ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 46,Issue 1,2020 Table of Contents
2020, 46(1):1-14.
DOI: 10.7519/j.issn.1000-0526.2020.01.001
Abstract:
By using the NCEP 2.5°×2.5° daily reanalysis data and daily precipitation data at 20:00 BT from Chinese meteorological stations in the summer of 1960-2015 (June-August), and the method of vorticity source equation and Eliassen-Palm flux, the wave sources, energy propagation of Rossby wave activities along the Asian subtropical westerly jet (ASWJ) in summer and its correlation with precipitation and anomalies in China are analyzed. The results show as follows. The sources of the quasi-stationary planetary waves at 200 hPa are mainly concentrated in the Mediterranean Sea, where the quasi-stationary Rossby waves in the Asian westerly jet are triggered and propagate eastward along the jet stream. In the process of eastward propagation, the wave-mean flow interactions in the southern side of the jet axis are relatively active. The convergence and divergence centers of the wave activity flux alternately distribute along the subtropical westerly jet, and the wave-mean flow interactions are the dynamic mechanism of the alternating variation of westerly intensity over ASWJ. The divergence of the five key areas of the wave action flux distributed alternately along ASWJ has a strong correlation, which is shown as different parts of the same Rossby wave train, of which the propagation of the Rossby wave energy at the wave source has the greatest influence on the strength of its downstream ASWJ.The magnitude of the zonal wind in the critical region of the jet stream is also closely related to the intensity and distribution of the divergence field of the wave-acting flux. The wave source flux divergence indices WFD-Ⅰ and WFC-Ⅱ which are located in the wave source and from the east of the Qinghai-Tibet Plateau to the Loess Plateau in China are more correlated with precipitation in southern and northern China. Statistical analysis in the summers of 56 years shows that when the WFD-Ⅰ is positive anomalous year, the proportion of precipitation in the key areas of the south is 62.5%, and when it is negative anomalous year, the proportion in the key areas of the north is 80%. When WFC-Ⅱ is positive anomalous year, the proportion in the key areas of the south is 66.7%, and when it is negative anomalous year, the proportion in the key areas in the north is 81.8%. Studying the circulation cause of precipitation anomaly in China caused by the wave activity flux〖HJ〗 divergence index WFD-Ⅰ anomalous years at wave source in summer, we find that when WFD-Ⅰ is positive anomalous year, the Rossby wave triggered by the upstream source region has a strong energy dispersion to the downstream region and the position is southerly, the wave-mean flow interaction leads to the intensification of high-altitude jet over southern China, the intensification of divergence and convergence configuration at high and low levels, and the intensification of vertical ascending movement, which are liable to cause more precipitation anomalies in southern China.When WFD-Ⅰis negative anomalous year, the meridional propagation of Rossby wave energy is stronger, while the zonal propagation is weaker. The key area of northern precipitation is controlled by wave activity flux divergence, the westerly jet at high altitude is strengthened, the divergence and convergence configuration at high and low levels and the vertical ascending motion are enhanced, which are beneficial to the development of precipitation in northern China.
By using the NCEP 2.5°×2.5° daily reanalysis data and daily precipitation data at 20:00 BT from Chinese meteorological stations in the summer of 1960-2015 (June-August), and the method of vorticity source equation and Eliassen-Palm flux, the wave sources, energy propagation of Rossby wave activities along the Asian subtropical westerly jet (ASWJ) in summer and its correlation with precipitation and anomalies in China are analyzed. The results show as follows. The sources of the quasi-stationary planetary waves at 200 hPa are mainly concentrated in the Mediterranean Sea, where the quasi-stationary Rossby waves in the Asian westerly jet are triggered and propagate eastward along the jet stream. In the process of eastward propagation, the wave-mean flow interactions in the southern side of the jet axis are relatively active. The convergence and divergence centers of the wave activity flux alternately distribute along the subtropical westerly jet, and the wave-mean flow interactions are the dynamic mechanism of the alternating variation of westerly intensity over ASWJ. The divergence of the five key areas of the wave action flux distributed alternately along ASWJ has a strong correlation, which is shown as different parts of the same Rossby wave train, of which the propagation of the Rossby wave energy at the wave source has the greatest influence on the strength of its downstream ASWJ.The magnitude of the zonal wind in the critical region of the jet stream is also closely related to the intensity and distribution of the divergence field of the wave-acting flux. The wave source flux divergence indices WFD-Ⅰ and WFC-Ⅱ which are located in the wave source and from the east of the Qinghai-Tibet Plateau to the Loess Plateau in China are more correlated with precipitation in southern and northern China. Statistical analysis in the summers of 56 years shows that when the WFD-Ⅰ is positive anomalous year, the proportion of precipitation in the key areas of the south is 62.5%, and when it is negative anomalous year, the proportion in the key areas of the north is 80%. When WFC-Ⅱ is positive anomalous year, the proportion in the key areas of the south is 66.7%, and when it is negative anomalous year, the proportion in the key areas in the north is 81.8%. Studying the circulation cause of precipitation anomaly in China caused by the wave activity flux〖HJ〗 divergence index WFD-Ⅰ anomalous years at wave source in summer, we find that when WFD-Ⅰ is positive anomalous year, the Rossby wave triggered by the upstream source region has a strong energy dispersion to the downstream region and the position is southerly, the wave-mean flow interaction leads to the intensification of high-altitude jet over southern China, the intensification of divergence and convergence configuration at high and low levels, and the intensification of vertical ascending movement, which are liable to cause more precipitation anomalies in southern China.When WFD-Ⅰis negative anomalous year, the meridional propagation of Rossby wave energy is stronger, while the zonal propagation is weaker. The key area of northern precipitation is controlled by wave activity flux divergence, the westerly jet at high altitude is strengthened, the divergence and convergence configuration at high and low levels and the vertical ascending motion are enhanced, which are beneficial to the development of precipitation in northern China.
