Abstract:Based on the analyses of lasting disaster weather of freezing rain and snow over South China during the January of 2008,the catastrophic flood over the Changjiang River basin during the summer of 1998 and the severe drought in Yunnan Province during the winter of 2009/2010,this paper emphasizes again that the combinational anomalies of atmospheric circulation system play important roles to the little probabilistic extreme weather and climate events.For the lasting disaster weather of freezing rain and snow in 2008,the combinational multiple circulation anomalies are clear,including Ural blocking high and a trough from Lake Baikal to Lake Balkhash that offer condition for continual cold air pouring southward from the west passage,and positive geopotential height anomalies over the eastern Asia and Japan that weaken the force of cold air from the north.Thus the front stays longer time over the South Mountain and its north area,which establishes background for continuous raining.Meanwhile,the Northwest Pacific subtropical high extents westward and its intensity also enhances,baring the cold air.The persistent strong Indian-Myanmar Trough and Northwest Pacific subtropical high transport warm and wet air to South China,and it is favorable to the occurrence of continuous rain.Persistent cold air activity and precipitation induce persistent low temperature,which creates conditions for the freezing weather.For the catastrophic flood over the Changjiang River basin in 1998,the combinational multiple circulation anomalies include the southwest monsoon surge,the Northwest Pacific subtropical high and cold air activities in summer,combined with the eastward propagation of convective system of the Tibetan Plateau.For the severe drought in Yunnan Province during the winter of 2009/2010,the combinational multiple circulation anomalies include that the Middle East subtropical jet at upper troposphere weakens,which influences Rossby wave and is unfavorable to the formation of the Tibetan Plateau-Bay of Bengal Trough;The Northwest Pacific subtropical high intensifies and shifts slightly southward,which inhibits the lower-level water vapor transmission into Yunnan;Teleconnection wave train anomaly caused by negative anomaly of NAO makes the cold air activity in the northeast of East Asia locate to the east and be difficult to reach the Yunnan region.It also makes the southern branch trough weak,and the warm and wet air could hardly reach to the Yunnan region.Generally the ENSO has a very important impact on weather and climate variations in China,but the influence is not same in every time and every region.The specific impact of ENSO must be analyzed case by case in order to determine its exact role in anomalous events,especially extreme weather and climate events.

Abstract:As an essential component of land evapotranspiration,canopy interception directly participates in the terrestrial water cycle.However,the significance of canopy interception on the global climate has long been underestimated.In this study,in order to explore the canopy interception's hydroclimatological effects,we examine the sensitivity of NCAR CAM-CLM coupled model to the changes of precipitation interception input parameter and canopy storage capacity parameter.The study results articulate the fact that the variations of interception can affect the land hydrology process and global climate.The canopy interception's modification alters the amount and portioning of global evapotranspiration,runoff,and 2 m temperature.The precipitation distributions between tropical land and ocean,and over mid-high latitude forests,are regulated by the interception-induce atmospheric circulation adjustment.We also indicate a potential link between canopy interception and vegetation photosynthesis,which varies with vegetation types.Upon comparing CLM4.5 simulations with GLEAMv3.0a data,the model canopy interception scheme overestimates the low PAI forest's canopy evaporation and underestimates the high PAI forest's,which in part lead to the bias of simulated evapotranspiration.Consequently,we induce a logic-curve interception equation into CLM4.5 and ameliorate the simulations of canopy evaporation and evapotranspiration over forests on the global scale.The new interception scheme reduces approximately 2%-5% of the evapotranspiration bias over Africa,the islands of Southeast Asia,the Indo-China Peninsula,eastern North America,and part of South America.It also lowers the canopy evaporation bias by 5%-30% over the forests in Africa,Southeast Asia and South America,as well as the boreal evergreen needle forests.

Abstract:According to the normal distribution characteristics of initial atmospheric errors,in order to describe the uncertainties in the initial conditions of the GRAPES global model,this paper used the Gausssian sampling method to construct initial perturbations for GRAPES global ensemble prediction system (GRAPE-GEPS) from GRAPES singular vectors (SVs),which are specifically designed for ensemble forecasting.Using the global assimilation analysis field of GRAPES,this paper carried out the ensemble experiments of GRAPES-GEPS with SV-based initial perturbations.Results show that the growths of ensemble spreads of geopotential height,wind speed and temperature increase quickly,and the growth rate remains stable during the forecast range.The small distance between ensemble mean RMSE and ensemble spread indicates that there are reasonable spread-skill relations in the GRAPES-GEPS.Compared with RMSE of unperturbed control forecast,there are clear advantages observed in RMSE of ensemble mean,particularly in the middle range forecasts.The stochastically perturbed parametrization tendency (SPPT) scheme is used to represent the model uncertainties in the GRAPES-GEPS.It can be seen that the inclusion of the SPPT scheme improves the ensemble spreads of geopotential height,temperature and wind speed at each forecast lead time in the Northern (Southern) Hemispheric extra-tropics and the tropics in particular,and improves the spread-skill relations as well.The SV-based initial perturbations and SPPT scheme have been used in the operational GRAPES-GEPS at China Meteorological Administration since December 2018.

