Mongolian Cyclone Research Articles

Heavy dust fall in Beijing, on April 16-17, 2006: Geochemical properties and indications of the dust provenance

A heavy dust fell in Beijing on April 16-17, 2006. The dust storm formed in middle and western Inner Mongolia, China, under a strong Mongolian Cyclone. During the dust fall, the near-surface wind speed was insignificant in Beijing. The minimal wind speed at ground level indicates that the dust must have been transported by upper northwestern winds, and the local dust of Beijing contributed little to dust fall. The lack of a contribution from local dust differed from previous dust fall events in Beijing. Therefore, this dust fall provides good information on the dust source. Dust samples colleted during this event and Pleistocene loess samples from the Beijing area were analyzed for magnetic susceptibility, bulk particle and quartz grain size distributions, bulk particle and quartz micro-textures, mineralogy, carbonate content, major element concentrations, trace element and rare earth element (REE) concentrations, and the oxygen isotope composition of quartz. The results indicate the following. (1) The dust of the April 2006 storm derives mainly from surface sediments in middle and western Inner Mongolia, with some minor contributions from anthropogenic emissions from coal combustion and mining. (2) The characteristics of the dust fall in China appear to vary with time and location, which has significance for palcoclimate reconstructions. (3) Many characteristics differ between the dust from 2006 event and Pleistocene loess in Beijing, and implying that the two have different sources. (4) The loess deposits found in Beijing and on the Loess Plateau also appear to differ in provenance.

Diagnosis and simulation of a rapidly developing cyclone related to a severe dust storm in East Asia

Mongolian cyclones are important to the outbreaks of severe dust storms in Northeast Asia. In this paper, we conduct a diagnostic study and a numerical simulation of a rapidly developing Mongolian cyclone that produced the April 5 to 7, 2000 severe dust storm in East Asia. The surface pressure of the cyclone decreased rapidly on April 5 to 6 causing strong surface winds. The diagnosis shows that the cyclone was a “dry cyclone”, as the convergence of moisture flux was weak and the baroclinic forcing was strong. The analysis of the Q vectors also reveals that ageostrophic wind was significant in the middle and upper part of the cyclone, resulting in strong vertical motion in the lower part. The three-dimensional structure of the cyclone is characterized by an ascending southern warm current and a descending northern cold current. This structure is favorable to the release of available potential energy and the intensification of the cyclone. In the second part of this study, we develop a coupled system of a dust emission scheme and a mesoscale numerical model (MM5V3) and applied the system to the simulation of the Mongolian cyclone. The main features of the cyclone identified from the diagnostic analysis are successfully reproduced. The predicted dust storm-affected area is found to be consistent with the meteorological observations and satellite remote sensing. It is shown that the coupled system is capable of predicting the spatial and temporal variations of the dust storm.

An Intensive Mongolian Cyclone Genesis Induced Severe Dust Storm

In this paper, a severe dust storm which occurred in northern China is presented and its associated physics investigated. The main sand source regions of this storm were from the Badanjilin Desert in western Inner Mongolia (IM), western Hunshandakend sand lands and the Gobi Desert in southern Mongolia. This dust storm process was a typical cyclonic dust storm, induced mainly by intensive development of a Mongolian cyclone rather than any other weather system. The formation of the strong surface winds was caused not only by the intensive development of a cyclone, and the passage of a cyclonic cold front, but also by a strong meso-scale pressure gradient. The former closely accorded with the severe dust storm while the latter induced the severe prefrontal dust storm. The dust raising mechanism could be described in the following manner: after obtaining much momentum from strong surface winds, the dust was raised upward by strong turbulence in the PBL and then by the systemic ascending motion of a cyclonic system. In addition, divergence-pumping in the upper troposphere indirectly transplanted dust upward.

Numerical Simulation of Synoptic Condition on a Severe Sand Dust Storm

By using observational data and MM5, an observational analysisand numerical study was conducted on the synoptic condition of a severe dust storm that was caused by a Mongolian cyclone whichoccurred from 6 to 8 April 2001. Results illustrated thatthe cyclogenesis was due to the isentropic potential vorticity (IPV) advection in the upper troposphere and the terrain modifiedbaroclinicity in the mid-lower troposphere. The Altai-Sayan complex of mountains blocked the lower level cold air and made the isentropic surface sharply steep. When the air slid down along the isentropic surface the increasing of baroclinicity anddecreasing of stability blew up the vertical vorticity development.The formation of the dust storm was a result of a cyclonic cold front passing across the area. The occurrence of this dust stormwas closely related to the strong surface wind, which was accompanied by a cold front passing, rather than the cyclogenesis, itself. Hence, the reason for the pre-front dust storm formulation was the formation of heating convection. Reasons behind the formation of a black storm (visibilitylower than 50 m), which occurred in the mid-north part ofInner Mongolia, lay in several aspects. Firstly, in thisarea the surface wind was strong, a direct result of thedownward transport in mid-lower troposphere. Secondly,the cold front passed over the effected area near sunsetso the air obtained much more surface heating to form adeeper mixed layer (ML). Thirdly, cooperation between thelower level wind and the terrain made the atmosphere inthis area and acquired the maximum advective contributionnecessary to form a deep post-front ML. The sensitivityexperiment revealed that surface heat flux was important to the frontal lifting. In addition, the forcing of surface heating wasalso seen as the primary forcing mechanism of frontogenesis. Meanwhile, removal of the surface heat flux made the atmosphericstratification became stable and the pre-storm ML very shallow,which weakened the strength of the dust storm.