J. Meteor. Res.
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2017 Vol. 31, No. 4
Published: 2017-08-28

An Overview of Mineral Dust Modeling over East Asia
Siyu CHEN, Jianping HUANG, Yun QIAN, Chun ZHAO, Litai KANG, Ben YANG, Yong WANG, Yuzhi LIU, Tiangang YUAN, Tianhe WANG, Xiaojun MA, Guolong ZHANG
2017, 31(4): 633-653 [Abstract]( 119 ) HTML PDF (5164 KB)  ( 247
Abstract:East Asian dust (EAD) exerts considerable impacts on the energy balance and climate/climate change of the earth system through its influence on solar and terrestrial radiation, cloud properties, and precipitation efficiency. Providing an accurate description of the life cycle and climate effects of EAD is therefore critical to better understanding of climate change and socioeconomic development in East Asia and even worldwide. Dust modeling has undergone substantial development since the late 1990s, associated with improved understanding of the role of EAD in the earth system. Here, we review the achievements and progress made in recent decades in terms of dust modeling research, including dust emissions, long-range transport, radiative forcing (RF), and climate effects of dust particles over East Asia. Numerous efforts in dust/EAD modeling have been directed towards furnishing more sophisticated physical and chemical processes into the models on higher spatial resolutions. Meanwhile, more systematic observations and more advanced retrieval methods for instruments that address EAD related science issues have made it possible to evaluate model results and quantify the role of EAD in the earth system, and to further reduce the uncertainties in EAD simulations. Though much progress has been made, large discrepancies and knowledge gaps still exist among EAD simulations. The deficiencies and limitations that pertain to the performance of the EAD simulations referred to in the present study are also discussed.
Observational Characteristics of Cloud Radiative Effects over Three Arid Regions in the Northern Hemisphere
Jiandong LI, Tianhe WANG, Ammara HABIB
2017, 31(4): 654-664 [Abstract]( 224 ) HTML PDF (7271 KB)  ( 135
Abstract:Cloud–radiation processes play an important role in regional energy budgets and surface temperature changes over arid regions. Cloud radiative effects (CREs) are used to quantitatively measure the aforementioned climatic role. This study investigates the characteristics of CREs and their temporal variations over three arid regions in central Asia (CA), East Asia (EA), and North America (NA), based on recent satellite datasets. Our results show that the annual mean shortwave (SW) and net CREs (SWCRE and NCRE) over the three arid regions are weaker than those in the same latitudinal zone of the Northern Hemisphere. In most cold months (November–March), the longwave (LW) CRE is stronger than the SWCRE over the three arid regions, leading to a positive NCRE and radiative warming in the regional atmosphere–land surface system. The cold-season mean NCRE at the top of the atmosphere (TOA) averaged over EA is 4.1 W m-2, with a positive NCRE from November to March, and the intensity and duration of the positive NCRE is larger than that over CA and NA. The CREs over the arid regions of EA exhibit remarkable annual cycles due to the influence of the monsoon in the south. The TOA LWCRE over arid regions is closely related to the high-cloud fraction, and the SWCRE relates well to the total cloud fraction. In addition, the relationship between the SWCRE and the low-cloud fraction is good over NA because of the considerable occurrence of low cloud. Further results show that the interannual variation of TOA CREs is small over the arid regions of CA and EA, but their surface LWCREs show certain decreasing trends that correspond well to their decreasing total cloud fraction. It is suggested that combined studies of more observational cloud properties and meteorological elements are needed for in-depth understanding of cloud–radiation processes over arid regions of the Northern Hemisphere.
