Downward longwave radiation estimates for clear-sky conditions over northeast Brazil

The main objective of this paper is to assess the performance of nine downward longwave radiation equations for clear-sky condition and develop a locally adjusted equation using the observed vapor pressure and air temperature data. The radiation and atmospheric parameters were measured during the months of October 2005 to June 2006 at a micrometeorological tower installed at the experimental site in a banana orchard in the semiarid region of Northeast Brazil. The comparative statistics for the performance of the downward longwave radiation calculation models during daytime and nighttime compared to measured data have shown that the parameterizations with more physical foundations have the best results. The locally adjusted equation and Sugita and Brutsaert model developed in 1993 showed errors less than 1.0% in comparison with measured values. Downward longwave radiation is one of the most expensive and difficult component of the radiation budget to be monitored in micrometeorological studies. Hence, the locally adjusted equation can be used to estimate downward longwave energy, needed as input to some agricultural and hydrological models, in semi-arid regions of the Northeast Brazil, where this component is not monitored.

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Estimation of All-weather Downward Longwave Radiation over the Tibetan Plateau

10.5194/egusphere-egu21-14096 ◽

2021 ◽

Author(s):

Lirong Ding ◽

Zhiyong Long ◽

Ji Zhou ◽

Shaofei Wang ◽

Xiaodong Zhang

Keyword(s):

Climate Change ◽

Tibetan Plateau ◽

Energy Budget ◽

Water Cycle ◽

Longwave Radiation ◽

Radiation Balance ◽

The Tibetan Plateau ◽

Clear Sky ◽

Downward Longwave Radiation ◽

Sky Conditions

The downward longwave radiation (DLR) is a critical parameter for radiation balance, energy budget, and water cycle studies at regional and global scales. The accurate estimation of the all-weather DLR with a high temporal resolution is important for the estimation of the surface net radiation and evapotranspiration. However, the most DLR products involve instantaneous DLR estimates based on polar orbiting satellite data under clear-sky conditions. To obtain an in-depth understanding of the performances of different models in the estimation of the DLR over the Tibetan Plateau, which is a focus area of climate change study, this study tested eight methods under clear-sky conditions and six methods under cloudy conditions based on ground-measured data. The results show that the Dilley and O&#8217;Brien model and the Lhomme model are most suitable under clear-sky conditions and cloudy conditions, respectively. For the Dilley and O&#8217;Brien model, the average root mean square error (RMSE) of the DLR under clear-sky conditions is approximately 22.5 W/m2 at nine ground sites; for the Lhomme model, the average RMSE is approximately 23.2 W/m2. Based on the estimated cloud fraction and meteorological data provided by the China land surface data assimilation system (CLDAS), the hourly all-weather daytime DLR with 0.0625&#176; over the Tibetan Plateau was estimated. The results show that the average RMSE of the estimated hourly all-weather DLR was approximately 26.4 W/m2. With the combined all-weather DLR model, the hourly all-weather daytime DLR dataset with a 0.0625&#176; resolution from 2008 to 2016 over the Tibetan Plateau was generated. This dataset can better contribute to studies associated with the radiation balance and energy budget, water cycle, and climate change over the Tibetan Plateau.

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A revisiting of the parametrization of downward longwave radiation in summer over the Tibetan Plateau based on high-temporal-resolution measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-4415-2020 ◽

2020 ◽

Vol 20 (7) ◽

pp. 4415-4426 ◽

Cited By ~ 1

Author(s):

Mengqi Liu ◽

Xiangdong Zheng ◽

Jinqiang Zhang ◽

Xiangao Xia

Keyword(s):

