2014 Vol. 20, No. 1
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2014, 20(1): 1-7.
Abstract:
El Niño Modoki, similar to but different from canonical El Niño, has been observed since the late 1970s. In this paper, using HadISST and NCEP/NCAR wind data, we analyze the relationship between El Niño Modoki and Sea Surface Temperature (SST) in the offshore area of China and its adjacent waters for different seasons. Our results show a significant negative correlation between El Niño Modoki in summer and SST in autumn in the offshore area of China and its adjacent waters, particularly for regions located in the east of the Kuroshio. It is also found that during El Niño Modoki period, anomalous northerlies prevail over the regions from the northern part of the Philippines to the offshore area of China, indicating that the northerlies are unfavorable for the transport of warm water from the western tropical Pacific to the mid-latitude area. Consequently, El Niño Modoki in summer may play a substantial role in cold SST anomalies in the offshore area of China and its adjacent waters in autumn through the influence of the Kuroshio, with a lagged response of the ocean to the atmospheric wind field.
El Niño Modoki, similar to but different from canonical El Niño, has been observed since the late 1970s. In this paper, using HadISST and NCEP/NCAR wind data, we analyze the relationship between El Niño Modoki and Sea Surface Temperature (SST) in the offshore area of China and its adjacent waters for different seasons. Our results show a significant negative correlation between El Niño Modoki in summer and SST in autumn in the offshore area of China and its adjacent waters, particularly for regions located in the east of the Kuroshio. It is also found that during El Niño Modoki period, anomalous northerlies prevail over the regions from the northern part of the Philippines to the offshore area of China, indicating that the northerlies are unfavorable for the transport of warm water from the western tropical Pacific to the mid-latitude area. Consequently, El Niño Modoki in summer may play a substantial role in cold SST anomalies in the offshore area of China and its adjacent waters in autumn through the influence of the Kuroshio, with a lagged response of the ocean to the atmospheric wind field.
2014, 20(1): 8-16.
Abstract:
In order to clarify the statistical pattern by which landfalling strong tropical cyclones (LSTCs) influenced the catastrophic migrations of rice brown planthopper (BPH), Nilaparvata lugens (st?l) in China, the data of the LSTCs in China and the lighting catches of BPH that covered the main Chinese rice-growing regions from 1979 to 2008 were collected and analyzed in this work with the assistance of ArcGIS9.3, a software of geographic information system. The results were as follows: (1) In China, there were 220 strong tropical cyclones that passed the main rice-growing regions and 466 great events of BPH’s immigration in the 30 years from 1979 to 2008. 73 of them resulted in the occurrence of BPH’s catastrphic migration (CM) events directly and 147 of them produced indirect effect on the migrations. (2) The number of the LSTCs was variable in different years during 1979 to 2008 and their influence was not the same in the BPH’s northward and southward migrations in the years. In the 30 years, the LSTCs brought more obvious influence on the migrations in 1980, 1981, 2005, 2006 and 2007. The influence was the most obvious in 2007 and all of the 7 LSTCs produced remarkable impact on the CMs of BPH’s populations. The effect of the LSTCs on the northward immigration of BPH’s populations was the most serious in 2006 and the influence on the southward immigration was the most remarkable in 2005. (3) In these years, the most of LSTCs occurred in July, August and September and great events of BPH's immigration occurred most frequently in the same months. The LSTCs played a more important role on the CM of BPH’s populations in the three months than in other months. (4) The analysis on the spatial distribution of the LSTCs and BPH’s immigration events for the different provinces showed that the BPH’s migrations in the main rice-growing regions of the Southeastern China were influenced by the LSTCs and the impact was different with the change of their spatial probability distribution during their passages. The most serious influence of the LSTCs on the BPH’s migrations occurred in Guangdong and Fujian provinces. (5)The statistical results indicated that a suitable insect source is an indispensable condition of the CMs of BPH when a LSTC influenced a rice-growing region.
