Non-LTE Limb IR Radiances Calculation In The Upper Atmosphere

The simulation of non-LTE (non-Local Thermodynarnic Equilibrium) IR radiative transfer in the upper atmosphere is widely used for various subjects. For the IR radiation in the upper atmosphere is influenced by the non-LTE, the Kirchhoff s law and Planck radiation law no longer apply. So non-LTE model for the calculation of IR radiative transfer in the upper atmosphere is needed.By using the line-by-line radiative transfer model RFM (Reference Forward Model), the altitude range of application of the LTE (Local Thermodynarnic Equilibrium) is presented for limb radiance. By researching the composition of spectral band, the contribution of every vibrational band to the total radiance is determined. Besides, the influence of the upper atmospheric environment on the IR limb radiance for 3-5μm and 8-14μm atmospheric window is analyzed. Finally, through the SABER limb radiance data, the RFM model is validated and the limb radiation characteristic in the channel is researched.By comparing modeling results calculated by the non-LTE model and LTE model, the altitude range of application of the LTE is determined for limb radiance. The analysis results show that, there is a large error of limb radiance above 30 km height calculated by LTE model for 4.3 μm spectral band in the day. There isn’t significant deviation between the non-LTE and LTE below about 55 km height for 15 μm,10 μm,9.6 μm,6.3 μm and 4.7 μm spectral bands and it can reach about 80 km for CO215μm spectral band, in both the day and the night.The SABER’s radiation curve with the height coincides with the RFM’s outcome and variation trend of limb radiance curve with height can be well revealed by the modeling result of RFM. So accuracy of the RFM model is verified in the upper atmosphere.Diurnal variation has an appreciable impact on the 3-5 μm region and the maximum difference is more than two orders of magnitude. In addition, the limb radiance of the day is larger than night’s radiance and the sun’s enhancement on the atmospheric radiation is obvious. Latitude and season’s effect on the limb radiance is complicated and the characteristic in the different altitude is different. What’s more, the different characteristic of diurnal variation, latitude and season will be presented in the different spectral region.