2009 Vol. 15, No. 1
2009, 15(1): 1-12.
Abstract:
On the basis of a comprehensive literature review and data analysis of global influenza surveillance, a transmission theory based numerical model is developed to understand the causative factors of influenza seasonality and the biodynamical mechanisms of seasonal flu. The model is applied to simulate the seasonality and weekly activity of influenza in different areas across all continents and climate zones around the world. Model solution and the good matches between model output and actual influenza indexes affirm that influenza activity is highly auto-correlative and relies on determinants of a broad spectrum. Internal dynamic resonance; variations of meteorological elements (solar radiation, precipitation and dewpoint); socio-behavioral influences and herd immunity to circulating strains prove to be the critical explanatory factors of the seasonality and weekly activity of influenza. In all climate regions, influenza activity is proportional to the exponential of the number of days with precipitation and to the negative exponential of quarter power of sunny hours. Influenza activity is a negative exponential function of dewpoint in temperate and arctic regions and an exponential function of the absolute deviation of dewpoint from its annual mean in the tropics. Epidemics of seasonal influenza could be deemed as the consequence of the dynamic resonance and interactions of determinants. Early interventions (such as opportune vaccination, prompt social distancing, and maintaining incidence well below a baseline) are key to the control and prevention of seasonal influenza. Moderate amount of sunlight exposure or Vitamin D supplementation during rainy and short-day photoperiod seasons, more outdoor activities, and appropriate indoor dewpoint deserve great attention in influenza prevention. To a considerable degree, the study reveals the mechanism of influenza seasonality, demonstrating a potential for influenza activity projection. The concept and algorithm can be explored for further applications.
On the basis of a comprehensive literature review and data analysis of global influenza surveillance, a transmission theory based numerical model is developed to understand the causative factors of influenza seasonality and the biodynamical mechanisms of seasonal flu. The model is applied to simulate the seasonality and weekly activity of influenza in different areas across all continents and climate zones around the world. Model solution and the good matches between model output and actual influenza indexes affirm that influenza activity is highly auto-correlative and relies on determinants of a broad spectrum. Internal dynamic resonance; variations of meteorological elements (solar radiation, precipitation and dewpoint); socio-behavioral influences and herd immunity to circulating strains prove to be the critical explanatory factors of the seasonality and weekly activity of influenza. In all climate regions, influenza activity is proportional to the exponential of the number of days with precipitation and to the negative exponential of quarter power of sunny hours. Influenza activity is a negative exponential function of dewpoint in temperate and arctic regions and an exponential function of the absolute deviation of dewpoint from its annual mean in the tropics. Epidemics of seasonal influenza could be deemed as the consequence of the dynamic resonance and interactions of determinants. Early interventions (such as opportune vaccination, prompt social distancing, and maintaining incidence well below a baseline) are key to the control and prevention of seasonal influenza. Moderate amount of sunlight exposure or Vitamin D supplementation during rainy and short-day photoperiod seasons, more outdoor activities, and appropriate indoor dewpoint deserve great attention in influenza prevention. To a considerable degree, the study reveals the mechanism of influenza seasonality, demonstrating a potential for influenza activity projection. The concept and algorithm can be explored for further applications.
2009, 15(1): 13-19.
Abstract:
In the typhoon adaptive observation based on conditional nonlinear optimal perturbation (CNOP), the ‘on-off’ switch caused by moist physical parameterization in prediction models prevents the conventional adjoint method from providing correct gradient during the optimization process. To address this problem, the capture of CNOP, when the “on-off” switches are included in models, is treated as non-smooth optimization in this study, and the genetic algorithm (GA) is introduced. After detailed algorithm procedures are formulated using an idealized model with parameterization “on-off” switches in the forcing term, the impacts of “on-off” switches on the capture of CNOP are analyzed, and three numerical experiments are conducted to check the effectiveness of GA in capturing CNOP and to analyze the impacts of different initial populations on the optimization result. The result shows that GA is competent for the capture of CNOP in the context of the idealized model with parameterization ‘on-off’ switches in this study. Finally, the advantages and disadvantages of GA in capturing CNOP are analyzed in detail.
In the typhoon adaptive observation based on conditional nonlinear optimal perturbation (CNOP), the ‘on-off’ switch caused by moist physical parameterization in prediction models prevents the conventional adjoint method from providing correct gradient during the optimization process. To address this problem, the capture of CNOP, when the “on-off” switches are included in models, is treated as non-smooth optimization in this study, and the genetic algorithm (GA) is introduced. After detailed algorithm procedures are formulated using an idealized model with parameterization “on-off” switches in the forcing term, the impacts of “on-off” switches on the capture of CNOP are analyzed, and three numerical experiments are conducted to check the effectiveness of GA in capturing CNOP and to analyze the impacts of different initial populations on the optimization result. The result shows that GA is competent for the capture of CNOP in the context of the idealized model with parameterization ‘on-off’ switches in this study. Finally, the advantages and disadvantages of GA in capturing CNOP are analyzed in detail.
