Short-Term Climate Variability and Atmospheric Teleconnections from Satellite-Observed Outgoing Longwave Radiation. Part II: Lagged Correlations

Abstract

As a sequel to Part I of this study, lagged relationships in atmospheric teleconnections associated with outgoing longwave radiation (OLR) are investigated using Lagged Cross Correlations (LCC). The feasibility of extratropical seasonal-to-interannual predictions using satellite-derived observation is also quantitatively assessed. It is found that the global influence of teleconnectivity of the atmosphere is strongest for diabatic forcing located near the equatorial central Pacific, but much reduced for forcings over the maritime continent and to the east of the dateline. The LCC patterns show that at zero-lag, the OLR fluctuation over the equatorial central Pacific is associated with simultaneous excitation of quasi-stationary waves in the tropics. These tropics–tropics teleconnections eventually (in about 5 months) transform into tropics–midlatitude and midlatitude–midlatitude teleconnections associated with possible excitation of extratropical quasi-stationary waves in both hemispheres. Analysis of the LCC pattern with the Southern Oscillation (SO) signal removed shows that during 1974–81, both the SO signal and the variability in the 2–3 month time scale contribute substantially to the observed LCC patterns. The presence of a convective heat source in the equatorial central Pacific is found to be important in forcing the tropics–midlatitude and the midlatitude–midlatitude teleconnections, which appear also to be phase-locked with the normal seasonal cycle. A mechanism is proposed to explain the observed lagged relationships. This mechanism is consistent with both internal atmospheric dynamics related to the seasonal cycle and with external influences such as sea surface temperature anomalies associated with the El Niño/Southern Oscillation. Initial assessment of the predictability of regional climate using satellite-derived atmospheric teleconnection shows that about 30–40% of the wintertime OLR variance over the southeastern United States is accounted for by a 5-month antecedent OLR variation over the equatorial central Pacific. Because of the close relation between OLR variation and synoptic disturbances, the satellite-derived teleconnections described in Part I and Part II of this study can be used to identified regions with potentially higher seasonal-to-interannual predictability.