Construction of Forecast and Early Warning System of Meteorological and Geological Disasters in Qinghai Province

Based on the meteorological and geological disaster data, ground observation data set, CLDAS grid point data set, and EC, BJ and other model product data during 2008-2020, the temporal and spatial distribution characteristics of meteorological and geological disasters and precipitation were analyzed, and the causes of the occurrence of meteorological geological disasters and the deviation of model precipitation forecast were revealed. Besides, an objective precipitation forecast system and a forecast and early warning system of meteorological and geological disasters were established. The results show that meteorological and geological disasters and precipitation were mainly concentrated from May to October, of which continuous precipitation appeared frequently in June and September, and convective precipitation was mainly distributed in July-August;the occurrence frequency of meteorological and geological disasters was basically consistent with the distribution of accumulated precipitation and short-term heavy precipitation, and they were mainly concentrated in the southern and eastern parts of Qinghai. Meteorological and geological disasters were basically caused by heavy rain and above, and meteorological and geological disasters were divided into three types: continuous precipitation(type I), short-term heavy precipitation(type II) and mixed precipitation(type III). For type I, the early warning conditions of meteorological and geological disasters in Qinghai are as follows: if the soil volumetric water content difference between 0-10 and 10-40 cm is ≤0.03 mm^(3)/mm^(3), or the soil volumetric water content at one of the depths is ≥0.25 mm^(3)/mm^(3), the future effective precipitation reaches 8.4 mm in 1 h, 10.2 mm in 2 h, 11.5 mm in 3 h, 14.2 mm in 6 h, 17.7 mm in 12 h, and 18.2 mm in 24 h, and such warning conditions are mainly used in Yushu, Guoluo, southern Hainan, southern Huangnan and other places. For type II, when the future effective precipitation is up to 11.5 mm in 1 h, 14.9 mm in 2 h, 16.2 mm in 3 h, 19.9 mm in 6 h, 25.3 mm in 12 h, and 26.3 mm in 24 h, such precipitation thresholds are mainly used in Hainan, Huangnan, and eastern Guoluo;as it is up to 13.3 mm in 1 h, 15.5 mm in 2 h, 16.6 mm in 3 h, 19.9 mm in 6 h, 31.1 mm in 12 h, and 34.0 mm in 24 h, such precipitation thresholds are mainly used in Hehuang valley. The precipitation thresholds of type III are between type I and type II, and closer to that of type II;such precipitation thresholds are mainly used in Hainan, Huangnan, and northern Guoluo. The forecasting ability of global models for heavy rain and above was not as good as that of mesoscale numerical prediction model, and global models had a wet bias for small-scale precipitation and a dry bias for large-scale precipitation;meso-scale models had a significantly larger precipitation bias. The forecast ability of precipitation objective forecast system constructed by frequency matching and multi-model integration has improved. At the same time, the constructed grid forecast and early warning system of meteorological and geological disasters is more precise and accurate, and is of instructive significance for the forecast and early warning of meteorological and geological disasters.

Meteorological Characteristics of a Typical Dust Weather Process in the Eastern Qinghai-Tibet Plateau

Based on the comprehensive ground observation and the remote sensing data of Fengyun-4 satellite of a typical sand-dust weather process in the eastern part of the Qinghai-Tibet Plateau from November 26 to 27,2018,the weather situation,air mass trajectory,meteorological conditions,and pollution characteristics of this process were analyzed.The results show that the floating dust process was caused by the transmission of the northwest cold air flow in the Tarim Desert area,which caused dust and sand mixed with the Qaidam Desert particles to be transported to Xining.The wind field change caused by the difference of ground heat in the eastern plateau was a potential factor for dust transmission,and tropospheric subsidence,temperature inversion conditions,and the decrease in wind speed over Xining Station were the direct factors leading to the daily change of pollutant concentration in this process.