Abstract:Based on the 10 m wind speed forecasts during the summer of 2012 from the ECMWF in the TIGGE datasets,a Kalman filter bias-correction combining with a sliding weight method has been done to calibrate the ensemble perturbed forecasts.The effect of this calibration method is examined.Then,the jumpiness index is used to analyse the results before and after calibration.Results show that:(1)In general,the calibration method can effectively reduce the RMSEs of the 10 m wind speed ensemble forecasts at different start times.When the start time is 0000 UTC,the correction results are better in the middle and low latitudes.When the start time is 1200 UTC,the correction results are better in the middle and high latitudes.(2)The calibration method has a good effect on improving the dispersion of ensemble members.The Talagrand pictures show that U-type and L-type distributions decrease after calibration.(3)Analysis of RMSE shows that the 10 m wind speed ensemble forecasts from ECMWF has great inconsistency of prediction.After calibration,the period-average forecast inconsistency indices of ensemble mean are lower than before,showing that the Kalman filter bias-correction method can reduce the forecast inconsistency of the 10 m wind speed ensemble forecasts.(4)In terms of the period-average inconsistency features of the 10 m wind speed ensemble forecasts from ECMWF,all average period-average inconsistency indices increase with the forecast range,in agreement with the practical experience that the forecasts are usually more consistent at short forecast ranges.(5)The calibration method has better effects on reducing the frequencies of flip,flip-flop and flip-flop-flip.The flip happens more frequently than the other two,and the frequency of flip-flop-flip is the lowest.

Abstract:The Weather Research and Forecasting(WRF) mesoscale numerical prediction model was used to construct mesoscale ensemble forecast from the aspects of model uncertainty.The focus was to compare and analyze the influence on precipitation forecast of mesoscale convection complex(MCC) exerted by the three methods,which were different physical parameterization method,the method of disturbing sensitive parameters in cumulus convection parameterization scheme and the stochastic physical perturbation method.The results showed that all of the three ensemble forecast methods could reflect the uncertainty of MCC precipitation forecast and they performed better than control forecast.Compared to the other two methods,the spatial distribution and intensity of ensemble mean 24-hour accumulated rainfall by stochastic physical perturbation method were closer to the reality.The 24-hour rainfall ETS of stochastic physical perturbation method was better than the other two methods.In terms of root mean square error (RMSE),the stochastic physical perturbation method had smaller RMSEs than the other two methods,while its dispersion was larger than the other two.In all,the stochastic physical perturbation method was superior to the other two methods.

Abstract:There are some advantages of high vertical resolution,including its high accuracy and the fact that it is less significantly affected by cloud and precipitation for GPS(Global Positioning System) radio occultation data.In the present study,a new adaptive vertical thinning scheme,which considers both the non-uniform layered characteristics of height-terrain following vertical coordinates and the features of radio occultation retrieved data,is developed so as to avoid redundancy of observations data in assimilating for regional GRAPES m3DVAR.The new thinning scheme for GPS radio occultation data is able to accord to the vertical coordinates of the GRAPES m3DVAR assimilation system and the characteristics of the vertical levels,so as to reasonably select the GPS occultation data and eliminate redundant data.The thinning scheme can improve the adjustments of the observations to the background fields for the assimilation of GPS occultation data,thereby effectively improving the subsequent assimilation analysis quality and prediction skill.A case experiment and batch test are performed to explore the impact of the new adaptive thinning scheme on the quality of analysis and forecast field.The study results indicate that GPS radio occultation data retrieved using the new adaptive thinning scheme lead to greater adjustments in the background fields,higher quality analysis,and smaller root-mean-square error of prediction of geopotential height,temperature,specific humidity and wind field,if the suitable sparse parameters are selected.In addition,the adaptive thinning scheme has a positive effect on improving the forecast of typhoon tracks.The results of the batch experiments have confirmed that the analysis field quality with the adaptive thinning scheme yields a significant improvement for the assimilation of temperature and vapor pressure retrieved from GPS radio occultation data.

