Current Issue

• Characteristics of Surface Energy Exchange in Emei Mountain Area on the Eastern Qinghai-Tibetan Plateau in Winter
• Zhao Lü;Maoshan LI;Xiaoran LIU;Shucheng YIN;Xingyu SONG;Wei FU;Lingzhi WANG;Lei SHU
• 2020 Vol. 39 (3): 445-458.  DOI:10.7522/j.issn.1000-0534.2019.00087.
• Abstract ( ) HTML ( ) PDF (4420KB) ( )
• This study analyzed the annual variation characteristics of the meteorological elements of the near surface data in the Emei Mountain area, the eastern margin of Qinghai-Tibetan Plateau.Its surface energy exchange were discussed by using eddy covariance, temperature prediction-correction (TDEC) and ordinary least square method.Also we compared the results of Emei site with that of Danka and Pailong Station, which located in the southeastern Tibetan Plateau.Sensible heat flux is the dominator of the land surface energy balance at Emei Mountain area in winter.The each component of surface radiation have a single peak in its diurnal variation.The peak value of shortwave radiation in Emei Mountain area appears around at 13:00 (Beijing Time, the same as after), while the long wave radiation reaches its peak value at about 14:00, one hour later than that of shortwave radiation.The monthly variation of surface albedo is evident, and its diurnal variation appears to be "U" shape.The value after sunrise and before sunset has a constant variation, which is smaller than other times.The albedo values after sunrise are not equal to that before sunset.The monthly average of surface albedo is 0.29.The phenomenon of non-closure-energy in Emei Mountain area is very obvious, and the energy closure has a notable difference between day and night time.Taking into account of the heat storage in the 0~5 cm soil layer, the best closing degree for daytime is 67.22% and nighttime is 65.09%.Comparative analysis with Danka Station and Pailong Station in southeastern Tibet shows that: The daily peak value of surface radiation at Pailong and Danka Station is later than that that at Emei Mountain Station.The surface albedo of Emei Mountain Station is higher than that of Danka and Pailong Station.The monthly variation of albedo at Emei Station is more significant than other two Tibetan sites.Emei Mountain site locates on the eastern margin of the Qinghai-Tibetan Plateau.The surface energy is greater than some of the sites on Qinghai-Tibetan Plateau.

• Temporal and Spatial Characteristics and Possible Causes Research of Qinghai-Tibetan Plateau Warming from 1980 to 2016
• Ying WEI;Keqin DUAN
• 2020 Vol. 39 (3): 459-466.  DOI:10.7522/j.issn.1000-0534.2019.00121.
• Abstract ( ) HTML ( ) PDF (5750KB) ( )
• In order to fully detect the temporal and spatial temperature changes on the Qinghai-Tibetan Plateau (QTP) during 1980-2016, The monthly mean surface air temperature at 2 m from the JRA-55 (TJ), ERA-Interim (TE) and MERRA (TM) were respectively compared with those observed value at meteorological stations in the QTP.All the data sets reveal QTP has experienced significant warming, with the annual warming trends of 0.52 (TO), 0.37 (TJ), 0.29 (TE) and 0.26 (TM) ℃·(10a)^-1, respectively.By comparison the annual and seasonal variations and trends of three reanalysis data with TO, it is found that the applicability of TJ is better than TE and TM in the eastern QTP.Then, TJ can be used to make up for the lack of observation in the western QTP.Generally, TJ shows there is a “dual-center” warming zone in the whole QTP, and the warming center in winter moves southward contrast to in summer.The maximum warming rate [0.9 ℃·(10a)^-1]in winter was larger than that[0.8 ℃·(10a)^-1] in summer.In addition, the summer warming trend in northern QTP is much higher than that in southern QTP, which is maybe related to latent heat caused by the precipitation change.While the highest warming rate in winter occurs on the central western QTP, which is may caused by the increase of net radiation budget due to the snow-albedo feedback.

• Analysis on the Source and Transport Characteristics of Moisture in Naqu of the Qinghai-Tibetan Plateau in Summer
• Yuting ZENG;Yu ZHANG;Ke ZHOU;Yuqi YAO;Linfeng YANG
• 2020 Vol. 39 (3): 467-476.  DOI:10.7522/j.issn.1000-0534.2019.00120.
• Abstract ( ) HTML ( ) PDF (5172KB) ( )
• As the Asian Water Tower, it’s of great significance to study the precipitation sources of the Qinghai-Tibetan Plateau for water security and water resources utilization in China.In order to study the characteristics of summer moisture transport in the middle of the plateau and understand the regional water cycle.In this paper, the daily data set of China's surface climate data and the HYSPLIT Lagrangian model driven by GDAS data are used to analyze the moisture transport track and the track of different grades of precipitation in summer of 2014 in Naqu area.Using the cluster analysis to get the moisture passages and the paticle tracking analysis to calculate the moisture contribution.The results show that, There are obvious monthly and ten day changes in the moisture transport trajectories in summer, which is mainly caused by the northward advance of summer monsoon.The Indian Ocean, the Arabian Sea, the Bay of Bengal, the Atlantic Ocean and Central Asia are the five main moisture transport passages.There are southern and western paths for light rain and moderate rain, but only southern paths for heavy rain.The moisture transport in the ocean plays a decisive role in the precipitation level.The area with high moisture source one day ago is the Yarlung Zangbo River Basin.The area with high moisture source three days ago is the border between India and Badan.The moisture source of heavy rain is more concentrated than that of light rain and moderate rain.There is a good correspondence between the region of moisture contribution concentration and the end point of moiture trace.In a nutshell, the moisture sources of different grades of precipitation are different.

