Diurnal cycles of cloud cover and its vertical distribution over the Tibetan Plateau revealed by satellite observations, reanalysis datasets, and CMIP6 outputs
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Published:2023-01-17
Issue:1
Volume:23
Page:743-769
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Zhao Yuxin, Li Jiming, Zhang Lijie, Deng Cong, Li Yarong, Jian Bida, Huang JianpingORCID
Abstract
Abstract. Diurnal variations in cloud cover and cloud vertical distribution
are of great importance to Earth–atmosphere system radiative budgets and
climate change. However, thus far these topics have received insufficient
attention, especially on the Tibetan Plateau (TP). This study focuses on the
diurnal variations in total cloud cover, cloud vertical distribution, and
cirrus clouds and their relationship to meteorological factors over the TP
based on active and passive satellite observations, reanalysis data, and
CMIP6 outputs. Our results are consistent with previous studies but provide
new insights. The results show that total cloud cover peaks at 06:00–09:00 UTC, especially over the eastern TP, but the spatial and temporal
distributions of clouds from different datasets are inconsistent. This could to some
extent be attributed to subvisible clouds missed by passive
satellites and models. Compared with satellite observations, the amplitudes
of the diurnal variations in total cloud cover obtained by the reanalysis
and CMIP6 models are obviously smaller. CATS can capture the varying pattern of
the vertical distribution of clouds and corresponding height of peak cloud
cover at middle and high atmosphere levels, although it underestimates the
cloud cover of low-level clouds, especially over the southern TP. Compared
with CATS, ERA5 cannot capture the complete diurnal variations in vertical
distribution of clouds and MERRA-2 has a poorer performance. We further
find that cirrus clouds, which are widespread over the TP, show significant
diurnal variations with averaged peak cloud cover over 0.35 at 15:00 UTC.
Unlike in the tropics, where thin cirrus (0.03< optical
depth <0.3) dominate, opaque cirrus clouds (0.3< optical
depth <3) are the dominant cirrus clouds over the TP. The seasonal
and regional averaged cloud cover of opaque cirrus reaches a daily maximum
of 0.18 at 11:00 UTC, and its diurnal cycle is strong positive correlation
with that of 250 hPa relative humidity and 250 hPa vertical velocity.
Although subvisible clouds (optical depth <0.03), which have a
potential impact on the radiation budget, are the fewest among cirrus clouds
over the TP, the seasonal and regional averaged peak cloud cover can reach
0.09 at 22:00 UTC, and their diurnal cycle correlates with that of the
250 hPa relative humidity, 2 m temperature, and 250 hPa vertical velocity.
Our results will be helpful to improve the simulation and retrieval of total
cloud cover and cloud vertical distribution and further provide an
observational constraint for simulations of the diurnal cycle of surface
radiation budget and precipitation over the TP region.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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