Climate Change ◽

Tibetan Plateau ◽

Longwave Radiation ◽

Radiation Budget ◽

Cloud Base ◽

The Tibetan Plateau ◽

Climate Change Research ◽

Clear Sky ◽

Downward Longwave Radiation ◽

Mean Square Errors

Abstract. The Tibetan Plateau (TP) is one of the research hot spots in the climate change research due to its unique geographical location and high altitude. Downward longwave radiation (DLR), as a key component in the surface energy budget, has practical implications for radiation budget and climate change. A couple of attempts have been made to parametrize DLR over the TP based on hourly or daily measurements and crude clear-sky discrimination methods. This study uses 1 min shortwave and longwave radiation measurements at three stations over the TP to parametrize DLR during summer months. Three independent methods are used to discriminate clear sky from clouds based on 1 min radiation and lidar measurements. This guarantees the strict selection of clear-sky samples that is fundamental for the parametrization of clear-sky DLR. A total of 11 clear-sky and 4 cloudy DLR parametrizations are examined and locally calibrated. Compared to previous studies, DLR parametrizations here are shown to be characterized by smaller root-mean-square errors (RMSEs) and higher coefficients of determination (R2). Clear-sky DLR can be estimated from the best parametrization with a RMSE of 3.8 W m−2 and R2>0.98. Systematic overestimation of clear-sky DLR by the locally calibrated parametrization in one previous study is found to be approximately 25 W m−2 (10 %), which is very likely due to potential residual cloud contamination on previous clear-sky DLR parametrization. The cloud base height under overcast conditions is shown to play an important role in cloudy DLR parametrization, which is considered in the locally calibrated parametrization over the TP for the first time. Further studies on DLR parametrization during nighttime and in seasons except summer are required for our better understanding of the role of DLR in climate change.

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Climatic features of the Mediterranean Sea detected by the analysis of the longwave radiative bulk formulae

Annales Geophysicae ◽

10.1007/s00585-000-1482-z ◽

2000 ◽

Vol 18 (11) ◽

pp. 1482-1487 ◽

Cited By ~ 4

Author(s):

M. E. Schiano ◽

M. Borghini ◽

S. Castellari ◽

C. Luttazzi

Keyword(s):

Mediterranean Sea ◽

Longwave Radiation ◽

Radiation Budget ◽

Clear Sky ◽

Radiative Processes ◽

Direct Measurements ◽

Climatic Regime ◽

The Mediterranean ◽

Sky Conditions ◽

Climatic Features

Abstract. Some important climatic features of the Mediterranean Sea stand out from an analysis of the systematic discrepancies between direct measurements of longwave radiation budget and predictions obtained by the most widely used bulk formulae. In particular, under clear-sky conditions the results show that the surface values of both air temperature and humidity over the Mediterranean Sea are larger than those expected over an open ocean with the same amount of net longwave radiation. Furthermore, the twofold climatic regime of the Mediterranean region strongly affects the downwelling clear-sky radiation. This study suggests that a single bulk formula with constant numerical coefficients is unable to reproduce the fluxes at the surface for all the seasons.Key words: Meteorology and Atmospheric dynamics (radiative processes) – Oceanography: general (marginal and semienclosed seas; marine meteorology)

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Evaluation of Atmospheric Downward Longwave Radiation in the Brazilian Pampa Region

Atmosphere ◽

10.3390/atmos12010028 ◽

2020 ◽

Vol 12 (1) ◽

pp. 28

Author(s):

Daniele Aimi ◽

Tamires Zimmer ◽

Lidiane Buligon ◽

Vanessa de Arruda Souza ◽

Roilan Hernandez ◽

...

Keyword(s):