• Projected Changes of Precipitation over the Qinghai-Tibetan Plateau Based on Dynamical Downscaling
• Hongwen ZHANG;Yanhong GAO
• 2020 Vol. 39 (3): 477-485.  DOI:10.7522/j.issn.1000-0534.2019.00125.
• Abstract ( ) HTML ( ) PDF (4071KB) ( )
• The General Circulation Models (GCMs) are not easy to reproduce the temporal-spatial patterns of precipitation in Qinghai-Tibetan Plateau (QTP) due to its current coarse resolution.To meet the requirement of high-resolution datasets for many applications, dynamical downscaling modeling (DDM) has been developed and proven to be an essential tool for achieving high-resolution climate data in study domain.DDM using a regional climate model WRF driven by a general circulation model CCSM4 has been adopted, the downscaling results for the historical period (1998 -2005) are evaluated for the wet season total precipitation rate and convective precipitation fraction over the QTP.The variations of total precipitation, stratiform precipitation and convective precipitation projected by CCSM4 and WRF are also analyzed.The results show that, compared with the coarse-resolution forcing, the DDM is able to better capture the spatial and elevation patterns of wet season total precipitation rate and convective precipitation fraction over the QTP in 1998 -2005.Compared with the uniform increase in CCSM, WRF also projects increasing precipitation for the future period 2070 -2099 under the two Representative Concentration Pathway (RCP) scenarios 4.5 and 8.5, with an increase in the northern QTP and a decrease in the southern QTP, the increase of total precipitation in northern QTP basically resulted from the increased convective precipitation, while the reduction of stratiform precipitation was the main reason for the reduced total precipitation in the southern QTP.Overall, regarding the entire TP, the contribution of increased convective precipitation was far larger than reduced stratiform precipitation to the total precipitation, and which was predominantly seen at the altitude below 4000 m.

• Evaluating Performance of Noah-MP LSM with GLDAS Forcing Data over Qinghai-Tibetan Plateau
• Wei HU;Weiqiang MA;Yaoming MA;Zhipeng XIE
• 2020 Vol. 39 (3): 486-498.  DOI:10.7522/j.issn.1000-0534.2019.00060.
• Abstract ( ) HTML ( ) PDF (3307KB) ( )
• Driven by GLDAS forcing data, the Noah-MP land surface model is used to evaluate its performance in simulating sensible and latent heat flux at six observation stations (Qomolangma Atmospheric and Environmental Observation and Research Station, QOMS; Nam Co Monitoring and Research Station for Multisphere Interactions, NAMOR; Ngari Desert Observation and Research Station, NASDE; Southeast Tibet Observation and Research Station for the Alpine Environment, SETS; Muztagh Ata Westerly Observation and Research Station, MASWE; Nagqu Station of Plateau Climate and Environment, NPCE) of different regions over Qinghai-Tibetan Plateau.The results with default multiple parameterization options indicate that comparing with the observations, the sensible heat flux is overestimated at most stations and in QOMS’s winter and spring, but underestimated in summer and autumn at this site.The latent heat flux is distinct in different stations and seasons: With better result at SETS, overestimated at QOMS and in NASDE’s spring, underestimated at MASWE, in NAMOR’s autumn and winter and NPCE’s summer.By analyzing the sensitivity of simulation results with different multiple parameterization options to select better combinations of these options which are more suitable for each station.New combinations give better root mean square error and correlation coefficient to simulations at a whole year level, but specific seasons at some stations have larger errors.This method provides accurate information of energy exchange and a reference for land surface and coupling models to the simulate heat source at these sites.