Analysis of Forecast Failure of a Regional Rainstorm in Qinghai

Based on the ground observation, ERA5 and other data, the regional rainstorm that occurred in northeastern Qinghai on the night of August 28, 2020 was analyzed. The results show that this precipitation occurred in the climate background of relatively high temperature, high humidity and extreme low pressure, and the precipitation process was divided into warm-area precipitation before the front and frontal precipitation, among which the warm-area precipitation was dominant, and it was a regional warm-area rainstorm. The global models, mesoscale models and forecasters as important operational reference all failed to make effective forecasts or prompts for the warm-area precipitation before the front in advance(24 or 12 h), the predicted precipitation was obviously small, and the predicted frontal precipitation by the models were obviously large. The western low-level meso-β-scale wind direction convergence system moving eastwards encountered the high-humidity area at the front of the meso-γ-scale wind speed convergence system to trigger this regional warm-area rainstorm. From the analysis of the mesoscale convergent system based on the vorticity budget equation, it is found that different terms played different roles in the process of warm-area rainstorm. The advective term dominated before the appearance of precipitation, which was favorable for the generation of mesoscale eddies. During the precipitation period, the torsion term and the convergence term were dominant. The torsion term was beneficial to the conversion of horizontal vorticity to vertical vorticity and the enhancement of precipitation intensity. Its maximum was generated 1-2 h earlier than the heavy precipitation. In the later period of precipitation, the convergence term was dominant, which was beneficial to the maintenance of precipitation. In the early stage of precipitation, the apparent heat source was located behind the apparent water vapor sink, which was conducive to the increase in the thickness of the heating column, and the precipitation intensity gradually increased. During the occurrence of heavy precipitation, the apparent heat source and the apparent water vapor sink basically coincided, and the latent heat released by condensation strengthened the upward movement, so that precipitation intensity increased. In this process, the water vapor mainly came from the southeast of the plateau(southwest airflow), followed by the plateau slope area(southeast airflow). During this regional warm-area rain that was wrongly predicted, the extreme minimum pressure, the torsional term in the vorticity budget equation and the abnormal water vapor transport have certain indications for the warm-area rainstorm.

Evaluation of Reanalysis Data Based on the Three-dimensional High-density Sounding Data of the Qinghai-Tibet Plateau

Based on the data of the third Qinghai-Tibet Plateau atmospheric science experiment from 2015 to 2017,the applicability of plateau weather systems and meteorological elements of two commonly used reanalysis data(NCEP/NCAR reanalysis data set,and ERA-Interim reanalysis data set)in the plateau was evaluated.Some conclusions are obtained as follows.Compared with EC reanalysis data,NCEP reanalysis data are more consistent with the scientific experimental data.The correlation of geopotential height is above 0.99,followed by temperature;The correlation of specific humidity is the worst.Seen from average deviation,geopotential height and temperature are both lower;for EC,the westerly and southerly winds are both weaker;for NCEP,westerly wind is weaker,while southerly wind is stronger;specific humidity is higher.From the perspective of monthly and seasonal distribution characteristics,the average deviation of geopotential height is larger in spring and summer,and that of temperature is slightly worse in late spring and early summer.In terms of wind field,EC deviation is more obvious in winter,while NCEP deviation is more obvious in late spring and early summer.Seen from spatial distribution,the deviations of geological height and temperature in the north of the plateau are smaller than those in the south of the plateau.For wind field,the westerly wind in the Qaidam Basin is weaker,and the southerly wind in the southern plateau is weaker.In vertical profile,the deviation of geopotential height at high levels is greater than that of low levels.The deviation of temperature and wind field is larger near the ground.The temperature at middle levels and the westerly wind at middle and high levels are smaller,and southerly wind is stronger for NCEP.The establishment of the three sounding stations(Gaize,Shenzha and Shiquanhe)is conducive to the discovery of plateau vortex and plateau shear line in the western plateau.The western plateau vortex and plateau shear line mostly appeared in the flood season.Most plateau weather systems were maintained within 24 h,and mainly appeared and disappeared in situ.The objective recognition rate of EC for plateau weather systems is higher than NCEP,so EC is more conducive to the diagnosis and analysis of evolution characteristics of plateau weather systems.

