Global Model Of Zenith Tropospheric Delay Proposed And Characteristics Of ZWD In ENSO Activities

It will be subject to bending and delay due to the influence of atmospheric refraction when the electromagnetic wave signal passes through the atmosphere.And the tropospheric delay in the line-of-sight can be obtained by multiplying the delay in the zenith direction and mapping function,thus the focus is currently centered on the zenith direction for the research and modeling of the troposphere,and a large number of empirical models have been successfully established with the base functions are given in advance.Therefore,this thesis attempts to construct a new empirical model using the characteristics of the zenith tropospheric delay dataset.On the other hand,a strong El Ni?o activity has occurred globally since 2015,which causes global climate disturbances,and zenith wet delay(ZWD)is closely related to meteorological parameters and the study of meteorological parameters under EI Ni?o-Southern Oscillation(ENSO)mainly focuses on precipitable water vapor(PWV)with little attention is paid to ZWD.Thus,this paper attempts to study the variation of ZWD under ENSO activities from this point of view.The main work of this thesis are as follows:(1)Global model of tropospheric delay,called GEOFT,was proposed using the global zenith tropospheric delay grid data,provided by GGOS Atmosphere from 2012 to 2015,and empirical orthogonal function(EOF)decomposition method.The results show that this model has a high correlation with the data involved in modeling,and the correlation coefficient exceeds 0.99;and its bias and RMS are-0.3 cm and 3.9 cm,respectively,compared to 2016 GGOS Atmosphere tropospheric delay products which is not involved in the model construction;its bias and RMS are-0.8 cm and 4.1 cm,respectively,with respect to tropospheric delay products provided IGS;and its bias and RMS are 2.5 cm and 5.7 cm,respectively,with respect to tropospheric delay products provided by COSMIC.Although the overall accuracy of this model is slightly worse than the GPT2w model,its time complexity is much better than that of the GPT2w model,the time cost by the GPT2w model is about 20 times that of the GEOFT model for calculating the COSMIC tropospheric delay data throughout the year.(2)The accuracy of ZWD grid products of GGOS Atmosphere in 2016 are assessed by using the radiosonde data provided by IGRA,and tropospheric delay products provided by IGS and the Saastamoninen model.The results show that the bias and RMS are-0.88 cm and 1.77 cm,respectively,compared to the radiosonde data;and the bias and RMS are-0.55 cm and 1.70 cm,respectively,compared to the IGS data.Then,the variation characteristics of ZWD product with respect to latitude,longitude,altitude,and day of year were analyzed.It is found that the accuracy in the middle and high latitudes is significantly better than that in the low latitudes,and the accuracy in the spring and winter season is significantly better than that in the summer and autumn,while the relationship with longitude and height is weak.(3)The characteristics of ZWD in ENSO activities are analyzed,and PWV and near-surface temperature are added for comparative analysis.First,EOF decomposition method is used to analyze the global variation characteristics of these three products.The result shows that the effects of El Ni?o and La Nina are mainly concentrated in low latitude regions for the second eigenvector field of ZWD and PWV.As for near-surface temperatures,the ENSO activity caused a reversal of the second eigenvector field.Second,the local variations of these three products are analyzed using the time series of detrended and moving averages.It is found that ZWD and PWV in the Pacific Ocean and Central Asia rise sharply when El Ni?o occurs.As for near-surface temperature,the method used in this thesis to detect variation on land is not significantly.However,the values in the Indian Ocean and the Pacific Ocean are significantly higher than normal levels when El Ni?o occurs,and anomalies in sea surface temperature will cause abnormal temperatures,and then cause changes in the global climate.