Experimental Data ◽

Longwave Radiation ◽

Climatic Conditions ◽

Correction Function ◽

Subtropical Climate ◽

Experimental Site ◽

Clear Sky ◽

Pampa Biome ◽

Downward Longwave Radiation ◽

New Equation

Atmospheric downward longwave radiation flux (L↓) is a variable that directly influences the surface net radiation and consequently, weather and climatic conditions. Measurements of L↓ are scarce, and the use of classical models depending on some atmospheric variables may be an alternative. In this paper, we analyzed L↓ measured over the Brazilian Pampa biome. This region is located in a humid subtropical climate zone and characterized by well defined seasons and well distributed precipitation. Furthermore, we evaluated the performance of the eleven classical L↓ models for clear sky with one-year experimental data collected in the Santa Maria experimental site (SMA) over native vegetation and high relative humidity throughout the year. Most of the L↓ estimations, using the original coefficients, underestimated the experimental data. We performed the local calibration of the L↓ equations coefficients over an annual period and separated them into different sky cover classifications: clear sky, partly cloudy sky, and cloudy sky. The calibrations decreased the errors, especially in cloudy sky classification. We also proposed the joint calibration between the clear sky emissivity equations and cloud sky correction function to reduce errors and evaluate different sky classifications. The results found after these calibrations presented better statistical indexes. Additionally, we presented a new empirical model to estimate L↓ based on multiple regression analysis using water vapor pressure and air temperature. The new equation well represents partial and cloudy sky, even without including the cloud cover parameterization, and was validated with the following five years in SMA and two years in the Cachoeira do Sul experimental site (CAS). The new equation proposed herein presents a root mean square error ranging from 13 to 21 Wm−2 and correlation coefficient from 0.68 to 0.83 for different sky cover classifications. Therefore, we recommend using the novel equation to calculate L↓ over the Pampa biome under these specific climatic conditions.

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Toward the Estimation of All-Weather Daytime Downward Longwave Radiation over the Tibetan Plateau

Atmosphere ◽

10.3390/atmos12121692 ◽

2021 ◽

Vol 12 (12) ◽

pp. 1692

Author(s):

Zhiyong Long ◽

Lirong Ding ◽

Ji Zhou ◽

Tianhao Zhou

Keyword(s):

Climate Change ◽

Tibetan Plateau ◽

Energy Budget ◽

Water Cycle ◽

Longwave Radiation ◽

Radiation Balance ◽

The Tibetan Plateau ◽

Clear Sky ◽

Downward Longwave Radiation ◽

Sky Conditions

Downward longwave radiation (DLR) is a critical parameter for radiation balance, energy budget, and water cycle studies at regional and global scales. Accurate estimation of the all-weather DLR with a high temporal resolution is important for the estimation of the surface net radiation and evapotranspiration. However, most DLR products involve instantaneous DLR estimates based on polar orbiting satellite data under clear-sky conditions. To obtain an in-depth understanding of the performances of different models in the estimation of DLR over the Tibetan Plateau, which is a focus area of climate change study, this study tests eight methods for clear-sky conditions and six methods for cloudy conditions based on ground-measured data. It is found that the Dilley and O’Brien model and the Lhomme model are most suitable for clear-sky conditions and cloudy conditions, respectively. For the Dilley and O’Brien model, the average root mean square error (RMSE) of DLR under clear-sky conditions is approximately 22.5 W/m2 for nine ground sites; for the Lhomme model, the average RMSE is approximately 23.2 W/m2. Based on the estimated cloud fraction and meteorological data provided by the China Land Surface Data Assimilation System (CLDAS), hourly all-weather daytime DLR with a 0.0625° resolution over the Tibetan Plateau is estimated. Results demonstrate that the average RMSE of the estimated hourly all-weather DLR is approximately 26.4 W/m2. With the combined all-weather DLR model, the hourly all-weather daytime DLR dataset with a 0.0625° resolution from 2008 to 2016 over the Tibetan Plateau is generated. This dataset can contribute to studies associated with the radiation balance and energy budget, water cycle, and climate change over the Tibetan Plateau.

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Evaluation of net shortwave radiation over China with a regional climate model

Climate Research ◽

10.3354/cr01598 ◽

2020 ◽

Vol 80 (2) ◽

pp. 147-163

Author(s):

X Liu ◽

Y Kang ◽

Q Liu ◽

Z Guo ◽

Y Chen ◽

...

