Song F.,University of Chinese Academy of Sciences |
Zhou T.,CAS Institute of Atmospheric Physics
Journal of Climate | Year: 2014
The climatology and interannual variability of EastAsian summer monsoon (EASM) are investigated by using 13 atmospheric general circulation models (AGCMs) from phase 3 of the Coupled Model Intercomparison Project (CMIP3) and 19 AGCMs from CMIP5. The mean low-level monsoon circulation is reasonably reproduced in themultimodel ensemblemean (MME) of CMIP3 and CMIP5AGCMs, except for a northward shift of the western Pacific subtropical high. However, themonsoon rainband known asmei-yu/baiu/changma (28°-38°N, 105°-150°E) is poorly simulated, although a significant improvement is seen from CMIP3 to CMIP5. The interannual EASM pattern is obtained by regressing the precipitation and 850-hPa wind on the observed EASM index. The observed dipole rainfall pattern is partly reproduced in CMIP3 and CMIP5 MME but with two deficiencies: weaker magnitude and southward shift of the dipole rainfall pattern. These deficiencies are closely related to the weaker and southward shift of the western Pacific anticyclone (WPAC). The simulation skill of the interannual EASM pattern has been significantly improved from CMIP3 to CMIP5 MME accompanied by the enhanced dipole rainfall pattern andWPAC. Analyses demonstrate that the tropical eastern Indian Ocean (IO) rainfall response to local warm SST anomalies and the associated Kelvin wave response over the Indo-western Pacific region are important to maintain the WPAC. A successful reproduction of interannual EASM pattern depends highly on the IO-WPACteleconnection. The significant improvement in the interannual EASMpattern from CMIP3 to CMIP5 MME is also due to a better reproduction of this teleconnection in CMIP5 models. © 2014 American Meteorological Society.
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.
Xia X.,CAS Institute of Atmospheric Physics
Annales Geophysicae | Year: 2012
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.
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.
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.
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.
Zhou L.-T.,CAS Institute of Atmospheric Physics
International Journal of Climatology | Year: 2011
The present study investigates the impact of the East Asian winter monsoon (EAWM) on winter (January, February, and March, or JFM in short) rainfall over southeastern China (including South China and central eastern China) and its dynamical process by using station observations for the period 1951-2003 and the ERA-40 reanalysis for the period 1958-2002. It is found that there is a significant correlation between interannual variations of the EAWM and JFM rainfall over southeastern China. Analyses show that in weak EAWM years southwesterly anomalies at 700 hPa dominate over South China Sea, which transports more moisture into southeastern China, favouring rainfall increase. At the same time, the East Asian westerly jet weakens and displaces southward, contributing to the increase in ascending motion over southeastern China. The air temperature over southeastern China shows an obvious decrease at 300 hPa and increase near the surface. This enhances the convective instability and weakens the potential vorticity (PV), which explains the strengthening of ascending motion and the increase in JFM rainfall over southeastern China. In addition, the EAWM has impacts independent of El Niño Southern Oscillation (ENSO) on JFM rainfall over southeastern China. Moreover, the rainfall anomalies over central eastern China are more closely related to the EAWM than that in South China. © 2010 Royal Meteorological Society.
Chen G.,CAS Institute of Atmospheric Physics
Journal of Climate | Year: 2015
In a recent paper, Kajikawa and Wang detected the interdecadal shift of the South China Sea summer monsoon (SCSSM) onset with a late SCSSM onset in an earlier epoch (1979-93) and an early SCSSM onset in a later epoch (1994-2008) and attributed this change to enhanced tropical cyclone (TC) activity and intraseasonal variability (ISV) related to 30-80-day and 10-25-day anomalies in the second epoch. This comment assesses the individual impact of TCs and ISV on the interdecadal change of the SCSSM onset by means of the removal of anomalies associated with TCs and ISV. Results herein show that TCs have no significant impact on the SCSSM onset in all years, except 2006 in which a strong and long-lived TC occurred over the South China Sea. After removing the 30-80-day anomaly, the difference in the mean SCSSM onset date in the two epochs decreases to some extent, implying that the 30-80-day anomaly can, in part, play a role in the interdecadal shift of the SCSSM onset. In contrast, the 10-25-day anomaly has an insignificant contribution to the interdecadal shift of the SCSSM onset. The discrepancy of ISV contribution results from the SCSSM background state, the magnitude and spatiotemporal scale of ISV, and the phase relationship between ISV and SCSSM transition from easterly to westerly. © 2015 American Meteorological Society.