Abstract:In this paper,in order to reduce or remove the noise components included in observations of surface temperature in China as much as possible and improve the quality of observations,a new single station quality control algorithm is proposed.The algorithm combines Ensemble Empirical Mode Decomposition (EEMD) and Cubic Exponential Smooth (CES).First,the EEMD method is used to decompose the temperature observations into a series of relatively stable intrinsic mode functions.Next,based on the energy density and the correlation criterion,the target component is analyzed and screened out to complete the data reconstruction.Finally,the CES method is used to establish a single station quality control model with the reconstructed data,and form an EEMD-CES quality control model.In order to test the feasibility and applicability of this method,this paper selects the surface hourly temperature observations from nine stations throughout the country for quality control in 2008.The results are then compared with the quality control effects of the traditional single station quality control method,empirical mode decomposition method,and cubic exponential smoothing method.The experimental results show that the quality control method based on EEMD-CES can effectively mark the suspicious value of data,and has a higher error detection rate and stronger adaptability than the traditional method.

Abstract:Based on the improved objective identification method of extratropical cyclones,this paper investigated the development rate and movement characteristics of extratropical cyclones at different scales in the Changjiang-Huaihe River Valley (CHRV) from April to June during 1986-2015.Results show that the overall cyclone development rate shows an upward trend first and then a downward trend,the larger spatial scale cyclone development rate shows a significant upward trend,and the middle scale cyclone development rate has no obvious change trend.The larger scale cyclone sources are concentrated at the junction of Hubei Province and Hunan Province.The middle scale cyclone sources are located in the eastern part of CHRV,such as Anhui Province.The sources of cyclones at different scales are located in the large value region of the non-adiabatic heating term in the whole atmosphere.During the initial stage of cyclone,there is a wind shear line in the CHRV.The wind speed in the northern CHRV is smaller than that in the southern CHRV.The geopotential height anomaly is negative in the lower troposphere and positive in the middle and upper troposphere over the CHRV,which belongs to a shallow low pressure system.All scale cyclones have east-moving and northeast-moving paths,but the larger scale cyclones have a larger proportion of northeast-moving path.

Abstract:Intertropical Convergence Zone(ITCZ),as one of the important systems of tropical atmosphere,has important impacts on global atmospheric circulation.Due to a range of factors,regional ITCZ has different characteristics.Among them,the Central and Eastern Pacific ITCZ(CEP-ITCZ) is located to the north of the equator year round with high particularity relative to other regions.In addition to seasonal movement,the meridian position of CEP-ITCZ is usually affected by El Niño events.Some researchers have found that the CEP-ITCZ is slightly southward in Central Pacific El Niño(CP-El Niño) year,and the southward extent is less than that in Eastern Pacific El Niño (EP-El Niño) year.Therefore,taking into account that the location and intensity of CP-El Niño and EP-El Niño are very different,their impacts on the CEP-ITCZ inevitably vary widely.Previous studies have not analyzed this variation in depth,especially the difference between the impacts from two types of El Niño on the intensity of CEP-ITCZ.The research about how the anomaly of SST (Sea Surface Temperature) impacts ITCZ is of great significance to the mechanism of air-sea interaction,climatic prediction and model assessment.In the passage,two sensitivity tests about impacts of SST anomaly on CEP-ITCZ were implied using MPAS-A(The Model for Prediction Across Scales-Atmosphere) model.Compared with the anomalies of real atmosphere in two types of El Niño years,the reasons why the CEP-ITCZ presents different characteristics in two types of El Niño were proposed.The results of CP-EL test show that due to the impact from the first mode of SST anomaly in the tropical Pacific,the anomalies of the meridional winds in the northern and southern hemispheres are comparable,and the anomalous cross-equatorial flow is weak,resulting in little changes in the CEP-ITCZ position.The anomalies of the meridional winds lead to the convergence zone slightly stronger.The precipitation of CEP-ITCZ is enhanced by both wind convergence and SST positive anomalies.These results are consistent with the anomalies of CEP-ITCZ in central pacific El Niño years.The results of EP-EL test show that due to the impacts from the first two modes of SST anomaly in the tropical Pacific,the anomalies of the meridional winds in the northern hemisphere are strong,which results in a higher extent of southward movement for the CEP-ITCZ.Due to the impacts from anomalous meridional wind,the anomalies of divergence show dipole-like pattern,which increases the width and weakens the central intensity of the convergence zone.These results are consistent with the anomalies of CEP-ITCZ in eastern pacific El Niño years.The second mode of SST anomaly may have an important impact on CEP-ITCZ.The intensities of the second mode of SST anomaly in two types of El Nino years are quite different,which results in the southward extent of CEP-ITCZ in CP-El Niño years is less than that in EP-El Niño years,while the precipitation intensities of the CEP-ITCZ in two types of El Niño years are similar.

