J. Meteor. Res.
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2018 Vol. 32, No. 4
Published: 2018-08-28

Long-Term Integration of a Global Non-Hydrostatic Atmospheric Model on an Aqua Planet
Xiaohan LI, Xindong PENG
2018, 32(4): 517-533 [Abstract]( 81 ) HTML PDF (8652 KB)  ( 142 Supplemental Material
Abstract:A global non-hydrostatic atmospheric model, i.e., GRAPES_YY (Global/Regional Assimilation and Prediction System on the Yin-Yang grid), with a semi-implicit semi-Lagrangian (SISL) dynamical core developed on the Yin-Yang grid was coupled with the physical parameterization package of the operational version of GRAPES. A 3.5-yr integration was carried out on an aqua planet to assess the numerical performance of this non-hydrostatic mo-del relative to other models. Specific aspects of precipitation and general circulation under two different sea surface temperature (SST) conditions (CONTROL and FLAT) were analyzed. The CONTROL SST peaked at the equator. The FLAT SST had its maximum gradient at about 20° latitude, giving a broad equatorial SST maximum in the tropics and flat profile approaching the equator. The tropical precipitation showed different propagation features in the CONTROL and FLAT simulations. The CONTROL showed tropical precipitation bands moving eastward with some envelopes of westward convective-scale disturbance. Less organized westward-propagating rainfall cells and bands were seen in the FLAT and the propagation of the tropical wave varied with the SST gradient. The Inter Tropical Convergence Zone (ITCZ), Hadley cell, and westerly jet core were weaker and more poleward as the SST profile flattened from the CONTROL to FLAT. The climatological structures simulated by GRAPES_YY, such as the distribution of precipitation and the large-scale circulation, fell within the bounds from other models. The stronger ITCZ precipitation, accompanied with stronger Hadley cells and convective heating in the CONTROL simulation, may be summed up as a result of stronger parameterized convection and the non-hydrostatic effects in GRAPES_YY. In addition, mechanism of the zonal mean circulation maintaining is analyzed for the different SST patterns referring the transient eddy flux.
Influence of the Boreal Summer Intraseasonal Oscillation on Extreme Temperature Events in the Northern Hemisphere
Yifei DIAO, Tim LI, Pang-Chi HSU
2018, 32(4): 534-547 [Abstract]( 112 ) HTML PDF (33033 KB)  ( 158 Supplemental Material
Abstract:The impact of the boreal summer intraseasonal oscillation (BSISO) on extreme hot and cool events was investigated, by analyzing the observed and reanalysis data for the period from 1983 to 2012. It is found that the frequency of the extreme events in middle and high latitudes is significantly modulated by the BSISO convection in the tropics, with a 3-9-day lag. During phases 1 and 2 when the BSISO positive rainfall anomaly is primarily located over a northwest-southeast oriented belt extending from India to Maritime Continent and a negative rainfall anomaly appears in western North Pacific, the frequency of extreme hot events is 40% more than the frequency of non-extreme hot events. Most noticeable increase appears in midlatitude North Pacific (north of 40°N) and higher-latitude polar region. Two physical mechanisms are primarily responsible for the change of the extreme frequency. First, an upper-tropospheric Rossby wave train (due to the wave energy propagation) is generated in response to a negative heating anomaly over tropical western North Pacific in phases 1 and 2. This wave train consists of a strong high pressure anomaly center northeast of Japan, a weak low pressure anomaly center over Alaska, and a strong high pressure anomaly center over the western coast of United States. Easterly anomalies to the south of the two strong midlatitude high pressure centers weaken the climatological subtropical jet along 40°N, which is accompanied by anomalous subsidence and warming in North Pacific north of 40°N. Second, an enhanced monsoonal heating over South Asia and East Asia sets up a transverse monsoonal overturning circulation, with large-scale ascending (descending) anomalies over tropical Indian (Pacific) Ocean. Both the processes favor more frequent extreme hot events in higher-latitude Northern Hemisphere. An anomalous atmospheric general circulation model is used to confirm the tropical heating effect.