2020, 46(1):15-28.
DOI: 10.7519/j.issn.1000-0526.2020.01.002
Abstract:
A torrential rainfall caused by Typhoon Goni during 23-24 August 2015 influenced some coastal areas in East China. This paper utilizes the ECMWF ensemble forecasts to study the key reason for the forecast uncertainty of the far distance torrential rainfall and uses the ensemble sensitivity method to investigate the sensitivity areas of the primary weather system. Meanwhile, the thermodynamic formation mechanisms of the torrential rainfall are also discussed. It is indicated that the predictability of ensemble forecasts of the typhoon-induced far distance torrential rainfall was obviously low and the significant forecast adjustment occurred just 24 hours before the torrential rainfall. At initial time when the systematic track error was minimum, the ensemble precipitation forecast was mostly close to the observation. But further analysis shows that the correlation between the deviation of typhoon track and the precipitation level is uncertainty. The contrastive analysis of the mid- and lower-circulations between two ensemble groups at different precipitation levels indicates that the forecast difference of the upper trough is the main cause for the forecast uncertainty. The eastward movement and intensification of the upper trough not only increased the baroclinic instability in the torrential rainfall area, but also enhanced the circulation magnitude in the side of the typhoon facing the area. The sensitivity analysis on 500 hPa geopotential height shows that, whether on the initial field or on the forecast fields, the mean precipitation in the torrential rainfall area has notable correlation with the movement and intensification of the upper trough. With the increasing forecast time, the areas with significant correlation expand downstream of the upper trough. In addition it is found that the movement of the upper trough can enhance (reduce) the intensification of the cold air on the left (right) side of the torrential rainfall area and make more moisture air on the right side of the typhoon transported to the torrential rainfall area.
A torrential rainfall caused by Typhoon Goni during 23-24 August 2015 influenced some coastal areas in East China. This paper utilizes the ECMWF ensemble forecasts to study the key reason for the forecast uncertainty of the far distance torrential rainfall and uses the ensemble sensitivity method to investigate the sensitivity areas of the primary weather system. Meanwhile, the thermodynamic formation mechanisms of the torrential rainfall are also discussed. It is indicated that the predictability of ensemble forecasts of the typhoon-induced far distance torrential rainfall was obviously low and the significant forecast adjustment occurred just 24 hours before the torrential rainfall. At initial time when the systematic track error was minimum, the ensemble precipitation forecast was mostly close to the observation. But further analysis shows that the correlation between the deviation of typhoon track and the precipitation level is uncertainty. The contrastive analysis of the mid- and lower-circulations between two ensemble groups at different precipitation levels indicates that the forecast difference of the upper trough is the main cause for the forecast uncertainty. The eastward movement and intensification of the upper trough not only increased the baroclinic instability in the torrential rainfall area, but also enhanced the circulation magnitude in the side of the typhoon facing the area. The sensitivity analysis on 500 hPa geopotential height shows that, whether on the initial field or on the forecast fields, the mean precipitation in the torrential rainfall area has notable correlation with the movement and intensification of the upper trough. With the increasing forecast time, the areas with significant correlation expand downstream of the upper trough. In addition it is found that the movement of the upper trough can enhance (reduce) the intensification of the cold air on the left (right) side of the torrential rainfall area and make more moisture air on the right side of the typhoon transported to the torrential rainfall area.
2020, 46(1):29-36.
DOI: 10.7519/j.issn.1000-0526.2020.01.003
Abstract:
The accurate predictions of the first-time landing position and the second-time landing strength are very difficult because of the rarely-seen close distance for the binary typhoons Nesat (No.1709) and Haitang (No.1710). Although CMA issued an accurate official forecast, the performance of most models including ECMWF and NCEP was far from satisfactory. In this paper, forecast experience and focus in the forecasting operation are analyzed and summarized. The rationality of model prediction for the large-scale circulation such as subtropical high is analyzed based on synoptic models, deviation revision experience and the performance of ensemble forecasting system. The main circulation is determined by analyzing the relative strength of the closest time of the binary typhoons, so as to judge the difference between the landing time of the two typhoons, their extreme strengths and onshore maintenance mechanisms. Paying close attention to two influencing factors of the typhoon track angle with Taiwan’s central mountain range and cross-island time is helpful to revise the typhoon strength of the second-time landing.
