ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 49,Issue 5,2023 Table of Contents
2023, 49(5):513-524.
DOI: 10.7519/j.issn.1000-0526.2023.021501
Abstract:
The upper-level cut-off cold vortex is an important part of the atmospheric circulation in the middle and high latitudes, and usually can lead to the convective instability as well as the occurrence and development of various high impact weather. The most common cut-off cold vortex in China is the northeast cold vortex, which can not only affect the weather and climate anomalies in the northeastern China, but also have a profound impact on the central and eastern China. Therefore, it is necessary to pay attention to the formation mechanism and prediction theory of cut-off cold vortex. Based on this, this paper reviews the main research progress in the formation mechanism and prediction methods of upper-level cut-off cold vortex in recent years. Firstly, the definition of cut-off cold vortex and its weather and climate characteristics are summarized. Secondly, the impacts of different weather and climate systems as well as the external forcing factors on the cut-off cold vortex are reviewed. Finally, the gaps and unsolved problems in the previous researches are pointed out.
The upper-level cut-off cold vortex is an important part of the atmospheric circulation in the middle and high latitudes, and usually can lead to the convective instability as well as the occurrence and development of various high impact weather. The most common cut-off cold vortex in China is the northeast cold vortex, which can not only affect the weather and climate anomalies in the northeastern China, but also have a profound impact on the central and eastern China. Therefore, it is necessary to pay attention to the formation mechanism and prediction theory of cut-off cold vortex. Based on this, this paper reviews the main research progress in the formation mechanism and prediction methods of upper-level cut-off cold vortex in recent years. Firstly, the definition of cut-off cold vortex and its weather and climate characteristics are summarized. Secondly, the impacts of different weather and climate systems as well as the external forcing factors on the cut-off cold vortex are reviewed. Finally, the gaps and unsolved problems in the previous researches are pointed out.
2023, 49(5):525-541.
DOI: 10.7519/j.issn.1000-0526.2022.082201
Abstract:
In recent years, the forecasting of tropical cyclone (TC) intensity has been improved. However, the intensity forecasting value is weaker in the years when TCs are frequently intensified over offshore waters. Focused on the factors affecting the intensified coastal TCs, this paper reviews the related research from two perspectives: environmental conditions and dynamic mechanism. Then a detailed analysis of the effects of environmental atmospheric, ocean forcing mechanisms, structural changes in the inner core and water phase change in spiral bands on the intensifying process of coastal TCs is performed. Such factors are good indicators for the forecasting of coastal TCs, and they act together in the TC intensifying process. Through comparing and summarizing relevant research results, a schematic model of impact factors is established in order to provide valuable reference for operational forecasting of the intensifying process of TCs over offshore waters.
In recent years, the forecasting of tropical cyclone (TC) intensity has been improved. However, the intensity forecasting value is weaker in the years when TCs are frequently intensified over offshore waters. Focused on the factors affecting the intensified coastal TCs, this paper reviews the related research from two perspectives: environmental conditions and dynamic mechanism. Then a detailed analysis of the effects of environmental atmospheric, ocean forcing mechanisms, structural changes in the inner core and water phase change in spiral bands on the intensifying process of coastal TCs is performed. Such factors are good indicators for the forecasting of coastal TCs, and they act together in the TC intensifying process. Through comparing and summarizing relevant research results, a schematic model of impact factors is established in order to provide valuable reference for operational forecasting of the intensifying process of TCs over offshore waters.
2023, 49(5):542-550.