In order to clarify the statistical pattern by which landfalling strong tropical cyclones (LSTCs) influenced the catastrophic migrations of rice brown planthopper (BPH), Nilaparvata lugens (st?l) in China, the data of the LSTCs in China and the lighting catches of BPH that covered the main Chinese rice-growing regions from 1979 to 2008 were collected and analyzed in this work with the assistance of ArcGIS9.3, a software of geographic information system. The results were as follows: (1) In China, there were 220 strong tropical cyclones that passed the main rice-growing regions and 466 great events of BPH’s immigration in the 30 years from 1979 to 2008. 73 of them resulted in the occurrence of BPH’s catastrphic migration (CM) events directly and 147 of them produced indirect effect on the migrations. (2) The number of the LSTCs was variable in different years during 1979 to 2008 and their influence was not the same in the BPH’s northward and southward migrations in the years. In the 30 years, the LSTCs brought more obvious influence on the migrations in 1980, 1981, 2005, 2006 and 2007. The influence was the most obvious in 2007 and all of the 7 LSTCs produced remarkable impact on the CMs of BPH’s populations. The effect of the LSTCs on the northward immigration of BPH’s populations was the most serious in 2006 and the influence on the southward immigration was the most remarkable in 2005. (3) In these years, the most of LSTCs occurred in July, August and September and great events of BPH's immigration occurred most frequently in the same months. The LSTCs played a more important role on the CM of BPH’s populations in the three months than in other months. (4) The analysis on the spatial distribution of the LSTCs and BPH’s immigration events for the different provinces showed that the BPH’s migrations in the main rice-growing regions of the Southeastern China were influenced by the LSTCs and the impact was different with the change of their spatial probability distribution during their passages. The most serious influence of the LSTCs on the BPH’s migrations occurred in Guangdong and Fujian provinces. (5)The statistical results indicated that a suitable insect source is an indispensable condition of the CMs of BPH when a LSTC influenced a rice-growing region.
2014, 20(1): 17-25.
Abstract:
There has been a lot of discussion about the atmospheric heat source over the Tibetan Plateau (TP) and the low-frequency oscillation of atmospheric circulation. However, the research on low-frequency oscillation of heat source over TP and its impact on atmospheric circulation are not fully carried out. By using the vertically integrated apparent heat source which is calculated by the derivation method, main oscillation periods and propagation features of the summer apparent heat source over the eastern TP (Q1ETP) are diagnosed and analyzed from 1981 to 2000. The results are as follows: (1) Summer Q1ETP has two significant oscillation periods: one is 10-20d (BWO, Quasi-Biweekly Oscillation) and the other is 30-60d (LFO, Low-frequency Oscillation). (2) A significant correlation is found between Q1ETP and rainfall over the eastern TP in 1985 and 1992, showing that the low-frequency oscillation of heat source is likely to be stimulated by oscillation of latent heat. (3) The oscillation of heat source on the plateau mainly generates locally but sometimes originates from elsewhere. The BWO of Q1ETP mainly exhibits stationary wave, sometimes moves out (mainly eastward), and has a close relationship with the BWO from the Bay of Bengal. Showing the same characteristics as BWO, the LFO mainly shows local oscillation, occasionally propagates (mainly westward), and connects with the LFO from East China. In summary, more attention should be paid to the study on BWO of Q1ETP.
There has been a lot of discussion about the atmospheric heat source over the Tibetan Plateau (TP) and the low-frequency oscillation of atmospheric circulation. However, the research on low-frequency oscillation of heat source over TP and its impact on atmospheric circulation are not fully carried out. By using the vertically integrated apparent heat source which is calculated by the derivation method, main oscillation periods and propagation features of the summer apparent heat source over the eastern TP (Q1ETP) are diagnosed and analyzed from 1981 to 2000. The results are as follows: (1) Summer Q1ETP has two significant oscillation periods: one is 10-20d (BWO, Quasi-Biweekly Oscillation) and the other is 30-60d (LFO, Low-frequency Oscillation). (2) A significant correlation is found between Q1ETP and rainfall over the eastern TP in 1985 and 1992, showing that the low-frequency oscillation of heat source is likely to be stimulated by oscillation of latent heat. (3) The oscillation of heat source on the plateau mainly generates locally but sometimes originates from elsewhere. The BWO of Q1ETP mainly exhibits stationary wave, sometimes moves out (mainly eastward), and has a close relationship with the BWO from the Bay of Bengal. Showing the same characteristics as BWO, the LFO mainly shows local oscillation, occasionally propagates (mainly westward), and connects with the LFO from East China. In summary, more attention should be paid to the study on BWO of Q1ETP.
