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Xia X.,CAS Institute of Atmospheric Physics
Journal of Geophysical Research: Atmospheres | Year: 2010

Long-term trends in cloud amount and sunshine duration have been studied based upon surface observations at 618 meteorological stations across China. The degree of agreement between the two measures at interannual and decadal scales is analyzed, and a further understanding of the trends in sunshine duration is presented. A significant decreasing trend has been derived for sunshine duration (SSD) and total cloud cover (TCC); however, low-level cloud cover (LCC) shows an increasing trend, although it is not significant at the 95% level. Interannual variability of SSD is strongly inversely correlated to that of TCC and LCC, indicating short-term variability of SSD is dominantly determined by cloudiness. A positive correlation between decadal changes in SSD and TCC suggests long-term change in TCC cannot account for the decreasing trend in SSD. Long-term change in LCC appears to be one of important contributors to the trend in SSD in southern China, where long-term changes in SSD are inversely correlated to those of LCC. The decreasing trend in SSD is contributed by the declines in average SSDs under clear sky (13%), cloudy (51%), and overcast conditions (36%), 30% of which is offset by an increase in the frequency of clear sky. Copyright 2010 by the American Geophysical Union. Source

An updated analysis of cloud cover during 1954-2005 in China was performed using homogeneous cloud cover data from 314 stations. Long-term changes in frequencies of different cloud cover categories and their contributions to long-term changes in cloud cover were assessed. Furthermore, aerosol effects on cloud cover trends were discussed based on comparison of cloud cover trends in polluted and mildly polluted regions. Frequencies of clear sky (cloud cover <20%) and overcast days (cloud cover >80%) were observed to increase by ∼2.2 days and decrease by ∼3.3 days per decade, respectively, which accounts for ∼80% of cloud cover reduction. Larger decreasing trends in cloud cover due to larger increase in clear sky frequency and larger decreases in overcast frequency were observed at stations with lower aerosol optical depth. There is no significant difference in trends regarding cloud cover, clear sky frequency, and overcast frequency between mountain and plain stations. These results are inconsistent with our expectation that larger decreasing trends in cloud cover should have been observed in regions with higher aerosol loading where more aerosols could lead to stronger obscuring effect on ground observation of cloud cover and stronger radiative effect as compared with the mildly polluted regions. Aerosol effect on decreasing cloud cover in China appear not to be supported by this analysis and therefore, further study on this issue is required. © Author(s) 2012. Source

Bai J.,CAS Institute of Atmospheric Physics
Atmospheric Environment | Year: 2011

Analyzing observational data for solar radiation, meteorological parameters and total ozone concentration during the period of January 1990 to December 1991 in Beijing enabled the development of an empirical method for estimation of UV irradiance (UVI) in clear skies. Predicted values from the model agreed well with observations. The mean relative bias for 24 months was 1.9%. UVI (290-400nm) in clear sky conditions from 1979 to 1998 was calculated, and its long-term variation showed a declining trend of -3.89%, which was accompanied by a decrease in total O3 of -5.75%, a decrease in scattering factor (S/D, the ratio of solar scattered to direct radiation) of -20.79%, and an increase in water vapor content of +4.76%. It is hypothesized that many substances in the atmosphere, including volatile organic compounds (VOCs) and their oxidation products, very fine particles and others absorb and/or utilize UV energy. The long-term UVI trends and its main controlling factors in four seasons during the previous 2 decades are discussed, UV energy consumption by atmospheric chemical and photochemical processes, is especially important during summer. © 2011 Elsevier Ltd. Source

Zhao D.,CAS Institute of Atmospheric Physics
Climate Dynamics | Year: 2013

Regional climate models (RCMs) can provide much more precise information on surface characteristics and mesoscale circulation than general circulation models. This potential for obtaining more detailed model results has motivated to a significant focus on RCMs development in East Asia. The Regional Integrated Environment Modeling System, version 2. 0 (RIEMS2. 0) has been developed from an earlier RCM, RIEMS1. 0, at the Key Laboratory of Regional Climate-Environment for East Asia and Nanjing University. To test the ability of RIEMS2. 0 to simulate long-term climate and climate changes in East Asia and to provide a basis for further development and applications, we compare simulated precipitation from 1979 to 2008 (simulation duration from 1 January 1978 to 31 December 2008) to observed meteorological data. The results show that RIEMS2. 0 reproduces the spatial distribution of precipitation in East Asia but that the simulation overestimates precipitation. The simulated 30-year precipitation average is 26 % greater than the observed precipitation. Simulated upper and root soil water correlate well with remote sensing derived soil moisture. Annual and interannual variation in the average precipitation and their anomalies are both well reproduced by the model. A further analysis of three subregions representing different latitude ranges shows that there is good correlation and consistency between the simulated results and the observed data. Annual variation, interannual variation of average precipitation, and the anomalies in the three sub-regions are also well captured by the model. The model's performance on atmospheric circulation and moisture transport simulations is discussed to explore the bias between the simulation and observations. In summary, RIEMS2. 0 shows stability and does well in both simulating long-term climate and climate changes in East Asia and in describing subregional characteristics. © 2013 Springer-Verlag Berlin Heidelberg. Source

Chen G.,CAS Institute of Atmospheric Physics
Journal of Climate | Year: 2011

The different modulation of El Niño Modoki and canonical El Niño events on tropical cyclone (TC) frequency over the South China Sea (SCS) during boreal summer and fall for 1960-2009 is investigated. The bootstrap resampling method and two-sample permutation procedure are applied to simulate sampling distributions and conduct statistical tests, respectively. Results from the hypothesis testing indicate that the above-normal TC frequency over the SCS occurs during June-August (JJA) for the El Niño Modoki years, whereas the below-normal TC frequency is significant during September-November (SON) for the canonical El Niño years. The remarkably opposite modulations can be attributed to the different large-scale circulation anomalies, which are consistent with Matsuno-Gill-type responses to the tropical heating source/sink oAver the western North Pacific (WNP) and Maritime Continent for two kinds of Pacific Ocean warming events. In response to a broad-scale convection anomaly over the WNP during JJA for El Niño Modoki, a zonally elongated cyclonic anomaly dominates the WNP and SCS, leading to enhanced TC activity. In contrast, during SON for the canonical El Niño, a markedly strengthened cooling source centered in the Maritime Continent induces an anticyclonic anomaly over the SCS, resulting in suppressed TC activity. © 2011 American Meteorological Society. Source

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