DOI: 10.7519/j.issn.1000-0526.2022.121801
Abstract:
Based on the airborne microwave radiometer （G-band water vapor radiometer, named GVR）, a retrieval algorithm of precipitation water vapor and liquid water 〖JP2〗path based on BP neural network and Decker〖JP〗 model is established by using the Beijing sounding data as the training data, and the airborne microwave radiation transfer equation as the forward algorithm. Compared to the GVR own algorithm, the observation height is added as an input variable. A new cloud model considering the influence of temperature on the cloud water phase, and the historical sounding data completed to increase the integral height to 30 km are applied in the new algorithm. The precipitation water vapor errors calculated by two algorithms are verified by using numerical simulation test, external field observation test and observation error transfer analysis. The results show that the correlation coefficient between the retrieval and probe values of the new and GVR own algorithms are 0.9988 and 0.9929 respectively. The retrieval value of the GVR own algorithm is generally lower than the sounding calculation value. The absolute errors of precipitation water vapor calculated by the new and GVR own algorithms are 0.05-1.30 mm and 0.2-3.0 mm, relative errors are 1%-10% and 4%-65%, the minimum relative error calculated by the new algorithm is 1% below 6 km, about 75% of new algorithm results are below 5% while only less than 1% of GVR own results are below 5%. Take the data observed on 20 November 2016 as an example. The errors caused by the GVR instrument observation errors that are calculated by the new algorithm and the GVR own algorithm retrieval formula are 0.05 mm and 0.06 mm at 3000 m height respectively. After of retrieval formula, with the increase of the water vapor detection value (the aircraft altitude drops), the transfer error increase of the GVR own algorithm is significantly higher than that of the new algorithm. The flight case on 30 June 2021 is selected to verify the liquid water path retrieval error of the two algorithms. The results show that the liquid water path ranges of the new algorithm and the own algorithm are 0 mm and 0-0.006 mm during cloudless periods over the plane. Error analysis shows that the new algorithm is effective for improving the retrieval accuracy of local precipitation water vapor and liquid water path.
Based on the airborne microwave radiometer （G-band water vapor radiometer, named GVR）, a retrieval algorithm of precipitation water vapor and liquid water 〖JP2〗path based on BP neural network and Decker〖JP〗 model is established by using the Beijing sounding data as the training data, and the airborne microwave radiation transfer equation as the forward algorithm. Compared to the GVR own algorithm, the observation height is added as an input variable. A new cloud model considering the influence of temperature on the cloud water phase, and the historical sounding data completed to increase the integral height to 30 km are applied in the new algorithm. The precipitation water vapor errors calculated by two algorithms are verified by using numerical simulation test, external field observation test and observation error transfer analysis. The results show that the correlation coefficient between the retrieval and probe values of the new and GVR own algorithms are 0.9988 and 0.9929 respectively. The retrieval value of the GVR own algorithm is generally lower than the sounding calculation value. The absolute errors of precipitation water vapor calculated by the new and GVR own algorithms are 0.05-1.30 mm and 0.2-3.0 mm, relative errors are 1%-10% and 4%-65%, the minimum relative error calculated by the new algorithm is 1% below 6 km, about 75% of new algorithm results are below 5% while only less than 1% of GVR own results are below 5%. Take the data observed on 20 November 2016 as an example. The errors caused by the GVR instrument observation errors that are calculated by the new algorithm and the GVR own algorithm retrieval formula are 0.05 mm and 0.06 mm at 3000 m height respectively. After of retrieval formula, with the increase of the water vapor detection value (the aircraft altitude drops), the transfer error increase of the GVR own algorithm is significantly higher than that of the new algorithm. The flight case on 30 June 2021 is selected to verify the liquid water path retrieval error of the two algorithms. The results show that the liquid water path ranges of the new algorithm and the own algorithm are 0 mm and 0-0.006 mm during cloudless periods over the plane. Error analysis shows that the new algorithm is effective for improving the retrieval accuracy of local precipitation water vapor and liquid water path.
2023, 49(5):551-562.
DOI: 10.7519/j.issn.1000-0526.2023.030301
Abstract:
Supersaturation in the cloud is the one of key factors affecting cloud macro and microproperties. The Explicit Mixing Parcel Model (EMPM) is used to study the evolution of supersaturation of cloud droplets during the entrainmentmixing process. The results show that in this process, the supersaturation decreases firstly due to the entrained dry air, and then increases due to the evaporation of droplets until the parcel restores new saturation. Then, the effects of different thermal, dynamic and microphysical factors on the reduction of supersaturation and saturation recovery time are analyzed. The sensitive test indicates that the factors of small reduction and quick recovery are the high relative humidity of the entrained dry air and the number concentration of initial cloud droplets. The higher humidity, the less effect of entrainment. The higher the number concentration， the smaller droplet size and the faster evaporation, and thus the supplement to the humidity of dry air is strong. The factor of large reduction and slow recovery is the large fraction of entrained dry air. The more the dry air is entrained, the more evaporation of droplets. The factor of large reduction and quick recovery is the high turbulent kinetic energy dissipation rate. The faster the mixing process, the faster cloud droplets evaporate. The results will help to improve the understanding of the entrainment mixing process and warm cloud precipitation theory.
