Under the severe situation of global warming, regional high temperature and drought events are becoming more frequent, posing a major threat to ecological environment, food security, economic development and life and health. From April to June 2024, high-temperature and drought events occurred again in North China, Northwest China, and Southwest China, causing significant losses in agricultural production. This study utilized various data to preliminarily analyze the characteristics and causes of the high-temperature and drought processes in above three regions. The results show that the drought in southwest China mainly occurred in April, while the drought in North China and Northwest China began to emerge in April, with the intensity gradually increasing and the range expanding from May to June. With the intensification of drought, the abnormal range of regional maximum temperature expanded significantly. The number of hot days in Northwest China reached a new record, and the highest temperature anomaly reached its peak in May, which was one month ahead of the most severe drought period (June) in this region. The high temperatures in southwest China and North China were close to historical extremes. Further analysis indicates that the drought in North China is mainly influenced by the circulation in the Pacific region, while high temperatures are mainly affected by the circulation in the low-latitude Pacific and the Western Pacific Warm Pool. The drought in Northwest China is mainly influenced by the Western Pacific Subtropical High and the Arctic Vortex in the Northern Hemisphere, and the main influence on high temperatures comes from the North Atlantic. The factors affecting high temperatures and drought in the Southwest China are more complex, but mainly concentrated in the Northern Hemisphere Subtropical High and the low-latitude Pacific and Indian Oceans. From the perspective of circulation and water vapor, the main causes of the drought in North China and Northwest China are the development and maintenance of the continental high pressure, while the drought process in Southwest China is affected by the northward shift of the Western Pacific Subtropical High, which allows the dry and hot air currents from the Indian subcontinent to control this area, leading to water vapor divergence and ultimately causing high-temperature drought.
The global climate model BCC-CSM2-MR (Beijing Climate Center-Climate System Model version 2-Medium Resolution) independently developed by the National (Beijing) Climate Center, which has participated in the Climate Model Inter-comparison Project Phase 6. Based on the BCC-CSM1.1m version, the BCC-CSM2-MR model is optimized in aspects of atmospheric radiation transport scheme, deep convection processes and gravity wave drag. Therefore, the improvement of the model’s ability to simulate precipitation and temperature in East Asia needs further assessment. Utilizing gridded observational datasets and station observations in China, the paper thoroughly compares the performances of BCC-CSM2-MR and BCC-CSM1.1m in simulating seasonal mean precipitation (temperature) and daily precipitation (temperature) extremes in East Asia. The results are as follows: (1) Compared with the BCC-CSM1.1m, the BCC-CSM2-MR improves the model performance in simulating seasonal mean precipitation in most sub-regions of East Asia, especially for summer precipitation in the Tibetan Plateau. In particular, the model can better reproduce the annual cycle of precipitation in southeastern China, the Korean Peninsula and Japan. (2) The ability of the BCC-CSM2-MR to simulate the seasonal mean temperature in East Asia has not been improved significantly, and the simulated biases of monthly temperature change in most sub-regions of East Asia are greater than those of the BCC-CSM1.1m. (3) In terms of daily extreme precipitation (temperature), the simulation ability of the BCC-CSM2-MR is obviously better than that of the BCC-CSM1.1m, which significantly improves the simulation ability of daily extreme precipitation (temperature) in southeast China. Overall, the improvement of the BCC-CSM2-MR in deep convection process parameter scheme is beneficial to the simulation of precipitation in East Asia.
From January to June 2023, meteorological droughts of varying degrees occurred in southwestern China, eastern North China, northern East China, central southern China, southern South China, and central Northeast China, seriously affecting agricultural production and restricting local economic development. To improve the ability to respond to drought disasters, timely carry out disaster prevention and reduction work, and conduct real-time summaries of drought situations. This article uses K index, MCI index, T-N flux and CABLE land surface model, as well as meteorological observation data, reanalysis data, soil moisture data to comprehensively analyze the spatiotemporal distribution characteristics and causes of regional drought events. The results are as follows: (1) In the first half of 2023, severe regional drought occurred in southwestern China and eastern Inner Mongolia. The southwestern region experienced a transition from sustained to sudden drought, while Inner Mongolia continued to experience drought. (2) During the same period, the 500 hPa geopotential height field showed a two trough and two ridge pattern at mid to high latitudes. The western Pacific subtropical high pressure abnormally extended westward and uplifted northward, and the Rossby waves at mid latitudes in Eurasia were abnormally weak, resulting in a weakening of the influence of flat westerly winds and cold air in mid to high latitudes, resulting in less precipitation in the southwest and eastern Inner Mongolia, leading to regional drought. (3) In the first half of 2023, the winter La Niña event shifted to the spring El Niño event, resulting in weak convective activity in the southwest region and triggering sustained hot and dry weather; The distribution of sea surface temperature sensitive areas in Inner Mongolia has led to the stability of its upstream high-pressure ridge, resulting in drought and limited rainfall in the eastern region of Inner Mongolia.
There are some systematic biases in prediction of solar radiation based on numerical models, the AVT method has been verified to reduce the prediction bias effectively. The AVT correction method was used to modify the forecasted solar radiation in two photovoltaic power plants in Hexi area of Gansu Province. The results state: (1) Before correction the forecast bias presented obviously diurnal variation with increase first and then decrease, while it wasn’t obvious after correction. There was a strong linear relationship between forecast deviation of solar radiation and observed values before correction, while it got weak after correction (the correlation coefficient and good fitting degree decreased). (2) There was obviously annual change characteristic of solar radiation with the highest forecast bias in spring, followed by summer, autumn and winter. After correction, its forecast bias was reduced in four seasons, especially in spring and summer.
The impacts of fake below-ground meridional wind (FBGMW) on the regional Hadley circulation in Africa (AFHC) in terms of the climatology, interannual variability, and linear trends have been analyzed based on seven reanalysis datasets by using the local partitioning method of the tropical overturning circulation (M1) and the three-pattern decomposition of global atmospheric circulation (M2). The results are as follows: (1) In terms of the climatology, the impacts of FBGMW on the intensity, common rising branch, and sinking branches in both hemispheres of the AFHC depended on the seasons and methods for the calculation of mas stream function. (2) Except for the common rising branch, the FBGMW had small impact on the interannual variability of the intensity of AFHC and the sinking branches location of AFHC in both hemispheres. No-considering FBGMW led to smaller interannual variability of the common rising branch of AFHC in winter and summer based on M1 method and in winter based on M2 Method, and larger interannual variability of the common rising branch of AFHC in autumn based on both methods. With no-considering FBGMW, the change of the interannual variability of the common rising branch of AFHC in spring based on M1 method and in spring and summer based on M2 method depended on the choice of the reanalysis data. (3) Although no-considering FBGMW, it had impact on the quantitative values of the linear trends of the intensity, common rising branch, and sinking branches location in both hemispheres of AFHC, the main conclusions of these linear trends did not change.
