The physical cause of amplified deep Arctic tropospheric warming in winter in the Barents-Kara Seas （BKS） is examined. The authors propose that changes in the atmospheric circulation patterns are important for deep ...The physical cause of amplified deep Arctic tropospheric warming in winter in the Barents-Kara Seas （BKS） is examined. The authors propose that changes in the atmospheric circulation patterns are important for deep Arctic tropospheric warming in winter. It is found that the retrograde Urals blocking （UB） event concurrent with a negative North Atlantic Oscillation （NAO-） that arises from a prior negative Arctic Oscillation （AO-） is not favorable for tropospheric warming because of less water vapor over the BKS. Such UB events are related to more winter BKS sea ice associated with the negative sea surface temperature （SST） anomaly in the BKS. In contrast, a UB occurring together with a positive North Atlantic Oscillation （NAO~） shows less movement and can significantly enhance tropospheric warming over the BKS through increasing tropospheric sensible heat energy due to a persistent BKS water vapor increase. This type of quasi-stationary UB event is related to prior less BKS sea ice associated with a positive BKS SST anomaly that coexists with the North Atlantic SST tripole structure. In summary, because warm, wet and low sea-ice winters in the BKS are related to UB events with an NAO~, and depend on the winter prior sea-ice condition, the tropospheric warming is to some extent a manifestation of the sea-ice-blocking-moisture feedback in the BKS.展开更多
Satellite altimeter SSH data in the Kuroshio Extension （KE） region gathered during the period January 1993 to December 2014 are analyzed using self-organizing map （SOM） analysis. Four spatial patterns （SOM1, SOM2...Satellite altimeter SSH data in the Kuroshio Extension （KE） region gathered during the period January 1993 to December 2014 are analyzed using self-organizing map （SOM） analysis. Four spatial patterns （SOM1, SOM2, SOM3, and SOM4） are extracted, and the corresponding time series are used to characterize the variation of the sea level anomaly. Except in some individual months, SOM1 and SOM2 with single-branch jet structures appear alternately during the periods 1993-1998 and 2002-2011. However, during 1999-2001 and 2012-2014, SOM3 and SOM4 with double-branch jet structures are dominant.The sea level anomalies exhibit interannual variations, while the KE stream demonstrates decadal variation. For SOM1, the change in the KE path is less evident, although the KE jet is strong and narrow. For SOM2, the KE jet is weakened and widened and its jet axis moves towards the southwest. Compared with the SOM3, for SOM4 the trough and ridge in the upstream KE region are deeper in the northeast-southwest direction, and accompanied by a jet weakening and splitting.This study shows that SOM analysis is a useful approach for characterizing KE variability.展开更多
基金supported by the National Natural Science Foundation of China[grant number 41430533],[grant number41375067]
文摘The physical cause of amplified deep Arctic tropospheric warming in winter in the Barents-Kara Seas （BKS） is examined. The authors propose that changes in the atmospheric circulation patterns are important for deep Arctic tropospheric warming in winter. It is found that the retrograde Urals blocking （UB） event concurrent with a negative North Atlantic Oscillation （NAO-） that arises from a prior negative Arctic Oscillation （AO-） is not favorable for tropospheric warming because of less water vapor over the BKS. Such UB events are related to more winter BKS sea ice associated with the negative sea surface temperature （SST） anomaly in the BKS. In contrast, a UB occurring together with a positive North Atlantic Oscillation （NAO~） shows less movement and can significantly enhance tropospheric warming over the BKS through increasing tropospheric sensible heat energy due to a persistent BKS water vapor increase. This type of quasi-stationary UB event is related to prior less BKS sea ice associated with a positive BKS SST anomaly that coexists with the North Atlantic SST tripole structure. In summary, because warm, wet and low sea-ice winters in the BKS are related to UB events with an NAO~, and depend on the winter prior sea-ice condition, the tropospheric warming is to some extent a manifestation of the sea-ice-blocking-moisture feedback in the BKS.
基金supported by the National Basic Research Program of China(973 Program)[grant number 2013CB956203]
文摘Satellite altimeter SSH data in the Kuroshio Extension （KE） region gathered during the period January 1993 to December 2014 are analyzed using self-organizing map （SOM） analysis. Four spatial patterns （SOM1, SOM2, SOM3, and SOM4） are extracted, and the corresponding time series are used to characterize the variation of the sea level anomaly. Except in some individual months, SOM1 and SOM2 with single-branch jet structures appear alternately during the periods 1993-1998 and 2002-2011. However, during 1999-2001 and 2012-2014, SOM3 and SOM4 with double-branch jet structures are dominant.The sea level anomalies exhibit interannual variations, while the KE stream demonstrates decadal variation. For SOM1, the change in the KE path is less evident, although the KE jet is strong and narrow. For SOM2, the KE jet is weakened and widened and its jet axis moves towards the southwest. Compared with the SOM3, for SOM4 the trough and ridge in the upstream KE region are deeper in the northeast-southwest direction, and accompanied by a jet weakening and splitting.This study shows that SOM analysis is a useful approach for characterizing KE variability.