Keyword(s):

Regional Climate Model ◽

Climate Model ◽

Regional Climate ◽

Radiant Energy ◽

Energy System ◽

Radiation Budget ◽

Shortwave Radiation ◽

Monsoon Region ◽

Clear Sky ◽

Sky Conditions

The regional climate model RegCM version 4.6, developed by the European Centre for Medium-Range Weather Forecasts Reanalysis, was used to simulate the radiation budget over China. Clouds and the Earth’s Radiant Energy System (CERES) satellite data were utilized to evaluate the simulation results based on 4 radiative components: net shortwave (NSW) radiation at the surface of the earth and top of the atmosphere (TOA) under all-sky and clear-sky conditions. The performance of the model for low-value areas of NSW was superior to that for high-value areas. NSW at the surface and TOA under all-sky conditions was significantly underestimated; the spatial distribution of the bias was negative in the north and positive in the south, bounded by 25°N for the annual and seasonal averaged difference maps. Compared with the all-sky condition, the simulation effect under clear-sky conditions was significantly better, which indicates that the cloud fraction is the key factor affecting the accuracy of the simulation. In particular, the bias of the TOA NSW under the clear-sky condition was <±10 W m-2 in the eastern areas. The performance of the model was better over the eastern monsoon region in winter and autumn for surface NSW under clear-sky conditions, which may be related to different levels of air pollution during each season. Among the 3 areas, the regional average biases overall were largest (negative) over the Qinghai-Tibet alpine region and smallest over the eastern monsoon region.

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An efficient hybrid method for estimating clear-sky surface downward longwave radiation from MODIS data

Journal of Geophysical Research Atmospheres ◽

10.1002/2016jd026250 ◽

2017 ◽

Vol 122 (5) ◽

pp. 2616-2630 ◽

Cited By ~ 14

Author(s):

Jie Cheng ◽

Shunlin Liang ◽

Wenhui Wang ◽

Yamin Guo

Keyword(s):

Hybrid Method ◽

Longwave Radiation ◽

Modis Data ◽

Clear Sky ◽

Downward Longwave Radiation

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Evaluation of Six High-Spatial Resolution Clear-Sky Surface Upward Longwave Radiation Estimation Methods with MODIS

Remote Sensing ◽

10.3390/rs12111834 ◽

2020 ◽

Vol 12 (11) ◽

pp. 1834

Author(s):

Boxiong Qin ◽

Biao Cao ◽

Hua Li ◽

Zunjian Bian ◽

Tian Hu ◽

...

Keyword(s):

Spatial Resolution ◽

High Spatial Resolution ◽

Hybrid Methods ◽

Longwave Radiation ◽

Surface Radiation ◽

Radiation Budget ◽

Estimation Methods ◽

Mean Bias Error ◽

Clear Sky ◽

Surface Radiation Budget

Surface upward longwave radiation (SULR) is a critical component in the calculation of the Earth’s surface radiation budget. Multiple clear-sky SULR estimation methods have been developed for high-spatial resolution satellite observations. Here, we comprehensively evaluated six SULR estimation methods, including the temperature-emissivity physical methods with the input of the MYD11/MYD21 (TE-MYD11/TE-MYD21), the hybrid methods with top-of-atmosphere (TOA) linear/nonlinear/artificial neural network regressions (TOA-LIN/TOA-NLIN/TOA-ANN), and the hybrid method with bottom-of-atmosphere (BOA) linear regression (BOA-LIN). The recently released MYD21 product and the BOA-LIN—a newly developed method that considers the spatial heterogeneity of the atmosphere—is used initially to estimate SULR. In addition, the four hybrid methods were compared with simulated datasets. All the six methods were evaluated using the Moderate Resolution Imaging Spectroradiometer (MODIS) products and the Surface Radiation Budget Network (SURFRAD) in situ measurements. Simulation analysis shows that the BOA-LIN is the best one among four hybrid methods with accurate atmospheric profiles as input. Comparison of all the six methods shows that the TE-MYD21 performed the best, with a root mean square error (RMSE) and mean bias error (MBE) of 14.0 and −0.2 W/m2, respectively. The RMSE of BOA-LIN, TOA-NLIN, TOA-LIN, TOA-ANN, and TE-MYD11 are equal to 15.2, 16.1, 17.2, 21.2, and 18.5 W/m2, respectively. TE-MYD21 has a much better accuracy than the TE-MYD11 over barren surfaces (NDVI < 0.3) and a similar accuracy over non-barren surfaces (NDVI ≥ 0.3). BOA-LIN is more stable over varying water vapor conditions, compared to other hybrid methods. We conclude that this study provides a valuable reference for choosing the suitable estimation method in the SULR product generation.

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