Two different periods of high dust weather frequency in northern China

This study reveals that, during the period 1966-2014, dust weather frequency （DWF） in northern China （north of 30°N） features two high-DWF periods, in 1966-1979 （PI） and 2000-2014 （P2）, when the linear trend of DWF is removed during the study period. Here, DWF denotes the number of days of dust weather events in the spring season （March-April-May）, including dust haze, blowing dust, and dust storms, which occurred in northern China. The results show that the DWF is much higher in PI than in P2, with increased DWF distributed over southern Xinjiang, the central part of northern China. The main cause is the SST difference in the Atlantic and Pacific between the two periods. It is also found that a meridional teleconnection over East Asia in PI and a zonal wave-like pattern over Eurasia in P2 at 200 hPa play a significant role in the interannual variability in the two periods, respectively. SST over the subtropical North Atlantic （extratropical SST between the Norwegian and Barents seas） may partly contribute to the upper-level meridional （zonal） teleconnection in PI （P2）.

Relationship between thermal anomalies in Tibetan Plateau and summer dust storm frequency over Tarim Basin,China

The dust storm is the most important and frequent meteorological disaster over Tarim Basin, which causes huge damages on local social economics. How to predict the springtime and summertime dust storm oc- currence has become a hot issue for meteorologists. This paper employed the data of dust storm frequency and 10-m wind velocity at 35 stations over Tarim Basin and the reanalysis data from the National Center for Environ- mental Prediction and the National Center for Atmospheric Research （NCEP/NCAR） during 1961-2007 to study the relationship between dust storm frequency （DSF） in summer over Tarim Basin and the thermal anomalies in Tibetan Plateau in May by using the statistical methods, such as Empirical Orthogonal Function （EOF）, correlation and binomial moving average. The results show when negative anomalies in Tibetan Plateau and positive anomalies in its southern region are present along 30~N （the second mode of surface temperature anomalies by EOF decomposition） in May, the time coefficient （PC2） plays an important role in summer DSF variation and has a close relation with the summer DSF at both inter-annual and decadal time scales. When negative anomalies in Tibetan Plateau and positive anomalies are present in its southern region （PC2 in positive phase）, there is an anomalous anticyclone in North China, which weakens the northwest wind and is not beneficial for cold air moving from high latitude to the Tarim Basin, and the circulation pattern is hard to result in dust storm weather. Furthermore, the sea level pressure （SLP） increased over Tarim Basin and the direction of SLP gradient reversed, which resulted in the 10-m wind velocity slowing down, so the DSF decreased. From above all, it can be conclude that the thermal anomalies in Tibetan Plateau in May has important effects on the summertime dust storm frequency over Tarim Basin and the PC2 can be used as a prediction factor for the summertime dust storm occurrence.

Relationship between East Asian Monsoon and Dust Weather Frequency over Beijing

The relationship between dust weather frequency （DWF）, which denotes the number of days of dust weather events, over Beijing and the East Asian Monsoon （EAM） was studied using DWF data for Beijing during the period 1951-2006. Results show that, during this period, the blowing-dust weather frequency （BDWF）, as well as the indices of East Asian winter monsoon （EAWM） and East Asian summer monsoon （EASM）, all decreased considerably, with a t-test confidence level of 99%. The correlation coeffcients between the chosen EAWM index and BDWF over Beijing in winter and the following spring were 0.34 and 0.33, respectively, with significance levels of 0.01 and 0.02, respectively. For the chosen EASM index and BDWF, these correlation coeffcients were 0.51 and 0.45, respectively, with both at a confidence level exceeding 99.9%. With the linear trends removed, the values （in the same order as above） were 0.14, 0.14, -0.12, and -0.09, all not significant at the 95% confidence level. Clearly, the EAM relates mainly to DWF over long timescales. To a certain extent, the EAM might have some impact on DWF by affecting the associated surface air temperature and precipitation during the corresponding time period in sand-dust source regions at the interannual scale. A stronger （weaker） EAWM might advance （suppress） the occurrence of DWF, and the opposite for the EASM.