Supersaturation in the cloud is the one of key factors affecting cloud macro and microproperties. The Explicit Mixing Parcel Model (EMPM) is used to study the evolution of supersaturation of cloud droplets during the entrainmentmixing process. The results show that in this process, the supersaturation decreases firstly due to the entrained dry air, and then increases due to the evaporation of droplets until the parcel restores new saturation. Then, the effects of different thermal, dynamic and microphysical factors on the reduction of supersaturation and saturation recovery time are analyzed. The sensitive test indicates that the factors of small reduction and quick recovery are the high relative humidity of the entrained dry air and the number concentration of initial cloud droplets. The higher humidity, the less effect of entrainment. The higher the number concentration， the smaller droplet size and the faster evaporation, and thus the supplement to the humidity of dry air is strong. The factor of large reduction and slow recovery is the large fraction of entrained dry air. The more the dry air is entrained, the more evaporation of droplets. The factor of large reduction and quick recovery is the high turbulent kinetic energy dissipation rate. The faster the mixing process, the faster cloud droplets evaporate. The results will help to improve the understanding of the entrainment mixing process and warm cloud precipitation theory.
2023, 49(5):563-573.
DOI: 10.7519/j.issn.1000-0526.2022.113001
Abstract:
In order to study the extrapolation predictability of cloud images or cloud clusters with different scales, two things were done. First, a cloud detection method suitable for FY-4 satellite infrared cloud images (10.8 μm) was designed, and the cloud clusters with different scales were separated by the regional recognition algorithm. Second, the optical flow method of HS global constraint scheme was used to carry out extrapolation test. The statistical results from 12 examples in 2020 show that in the extrapolation forecasting of brightness temperature, the available optical flow information is close to 6 h. The RMSE of bright temperatures in 0.5, 1 and 6 hours are about 4.4, 7.1 and 16.7 K respectively. The accuracy of extrapolation prediction decreases with the increasing of time length in forecasting. In addition, because of diurnal variations in brightness temperature, the cloud detection results are used in the following extrapolation tests. In the short-time (0-1 h) extrapolation forecast, the error increase is mainly caused by the deviations from cloud location. During the first to sixth hours, the main forecast error is caused by the prediction errors in cloud location and cloud area. The accuracy of extrapolation forecasting decreases as the spatial scale of the cloud cluster decreases. The useable time lengths of extrapolating cloud clusters in scales >2000 km, 200-2000 km, 20-200 km, and <20 km are shorter than 6 h, 1.5 h, 1 h and 15 min, respectively. The extrapolated results in all scales are similar with that in the scale >2000 km. The research results can give a significant guide in extrapolation forecasting of infrared cloud image in operational applications.
In order to study the extrapolation predictability of cloud images or cloud clusters with different scales, two things were done. First, a cloud detection method suitable for FY-4 satellite infrared cloud images (10.8 μm) was designed, and the cloud clusters with different scales were separated by the regional recognition algorithm. Second, the optical flow method of HS global constraint scheme was used to carry out extrapolation test. The statistical results from 12 examples in 2020 show that in the extrapolation forecasting of brightness temperature, the available optical flow information is close to 6 h. The RMSE of bright temperatures in 0.5, 1 and 6 hours are about 4.4, 7.1 and 16.7 K respectively. The accuracy of extrapolation prediction decreases with the increasing of time length in forecasting. In addition, because of diurnal variations in brightness temperature, the cloud detection results are used in the following extrapolation tests. In the short-time (0-1 h) extrapolation forecast, the error increase is mainly caused by the deviations from cloud location. During the first to sixth hours, the main forecast error is caused by the prediction errors in cloud location and cloud area. The accuracy of extrapolation forecasting decreases as the spatial scale of the cloud cluster decreases. The useable time lengths of extrapolating cloud clusters in scales >2000 km, 200-2000 km, 20-200 km, and <20 km are shorter than 6 h, 1.5 h, 1 h and 15 min, respectively. The extrapolated results in all scales are similar with that in the scale >2000 km. The research results can give a significant guide in extrapolation forecasting of infrared cloud image in operational applications.
2023, 49(5):574-587.