2014, 20(1): 26-34.
Abstract:
In this work, an index of tropical 20-90 d oscillation (intra-seasonal oscillation; ISO) in the western North Pacific (WNP) was determined via the combined empirical orthogonal function (EOF) method using daily outgoing longwave radiation (OLR) field data from the National Oceanic and Atmospheric Administration (NOAA), daily wind field data (at 850 hPa) from the European Centre for Medium-Range Weather Forecasts (ECMWF) and referencing the Madden-Julian oscillation (MJO) index proposed by Wheeler and Hendon. An in-depth investigation was conducted to examine the impact of the ISO on changes in tropical cyclone (TC) tracks in the WNP during different ISO phases. The research results indicate that during the easterly phase of the ISO, under the impact of the northeastern airflow of anti-cyclonic ISO circulation, the easterly airflow south of the western Pacific subtropical high is relatively weak, and TCs generated in the subtropical high tend to change their tracks east of 140°E; during the westerly phase, there is a relatively high probability that TCs change their tracks west of 140°E. This work also analyzed the ISO flow field situation in cases of typhoons and determined that the track of a tropical cyclone will experience a sudden right turn when the center of the ISO cyclonic (anti-cyclonic) circulation coincides with that of the cyclone.
In this work, an index of tropical 20-90 d oscillation (intra-seasonal oscillation; ISO) in the western North Pacific (WNP) was determined via the combined empirical orthogonal function (EOF) method using daily outgoing longwave radiation (OLR) field data from the National Oceanic and Atmospheric Administration (NOAA), daily wind field data (at 850 hPa) from the European Centre for Medium-Range Weather Forecasts (ECMWF) and referencing the Madden-Julian oscillation (MJO) index proposed by Wheeler and Hendon. An in-depth investigation was conducted to examine the impact of the ISO on changes in tropical cyclone (TC) tracks in the WNP during different ISO phases. The research results indicate that during the easterly phase of the ISO, under the impact of the northeastern airflow of anti-cyclonic ISO circulation, the easterly airflow south of the western Pacific subtropical high is relatively weak, and TCs generated in the subtropical high tend to change their tracks east of 140°E; during the westerly phase, there is a relatively high probability that TCs change their tracks west of 140°E. This work also analyzed the ISO flow field situation in cases of typhoons and determined that the track of a tropical cyclone will experience a sudden right turn when the center of the ISO cyclonic (anti-cyclonic) circulation coincides with that of the cyclone.
2014, 20(1): 35-44.
Abstract:
NCEP GFS (Global Forecast System) analytical data (available 4 times per day), satellite cloud image data and real-time observations of path and intensity of Typhoon Morakot are employed to investigate the variation of synoptic dynamics in its intensity and structure before and after the landing. This study intends to offer some hints for the forecast of intensity and structure of typhoons. Results show that in the tangential direction, the averaged asymmetry amplitude of wind on the radius of a large-value center of the low-level wind can be used as an important parameter for diagnosing the intensity of typhoons. Besides, the maximum of the upper dry potential vorticity in Morakot’s center tends to extend downward along the intensive gradient of tangential wind situated on the inner side of a large-value center of the low-level tangential wind. Additionally, the radial advection of the tangential wind determines the variation of tangential wind in conjunction with the vertical transmission of the tangential wind, the inertial centrifugal force and the Coriolis force. These four items are dominant in the motion equation of tangential wind based on a cylindrical coordinate without the effects of friction and turbulence. Moreover, the low-level convergence center of the typhoon has a tendency of shifting and developing along the intensive gradient of the tangential wind in the tangential direction.
