黄河中下游地区夏季旱涝年低频振荡特征分析

利用1971-2010年NCEP/NCAR逐日再分析资料和黄河流域67个测站逐日降水资料, 对黄河中下游地区旱涝年的低频振荡特征进行了分析.结果表明: 黄河流域30~60 d低频降水呈现区域性分布的特征, 大值区位于黄河中下游地区, 10~20 d低频降水呈现整体性分布.黄河中下游地区旱涝年夏季降水普遍存在10~20 d和30~60 d的低频振荡, 10~20 d振荡强度整体上均强于30~60 d振荡,10~20 d低频振荡在旱涝年差异不显著.涝年30~60 d低频振荡较旱年显著, 涝年和旱年30~60 d低频振荡的传播特征不相同, 同时涝年的30~60 d低频振荡的传播特征也存在差异.影响涝年30~60 d低频降水的主要原因是低纬的低频振荡强度增强向北传播到黄河流域, 以及青藏高原热源的低频振荡向东北传播与西太平洋热源的低频振荡向西传播在黄河中下游交汇.正常年份的低频降水主要受低纬低频振荡向北传播的影响.

Analysis of the LFO Characteristics During Summer Drought/Flood Years over the Middle and Lower Reaches of the Yellow River

Using the daily NCEP/NCAR reanalysis dataset and the observation rainfall data in the middle and lower reaches of the Yellow River from 1971 to 2010, the characteristics of low-frequency oscillation (LFO) during drought/flood years over the middle and lower reaches of the Yellow River are analyzed. The results show that LFO of 10~20 d and 30~60 d universal exist in the middle and lower reaches of the Yellow River in drought and flood years, of which LFO of 30~60 d presents the characteristics of regional distribution, with large value in the middle and lower reaches. LFO of 10~20 d shows the integrity distribution. LFO of 10~20 d is stronger than that of LFO of 30~60 d in the whole. LFO of 30~60 d is more notable in flood years than in drought years. LFO of 30~60 d propagation characteristics in flood years is not the same as in drought years. Meanwhile the LFO of 30~60 d propagation characteristics in flood years are also different. There are two causes to impact the low frequency precipitation in the flood years. One is the LFO intensity strengthening in low-latitude and spreading northward to the Yellow River basin;another is the LFO of heat sources in the Tibet Plateau eastward spreading and intersecting with the LFO of heat sources westward spreading from West Pacific at the middle and lower reaches of the Yellow River. In the normal year low-frequency precipitation is mainly affected by the impact of the low-latitude LFO northward spreading, when LFO in low-latitude northward spreading intersects with the LFO westward spreading from West Pacific over the middle and lower reaches of the Yellow River.