Joint Impacts of SSTA in Tropical Pacific and Indian Oceans on Variations of the WPSH
Daili QIAN, Zhaoyong GUAN, Weiya TANG
2018, 32(4): 548-559 [Abstract]( 63 ) HTML PDF (6228 KB)  ( 91 Supplemental Material
Abstract:Using the NCEP/NCAR reanalysis and HadISST sea surface temperature (SST) data, the joint effects of the tropi-cal Indian Ocean and Pacific on variations of area of the summertime western Pacific subtropical high (WPSH) for period 1980-2016 are investigated. It is demonstrated that the central tropical Indian Ocean (CTI) and central equatorial Pacific (CEP) are two key oceanic regions that affect the summertime WPSH. During autumn and winter, warm SST anomalies (SSTAs) in CEP force the Walker circulation to change anomalously, resulting in divergence anomalies over the western Pacific and Maritime Continent (MC). Due to the Gill-type response, the abnormal anticyclonic circulation is generated over the western Pacific and South China Sea (SCS). In the subsequent spring, the warm SSTAs in CEP weaken, while the SST over CTI demonstrates a lagged response to Pacific SSTA. The warm CTI-SSTA and CEP-SSTA cooperate with the eastward propagation of cold Kelvin waves in the western Pacific, leading to the eastward shift of the abnormal divergence center that originally locates at the western Pacific and MC. The anticyclone forced by this divergence subsequently moves eastward, leading to the intensification of the negative vorticity there. Meanwhile, warm SSTA in CTI triggers eastward propagating Kelvin waves, which lead to easterly anomalies over the equatorial Indian Ocean and Indonesia, being favorable for maintenance and intensification of the anticyclone over the SCS and western Pacific. The monsoonal meridional-vertical circulation strengthens, which is favorable for the intensification of the WPSH. Using SSTA over the two key oceanic regions as predictors, a multiple regression model is successfully constructed for prediction of WPSH area. These results are useful for our better understanding the variation mechanisms of WPSH and better predicting summer climate in East Asia.
Sensitivity Experiments on the Poleward Shift of Tropical Cyclones over the Western North Pacific under Warming Ocean Conditions
Yixuan SHEN, Yuan SUN, Zhong ZHONG, Kefeng LIU, Jian SHI
2018, 32(4): 560-570 [Abstract]( 93 ) HTML PDF (5303 KB)  ( 97 Supplemental Material
Abstract:Recent studies found that in the context of global warming, the observed tropical cyclones (TCs) exhibit significant poleward migration trend in terms of the mean latitude where TCs reach their lifetime-maximum intensity in the western North Pacific (WNP). This poleward migration of TC tracks can be attributed to not only anthropogenic forcing (e.g., continuous increase of sea surface temperature (SST)), but also impacts of other factors (e.g., natural variability). In the present study, to eliminate the impacts of other factors and thus focus on the impact of unvaried SST on climatological WNP TC tracks, the mesoscale Weather Research and Forecasting (WRF) model is used to conduct a suite of idealized sensitivity experiments with increased SST. Comparisons among the results of these experiments show the possible changes in climatological TC track, TC track density, and types of TC track in the context of SST increase. The results demonstrate that under the warmer SST conditions, the climatological mean TC track systematically shifts poleward significantly in the WNP, which is consistent with the previous studies. Meanwhile, the ocean warming also leads to the decreased (increased) destructive potential of TCs in low (middle) latitudes, and thus northward migration of the region where TCs have the largest impact. Further results imply the possibility that under the ocean warming, the percentage of TCs with westward/northwestward tracks decreases/increases distinctly.
Raindrop Size Distribution Parameters Retrieved from Guangzhou S-band Polarimetric Radar Observations
Xiantong LIU, Qilin WAN, Hong WANG, Hui XIAO, Yu ZHANG, Tengfei ZHENG, Lu FENG
2018, 32(4): 571-583 [Abstract]( 68 ) HTML PDF (3912 KB)  ( 68 Supplemental Material
Abstract:According to the statistical shape-slope (μ-Λ) relationship observed for the first time by several 2D-Video-Distrometers (2DVD) in southern China, a constrained gamma (C-G) model was proposed for the retrieval of rain drop size distributions (DSDs) from Guangzhou S-band polarimetric radar observations. Two typical precipitation processes were selected to verify the accuracy of the retrieval scheme. The μ-Λ relationship:Λ=0.0241μ2 + 0.867μ + 2.453 was obtained based on the 2DVD observation results from at Huizhou Longmen station, which is a very representative location in the area. Relying on the Guangzhou polarimetric radar measurements of radar reflectivity (ZHH) and differential reflectivity (ZDR), the gamma (Γ) size distribution parameters (N0, μ, and Λ) can be retrieved by the C-G model retrieval scheme. The results show that the Guangzhou polarimetric radar retrievals of DSDs were close to the 2DVD observations at Guangzhou Maofengshan station. The rain rate, mass mean diameter, and normalized intercept parameter of radar retrievals were in good agreement with the 2DVD observations, and the relative errors were less than 10%. The overall accuracy of the retrieval scheme was high. The retrieval scheme has established the relationship between the polarimetric radar measurements and gamma size distribution parameters. It will be helpful to in-depth research and application of the dual-polarization radar data in microphysical precipitation processes analysis, as well as convection-resolved numerical model data assimilation and prediction effect evaluation.
