In Press

Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes/issues, but are citable by Digital Object Identifier (DOI).
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Original Paper
Meridional Displacement of the East Asian Upper-tropospheric Westerly Jet and Its Relationship with the East Asian Summer Rainfall in CMIP5 Simulations
Yuhan YAN, Chaofan LI, Riyu LU
, Available online   , Manuscript accepted  25 June 2019, doi: 10.1007/s00376-019-9066-1
Abstract:
As the first leading mode of upper-tropospheric circulation in observations, the meridional displacement of the East Asian westerly jet (EAJ) varies closely with the East Asian rainfall in summer. In this study, the interannual variation of the EAJ meridional displacement and its relationship with the East Asian summer rainfall are evaluated, using the historical simulations of CMIP5 (phase 5 of the Coupled Model Intercomparison Project). The models can generally reproduce the meridional displacement of the EAJ, which is mainly manifested as the first principal mode in most of the simulations. For the relationship between the meridional displacement of the EAJ and East Asian rainfall, almost all the models depict a weaker correlation than observations and exhibit considerably large spread across the models. It is found that the discrepancy in the interannual relationship is closely related to the simulation of the climate mean state, including the climatological location of the westerly jet in Eurasia and rainfall bias in South Asia and the western North Pacific. In addition, a close relationship between the simulation discrepancy and intensity of EAJ variability is also found: the models with a stronger intensity of the EAJ meridional displacement tend to reproduce a closer interannual relationship, and vice versa.
Investigating the Transport Mechanism of PM2.5 Pollution during January 2014 in Wuhan, Central China
Miaomiao LU, Xiao TANG, Zifa WANG, Lin WU, Xueshun CHEN, Shengwen LIANG, Hui ZHOU, Huangjian WU, Ke HU, Longjiao SHEN, Jia YU, Jiang ZHU
, Available online   , Manuscript accepted  25 June 2019, doi: 10.1007/s00376-019-8260-5
Abstract:
Severe haze pollution that occurred in January 2014 in Wuhan was investigated. The factors leading to Wuhan’s PM2.5 pollution during this month were further investigated and the characteristics and formation mechanism were found to be significantly different from other megacities, like Beijing. Both the growth rates and decline rates of PM2.5 concentrations in Wuhan were lower than those in Beijing, but the monthly PM2.5 value was approximately twice that in Beijing. Furthermore, the sharp increases of PM2.5 concentrations were often accompanied by strong winds. A high-precision modeling system with an online source-tagged method was established to explore the formation mechanism of five haze episodes. The long-range transport of the polluted air masses from the North China Plain (NCP) was the main factor leading to the sharp increases of PM2.5 concentrations in Wuhan, which contributed 92.3 μg m−3 of the PM2.5 concentrations and 38.5% of polluted days. Furthermore, the change in meteorological conditions such as weakened winds and stable weather conditions led to the accumulation of air pollutants in Wuhan after the long-range transport. The contribution from Wuhan and surrounding cities to the PM2.5 concentrations was determined to be 67.4% during this period. Under the complex regional transport of pollutants from surrounding cities, the NCP, East China, and South China, the five episodes resulted in 30 haze days in Wuhan. The findings reveal important roles played by transregional and intercity transport in haze formation in Wuhan.
Atmospheric Warming Slowdown during 1998-2013 Associated with Increasing Ocean Heat Content
Changyu LI, Jianping HUANG, Yongli HE, Dongdong LI, Lei DING
, Available online   , Manuscript accepted  25 June 2019, doi: 10.1007/s00376-019-8281-0
Abstract:
Although atmospheric greenhouse gas concentrations continuously increased, there was relatively little change in global-averaged surface temperatures from 1998 to 2013, which is known as atmospheric warming slowdown. For further understanding the mechanism involved, we explored the energy redistribution between the atmosphere and ocean in different latitudes and depths by using data analysis as well as simulations of a coupled atmosphere–ocean box model. The results revealed that, compared with observational changes of ocean heat content (OHC) associated with rapid warming, the OHC changes related to warming slowdown are relatively larger in multiple ocean basins, particularly in the deeper layer of the Atlantic. The coupled box model also showed that there is a larger increasing trend of OHC under the warming slowdown scenario than the rapid warming scenario. Particularly, during the warming slowdown period, the heat storage in the deeper ocean increases faster than the ocean heat uptake in the surface ocean. The simulations indicated that the warming patterns under the two scenarios are accompanied by distinct outgoing longwave radiation and atmospheric meridional heat transport, as well as other related processes, thus leading to different characteristics of ocean heat uptake. Due to the global energy balance, we suggest this slowdown has a tight relationship with the accelerated heat transport into the global ocean.