Huang P.,CAS Institute of Atmospheric Physics
Journal of Climate | Year: 2015
The seasonal changes in tropical SST under global warming are investigated based on the representative concentration pathway 8.5 (RCP8.5) and historical runs in 31 models from phase 5 of CMIP (CMIP5). The tropical SST changes show three pronounced seasonal patterns: the peak locking to the equator throughout the year and the weaker equatorial changes and stronger hemispheric asymmetric changes (HACs) in boreal autumn. Themagnitude of the seasonal patterns is comparable to the tropical-mean warming and the annual-mean patterns, implying great impacts on global climate changes. The peak locking to the equator is a result of the equatorial locking of the minimum damping of climatological latent heat flux and the ocean heat transport changes.Excluding the role of ocean heat transport suggested in previous studies, theweaker equatorialwarming in boreal autumn is contributed by stronger evaporation damping as a result of stronger climatological evaporation and increased surface wind speed. The seasonal variations of the HAC are driven by the variations of the damping effect of climatological evaporation. In boreal summer, the damping effect of climatological evaporation, which is greater in the SouthernHemisphere, promotes the development of theHAC. Consequently, the HAC peaks in boreal autumn when the damping effect of climatological evaporation transforms to a reverse meridional pattern, which is greater in the Northern Hemisphere. The wind-evaporation-SST feedback, as the key process of the annual-mean HAC, amplifies the seasonal variations of the HAC in tropical SST. © 2015 American Meteorological Society.
Wang L.,CAS Institute of Atmospheric Physics |
Chen W.,CAS Institute of Atmospheric Physics
Journal of Climate | Year: 2014
The thermal contrast between the Asian continent and the adjacent oceans is the primary aspect of the East Asian winter monsoon (EAWM) that can be well represented in the sea level pressure (SLP) field. Based on this consideration, a new SLP-based index measuring the intensity of the EAWM is proposed by explicitly taking into account both the east-west and the north-south pressure gradients around East Asia. The new index can delineate the EAWM-related circulation anomalies well, including the deepened (shallow) midtropospheric East Asian trough, sharpened and accelerated (widened and decelerated) upper-tropospheric East Asian jet stream, and enhanced (weakened) lower-tropospheric northerly winds in strong (weak) EAWM winters. Compared with previous indices, the new index has a very good performance describing the winter-mean surface air temperature variations over East Asia, especially for the extreme warm or cold winters. The index is strongly correlated with several atmospheric teleconnections including the Arctic Oscillation, the Eurasian pattern, and the North Pacific Oscillation/western Pacific pattern, implying the possible internal dynamics of theEAWMvariability. Meanwhile, the index is significantly linked to El Niño-Southern Oscillation (ENSO) and the sea surface temperature (SST) over the tropical Indian Ocean. Moreover, the SST anomalies over the tropical Indian Ocean are more closely related to the index than ENSO as an independent predictor. This adds further knowledge to the prediction potentials of the EAWM apart from ENSO. The predictability of the index is high in the hindcasts of the Centre National de Recherches Météorologiques (CNRM) model from Development of a European Multimodel Ensemble System for Seasonal-to-Interannual Prediction (DEMETER). Hence, it would be a good choice to use this index for the monitoring, prediction, and research of the EAWM. © 2014 American Meteorological Society.