• Analysis of Precipitation Recycling Ratio Based on GLDAS and Reanalysis Data over the Qinghai-Tibetan Plateau
• Yu XU;Yanhong GAO
• 2020 Vol. 39 (3): 499-510.  DOI:10.7522/j.issn.1000-0534.2020.00013.
• Abstract ( ) HTML ( ) PDF (1867KB) ( )
• Precipitation recycling ratio is the local evaporation that contributes to the local precipitation.It is an indication of land-atmosphere interaction over the Qinghai-Tibetan Plateau (QTP).This study was based on the Global Land Data Assimilation Systems (GLDAS) and the ERA-Interim (ERAI) data by using the Quasi-isentropic backward trajectory (QIBT) model.The study used the precipitation and evaporation from the GLDAS and other variables from the ERAI data to run the QIBT model.The precipitation recycling ratio was analyzed in 2001, a climatological averaged precipitation year.To evaluate the influence of the precipitation and evaporation to the results of precipitation recycling ratio, two tests were applied.One is to replace the precipitation and evaporation from the GLDAS with that from the ERAI.After the precipitation and evaporation in the GLDAS were replaced with that in the ERAI, the influence of the replacement was evaluated.Another is to replace the precipitation and evaporation in 2001 with that in extreme wet and dry years during 1982 -2011 (30 years).The variations of precipitation recycling ratio in extreme wet and dry year were also evaluated.The results are as follows: Precipitation recycling ratio in the northwest is stronger than that in the southeast over the QTP.The average precipitation recycling ratio is 0.42 over the QTP with the precipitation and evaporation from the GLDAS.Precipitation recycling ratio in some regions in the northern part of the QTP is larger than 0.50.Precipitation recycling ratio is 0.28 when the precipitation and evaporation in the GLDAS were replaced with the precipitation and evaporation in the ERAI.Precipitation recycling ratio is 0.31 for extreme dry year and 0.25 for extreme wet year.Precipitation recycling ratio is stronger in the extreme dry year than in the extreme wet year.The influence of replacement from GLDAS to ERAI is larger than that of replacement from normal year to extreme years.The higher precipitation in the ERAI than the GLDAS is the reason for the lower precipitation recycling ratio for the ERAI.Apparently, precipitation overestimation is responsible for the underestimation of precipitation recycling ratio in the ERAI.The deeply reason is that hourly precipitation in the ERAI is different from that in the GLDAS.ERAI underestimates the small and medium rainfall events, and overestimates the heavy rainfall events at the same time.In conclusion, the accuracy of precipitation is the most important factor in the study of the precipitation recycling ratio over the Tibetan Plateau.

• Applications and Evaluations of Dynamic Root Scheme with Carbon-Water-Nitrogen Interactions in Land Surface Model SSiB4
• Yifan ZHANG;Xin MIAO;Weidong GUO
• 2020 Vol. 39 (3): 511-522.  DOI:10.7522/j.issn.1000-0534.2020.00005.
• Abstract ( ) HTML ( ) PDF (5175KB) ( )
• Root system is an important part of vegetation. The dynamic changes of root system can change soil moisture by adjusting the amount of water absorbed from root system, and then affect the biophysical processes such as soil evaporation and the biochemical processes such as transpiration and photosynthesis of vegetation. Eventually, the material cycle and the hydrothermal cycle of the ecosystem are changed by the dynamic changes of root system accordingly. In this study, soil water stress and soil nutrient (nitrogen) stress were considered to simulate the dynamic distribution of root carbon in different soil layers, and the dynamic change of root system was characterized by the ratio of carbon content in root system. Based on SSiB4 model, the single-point simulation experiment was carried out at BRSa3 site in Amazon region and CN-Qia site in Qianyanzhou, China to study the effects of dynamic root system scheme on the simulation of soil moisture and land-atmosphere flux. The results showed that the dynamic distribution of root enables more soil water to be absorbed, which improved the simulation effect of shallow soil moisture, and then improved the simulation accuracy of carbon dioxide flux, sensible heat flux and latent heat flux. At the BRSa3 and CN-Qia sites, the correlation coefficients between the observed and simulated daily mean values of soil moisture were increased by 0.02 and 0.04, respectively, and the correlation coefficients of carbon dioxide were increased by 0.76 and 0.13, respectively, which all passed the 99% significance test. The simulation of carbon absorption capacity of BRSa3 site in dry season and CN-Qia site in summer has been improved, and the absolute deviation was improved by 33%, 106%, respectively. The correlation coefficients between observed and simulated daily mean carbon dioxide flux were increased by 0.17 and 0.26, which passed the 99% significance test. In general, all the variables were closer to the observed values after considering the dynamic root system scheme during the simulated time, and the improvements of soil moisture and carbon dioxide flux were more evident than that of sensible heat flux and latent heat flux. The indirect effect of soil moisture on sensible heat flux and latent heat flux through physical processes of soil may be the main reason for the differences of the results. The improvements were more evident at BRSa3 site. The root depth and structure of different vegetation cover types may be the main reason for the differences of the results.

