| The Southern Ocean plays an important role in global climate research,affecting global atmospheric circulation,ocean circulation,weather and climate changes.The temperature inversion(TI)and specific humidity inversion(SHI)are common over the Southern Ocean,which distribution and variation have important effects on the exchange of matter and flux between ocean,ice and air.Understanding the characteristics and spatial-temporal distribution of the TI and SHI over the Southern Ocean is of great significance for studying the atmospheric features of the Southern Ocean and its influence on the global climate system.However,due to the complex natural environment of the Southern Ocean,there are many limitations in the spatiotemporal resolution and accuracy of atmospheric observation data,which makes it difficult to carry out in-depth research on the characteristics of TI and SHI over the Southern Ocean.Satellite data can make up for the shortage of conventional observation data in the polar regions,and the Atmospheric Infrared Sounder(AIRS),which is carried on the Aqua satellite,can carry out exploration in a larger space range.In order to verify the accuracy of the Atmospheric Infrared Sounder(AIRS)products in the Southern Ocean and further evaluate the reliability of TI and SHI characteristics over the Southern Ocean,this study compared and analyzed the temperature and humidity profiles of Integrated Global Radiosonde Archive Version 2(IGRA2)and AIRS from 2004 to 2020,based on the AIRS Version 6(V6)and Version 7(V7)data and using the radiosonde data from the IGRA2 as the reference.We also evaluated the results of the characteristics of TI and SHI estimated by AIRS with different versions under different cloud are evaluated.According to the previous research,there are many surface-base TI and SHI in the polar regions.Therefore,based on the AIRS V7 product data for the 1000-500 h Pa profile,this study considered the effect of sea surface data on evaluating the characteristics of TI and SHI over the Southern Ocean,investigated the spatial-temporal distribution of surface-based TI and SHI of the Southern Ocean The spatial-temporal distribution and variation of TI and SHI characteristics in the middle and lower troposphere over the Southern Ocean from 2004 to 2020 are studied.In addition,to further explore the mechanism of TI and SHI over the Southern Ocean,this study analyzed the correlation between TI characteristics and SHI characteristics over the Southern,and further discussed the impact of different surface meteorological conditions on TI and SHI characteristics over the Southern Ocean.The main conclusions of this study are summarized as follows:The accuracy of AIRS temperature and humidity profiles differs among different versions,which the accuracy of AIRS V7 temperature profile inversion is higher than that of V6,while the accuracy of AIRS specific humidity profile is better than that of V7.In addition to the smaller deviation of V6 in the bottom temperature inversion,V7 in other standard pressure layers showed better data accuracy,and V7 was less affected by CF,showing better data stability.Verification of different versions of AIRS specific humidity profiles under different cloud showed that the accuracy of AIRS specific humidity data in the upper profile was lower than that in the lower profile.Except for the relatively small deviation in the V7 specific humidity data at 600-500 h Pa,the specific humidity deviation of V7 at other standard pressure layers are greater than that of V6.In addition,specific humidity of AIRS is greatly influenced by CF,so the impact of clouds on data accuracy should be taken into account when using AIRS specific humidity data for research.The accuracy of AIRS products in estimating the TI and SHI characteristics over the Southern Ocean is good even when the CF is large.Therefore,AIRS can accurately estimate the TI and SHI characteristics of the Southern Ocean.Compared with the V7,the error of the SHI frequency estimated by V6 was smaller.With the increase of CF,the accuracy of the SHI intensity estimated by V6 was gradually improved,but when V7 estimate the SHI intensity,they are less affected by cloud cover.The data products have better stability under different CF conditions.In addition,the difference in the TI frequency estimated by AIRS data mainly exists in the coastal and the ice shelf areas,while the differences in the TI intensity generally existed in the lower latitudes of the Southern Ocean.The difference of the SHI frequency between the two versions mainly existed in the autumn and winter seasons on the ice shelves and the oceans near the land.However,the difference of the SHI intensity was greatly different in different seasons.The SHI estimated by V7 in most areas of the Southern Ocean in spring and summer was weaker than that estimated V6,while the opposite was true in autumn and winter.The characteristics of TI and SHI in the Southern Ocean show obvious seasonal distribution and change law,and the TI and SHI are more frequent and stronger in autumn and winter.In the study of the spatial distribution of lower TI frequency in different seasons of the Southern Ocean,it is found that compared with spring and summer,the TI are relatively frequent in the Ronne Ice Shelf,Ross Ice Shelf and Weddell Sea in autumn and winter,and the TI frequency in most areas is higher than 80%.On the whole,the intensity of lower TI in the Southern Ocean gradually decreases with the decrease of latitude,and the TI intensity is most significant in the Ronne Ice Shelf,Ross Ice Shelf and the floating ice area near the Antarctic Peninsula.The frequency(intensity)of surface-based TI in the Southern Ocean gradually decreases(weakens)with the decrease of latitude.The phenomenon of surface-based TI in the Southern Ocean plays a dominant role in the study of lower TI in the Southern Ocean.The lower TI intensity is mostly based on the surface-based TI intensity in the ocean surface,and the intensity of inversion layer in the middle troposphere is relatively weak.The frequency(intensity)of lower SHI showed the characteristics of low(weak)in spring and summer and high(strong)in autumn and winter.The lower SHI in the Southern Ocean was the least in summer and the most in autumn.The lower SHI intensity is the weakest in spring and the strongest in the Southern Ocean between 60°S and 70°S in autumn.In the Southern Ocean,surfacebased SHI is relatively rare,and the frequency is less than 60%.The surface-based SHI intensity is the weakest in the southern Ocean south of 70°S in summer,and generally stronger in winter.In general,in addition to summer,in the other three seasons,the lower TI frequency is also higher in the place where the phenomenon of lower TI is more frequent.The analysis of the sea surface meteorological conditions of the Southern Ocean shows that the lower the surface temperature of the Southern Ocean,the more frequent and stronger the TI intensity.The change of sea surface specific humidity in summer caused little change of SHI intensity,and the SHI intensity in the other three seasons was more sensitive to the change of sea surface specific humidity.In general,the lower the specific humidity of the Southern Ocean surface,the more frequent the SHI frequency. |
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