2009, 15(1): 20-27.
Abstract:
Using correlation analyses, composite analyses, and singular value decomposition, the relationship between the atmospheric cold source over the eastern Tibetan Plateau and atmospheric/ocean circulation is discussed. In winter, the anomaly of the strong (weak) atmospheric cold source over the eastern plateau causes low-level anomalous north (south) winds to appear in eastern China and low-level anomaly zonal west (east) winds to prevail in the equatorial Pacific from spring to autumn. This contributes to the anomalous warm (cold) sea surface temperature the following autumn and winter. In addition, the anomalous variation of sea surface temperature over the equatorial middle and eastern Pacific in winter can influence the snow depth and intensity of the cold source over the plateau in the following winter due to variation of the summer west Pacific subtropical high.
Using correlation analyses, composite analyses, and singular value decomposition, the relationship between the atmospheric cold source over the eastern Tibetan Plateau and atmospheric/ocean circulation is discussed. In winter, the anomaly of the strong (weak) atmospheric cold source over the eastern plateau causes low-level anomalous north (south) winds to appear in eastern China and low-level anomaly zonal west (east) winds to prevail in the equatorial Pacific from spring to autumn. This contributes to the anomalous warm (cold) sea surface temperature the following autumn and winter. In addition, the anomalous variation of sea surface temperature over the equatorial middle and eastern Pacific in winter can influence the snow depth and intensity of the cold source over the plateau in the following winter due to variation of the summer west Pacific subtropical high.
2009, 15(1): 28-37.
Abstract:
There is an urgent need for the development of a method that can undertake rapid, effective, and accurate monitoring and identification of fog by satellite remote sensing, since heavy fog can cause enormous disasters to China’s national economy and people's lives and property in the urban and coastal areas. In this paper, the correlative relationship between the reflectivity of land surface and clouds in different time phases is found, based on the analysis of the radiative and satellite-based spectral characteristics of fog. Through calculation and analyses of the relative variability of the reflectivity in the images, the threshold to identify quasi-fog areas is generated automatically. Furthermore, using the technique of quick image run-length encoding, and in combination with such practical methods as analyzing texture and shape fractures, smoothness, and template characteristics, the automatic identification of fog and fog-cloud separation using meteorological satellite remote sensing images are studied, with good results in application.
There is an urgent need for the development of a method that can undertake rapid, effective, and accurate monitoring and identification of fog by satellite remote sensing, since heavy fog can cause enormous disasters to China’s national economy and people's lives and property in the urban and coastal areas. In this paper, the correlative relationship between the reflectivity of land surface and clouds in different time phases is found, based on the analysis of the radiative and satellite-based spectral characteristics of fog. Through calculation and analyses of the relative variability of the reflectivity in the images, the threshold to identify quasi-fog areas is generated automatically. Furthermore, using the technique of quick image run-length encoding, and in combination with such practical methods as analyzing texture and shape fractures, smoothness, and template characteristics, the automatic identification of fog and fog-cloud separation using meteorological satellite remote sensing images are studied, with good results in application.
2009, 15(1): 38-44.
Abstract:
The relationship between global warming and the variation in tropical cyclone (TC) genesis frequency is analyzed using the data of the Tropical Cyclone Year Book by the China Meteorological Administration and the National Centers for Environmental Prediction (NCEP) reanalysis data from 1949 to 2007. The observational results indicate that the average sea surface temperature (SST) in the Intertropical Convergence Zone (ITCZ) region (10°N –C 20°N, 100°E –C 140°E) increases by 0.6°C against the background of global warming, while the frequency of tropical cyclone geneses in this region decreases significantly. Generally, the rise of SSTs is favorable for the genesis of tropical cyclones, but it is now shown to be contrary to the normal effect. Most of the tropical cyclones in the western North Pacific (WNP) are generated in the ITCZ. This is quite different from the case in the Atlantic basin in which the tropical cyclones are mostly generated from the easterly wave. Our research results demonstrate that the ITCZ has a weakening trend in strength, and it has moved much more equatorward in the past 40 years; both are disadvantageous to the formation of tropical cyclones. Furthermore, our study also found that the ridge of the subtropical high tends to shift slightly equatorward, which is another adverse mechanism for the formation of tropical cyclones.