Analysis of Predictability of Local Rainstorm in Qinghai during August 19-20,2019

Based on conventional meteorological observation data,ECMWF model data,etc.,the causes of rainstorm in the northeast of Qinghai from the afternoon to the night of August 19,2019 were analyzed,and the causes and predictability of major forecast errors were discussed.The results show that there was high temperature,high humidity and high energy in the middle and low layers in the early period of rainstorm.As the subtropical high retreated eastwards,the high-altitude trough of the westerly belt and the vertical shear line of the plateau moved eastwards to make ground cold air move eastwards,and local short-term heavy precipitation appeared under the influence of this weather system.At the same time,the high-level dry and cold air moved into convective unstable areas.The wind speed at 700 hPa strengthened,and the low-level jet stream appeared to aggravate the instability of atmospheric stratification,which was more conducive to the generation of convection.The forecast results of precipitation based on various numerical models were significantly smaller,and the predicted western cold air was obviously weaker,which was also one of the reasons why the weak transportation of the western water vapor resulted in a small value of predicted precipitation.In the adjustment of model forecast,the proportion and amount of convective precipitation should be adjusted to be large,which has a certain indicating significance for the forecast of convective precipitation.In short-term nowcasting,the deviation of major weather systems predicted based on the model should be corrected in real time,and attention should be paid to the location of ground specific humidity and the convergence line.The falling area of heavy precipitation can be judged according to the high-value area of specific humidity,and the maximum of specific humidity appeared 1-2 h earlier than short-term heavy rainfall.

Structural Characteristics of the Spring Transverse Shear Line over the Qinghai-Tibet Plateau and the Influence Mechanism of the Upper-level Jet on Its Evolution

Based on the four-times-daily ERA-Interim data with the resolution of 0.75°×0.75°,the structure and evolution characteristics of a transverse shear line(TSL)over the Qinghai-Tibet Plateau in April 2017 were analyzed,and the influence mechanism of the frontogenesis and frontolysis caused by the upper-level jet on its evolution was also investigated.The results show that the TSL was mainly located near the axis of the positive vorticity zone,which was a low-value area of the wind speed.It was a shallow baroclinic system with weak ascending motion.In the vertical direction,the TSL extended to the lowest height at 00:00 and the highest at 18:00.In the horizontal direction,the length of the TSL in the east-west direction was relatively shorter during 00:00-06:00 and relatively longer during 12:00-18:00.Besides,the position of the TSL was slightly northward at 06:00 and slightly southward at 18:00.The moving direction of the TSL was generally consistent with that of the upper-level jet.In addition,the vertical stretching height of the TSL and the near-surface wind speed were positively correlated with the intensity of the upper-level jet.The calculation by frontogenesis function indicates that the frontogenesis(frontolysis)was conducive to the formation(weakening)and strengthening(dissipation)of the TSL.The horizontal deformation-induced and diabatic heating-induced frontogenesis were favorable for the formation of the TSL,while the middle-level horizontal convergence-induced and diabatic heating-induced frontogenesis were beneficial to its maintenance.Besides,the moving direction and baroclinicity of the TSL over the Qinghai-Tibet Plateau were determined by the horizontal deformation-induced frontogenesis.In the frontogenesis function,the terms of horizontal deformation and horizontal convergence together determined the position of the TSL,and the diabatic heating term was conducive to the upward extension of the TSL.

Study of a Horizontal Shear Line over the Qinghai–Tibetan Plateau and the Impact of Diabatic Heating on Its Evolution

Based on the 4 times daily 0.75°× 0.75° ERA-Interim data, the structural evolution of a Qinghai-Tibetan Plateau horizontal （east-west-oriented） shear line （TSL） during 15-19 August 2015 and the effect of diabatic heating on its evolution were analyzed. The results show that the TSL possessed a vertical thickness of up to 1.5 km （approxim-ately 600-450 hPa）, and was baroclinic in nature. Weak ascending motions occurred near the TSL, accompanied with more significant gradients in dew point temperature than in temperature. The TSL was characterized by diurnal vari- ations in its appearance and structure. It was relatively full in shape （broken） and was the lowest （highest） in vertical extent at 0000 （1800） UTC, and veered clockwise （anticlockwise） dttring 0000--0600 （1200-1800） UTC. When the north-south span of the TSL increased, it was prone to fracturing; and it disappeared when the dew point temperat-ure gradients to its either side decreased. When the TSL moved northward （southward）, its western （eastern） section broke up, while the eastern （western） section inclined to regenerate or merge. The TSL tended to move towards the positive vorticity areas with significant increases in vorticity. When the positive vorticity center moved down, the height of TSL decreased. Further analysis shows that the plateau surface heating dominated the vorticity attribute of the TSL and its movement, with different contributions from local variation, horizontal advection, and vertical advec-tion of the diabatic heating to the TSL at different heights.