opening title page

On the Delayed Atmospheric ResponseOn the Delayed Atmospheric Responseto ENSO SSTto ENSO SST

Hui SuHui Su****, J. David Neelin, J. David Neelin**** and Joyce E. Meyerson and Joyce E. Meyerson**

Dept. of Atmospheric Sciences*, Inst. of Geophysicsand Planetary Physics**, U.C.L.A.

http://www.atmos.ucla.edu/~csi

On the Delayed Atmospheric ResponseOn the Delayed Atmospheric Responseto ENSO SSTto ENSO SST

Hui SuHui Su****, J. David Neelin, J. David Neelin**** and Joyce E. Meyerson and Joyce E. Meyerson**

Dept. of Atmospheric Sciences*, Inst. of Geophysicsand Planetary Physics**, U.C.L.A.

• 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 DepthENSO SST FrequencyFraction 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...)

^̂

^̂

^̂

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

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

OBSPAC Mask RegionOBSPAC Mask Region

Lead/Lag Regression <T>´-Niño3.4 SSTaLead/Lag Regression <T>´-Niño3.4 SSTa --comp--comp

<T>´ lags Niño3.4 SSTa•OBS SST:

3 Months•OBSPAC SST+ML:

2 Months•CLIM+OBSPAC SST

1 Month

^

^̂

Lead/Lag Regression <T>´-Niño3.4 SSTaLead/Lag Regression <T>´-Niño3.4 SSTa depth

•Phase Lag is not a monotonic function of mixed-layer ocean depth

•Amplitude of <T>´ decreases as mixed-layer ocean depth increases

^

^̂

Mask RegionsMask Regions

Lead/Lag RegressionLead/Lag Regression Ta-NINO34a-area Ta-NINO34a-area <T>´-Niño3.4 SSTa<T>´-Niño3.4 SSTa -depth-depth

•Lag reduces as area of mixed-layer ocean region decreases

(CLIMSST in the Atlantic or the Indian Ocean)

^̂

ENSOCOMP Mask RegionENSOCOMP Mask Region

QTCM Experiments with prescribedQTCM Experiments with prescribedsinusoidal SST forcingsinusoidal 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

^

^

A Simple Analytical ModelA Simple Analytical Model

Approximate Linearization of FluxesApproximate Linearization of Fluxes

Analytical ResultsAnalytical Results

•Modeled lag and amplitude are smaller than analytical results

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

^̂

Analytical Results Analytical Results withoutwithout advection of advection of TT and and qq

•Lag and amplitude increased when anomalous advection of T and q are suppressed

Lead/Lag Regression <T>´-Niño3.4 SSTa Lead/Lag Regression <T>´-Niño3.4 SSTa withwith and and withoutwithout Advection Anomaly Advection Anomaly

•Lag and amplitude increased when anomalous advection of T and q are suppressed

^̂

SummarySummary• 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.

•

•

•

^

SummarySummary• 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.

•

•

^

^

SummarySummary• 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.

•

^

^

^

SummarySummary• 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.

^

^

^

^

SummarySummary• 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.

^

^

^

^