A dipole pattern of summer precipitation over the mid-high latitudes of Asia, which is characterized by opposing summer precipitation variations between the Mongolian and Northeast China(MNC) region and the West Siberian Plain(WSP), is found to be clear and stable on both interdecadal and interannual scales during 1981–2011. Spring snow cover anomalies over a small region within the WSP and the Heilongjiang River(HR) region are closely related to the variation of this dipole mode during the subsequent summer, and they can therefore be considered as forecasting factors. Our statistical results imply a potential process explaining the relationship between the spring snow anomalies and the summer rainfall dipole. Corresponding to the snow anomalies, Rossby waves propagate along a path from the WSP region, via the Mongolian Plateau, to the Stanovoy Range during summer. At the same time, Rossby-wave energy divergences and convergences along this path maintain and reinforce an anomalous cyclone and anticyclone pairing over the Asian continent, which is significantly linked to opposite summer precipitation anomalies between the MNC and WSP regions. Numerical experiments are needed to further confirm the above conjecture and demonstrate the detailed physical mechanisms linking the spring snow cover anomalies and summer precipitation dipole.
Impacts of land models and initial land conditions(ICs) on the Asian summer monsoon,especially its onset,were investigated using the NCEP Climate Forecast System(CFS).Two land models,the Oregon State University(OSU) land model and the NCEP,OSU,Air Force,and Hydrologic Research Laboratory(Noah) land model,were used to get parallel experiments.The experiments also used land ICs from the NCEP/Department of Energy(DOE) Global Reanalysis 2(GR2) and the Global Land Data Assimilation System(GLDAS).Previous studies have demonstrated that,a systematic weak bias appears in the modeled monsoon,and this bias may be related to a cold bias over the Asian land mass.Results of the current study show that replacement of the OSU land model by the Noah land model improved the model's cold bias and produced improved monsoon precipitation and circulation patterns.The CFS predicted monsoon with greater proficiency in El Nin o years,compared to La Nin a years,and the Noah model performed better than the OSU model in monsoon predictions for individual years.These improvements occurred not only in relation to monsoon onset in late spring but also to monsoon intensity in summer.Our analysis of the monsoon features over the India peninsula,the Indo-China peninsula,and the South Chinese Sea indicates different degrees of improvement.Furthermore,a change in the land models led to more remarkable improvement in monsoon prediction than did a change from the GR2 land ICs to the GLDAS land ICs.
The skewness of subsurface temperature anomaly in the equatorial Pacific Ocean shows a significant asymmetry between the east and west.A positive temperature skewness appears in the equatorial eastern Pacific,while the temperature skewness in the western and central Pacific is primarily negative.There is also an asymmetry of the temperature skewness above and below the climatological mean thermocline in the central and western Pacific.A positive skewness appears below the thermocline,but the skewness is negative above the thermocline.The distinctive vertical asymmetry of the temperature skewness is argued to be attributed to the asymmetric temperature response to upward and downward thermocline displacement in the presence of the observed upper-ocean vertical thermal structure.Because of positive(negative) second derivative of temperature with respect to depth below(above) the thermocline,an upward and a downward shift of the thermocline with equal displacement would lead to a negative temperature skewness above the thermocline but a positive skewness below the thermocline.In the far eastern equatorial Pacific,the thermocline is close to the base of the mixed layer,the shape of the upper-ocean vertical temperature profile cannot be kept.Positive skewness appears in both below the thermocline and above the thermocline in the far eastern basin.Over the central and eastern Pacific,the anomalies of the subsurface waters tend to entrain into the surface mixed layer(by climatological mean upwelling) and then affect the SST.Hence,the positive(negative) subsurface skewness in the far eastern(central) Pacific may favor positive(negative) SST skewness,which is consistent with the observational fact that more La Nia(El Nio) occur in the central(eastern) Pacific.The present result implies a possible new paradigm for El Nio and La Nia amplitude asymmetry in the eastern Pacific.
In this study, the effect of the tropical North Atlantic (TNA) sea surface temperature (SST) variation in inducing the circulation anomaly in the Indo-East Asian monsoon (IEAM) region is investigated through the observational analysis and numerical model-ing. The observational analysis shows that the TNA summer SST is positively correlated with the preceding winter Ni?o3 SST and is simultaneously correlated with the circulation in the IEAM region. The simultaneous circulation pattern resembles that of the ENSO-decaying summer. The positive correlation between the TNA SST and the Ni?o3 region SST is primarily ascribed to the surface latent heat flux and short wave radiation anomalies induced by the ENSO teleconnection. Coupled general circulation model experiments show that, while including the air-sea coupling in the Atlantic, the model can reproduce the main features of the IEAM circulation, such as an anomalous anticyclone over the western North Pacific (WNP) and southerly anomalies over southeast China. While the climatological Atlantic SST is prescribed, the circulation over the WNP displays a significantly dif-ferent pattern, with an eastward migration of the WNP anticyclone and the associated northerly anomalies over southeast China. It is argued that anticyclonic shear and Ekman divergence associated with the atmospheric Kelvin wave response to the TNA warm SSTA forcing is the primary mechanism for the generation of the anomalous anticyclone in WNP. The results presented in this study provide a teleconnection pattern between TNA and short-term climate variability in IEAM region.
As the summit of the Antarctic Plateau, Dome A has been received international attentions.In this paper, observational data of an automatic weather station (AWS) at Dome A in 2005–2007 were used to analyze the seasonal variations of air temperatures near the ground and snow temperatures within a depth of 10 m. Analyses on the air temperatures show a typical feature of the coreless winter, and strong inversion maintains during the long winter. Accordingly the stratification near the ground is dominated by the near-neutral stable states. Seasonal fluctuations of the snow temperature decrease in amplitude and lag in phase with depth increasing, which leads to distinct seasonal temperature profiles within the depth of 10 m. Measurements show the mean annual air temperature near ground is about 5°C higher than the 10 m firn temperature due to the strong inversion near the ground. However, our estimation of the annual mean of air temperature at the ground based on the boundary layer theory is close to the mean 10 m firn temperature. The lowest air temperature (–82.7°C) currently measured at the Dome A is not the lowest one ever recorded in Antarctica, but the extremely low mean 10 m firn temperature (–58.2°C) indicates very low ground temperature. Given the prominent inversion near the ground, it is expected that Dome A might house the lowest ground temperature on the planet.
A vertical one-dimensional numerical model for heat transferring within the near-surface snow layer of the Antarctic Ice Sheet was developed based on simplified parameterizations of associated physical processes for the atmosphere, radiation, and snow/ice systems. Using the meteorological data of an automatic weather station (AWS) at Dome A (80°22′S, 70°22′E), we applied the model to simulate the seasonal temperature variation within a depth of 20 m. Comparison of modeled results with observed snow temperatures at 4 measurement depths (0.1, 1, 3, 10 m) shows good agreement and consistent seasonal variations. The model results reveal the vertical temperature structure within the near-surface snow layer and its seasonal variance with more details than those by limited measurements. Analyses on the model outputs of the surface energy fluxes show that: 1) the surface energy balance at Dome A is characterized by the compensation between negative net radiation and the positive sensible fluxes, and 2) the sensible heat is on average transported from the atmosphere to the snow, and has an evident increase in spring. The results are considered well representative for the highest interior Antarctic Plateau.
CHEN BaiLian1,3, ZHANG RenHe2, SUN ShuFen1, BIAN LinGen2, XIAO CunDe4,2 & ZHANG TingJun5 1 Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
