CH4 Monitoring and Background Concentration at Zhongshan Station, Antarctica

Background CH4 concentration and seasonal variations measured at Zhongshan Station (69°22'2''S, 76°21'49''E, 18.5 m) in Antarctica from 2008 through 2013 are presented and discussed. From 2008-2013 CH4 was measured in weekly flask samples and started on line measurement by Picarro CO2/CH4/H2O analyzer from March, 2010-2013. These CH4 measurements show the expected growth period of CH4 concentration during February (Antarctic spring) with a peak in September (fall). Irrespective of wind direction, CH4 concentrations distribute evenly after the removal of polluted air from station operations, accounting for 1% of the data. The mean daily cycle of CH4 concentration in all four seasons is small. The monthly mean CH4 concentration at Zhongshan station is similar to those at other stations in Antarctica showing that CH4 observed in Antarctica is fully mixed in the atmosphere as it is transported from the northern through the southern hemisphere. The annual CH4 increase in recent years at Zhongshan station is 4.8 ppb·yr-1.

Surface Ozone Monitoring and Background Concentration at Zhongshan Station, Antarctica

The background surface O3 concentrations and seasonal changes observed at the Zhongshan Station (69°22'2''S, 76°21'49''E;18.5 m), east Antarctica from 2008 to 2013 are presented. Irrespective of wind direction, surface O3 concentrations distribute evenly after the removal of polluted air from station operations, accounting for 1.1% of the data. These O3 exhibit the expected lowest in summer, with a peak in winter. The daily range of average O3 in all four seasons is small. The monthly mean O3 is similar to that of other stations in Antarctica, with seasonal CO2 amplitudes in the order of 15 ppb to 35 ppb. Surface O3 significantly negatively correlated with UVB in the spring and autumn, with correlation coefficients of 0.50 and 0.57 under the 0.01 significance test. Furthermore, the surface O3 concentration during polar nights was 1 - 2 times higher than that during polar days. Thus, the chemical effect of the aurora lights was the dominant cause of ozone destruction, showing that surface O3 observed in Antarctica has a small interferences from human activities in the atmosphere as it moves from the north through the southern hemisphere.

Current and Future Precipitation Extremes over Mississippi and Yangtze River Basins as Simulated in CMIP5 Models

Both central-eastern U.S. and China are prone to increasing flooding from Mississippi River and Yangtze River basins respectively. This paper contrasts historical and projected spatialtemporal distribution of extreme precipitation in these two large river basins using 31 CMIP5（coupled model intercomparison project phase 5） models＇ historical and RCP8.5（representative concentration pathway） experiments. Results show that（1） over both river basins, the heaviest rainfall events have increased in recent decades while the lightest precipitation reduced in frequency. Over Mississippi River Basin, both the lightest precipitation（〈2.5 mm/day） and heaviest（〉50 mm/day） would decrease in frequency notably after mid-2020 s while intermediate events occur more frequently in future; whereas over the Yangtze River Basin, all categories of precipitation are projected to increase in frequency over the coming decades.（2） Although the consensus of CMIP5 models was able to reproduce well domain-time mean and even time-averaged spatial distribution of precipitation, they failed to simulate precipitation trends both in spatial distribution and time means. In a similar fashion, models captured well statistics of precipitation but they had difficulty in representing temporal variations of different precipitation intensity categories.（3） The well-documented 2nd half of the 20 th century surface summer cooling over the two river basins showed different associations with precipitation trends with higher anti-correlation between them over the U.S. region, implying different processes contributing to the cooling mechanisms of the two river basins.

On the surface fluxes characteristics and roughness lengths at Zhongshan station,Antarctica

Over Antarctica,surface fluxes play an important role in the local atmospheric dynamical processes.To reveal the surface fluxes characteristics and aerodynamic and thermal roughness lengths over Zhongshan station,Antarctica,this paper analyzes the data observed at the station during 3 March 2008 through 15 February 2009.It is found that easterlies dominated this site throughout the whole year,with a maximum(average)speed of 25(5.6)m s−1 at 3.9 m height,and the annual maximum(minimum)surface temperature reached 291.05(230.05)K,while the annual maximum(minimum)air-specific humidity was 4.1(0.05)g/kg at 3.9 m height.The maximum(minimum)values of seasonal mean temperature,humidity,each radiation components,sensible and latent heat flux occurred in summer(winter),while for the seasonal averaged wind speed andτthe minimums(maximums)appeared in summer(autumn).After comparing with a partially linear regression method for aerodynamic roughness length and four previous equations that derive thermal roughness length from surface Reynolds number,constant values of aerodynamic roughness length as 3.6×10^(−3)m and thermal roughness length as 1.2×10^(−4)m at this site were validated by using the other three level observations and suggested for future studies.

Combining Monte Carlo and Ensemble Probabilities in Tropical Cyclone Forecasts near Landfall

The Monte Carlo probability(MCP)model,which has been used for official tropical cyclone(TC)warnings to the public by the United States’National Hurricane Center(NHC),can estimate the probability of wind speed in the vicinity of a TC during the forecast period.It has been successful in the operational environment for many years.However,due to its strong dependence on a given forecast track(e.g.,forecast from the NCEP Global Forecast System),the MCP model may generate a poor probability map for TCs near landfall.In this study,we proposed and tested a modified MCP method for TC forecasts near landfall.We first adjusted the MCP model by adding limits to the direction angle and motion distance to deal with the substantial change in TC moving direction and the low wind speeds during landfall.Then,we combined ensemble probability maps generated from ECMWF,United Kingdom Met Office(UKMO),and NCEP ensemble forecasts,obtained from The International Grand Global Ensemble(TIGGE),into the MCP model to configure a modified MCP model.Wind speed probability maps for the 0-120-h forecast from both the original and modified MCP models are compared.It is found that the modified MCP model can provide a better wind speed probability map during landfall,especially at wind speeds of 20-64 kt near TC landfall.The results from this study prove the benefits of combining the MCP model with ensemble forecasting in potential applications for improved TC forecasts.