Ziyin Zhang

WITHDRAWN: Cause and predictability for the severe haze pollutions in downtown Beijing during November–December 2015

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Evaluation of the twentieth century reanalysis dataset in describing East Asian winter monsoon variability

The Twentieth Century Reanalysis (20thCR) dataset released in 2010 covers the period 1871–2010 and is one of the longest reanalysis datasets available worldwide. Using ERA-40, ERA-Interim and NCEP-NCAR reanalysis data, as well as HadSLP2 data and meteorological temperature records over eastern China, the performances of 20thCR in reproducing the spatial patterns and temporal variability of the East Asian winter monsoon (EAWM) are examined. Results indicate that 20thCR data: (1) can accurately reproduce the most typical configuration patterns of all sub-factors involved in the EAWM system, albeit with some differences in the main circulation fields over East Asia in comparison to ERA-40 reanalysis data; (2) is reliable and stable in describing the temporal variability of EAWM since the 1930s; and (3) can describe the high-frequency variability of EAWM better than the low-frequency fluctuations, especially in the early period. In conclusion, caution should be taken when using 20thCR data to study interdecadal variabilities or long-term trends of the EAWM, especially prior to the 1930s.

Is the Antarctic oscillation trend during the recent decades unusual

Abstract The Antarctic oscillation (AAO) has been characterized by a persistently positive trend in summer (December–January–February, DJF) during the last 50 years. Thus, the question has arisen of whether the trend is unusual. By investigating five reconstructed historical AAO time series for the past 500 years, recurrences of similar and even stronger trends have been found, indicating that the recent DJF AAO trend is not unprecedented in a historical perspective. To estimate the possible roles played by greenhouse gases or/and ozone, an analysis for DJF AAO trends during the 1969–98 period was conducted using three multiple model ensembles derived from the projects of ‘The twentieth-century climate in coupled models’ (20C3M) and ‘Pre-industrial control experiment models’ (PICTL) of the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC AR4). The results show that the ozone depletion over Antarctica and global warming may play significant roles in the strengthening trend. Combining the simulations and reconstructions we emphasize that the AAO trend related to global warming may get much stronger when enhanced by low-frequency natural variability.

Numerical simulations of the effects of regional topography on haze pollution in Beijing

In addition to weather conditions and pollutant emissions, the degree to which topography influences the occurrence and development of haze pollution in downtown Beijing and the mechanisms that may be involved remain open questions. A series of atmospheric chemistry simulations are executed by using the online-coupled Weather Research and Forecasting with Chemistry (WRF-Chem) model for November-December 2015 with different hypothetical topographic height scenarios. The simulation results show that topography exerts an important influence on haze pollution in downtown Beijing, particularly the typical development of haze pollution. A possible mechanism that underlies the response of haze pollution to topography is that the mountains that surround Beijing tend to produce anomalous southerly winds, high relative humidity, low boundary layer heights, and sinking motion over most of Beijing. These conditions favor the formation and development of haze pollution in downtown Beijing. Furthermore, the reduction percentage in PM2.5 concentrations due to reduced terrain height in the southerly wind (S) mode is almost three times larger than that in the northerly wind (N) mode. In the context of the regional topography, the simple S and N modes represent useful indicators for haze prediction in Beijing to some extent, especially over medium to long time scales.

Simulation and causes of eastern Antarctica surface cooling related to ozone depletion during austral summer in FGOALS-s2

Two parallel sets of numerical experiments (an ozone-hole simulation and a non-ozone-hole simulation) were performed to investigate the effect of ozone depletion on surface temperature change using the second spectral version of the Flexible Global Ocean-Atmosphere-Land System model (FGOALS-s2), focusing on the eastern Antarctica (EA) continent in austral summer. First, we evaluated the ability of the model to simulate the EA surface cooling, and found the model can successfully reproduce the cooling trend of the EA surface, as well as the circulation change circling the South Pole in the past 30 years. Second, we compared the two experiments and discovered that the ozone depletion causes the cooling trend and strengthens the circumpolar westerly flow. We further investigated the causes of the EA surface cooling associated with the ozone hole and found two major contributors. The first is the ozone-hole direct radiation effect (DRE) upon the surface that happens because the decrease of the downward longwave (LW) radiation overcomes the increase of the downward shortwave (SW) radiation under clear sky. The second is the cloud radiation effect (CRE) induced by ozone depletion, which happens because the decreased downward SW radiation overcomes the increased downward LW radiation in the case of increased cloud. Although the CRE is theoretically opposite to the DRE, their final net effect makes comparable contributions to the EA surface cooling. Compared with the surface radiation budget, the surface heat flux budgets have a much smaller contribution. We additionally note that the CRE is basically ascribed to the circulation change.