NCEP GFS (Global Forecast System) analytical data (available 4 times per day), satellite cloud image data and real-time observations of path and intensity of Typhoon Morakot are employed to investigate the variation of synoptic dynamics in its intensity and structure before and after the landing. This study intends to offer some hints for the forecast of intensity and structure of typhoons. Results show that in the tangential direction, the averaged asymmetry amplitude of wind on the radius of a large-value center of the low-level wind can be used as an important parameter for diagnosing the intensity of typhoons. Besides, the maximum of the upper dry potential vorticity in Morakot’s center tends to extend downward along the intensive gradient of tangential wind situated on the inner side of a large-value center of the low-level tangential wind. Additionally, the radial advection of the tangential wind determines the variation of tangential wind in conjunction with the vertical transmission of the tangential wind, the inertial centrifugal force and the Coriolis force. These four items are dominant in the motion equation of tangential wind based on a cylindrical coordinate without the effects of friction and turbulence. Moreover, the low-level convergence center of the typhoon has a tendency of shifting and developing along the intensive gradient of the tangential wind in the tangential direction.
2014, 20(1): 45-56.
Abstract:
Based on Hadley Center monthly global SST, 1960-2009 NCEP/NCAR reanalysis data and observation rainfall data over 160 stations across China, the combined effect of Indian Ocean Dipole (IOD) and Pacific SSTA (ENSO) on winter rainfall in China and their different roles are investigated in the work. The study focuses on the differences among the winter precipitation pattern during the years with Indian Ocean Dipole (IOD) only, ENSO only, and IOD and ENSO concurrence. It is shown that although the occurrences of the sea surface temperature anomalies of IOD and ENSO are of a high degree of synergy, their impacts on the winter precipitation are not the same. In the year with positive phase of IOD, the winter rainfall will be more than normal in Southwest China (except western Yunnan), North China and Northeast China while it will be less in Yangtze River and Huaihe River Basins. The result is contrary during the year with negative phase of IOD. However, the impact of IOD positive phase on winter precipitation is more significant than that of the negative phase. When the IOD appears along with ENSO, the ENSO signal will enhance the influence of IOD on winter precipitation of Southwest China (except western Yunnan), Inner Mongolia and Northeast China. In addition, this paper makes a preliminary analysis of the circulation causes of the relationship between IOD and the winter rainfall in China.
Based on Hadley Center monthly global SST, 1960-2009 NCEP/NCAR reanalysis data and observation rainfall data over 160 stations across China, the combined effect of Indian Ocean Dipole (IOD) and Pacific SSTA (ENSO) on winter rainfall in China and their different roles are investigated in the work. The study focuses on the differences among the winter precipitation pattern during the years with Indian Ocean Dipole (IOD) only, ENSO only, and IOD and ENSO concurrence. It is shown that although the occurrences of the sea surface temperature anomalies of IOD and ENSO are of a high degree of synergy, their impacts on the winter precipitation are not the same. In the year with positive phase of IOD, the winter rainfall will be more than normal in Southwest China (except western Yunnan), North China and Northeast China while it will be less in Yangtze River and Huaihe River Basins. The result is contrary during the year with negative phase of IOD. However, the impact of IOD positive phase on winter precipitation is more significant than that of the negative phase. When the IOD appears along with ENSO, the ENSO signal will enhance the influence of IOD on winter precipitation of Southwest China (except western Yunnan), Inner Mongolia and Northeast China. In addition, this paper makes a preliminary analysis of the circulation causes of the relationship between IOD and the winter rainfall in China.
2014, 20(1): 57-65.
