A New Empirical Estimation Scheme for Daily Net Radiation at the Ocean Surface

Jianghai Peng,Jiakun Han,Shunlin Liang,Qiang Liu,Yunjun Yao,Bo Jiang,Shaopeng Li,Hongkai Chen,Jie Cheng,Kun Jia,Xiaotong Zhang,Hui Liang

doi:10.3390/rs13204170

Abstract

Ocean surface net radiation (Rn) is significant in research on the Earth’s heat balance systems, air–sea interactions, and other applications. However, there have been few studies on Rn until now. Based on radiative and meteorological measurements collected from 66 globally distributed moored buoys, it was found that Rn was dominated by downward shortwave radiation (Rg↓) when the length ratio of daytime (LRD) was greater than 0.4 but dominated by downward longwave radiation (Rl↓) for the other cases (LRD ≤ 0.4). Therefore, an empirical scheme that includes two conditional models named Case 1 (LRD > 0.4) utilizing Rg↓ as a major input and Case 2 (LRD ≤ 0.4) utilizing Rl↓ as a major input for Rn estimation was successfully developed. After validation against in situ Rn, the performance of the empirical scheme was satisfactory with an overall R2 value of 0.972, an RMSE of 9.768 Wm−2, and a bias of −0.092 Wm−2. Specifically, the accuracies of the two conditional models were also very good, with RMSEs of 9.805 and 2.824 Wm−2 and biases of −0.095 and 0.346 Wm−2 for the Case 1 and Case 2 models, respectively. However, due to the limited number of available samples, the performances of these new models were poor in coastal and high-latitude areas, and the models did not work when the LRD was too small (i.e., LRD < 0.3). Overall, the newly developed empirical scheme for Rn estimation has strong potential to be widely used in practical use because of its simple format and high accuracy.

Highlights

Ocean surface all-wave net radiation (Rn ) is the sum of the downward and upward shortwave and longwave radiation at the ocean surface
The objective of this study is to develop a new scheme for estimating the daily ocean surface Rn empirically in a simple way based on measurements collected from more than 60 global moored buoy sites
Compared with the fitting results from Equation (12) (Figure 3), the accuracy of the Rn estimations from the new model was significantly improved as the R2 value increased from 0.925 to 0.971 and the RMSE decreased from 15.501 Wm−2 to 9.650 Wm−2

Summary

Introduction

Ocean surface all-wave net radiation (Rn ) is the sum of the downward and upward shortwave and longwave radiation at the ocean surface. Woods Hole Oceanographic Institution (WHOI) focuses on the study of physical processes in the upper ocean and at the air–sea interface using moored surface buoys equipped with meteorological and oceanographic sensors. These observations enable the first accurate quantification of the annual cycle of net air–sea heat exchange and wind stress from a Southern Ocean location [34]. Observations from 66 moored buoy sites have been widely applied in previous studies, such as air–sea interaction studies [13,39,40,41], ENSO prediction [42], and monsoon variability studies [23]

Objectives

Results

Conclusion