利用COSMIC掩星资料研究对流层/下平流层大气比湿对ONI指数的响应

本文利用2006年6月至2014年6月COSMIC掩星观测的水汽廓线, 分析了对流层/下平流层(TLS)比湿信号对ENSO的响应.在数据处理中, 将COSMIC掩星水汽廓线计算得到的全球比湿数据内插为1000~30 hPa区间水平分辨率为5°×5°的三维格网, 在各等压面上求取各格网点去除年/月际信号后的比湿月异常值.然后在对比湿月异常时间序列低通滤波的基础上, 进行经验正交分解(EOF)得到比湿主成分, 并对该主成分信号进行二项式平滑; 接下来将平滑后的主成分信号与反映ENSO活动的ONI指数进行相关处理, 得到各等压面主成分信号相对于ONI指数的相关系数及对应的时间延迟.论文分析了包括Niño-3.4的5个代表性区域的TLS比湿异常主成分信号, 结果表明:在各区域, 采用本文先低通滤波再EOF分解的处理方法获得的TLS比湿异常主成分信号与ONI指数均有很强相关性, 对流层相关系数绝对值达0.8以上, 低平流层高于0.7, 在300~200 hPa的上对流层达到峰值; 各等压面上比湿异常主成分信号相对于ONI指数的时间延迟不尽相同, 在对流层中比湿异常主成分信号普遍滞后于ONI指数1~6个月; 在各区域, 比湿异常主成分与ONI指数相关系数绝对值达到最大的等压面都接近250 hPa, 最大相关系数绝对值均达到0.9以上.进一步对全球250 hPa等压面比湿异常主成分与ONI指数相关性的分析表明:两者强相关的区域主要集中在热带; 在这些强相关区域, 比湿异常主成分相对于ONI主要表现为滞后, 且相关系数越大, 相应的时间延迟越短.

Specific humidity response in the troposphere and lower stratosphere to ONI revealed by COSMIC observations

Using GPS Radio Occultation (RO) water vapor profiles obtained by Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission from June 2006 to June 2014,we analyze the response of specific humidity signals in the Troposphere and Lower Stratosphere (TLS) to the El Niño-Southern Oscillation (ENSO). The COSMIC specific humidity data is interpolated on a three-dimensional grid in the altitude range of 1000~30 hPa with the horizontal resolution of over the globe. Over each pressure level, the monthly specific humidity anomalies for each grid point are got after the annual and monthly variations are separated. By low-pass filtering, the anomalies are analyzed using Empirical Orthogonal Function (EOF) and binomial smoothing techniques, and the smoothed principal components of TLS specific humidity are determined. Finally, the correlation coefficients and time delays of the principal components of TLS specific humidity relative to the Oceanic Niño Index (ONI) are calculated over each pressure level. The specific humidity over five representative geographic regions, including the Niño-3.4 region, are processed at first. It is found that over each region, the characteristic principal components signals derived from the specific humidity anomalies in TLS are highly correlated with the ONI. The absolute values of the correlation coefficients between the specific humidity and ONI are greater than 0.8 and 0.7 in the troposphere and lower stratosphere, and are the largest at the pressure levels of 300 hPa to 200 hPa. The time delays of the principal components relative to the ONI are different over different pressure levels. In the troposphere, the principal components generally lag behind ONI for 3 months to 6 months. Over all the five regions, the largest absolute values of the correlation coefficients between the principal components and ONI, which are all greater than 0.9, generally occur on the pressure levels close to 250 hPa. Then the correlations between the principal components on the pressure level of 250 hPa and ONI is analyzed over the globe. It is found that high correlations mainly occur over tropics and that principal components signals generally lag behind the ONI over these regions with shorter lagging time corresponding to higher correlations.