Improved Algorithms for Removing Isolated Non-Meteorological Echoes and Ground Clutters in CINRAD
Haibo ZOU, Shuwen ZHANG, Xudong LIANG, Xueting YI
2018, 32(4): 584-597 [Abstract]( 90 ) HTML PDF (6935 KB)  ( 75 Supplemental Material
Abstract:Using China New Generation Weather Radar (CINRAD) level-Ⅱ data, the original algorithms for removing isolated non-meteorological echoes and ground clutters in radar data, which have been applied to Weather Surveillance Radar-1988 Doppler (WSR-88D) in the USA and Severe Weather Automatic Nowcast (SWAN) system in China, are modified and improved. To remove isolated non-meteorological echoes, the new algorithm introduces a constraint parameter (Po) to distinguish whether a window of 5×5 points is isolated as external echoes. A statistical analysis of 150 radar scans (5 cases, with each case comprising 30 scans) under three different echo types (small-scale convection, typhoon, and large-scale synoptic system) shows that the constraint parameter Po ≤ 0.167 is suitable for removing isolated non-meteorological echoes while preserving the edge of meteorological echoes. A new parameter, NDZ, which promotes the ability of the algorithm to identify the ground clutters appearing at two adjacent elevation angles, is constructed based on the vertical continuity of reflectivity. These improved algorithms are tested for four cases (three cases of isolated non-meteorological echoes and one case of ground clutters). Based on the statistics of 232 volume scans of radar data (on a temporal resolution of 1 h) measured at Nanchang station from 0000 UTC 5 to 1600 UTC 14 March 2015, it is found that the improved algorithms not only eliminate most (over 95% under clear-sky conditions) of the isolated non-meteorological echoes and ground clutters (including those appearing at two adjacent elevation angles), but also well preserve the structure of meteorological echoes (storms).
Statistics of the Z-R Relationship for Strong Convective Weather over the Yangtze-Huaihe River Basin and Its Application to Radar Reflectivity Data Assimilation for a Heavy Rain Event
Xue FANG, Aimei SHAO, Xinjian YUE, Weicheng LIU
2018, 32(4): 598-611 [Abstract]( 66 ) HTML PDF (7570 KB)  ( 72 Supplemental Material
Abstract:The relationship between the radar reflectivity factor (Z) and the rainfall rate (R) is recalculated based on radar observations from 10 Doppler radars and hourly rainfall measurements at 6529 automatic weather stations over the Yangtze-Huaihe River basin. The data were collected by the National 973 Project from June to July 2013 for severe convective weather events. The Z-R relationship is combined with an empirical qr-R relationship to obtain a new Z-qr relationship, which is then used to correct the observational operator for radar reflectivity in the three-dimensional variational (3DVar) data assimilation system of the Weather Research and Forecasting (WRF) model to improve the analysis and prediction of severe convective weather over the Yangtze-Huaihe River basin. The performance of the corrected reflectivity operator used in the WRF 3DVar data assimilation system is tested with a heavy rain event that occurred over Jiangsu and Anhui provinces and the surrounding regions on 23 June 2013. It is noted that the observations for this event are not included in the calculation of the Z-R relationship. Three experiments are conducted with the WRF model and its 3DVar system, including a control run without the assimilation of reflectivity data and two assimilation experiments with the original and corrected reflectivity operators. The experimental results show that the assimilation of radar reflectivity data has a positive impact on the rainfall forecast within a few hours with either the original or corrected reflectivity operators, but the corrected reflectivity operator achieves a better performance on the rainfall forecast than the original operator. The corrected reflectivity operator extends the effective time of radar data assimilation for the prediction of strong reflectivity. The physical variables analyzed with the corrected reflectivity operator present more reasonable mesoscale structures than those obtained with the original reflectivity operator. This suggests that the new statistical Z-R relationship is more suitable for predicting severe convective weather over the Yangtze-Huaihe River basin than the Z-R relationships currently in use.
