冬季北极涛动对印缅地区植被NPP的显著影响

Significant linkage of Arctic Oscillation to vegetation net primary productivity over Indo-Myanmar in winter

本文基于北极涛动(AO)指数、植被净初级生产力(NPP)和气象数据,利用回归分析、合成分析等方法定量分析了1981—2018年印缅地区植被NPP与AO的联系,结果表明:①印缅地区冬季NPP与同期AO存在明显的同位相变化,对应冬季AO指数偏高(低)一倍标准差,区域平均NPP显著增加(减少)6.50 gC·m^(-2),最大增量(减少量)为20.60 gC·m^(-2),AO与NPP时间序列的相关系数达0.57;②AO主要通过波列影响印缅地区的大气环流,进而影响其降水,造成NPP的异常。伴随AO偏强正(负)位相时,一支沿副热带急流东传的Rossby波在孟加拉湾—印缅地区对流层中低层为气旋(反气旋)环流异常,造成南支槽偏强(弱),槽前西南气流水汽输送偏强(弱),同时伴随槽前上升运动偏强(弱),均利于印缅地区降水偏多(少),对应冬季AO指数偏高(低)一倍标准差,降水均显著增加,分辨率较高的ERA5和GPCC降水显著增加(减少)12.00 mm以上,AO异常年份的降水合成,其值超过90.00 mm,区域平均降水与AO指数的相关系数达0.50以上(p<0.01)。伴随1.00 mm的降水增加(减少),NPP增加(减少)超过10.10 gC·m^(-2),二者时间序列的相关系数超过0.40(p<0.01)。

The connection between Arctic Oscillation(AO)and net primary productivity(NPP)of vegetation in the Indo-Myanmar region during the period from 1981 to 2018 was quantitatively analyzed using regression analysis,composite analysis,and other methods based on AO index,vegetation NPP,and meteorological data.The results revealed that:(1)There is a significant in-phase relationship between winter AO and NPP in the Indo-Myanmar region,with a regional average NPP increasing(decreasing)significantly by 6.50 gC·m^(-2),and the maximum increment(decrement)reaching 20.60 gC·m^(-2) corresponding to a one standard deviation increase(decrease)of winter AO index.The correlation coefficient between AO and NPP time series reaches 0.57.(2)The AO primarily affects the atmospheric circulation over the Indo-Myanmar region through wave propagation,which in turn impacts precipitation and ultimately leads to abnormal NPP.During the positive(negative)phase of AO,a Rossby wave propagates eastward along the subtropical jet,resulting in anomalous cyclonic(anticyclonic)circulation in the mid-lower troposphere over the Bay of Bengal-Indo-Myanmar region.This tends to strengthen(weaken)the South-Branch Trough,which in turn enhances(weakens)the southwestward moisture transport and ascending motion ahead of the trough,both of which favor above-normal(below-normal)precipitation in the Indo-Myanmar region.With a one standard deviation increase(decrease)in the winter AO index,precipitation from five datasets significantly increases,with ERA5 and GPCC datasets showing a significant increase(decrease)of more than 12 mm at higher resolutions.The precipitation of anomalously positive AO years minus its negative ones can exceed 90 mm,and all of the correlation coefficients between the regional average precipitation and the AO index reach more than 0.50(p<0.01).Accompanied by a 1 mm increase(decrease)in precipitation,the NPP increase(decrease)exceeds 10.10 gC·m^(-2),and the correlation coefficients of the two time series exceed 0.40(p<0.01).