The accurate predictions of the first-time landing position and the second-time landing strength are very difficult because of the rarely-seen close distance for the binary typhoons Nesat (No.1709) and Haitang (No.1710). Although CMA issued an accurate official forecast, the performance of most models including ECMWF and NCEP was far from satisfactory. In this paper, forecast experience and focus in the forecasting operation are analyzed and summarized. The rationality of model prediction for the large-scale circulation such as subtropical high is analyzed based on synoptic models, deviation revision experience and the performance of ensemble forecasting system. The main circulation is determined by analyzing the relative strength of the closest time of the binary typhoons, so as to judge the difference between the landing time of the two typhoons, their extreme strengths and onshore maintenance mechanisms. Paying close attention to two influencing factors of the typhoon track angle with Taiwan’s central mountain range and cross-island time is helpful to revise the typhoon strength of the second-time landing.
2020, 46(1):37-49.
DOI: 10.7519/j.issn.1000-0526.2020.01.004
Abstract:
Based on the observed daily precipitation and sunshine hour data in Sichuan Province, the NCEP/NCAR reanalysis daily and monthly data, and the NOAA monthly sea surface temperature data, the variation characteristics of the autumn rainy and sunless weather and its mechanism of the Sichuan in 2017 have been analyzed by the modern statistics methods in this paper. The results showed that the stage characteristics of autumn rain in Sichuan from September to October of 2017 were obvious, showing the characteristics of more rainy days, less sunshine and longer duration of rainy and sunless weather. The area between Baykal Lake and Balkhash Lake was under a wide and inclined low trough in the middle layer of troposphere, which is beneficial to the movement of cold airflow to the southeast, influencing Sichuan. At the same time, the Western Pacific subtropical high was stronger, stretching more westward than normal, and finally the cold and warm airflows met in Sichuan and formed continuous precipitation in September. In October, the Western Pacific subtropical high was stronger, stretching more westward and northward than normal, while the Indian-Burma trough was deeper at 500 hPa, which is beneficial to the water vapor transport to Sichuan from Bay of Bengal and Western Pacific. This is favorable for the continuous precipitation in Sichuan. Further analysis showed that the characteristics of Rossby wave propagation is beneficial to the continuation and maintenance of the Eurasian circulation in the middle and high latitudes, and the Rossby wave energy dispersion is an important cause of maintaining the low trough on the area between Baykal Lake and Balkhash Lake in September. In addition, the sea surface temperature in the equatorial central and eastern Pacific obviously continues to be lower, making the Western Pacific subtropical high become stronger, stretching more westward and northward and Indian-Burma trough was deeper than normal from September to October. Therefore, the influence of the external forcing signal of sea surface temperature and the circulation anomaly caused by the Rossby wave energy dispersion led to the persis-tence of rainy and sunless weather in Sichuan from September to October of 2017.
Based on the observed daily precipitation and sunshine hour data in Sichuan Province, the NCEP/NCAR reanalysis daily and monthly data, and the NOAA monthly sea surface temperature data, the variation characteristics of the autumn rainy and sunless weather and its mechanism of the Sichuan in 2017 have been analyzed by the modern statistics methods in this paper. The results showed that the stage characteristics of autumn rain in Sichuan from September to October of 2017 were obvious, showing the characteristics of more rainy days, less sunshine and longer duration of rainy and sunless weather. The area between Baykal Lake and Balkhash Lake was under a wide and inclined low trough in the middle layer of troposphere, which is beneficial to the movement of cold airflow to the southeast, influencing Sichuan. At the same time, the Western Pacific subtropical high was stronger, stretching more westward than normal, and finally the cold and warm airflows met in Sichuan and formed continuous precipitation in September. In October, the Western Pacific subtropical high was stronger, stretching more westward and northward than normal, while the Indian-Burma trough was deeper at 500 hPa, which is beneficial to the water vapor transport to Sichuan from Bay of Bengal and Western Pacific. This is favorable for the continuous precipitation in Sichuan. Further analysis showed that the characteristics of Rossby wave propagation is beneficial to the continuation and maintenance of the Eurasian circulation in the middle and high latitudes, and the Rossby wave energy dispersion is an important cause of maintaining the low trough on the area between Baykal Lake and Balkhash Lake in September. In addition, the sea surface temperature in the equatorial central and eastern Pacific obviously continues to be lower, making the Western Pacific subtropical high become stronger, stretching more westward and northward and Indian-Burma trough was deeper than normal from September to October. Therefore, the influence of the external forcing signal of sea surface temperature and the circulation anomaly caused by the Rossby wave energy dispersion led to the persis-tence of rainy and sunless weather in Sichuan from September to October of 2017.
2020, 46(1):50-62.
DOI: 10.7519/j.issn.1000-0526.2020.01.005
Abstract:
Based on the single-station CAPPI grid data after strict quality control, this paper studies the echo intensity consistency on the equidistant line in the overlapping area of adjacent weather radar observations. According to the elements of radar detection coverage, altitude and precipitation intensity, the automatic matching program of adjacent radar and the automatic selection program of contour plane are compiled, and the homogeneity algorithm of adjacent weather radar is established. Then, three kinds of criteria for evaluating the homogeneity of weather radar echo observation differences in China are formulated, which are credible, suspicious and false, and also the conditions for meeting the evaluation criteria are given. A national real-time weather radar homogeneity evaluation system is successfully established. The evaluation results show that the homogeneity evaluation system can detect the echo consistency of different bands, different radar models and adjacent radars in different provinces in real time and efficiently, and give the evaluation results. By evaluating the homogeneity of one-hour precipitation process of radar in Zhejiang, Fujian and Guangdong Provinces, 27 S-band radars participated in the evaluation. The overall credibility rate of the 27 radars was 85.19%, the suspicious rate was 11.11% and the suspicious error rate was 3.7%. In addition, the problems of low radar echo intensity, beam blocking and electromagnetic interference are successfully detected. The uniformity analysis of radar echo at Linyi Station shows that the evaluation system can alarm in time, detect the deviation of radar echo position pointing at Linyi Station, and the azimuth of antenna shifts clockwise by 16.88°, which shortens the fault detection time.
