Abstract
Cloud top height (CTH) is an essential pareter for the general circulation model in understanding the impact of clouds on the Earth’s radiation budget and global climate change. This paper compares the CTH products, derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), onboard the Aqua and Terra satellites with ground-based Ka band radar data in Beijing from 2014 to 2017. The aim was to investigate the data accuracy and the difference in CTH measurements between passive satellite data and active ground-based radar data. The results show that MODIS, on average, underestimates CTH relative to radar by −1.08 ± 2.48 km, but with a median difference of −0.65 km and about 48% of differences are within 1 km. Statistically, MODIS CTHs which are greater than 6 km show lower discrepancy to radar CTH than those of MODIS CTHs less than 4 km. The CTH difference is independent of cloud fraction and cloud layer. It shows strong dependence on cloud depth, decreasing as cloud depth increases. There is a tendency for MODIS to underestimate high thin clouds but overestimate low thin clouds relative to radar. Total ozone, SO2, CO, NO2, aerosol PM10, total water vapor and temperature inversion show unobvious influences in the CTH discrepancy. It is shown that the MODIS CO2-slicing technique performs much better than IRW (infrared window) technique when cloud layer is higher than 2 km. The average difference calculated from all comparisons by CO2-slicing technique and IRW technique is 0.09 ± 1.58 km, and −2.20 ± 2.73 km, respectively.
Highlights
Clouds cover more than 50% of the globe
The aim of this paper is to investigate the difference of the Moderate Resolution Imaging Spectroradiometer (MODIS) Cloud top height (CTH) products with ground-based radar data obtained in Beijing, over a long-term period, and to investigate its relationship with the cloud properties and atmospheric parameters
This paper focuses on quantifying the CTH differences between MODIS and Ka band polarization Doppler radar (KPDR), analyzing the relationships of these differences with the physical properties of cloud and investigating impacts of local atmospheric parameters on CTH differences
Summary
Clouds cover more than 50% of the globe. They play important roles in regulating the energy budget and hydrological cycle of the Earth–atmosphere system [1,2,3,4]. Clouds are one of the least-understood components, as well as being one of the largest uncertainty sources, in general circulation model (GCM) simulations [5,6,7]. MODIS measures the infrared (IR) brightness temperature of the cloud to derive CTH and most passive satellite imaging instruments in operation are using similar method to derive CTH [8,9,10,11,12,13]. Since its launch in 2000, MODIS onboard the Aqua and Terra satellites has provided long-term
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