Interannual Variability of Summertime Outgoing Longwave Radiation over the Maritime Continent in Relation to East Asian Summer Monsoon Anomalies
Qi XU, Zhaoyong GUAN
2017, 31(4): 665-677 [Abstract]( 58 ) HTML PDF (7364 KB)  ( 91
Abstract:The Maritime Continent (MC) is under influences of both the tropical Pacific and the Indian Ocean. Anomalous convective activities over the MC have significant impacts on the East Asian summer monsoon (EASM) and climate in China. In the present study, the variation in convective activity over the MC in boreal summer and its relationship to EASM anomalies are investigated based on regression analysis of NCEP-NCAR reanalysis and CMAP [Climate Prediction Center (CPC) Merged Analysis of Precipitation] data, with a focus on the impacts of ENSO and the In-dian Ocean Dipole (IOD). The most significant interannual variability of convective activity is found over 10°S-10°N, 95°-145°E, which can be roughly defined as the key area of the MC (hereafter, KMC). Outgoing longwave radiation anomaly (OLRA) exhibits 3- to 7-yr periodicities over the KMC, and around 70% of the OLRA variance can be explained by the ENSO signal. However, distinct convection and precipitation anomalies still exist over this region after the ENSO and IOD signals are removed. Abnormally low precipitation always corresponds to positive OLRA over the KMC when negative diabatic heating anomalies and anomalous cooling of the atmospheric column lead to abnormal descending motion over this region. Correspondingly, abnormal divergence occurs in the lower troposphere while convergence occurs in the upper troposphere, triggering an East Asia-Pacific/Pacific-Japan (EAP/PJ)-like anomalous wave train that propagates northeastward and leads to a significant positive precipitation anomaly from the Yangtze River valley in China to the islands of Japan. This EAP/PJ-like wave pattern becomes even clearer after the removal of the ENSO signal and the combined effects of ENSO and IOD, suggesting that convective anomalies over the KMC have an important impact on EASM anomalies. The above results provide important clues for the prediction of EASM anomalies and associated summer precipitation anomalies in China.
Statistical Modeling of CMIP5 Projected Changes in Extreme Wet Spells over China in the Late 21st Century
Lianhua ZHU, Yun LI, Zhihong JIANG
2017, 31(4): 678-693 [Abstract]( 80 ) HTML PDF (8558 KB)  ( 140
Abstract:The observed intensity, frequency, and duration (IFD) of summer wet spells, defined here as extreme events with one or more consecutive days in which daily precipitation exceeds a given threshold (the 95th percentile), and their future changes in RCP4.5 and RCP8.5 in the late 21st century over China, are investigated by using the wet spell model (WSM) and by extending the point process approach to extreme value analysis. Wet spell intensity is modeled by a conditional generalized Pareto distribution, frequency by a Poisson distribution, and duration by a geometric distribution, respectively. The WSM is able to realistically model summer extreme rainfall spells during 1961-2005, as verified with observations at 553 stations throughout China. To minimize the impact of systematic biases over China in the global climate models (GCMs) of the Coupled Model Intercomparison Project Phase 5 (CMIP5), five best GCMs are selected based on their performance to reproduce observed wet spell IFD and average precipitation during the historical period. Furthermore, a quantile-quantile scaling correction procedure is proposed and applied to produce ensemble projections of wet spell IFD and corresponding probability distributions. The results show that in the late 21st century, most of China will experience more extreme rainfall and less low-intensity rainfall. The intensity and frequency of wet spells are projected to increase considerably, while the duration of wet spells will increase but to a much less extent. The IFD changes in RCP8.5 are in general much larger than those in RCP4.5.
Climate Characteristics of Abnormal Double-Blocking Activities over the Ural Mountains and Sea of Okhotsk
Gang LIU, Tao WANG, Xueyan YANG, Yishu WANG, Xu YANG, Yan CUI
2017, 31(4): 694-707 [Abstract]( 40 ) HTML PDF (9884 KB)  ( 53
Abstract:By using NCEP-NCAR daily reanalysis data for June-August of 1948-2009, the synoptic situation of the double-blocking high pressure process over the Ural Mountains-Sea of Okhotsk region was identified objectively, and the climatic characteristics and dynamic mechanism during the double blockings were also investigated. The results suggest that the Urals-Okhotsk double-blocking high experienced obviously an abrupt change around 1977. After the change, the occurrence frequency and number of sustained days of the blocking high reduced significantly. Moreover, the zonal spacing between the Urals blocking and the Okhotsk blocking also decreased, while their meridional locations did not change much. The double blockings became strengthened in general, and the blocking high over the Sea of Okhotsk extended northward evidently. However, during the process without double-blocking activities, the intensity and location of the double-blocking high showed no noticeable variation before and after the abrupt change. In addition, dynamic diagnosis shows that after the abrupt change, the energy of the double-blocking high mainly propagated vertically from low to high levels, and transferred horizontally from low to high latitudes; whereas, previously, before the abrupt change, this occurred from high to low latitudes. Meanwhile, the development of a low pressure system was fueled between the double blockings, which meant that the double-blocking activity was beneficial to the maintenance and development of the Northeast China cold vortex. In short, diagnosis of the wave energy has provided us with a better explanation of the life cycle characteristics of this double-blocking phenomenon before and after 1977.