Abstract:Using the global monthly sea surface temperature(SST) from the Hadley Climate Prediction and Research Center,NCEP/NCAR daily wind field and specific humidity,and 753-station daily precipitation and 160-station monthly precipitation data from the National Meteorological Information Center,the differences in the low-frequency characteristics of the precipitation and its related moisture transport paths in the Yangtze River-Yellow River Basin in the following summer of eastern Pacific(EP) and central Pacific(CP) type El Niño events are analyzed.For the sake of clarity,precipitation is distinguished as EP-type and CP-type precipitation.The results reveal the following:1)For EP-and CP-type precipitation,the most significant frequency oscillation period is 10-20 d,followed by 20-30 d,while the weakest is 30-60 d.For the typical 7-year average time series of precipitation,the most significant is 10-20 d,followed by the 20-30 d low-frequency oscillation period for EP-type precipitation,yet for CP precipitation there is only 10-20 d significant low-frequency oscillation period.2)The zonal and meridional vapor flux are of significant 10-20 d,20-30 d and 30-60 d low-frequency oscillation periods,among which 10-20 d is the most significant,and this characteristic is more obvious especially for meridional vapor flux.When comparing the two types of events,the significance of the 10-20 d and 20-30 d low frequency cycles are equivalent for both the EP-and the CP-type zonal water vapor fluxes,and the 30-60 d cycle of EP-type zonal water vapor flux is slightly stronger than that of the CP-type.In the meridional water vapor flux,the EP-type is slightly weaker(stronger) than the CP-type in the low frequency period of 20-30 d (30-60 d).3) The main low-frequency water vapor circulation systems which affect the low-frequency heavy precipitation over the Yangtze River-Yellow River Basin in the following summer between the EP-and CP-type El Niño events are different.The main and most common 10-20 d vapor circulation systems affecting both the EP-and CP-type low-frequency precipitation include the anomalous anticyclonic moisture circulation around the Philippines,the anomalous cyclonic(anticyclonic) moisture circulation to the Bohai Gulf (southeastern Sea of Japan).In addition,the 10-20 d vapor circulation systems which affect the EP(CP) type low-frequency precipitation also include the anomalous cyclonic moisture circulation to the northeast of the Balkhash (the anomalous cyclonic moisture circulation pairs around the Bay of Bengal and to the west of Sumatra,and the anomalous cyclonic and anticyclonic moisture circulation to the western and eastern sides of Lake Baikal,respectively).4)The water vapor sources of low-frequency strong precipitation for both the EP-and CP-type heavy precipitation in the summer of the following year are also different over the Yangtze River-Yellow River Basin.Warm vapor originates from the South China Sea,cold vapor from the northwest Pacific,and cold air from the northeast of Balkhash and northeast of Lake Baikal for the EP-type precipitation.A small amount of warm vapor originates from the Arabian Sea and Indian Ocean,while a large amount of warm vapor originates from the tropical Western Pacific,and cold air from the northeast to Lake Baikal for CP-type precipitation.

Abstract:Based on the 0.5°×0.5° ERA-interim reanalysis data,a heavy rainfall event that occurred on June 5,2016 in Zhengzhou was simulated using the Advanced Research Weather Research and Forecasting Model (WRF-ARW) coupled with a slab urban canopy model (UCM).Sensitivity experiments with the modified land-use categories and terrain height are conducted to investigate the impacts from urbanization and topography of the mountain to the northwest of Zhengzhou on this heavy rainfall event.The conclusions can be summarized as follows:
1)The results show that the severe rainfall events are mainly favored by the ageostrophic-forced ascending motion associated with an eastward-migrating upper-level trough and the unstable convective stratification in the vicinity of Zhengzhou.
2)The precipitation pattern simulated in the control experiment is well consistent with the observational data.The sensitivity experiment (NO_CITY) in which the land-use category of Zhengzhou is changed from urban land to grass features significantly lower rainfall amount in the urban area comparing with the control experiment (CTL).Further analysis shows that the urban surface temperature in NO_CITY are clearly decreased comparing to that in CTL since the modified land-use type weakens the thermodynamical effect of urban surface.The decreased surface temperature in turn suppresses the sensible heat flux and leads to weak ascent in the center of Zhengzhou.It is indicated that the effect of urban heat island tends to enhance upward motion and thus convection in the urban area,which increases the rainfall amount and results in the precipitation more concentrated in the city.
3) The sensitivity experiment in which the mountain to the northwest of Zhengzhou has a reduced orographic height (LOW_MONT) also shows lower rainfall amount than CTL.The results show that this remarkable difference can be attributed to two main factors.Firstly,the gravity wave excited by the orographic effect can promote the convection in Zhengzhou region and thus increase the rainfall in urban area.The lower the mountain is,the weaker the gravity wave excited will be.Hence,the convection in Zhengzhou in LOW_MONT is suppressed,which results in a lower rainfall amount.Secondly,through examining the low-level relative humidity field,it is found that the mountain to the northwest of Zhengzhou plays an important role in hampering the northward transport of the low-level dry air.Therefore,as the height of the mountain is artificially lowered,a larger amount of low-level dry air is advected northwards and thus lowers the relative humidity in Zhengzhou region.The decreased low-level relative humidity enhances the evaporation cooling,and thus the cold pool is associated with the precipitation.The strong cold pool helps the rain band to move fast.The faster the rain band moves,the less time the rainfall will sustain.Therefore,this effect leads to a further decrease in the total rainfall in LOW_MONT experiment.