Study of a Horizontal Shear Line over the Qinghai-Tibetan Plateau and the Impact of Diabatic Heating on Its Evolution
Qin GUAN, Xiuping YAO, Qingping LI, Yuancang MA, Honghua ZHANG
2018, 32(4): 612-626 [Abstract]( 55 ) HTML PDF (6972 KB)  ( 56 Supplemental Material
Abstract:Based on the 4 times daily 0.75°×0.75° ERA-Interim data, the structural evolution of a Qinghai-Tibetan Plateau horizontal (east–west-oriented) shear line (TSL) during 15–19 August 2015 and the effect of diabatic heating on its evolution were analyzed. The results show that the TSL possessed a vertical thickness of up to 1.5 km (approximately 600–450 hPa), and was baroclinic in nature. Weak ascending motions occurred near the TSL, accompanied with more significant gradients in dew point temperature than in temperature. The TSL was characterized by diurnal variations in its appearance and structure. It was relatively full in shape (broken) and was the lowest (highest) in vertical extent at 0000 (1800) UTC, and veered clockwise (anticlockwise) during 0000–0600 (1200–1800) UTC. When the north-south span of the TSL increased, it was prone to fracturing; and it disappeared when the dew point temperature gradients to its either side decreased. When the TSL moved northward (southward), its western (eastern) section broke up, while the eastern (western) section inclined to regenerate or merge. The TSL tended to move towards the positive vorticity areas with significant increases in vorticity. When the positive vorticity center moved down, the height of TSL decreased. Further analysis shows that the plateau surface heating dominated the vorticity attribute of the TSL and its movement, with different contributions from local variation, horizontal advection, and vertical advection of the diabatic heating to the TSL at different heights.
Characteristics of Spatiotemporal Distribution of Sea Surface Wind along the East Coast of Guangdong Province
Fei LIAO, Hua DENG, Pak-wai CHAN
2018, 32(4): 627-635 [Abstract]( 58 ) HTML PDF (2872 KB)  ( 99 Supplemental Material
Abstract:We analyzed the frequency distribution characteristics of wind speeds occurring at different offshore sites within a range of 0-200 km based on the sea surface wind data captured via buoys and oil platforms located along the east coast of Guangdong Province. The results of the analysis showed that average wind speed measured for each station reached a maximum in winter while minima occurred in summer, corresponding to obvious seasonal variation, and average wind speed increased with offshore distance. The prevailing wind direction at the nearshore site is the easterly wind, and the frequency of winds within 6-10 m s-1 is considerable with that of winds at > 10 m s-1. With the increase of the offshore distance, the winds were less affected by the land, and the prevailing wind direction gradually became northerly winds, predominately those at > 10 m s-1. For areas of shorter offshore distance (< 100 km), surface wind speeds fundamentally conformed to a two-parameter Weibull distribution, but there was a significant difference between wind speed probability distributions and the Weibull distribution in areas more than 100 km offshore. The mean wind speeds and wind speed standard deviations increased with the offshore distance, indicating that with the increase of the wind speed, the pulsation of the winds increased obviously, resulting in an increase in the ratio of the mean wind speed to the standard deviation of wind speed. When the ratio was large, the skewness became negative. When a relatively great degree of dispersion was noted between the observed skewness and the skewness corresponding to the theoretical Weibull curve, the wind speed probability distribution could not be adequately described by a Weibull distribution. This study provides a basis for the verification of the adaptability of Weibull distribution in different sea areas.