The relationship between global warming and the variation in tropical cyclone (TC) genesis frequency is analyzed using the data of the Tropical Cyclone Year Book by the China Meteorological Administration and the National Centers for Environmental Prediction (NCEP) reanalysis data from 1949 to 2007. The observational results indicate that the average sea surface temperature (SST) in the Intertropical Convergence Zone (ITCZ) region (10°N –C 20°N, 100°E –C 140°E) increases by 0.6°C against the background of global warming, while the frequency of tropical cyclone geneses in this region decreases significantly. Generally, the rise of SSTs is favorable for the genesis of tropical cyclones, but it is now shown to be contrary to the normal effect. Most of the tropical cyclones in the western North Pacific (WNP) are generated in the ITCZ. This is quite different from the case in the Atlantic basin in which the tropical cyclones are mostly generated from the easterly wave. Our research results demonstrate that the ITCZ has a weakening trend in strength, and it has moved much more equatorward in the past 40 years; both are disadvantageous to the formation of tropical cyclones. Furthermore, our study also found that the ridge of the subtropical high tends to shift slightly equatorward, which is another adverse mechanism for the formation of tropical cyclones.
2009, 15(1): 45-48.
Abstract:
An explicit simulation with a fine mesh at intervals of 6 km is used to explore the inner-core structures of Vongfong (0214). The dynamic mechanism for the inshore strengthening of Vongfong is examined. It is found as follows. (1) The radius of maximum wind of the axisymmetric structures of the typhoon decreased with height during its mature stage. When Vongfong was inshore, the strongest low-layer inflow located in front of it and the outflow was to the rear of it, which was just reversed from the Atlantic hurricanes and other Pacific typhoons. (2) The dynamic and thermodynamic fields were highly asymmetric in structure. Convection was stronger in the northwest quadrant of the typhoon than in the southeast; the strongest convective cloud bands were consistent with the maximum wind region. During its strengthening stage, it was cold west of and warm east of the eye in the lower layer but warm in the west and cold in the east of the mid-upper layer. During its mature stage, a warm-core structure was evident in the lower and middle-upper layer. (3) The interactions between a mid-latitude cold low in the middle-upper troposphere and the typhoon were responsible for the latter to strengthen inshore. Firstly, the outer circulation of the cold low entered the typhoon from the middle troposphere when an outer cold airflow from the cold low flowed into the northwest quadrant of the typhoon so that geopotentially instable energy increased and convection developed. Secondly, the downdraft in the cold low was just the corresponding branch of the secondary circulation of the typhoon system; when the cold low weakened while moving south, the typhoon strengthened inshore. Due to the CISK mechanism, these two phenomena might be realized.
An explicit simulation with a fine mesh at intervals of 6 km is used to explore the inner-core structures of Vongfong (0214). The dynamic mechanism for the inshore strengthening of Vongfong is examined. It is found as follows. (1) The radius of maximum wind of the axisymmetric structures of the typhoon decreased with height during its mature stage. When Vongfong was inshore, the strongest low-layer inflow located in front of it and the outflow was to the rear of it, which was just reversed from the Atlantic hurricanes and other Pacific typhoons. (2) The dynamic and thermodynamic fields were highly asymmetric in structure. Convection was stronger in the northwest quadrant of the typhoon than in the southeast; the strongest convective cloud bands were consistent with the maximum wind region. During its strengthening stage, it was cold west of and warm east of the eye in the lower layer but warm in the west and cold in the east of the mid-upper layer. During its mature stage, a warm-core structure was evident in the lower and middle-upper layer. (3) The interactions between a mid-latitude cold low in the middle-upper troposphere and the typhoon were responsible for the latter to strengthen inshore. Firstly, the outer circulation of the cold low entered the typhoon from the middle troposphere when an outer cold airflow from the cold low flowed into the northwest quadrant of the typhoon so that geopotentially instable energy increased and convection developed. Secondly, the downdraft in the cold low was just the corresponding branch of the secondary circulation of the typhoon system; when the cold low weakened while moving south, the typhoon strengthened inshore. Due to the CISK mechanism, these two phenomena might be realized.
2009, (1): 49-53.
Abstract:
Both of Typhoon Winnie (9711) and Matsa (0509) underwent an extratropical transition (ET) process when they moved northward after landfall and affected Liaodong Peninsula. However, Matsa produced half as much rainfall as Winnie, although it struck Liaodong Peninsula directly while Winnie passed through the Bohai Sea. The relations between the ET processes and the precipitation over Liaodong Peninsula are examined. The result shows that the precipitation difference between Winnie and Matsa was closely related to the interactions between the westerly systems and typhoons during their ET processes. Winnie was captured by the upper westerly trough and then coupled with it when moving to the mid-latitudes, and the positive anomaly of moist potential vorticity (MPV) was transported downward from the upper troposphere over the remnant circulation of the tropical cyclone (TC). It was favorable to the interaction between tropical warm and wet air and westerly cold air, causing convective cloud clusters to form and develop. The rain belt composed of several meso-β cloud clusters over the Liaodong Peninsula, resulting in heavy rainfall. On the other hand, Matsa did not couple with any upper trough during its ET process and the positive anomaly of MPV in the upper troposphere and its downward transfer were weak. Only one meso-β cloud cluster occurred in Matsa’s rain belt during its ET process that tended to lessen rainfall over Liaodong Peninsula.