Based on the single-station CAPPI grid data after strict quality control, this paper studies the echo intensity consistency on the equidistant line in the overlapping area of adjacent weather radar observations. According to the elements of radar detection coverage, altitude and precipitation intensity, the automatic matching program of adjacent radar and the automatic selection program of contour plane are compiled, and the homogeneity algorithm of adjacent weather radar is established. Then, three kinds of criteria for evaluating the homogeneity of weather radar echo observation differences in China are formulated, which are credible, suspicious and false, and also the conditions for meeting the evaluation criteria are given. A national real-time weather radar homogeneity evaluation system is successfully established. The evaluation results show that the homogeneity evaluation system can detect the echo consistency of different bands, different radar models and adjacent radars in different provinces in real time and efficiently, and give the evaluation results. By evaluating the homogeneity of one-hour precipitation process of radar in Zhejiang, Fujian and Guangdong Provinces, 27 S-band radars participated in the evaluation. The overall credibility rate of the 27 radars was 85.19%, the suspicious rate was 11.11% and the suspicious error rate was 3.7%. In addition, the problems of low radar echo intensity, beam blocking and electromagnetic interference are successfully detected. The uniformity analysis of radar echo at Linyi Station shows that the evaluation system can alarm in time, detect the deviation of radar echo position pointing at Linyi Station, and the azimuth of antenna shifts clockwise by 16.88°, which shortens the fault detection time.
2020, 46(1):63-72.
DOI: 10.7519/j.issn.1000-0526.2020.01.006
Abstract:
Three cases of severe convection with different intensities, including supercell, common hail storm and non-hail storm, observed by Xiamen S-band dual-polarization radar are presented in this paper. The characteristic differences of dual-polarization radar in these cases, containing differential reflectivity (ZDR), specific differential phase (KDP) and co-polar correlation coefficient (CC) during storm developing from growing stage to mature stage were analyzed. The ZDR and KDP columns are common features existing in these different intensities of storms. The supercell and common hail storm also have CC hole characteri-stics, featuring the inflow area near ground. In addition, ZDR arc and KDP foot also appear at low level and CC low value region with big hails at high level in mature stage of supercell. The variation of ZDR column can be used to identify super-cooled water area and forecast the developing trend of severe convective clouds. The CC hole can be used to identify the inflow area of convective cell. Then KDP column, KDP foot or its vacancy can be used to identify the areas of heavy rain or big hails. Therefore, the feature identification of dual-polarization radar have great potentials in short-term early warning of severe convection and hail suppression.
Three cases of severe convection with different intensities, including supercell, common hail storm and non-hail storm, observed by Xiamen S-band dual-polarization radar are presented in this paper. The characteristic differences of dual-polarization radar in these cases, containing differential reflectivity (ZDR), specific differential phase (KDP) and co-polar correlation coefficient (CC) during storm developing from growing stage to mature stage were analyzed. The ZDR and KDP columns are common features existing in these different intensities of storms. The supercell and common hail storm also have CC hole characteri-stics, featuring the inflow area near ground. In addition, ZDR arc and KDP foot also appear at low level and CC low value region with big hails at high level in mature stage of supercell. The variation of ZDR column can be used to identify super-cooled water area and forecast the developing trend of severe convective clouds. The CC hole can be used to identify the inflow area of convective cell. Then KDP column, KDP foot or its vacancy can be used to identify the areas of heavy rain or big hails. Therefore, the feature identification of dual-polarization radar have great potentials in short-term early warning of severe convection and hail suppression.
2020, 46(1):73-79.
DOI: 10.7519/j.issn.1000-0526.2020.01.007
Abstract:
FY-3C is the second generation polar meteorological satellite which was developed by China independently and launched in 2013. MWRI (microwave radiance imager) is an important microwave load which can monitor air, ocean and land. As a product of MWRI, TPW (total precipitable water) can be used in numerical weather prediction and climate research. But, the effect of the application relies on the accuracy of TPW. Based on the 4-year satellite observation data, the quality of TPW products is validated by comparing the TPW products with the radiosonde TPW or SSMIS TPW products. As a result, the RMSE (root mean square error) of orbit product is 2.6 mm and the average relative error is 7%. What’s more, the RMSE of day product is 3 mm and 2.1 mm when separately compared with SSMIS and radiosonde. The accuracy of month product is stable and the RMSE is less than 1.3 mm. Above findings show that FY-3C MWRI TPW products have a high precision and good stability, and have the application ability in weather and climate field.