Developing the Science Product Algorithm Testbed for Chinese Next-Generation Geostationary Meteorological Satellites: Fengyun-4 Series
Min MIN, Chunqiang WU, Chuan LI, Hui LIU, Na XU, Xiao WU, Lin CHEN, Fu WANG, Fenglin SUN, Danyu QIN, Xi WANG, Bo LI, Zhaojun ZHENG, Guangzhen CAO, Lixin DONG
2017, 31(4): 708-719 [Abstract]( 185 ) HTML PDF (6475 KB)  ( 281
Abstract:Fengyun-4A (FY-4A), the first of the Chinese next-generation geostationary meteorological satellites, launched in 2016, offers several advances over the FY-2: more spectral bands, faster imaging, and infrared hyperspectral measurements. To support the major objective of developing the prototypes of FY-4 science algorithms, two science product algorithm testbeds for imagers and sounders have been developed by the scientists in the FY-4 Algorithm Working Group (AWG). Both testbeds, written in FORTRAN and C programming languages for Linux or UNIX systems, have been tested successfully by using Intel/g compilers. Some important FY-4 science products, including cloud mask, cloud properties, and temperature profiles, have been retrieved successfully through using a proxy imager, Himawari-8/Advanced Himawari Imager (AHI), and sounder data, obtained from the Atmospheric InfraRed Sounder, thus demonstrating their robustness. In addition, in early 2016, the FY-4 AWG was developed based on the imager testbed—a near real-time processing system for Himawari-8/AHI data for use by Chinese weather forecasters. Consequently, robust and flexible science product algorithm testbeds have provided essential and productive tools for popularizing FY-4 data and developing substantial improvements in FY-4 products.
Assimilation of HY-2A Scatterometer Ambiguous Winds Based on Feature Thinning
Boheng DUAN, Weimin ZHANG, Xiaoqun CAO, Yi YU, Haijin DAI
2017, 31(4): 720-730 [Abstract]( 193 ) HTML PDF (4822 KB)  ( 87
Abstract:This paper focuses on the data assimilation methods for sea surface winds, based on the level-2B HY-2A satellite microwave scatterometer wind products. We propose a new feature thinning method, which is herein used to screen scatterometer winds while maintaining the key structure of the wind field in the process of data thinning for high-resolution satellite observations. We also accomplish feeding the ambiguous wind solutions directly into the data assimilation system, thus making better use of the retrieved information while simplifying the assimilation process of the scatterometer products. A numerical simulation experiment involving Typhoon Danas shows that our method gives better results than the traditional approach. This method may be a valuable alternative for operational satellite data assimilation.
Assimilation of Total Lightning Data Using the Three-Dimensional Variational Method at Convection-Allowing Resolution
Rong ZHANG, Yijun ZHANG, Liangtao XU, Dong ZHENG, Wen YAO
2017, 31(4): 731-746 [Abstract]( 155 ) HTML PDF (6664 KB)  ( 160
Abstract:A large number of observational analyses have shown that lightning data can be used to indicate areas of deep convection. It is important to assimilate observed lightning data into numerical models, so that more small-scale information can be incorporated to improve the quality of the initial condition and the subsequent forecasts. In this study, the empirical relationship between flash rate, water vapor mixing ratio, and graupel mixing ratio was used to adjust the model relative humidity, which was then assimilated by using the three-dimensional variational data assimilation system of the Weather Research and Forecasting model in cycling mode at 10-min intervals. To find the appropriate assimilation time-window length that yielded significant improvement in both the initial conditions and subsequent forecasts, four experiments with different assimilation time-window lengths were conducted for a squall line case that occurred on 10 July 2007 in North China. It was found that 60 min was the appropriate assimilation time-window length for this case, and longer assimilation window length was unnecessary since no further improvement was present. Forecasts of 1-h accumulated precipitation during the assimilation period and the subsequent 3-h accumulated precipitation were significantly improved compared with the control experiment without lightning data assimilation. The simulated reflectivity was optimal after 30 min of the forecast, it remained optimal during the following 42 min, and the positive effect from lightning data assimilation began to diminish after 72 min of the forecast. Overall, the improvement from lightning data assimilation can be maintained for about 3 h.
