Study On The Climatic Characteristics And Influence Of Sand-dust Weather In Northwest China

As one of the areas with frequent sand-dust event occurrences,The effect ofsand-dust events on coo-environment of Northwest China have been highly regarded bythe government and the whole society. On the basis of the statistics, diagnosis, andnumerical simulation, the sand-dust weather of Northwest China is studied.Results show that the climatic characteristics of sand-dust events in the NorthwestChina are: the numbers of sand dust days in the most part of the Northwest China ismore than 5 days. The high frequency areas with sand-dust occurrence days more than50 days are mainly in the deserts and their surroundings. The events are frequent inspring and scarce in autumn. The occurrence days of sand-dust in the last four decadesappears a generally decrease trend which is more significant in the high frequency areas.There is a transform from a relative frequent period to a relative scarce period in themiddle 1970s. The negative anomaly of sand dust days in the Northwest chinacompanied with the negative anomaly of geopotential height in the north Pacific, theabnormal strong 500hpa ridge of high pressure, and the abnormal high geopotentialheight field in the extratropical latitude of Asia, and vice versa. The typical EL Nine (LaNina)style of the sea surface temperature in spring of Pacific consist with thenegative(positive) anomaly of sand dust days in the same period.The key points of the sand-dust event prediction is obtained by use of thediagnosis, numerical analysis, and the synoptic characteristics of sand-storm weather:the sand dust event is triggered by the strong upper cold air, the vigorous developmentof the surface Mongolia cycle and its cold front, and the meso-scale shear-line. Intensesand storms occur in the right side of the front area of front part of 200hPa upper air jetstream center. Sand-storms appear in the unstable atmospheric stratification, wherein theevent companied with accumulation and release process of energy. CUACE-Dust modelsystem has the forecast ability of sand dust weather event.Helicity reflect the characteristics of dynamic field near the sandstorm, and thecombination of the horizontal and vertical helicity can provide instruction in sand-stormprediction, and pertinence to the prediction. On the one hand, the horizontal helicity hasmore instructive meaning for prediction, on the other hand, the vertical helicity canmore reflect the maintenance and development of the system, as well as the acuteextend of the synoptic phenomenal. The distribution of helicity over the sandstorm areawas negative at higher levels and positive at lower levels. The heavier is the sandstormas the positive helicity enhanced and the height increased. Strengthen of the positivevalue area of horizontal helicity occurred earlier than the sand-storm.Results show: sand-storm events have evident effect on the environments, such asair quality, acid rain, and radiation. Frequency of sand dust event in spring of Hexicorridor is positive relate to the PM₁₀ concentration in Lanzhou. Analysis via definition of index present that the 8.8% (13.9%, 23.1%) of the yearly(March, April) PM₁₀ massconcentration is the result of the PM₁₀ transportation from sand dust event of Hexicorridor to Lanzhou. The spatial distribution of acid rain in the northeast Qinghai-TibetPlateau is influenCed by sand dust, with the weak alkali or neutral pH value for theprecipitation in the high frequency areas with sand-dust. The small probability for acidaccompanied with relative more sand-dust in spring. The sand-dust events in Lanzhouand Xifeng stations can make pH value increased 0.7.During sand-dust events, turbidity of atmosphere increased significantly and theevents apparently influenCed the solar radiation. Scatter radiation increased12.66-18.00%, with net radiation, total radiation, reflection radiation and directradiation deCreased 6.68-45.79%,12.97-47.80%,13.19-57.49% and 47.81-87.45%,respectively, with respect to the clear sky. Strength of every radiation decreasedevidently in the vigorous period of sand-storm, with the significant decrease ofcorresponding surface temperature.