Two Opposite Extreme Events in Seasonal Mean Winter Rainfall over East China during the Past Three Decades

In this study,the extremes of winter seasonal mean precipitation have been investigated by using daily precipitation data from 91 stations in East China,the National Centers for Environmental Prediction/the National Center for Atmospheric Research （NCEP/NCAR） monthly reanalysis,and sea surface temperature data from the Hadley Centre for 1979-2007.The largest anomalous rainfall amount was observed in regions south of the Yangtze River.In the most recent three decades,extreme events in the seasonal mean winter precipitation occurred in 1985 and 1997.Because it was influenced mainly by a La Ni（n）a event,the precipitation in 1985 showed a deficit following a stronger winter monsoon.The rainfall amount in 1997 was influenced by E1 Ni（n）o and was significantly larger than normal with a weaker winter monsoon.Both the circulation anomalies and wave energy dispersions during the winters of 1985 and 1997 differed significantly.In 1985,the North Atlantic Oscillation anomalously excited the Eurasian-Pacific teleconnection and circumglobal teleconnection phenomena.Consequently,Rossby wave energy propagated along the north and south branches of the westerlies,strengthening the East Asian trough along with a stronger winter monsoon,which facilitated the wintertime dry extreme in East China.In 1997,however,Rossby wave energy propagated from low latitudes northeastward into the southern part of China,resulting in a weaker winter monsoon and the wettest winter.The results of this study will be helpful for future monitoring and prediction of extreme winter rainfall events in East China.

The Interrelation between the NAO （North Atlantic Oscillation） and Regulated River Discharges at the Baltic Sea Drainage Basin

Both winter DJF （December, January, February） months and DJF season means long-term data series of 50 regulated rivers discharges rates and the NAO indices were analyzed for different spans. This study is dictated for： （1） detecting the exclusive impacts of the positive phases of NAO indices on rivers discharges rates by estimating the Linear Correlation Coefficient; （2） modeling the interrelations between the discharges rates and NAO indices by estimating the Linear Regression Models, both for manifesting the impact of the positive phase of NAO index; （3） estimating the Linear Trend Coefficient in the discharge series, for manifesting the contribution of the positive phase of NAO index. Discharge rates are mainly influenced by the two mechanisms： the positive phase of NAO index and the environmental conditions in specific catchments, that is where, the positive phase of the NAO index manifest its impact on the related rivers discharges and its contribution in the related configured trends. The discharges fluctuations patterns show some increase in the discharges values have been occurred in regions around the Northern Baltic Proper as well as in Southern Finland and Sweden. The rivers such as Lagan, Nissan, Helgean, Venta, Pamu, Porvoonjoki, Lapuanjoki, Oulujoki, Kyronjoki, Wisla, Eurajoki, Odra, Lielupe, Gota alv, Motala strom, Nykopingsan, Vuoksi, Kalajoki and Simojoki haven not linear discharges changes registered depending on the specificity of the environmental conditions at the catchments areas for those rivers. The positive phase of NAO index has a linear relation with impacted river discharge.

Variations in air temperature during the last 100 years revealed by δ^(18)O in the Malan ice core from the Tibetan Plateau

By comprehensive analyses, it was found that the variations in d 18O recorded in Malan ice core from theKekexili Region on the Tibetan Plateau could represent thechanges in air temperature during the summer half year (from May to October) over the Kekexili Region and the northern margin of the Tibetan Plateau. The general increase trend in d18O in this ice core during the past century indicated climate warming, and it was estimated that air temperature during the summer half-year rose about 1.2C over there then. However, this ice core record documented that the study area has been cooling while most of the world has been dramatically warming since the late 1970s. A teleconnection was foundbetween the variations in d 18O in the Malan ice core and the North Atlantic Oscillation. Moreover, the variations in d 18O in this ice core were similar to that in the summer half-year air temperature over the southern Tibetan Plateau on thecenturial time scale, but opposite on the multidecadal timescale.