影响1991年和1994年南海夏季风爆发迟早的物理因子探讨

The Comparison between the Mechanism of the Early(1994) and Later(1991) Onset of the South China Sea Summer Monsoon

通过使用美国NCEP/NCAR再分析资料 ,利用纬向平均的局地经向环流模式成功地模拟了 1 991年 (爆发晚年 )和 1 994年 (爆发早年 )南海夏季风的建立过程 ,经过分析发现 ,虽然南海夏季风爆发时近地面南风均含有由气压梯度力驱动的地转成分和由除了气压梯度力外的所有动力和热力驱动的非地转成分 ,且与三维温度梯度有关的温度平流和对流均有正贡献作用 ,但各因子在 (这两年对南海夏季风环流建立时起正贡献的 )排序上有明显的差异 ,主要的差异为 :对 1 991年 6月 7日 0 0UTC而言 ,引起地转风的气压梯度力和引起非地转风的热力及动力的合力作用相当。在引起地转偏差的因子中 ,起正贡献作用的主要因子是潜热加热。而对 1 994年 5月 2日 0 0UTC而言 ,气压梯度力作用相对较小 ,在引起地转偏差的因子中 ,起正贡献作用的最大因子是平均纬向温度平流。另外 ,边界效应独自对模拟的南海近地面最大南风的贡献占 42 %。引起南海近地层非地转南风的热力和动力因子 (稳定度 )在 1 994年 5月 2日 0 0UTC(早年 )均比 1 991年 6月 7日 0 0UTC(晚年 )大 (小)

The meridional circulations during late(early) summer monsoon onset [i.e., June 1～15, 1991 (April 26～May 10,1994)] over South China Sea are successfully simulated by the local meridional circulation model, and main factors affecting the meridional circulations at 00UTC 7 June 1991 and 00UTC 2 May 1994 are compared based on the NCEP/NCAR reanalysis data. The results show that for the late onset year (1991) pressure gradient force (responsible for geostrophic wind) shares equal contribution with other thermodynamic and dynamic forces(responsible for ageostrophic wind) at 00UTC 7 June 1991. Among the ageostrophic factors, the major contribution comes from latent heat. While for the early onset year at 00UTC 2 May 1994, ageostrophic factors play a significant role. Among the ageostrophic factors, the mean mode of zonal temperature advection is the most important one. In addition, the comparison also shows that not only the hydrodynamic stability was weaker but also cross-equatorial flow around 105°E was stronger at 00UTC 2 May 1994 than at 00UTC 7 June 1991.