Influences of the NAO on the North Atlantic CO2 Fluxes in Winter and Summer on the Interannual Scale
Yujie JING, Yangchun LI, Yongfu XU, Guangzhou FAN
, Available online   , Manuscript accepted  25 June 2019, doi: 10.1007/s00376-019-8247-2
Abstract:
The differences in the influences of the North Atlantic Oscillation (NAO) on the air–sea CO2 fluxes (fCO2) in the North Atlantic (NA) between different seasons and between different regions are rarely fully investigated. We used observation-based data of fCO2, surface-ocean CO2 partial pressure (pCO2sea), wind speed and sea surface temperature (SST) to analyze the relationship between the NAO and fCO2 of the subtropical and subpolar NA in winter and summer on the interannual time scale. Based on power spectrum estimation, there are significant interannual signs with a 2–6 year cycle in the NAO indexes and area-averaged fCO2 anomalies in winter and summer from 1980 to 2015. Regression analysis with the 2–6 year filtered data shows that on the interannual scale the response of the fCO2 anomalies to the NAO has an obvious meridional wave-train-like pattern in winter, but a zonal distribution in summer. This seasonal difference is because in winter the fCO2 anomalies are mainly controlled by the NAO-driven wind speed anomalies, which have a meridional distribution pattern, while in summer they are dominated by the NAO-driven SST anomalies, which show distinct zonal difference in the subtropical NA. In addition, in the same season, there are different factors controlling the variation of pCO2sea in different regions. In summer, SST is important to the interannual variation of pCO2sea in the subtropical NA, while some biogeochemical variables probably control the pCO2sea variation in the subpolar NA.
Antarctic Radiosonde Observations Reduce Uncertainties and Errors in Reanalyses and Forecasts over the Southern Ocean: An Extreme Cyclone Case
Kazutoshi SATO, Jun INOUE, Akira YAMAZAKI, Naohiko HIRASAWA, Konosuke SUGIURA, Kyohei YAMADA
, Available online   , Manuscript accepted  30 April 2019, doi: 10.1007/s00376-019-8231-x
Abstract:
Cyclones with strong winds can make the Southern Ocean and the Antarctic a dangerous environment. Accurate weather forecasts are essential for safe shipping in the Southern Ocean and observational and logistical operations at Antarctic research stations. This study investigated the impact of additional radiosonde observations from Research Vessel "Shirase" over the Southern Ocean and Dome Fuji Station in Antarctica on reanalysis data and forecast experiments using an ensemble data assimilation system comprising the Atmospheric General Circulation Model for the Earth Simulator and the Local Ensemble Transform Kalman Filter Experimental Ensemble Reanalysis, version 2. A 63-member ensemble forecast experiment was conducted focusing on an unusually strong Antarctic cyclonic event. Reanalysis data with (observing system experiment) and without (control) additional radiosonde data were used as initial values. The observing system experiment correctly captured the central pressure of the cyclone, which led to the reliable prediction of the strong winds and moisture transport near the coast. Conversely, the control experiment predicted lower wind speeds because it failed to forecast the central pressure of the cyclone adequately. Differences were found in cyclone predictions of operational forecast systems with and without assimilation of radiosonde observations from Dome Fuji Station.
Stratospheric Ozone-induced Cloud Radiative Effects On Antarctic Sea Ice
Yan XIA, Yongyun HU, Jiping LIU, Yi HUANG, Fei XIE, Jintai LIN
, Available online   , Manuscript accepted  19 April 2019, doi: 10.1007/s00376-019-8251-6
Abstract:
Recent studies demonstrate that the Antarctic Ozone Hole has important influences on Antarctic sea ice. While most of these works have focused on effects associated with atmospheric and oceanic dynamic processes caused by stratospheric ozone changes, here we show that stratospheric ozone-induced cloud radiative effects also play important roles in causing changes in Antarctic sea ice. Our simulations demonstrate that the recovery of the Antarctic Ozone Hole causes decreases in clouds over Southern Hemisphere (SH) high latitudes and increases in clouds over the SH extratropics. The decrease in clouds leads to a reduction in downward infrared radiation, especially in austral autumn. This results in cooling of the Southern Ocean surface and increasing Antarctic sea ice. Surface cooling also involves ice-albedo feedback. Increasing sea ice reflects solar radiation and causes further cooling and more increases in Antarctic sea ice.