A physical parameterization for cloudy-sky downward longwave radiation: Validation for tropical and subtropical regions in Brazil

IF 1.8 4区地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS

Journal of Atmospheric and Solar-Terrestrial Physics Pub Date : 2025-04-19 DOI:10.1016/j.jastp.2025.106512

José Marcelo Lopes Júnior , Juan Carlos Ceballos , Simone Marilene Sievert da Costa , Francisco Luiz Leitão de Mesquita , Hallan Souza de Jesus , André Rodrigues Gonçalves

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Abstract

Downward longwave radiation is a crucial component of the surface radiation balance and is essential for a better understanding of the greenhouse effect. It is strongly influenced by atmospheric temperature, water vapor content, and cloudiness. This study proposes a new model to estimate downward longwave radiation under cloudy sky conditions, suitable for the application of remote sensing data. The Santa Barbara DISORT Atmospheric Radiative Transfer code was employed to develop parameterizations for cloud and atmospheric processes. The simulations indicated that the emissivity of a stratiform cloud when the cloud is thicker than 300 m (ε = 0.985) approaches that of a blackbody. It is shown that atmospheric emissivity and transmittance can be parameterized as functions of precipitable water content below cloud base. The model was validated using observational data from six different sites in Brazil. The parameterizations of primary model variables (atmospheric layer emissivity, atmospheric transmittance, and precipitable water below the cloud base) generally showed good agreement with radiosonde data. The parameterization of precipitable water in the sub-cloud atmosphere yielded good results, with a maximum RMSE of 0.44 g cm⁻². The developed model presents an average overestimation of only 14 W m⁻², corresponding to a percentage error of 3.5 %, and an overall average RMSE of 18.3 W m⁻² (4.6 %). It shows satisfactory performance and is suitable for application in tropical and subtropical regions, as the underlying physics of this method is consistent worldwide.

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阴天向下长波辐射的物理参数化：对巴西热带和亚热带地区的验证

向下的长波辐射是地表辐射平衡的重要组成部分，对更好地了解温室效应至关重要。它受大气温度、水蒸气含量和云量的强烈影响。本文提出了一种适合于遥感数据应用的多云条件下下向长波辐射估算新模型。使用圣巴巴拉DISORT大气辐射传输代码开发云和大气过程的参数化。模拟结果表明，当层状云厚度大于300 m时，其发射率（ε = 0.985）接近黑体的发射率。结果表明，大气发射率和透射率可以作为云基下可降水量的函数参数化。利用巴西六个不同地点的观测数据验证了该模型。主要模式变量（大气发射率、大气透过率和云底以下可降水量）的参数化总体上与探空数据吻合良好。云下大气可降水量的参数化结果较好，RMSE最大值为0.44 g cm−2。所开发的模型平均高估仅为14 W m−2，对应于3.5%的百分比误差，总体平均RMSE为18.3 W m−2（4.6%）。由于该方法的基础物理性质在世界范围内是一致的，因此它具有令人满意的性能，适用于热带和亚热带地区。

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来源期刊

Journal of Atmospheric and Solar-Terrestrial Physics 地学-地球化学与地球物理

CiteScore

4.10

自引率

5.30%

发文量

审稿时长

6 months

期刊介绍： The Journal of Atmospheric and Solar-Terrestrial Physics (JASTP) is an international journal concerned with the inter-disciplinary science of the Earth''s atmospheric and space environment, especially the highly varied and highly variable physical phenomena that occur in this natural laboratory and the processes that couple them. The journal covers the physical processes operating in the troposphere, stratosphere, mesosphere, thermosphere, ionosphere, magnetosphere, the Sun, interplanetary medium, and heliosphere. Phenomena occurring in other "spheres", solar influences on climate, and supporting laboratory measurements are also considered. The journal deals especially with the coupling between the different regions. Solar flares, coronal mass ejections, and other energetic events on the Sun create interesting and important perturbations in the near-Earth space environment. The physics of such "space weather" is central to the Journal of Atmospheric and Solar-Terrestrial Physics and the journal welcomes papers that lead in the direction of a predictive understanding of the coupled system. Regarding the upper atmosphere, the subjects of aeronomy, geomagnetism and geoelectricity, auroral phenomena, radio wave propagation, and plasma instabilities, are examples within the broad field of solar-terrestrial physics which emphasise the energy exchange between the solar wind, the magnetospheric and ionospheric plasmas, and the neutral gas. In the lower atmosphere, topics covered range from mesoscale to global scale dynamics, to atmospheric electricity, lightning and its effects, and to anthropogenic changes.