• Simulate of Convective Boundary Layer Characteristics in the Loess Plateau by WRF Large-Eddy
• Xuetao LI;Jiening LIANG;Qi GUO;Lili XU;Lei ZHANG
• 2020 Vol. 39 (3): 523-531.  DOI:10.7522/j.issn.1000-0534.2019.00050.
• Abstract ( ) HTML ( ) PDF (7374KB) ( )
• The vertical transport of physical quantities caused by atmospheric turbulence plays an important role in the atmospheric process.Studying the characteristics of the convective boundary layer is of great significance for analyzing the diffusion conditions of pollutants, understanding the exchange mechanism of materials and energy between land and air, and improving the ability of numerical model simulation.Due to the limited number of flux observation stations and low spatial-temporal resolution in many regions, in order to study the structure and characteristics of the atmospheric boundary layer in the Loess Plateau, the Weather Research and Forecasting Model (WRF) and the WRF Large-Eddy Simulation (WRF-LES) are nested.The characteristics of the boundary layer structure driven by heat under the condition of summer temperature and humidity on the Loess Plateau were analyzed.The results show that: (1) The surface wind field and temperature field simulated by WRF-LES can display the typical turbulent structure of the boundary layer well, and the simulation results of other meteorological elements also conform to the boundary layer law.(2) The vertical turbulence intensity is the highest at the height of 1000 m where the top of the mixed layer is located.The strong entrainment results in a reduction in the scale of the turbulence and an increase in the number of vortices.(3) Under the parameterization scheme selected in the simulation area, the default value of 0.1 m is replaced by the actual roughness in summer of 0.062 m.It is found that the simulated temperature using the actual roughness is 0.4 K lower than before, which is closer to the observed data in the center of the simulated area, indicating that the reasonable roughness is important to improve the simulation of WRF-LES.

• Quantitative Analysis of Changes of Summer Extremes Temperature and Precipitation Days over China with Respect to the Mean Temperature Increase
• Juan LI;Huiping YAN;Zhiwei ZHU
• 2020 Vol. 39 (3): 532-542.  DOI:10.7522/j.issn.1000-0534.2019.00042.
• Abstract ( ) HTML ( ) PDF (5101KB) ( )
• The frequency of extreme high temperature, extreme low temperature and extreme precipitation are to a large extent the response to the global mean temperature.Using the Homogeneous temperature data at 549 stations and precipitation data at 559 stations over China, the changes of summer extremes temperature and precipitation days over China with respect to the mean temperature increase are quantitative analyzed.Results show that: The national average changes of extreme high temperature, extreme low temperature and extreme precipitation days are 5.69, -5.3 and 0.69 days for every Celsius degree increase of the global mean temperature; From regional aspect, for every Celsius degree increase of the global mean temperature, the extreme high temperature days increased 8~10 days in southeastern China and Sichuan province, the extreme low temperature days decreased 10 days in northeastern China, and the number of days of extreme precipitation in the northwest of China has the greatest increase that reaches 4~6 days.Based on above results, using projected global mean temperature from five global coupled climate models, the amount of variation of these climate extremes is largest under RCP8.5 (Representative Concentration Pathways 8.5) scenarios.Under RCP8.5 scenarios, the national average of the number of days of extreme high temperature, extreme low temperature and extreme precipitation in China will increase 23 days, decrease 22 days and increase 3 days respectively in the next 100 years.As to region, the number of days of extreme high temperature will increase 42 days in the south of China, the number of days of extreme low temperature will decrease 33 days in the north of China and the number of days of extreme precipitation will increase 16 days in the northwest of China under RCP8.5 scenarios in the next 100 years.The above results suggest that a series of measures tackling climate change are imperative.

• Simulation Analysis on Retrieving Capabilities for Rain Drop Size Distribution and Air Vertical Motion with Single and Dual Wave Length Cloud Radars
• Chenyu ZHENG;Liping LIU
• 2020 Vol. 39 (3): 543-559.  DOI:10.7522/j.issn.1000-0534.2019.00126.
• Abstract ( ) HTML ( ) PDF (9165KB) ( )
• The factors such as the turbulence and the sensitivity of radar detection affect, the Doppler spectral and, introduce error of the air vertical motion velocity and Rain Drop Size Distributions (DSD) retrievals with single wavelength cloud radar.However, the dual-wavelength cloud radar, which uses the differences of reflectivity spectra density for two wavelengths due to Mie scattering, not only improves the detection accuracy of the air vertical motion velocity and DSD, but also reduces the errors of the attenuation correction.A Ka/Ku dual-wavelength cloud radar in Chinese Academy of Meteorological Sciences was used to observe clouds and precipitations in Longmen, Guangdong Province.In this paper, under the assumption of the Gamma’s DSD, the effects of temperature and turbulence on the ratio of Ka-band and Ku-band reflectivity density spectra and their relationships with DSD parameters were analyzed, the effects of the sensitivity of the cloud radar on retrieved air vertical velocity, DSD and attenuation correction were simulated, The advantages of the Ka/Ku dual-wavelength radar on detecting micro-precipitation dynamics and microphysical parameters were discussed.The results show that, the variations of temperature affect the value of maximum ratio of the power spectrum for the two bands, but don’t affects the peak position.The effects of turbulence on the peak position are less than 0.5 m·s^-1.Secondly, the effects of turbulence, and reflectivity sensitivity on air vertical velocities retrieved by single-band cloud radar are far greater than that by dual-wavelength cloud radar.Turbulence underestimated the air vertical velocity and the low, radar sensitivity overestimated it.Thirdly, for single wavelength cloud radar, turbulence expanded the DSD, underestimated the number contend for small drops, liquid water content (LWC) and attenuation coefficient.Low radar sensitivity narrowed the DSD, overestimated the number contend for small drops, LWC and attenuation coefficient.Finally, the precipitation cases during April 15 and 16, 2019 were chosen to examine the retrieval of air vertical motion and compared with the simulation result.The work provides base for retrieval of the microphysical and dynamic parameters of cloud and precipitation with both single-band and dual-band cloud radars.