Abstract:
Using the NCEP 1 °×1 ° reanalysis data, several obvious differences of the structural characteristics of developed versus undeveloped mid-level vortexes are studied. First, the central vorticity of the developed mid-level vortex increases towards higher levels while the undeveloped one decreases. The low-level convergence structure maintains well in the developed mid-level vortex whereas the undeveloped one does badly. Second, on the one hand, according to the symmetric analysis, the horizontal wind field and wind vertical section of the developed mid-level vortex are well symmetric while those of the undeveloped one are less symmetric. Meanwhile, weak wind vertical shear help the developed mid-level vortex to establish a warm core in upper- and mid-levels of the troposphere. On the other hand, according to the balance analysis, better balance between wind and pressure is shown in the mid- and lower-levels of the troposphere of the developed mid-level vortex than in those of the undeveloped vortex. Third, positive anomaly of potential vorticity is enhanced and developed in the vertical direction of the developed vortex. However, the undeveloped vortex weakens with a weak positive anomaly.
Using the NCEP 1 °×1 ° reanalysis data, several obvious differences of the structural characteristics of developed versus undeveloped mid-level vortexes are studied. First, the central vorticity of the developed mid-level vortex increases towards higher levels while the undeveloped one decreases. The low-level convergence structure maintains well in the developed mid-level vortex whereas the undeveloped one does badly. Second, on the one hand, according to the symmetric analysis, the horizontal wind field and wind vertical section of the developed mid-level vortex are well symmetric while those of the undeveloped one are less symmetric. Meanwhile, weak wind vertical shear help the developed mid-level vortex to establish a warm core in upper- and mid-levels of the troposphere. On the other hand, according to the balance analysis, better balance between wind and pressure is shown in the mid- and lower-levels of the troposphere of the developed mid-level vortex than in those of the undeveloped vortex. Third, positive anomaly of potential vorticity is enhanced and developed in the vertical direction of the developed vortex. However, the undeveloped vortex weakens with a weak positive anomaly.
2014, 20(1): 74-86.
Abstract:
The NCEP 1°×1° reanalysis of June-to-September dataset between 2002 to 2009 is used in this study to conduct statistical analysis of the relationship between the environmental potential vorticity (PV) on 150 hPa located at the south edge of South Asia High (SAH) and TCs making landfall. The results show that 23 of the TCs are affected by the PV on 150 hPa located at the south edge of SAH between 2002 to 2009, and three TCs' center pressure decline after the high-value environmental PV moves to the center of the TCs. These three TCs are Senlaku (0216), Bilis (0604) and Linfa (0903). Through diagnostic analysis from the viewpoint of isolines, we determined the relationship between the intensification of these TCs and the PV anomaly at high levels; the isentropic surface is close to the high level’s PV anomaly under the influence of the 150-hPa PV anomaly, leading to the decline of isentropic surfaces on both sides of the PV anomaly. Then the warm core of the middle and high levels of the TC strengthens and PV increases at the middle level, and both of them are beneficial to the reinforcement of the cyclonic vorticity in the low level. As a result, the center pressure of the TC declines. According to Wu’s theory of Slantwise Vorticity Development (SVD), the incline of the isentropic surfaces leads to the development of vertical vorticity, contributing to the vertical motion and the release of the latent heat. Then the warm core of the TC strengthens and the TC strengthens, too. Otherwise, piecewise PV inversion also shows that the high-level PV influences the mid-level more than the low level.
The NCEP 1°×1° reanalysis of June-to-September dataset between 2002 to 2009 is used in this study to conduct statistical analysis of the relationship between the environmental potential vorticity (PV) on 150 hPa located at the south edge of South Asia High (SAH) and TCs making landfall. The results show that 23 of the TCs are affected by the PV on 150 hPa located at the south edge of SAH between 2002 to 2009, and three TCs' center pressure decline after the high-value environmental PV moves to the center of the TCs. These three TCs are Senlaku (0216), Bilis (0604) and Linfa (0903). Through diagnostic analysis from the viewpoint of isolines, we determined the relationship between the intensification of these TCs and the PV anomaly at high levels; the isentropic surface is close to the high level’s PV anomaly under the influence of the 150-hPa PV anomaly, leading to the decline of isentropic surfaces on both sides of the PV anomaly. Then the warm core of the middle and high levels of the TC strengthens and PV increases at the middle level, and both of them are beneficial to the reinforcement of the cyclonic vorticity in the low level. As a result, the center pressure of the TC declines. According to Wu’s theory of Slantwise Vorticity Development (SVD), the incline of the isentropic surfaces leads to the development of vertical vorticity, contributing to the vertical motion and the release of the latent heat. Then the warm core of the TC strengthens and the TC strengthens, too. Otherwise, piecewise PV inversion also shows that the high-level PV influences the mid-level more than the low level.
