Vol.29, NO.4, 2018

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REVIEWS
A Review on Main Meteorological Disaster of Double-cropping Rice in China
Lü Xiaomin, Zhou Guangsheng
2018, 29(4): 385-395. DOI: 10.11898/1001-7313.20180401
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Abstract:
With the background of climate warming, the occurrence frequency and intensity of agricultural meteorological disasters in China increase significantly, and challenges of responding to agrometeorological disasters become more severe. The key to solving the national major needs lies in clarifying processes of agricultural meteorological disasters and their techniques for disaster reduction and production protection. China is the largest rice producer of the world and its rice production ranks first in domestic growing grain. Among them, the double-cropping rice has a wide range of cultivation, accounting for about 70% of total rice production in China, and is mainly distributed in the mid-lower reaches of the Yangtze and South China.Heat damage, flood, drought and cold injury are major meteorological disasters seriously affecting the growth and development of double-cropping rice in China. On the basis of researches at home and abroad, the recent progresses on major meteorological disasters (cold damage, high temperature disaster, flood, and drought) in double-cropping rice are reviewed. Occurrence characteristics, temporal and spatial distribution patterns of major meteorological disasters (cold damage, high temperature disaster, flood, and drought) and their impacts on production are revealed. Influencing mechanisms of major meteorological disasters on double-cropping rice growth and yield are analyzed. Advantages and disadvantages of long-term, medium and short-term monitoring and early warning methods (site monitoring, remote sensing monitoring, indicator warning, mathematical statistical analysis and dynamic mechanism model) against major meteorological disasters of double-cropping rice are checked, and techniques of reducing meteorological disasters are summarized. In view of the current spatial and temporal distribution of climatic resources and deficiencies of the research on meteorological disasters of double-cropping rice, scientific issues calling for more attention in the future research are proposed, namely, meteorological disaster process and its dynamic monitoring index system, the occurrence pattern of meteorological disasters and remote sensing monitoring technology under climate warming, the response of meteorological disasters to climate change and dynamic assessment technology of meteorological disaster damage, satellite-ground coupled numerical model development for meteorological disaster processes of double-cropping rice, adaptability of double-cropping rice planting systems to climate change, as well as new techniques and demonstrations for meteorological disaster reduction. These researches would provide further basis and technical support for the effective mitigation of meteorological disasters, and ensure stable production and guarantee high yields of double-cropping rice.
Pattern Classification of Heavy Rainfall in Jianghuai Region and Associated Circulations
Tan Guirong, Fan Yiyuan, Niu Ruoyun
2018, 29(4): 396-409. DOI: 10.11898/1001-7313.20180402
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Abstract:
Newly reconstructed dataset of regional historical heavy rain events, daily rainfall data of 2474 observational stations in China and NCEP/NCAR reanalysis data during 1981-2016, 1-10 d rainfall products of 2016 from ECMWF and T639 models are used to study heavy rainfall events in Jianghuai Region.Firstly, typical rain patterns are refined by empirical orthogonal function (EOF) based on 72 heavy rainfall cases. And then the classification of the regional heavy rainfall patterns for all heavy rainfall cases is done objectively through taking corresponding circulation patterns of basic rain patterns as targets with an analogue method.Furthermore, circulation characteristics of heavy rainfall patterns in Jianghuai Region are investigated. From the prophase of heavy rainfall at 500 hPa height fields, for Type QⅠ there is an enhancing large low vortex and it splits into two centers forming a circulation type of two troughs and one ridge, with marked anomalies but small amplitudes at low latitudes near Jianghuai Region. Both Type QⅡ and Type QⅢ is dominated by meridional circulation, but Type QⅡ is dominated by negative anomalies over mid-high latitudes of Asian, and then gradually one trough and one ridge develop, with the western Pacific subtropical high(WPSH) extending further westward at low latitudes. Type QⅢ is dominated by two ridges and one trough forms at mid-latitudes, with the WPSH weaker and unremarkable. However, synoptic systems of all three patterns move slowly, and Jianghuai Region is under the control of a relatively low system by the northwest side of WPSH, which is prevail to the heavy rainfall over this region. The jet stream locates to the north of Jianghuai Region with an anomalous divergence over the region at 200 hPa, but the strength of the jet stream is different for different patterns.Finally, the relationship between circulation patterns and related heavy rain are investigated. The circulation fields are estimated using height field analogue method with different leading time from 10 d to 0, and correlation coefficients between these parameters and the observation are considerable high, such as the height of 500 hPa, meridional wind component at 850 hPa, relative humidity at 700 hPa, and zonal wind at 200 hPa. Threat scores (TS) of the rainfall for days with daily rainfall more than 25 mm and 50 mm are also checked. TS in independent experiments of different lead time from 1 d to 10 d are higher than those from ECMWF and T639 models for events with daily rainfall more than 25 mm.