• Characteristics and Mechanism of Monsoon Circulation Anomalies in Extreme Autumn Rain Over West China in 2017
• Yuanyuan BAO;Yong LI;Zhiming KANG
• 2020 Vol. 39 (3): 560-569.  DOI:10.7522/j.issn.1000-0534.2019.00056.
• Abstract ( ) HTML ( ) PDF (8201KB) ( )
• NCEP/NCAR reanalysis data and NOAA OLR, Sea Surfact Temperature Anomalies (SSTA) data were used here to analyze the anomalous features of summer monsoon circulations in 2017 with extremely strong autumn precipitation Huaxi over western China, and to explore the mechanisms.The results show that WPSH is stronger and more northwestward, SAH (South Asia High) is stronger and more northeastward, Southwest Monsoon and Southeast Monsoon are both stronger, converge to Huaxi and meet with dry air, and work together to form an extreme strong autumn rain.The SST in the western equatorial Pacific and the Middle East have the positive and negative anomalies contrasted sharply, resulting in a strong Walker circulation, which made the typhoon in the western equatorial Pacific and the South China Sea active and formed a strong heat source.The central ascending airflow forms a strong secondary circulation with the tropical subsidence airflow south of 10°S; Various factors jointly strengthen WPSH and the southeast monsoon and guide the western Pacific and South China Sea water vapor into Huaxi.The cold air of Qinghai-Tibetan Plateau was weak with strong sensible heat.The convective and condensation latent heat was strong over northeastern Qinghai-Tibetan Plateau and Huaxi.So that the heat source was obviously stronger with significantly higher upper middle level temperature.It is beneficial to SAH, WPSH.It is another important reason for extreme heavy rain over Huaxi.In this case, the anomalous variation of the equatorial Pacific SST occurred in the late summer, one month before WPSH’s changing from weaker to stronger and is particularly important for short-term climate prediction and extended forecast.

• Study on the Impacts of DSD Parameters on Precipitation Estimation Using Dual-Frequency Radar
• Shengnan LIU;Gaili WANG
• 2020 Vol. 39 (3): 570-580.  DOI:10.7522/j.issn.1000-0534.2019.00092.
• Abstract ( ) HTML ( ) PDF (3828KB) ( )
• Compared with Doppler radar， which uses radar reflectivity-rainfall rate (Z-R) relationship to estimate precipitation rates， the dual-frequency radar can provide more accurate estimates of precipitation rates based on retrieving the Rain Drop Size Distribution (DSD) parameters.However， actual DSD spectra varies with time and space and is difficult to be described accurately.The purpose of this study is to evaluate the retrieval errors caused by DSD models adopted in Ku/Ka-band dual-frequency radar retrieval.Based on continuous summer DSD data from PARSIVEL disdrometer at Longmen and Naqu observatories， the radar effective reflectivity factors at the Ka and Ku bands are calculated.Then， the median mass-weighted diameter D_m， attenuation coefficients k and rain rates R obtained from the DSD estimated by dual-frequency techniques are compared with those directly computed from DSD spectra measured by the disdrometer to investigate the impact of DSD model on the dual-frequency retrieval techniques and compare the differences between different regions.Overall， a gamma DSD model with fixed μ values of 2， 3 or 4 could yield consistent and fairly accurate retrievals， although the impacts of DSD parameters on the dual-frequency radar retrieval technique in Naqu and Longmen regions are different.In Longmen region， the relative biases of the retrieved D_m， the Ka-band attenuation coefficient k_Ka， the Ku-band attenuation coefficient k_Ku and R are less than ±10% bias when the shape factor μ of the gamma distribution ranges from 2 to 4.In terms of k_Ka and rain rate of 5~40 mm·h^-1， the Gamma DSD model with μ=3 in Longmen region could yield the best accuracy and the relative bias fluctuates around 0， while the Gamma DSD model with μ=4， 6 in the Naqu region could produce the smallest errors.

