scholarly journals GCM experiments on changes in atmospheric predictability associated with the PNA pattern and tropical SST anomalies

2002 ◽  
Vol 54 (4) ◽  
pp. 317-329 ◽  
Author(s):  
Jian Sheng
Keyword(s):  
Tropical Sst Anomalies ◽  
Atmospheric Predictability ◽  
Sst Anomalies

scholarly journals Predictability of Extratropical Upper-Tropospheric Circulation in the Southern Hemisphere by Its Main Modes of Variability

2020 ◽  
Vol 33 (4) ◽  
pp. 1405-1421 ◽  
Author(s):  
Marisol Osman ◽  
Carolina S. Vera
Keyword(s):  
Southern Hemisphere ◽  
Modes Of Variability ◽  
Climate Anomalies ◽  
Temperature And Precipitation ◽  
Second Mode ◽  
Tropospheric Circulation ◽  
Tropical Sst Anomalies ◽  
Significant Temperature ◽  
Precipitation Anomalies ◽  
Sst Anomalies

AbstractThe predictability and forecast skill of the models participating in the Climate Historical Forecast Project (CHFP) database is assessed through evaluating the representation of the upper-tropospheric extratropical circulation in the Southern Hemisphere (SH) in winter and summer and its main modes of variability. In summer, the predictability of 200-hPa geopotential height anomalies mainly comes from the ability of the multimodel ensemble mean (MMEM) to forecast the first three modes of interannual variability with high fidelity. The MMEM can reproduce not only the spatial patterns of these modes but also their temporal evolution. On the other hand, in JJA only the second and fourth modes of variability are predictable by the MMEM. These seasonal differences in the performance of the MMEM seem to be related to the role that the sea surface temperature (SST) anomalies have in influencing the variability of each mode. Accordingly, modes that are strongly linked to tropical SST anomalies are better forecast by the MMEM and show less spread among models. The analysis of both 2-m temperature and precipitation anomalies in the SH associated with the predictable modes reveals that DJF predictable modes are accompanied by significant temperature anomalies. In particular, temperatures at polar (tropical) latitudes are significantly correlated with the first (second) mode. Furthermore, these links obtained with observations are also well forecast by the MMEM and can help to improve seasonal forecast of climate anomalies in those regions with low skill.

scholarly journals Asymmetric Modulation of ENSO Teleconnections by the Interdecadal Pacific Oscillation

2018 ◽  
Vol 31 (18) ◽  
pp. 7337-7361 ◽  
Author(s):  
Bo Dong ◽  
Aiguo Dai ◽  
Mathias Vuille ◽  
Oliver Elison Timm
Keyword(s):  
Wave Train ◽  
Surface Air Temperature ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Reanalysis Data ◽  
Interdecadal Pacific Oscillation ◽  
Enso Teleconnections ◽  
Asymmetric Modulation ◽  
Tropical Sst Anomalies ◽  
Sst Anomalies

Remote influences of ENSO are known to vary with different phases of the interdecadal Pacific oscillation (IPO). Here, observational and reanalysis data from 1920 to 2014 are analyzed to present a global synthesis of the IPO’s modulation on ENSO teleconnections, followed by a modeling investigation. Regressions of surface air temperature T, precipitation P, and atmospheric circulations upon IPO and ENSO indices reveal substantial differences between ENSO and IPO teleconnections to regional T and P in terms of spatial pattern, magnitude, and seasonality. The IPO’s modulation on ENSO teleconnections asymmetrically varies with both IPO and ENSO phases. For a given ENSO phase, IPO’s modulations are not symmetric between its two phases; for a given IPO SST anomaly, its influence depends on whether it is superimposed on El Niño, La Niña, or neutral ENSO. The IPO modulations are linked to the atmospheric response to tropical SST anomalies, manifested in the local Hadley circulation and the local Walker circulation at low latitudes and the Rossby wave train in the extratropics, including the Pacific–North American (PNA) pattern in the Northern Hemisphere. A set of numerical experiments using CAM5 forced with different combinations of the IPO- and ENSO-related SSTs further shows that the asymmetric modulation arises from the nonlinear Clausius–Clapeyron relation, so that the atmospheric circulation response to the same IPO-induced SST departure is larger during a warm rather than a cold ENSO phase, and the response to a warm IPO state is larger than that to a cold IPO state. The asymmetry depends primarily on the tropical Pacific mean state and tropical SST anomalies and secondarily on extratropical SST anomalies.

scholarly journals Tropical Atlantic SST Forcing of Coupled North Atlantic Seasonal Responses

2005 ◽  
Vol 18 (3) ◽  
pp. 480-496 ◽  
Author(s):  
Shiling Peng ◽  
Walter A. Robinson ◽  
Shuanglin Li ◽  
Martin P. Hoerling
Keyword(s):  
North Atlantic ◽  
Late Winter ◽  
Positive Anomaly ◽  
Tropical Atlantic ◽  
Early Winter ◽  
Transient Eddy ◽  
The North ◽  
Tropical Sst Anomalies ◽  
The North Atlantic ◽  
Sst Anomalies

Abstract Recent observational studies reveal that a fall Pan-Atlantic sea surface temperature (SST) anomaly, composed of a horseshoe-like dipole in the North Atlantic and a southern center in the equatorial Atlantic, tends to precede the winter North Atlantic Oscillation (NAO) and its related SST tripole by several months. This study seeks to understand this relationship using large ensembles of atmospheric general circulation model (AGCM) experiments and experiments with the AGCM coupled to a mixed layer ocean (AGCM_ML). The models are forced either by the North Atlantic horseshoe (NAH) or by the tropical SST anomalies over the boreal winter months. The AGCM results show that the NAH anomaly induces a baroclinic response in geopotential heights throughout the winter, with little projection on the NAO. Since the NAH anomaly is ineffective in forcing the wintertime NAO, it cannot account for observations that the NAH SST leads the NAO. In contrast, in the AGCM_ML, the coupled North Atlantic response forced by the tropical anomaly exhibits a strong seasonal dependence. In early winter, the positive anomaly induces a trough east of Newfoundland with a wave train to the northeast, and in late winter the response projects strongly on a negative NAO. Correspondingly, the extratropical SST response features an NAH-like pattern in early winter and a tripole in late winter. These results suggest that tropical Atlantic SST anomalies can significantly influence the coupled extratropical variability. The observed relationship between the fall NAH SST and the winter NAO (or the SST tripole) may be a consequence of persistent forcing of the seasonally varying atmosphere by tropical SST anomalies. Comparisons with the parallel AGCM results indicate that the largely sign-symmetric NAO responses developed in the AGCM_ML are in part due to active extratropical SST feedbacks. Diagnostic experiments using a linear model further illustrate that, in the absence of transient-eddy feedbacks, an idealized tropical heating induces anomalous flows that are qualitatively similar in early and late winter, with a trough southeast of Newfoundland and a ridge to the northeast. The enhanced seasonality in the SST-induced coupled response likely arises from the seasonal modulation of transient-eddy feedbacks on the heating-forced anomalous flow.

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