Simulation of the Urbanization Impact on Precipitation of Landfalling Tropical Cyclone Nida(2016)
Yang Ting, Duan Yihong, Xu Jing, Feng Jianing
2018, 29(4): 410-422. DOI: 10.11898/1001-7313.20180403
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For more than half a century, changes in atmosphere induced by the land use change associated with urbanization have drawn increasing attention. However, it is still unclear how urbanization affects landfalling tropical cyclone (TC) precipitation, which may complicate precipitation processes during TC landfalls. TC precipitation is always hard to predict accurately, which still deserves further research.Several numerical experiments of tropical cyclone Nida(2016) making landfall in Guangdong Province are conducted using the Advanced Research Weather Research and Forecast system (WRF) to evaluate the urbanization effects on TC precipitation during its landfall. Specifically, WRF is coupled with the urban canopy model (UCM), and different land use data (new and old) are used for sensitive experiments. The tropical cyclone Nida(2016) landed around Shenzhen, Guangdong Province on 1 August 2016. The model performance on the track, intensity and precipitation of tropical cyclone Nida is evaluated.Both simulated spatial distribution of 6-hour (from 2200 UTC 1 Aug to 0400 UTC 2 Aug) accumulated precipitation are quite consistent with observations, indicating that the coupled UCM model simulation results are credible. Tracks and accumulated precipitation of the typhoon during landfall can be reproduced reasonably well. No significant difference of simulated TC tracks is found between experiments with and without the updated underlying surface and the coupling of the UCM, indicating that the land use change cannot strikingly affect the track. Although simulations fail to accurately capture the post landfalling intensity changes, storms simulated in experiments including the UCM and latest land use data show more rapid weakening rates after landfall, which are closer to observations. Spatial distributions of simulated 6-hour accumulated precipitation are quite consistent with observations. Furthermore, urban canopy tends to reduce TC precipitation in the urban region while the underlying surface change due to urbanization tends to increase TC precipitation. Urban canopy diminishes vapor transports and corresponding convection, resulting in a decrease in accumulated precipitation. By contrast, land use change due to urbanization decelerates the near-surface wind velocity and decreases surface latent heat fluxes, but strengthens updrafts in the urban region and increases convective available potential energy. As a result, the land use change still leads to enhancement of TC precipitation.These results show that land use change due to urbanization (use of urban canopy) tends to limit TC precipitation after landfall. The rainfall enhancement by land use change due to urbanization is partly offset by the suppression due to use of urban canopy. This will significantly affect the precipitation process of landfalling TCs, and should be taken into account in numerical simulations.
The Impact of Initial Conditions on Soil Moisture Predictability in Early Summer in Eastern China
Li Yanda, Wu Tongwen, Liu Xiangwen, Jie Weihua
2018, 29(4): 423-435. DOI: 10.11898/1001-7313.20180404
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Soil moisture has an important impact on weather and climate. Some previous soil moisture initialization experiments indicate that appropriate initial soil moisture can improve the forecasting skill of the model. The development of land surface initialization method is the urgent demand for improving the forecasting ability of the land model. However, studies about the predictability of the soil moisture in model are still relatively insufficient. To investigate the impact of soil moisture initial value on the prediction of soil moisture in BCC_CSM2_MR model, two experiments are carried out using a respectively true initial value of soil moisture (OH experiment) and an ideal initial value of soil moisture climatology (CH experiment). The lack of soil moisture observations and coordination between the observation and model is a difficult problem in the development of land initialization method. The GSWP (Global Soil Wetness Project) introduces a new method to get the appropriate land initial data. The method indicates land initial data can be obtained using the accurate observed field (including atmospheric field, precipitation data, and radiation field) to force the land model. Therefore, an OF experiment is designed, which forces BCC_CSM model from 1994 to 2013 by using the NCEP atmospheric reanalysis data and China National Meteorological Information Center (NMIC) precipitation data to produce a good model initial value. The soil moisture from OF experiment can reflect the observed distribution and variation of soil moisture over eastern China as the corresponding correlation is high. Thus, it will be used as observations. Based upon soil moisture data from OF experiment, OH and CH experiments are respectively initialized on 1 May during 1994-2013, and the lead time is six months. Comparison of two hindcast experiments shows that the predictability of soil moisture in BCC_CSM model is about 3 pentads in surface layer and even exceeds 1 month in deep layer in some regions of China. At the same time, soil moisture initialization has an impact on forecast skill of soil moisture. This impact can reach 2-3 pentads in surface layer and longer in deeper layer. Variations of soil moisture in shallow layers strongly depend on variations of rainfall, and there is a 1-2 days lag between variations of soil moisture and rainfall, but about 5 days for that in the middle layers.