FY-3C is the second generation polar meteorological satellite which was developed by China independently and launched in 2013. MWRI (microwave radiance imager) is an important microwave load which can monitor air, ocean and land. As a product of MWRI, TPW (total precipitable water) can be used in numerical weather prediction and climate research. But, the effect of the application relies on the accuracy of TPW. Based on the 4-year satellite observation data, the quality of TPW products is validated by comparing the TPW products with the radiosonde TPW or SSMIS TPW products. As a result, the RMSE (root mean square error) of orbit product is 2.6 mm and the average relative error is 7%. What’s more, the RMSE of day product is 3 mm and 2.1 mm when separately compared with SSMIS and radiosonde. The accuracy of month product is stable and the RMSE is less than 1.3 mm. Above findings show that FY-3C MWRI TPW products have a high precision and good stability, and have the application ability in weather and climate field.
2020, 46(1):80-88.
DOI: 10.7519/j.issn.1000-0526.2020.01.008
Abstract:
Precipitation is likely to take place as precipitable water vapor (PWV) of the atmosphere reaches a certain value. Thus, the threshold of PWV (PWVt), which can be regarded as the research bridge between PWV and precipitation. In the aim of calculating PWVt precisely, this paper has brought in “precipitable water vapor saturation (PWVsat)” of the atmosphere and deduced the computing formula of PWVsat under various atmosphere conditions. From the formula, it is shown that PWVsat is a function of surface temperature (ts), which indicates the maximum water vapor that a bottom-up saturated atmosphere is capable to hold. The atmosphere needs to be wet enough to form clouds and rains. Therefore, it is inferred that ts is a factor in PWVt. To prove that, PWVt and ts of 36 gauge stations ranging from May 2015 to October 2016 are studied and 1122 precipitation cases are selected and fitted. The results show that the fitting formula of PWVt and computing formula of PWVsat are highly alike, proving the 2 variables are closely correlated. Meanwhile, fitting parameters of each of 36 stations are given for relating PWV to precipitation. This method has gone through statistical examination to find that its accuracy rate, missing rate and vacancy rate to be 93.69%, 2.32% and 3.99% respectively in precipitation prediction, which denotes a sound application value in predicting rainfall. Finally, the method is applied in a rainfall case to show that PWVt can predict precipitation well, and the difference between PWV and PWVt is correlated to precipitation amount.
Precipitation is likely to take place as precipitable water vapor (PWV) of the atmosphere reaches a certain value. Thus, the threshold of PWV (PWVt), which can be regarded as the research bridge between PWV and precipitation. In the aim of calculating PWVt precisely, this paper has brought in “precipitable water vapor saturation (PWVsat)” of the atmosphere and deduced the computing formula of PWVsat under various atmosphere conditions. From the formula, it is shown that PWVsat is a function of surface temperature (ts), which indicates the maximum water vapor that a bottom-up saturated atmosphere is capable to hold. The atmosphere needs to be wet enough to form clouds and rains. Therefore, it is inferred that ts is a factor in PWVt. To prove that, PWVt and ts of 36 gauge stations ranging from May 2015 to October 2016 are studied and 1122 precipitation cases are selected and fitted. The results show that the fitting formula of PWVt and computing formula of PWVsat are highly alike, proving the 2 variables are closely correlated. Meanwhile, fitting parameters of each of 36 stations are given for relating PWV to precipitation. This method has gone through statistical examination to find that its accuracy rate, missing rate and vacancy rate to be 93.69%, 2.32% and 3.99% respectively in precipitation prediction, which denotes a sound application value in predicting rainfall. Finally, the method is applied in a rainfall case to show that PWVt can predict precipitation well, and the difference between PWV and PWVt is correlated to precipitation amount.
2020, 46(1):89-97.
DOI: 10.7519/j.issn.1000-0526.2020.01.009
Abstract:
Three experiments of boundary-layer meteorological profiles observed by rotorcraft unmanned aerial vehicle (UAV) were carried out in spring (28-30 March), summer (20-26 June) and autumn (5-13 September) 2018 respectively in Sheyang Station of Yancheng, Jiangsu Province, and compared with L-band radar sounding data to verify the accuracy of UAV observation data. The results show that the observation data of temperature, relative humidity, wind direction and wind speed vertical profile measured by UAV are in good agreement with the observation data of the L-band radar sounding data. The correlation coefficients of temperature (T), relative humidity (RH), wind direction (WD) and wind speed (WS) of UAV and L-band radar sounding are 0.98, 0.98, 0.98 and 0.91, respectively. The absolute deviations of T, RH, WD and WS are 0.57℃, 4.25%, 11.5° and 1.88 m·s-1 respectively. Since UAV measures the instantaneous wind speed at corresponding height, it can better reflect the subtle variation of wind speed characteristics in boundary layer. The summer UAV experiment recorded detailed changes of boundary layer structure during a heavy fog process. The boundary-layer structure and fog macro-characteristics observed by the UAV during this process were similar as that of L-band radar. The results show that UAV has a promising prospect in the application of boundary layer meteorological observation.
