Researches On Near Space Atmosphere Variational Data Assimilation Technology Based On Satellite Data

Near space is part of the earth's atmosphere,ranging from 20 to 100 kilometers,which is gradually making a sensation among various countries.Researches of near space environment,which can provide scientific support for the exploration and utilization of near space,become hot issues nowadays.The analysis of satellite observation data and its application in data assimilation can help us get more about the features and laws of the atmosphere,and improve the accuracy of numerical model forecast.In recent years,quantities of remote sensing detection data have provided global coverage.However,the researches about the features of near space atmosphere are not sufficient.Meanwhile,numerical model becomes an important aspect of near space research.As a necessary part of numerical model for providing initial values,data assimilation becomes an important research direction of the near space environment.In this paper,satellite data is used in analyzing the features of the near space environment,and it is also used in near space data assimilation to provide accurate initial values for numerical models.The main contents are as follows:(1)GPS phase delay contains a lot of information that can be used to obtain atmospheric parameters with certain methods.An algorithm combined with a empirical model to obtain the refractive index using one-dimensional variational(1DVAR)assimilation is studied based on Ground-based GPS phase delay.The assimilation experiment is accomplished using simulated data and measured data of GPS phase delay.The result shows that the 1DVAR assimilation algorithm can get atmospheric refractive index of high precision from 0-60 km.The refractive index got from the assimilation experiment is used to correct the radio wave refraction,and the correction result is very good,and the accuracy is about 1mm scale.(2)The near space global atmospheric temperature field from 20-100 km is achieved using 3-dimensional variational(3DVAR)assimilation method,of which the observation data is taken from SABER temperature data and the background data is taken from NSSC(National Space Science Center)Near Space Atmospheric Data Assimilation and Forecast System.Obvious variations can be seen in the near space global atmospheric temperature field after 3DVAR assimilation.An evaluation analysis based on statistical method has been accomplished.The results indicate that the errors of the near space global atmospheric temperature field get a general decrease after 3DVAR assimilation,with the maximum error decreasing from 17 K to 7K.The application of this 3DVAR assimilation algorithm can provide more accurate initial fields to near space atmospheric environment forecast model.(3)The 3DVAR cycle assimilation experiment is performed,of which the observation data is taken from AURA\MLS temperature data and the background data is taken from NSSC Near Space Atmospheric Data Assimilation and Forecast System.The near space global atmospheric temperature field from 20-100 km is achieved.Obvious variations can be seen in the near space global atmospheric temperature field after the 3DVAR cycle assimilation.An evaluation analysis based on statistical method has been accomplished.The results indicate that the errors of the near space global atmospheric temperature field get a general decrease after 3DVAR cycle assimilation,with the maximum error decreasing from 10 K to 4K below 80 km while 22 K to 7K above 80 km.Compared to single-pass 3DVAR assimilation,3DVAR cycle assimilation can enlarge the coverage area of the observation data.(4)Atmospheric temperature measured by AURA\MLS instrument is compared with that measured by TIMED\SABER instrument from 20 to 90 km.The absolute temperature deviation of AURA\MLS minus TIMED\SABER is calculated and the average temperature deviation is discussed about its feature of how it varies with latitude,longitude and altitude,which can provide references for satellite data application.The conclusions are as follows.The average temperature deviation at 20-80 km is smaller than ±6K,the relative deviation is smaller than 3%;the average temperature deviation at 80-92 km gradually varies to-10 K,the relative deviation is smaller than 9%.The variation tendency of average temperature deviation profiles is consistent at mid and low latitude,with a positive deviation peak of 3K at 45-50 km.The average temperature deviation varies obviously with latitude and varies far less with longitude.(5)The bias between the systematic error of AURA\MLS and that of TIMED\SABER is eliminated by the absolute temperature deviation of AURA\MLS minus TIMED\SABER.With the TIMED\SABER and AURA\MLS observation data after bias elimination,near space global atmospheric temperature field from 20-92 km is achieved using 3DVAR assimilation method,of which the background data is taken from NSSC Near Space Atmospheric Data Assimilation and Forecast System.Obvious variations can be seen in the near space global atmospheric temperature field after 3DVAR assimilation.An evaluation analysis based on statistical method has been accomplished.The results indicate that the errors of the near space global atmospheric temperature field get a general decrease after 3DVAR assimilation,with the maximum error decreasing from 10 K to 4K.The application of this 3DVAR assimilation algorithm can cover the shortage that the data of one satellite cannot make a global coverage.(6)Near space atmospheric temperature,atmospheric density,and standard deviation of temperature are calculated using AURA\MLS satellite data.And the distribution characteristics of them are analyzed.Reasons of how the waves effect the distribution of the temperature standard deviation are discussed.The conclusions are as follows.At 30 km in stratosphere,atmospheric disturbance is stronger in mid and high latitudes of winter hemisphere as a result of the planetary wave and gravity wave.In January and July,atmospheric disturbance in the low latitudes is stronger than that in the mid and high latitudes of the summer hemisphere as a result of the travelling planetary waves and gravity waves.The influence on low latitudes from gravity waves can also be seen in April and October.At 70 km in mesosphere,atmospheric disturbance remains stronger in mid and high latitudes of winter hemisphere as a result of the planetary wave and gravity wave.Because of the enhancement of the gravity waves and the arising of the atmospheric tides,atmospheric disturbance in low latitudes in mesosphere is stronger than that in stratosphere.At 92 km in lower thermosphere,atmospheric disturbance is stronger in low latitudes as a result of the non-migrating diurnal tides(DE3).Atmospheric disturbance is stronger in mid and high latitudes of summer hemisphere than that in low latitudes as a result of the gravity waves.