DOI: 10.7519/j.issn.1000-0526.2023.013002
Abstract:
Based on hourly observation from 74 meteorological stations in Zhejiang Province, the models of ordinary linear regression and those considering spatial heterogeneity are adopted to explore the spatial estimation and impact factors of summer afternoon precipitation in Zhejiang Province in this study. It is found that the summer afternoon precipitation in Zhejiang Province shows a decreasing trend from the southwest to northeast. The two main precipitation centers in the south and north form the southwest-northeast major rain band. Geographical, topographic and meteorological factors jointly affect the spatial distribution of summer afternoon precipitation in Zhejiang Province. The model of geographically neural network weighted regression (GNNWR) based on neural network and considering the spatial heterogeneity works significantly better than the models of ordinary linear regression and the geographically weighted regression, in terms of model performance and spatial distribution pattern of estimated precipitation, which suggests that the GNNWR model has the value of further application in the field of meteorology.
Based on hourly observation from 74 meteorological stations in Zhejiang Province, the models of ordinary linear regression and those considering spatial heterogeneity are adopted to explore the spatial estimation and impact factors of summer afternoon precipitation in Zhejiang Province in this study. It is found that the summer afternoon precipitation in Zhejiang Province shows a decreasing trend from the southwest to northeast. The two main precipitation centers in the south and north form the southwest-northeast major rain band. Geographical, topographic and meteorological factors jointly affect the spatial distribution of summer afternoon precipitation in Zhejiang Province. The model of geographically neural network weighted regression (GNNWR) based on neural network and considering the spatial heterogeneity works significantly better than the models of ordinary linear regression and the geographically weighted regression, in terms of model performance and spatial distribution pattern of estimated precipitation, which suggests that the GNNWR model has the value of further application in the field of meteorology.
2023, 49(5):588-599.
DOI: 10.7519/j.issn.1000-0526.2022.051102
Abstract:
Model forecast performance and forewarning service validity of disastrous heavy precipitation have been among the chief concerns in professional meteorological service. In view of these concerns, the evaluation of the power-grid-system-oriented meteorological forewarning for heavy precipitation in the main flood season (June-September, 2019) in the Beijing-Tianjin-Hebei Region is chosen as an example, in order to carry out in-depth analysis on using MODE (method for object-based diagnostic evaluation) in the inspection of short-term forecast and nowcast from two aspects, namely, target recognition of precipitation and target matching of precipitation. The results show that heavy precipitation in the main flood season of the Beijing-Tianjin-Hebei Region is mainly concentrated from afternoon to the first half of the night, characterized by large in precipitation intensity, small in range, easy false-alarms, and difficulty in predicting their spatial characteristics. The correlation coefficient of diurnal variation of the heavy precipitation frequency of short-term forecast and nowcast ranges from 0.78 to 0.94, while that of the diurnal variation of range is from 0.6 to 0.82. The forecast effect of moving path and rainfall intensity is slightly better than that of the falling area. The shorter the forecast time, the better the forecast effect of heavy precipitations and their spatial characteristics. The comprehensive forecast evaluation method put forward in the paper can make up for the shortcomings of traditional inspection methods. It can explore the potential and limitations of forecast, and provide reference for accurate and specialized meteorological services.
Model forecast performance and forewarning service validity of disastrous heavy precipitation have been among the chief concerns in professional meteorological service. In view of these concerns, the evaluation of the power-grid-system-oriented meteorological forewarning for heavy precipitation in the main flood season (June-September, 2019) in the Beijing-Tianjin-Hebei Region is chosen as an example, in order to carry out in-depth analysis on using MODE (method for object-based diagnostic evaluation) in the inspection of short-term forecast and nowcast from two aspects, namely, target recognition of precipitation and target matching of precipitation. The results show that heavy precipitation in the main flood season of the Beijing-Tianjin-Hebei Region is mainly concentrated from afternoon to the first half of the night, characterized by large in precipitation intensity, small in range, easy false-alarms, and difficulty in predicting their spatial characteristics. The correlation coefficient of diurnal variation of the heavy precipitation frequency of short-term forecast and nowcast ranges from 0.78 to 0.94, while that of the diurnal variation of range is from 0.6 to 0.82. The forecast effect of moving path and rainfall intensity is slightly better than that of the falling area. The shorter the forecast time, the better the forecast effect of heavy precipitations and their spatial characteristics. The comprehensive forecast evaluation method put forward in the paper can make up for the shortcomings of traditional inspection methods. It can explore the potential and limitations of forecast, and provide reference for accurate and specialized meteorological services.
2023, 49(5):600-610.