Three experiments of boundary-layer meteorological profiles observed by rotorcraft unmanned aerial vehicle (UAV) were carried out in spring (28-30 March), summer (20-26 June) and autumn (5-13 September) 2018 respectively in Sheyang Station of Yancheng, Jiangsu Province, and compared with L-band radar sounding data to verify the accuracy of UAV observation data. The results show that the observation data of temperature, relative humidity, wind direction and wind speed vertical profile measured by UAV are in good agreement with the observation data of the L-band radar sounding data. The correlation coefficients of temperature (T), relative humidity (RH), wind direction (WD) and wind speed (WS) of UAV and L-band radar sounding are 0.98, 0.98, 0.98 and 0.91, respectively. The absolute deviations of T, RH, WD and WS are 0.57℃, 4.25%, 11.5° and 1.88 m·s-1 respectively. Since UAV measures the instantaneous wind speed at corresponding height, it can better reflect the subtle variation of wind speed characteristics in boundary layer. The summer UAV experiment recorded detailed changes of boundary layer structure during a heavy fog process. The boundary-layer structure and fog macro-characteristics observed by the UAV during this process were similar as that of L-band radar. The results show that UAV has a promising prospect in the application of boundary layer meteorological observation.
2020, 46(1):98-107.
DOI: 10.7519/j.issn.1000-0526.2020.01.010
Abstract:
Take the capsizing accident of cruise ship “Oriental Star” as an example. The analysis of the previous study and the field investigation shows that on 1 June 2015, from 21:00 BT to 21:15 BT, severe weather such as thunderstorms, strong winds, heavy rains and tornadoes hit the investigation area. The duration was about 30 minutes. The disaster process was characterized by the most severe windstorms, with spatial discontinuities and small scales. The survey results show that there were vertical shear and horizontal shear in the wind field along the Yangtze River in the accident area. Radar monitoring showed that the mesocyclone moved from the west bank of the Yangtze River to the east bank, having vortex cha-racteristics. This process was mainly based on windstorms. The severely affected area was concentrated within the range 8 km north of the accident, the Sitai village on the east bank of the Yangtze River, which is about 4 km away from the accident, was the most seriously affected, This region had strong wind shear and signs of divergence.The main affected objects were trees, crops, houses, boats, etc., causing the most damage to trees, a total of 31 disaster sites, accounting for 72.1% of the total survey sites. In the accident area, the trees on the west bank of the Yangtze River were broken or the direction of lodging was mainly southeastward, the trees on the east bank was mainly eastward. So, the direction of the trees dumping was clearly consistent. However, there were horizontal shears on both sides of the Yangtze Ri-ver, and the wind direction was deflected by nearly 90°. The quantitative evaluation method of wind disaster was explored by combining actual disaster with mechanical model. Take the severely affected poplar as an example, the anti-overturning moment calculation method was used to estimate the disaster rate. The results show that strong wind was one of the important causes of the accident. The wind speed of the di-saster was 28.7 m·s-1, reaching Grade 10 or above.
Take the capsizing accident of cruise ship “Oriental Star” as an example. The analysis of the previous study and the field investigation shows that on 1 June 2015, from 21:00 BT to 21:15 BT, severe weather such as thunderstorms, strong winds, heavy rains and tornadoes hit the investigation area. The duration was about 30 minutes. The disaster process was characterized by the most severe windstorms, with spatial discontinuities and small scales. The survey results show that there were vertical shear and horizontal shear in the wind field along the Yangtze River in the accident area. Radar monitoring showed that the mesocyclone moved from the west bank of the Yangtze River to the east bank, having vortex cha-racteristics. This process was mainly based on windstorms. The severely affected area was concentrated within the range 8 km north of the accident, the Sitai village on the east bank of the Yangtze River, which is about 4 km away from the accident, was the most seriously affected, This region had strong wind shear and signs of divergence.The main affected objects were trees, crops, houses, boats, etc., causing the most damage to trees, a total of 31 disaster sites, accounting for 72.1% of the total survey sites. In the accident area, the trees on the west bank of the Yangtze River were broken or the direction of lodging was mainly southeastward, the trees on the east bank was mainly eastward. So, the direction of the trees dumping was clearly consistent. However, there were horizontal shears on both sides of the Yangtze Ri-ver, and the wind direction was deflected by nearly 90°. The quantitative evaluation method of wind disaster was explored by combining actual disaster with mechanical model. Take the severely affected poplar as an example, the anti-overturning moment calculation method was used to estimate the disaster rate. The results show that strong wind was one of the important causes of the accident. The wind speed of the di-saster was 28.7 m·s-1, reaching Grade 10 or above.
2020, 46(1):108-118.
