Diurnal cycle and seasonal variation of cloud cover over the Tibetan Plateau as determined from Himawari-8 new-generation geostationary satellite data

Huazhe Shang,Dabin Ji,Ziming Wang,Tianxing Wang,Takashi Y Nakajima,Shenshen Li,Run Ma,Husi Letu,Jiancheng Shi,Yonghui Lei

doi:10.1038/s41598-018-19431-w

Abstract

Analysis of cloud cover and its diurnal variation over the Tibetan Plateau (TP) is highly reliant on satellite data; however, the accuracy of cloud detection from both polar-orbiting and geostationary satellites over this area remains unclear. The new-generation geostationary Himawari-8 satellites provide high-resolution spatial and temporal information about clouds over the Tibetan Plateau. In this study, the cloud detection of MODIS and AHI is investigated and validated against CALIPSO measurements. For AHI and MODIS, the false alarm rate of AHI and MODIS in cloud identification over the TP was 7.51% and 1.94%, respectively, and the cloud hit rate was 73.55% and 80.15%, respectively. Using hourly cloud-cover data from the Himawari-8 satellites, we found that at the monthly scale, the diurnal cycle in cloud cover over the TP tends to increase throughout the day, with the minimum and maximum cloud fractions occurring at 10:00 a.m. and 18:00 p.m. local time. Due to the limited time resolution of polar-orbiting satellites, the underestimation of MODIS daytime average cloud cover is approximately 4.00% at the annual scale, with larger biases during the spring (5.40%) and winter (5.90%).

Highlights

The Tibetan Plateau (TP), which is the highest and largest plateau on Earth, is well known to modulate regional and global atmospheric circulation by acting as an elevated heat source and a very large natural barrier[1,2,3,4]
Investigating semidiurnal cycles in cloud cover over the TP with Advanced Himawari Imager (AHI) and Moderate resolution imaging spectroradiometer (MODIS) can help elucidate the uncertainties of cloud-cover statistics that are estimated from polar-orbiting satellites
Cloud discrimination over the Tibetan Plateau is analyzed by the MODIS and AHI sensors

Summary

Introduction

The Tibetan Plateau (TP), which is the highest and largest plateau on Earth, is well known to modulate regional and global atmospheric circulation by acting as an elevated heat source and a very large natural barrier[1,2,3,4]. The diurnal variation in cloud cover over the TP links convection and precipitation processes and has shown potential in disaster mitigation, precipitation forecasting and numerical-model validation Studies on these topics are scarce[7,8,9], likely for the following three reasons: 1) a lack of ground observations of clouds10, 2) the limited temporal resolution of polar-orbiting satellites[11,12], and 3) the inability of first-generation geostationary satellites to provide accurate cloud discrimination[13,14,15]. The cloud dataset from the newly launched Himawari-8 geostationary satellite that includes the Advanced Himawari Imager (AHI) with 16 bands that span from 0.47 μm to 13.3 μm, facilitates the accurate determination of cloud properties with a spatial resolution of 2 km and a temporal resolution of 10 min[20].

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Results

Conclusion