太阳活动11年周期变化对南海夏季风爆发的可能影响

利用1948—2017年再分析资料以及反映太阳周期活动的太阳黑子数资料，研究了太阳活动11年周期变化对南海夏季风爆发早晚的可能影响及相关的物理过程，发现太阳黑子数与南海夏季风建立日期之间存在显著的正相关关系，即太阳活动偏强（弱）年南海夏季风爆发偏晚（早）。对相关大气环流特征进行合成分析表明，太阳活动峰值（谷值）年，5月菲律宾附近上空往往出现异常反气旋（气旋），西太平洋副热带高压偏强、西伸（偏弱、东撤）。一方面，这与赤道以南海洋性大陆的对流活动异常以及与之相联系的局地经向环流密切相关，另一方面，热带印度洋-西太平洋沿赤道的纬向Walker环流异常对此也有一定贡献。进一步的研究揭示出太阳活动影响南海夏季风爆发的信号最初很可能来源于平流层温度的响应，随着太阳辐射增强，春季前期整个南半球对流层下层-平流层上层一致偏暖，温度梯度的变化削弱了对流层的平均经圈环流，导致大气质量的重新分布，引起低层出现负的南极涛动（AAO）型分布，在南半球中纬度地区形成气旋性环流异常，造成索马里越赤道气流建立偏晚，进而有利于南海夏季风爆发的推迟。 

POSSIBLE INFLUENCES OF THE SOLAR CYCLE ON THE ONSET OF SOUTH CHINA SEA SUMMER MONSOON

The possible influence of the 11-year solar cycle on the onset of the South China Sea summer monsoon (SCSSM) is investigated based on the reanalysis dataset and observational sunspot number (SSN) from 1948—2017. It is found that the SSN is significantly correlated to the SCSSM with stronger (weaker) solar activity corresponding to later (earlier) outbreak of the SCSSM. Using composite analysis, it is revealed that during the peak (valley) years of SSN, an anomalous anticyclone (cyclone) appears around the Philippines in May, concurrent with the westward-shifting (eastward-shifting) and intensified (declined) western Pacific Subtropical High (WPSH). This can be attributed to the change of the local meridional circulation related to the convective activity over the maritime continent south of equator and the variations of the Walker circulation over the tropical Indo-Pacific region. Further examinations indicate the solar signals on SCSSM may originate from the temperature responses in the stratosphere. With the enhancement of solar irradiance, the upper-troposphere to the lower-stratosphere over the entire southern hemisphere is warmer in March and April. Through modulating the mean meridional circulation, there is a negative Antarctic Oscillation (AAO) pattern in the lower troposphere induced by the redistribution of the atmosphere mass. The subsequent cyclonic circulation anomalies in the mid-latitudes delay the establishment of the Somali cross equatorial flows when the solar activity is stronger and the SASSM onset tends to occur later accordingly.