DOI: 10.7519/j.issn.1000-0526.2023.012902
Abstract:
Taking the main urban area of Hefei as an example, this paper uses meteorological observation data, satellite remote sensing data, geographic information data and other data to classify the ventilation potential of the main urban area of Hefei by calculating urban ecological parameters such as sky openness and surface roughness, and then we give suggestions on the construction of ventilation corridors. The results show that the heat island effect is serious in Hefei Economic and Technological Development Zone and Shuangfeng Development Zone. The sky view factor in the central area is poor with most areas below 0.5, and the surface roughness along the South Feihe River is lower, but the surface roughness on both sides is higher. The surface ventilation potential is moderate in most area of the region, except the higher ventilation potential in the southeast area near Chaohu Lake and the coast of the South Feihe River. The ventilation potential in the building area and the northwest area of this region is poor. Based on the wind direction rose diagram and the analysis of urban space thermal environment, we construct six ventilation corridors with four longitudinal and two horizontal lines preliminarily constructed.
Taking the main urban area of Hefei as an example, this paper uses meteorological observation data, satellite remote sensing data, geographic information data and other data to classify the ventilation potential of the main urban area of Hefei by calculating urban ecological parameters such as sky openness and surface roughness, and then we give suggestions on the construction of ventilation corridors. The results show that the heat island effect is serious in Hefei Economic and Technological Development Zone and Shuangfeng Development Zone. The sky view factor in the central area is poor with most areas below 0.5, and the surface roughness along the South Feihe River is lower, but the surface roughness on both sides is higher. The surface ventilation potential is moderate in most area of the region, except the higher ventilation potential in the southeast area near Chaohu Lake and the coast of the South Feihe River. The ventilation potential in the building area and the northwest area of this region is poor. Based on the wind direction rose diagram and the analysis of urban space thermal environment, we construct six ventilation corridors with four longitudinal and two horizontal lines preliminarily constructed.
2023, 49(5):611-623.
DOI: 10.7519/j.issn.1000-0526.2022.121501
Abstract:
Based on the provincial annual drought disaster losses and socio-economic data of China from 2004 to 2019, spatio-temporal variation characteristics are analyzed for the three loss indexes and their loss rates, including the crop area, population affected by drought and direct economic loss caused by droughts. Risk assessment of drought loss rates for different hazard bearing bodies are carried out by the information diffusion method so as to understand the drought risk pattern and provide reference for improving the ability of drought risk management. The results show that the annual disaster loss rates of the three indexes caused by drought tend to decrease in China during 2004 and 2019, in which the loss rates of crop area and population show decreasing trends significantly. This is the result of the increase of annual precipitation, decrease of annual drought cumulative intensity and days with moderate drought grade and above, as well as the enhancement of drought resistance capacity. The drought risk patterns of the three types of hazard bearers are different. When the annual rate of crop area affected by drought to sown area is greater than and equal to 20%, only Ningxia, Shanxi, Inner Mongolia and Gansu have a higher exceeding possibility level. When the rate of population affected by drought to total population is greater than and equal to 30% and the rate of direct economic losses to GDP is greater than and equal to 1%, the exceeding probability is small and there is no province with high or higher possibility grade. Under the level of 20-year return period of annual rate of crop area affected by drought to sown area, the serious drought area distributed in the whole Northwest China, eastern Southwest China and the provinces of Hubei, Hunan, Zhejiang and Hainan. Under the level of 20-year return period of annual rate of population affected by drought to total population, the serious drought area was located in the middle and east of Northwest China, eastern Southwest China, and the provinces of Anhui, Shanxi, Inner Mongolia. Under the level of 20-year return period of annual rate of direct economic losses to GDP, the serious drought area is located in Northeast China, central Northwest China, eastern Southwest China as well as the provinces of Inner Mongolia, Hainan.