• Analysis on the Impact of ENSO Events Seasonal Evolution on Summer Rainfall Anomalies in Southwest China
• Yishu PANG;Ningsheng QIN;Chunxue WANG;Yu LUO
• 2020 Vol. 39 (3): 581-593.  DOI:10.7522/j.issn.1000-0534.2019.00044.
• Abstract ( ) HTML ( ) PDF (9445KB) ( )
• Based on monthly summer precipitation at 120 stations in Southwest China, monthly Ni?o3.4 indices from CPC, monthly circulation data from NCEP/NCAR and other meteorological data, the influence of ENSO event evolution on summer precipitation in southwest China and its mechanism are analyzed in this paper.As the results shown, the attenuation of ENSO events has an important effect on Precipitation in Southwest China.This effect closely relates to the end season of ENSO events and mainly due to the influence of SST in the equatorial Middle East Pacific on Philippine convective activities, which continuously modulate the West Pacific Subtropical High (WPSH).In El Ni?o (La Ni?o) decay years, the WPSH develops stronger and more southwest (weaker and more northeast) due to more (less) energy releases in the equatorial Middle East Pacific Ocean.That strengthens (restrains) the transport of water vapor from the South China Sea, and affects the water vapor transportation from the Bay of Bengal and then affects the anomalous distribution of precipitation in southwest China.Moreover, this influence is significant in more area of Southwest China with the delay of the end season of ENSO events, especially in El Ni?o decay years.For the cumulative release effect of energy, the monthly cumulative SST in the zone of Ni?o3.4 from pre-September is better to indicate the change of the summer WPSH than monthly SST.When the accumulated SST in April and May exceeds (±0.5), its sign consistency rate with the area and intensity index of summer WPSH is 100%.Thus, the summer abnormal precipitation in Southwest China could be judged from the intensity and magnitude of WPSH which could be forecasted with the accumulated SST.

• Assessment of Satellite and Reanalysis Precipitation Data in Chongqing
• Yan YAN;Gang LIU;Jun HE;Dexian FANG;Zheng WU;Shaoying CHEN;Jianping TANG
• 2020 Vol. 39 (3): 594-608.  DOI:10.7522/j.issn.1000-0534.2019.00040
• Abstract ( ) HTML ( ) PDF (10056KB) ( )
• The hourly precipitation data observed at 34 gauge stations in Chongqing during 1998-2012 is compared with the satellite products [Tropical Rainfall Measuring Mission (TRMM), Climate Prediction Center morphing technique (CMORPH)] and reanalysis data [ECMWF Re-Analysis Interim (ERAIN), Modern-Era Retrospective Analysis for Research and Applications (MERRA), Climate Forecast System Reanalysis (CFSR), Japanese 55-year Reanalysis (JRA55)].The reliability of the precipitation products in high spatiotemporal resolution is analyzed, and the accuracy in diurnal variation is also evaluated.The results show the daily precipitation in Chongqing is generally overestimated by the reanalysis data while the satellite products show agreement with the observations.TRMM is accurate and close to the observational data in the southwest and southeast.CMORPH works best in the northeast while underestimates the rainfall in the other areas.There are evident differences in precipitation intensity and frequency between the satellite and observational data, while the reanalysis data appears to be in agreement with the observations.The peak time of precipitation diurnal variation is mostly from midnight to dawn and displays a hysteresis from the southwest to northeast.The precipitation amount (PA), intensity (PI) and frequency (PF) in the satellite products show the hysteresis from the southwest to northeast, too.There is significant difference in diurnal cycle of precipitation between the reanalysis and satellite data over complex terrain.The reanalysis data overestimates the precipitation from 12:00 to 17:00(Beijing time), especially in the mountainous areas in summer.

• Establishment of Model Prototype of Raindrop Dropping Process
• Qiang JIANG;Jianchun BIAN;Yan LI
• 2020 Vol. 39 (3): 609-619.  DOI:10.7522/j.issn.1000-0534.2020.00004.
• Abstract ( ) HTML ( ) PDF (3341KB) ( )
• As an essential part of physical process on cloud and precipitation， the falling process of raindrops is mainly related to evaporation and raindrop fallspeed.For a single cloud droplet in the stationary atmosphere， Maxwell's theory produces the mass growth formula of particles during the condensation process.In this study， the falling process of raindrops focuses on the evaporation process rather than the condensation process.Based on Maxwell’s theory， raindrops are assumed to be spherical particles， to produce its drop process by solving the original equation solved with difference method， and modifying the Maxwell theory by adding effects of ventilation and surface.For the issue of raindrop fallspeed， using the sounding data of Kunming station in 2015， the raindrops sample are divided into three groups according to different diameter (>1 μm).Neglecting the short acceleration process of raindrops， the balance between drag force and the gravity is considered for discussion.The relationship between the fallspeed and radius at the initial height is obtained by fitting with the least square method.And then the functional relationship between the fallspeed and radius at any height is obtained by combining some assumptions and theoretical derivation.Finally， several sensitivity experiments on relative humidity are tested by using this model.The result shows that decreasing the ambient relative humidity will accelerate the evaporation of small raindrops.Based on Maxwell's theory and other previous studies， this paper has obtained a more reasonable raindrop falling model by considering evaporation process through some assumptions， which is helpful to represent the realistic falling process of raindrops better.

