Discrimination Of GPS Occultation Observation Error And Boundary Layer Height

The bending angle and refractivity of Global Positioning System Radio Occultation(GPS RO)retrieval products contain a large amount of valuable information of planetary boundary layer.It has been shown that the vertical gradient of refractivity and bending angle can be used to determine the height of planetary boundary layer(PBLH).However,GPS RO signals are prone to multi-path effect in the lower atmosphere,which will bring great errors to the bending angle and refractivity retrieval.The local spectral width(LSW)and the vertical gradient of refractivity can be used to provide a feasible quality control scheme for the application of GPS RO data in the PBLH.In order to verify the effectiveness of PBLH determined by GPS RO,the radiosonde data and COSMIC(Constellation Observing System for Meteorology,Ionosphere and Climate)RO data are spatiotemporal matched.The correlation coefficient of selected PBLH determined by radiosonde and GPS RO is 0.771,which has good consistency.Global marine data of COSMIC RO from 2007 to 2014 were used,and the extreme values of bending angle and refractivity gradient were used to determine the global marine PBLH(respectively referred to as PBLBA and PBLN).Marine PBLH decreases gradually from the equator to the north and south poles,using COSMIC global marine RO data from 2007 to 2014,the marine boundary layer height(PBLBA and PBLN)is determined by the extreme values of bending angle and refractivity gradient respectively.PBL1BA,PBL2BA,PBL1N and PBL2N can reach 2.2km,2.4km,1.8km and 2.0km in the equatorial region.The absolute of extreme values of bending angle and refractivity gradient is also larger at low latitudes.The extreme values of PBL1BA and PBL1N can reach-65mrad/km and-85N-unit/km respectively.The absolute of extreme values of PBL2BA and PBL2N are relatively small,which indicates that the structure of the first boundary layer is clearer.The relationship between the LSW corresponding to PBLH,the vertical gradient of the refractivity and the PBLdiff(PBLdiff=PBLBA-PBLN)are further discussed.The results show that there is an obvious linear relationship between the vertical gradient of refractivity and LSW,The correlation coefficients can reach 0.60 and 0.68 at PBLH1 and PBLH2.The gradient of refravtivity is mainly composed of dry term and wet term.In low latitudes,the wet term is the main contribution of the the gradient of refractivity.The correlation coefficient between the vertical gradient of the wet term and the LSW at PBLH1 and PBLH2 can reach 0.68 and 0.69.The PBL1diff increases with the vertical refractivity gradient.When the absolute values of the refractivity gradient reach 80 N-unit/km and 100 N-unit/km,PBLdiff can reach 100 meters and 160 meters.