Possible influence of Arctic Oscillation on dust storm frequency in North China

This study has investigated the influence of Arctic Oscillation （AO） on dust storm frequency in North China in spring seasons during 1961-2007. There is a significant linkage between dust storm frequency and AO; a negative （positive） AO phase is related to an increased （decreased） dust storm frequency in North China. This relationship is closely related to changes in the cold air activity in Mongolia. The cold air activity exerts large impacts on the dust storm frequency; the frequency of cold air activity over Mongolia not only positively correlates with the dust storm frequency in North China, but also shows a long-term decreasing trend that is an important reason for the long-term decreasing of dust storm frequency in North China. The AO has large influence on the frequency of cold air activity over Mongolia; a negative （positive） AO phase is highly related to an increased （decreased） frequency of cold air activity over Mongolia, which results in an increased （decreased） dust storm frequency in North China.

Charge density fluctuation of low frequency in a dusty plasma

The charge density fluctuation of low frequency in a dusty plasma, which is derived from the longitudinal dielectric permittivity of the dusty plasma, has been studied by kinetic theory. The results show that the P value, which describes the relative charge density on the dust in the plasma, and the charging frequency of a dust particle Ωc, which describes the ratio of charge changing of the dust particles, determine the character of the charge density fluctuation of low frequency. For a dusty plasma of P<<1, when the charging frequency Ωc is much smaller than the dusty plasma frequency wd, there is a strong charge density fluctuation which is of character of dust acoustic eigen wave. For a dusty plasma of P>>1, when the frequency Ωc, is much larger than wd there are weaker fluctuations with a wide spectrum. The results have been applied to the ionosphere and the range of radius and density of dust particles is found, where a strong charge density fluctuation of low frequency should exist.

Seasonal Prediction of Spring Dust Weather Frequency in Beijing

In this paper, seasonal prediction of spring dust weather frequency （DWF） in Beijing during 1982–2008 has been performed. First, correlation analyses are conducted to identify antecedent climate signals during last winter that are statistically significantly related to spring DWF in Beijing. Then, a seasonal prediction model of spring DWF in Beijing is established through multivariate linear regression analysis, in which the systematic error between the result of original prediction model and the observation, averaged over the last 10 years, is corrected. In addition, it is found that climate signals occurring synchronously with spring dust weather, particularly meridional wind at 850 hPa over western Mongolian Plateau, are also linked closely to spring DWF in Beijing. As such, statistical and dynamic prediction approaches should be combined to include these synchronous predictors into the prediction model in the real-time operational prediction, so as to further improve the prediction accuracy of spring DWF in Beijing, even over North China. However, realizing such a prediction idea in practice depends essentially on the ability of climate models in predicting key climate signals associated with spring DWF in Beijing.

Links between winter dust over the Tibetan Plateau and preceding autumn sea ice variability in the Barents and Kara Seas

The Tibetan Plateau(TP)is characterized by heavily local dust activities,however,the mechanism of interannual variations of winter dust frequency over the TP remain poorly understood.Previous studies showed the autumn Arctic sea ice could significantly influence the winter climate over Eurasia.Whether autumn sea ice affects winter dust activity over the TP or not?Here,we used an integrated surface database to investigate possible mechanisms for interannual variability in the frequency of winter dust events above the TP.This variability,which is thought to be mainly caused by local dust emissions,shows significant correlations with sea ice concentration(SIC)in the Barents and Kara Seas during the preceding autumn.Low Barents-Kara SIC is accompanied by reduced snow depth over northern Eurasia between autumn and winter,which can enhance the Eurasian mid-latitude westerly jet stream.This strengthening increases the cyclogenesis and occurrence of strong surface wind speeds in winter,especially over the TP.In addition,a lower SIC is closely associated with reduced precipitation and snow cover in late autumn and winter over the TP,which in turn enhances warming of the land surface and reduces the area of frozen ground.These anomalies in atmospheric circulation patterns and local surface conditions promote dust events above the TP during winter.The ensemble means of Atmospheric Model Intercomparison Project experiments from Phase 6 of the Coupled Model Inter-comparison Project and the Community Atmosphere Model version 4 can generally reproduce the atmospheric circulation anomalies associated with decreased Barents-Kara SIC.This study reveals the crucial effect that SIC anomalies in the Barents and Kara Seas have on winter dust activities over the TP.