Uncertainty in Simulating the Impact of Cultivar Improvement on Winter Wheat Phenology in the North China Plain
Dingrong WU, Chunyi WANG, Fang WANG, Chaoyang JIANG, Zhiguo HUO, Peijuan WANG
2018, 32(4): 636-647 [Abstract]( 60 ) HTML PDF (3407 KB)  ( 63 Supplemental Material
Abstract:The phenology model is one of the major tools in evaluating the impact of cultivar improvement on crop phenology. Understanding uncertainty in simulating the impact is an important prerequisite for reliably interpreting the effect of cultivar improvement and climate change on phenology. However, uncertainty induced by different temperature response functions and parameterization methods have not been properly addressed. Based on winter wheat phenology observations during 1986-2012 in 47 agro-meteorology observation stations in the North China Plain (NCP), the uncertainty of the simulated impacts caused by four widely applied temperature response functions and two parameterization methods were investigated. The functions were firstly calibrated using observed phenology data during 1986-1988 from each station by means of two parameterization methods, and were then used to quantify the impact of cultivar improvement on wheat phenology during 1986-2012. The results showed that all functions and all parameterization methods could reach acceptable precision (RMSE < 3 days for all functions and parameterization methods), however, substantial differences exist in the simulated impacts between different functions and parameterization methods. For vegetative growth period, the simulated impact is 0.20 day (10 yr)-1[95% confidence interval:-2.81-3.22 day (10 yr)-1] across the NCP, while for reproductive period, the value is 1.50 day (10 yr)-1[-1.03-4.02 day (10 yr)-1]. Further analysis showed that uncertainty can be induced by both different functions and parameterization methods, while the former has greater influence than the latter. During vegetative period, there is a significant positive linear relationship between ranges of simulated impact and growth period average temperature, while during reproductive period, the relationship is polynomial. This highlights the large inconsistency that exists in most impact quantifying functions and the urgent need to carry out field experiment to provide realistic impacts for all functions. Before applying a simulated effect, we suggest that the function should be calibrated over a wide temperature range.
Seasonal Variations of Aerosol Optical Depth over East China and India in Relationship to the Asian Monsoon Circulation
Fenhua MA, Zhaoyong GUAN
2018, 32(4): 648-660 [Abstract]( 58 ) HTML PDF (8335 KB)  ( 96 Supplemental Material
Abstract:Seasonal variation features of aerosol optical depth (AOD) over East China and India in association with the Asian monsoon system are investigated, based on the latest AOD data derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite, the NCEP Final (FNL) Operational Global Analysis data, the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) data, and the NCEP/NCAR reanalysis data from March 2000 to February 2017. The results indicate that AOD in East China is significantly larger than that in India, especially in spring. The seasonal mean AOD in East China is high in both spring and summer but low in fall and winter. However, the AOD averaged over India is highest in summer and lower in spring, fall, and winter. Analysis reveals that AOD is more closely related to changes in surface wind speed in East China, while no obvious relation is found between precipitation and the AOD distribution on the seasonal timescale. As aerosols are mainly distributed in the atmospheric boundary layer (ABL), the stability of the ABL represented by Richardson number (Ri) is closely correlated with spatial distribution of AOD. The upper and lower tropospheric circulation patterns significantly differ between East China and India, resulting in different effects on the AOD. The effect of advection associated with lower tropospheric circulation on the AOD and the influence of convergence and divergence on the AOD distribution play different roles in maintaining the AOD in East China and India. These results improve our understanding of the mechanism responsible for and differences among the aerosol changes in East China and India.
A Preliminarily Statistic and Synoptic Study about the Basic Currents over Southeastern Asia and the Initiation of Typhoons
Yi-Bing XIE, Shou-Jun CHEN, I-Liang CHANG, Yin-Liang HUANG
2018, 32(4): 661-669 [Abstract]( 108 ) HTML PDF (6929 KB)  ( 94 Supplemental Material
Abstract:The relation between the basic currents of the low latitudes and the initiation of typhoons is investigated statistically and synoptically by means of recent aerological data. It is shown that about 80% of typhoons developed in the eastern part of the equatorial convergence zone between the equatorial westerlies and trade wind of West Pacific Ocean. The equatorial westerly is a large scale and quasi-steady phenomenon; therefore, it is probably reasonable to be called "basic current" and typhoons are considered as vortices of smaller scale. There is a quite definite relationship between the time, position, frequency of the initiation of typhoons and the position, strength of the basic currents in the low latitudes. There is a quasi-periodical variation of the strength and position of the basic currents with a period longer than one month. This fact may be helpful for the extended forecast the initiation and development of typhoons.
Shuping LI, Wei HOU, Guolin FENG
2018, 32(4): 670-670 [Abstract]( 12 ) HTML PDF (809 KB)  ( 7
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