temperature Anomalies ( ´ ) 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 ´ 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 ´ (Radiation, Surface Heat Fluxes, Advection of Temperature and Moisture from Tropics...)^^ ^

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

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

OBSPAC Mask Region

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

Lead/Lag Regression ´-Niño3.4 SSTa Lead/Lag Regression ´-Niño3.4 SSTa depth Phase Lag is not a monotonic function of mixed-layer ocean depth Amplitude of ´ decreases as mixed-layer ocean depth increases ^^

Mask Regions

Lead/Lag Regression Ta-NINO34a-area ´-Niño3.4 SSTa -depth Lag reduces as area of mixed- layer ocean region decreases (CLIMSST in the Atlantic or the Indian Ocean)^

ENSOCOMP Mask Region

QTCM Experiments with prescribed sinusoidal SST forcing Phase lag of ´ is not a monotonic function of MLD Phase lag increases as SST forcing period increases Amplitude of ´ decreases as MLD increases Amplitude increases as SST forcing period increases ^ ^

A Simple Analytical Model

Approximate Linearization of Fluxes

Analytical Results Modeled lag and amplitude are smaller than analytical results

Evolution of SST Forcing, ´ and Fluxes Tropical Mean Heat and Moisture Transports to Extratropics Comparable to Tropical Mean OLR Anomalies^

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

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

Summary The lag of ' 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. ^

Summary The lag of ' 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 ' depend on mixed-layer ocean depth, ENSO SST forcing period and areal fraction of mixed-layer ocean region. ^ ^

Summary The lag of ' 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 ' 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 ' can be qualitatively explained by the simple analytical model, but quantitative disagreement exists, with modeled lags smaller than analytical results. ^ ^ ^

Summary The lag of ' 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 ' 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 ' 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 ' 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. ^ ^ ^ ^

Summary The lag of ' 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 ' 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 ' 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 ' 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. ^ ^ ^ ^