Evaluation of Quasi-biweekly Oscillation Prediction in the Asian Summer Monsoon Regions by BCC S2S Model
He Zheng, Hsu Pang, Gao Yingxia
2018, 29(4): 436-448. DOI: 10.11898/1001-7313.20180405
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The quasi-biweekly oscillation (QBWO) plays an important role in global weather and climate change. It's a very important source of sub-seasonal to seasonal (S2S) predictability. Using the sub-seasonal to seasonal forecast model of Beijing Climate Center (BCC S2S), the boreal summer QBWO is simulated, the forecast skill is discussed, and the model bias is analyzed. QBWO can be obtained from the third and fourth modes of multivariate empirical orthogonal function (MV-EOF) analysis on daily anomalies of outgoing longwave radiation (OLR) and zonal wind at 850 hPa (U850) in the Asian monsoon region. According to reanalysis data, QBWO shows a northeast-southwest-tilted convection-circulation structure, propagating north/northwestward from the equatorial western Pacific and Indian Ocean. The forecast skill of BCC S2S on QBWO decreases as the forecast lead time increases, and biases become very significant in the period, propagation characteristics and strength when the lead time comes to 9 days. BCC S2S reveals a higher forecast skill of QBWO structure and propagation over the western North Pacific, while it significantly underestimated convection signal of QBWO over the tropical Indian Ocean. The convection-circulation wave structure of QBWO in 9-day lead time prediction over the Indian Ocean is loose and appears over the Arabian Sea (instead of over the tropical eastern Indian Ocean and Bay of Bengal where the reanalyzed QBWO is active). It suggests that the unrealistic Indian Ocean QBWO is related to biases of model mean state. The simulated low-level moisture and convection during boreal summer are enhanced over the western Pacific and the Arabian Sea. However, the model underestimates the abundant moisture and vigorous convection over the eastern Indian Ocean and Bay of Bengal. BCC S2S captures the structure and propagation of QBWO over the western North Pacific, but slightly underestimates the strength of QBWO wave train. This underestimation of QBWO convection might be attributable to the relatively weaker vorticity to the northwest of QBWO convection. By diagnosing the vorticity equation, it's found that although the model well simulates positive contributions of geostrophic vorticity advection and convergence effects to the northwest of convection, these contributions are still underestimated. Moreover, the simulated relative vorticity advection shows an opposite effect to reanalysis data in the 9-day lead time prediction, weakening the favorable environment of QBWO development associated with positive vorticity to the northwestern part of convection.
Establishment and Verification of Single Threshold Temperature Model for Partition Precipitation Phase Separation
Liu Yulian, Ren Guoyu, Sun Xiubao
2018, 29(4): 449-459. DOI: 10.11898/1001-7313.20180406
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Precipitation is an important parameter to characterize climate characteristics and climate change in a region. It is a key link in global water cycle and energy cycle. Under the same rainfall conditions, effects of different-phase precipitation in the earth's surface system are significantly different. The social and economic impacts produced by them also have significant differences. It is of great theoretical and practical significance to distinguish and recognize snowfall characteristics, their anomalies and causes. In addition, when monitoring and studying the global climate change background and long-term changes of the extreme precipitation events above the sub-continental scale, it is also necessary to distinguish rainfall and snowfall information from historical precipitation data.A statistical model with single temperature thresholds is established for separating cold season rainfall and snowfall with independent samples of different climate zones to the north of the Yangtze River in mainland China (north of 30°N). The applicability of the model is tested, and the deviation of the model on sleet recognizing is analyzed.Results show that correlations between estimated temperature thresholds and actual thresholds pass the significance level test for three areas, i.e., Eastern Monsoon Region, Northwest Arid Region and Qinghai-Tibet Plateau. Models for three areas can well simulate the temperature thresholds, the range and regional characteristics. Simulations in East Monsoon Region and Qinghai-Tibet Plateau are better than those in Northwest Arid Region. Among all of the stations in three regions, stations with absolute bias of the simulated threshold temperature less than 1℃ account for more than 74%, and stations with standard deviation biases between -0.5-0.5℃ account for 77%, and those between -1.0-1.0℃ account for 90%. When the daily mean temperature gets lower than thresholds, ratios of sleet days and precipitation compared to snow days and actual precipitation are slightly smaller in the north and larger in the south. In the south of Eastern Monsoon Region, ratios are more than 1. Statistical models can also be used to determine the distribution of the ratio in different areas.Climate types to north of the Yangtze River include temperate monsoon climate, temperate continental climate, and high-cold climate. Results of the independent sample test in three climatic zones indicate that applying this model to estimate the threshold temperature of precipitation phase in sub-continental snow-rich areas, although still limited, is basically feasible.