DOI: 10.7519/j.issn.1000-0526.2020.01.011
Abstract:
Based on the TIGGE datasets from the European Centre for Medium Range Weather Forecasts (ECMWF), the United Kingdom Met Office (UKMO), the China Meteorological Administration (CMA), and the Japan Meteorological Agency (JMA), and its multi-center ensemble systems, and observations in the Qingjiang River Basin, Bayesian model averaging (BMA) probability forecast models were established. The results showed that the optimal length of the training period is about 40 days, and the BMA models for multi-center ensemble outperform those for single center system for lead times of 24 h. The mean absolute error (MAE) and continuous ranked probability score (CRPS) skills of the BMA models are improved approximately 11% and 15%, respectively, compared with those of raw ensemble forecasts. In operation, when the BMA 90 percentile predicted precipitation is extreme precipitation ［［50-100) mm·(24 h)-1］, the 75-90 percentiles predicted precipitation could be used as the forecast reference, and the heavy precipitation warning could be carried out. For the forecast of severe precipitation ［［50-100) mm·(24 h)-1］, the forecast result of the 50-75 percentile predicted by BMA can be taken as a reference, while for the general precipitation ［≤25 mm·(24 h)-1］, the reference of BMA deterministic forecast is relatively strong. BMA probability forecast could give both the PDF curve with full probability and the probability greater than a certain precipitation intensity, which could provide the basis for the probability forecast in operation. However, the small probability value is often ignored, resulting in omission. So how to capture more useful information through the probabilistic prediction method and increase the accuracy of the prediction of extreme weather events will be a challenge for the probabilistic prediction technology.
Based on the TIGGE datasets from the European Centre for Medium Range Weather Forecasts (ECMWF), the United Kingdom Met Office (UKMO), the China Meteorological Administration (CMA), and the Japan Meteorological Agency (JMA), and its multi-center ensemble systems, and observations in the Qingjiang River Basin, Bayesian model averaging (BMA) probability forecast models were established. The results showed that the optimal length of the training period is about 40 days, and the BMA models for multi-center ensemble outperform those for single center system for lead times of 24 h. The mean absolute error (MAE) and continuous ranked probability score (CRPS) skills of the BMA models are improved approximately 11% and 15%, respectively, compared with those of raw ensemble forecasts. In operation, when the BMA 90 percentile predicted precipitation is extreme precipitation ［［50-100) mm·(24 h)-1］, the 75-90 percentiles predicted precipitation could be used as the forecast reference, and the heavy precipitation warning could be carried out. For the forecast of severe precipitation ［［50-100) mm·(24 h)-1］, the forecast result of the 50-75 percentile predicted by BMA can be taken as a reference, while for the general precipitation ［≤25 mm·(24 h)-1］, the reference of BMA deterministic forecast is relatively strong. BMA probability forecast could give both the PDF curve with full probability and the probability greater than a certain precipitation intensity, which could provide the basis for the probability forecast in operation. However, the small probability value is often ignored, resulting in omission. So how to capture more useful information through the probabilistic prediction method and increase the accuracy of the prediction of extreme weather events will be a challenge for the probabilistic prediction technology.
2020, 46(1):119-128.
DOI: 10.7519/j.issn.1000-0526.2020.01.012
Abstract:
The automatic monitoring system for crops has the advantages of automatic, non-contact and non-destructive, and is a useful supplement to traditional agrometeorological observations. The charge coupled device (CCD) sensor protects the cover from water, dust, fog-haze, rain and snow, etc., which may cause observation data error of automatic crop monitoring system. Therefore, the quality control is the basis for the rational usage of the automatic crop monitoring system. Based on the historical crop image data of Zhengzhou, Tai’an and Gucheng, this paper designs a quality control method for image data based on color feature parameter detection and dark channel prior histogram detection. According to different weather conditions,we carried out quality control on the summer maize and winter wheat image observation data in 2010-2012, and the effects were tested. The results show that both types of inspection methods can determine the anomaly data of image observation data in the automatic crop monitoring system. The color feature parameter detection method can effectively identify the missing image of pixels, and the accuracy rate can reach 100%. The proposed method based on the histogram of dark channel can effectively identify the contaminated image, with the average precision being 95.7% and recall average 87.5%. This quality control method can reduce the error between the model estimate and the observed data. At present, this method has been applied to automatic agricultural meteorology observation oprational software.
The automatic monitoring system for crops has the advantages of automatic, non-contact and non-destructive, and is a useful supplement to traditional agrometeorological observations. The charge coupled device (CCD) sensor protects the cover from water, dust, fog-haze, rain and snow, etc., which may cause observation data error of automatic crop monitoring system. Therefore, the quality control is the basis for the rational usage of the automatic crop monitoring system. Based on the historical crop image data of Zhengzhou, Tai’an and Gucheng, this paper designs a quality control method for image data based on color feature parameter detection and dark channel prior histogram detection. According to different weather conditions,we carried out quality control on the summer maize and winter wheat image observation data in 2010-2012, and the effects were tested. The results show that both types of inspection methods can determine the anomaly data of image observation data in the automatic crop monitoring system. The color feature parameter detection method can effectively identify the missing image of pixels, and the accuracy rate can reach 100%. The proposed method based on the histogram of dark channel can effectively identify the contaminated image, with the average precision being 95.7% and recall average 87.5%. This quality control method can reduce the error between the model estimate and the observed data. At present, this method has been applied to automatic agricultural meteorology observation oprational software.
2020, 46(1):129-137.