• A Response Effectiveness Evaluation for an Artificial Seeding Case of Winter Stratiform Clouds
• Zengmei KANG;Yuwen SUN;Xiaobo DONG;Xiaoshen SUN;Rong MAI;Zhijun ZHAO
• 2020 Vol. 39 (3): 620-627.  DOI:10.7522/j.issn.1000-0534.2019.00045.
• Abstract ( ) HTML ( ) PDF (9278KB) ( )
• On January 22, 2018, an inverted trough was passing through the urban area in Xingtai where stratiform clouds were developed in low altitude.A particle measuring system mounted on King Air was used to complete and track the seeding operation.By comparing the microphysical variation of different-scale cloud particles before and after the seeding with satellite results, the artificial seeding was found successfully effective.After the seeding, the result response of target cloud is the key for the chain of evidence between precipitation augmentation and cloud seeding.When cloud condensation nuclei were rather uniform and the cloud was considered as one layer that a shallow cloud layer was formed, the cloud particles would grow homogeneously into supercooled water droplets with diameter between 4~6 μm, which would further form into the water cloud.The maximum liquid content was 0.2 g·m^-2.After the seeding, artificial ice nucleus consumed abundant supercooled water and further grew into ice crystals and ice crystal aggregations.The cloud particle concentration dropped from 200 cm^-3 into 15 cm^-3 because of the seeding, while for the same reason, the concentration of 100~1000 μm ice and snow crystals as well as the concentration of precipitation particles over 1000 μm increased to 150 L^-1 and 70 L^-1 respectively.Also, the presence of snowflakes with a diameter of 6000 μm showed the evidence of positive effect in facilitating snowing.Since the seeding area was targeting at cloudless or partly cloudy area, the dark cloud band was found in the Himawari-8 satellite cloud pictures along the seeding trajectory clearly proved the seeding operation with significantly effective results.

• Applicability Evaluation of Drought Indices in Northern China and the Reasons for Their Differences
• Suping WANG;Jinsong WANG;Qiang ZHANG;Yiping LI
• 2020 Vol. 39 (3): 628-640.  DOI:10.7522/j.issn.1000-0534.2019.00049.
• Abstract ( ) HTML ( ) PDF (9188KB) ( )
• Drought monitoring is an essential component of drought research.It is normally performed using various drought indices.A number of drought indices have been introduced and applied in different regions.But some of those are region specific and have limitations of applicability in other climatic conditions.Based on daily meteorological data from 267 weather stations and soil relative humidity of 20 cm from 3 agrometeorological sites, the applicability of five drought indices include in MCI、 K、 SPI、 SPEI and Pa in Northern China were evaluated and the reasons for the difference of the monitoring results were discussed.The results showed that for the ability of drought monitoring, MCI and K indices have the best performances.MCI is particularly advantageous in spring in the study area.K index is slightly better than MCI in the easterly and southerly regions in summer, autumn and winter.Pa and SPI index performance well in summer and autumn, and SPEI do best in summer.The low monitoring accuracy of Pa, SPI and SPEI is mainly due to the light monitoring of these indexes or the high frequency of missing, while the K index also has a high frequency of missing in spring in the northeast region, up to 29%.The monitoring ability of various drought indexes is closely related to the drought factors and their time scales which are considered respectively.Taken together, MCI and K are better than other indices in the study area.

• Characteristics of Winter Wind Field in Lanzhou Based on Scanning Lidar and Its Relation to Air Pollution
• Qianqian Wang;Ye Yu;Longxiang Dong;Suping Zhao;Guo Zhao;Tong Zhang
• 2020 Vol. 39 (3): 641-650.  DOI:10.7522/j.issn.1000-0534.2019.00009.
• Abstract ( ) HTML ( ) PDF (3812KB) ( )
• Based on wind profiles obtained from Scanning Lidar, the characteristics of wind field from 1 December 2017 to 28 February 2018 in Lanzhou were analyzed.Through the cluster analysis, the weather types affecting Lanzhou area in winter was obtained.The characteristics of wind field under different weather types and the diurnal variation characteristic were analyzed.The results show that, winter low-level wind speed during the study period were very low, and were dominated by easterly wind.The diurnal variation of wind field was obvious, with higher wind speed from the afternoon to the evening than during other times.There was westerly wind at the height between 250 m and 700 m from night to the next morning, while easterly wind prevailed the rest of time below 800 m.In addition, local circulation was dominant when the study area was controlled by weak high-pressure, and the related low wind and strong downdraft led to serious pollution.The wind direction with the maximum air pollution index was different at each height and the pollution index decreased rapidly above 200 m.Increase the emission height of pollutants above 200 m can effectively reduce the concentration of near-surface pollutants.

