中国周边海域SST日变化及其对区域气候的影响

Sea surface temperature (SST) is the most important factor in air-sea interaction. SST is the most important information the lower boundary of the atmosphere and the upper boundary of the ocean, so SST influences weather and climate. It was known that the diurnal amplitude depended on cloudiness and wind stress, and SST (not Skin temperature) could reach about 1.5K on clear, calm days. In relatively recent years, larger diurnal SST variations have been reported; The diurnal amplitudes of SST was observed more than 3K in lots of area. Even, it was reported an example of diurnal SST amplitude reaching 6.6K locally off California using the AVHRR SST. Without considering the diurnal changes of SST or the underestimated, may cause the diurnal SST difference of 1 K. If the warm layer cannot be reproduced correctly, the surface net heat flux from the ocean decreases by 40 W m-2 in the daytime. That quantity of heat flux difference could not cause temperature change very much. But for atmosphere the difference should not be ignored, because the heat capacity of the atmosphere is far less than the ocean, thus, that difference enough causes instability in lower atmosphere. Global climate modeling studies show that without SST diurnal cycle considered, the model has undesirable consequences, including too large ENSO variability, much too cold Pacific equatorial SST, and no deep-cycle turbulence and so on, since the climate system is a highly nonlinear system. Coupled SST diurnal cycle to regional climate model shows that it will reduce 40% (2K) bias in seasonal climate forecasting in North America. There are not many studies focused on the ocean around China about SST diurnal variation characteristics. Because of the high frequency SST diurnal variation of observation data is limited, through data analysis to study the effect of SST on regional climate is difficult. Numerical model simulation is the best compensatory method. The upper ocean mixing layer model which can reproduce on diurnal variation of SST efficiently still need to be improved. We need do more on introduction of the model to regional climate model, estimating the underlying surface physical process more reasonably and realistically, thereby improving regional climate model simulation capability has practical application value. This study will collect the high frequency observation of sea surface temperature and fluxes, develop better ocean upper mixed layer model to study the temporal and spatial evolution of SST diurnal cycle and variation in the area of North India Ocean and Northwest Pacific, where the dynamic and thermo system impact on China climate. Introduce newest version of CWRF (the climate extension of WRF model) from Maryland University, then coupled the ocean model in CWRF. Study the climate characteristic of SST diurnal cycle and its impact on China climate, and the influence mechanism will be discussed in detail through lots of numerical experiments.

SST是海气相互作用重要因子。表面1m海水吸收60%的短波辐射，可升1.5K以上。超过3度以上的SST（非皮温）日变化也越来越多的被观测到。有无SST日变化，会造成平均日海温相差1K以上，导致表面通量相差40Wm-2，足以导致大气下层不稳定。 全球气候模拟研究发现，由于气候系统的强非线性，缺少SST日变化的过程，导致明显气候信号偏差，同样北美区域研究表明，考虑SST日变化的短期气候预测试验，可减少美国东部大陆月平均T2m表面温度40%（2K）偏差。受观测时空覆盖率限制，目前影响中国区域气候海域的SST日变化及其影响研究不多。 本研究拟通过收集SST及有关通量观测数据，研发海洋混合层数值，开展分析模拟，研究中国周边海域SST日变化时空规律，并将其与区域气候模式耦合，通过数值试验研究SST日变化对中国短期区域气候的影响。

本项目利用数值模拟为主的方法研究了中国近海海表温度（SST）日变化(DSST)规律及其对区域气候的影响，主要研究成果包括：研发了一套自主海洋混合层模式、制作了一套31年全球逐时SST分析数据集并投入业务应用、基本定量化地分析了SST日变化对中国区域气候的影响。主要结论如下：.（1）中国近海SST日变化气候特征研究.收集整理了中国近海高频观测数据，对各海区海洋DSST时空规律特征进行了统计分析。分析结果表明中国近海海域DSST具有明显的季节变化特征。渤海、黄海北部、东海北部呈两季型，其DSST在春夏季明显且幅度一致，而秋冬季日变化小。而东海南部和南海北部等四季型海域的DSST幅度四季分明。.（2）用于研究日变化的大气数据可用性分析.基于经验统计模型，利用美国国家数据与浮标中心(NDBC)近年来的观测数据，建立了DSST经验估计模型。将美国、欧洲再分析资料分别驱动该经验模型，进行了各自30年的DSST估算，得到三套DSST逐日数据集，其中使用美国CFSR再分析资料的计算结果与观测数据的相关性最高，可用为本项目的主要大气强迫数据源。.（３）自主模式研发与业务化应用.自主研发了一维的海洋上混合层模式，理想试验及浮标观测验证表明该模式DSST模拟精度优异。将一维的海洋上混合层模式扩展到二维，制作了31年的全球逐时高分辨率SST分析数据集，其DSST气候统计特征与经验模型计算得到的DSST气候特征相似。该数据已经成功应用于国家海洋环境预报中心气候预测业务工作中。.（４）SST日变化对中国区域气候影响研究.通过模式改进及参数化方案敏感性试验，建立了适用于中国区域气候研究数值模拟系统，并利用上述SST分析数据集，研究了DSST对中国区域气候的影响。分析表明，SST对局地的热力、动力及降水的影响可超过10%。其主要的影响机制是SST日变化会对海表热力、水汽交换产生影响，进而影响表面动力场，通过物理过程影响中高层的环流结构，对整个大气气候特征产生影响。