DOI: 10.7519/j.issn.1000-0526.2020.01.013
Abstract:
To better understand the basic features and causes of the climate anomalies in summer 2019 (June-July-August 2019) in China, this paper analyzes the spatio-temporal distributions of the precipitation and temperature in the period, as well as the features of the general circulation in East Asia on the basis of the observation data and the NECP/NCAR reanalysis data. The possible reason why less precipitation occurred in the middle and lower reaches of the Yangtze River under an El Ni〖AKn~D〗o event is also diagnosed preliminarily. The results illustrate that in the summer of 2019, the temperature was warmer than normal in most regions in China, and the national averaged precipitation was close to normal, but the distribution of droughts and floods had obvious spatial differences. The main rainfall centers in eastern China were located from the regions south of the Yangtze River (Jiangnan) to South China and in Northeast China, while persistent meteorological droughts occurred in Yunnan Province and the Huanghuai Region. The precipitation in eastern China also showed remarkable intraseasonal variation, especially in the Jiangnan Region. In early summer, the precipitation in Jiangnan occurred in a high frequency, causing serious floods. In late summer, the precipitation decreased rapidly but high temperature developed rapidly. The pre-flood season in South China and the Chinese Meiyu season in the south of the Yangtze River both began earlier and ended late. In the summer of 2019, the atmospheric circulation in Eurasian Continent presented a typical negative-positive-negative pattern. The sustained trough over the Yellow Sea of China and the Japan Sea resulted in a more southward and westward western Pacific subtropical high (WPSH). This trough was also the direct cause for the less rainfall in the middle and lower reaches of the Yangtze River and more rainfall in the south of the Yangtze River. It was obviously by south in the early summer, which is consistent with the evolution of the WPSH. However in the late summer, the trough weakened and moved northward, and the WPSH traveled northward rapidly, which led the rain belt to move rapidly to northern China.
To better understand the basic features and causes of the climate anomalies in summer 2019 (June-July-August 2019) in China, this paper analyzes the spatio-temporal distributions of the precipitation and temperature in the period, as well as the features of the general circulation in East Asia on the basis of the observation data and the NECP/NCAR reanalysis data. The possible reason why less precipitation occurred in the middle and lower reaches of the Yangtze River under an El Ni〖AKn~D〗o event is also diagnosed preliminarily. The results illustrate that in the summer of 2019, the temperature was warmer than normal in most regions in China, and the national averaged precipitation was close to normal, but the distribution of droughts and floods had obvious spatial differences. The main rainfall centers in eastern China were located from the regions south of the Yangtze River (Jiangnan) to South China and in Northeast China, while persistent meteorological droughts occurred in Yunnan Province and the Huanghuai Region. The precipitation in eastern China also showed remarkable intraseasonal variation, especially in the Jiangnan Region. In early summer, the precipitation in Jiangnan occurred in a high frequency, causing serious floods. In late summer, the precipitation decreased rapidly but high temperature developed rapidly. The pre-flood season in South China and the Chinese Meiyu season in the south of the Yangtze River both began earlier and ended late. In the summer of 2019, the atmospheric circulation in Eurasian Continent presented a typical negative-positive-negative pattern. The sustained trough over the Yellow Sea of China and the Japan Sea resulted in a more southward and westward western Pacific subtropical high (WPSH). This trough was also the direct cause for the less rainfall in the middle and lower reaches of the Yangtze River and more rainfall in the south of the Yangtze River. It was obviously by south in the early summer, which is consistent with the evolution of the WPSH. However in the late summer, the trough weakened and moved northward, and the WPSH traveled northward rapidly, which led the rain belt to move rapidly to northern China.
2020, 46(1):138-144.
DOI: 10.7519/j.issn.1000-0526.2020.01.014
Abstract:
The main characteristics of the general atmospheric circulation in October 2019 are as follows. Over the Northern Hemisphere, the polar vortex showed a dipole pattern. The circulation presented a four-wave pattern in middle-high latitudes. The western North Pacific subtropical high was distributed in the east-west direction, which was much stronger and westward than normal. The monthly mean precipitation amount was 36.6 mm, which was close to the climatological mean (35.8 mm). The monthly mean temperature was 11.1℃, 0.8℃ higher than normal (10.3℃). Two torrential rain processes occurred du-ring this month. One was led by Typhoon Mitag, and the other was caused by high-level trough and shear line. There were four cold air processes, two of which were cold-air outbreak processes and the other two were strong cold air processes. One blowing sand weather event occurred in the northern region. Typhoon Mitag landed the coast of Putuo, Zhoushan of Zhejiang Province at 20:30 BT 1 October 2019.
The main characteristics of the general atmospheric circulation in October 2019 are as follows. Over the Northern Hemisphere, the polar vortex showed a dipole pattern. The circulation presented a four-wave pattern in middle-high latitudes. The western North Pacific subtropical high was distributed in the east-west direction, which was much stronger and westward than normal. The monthly mean precipitation amount was 36.6 mm, which was close to the climatological mean (35.8 mm). The monthly mean temperature was 11.1℃, 0.8℃ higher than normal (10.3℃). Two torrential rain processes occurred du-ring this month. One was led by Typhoon Mitag, and the other was caused by high-level trough and shear line. There were four cold air processes, two of which were cold-air outbreak processes and the other two were strong cold air processes. One blowing sand weather event occurred in the northern region. Typhoon Mitag landed the coast of Putuo, Zhoushan of Zhejiang Province at 20:30 BT 1 October 2019.
Mobile website
® 2024 All Rights Reserved
Supported by:Beijing E-Tiller Technology Development Co., Ltd.
ISSN:1000-0526 CN:11-2282/P