Trends in Downwelling Longwave Radiance over the Southern Great Plains

Downwelling longwave radiation is an important part of the surface energy budget. Spectral trends in the downwelling longwave radiance (DLR) provide insight into the radiative drivers of climate change. In this research, we process and analyze a 23-year DLR record measured by the Atmospheric Emitted Radiance Interferometers (AERI) at the Atmospheric Radiation Program Southern Great Plains (SGP) site. Two AERIs were deployed at SGP with an overlapping observation period of about 10 years, which allows us to examine the consistency and accuracy of the measurements and to account for discrepancies between them due to errors associated with the instruments themselves. We then analyzed the all-sky radiance trends in DLR, which are associated with the surface warming trend at SGP during this same period and also the complex changes in meteorological conditions. For instance, the observed radiance in the CO2 absorption band follows closely the near-surface air temperature variations. The significant positive radiance trends in weak absorption channels, such as in the wings of the CO2 band and in the weak absorption channels in the H2O vibration-rotational band, show earlier detectability of climate change. The magnitude of the radiance trend uncertainty in the DLR record mainly results from internal climate variability rather than from measurement error, which highlights the importance of continuing the DLR spectral measurements to unambiguously detect and attribute climate change.

下行长波辐射（Downwelling Longwave Radiation）是地表能量收支的重要组成部分。下行长波辐亮度（Downwelling Longwave Radiance, DLR）的光谱变化趋势，可为气候变化的辐射驱动因子提供研究视角。本研究对大气辐射计划（Atmospheric Radiation Program）南大平原（Southern Great Plains, SGP）观测场由大气发射辐亮度干涉仪（Atmospheric Emitted Radiance Interferometers, AERI）获取的23年DLR观测记录进行了处理与分析。该站点共部署两台AERI，其观测重叠时长约为10年，这使得我们能够检验观测数据的一致性与准确性，并量化因仪器自身误差引发的观测差异。随后，我们分析了全天空条件下DLR的辐亮度变化趋势，该趋势与同期SGP站点的地表增温趋势以及气象条件的复杂变化密切相关。例如，CO₂吸收带内的观测辐亮度与近地表气温变化高度吻合。在弱吸收通道（如CO₂吸收带翼区以及H₂O振动-转动带内的弱吸收通道）中观测到的显著正辐亮度趋势，表明气候变化可被更早探测到。DLR记录中的辐亮度趋势不确定性主要源自内部气候变率而非测量误差，这凸显了持续开展DLR光谱观测对于明确探测气候变化并对其成因进行归因的重要意义。