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Variation characteristics of agricultural boundary temperature in main agricultural regions

in basins of the Brahmaputra River and its two tributaries in Xizang from 1981 to 2022

GUO Yinan, HUANG Zhicheng, DU Jun, XU Wei

Journal of Arid Meteorology 2024, 42 (1): 47-53. DOI: 10. 11755/j. issn. 1006-7639（2024）-01-0047

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The mean daily temperature of 10 ℃ is the lower limit temperature for the suitable growth of thermophilic crop. The ≥10 ℃ active accumulated temperature (ATT10) is one of the important indexes to measure the heat resources in the main agricultural regions of the Brahmaputra River and its two tributaries over Xizang (BRTX). Based on the daily average temperature data of 9 meteorological stations in BRTX from 1981 to 2022, the linear trend estimation, Pearson coefficient, Mann-Kendall test and R/S analysis method were used to analyze climate change characteristics of ≥10 ℃ boundary temperature (BT10). The results are as follows: (1) With the increase of altitude, the BT10 showed obvious vertical zonal characteristics in the main agricultural regions of BRTX, including the delay of initial date, the advance of the last day, the decrease of duration days and the ATT10. (2) From 1981 to 2022, the initial date of BT10 was advanced by -2.53 d·(10 a)-1, and the final date delayed with a rate of 3.33 d·(10 a)-1, the duration days and ATT10 significantly increased with a rate of 5.87 d·(10 a)-1 and 106.19 °C·d·(10 a)-1, respectively. Compared with the Qinghai-Xizang Plateau, the magnitude of BT10 change was significantly larger. (3) The 1980s was the decade with the latest initial date, the earliest final date, the shortest duration days and the lowest ATT10 in the past 40 years, while the 21st century was the opposite. (4) The H indexes of the BT10 were all greater than 0.65, indicating that in the future the BT10 will maintain a strong persistence of earlier initial day, later final day, prolonged duration days and increased ATT10. The mutation change of the initial date of BT10 occurred in the early 1990s, while the abrupt change of the final date, duration days and ATT10 occurred in the first decade of the 21st century.

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Relationship between extremely low temperature in spring in Shandong Province and North Atlantic SST in preceding winter

XU Weiping, MENG Xiangxin, GU Weizong, BO Zhongkai

Journal of Arid Meteorology 2022, 40 (2): 202-211. DOI: 10.11755/j.issn.1006-7639（2022）-02-0202

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Based on daily temperature data from 122 national meteorological stations in Shandong Province from 1961 to 2018, three extreme low temperature indices were calculated, and it was found that the occurrence frequency of extremely low temperature events defined by the scale of drop in daily minimum temperature in 24 hours could better reflect the characteristics of extremely low temperature in spring in Shandong. And on this basis, ERA-Interim monthly reanalysis data and Hadley sea surface temperature data were used to analyze the spatial and temporal distribution characteristics of occurrence frequency of extremely low temperature events in spring in Shandong and the anomalous characteristics of atmospheric circulation. The results are as follows: (1) The occurrence frequency of extremely low temperature events had multi-time scale variation characteristics in spring in Shandong. (2) The obvious wave train structure on 500 hPa geopotential height field was existed in mid-high latitudes in the typical extreme low temperature years in spring in Shandong. (3) The North Atlantic Ocean to the south of Greenland was a key area for vertical wave flux transmission. In this key area, the energy in the lower layer transmitted upward, and dispersed outward in the upper layer, which was beneficial to the maintenance and enhancement of the extremely low temperature in spring in Shandong. (4) The triple pole mode of sea surface temperature in the North Atlantic in the preceding winter had a significant positive correlation with the occurrence frequency of extremely low temperature events in spring in Shandong. The triple pole mode of sea surface temperature excited the Eurasian wave, which led to the deepening and strengthening of 500 hPa trough over the Lake Baikal area. Due to the influence of cold air behind the trough, the extremely low temperature events occurred frequently in spring in Shandong.

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Study and Application of Discriminant Criterion of Winter Precipitation Phase in Tianjin

CHEN Hong, YU Wentao, XU Wei, YANG Xiaojun, SUN Jianyuan, CHEN Kaihua

Journal of Arid Meteorology 2021, 39 (4): 670-677.

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Based on conventional meteorological observation data in Tianjin and the ECWMF ERAInterim reanalysis data (0.125°×0.125°), the transformation processes of raintosleet and then sleettosnow were analyzed from October to next April during 2000-2015 in Tianjin. The humidity and geopotential thickness during the transformation process of precipitation phases were analyzed, and 9 factors, namely temperature on 850 hPa, 925 hPa,1000 hPa and surface, thickness from 1000 to 850 hPa and from 850 to 700 hPa, 0 ℃ layer height, -4 ℃ layer height and 925 hPa relative humidity, were identified, which had close relationship with transformation process of precipitation phases. Further, their corresponding threshold indexes for different precipitation phases were given. And through the analysis of 3 weather cases, the usability of the indicators had been further verified. The discriminant equation for precipitation phases was established by using the 9 factors, it was found that the backtesting discriminant accuracy for rain and snow was higher than 80%.