• Factors Related to the Interannual Variations of Spring Surface Winds over the Pastoral Transitional Zone in Northern China
• Yihong HU;Daoyi GONG;Rui MAO;Jing YANG;Xiaoxue SHI
• 2020 Vol. 39 (3): 651-661.  DOI:10.7522/j.issn.1000-0534.2019.00046.
• Abstract ( ) HTML ( ) PDF (3318KB) ( )
• The possible influence of the atmospheric circulation and the land surface factors on interannual variation of wind speed over pastoral transitional zone in northern China in spring has been investigated, by employing daily wind speed observations for 15 meteorological stations, the ERA-Interim reanalysis data, and the GLASS leaf area index data.The results show that, in addition to a weakening trend (-0.10 m·s^-1 per decade), the spring wind also experiments strong year-to-year variations.During the period of 1979 -2016, the interannual components accounts for 58% of the total variance.The wind interannual variability is strongly related to the anomalous cyclonic circulation in northeastern Asia.It strength, as being measured as the mean 700 hPa heights over 46°N -55°N and 116°E -130°E, has a significant correlation (-0.83) with the surface wind of the study area.When the anomalous cyclonic circulation is strengthened, there is an anomalous northwesterly wind over pastoral transitional zone, which subsequently results in stronger winds.Interannual changes of the anomalous cyclonic circulation is related to the planetary atmospheric circulation over the northern hemisphere, as demonstrated by its significant correlation with the Arctic Oscillation (r=0.41).Surface roughness is an important aerodynamic parameter with respect to the near surface vertical wind transport.Observations show that the leaf area index changes out-of-phase with wind speed.Annual scatter diagram shows that when the leaf area index increases 1 unit, the wind speed tends to decrease by approximate 1.57 m·s^-1.Their interannual variations from 1982 -2014 yield a significant correlation of -0.61.There is also a negative correlation between NDVI and wind speed, but the correlation is not significant.It is probably because the leaf area index can better reflect the long-term variation of aerodynamic properties.The change of land surface physical conditions may also affect winds through the land-air heat flux.Analysis show that the interannual variations of surface wind are significantly related to the boundary layer height (r=0.57), sensible heat flux (r=0.39), and latent heat flux (r=-0.39).If only days with smaller wind speed (≤3 m·s^-1) are considered, their relationship becomes more evident (r=0.59, 0.60 and -0.57, respectively).

• Influence of the West Pacific Subtropical High on Forest Fires in China
• Yujie LI;Xiaoqing GAO;Jingjin MA;Liwei YANG
• 2020 Vol. 39 (3): 662-672.  DOI:10.7522/j.issn.1000-0534.2020.00015.
• Abstract ( ) HTML ( ) PDF (13306KB) ( )
• Forests are the foundation for sustained, healthy and rapid development of the entire national economy. Forest fires have a huge impact on global ecosystems and human society. China is a country with abundant forest species but insufficient per capita possession. The management and prediction of forest fires is an indispensable part of forest protection in China. This paper uses the monthly data of 500 hPa potential height field in NCEP/NCAR reanalysis dataset I, the forest fire data in China from 2007 to 2017 which provided by the Chinese Academy of Forestry, monthly data of the temperature and precipitation at 512 meteorological observation stations. The aim of the paper is to analyze the impact of the West Pacific subtropical high on forest fires in China. The following conclusions have been drawn: (1) Since 2007, the number of forest fires in the country has shown a downward trend. On average, the number of fires in the year is 940. The higher three years with fire occurrence are 2007, 2008 and 2009, and the lower three years are 2016, 2015 and 2012.The three months in which forest fires occur more frequently are March, February, and April, and the less three months are September, August, and July. (2) China's forest fires are mainly distributed in the Northeastern China, some provinces in East China, Central China, South China, and some provinces in Southwestern China. There were more fires in 2007 -2010, and fewer fires occurred in 2011 -2016. There were more forest fires in spring and winter, and fewer fires in summer, respectively. (3) The occurrence of forest fires is affected by temperature and precipitation, and has a significant negative correlation with precipitation and a significant positive correlation with temperature. (4) The West Pacific subtropical high has a certain directive effect on forest fires in China. Subtropical high ridge index, subtropical high area index, and subtropical high ridge point all have significant negative correlations with the number of forest fires. With the increase in the intensity of the West Pacific subtropical high, the northward and westward extension of West Pacific subtropical high, the risk of forest fires in southern China is reduced. This study considers the impact of the West Pacific subtropical high on forest fires and has important implications for the control and prediction of forest fires in China, and has a certain directive significance for the usage of the researches on the West Pacific subtropical high.