Performance Tests and Outdoor Comparison Observations of Domestic Remade ECC Ozonesondes
Zheng Xiangdong, Xuan Yuejian, Lin Weili, Tang Jie, Tian Hongmin, Zhang Jinqiang, Xing Yi
2018, 29(4): 460-473. DOI: 10.11898/1001-7313.20180407
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The electrochemical concentration cell (ECC) type ozone sonde, developed by Institute of Atmospheric Physics(IAP), Chinese Academy of Sciences(CAS) is tested through indoor basic examinations and outdoor flying comparison observations with imported ECC ozonesondes. Indoor tests for IAP ozone sonde include the sonde background current (Ibg), the response time and the influences of SO2 and NO2 on ozone measurements, and the low pressure pump efficiency (Cef). Results show that Ibg is less than 0.1 μA and it decreases with the growth of altitude. The response time is 21-26 s. Ozone concentration is much underestimated/overestimated as SO2/NO2 gas is input to the ozone sonde. Cef is about 1.0 as the atmospheric pressure is more than 100 hPa while it rises with the decrease of atmospheric pressure, reaching 1.17 ±0.10-1.28 ±0.16 as the pressure is 10 to 5 hPa. Cef of IAP ozonesonde is higher than that of imported products with the value of about 1.055. Outdoor comparison observation shows that IAP and imported ozonesonde have good compatibility in the radiosonde platform and sampling pumps. The ozone vertical profiles from each sonde show generally consistent with each other. The ratio of total ozone measured by IAP ozonesonde to that from Brewer observations is 0.9-1.1. Ozone concentration difference is effectively reduced in the lower stratosphere when Cef and Ibg of IAP ozonesonde is used. Applications of Cef and Ibg of IAP ozonesonde contributed to 15 DU and 4-6 DU column ozone. The mean absolute difference of tropospheric ozone partial pressure are stable and its values are less than 0.5 mPa, and the stratospheric difference doesn't exceed 1.0 mPa, although the impact from the pump on IAP ozonesonde is obvious. An international low-pressure environment simulation cabin comparison test is necessary for IAP ozonesonde. The stability of Cef of this radiosonde system should be improved, and it suggests that filtering algorism should be added to data depressing (including meteorology and ozone processing) to decrease data oscillations.
