Improving the Understanding of CrIS Full Spectral Resolution Nonlocal Thermodynamic Equilibrium Radiances Using Spectral Correlation
Improving the Understanding of CrIS Full Spectral Resolution Nonlocal Thermodynamic Equilibrium Radiances Using Spectral Correlation
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DOI：
10.1029/2020jd032710
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发表时间：
2020-08
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通讯作者：
Zhenglong Li;W. Menzel;James Jung;A. Lim;Jun Li;M. Matricardi;M. López‐Puertas;S. Desouza-Machado;L. Strow
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作者：
Zhenglong Li;W. Menzel;James Jung;A. Lim;Jun Li;M. Matricardi;M. López‐Puertas;S. Desouza-Machado;L. Strow
近几年来，快速辐射传输模式（RTM）对白天非局域热力学平衡（NLTE）排放的模拟研究取得了重大进展。然而，NLTE仍然是阻碍高光谱短波红外（SWIR）辐射观测被同化到数值天气预报（NWP）模式中的一个重要原因。为了更好地理解现有基于RTM的NLTE模拟的局限性，本研究引入了一种新的统计方法，称为估计非局部热平衡的光谱相关性（SCENTE），以估计跨轨道红外探测器（CrIS）SWIR辐射观测中的NLTE辐射。SCENTE适用于四个典型的季节，包括春分，夏至，秋分和冬至。通过对CrIS SWIR亮温（BT）的计算/背景减观测（BMO）分析，结果表明：SCENTE能很好地表征NLTE，其标准差（STD）在白天和夜间都与观测噪声相当，而社区RTM（CRTM）在夜间的STD明显更大，这主要是由于在昼夜分界线之外缺乏日间NLTE，以及缺乏与极光相关的NLTE。对BMO偏差的详细研究表明，CRTM低估了白天SWIR NLTE效应0.76 K，而SCENTE高估了SWIR NLTE效应0.70 K。高估是因为SCENTE在训练中使用了CRTM模拟的SWIR局部热力学平衡（LTE）辐射，而BT中低估了0.70 K。SCENTE是基于RTM的模拟的补充，可用于SWIR辐射的质量控制，用于大气探测的同化和反演。
In recent years, significant progress has been made in fast radiative transfer model (RTM) simulation of daytime nonlocal thermodynamic equilibrium (NLTE) emission. However, NLTE remains as one important reason that prevents the hyperspectral shortwave infrared (SWIR) radiance observations from being assimilated into numerical weather prediction (NWP) models. To better understand the limitations of existing RTM‐based NLTE simulation, this study introduces a new statistical method, called Spectral Correlations to Estimate Non‐Local Thermal Equilibrium (SCENTE), to estimate the NLTE radiances in the Cross‐track Infrared Sounder (CrIS) SWIR radiance observations. SCENTE is applied to four typical season days, including spring equinox, summer solstice, fall equinox, and winter solstice. By analyzing calculation/background minus observation (BMO) of CrIS SWIR brightness temperature (BT), results show that SCENTE characterizes the NLTE well with standard deviation of differences (STD) comparable to observation noise for both daytime and nighttime, while the community RTM (CRTM) has substantially larger STD at night, mainly due to the lack of daytime NLTE just beyond the day/night terminator and the lack of aurora‐related NLTE. Detailed investigation of the biases of BMO shows that CRTM underestimates daytime SWIR NLTE effects by 0.76 K, while SCENTE overestimates SWIR NLTE effects by 0.70 K. The overestimation is because SCENTE uses CRTM‐simulated SWIR local thermodynamic equilibrium (LTE) radiances in the training, which is underestimated by 0.70 K in BT. SCENTE, complementary to RTM‐based simulations, can be used for quality control of SWIR radiances for assimilation and retrieval of atmospheric soundings.