Abstract:In this study,based on the observational data and simulations of eight coupled climate models ensemble and regional climate model(RegCM4),the performance of models are evaluated by means of the methods of variance analysis,correlation analysis,trend analysis and perturbation,and the precipitation change in Jiangsu Province in the future is projected under the scenario of RCP8.5.The study results show that the annual mean precipitation of Jiangsu Province will gradually increase in the future,and the linear increase rate is about 7 mm/(10 a) in the global model simulation,and 1.5 mm/(10 a) in the regional model simulation.The annual mean precipitation in Jiangsu Province will increase by about 2% by 2050,but the change in the regional model simulation is not significant.According to the regional model simulation,the summer precipitation will increase in the future,by up to 20%-30%,but the rate of increase will decrease with time.In the global model simulation,the summer precipitation will have decreased by about 10% by 2050 compared with that at present.The winter precipitation in the regional model simulation will have decreased in different periods in the future,and may be reduced by about 30%-40% compared with that at present.The winter precipitation in the global model simulation in the future will first be reduced,then increased,and by 2050 it will be about 10% higher than that today.For different seasons,the precipitation change in the southern region is more remarkable than that in the northern region.In the case of extreme precipitation,the light rain days in Jiangsu Province decrease,mainly in the southern region,while the heavy rain days increase slightly,but not significantly.However,due to the performance of the global models themselves,the dependence of the regional models on the global models,and the uncertainty of greenhouse gas emissions,the projected results remain uncertain.More global and regional models and further tests are needed in the future to reduce the uncertainty of the projections.

Abstract:With the rapid development of coastal cities,the urban climate and environment have gradually become deteriorated.Therefore,it is urgent and important to assess the effects of sea-land breeze,which appears under weak atmospheric circulation,on improving the urban environment.In this paper,Jinjiang was taken as an example,which is a highly developed coastal city in Fujian Province,China.Based on the wind observations from distributed meteorological stations in Jinjiang,the characteristics of sea-land breeze in two different typical days were analyzed.Then,the weather research and forecasting (WRF) model,coupled with a land surface model (Noah) and an urban canopy model (BEP),was applied to simulate the wind fields over two days.Next,the local wind was decomposed from the simulation results and used to identify sea-land breezes in the Jinjiang area.Validation of sea-land breezes from the WRF simulations was conducted,and their spatial distribution were analyzed.The results showed that the simulated temporal series of hourly local wind directions were highly consistent with the observations without a significant difference at the 0.05 level,while the simulated local wind speed shows significant deviation from the observed data,with an average difference of about 1 m/s.At the same time,there were also some difference between the simulated and observed data in terms of the retrieved starting time,end time and duration for both sea and land breezes.The spatial distributions of the sea and land breezes over the two days were consistent with those of the starting time,and it was not apparent that the emergence of sea-land breezes could be suppressed merely due to distance from the shore.The above-mentioned results indicated that the WRF model is able to simulate sea-land breeze,and extract its characteristics accurately,although there remain some uncertainties in the simulated wind speed.The results also provide a reference to the planning of Jinjiang City,and suggestions to the improvement of its urban micro-environment.

Abstract:Deserts occupy 1/4 of the earth's land area.All sectors of society have always paid much more attention to the effects of desert weather and climate on global ecology,environment and climate.Firstly,this paper briefly reviewed the development history of desert meteorology,referring to the representative works concerning desert meteorology at home and abroad.Further,this paper illustrated the research progress of desert meteorology at the several aspects,including physical properties of desert surface,desert weather and desert boundary layer,desert climate,and effects of desert on regional and global environment.Finally,this paper puts forward the prospects of desert meteorology research.