Based on the provincial annual drought disaster losses and socio-economic data of China from 2004 to 2019, spatio-temporal variation characteristics are analyzed for the three loss indexes and their loss rates, including the crop area, population affected by drought and direct economic loss caused by droughts. Risk assessment of drought loss rates for different hazard bearing bodies are carried out by the information diffusion method so as to understand the drought risk pattern and provide reference for improving the ability of drought risk management. The results show that the annual disaster loss rates of the three indexes caused by drought tend to decrease in China during 2004 and 2019, in which the loss rates of crop area and population show decreasing trends significantly. This is the result of the increase of annual precipitation, decrease of annual drought cumulative intensity and days with moderate drought grade and above, as well as the enhancement of drought resistance capacity. The drought risk patterns of the three types of hazard bearers are different. When the annual rate of crop area affected by drought to sown area is greater than and equal to 20%, only Ningxia, Shanxi, Inner Mongolia and Gansu have a higher exceeding possibility level. When the rate of population affected by drought to total population is greater than and equal to 30% and the rate of direct economic losses to GDP is greater than and equal to 1%, the exceeding probability is small and there is no province with high or higher possibility grade. Under the level of 20-year return period of annual rate of crop area affected by drought to sown area, the serious drought area distributed in the whole Northwest China, eastern Southwest China and the provinces of Hubei, Hunan, Zhejiang and Hainan. Under the level of 20-year return period of annual rate of population affected by drought to total population, the serious drought area was located in the middle and east of Northwest China, eastern Southwest China, and the provinces of Anhui, Shanxi, Inner Mongolia. Under the level of 20-year return period of annual rate of direct economic losses to GDP, the serious drought area is located in Northeast China, central Northwest China, eastern Southwest China as well as the provinces of Inner Mongolia, Hainan.
2023, 49(5):624-632.
DOI: 10.7519/j.issn.1000-0526.2022.101201
Abstract:
Due to the influence of the terrain difference, the model wind speed prediction may deviate from the actual observation. Monin-Obukhov similarity theory shows that the vertical change of wind speed near the ground conforms to the logarithmic rate characteristics. Based on this similarity theory, the deviation revision scheme is constructed to revise the wind speed forecast from the model terrain to the actual terrain, and 〖JP2〗the atmospheric stability determination factor is introduced to the scheme. After analyzing more than 760 stations in North China in summer and winter, we have found that the average deviation of wind speed forecast within 12 h can be reduced by more than 20%, the 24 h decline can also reach more than 10%, and the root mean square error of wind speed within different forecast periods can also be reduced by 5%-8%. This indicates that the revised scheme has a very obvious positive effect on the wind speed prediction of the model.
Due to the influence of the terrain difference, the model wind speed prediction may deviate from the actual observation. Monin-Obukhov similarity theory shows that the vertical change of wind speed near the ground conforms to the logarithmic rate characteristics. Based on this similarity theory, the deviation revision scheme is constructed to revise the wind speed forecast from the model terrain to the actual terrain, and 〖JP2〗the atmospheric stability determination factor is introduced to the scheme. After analyzing more than 760 stations in North China in summer and winter, we have found that the average deviation of wind speed forecast within 12 h can be reduced by more than 20%, the 24 h decline can also reach more than 10%, and the root mean square error of wind speed within different forecast periods can also be reduced by 5%-8%. This indicates that the revised scheme has a very obvious positive effect on the wind speed prediction of the model.
2023, 49(5):633-640.
DOI: 10.7519/j.issn.1000-0526.2023.042501
Abstract:
The main characteristics of the general atmospheric circulation in February 2023 are as follows. Two polar vortex centers existed in the Northern Hemisphere, with the sub-center located along the Sea of Okhotsk and stronger than normal. The atmospheric circulation over mid-high latitudes of Eurasia changed from multi-wave type to “two-trough-and-one-ridge” type. Most of the mid-high latitude region of China was in the frontal zone ahead of ridge, with a positive anomaly before the trough range, so the associated cold air activities were more in number but weaker in intensity. The southern branch trough with regular position and intensity held a more frequency of rain and snow events in the northern China and phased continuously rainy weather in the southern China. The February average temperature over China was 0.3℃, 1.6℃ warmer than normal, and the monthly average precipitation was 15.5 mm, 5% less than normal.
The main characteristics of the general atmospheric circulation in February 2023 are as follows. Two polar vortex centers existed in the Northern Hemisphere, with the sub-center located along the Sea of Okhotsk and stronger than normal. The atmospheric circulation over mid-high latitudes of Eurasia changed from multi-wave type to “two-trough-and-one-ridge” type. Most of the mid-high latitude region of China was in the frontal zone ahead of ridge, with a positive anomaly before the trough range, so the associated cold air activities were more in number but weaker in intensity. The southern branch trough with regular position and intensity held a more frequency of rain and snow events in the northern China and phased continuously rainy weather in the southern China. The February average temperature over China was 0.3℃, 1.6℃ warmer than normal, and the monthly average precipitation was 15.5 mm, 5% less than normal.
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ISSN:1000-0526 CN:11-2282/P