Characteristics of Atmospheric Hydrogen Peroxide at an Urban Site in Beijing During Winter and Spring
Gong Yishu, Xu Xiaobin, Xu Wanyun, Zhang Gen
2018, 29(4): 474-486. DOI: 10.11898/1001-7313.20180408
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As a photochemical produced oxidant, gaseous hydrogen peroxide (H2O2) plays an important role in aerosols and acid rain production. However, not many measurements of gaseous H2O2 have been made in China in the past few years and further studies especially the level and trend of H2O2 in smog are needed. To make up for the lack of H2O2 data and provide support for air quality improvement in China, an observation experiment on gaseous H2O2 is carried out from 27 Dec 2016 to 28 Apr 2017 at an urban site in the northwest of mega-city Beijing, using a two-channel H2O2 monitor AL2021. The concentration level, variation and influence factors under different conditions are analyzed with several simultaneously observed pollutants (O3, PAN, NOX, PM2.5, etc.) and meteorological parameters. The mean mixing ratio of H2O2 for the entire period is (0.65±0.59)×10-9, with a higher mean of (0.83±0.67)×10-9 in spring and a lower mean of (0.51±0.47)×10-9 in winter. Day peaks with the value higher than 2×10-9 is also detected in winter indicating that high concentration of H2O2 can also happen under certain conditions. The concentration of H2O2 shows pronounced diurnal cycles with peaks in the period of 1800-2100 BT, occurring later than those reported for other sites in China or foreign countries and shows a delay of about 4 to 7 hours compared with the peaking time of O3. H2O2 level is found to be negatively correlated with relative humidity (RH), especially when only considering the maximum H2O2 level under RH over 55%. This is consistent with the uptake of gaseous H2O2 by water-containing aerosol particles under higher RH conditions. The H2O2 peaking time and peak level are closely related with RH as well as other factors, such as NOX. Under conditions of daily RH lower than 55%, H2O2 level can reach a mean peak value of 1.52×10-9 with peaking times during 1800-2400 BT, while it peaks lower (1×10-9) and earlier (before 1700 BT) with the daily mean RH higher than 65%. H2O2, O3 and PAN show different diurnal patterns and levels under different pollution conditions. H2O2 shows smaller average level differences for clean and hazy days, with a higher peak but a lower level during 1100-1500 BT under the clean condition. O3 shows a higher mixing ratio under clean condition than under hazy condition, while PAN reveals an opposite trend. Results also indicate that dynamical transport could be an important influencing factor of variations and levels of H2O2 and O3. The impact of photochemistry on haze formation in colder months in the urban environment of Beijing and its feedback warrant further studies, particularly the role of H2O2 in the formation of sulfate aerosol.
Simulation of Structure Height Influences on Electromagnetic Field of Lightning Return Stroke
Su Zhiguo, Lü Weitao, Chen Lüwen, Ma Ying, Wu Bin, Qi Qi, Wu Shanshan
2018, 29(4): 487-495. DOI: 10.11898/1001-7313.20180409
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With the development of economy and society and the continuous acceleration of urbanization, there are more and more tall-objects in urban area. Tall-objects can attract nearby downward lightning and trigger upward lightning. When a thunderstorm occurs, tall-object may be struck multiple times, which lead to a severe lightning electromagnetic environment in the vicinity. Therefore, the study of lightning striking to tall-object is of significance to the lightning protection of nearby equipment and cables.An electromagnetic model of lightning striking to tall-object is developed based on the three-dimensional finite-difference time-domain (FDTD) numerical method. Using FDTD method, the propagation law of lightning vertical electric field, the azimuthal magnetic field and the horizontal electric field along the ground surface, produced by negative cloud-to-ground lightning flash to tall-object, is investigated considering cases of different heights (100-600 m) of tall-objects.The amplitude of lightning short-circuit current waveform is 11 kA, and the corresponding 10%-to-90% rise-time is 0.15 μs. Simulation results show that the height of the tall-object plays an important role on the peak value of lightning electric field. For example, for the case of distance d=100 m, the peak value of vertical electric field decreases from 8.59 kV·m-1 to 3.41 kV·m-1 with the height of the tall-object increasing from 100 m to 600 m (decrement:63%). Moreover, for horizontal electric field, the positive peak value increases from 0.7 kV·m-1 to 1.29 kV·m-1 (increment:84%), and the amplitude of negative peak increases up to 130%. The peak value of azimuthal magnetic field and horizontal electric field will increase with the tall-object height, when the distance of the observation point is constant. However, for the case of distance d=100 m, 300 m, the vertical electric field peak will decrease with the tall-object height increasing. Furthermore, for the case of d=500 m, the vertical electric field peak increase first and then decrease with the height. In addition, the tall-object height has an effect on the dependence of vertical electric field peak on distance d. For relative lower/taller strike object, the peak value of the corresponding vertical electric field attenuates quickly/slowly with the observation distance d. Results obtained are very useful for lightning protection design of power cables and electronic equipment in the vicinity of tall objects.