2014, 20(1): 87-92.
Abstract:
Based on the tropical cyclone data from the Central Meteorological Observatory of China, Japan Meteorological Agency, Joint Typhoon Warning Center and European Centre for Medium-Range Weather Forecasts (ECMWF) during the period of 2004 to 2009, three consensus methods are used in tropical cyclone (TC) track forecasts. Operational consensus results show that the objective forecasts of ECMWF help to improve consensus skill by 2%, 3%-5% and 3%-5%, decrease track bias by 2.5 km, 6-9 km and 10-12 km for the 24 h, 48 h and 72 h forecasts respectively over the years of 2007 to 2009. Analysis also indicates that consensus forecasts hold positive skills relative to each member. The multivariate regression composite is a method that shows relatively low skill, while the methods of arithmetic averaging and composite (in which the weighting coefficient is the reciprocal square of mean error of members) have almost comparable skills among members. Consensus forecast for a lead time of 96 h has negative skill relative to the ECMWF objective forecast.
Based on the tropical cyclone data from the Central Meteorological Observatory of China, Japan Meteorological Agency, Joint Typhoon Warning Center and European Centre for Medium-Range Weather Forecasts (ECMWF) during the period of 2004 to 2009, three consensus methods are used in tropical cyclone (TC) track forecasts. Operational consensus results show that the objective forecasts of ECMWF help to improve consensus skill by 2%, 3%-5% and 3%-5%, decrease track bias by 2.5 km, 6-9 km and 10-12 km for the 24 h, 48 h and 72 h forecasts respectively over the years of 2007 to 2009. Analysis also indicates that consensus forecasts hold positive skills relative to each member. The multivariate regression composite is a method that shows relatively low skill, while the methods of arithmetic averaging and composite (in which the weighting coefficient is the reciprocal square of mean error of members) have almost comparable skills among members. Consensus forecast for a lead time of 96 h has negative skill relative to the ECMWF objective forecast.
2014, 20(1): 66-73.
Abstract:
Leveraging the commercial CFD software FLUENT, the fine-scale three-dimensional wind structure over the Paiya Mountains on the Dapeng Peninsula near Shenzhen, a city on the seashore of South China Sea, during the landfall of Typhoon Molave has been simulated and analyzed. Through the study, a conceptual wind structure model for mountainous areas under strong wind condition is established and the following conclusions are obtained as follows: (1) FLUENT can reasonably simulate a three-dimensional wind structure over mountainous areas under strong wind conditions; (2) the kinetic effect of a mountain can intensify wind speed in the windward side of the mountain and the area over the mountain peak; and (3) in the leeward side of the mountain, wind speed is relatively lower with relatively stronger wind shear and turbulence.
Leveraging the commercial CFD software FLUENT, the fine-scale three-dimensional wind structure over the Paiya Mountains on the Dapeng Peninsula near Shenzhen, a city on the seashore of South China Sea, during the landfall of Typhoon Molave has been simulated and analyzed. Through the study, a conceptual wind structure model for mountainous areas under strong wind condition is established and the following conclusions are obtained as follows: (1) FLUENT can reasonably simulate a three-dimensional wind structure over mountainous areas under strong wind conditions; (2) the kinetic effect of a mountain can intensify wind speed in the windward side of the mountain and the area over the mountain peak; and (3) in the leeward side of the mountain, wind speed is relatively lower with relatively stronger wind shear and turbulence.
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