Improving the Extreme Rainfall Forecast of Typhoon Morakot (2009) by Assimilating Radar Data from Taiwan Island and Mainland China
Xuwei BAO, Dan WU, Xiaotu LEI, Leiming MA, Dongliang WANG, Kun ZHAO, Ben Jong-Dao JOU
2017, 31(4): 747-766 [Abstract]( 83 ) HTML PDF (20626 KB)  ( 97
Abstract:This study examined the impact of an improved initial field through assimilating ground-based radar data from mainland China and Taiwan Island to simulate the long-lasting and extreme rainfall caused by Morakot (2009). The vortex location and the subsequent track analyzed through the radial velocity data assimilation (VDA) are generally consistent with the best track. The initial humidity within the radar detecting region and Morakot's northward translation speed can be significantly improved by the radar reflectivity data assimilation (ZDA). As a result, the heavy rainfall on both sides of Taiwan Strait can be reproduced with the joint application of VDA and ZDA. Based on sensitivity experiments, it was found that, without ZDA, the simulated storm underwent an unrealistic inward contraction after 12-h integration, due to underestimation of humidity in the global reanalysis, leading to underestimation of rainfall amount and coverage. Without the vortex relocation via VDA, the moister (drier) initial field with (without) ZDA will produce a more southward (northward) track, so that the rainfall location on both sides of Taiwan Strait will be affected. It was further found that the improvement in the humidity field of Morakot is mainly due to assimilation of high-value reflectivity (strong convection) observed by the radars in Taiwan Island, especially at Kenting station. By analysis of parcel trajectories and calculation of water vapor flux divergence, it was also found that the improved typhoon circulation through assimilating radar data can draw more water vapor from the environment during the subsequent simulation, eventually contributing to the extreme rainfall on both sides of Taiwan Strait.
Influences of the Three Gorges Dam in China on Precipitation over Surrounding Regions
Yan LI, Weican ZHOU, Xianyan CHEN, Dexian FANG, Qianqian ZHANG
2017, 31(4): 767-773 [Abstract]( 49 ) HTML PDF (2859 KB)  ( 83
Abstract:Impacts of the Three Gorges Dam (TGD) in China on the regional pattern and annual amount of precipitation around the Three Gorges Reservoir (TGR) are examined by comparing observations before and after the operation of TGD (1984-2003 and 2004-13). Empirical orthogonal function (EOF) analysis of the annual precipitation anomalies clearly indicates that the land-use change associated with the construction of TGD has not significantly changed the precipitation pattern. To investigate the impacts of TGD on the rainfall amount, we compare the relative variations of atmospheric variables related to precipitation formation in three spatial bands: over TGR, near TGR, and far from TGR. It is found that the differences in annual rainfall over TGD between the two periods before and after the operation of TGD are small, suggesting a weak impact of TGD on the rainfall amount. The TGD water level increased from 66 m before June 2003 to 175 m after 2010, and this may have slightly reduced precipitation on the local scale.
Reconstructing Missing Hourly Real-Time Precipitation Data Using a Novel Intermittent Sliding Window Period Technique for Automatic Weather Station Data
Nagaraja HEMA, Krishna KANT
2017, 31(4): 774-790 [Abstract]( 83 ) HTML PDF (2498 KB)  ( 73
Abstract:Precipitation is the most discontinuous atmospheric parameter because of its temporal and spatial variability. Precipitation observations at automatic weather stations (AWSs) show different patterns over different time periods. This paper aims to reconstruct missing data by finding the time periods when precipitation patterns are similar, with a method called the intermittent sliding window period (ISWP) technique—a novel approach to reconstructing the majority of non-continuous missing real-time precipitation data. The ISWP technique is applied to a 1-yr precipitation dataset (January 2015 to January 2016), with a temporal resolution of 1 h, collected at 11 AWSs run by the Indian Meteorological Department in the capital region of Delhi. The acquired dataset has missing precipitation data amounting to 13.66%, of which 90.6% are reconstructed successfully. Furthermore, some traditional estimation algorithms are applied to the reconstructed dataset to estimate the remaining missing values on an hourly basis. The results show that the interpolation of the reconstructed dataset using the ISWP technique exhibits high quality compared with interpolation of the raw dataset. By adopting the ISWP technique, the root-mean-square errors (RMSEs) in the estimation of missing rainfall data—based on the arithmetic mean, multiple linear regression, linear regression, and moving average methods—are reduced by 4.2%, 55.47%, 19.44%, and 9.64%, respectively. However, adopting the ISWP technique with the inverse distance weighted method increases the RMSE by 0.07%, due to the fact that the reconstructed data add a more diverse relation to its neighboring AWSs.