Preliminary Study on Millimeter Wave Attenuation Characteristics Combined with Wind Profiler
Zhong Zhengyu, Ma Shuqing, Yang Ling, Huang Shurong, Tang Yingjie
2018, 29(4): 496-504. DOI: 10.11898/1001-7313.20180410
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Millimeter wave is easily impacted by the attenuation of precipitation, and the energy of electromagnetic wave emitted by millimeter-wave cloud radar is often absorbed and scattered by the precipitation particles. Electromagnetic wave attenuation makes the radar echo intensity less than the actual echo intensity and affects the detection accuracy. However, wind profiler is invented to detect the turbulence of clear air and it can detect precipitation particles. For the L-band wind profiler with a wavelength of 220 mm, the attenuation caused by rainfall is negligible. Therefore, detection results of wind profiler can be considered as no attenuation. A millimeter-wave cloud radar is installed in Meteorological Observation Center of CMA, and its observations of precipitation are compared with data of an L-band wind profiler from 1 May 2016 to 31 July 2016. The millimeter-wave cloud radar has three kinds of pulse width (2 μs, 5 μs and 20 μs), and the wind profiler has also three detection modes (low, medium, and high). Because the temporal resolution of two radars is different, to make sure that the observation time are consistent and samples of data for analysis is sufficient, the difference of observation time for each group of data is set within 120 s. The data for comparison and analysis comes from 2 μs and 5 μs modes of millimeter-wave cloud radar, low and medium mode of wind profiler. Reflectivity factors are calculated using the power spectrum data of wind profiler and I, Q data of millimeter-wave cloud radar. The processing method of power spectrum and calculation method of reflectivity factor are also introduced. The relationship between the attenuation and the falling velocity of precipitation particles is initially analyzed.Results indicate that the attenuation of millimeter wave caused by precipitation is obvious. If precipitation particles are uniform in the range of radar observation, there is a positive correlation between the attenuation of the millimeter wave radar and the falling velocity of precipitation particles. And the longer distance the millimeter-wave travels, the greater the attenuation is. The variation of reflectivity factor caused by attenuation is about 1-7 dB, 2-11 dB when the falling velocity of precipitation particles is within the range of 3.5-7.5 m·s-1 at the height range of 1110-2430 m, 1110-3510 m. Results are consistent under different detection mode of the millimeter-wave radar and the wind profiler.
Effects of Low Temperature During Ear Differentiation Stage on Yield Components of Spring Maize
Guo Chunming, Ren Jingquan, Cao Tiehua, Xu Chen, Li Jianping, Qu Simiao
2018, 29(4): 505-512. DOI: 10.11898/1001-7313.20180411
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Low temperature and cold damage are the main agrometeorological disasters which affects the spring maize in Northeast China. The response of spring maize to low temperature and cold damage is investigated, and the influence level of the obstacle type of low temperature on spring maize breeding is confirmed. Selecting Zhengdan958 species of spring maize, artificial climate laboratory is used to simulate low temperature environment as 13℃(T1), 15℃(T2) and 17℃(T3), and effects of low temperature on yield components and photosynthetic rate in the ear differentiation stage(early stage, middle stage, late stage) of spring maize are studied. Results show that yield components and photosynthetic characteristics change with similar trends after being affected by different low temperatures during the ear differentiation stage. Compared with control check, there is no significant change in ear diameter and 100-grain weight under low temperature treatment, while the ear length and the kernel numbers per panicle decreased significantly, and the weight of the panicle also has a significantly reduction. Lower temperature and longer duration lead to heavier effects. Effects of low temperature during the early stage on the kernel numbers per panicle are the heaviest, lower during middle stage and the much weaker during late stage. During the early ear differentiation stage, compared with control check, the kernel numbers per panicle are reduced significantly by 28.5%, 28.4%, 16.5%, and the weight of the panicle decrease significantly by 31.5%, 29.4%, 21.1% under T1, T2 and T3 in three days. The kernel numbers per panicle are reduced significantly by 36%, 36.6%, 28.8%, and the weight of the panicle decrease significantly by 38%, 35.8%, 23.9% in five days. The net photosynthetic rate, stomatal conductance, intercellular CO2 concentration and transpiration rate of leaves decrease significantly under low temperature. During the early ear differentiation stage, compared with control check, the net photosynthetic rate decrease by 36.2%, 26.5%, 24.4% under the treatment of T1, T2 and T3 in three days, and the net photosynthetic rate decrease by 63.8%, 53.3% and 47.1% in five days. The decrease of kernel numbers per panicle in spring maize caused by low temperature during the ear differentiation stage is the main cause of the yield reduction. One of the factors leading to the decrease of net photosynthetic rate is the restrictive effect of stoma of spring maize. Results above can be used as a reference for evaluating the impact of low temperature and cold damage on spring maize.
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