Comparison of Spatial Interpolation Methods for Gridded Bias Removal in Surface Temperature Forecasts
Seyedeh Atefeh MOHAMMADI, Majid AZADI, Morteza RAHMANI
2017, 31(4): 791-799 [Abstract]( 49 ) HTML PDF (2238 KB)  ( 116
Abstract:All numerical weather prediction (NWP) models inherently have substantial biases, especially in the forecast of near-surface weather variables. Statistical methods can be used to remove the systematic error based on historical bias data at observation stations. However, many end users of weather forecasts need bias corrected forecasts at locations that scarcely have any historical bias data. To circumvent this limitation, the bias of surface temperature forecasts on a regular grid covering Iran is removed, by using the information available at observation stations in the vicinity of any given grid point. To this end, the running mean error method is first used to correct the forecasts at observation stations, then four interpolation methods including inverse distance squared weighting with constant lapse rate (IDSW-CLR), Kriging with constant lapse rate (Kriging-CLR), gradient inverse distance squared with linear lapse rate (GIDS-LR), and gradient inverse distance squared with lapse rate determined by classification and regression tree (GIDS-CART), are employed to interpolate the bias corrected forecasts at neighboring observation stations to any given location. The results show that all four interpolation methods used do reduce the model error significantly, but Kriging-CLR has better performance than the other methods. For Kriging-CLR, root mean square error (RMSE) and mean absolute error (MAE) were decreased by 26% and 29%, respectively, as compared to the raw forecasts. It is found also, that after applying any of the proposed methods, unlike the raw forecasts, the bias corrected forecasts do not show spatial or temporal dependency.
Spatial and Temporal Changes in Vapor Pressure Deficit and Their Impacts on Crop Yields in China during 1980-2008
Shuai ZHANG, Fulu TAO, Zhao ZHANG
2017, 31(4): 800-808 [Abstract]( 77 ) HTML PDF (5784 KB)  ( 116
Abstract:Vapor pressure deficit (VPD) is a widely used measure of atmospheric water demand. It is closely related to crop evapotranspiration and consequently has major impacts on crop growth and yields. Most previous studies have focused on the impacts of temperature, precipitation, and solar radiation on crop yields, but the impact of VPD is poorly understood. Here, we investigated the spatial and temporal changes in VPD and their impacts on yields of major crops in China from 1980 to 2008. The results showed that VPD during the growing period of rice, maize, and soybean increased by more than 0.10 kPa (10 yr)-1 in northeastern and southeastern China, although it increased the least during the wheat growing period. Increases in VPD had different impacts on yields for different crops and in different regions. Crop yields generally decreased due to increased VPD, except for wheat in southeastern China. Maize yield was sensitive to VPD in more counties than other crops. Soybean was the most sensitive and rice was the least sensitive to VPD among the major crops. In the past three decades, due to the rising trend in VPD, wheat, maize, and soybean yields declined by more than 10.0% in parts of northeastern China and the North China Plain, while rice yields were little affected. For China as a whole, the trend in VPD during 1980-2008 increased rice yields by 1.32%, but reduced wheat, maize, and soybean yields by 6.02%, 3.19%, and 7.07%, respectively. Maize and soybean in the arid and semi-arid regions in northern China were more sensitive to the increase in VPD. These findings highlight that climate change can affect crop growth and yield through increasing VPD, and water-saving technologies and agronomic management need to be strongly encouraged to adapt to ongoing climate change.
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