Both of Typhoon Winnie (9711) and Matsa (0509) underwent an extratropical transition (ET) process when they moved northward after landfall and affected Liaodong Peninsula. However, Matsa produced half as much rainfall as Winnie, although it struck Liaodong Peninsula directly while Winnie passed through the Bohai Sea. The relations between the ET processes and the precipitation over Liaodong Peninsula are examined. The result shows that the precipitation difference between Winnie and Matsa was closely related to the interactions between the westerly systems and typhoons during their ET processes. Winnie was captured by the upper westerly trough and then coupled with it when moving to the mid-latitudes, and the positive anomaly of moist potential vorticity (MPV) was transported downward from the upper troposphere over the remnant circulation of the tropical cyclone (TC). It was favorable to the interaction between tropical warm and wet air and westerly cold air, causing convective cloud clusters to form and develop. The rain belt composed of several meso-β cloud clusters over the Liaodong Peninsula, resulting in heavy rainfall. On the other hand, Matsa did not couple with any upper trough during its ET process and the positive anomaly of MPV in the upper troposphere and its downward transfer were weak. Only one meso-β cloud cluster occurred in Matsa’s rain belt during its ET process that tended to lessen rainfall over Liaodong Peninsula.
2009, 15(1): 54-58.
Abstract:
The latest version of sea spray flux parameterization scheme developed by Andreas is coupled with the PSU/NCAR model MM5 in this paper. A western Pacific tropical cyclone named Nabi in 2005 is simulated using this coupled air-sea spray modeling system to study the impacts of sea spray evaporation on the evolution of tropical cyclones. The results demonstrate that sea spray can lead to a significant increase of heat fluxes in the air-sea interface, especially the latent heat flux, the maximum of which can increase by up to about 35% - 80% The latent heat flux seems to be more important than the sensible heat flux for the evolution of tropical cyclones. Regardless of whether sea spray fluxes have been considered, the model can always simulate the track of Nabi well, which seems to indicate that sea spray has little impact on the movement of tropical cyclones. However, with sea spray fluxes taken into account in the model, the intensity of a simulated tropical cyclone can have significant increase. Due to the enhancement of water vapor and heat from the sea surface to the air caused by sea spray, the warm core structure is better-defined, the minimum sea level pressure decreases and the vertical speed is stronger around the eye in the experiments, which is propitious to the development and evolution of tropical cyclones.
The latest version of sea spray flux parameterization scheme developed by Andreas is coupled with the PSU/NCAR model MM5 in this paper. A western Pacific tropical cyclone named Nabi in 2005 is simulated using this coupled air-sea spray modeling system to study the impacts of sea spray evaporation on the evolution of tropical cyclones. The results demonstrate that sea spray can lead to a significant increase of heat fluxes in the air-sea interface, especially the latent heat flux, the maximum of which can increase by up to about 35% - 80% The latent heat flux seems to be more important than the sensible heat flux for the evolution of tropical cyclones. Regardless of whether sea spray fluxes have been considered, the model can always simulate the track of Nabi well, which seems to indicate that sea spray has little impact on the movement of tropical cyclones. However, with sea spray fluxes taken into account in the model, the intensity of a simulated tropical cyclone can have significant increase. Due to the enhancement of water vapor and heat from the sea surface to the air caused by sea spray, the warm core structure is better-defined, the minimum sea level pressure decreases and the vertical speed is stronger around the eye in the experiments, which is propitious to the development and evolution of tropical cyclones.
2009, 15(1): 59-62.
Abstract:
Based on the data of 1950 –C 1999 monthly global SST from Hadley Center, NCAR/NCEP reanalysis data and rainfall over 160 weather stations in China, investigation is conducted into the difference of summer rainfall in China (hereafter referred to as the “CS rainfall”) between the years with the Indian Ocean Dipole (IOD) occurring independently and those with IOD occurring along with ENSO so as to study the effects of El Niño - Southern Oscillation (ENSO) on the relationship between IOD and the CS rainfall. It is shown that CS rainfall will be more than normal in South China (centered in Hunan province) in the years of positive IOD occurring independently; the CS rainfall will be less (more) than normal in North China (Southeast China) in the years of positive IOD occurring together with ENSO. The effect of ENSO is offsetting (enhancing) the relationship between IOD and summer rainfall in Southwest China, the region joining the Yangtze River basin with the Huaihe River basin (hereafter referred to as the “Yangtze-Huaihe basin”) and North China (Southeast China). The circulation field is also examined for preliminary causes of such an influence.
Based on the data of 1950 –C 1999 monthly global SST from Hadley Center, NCAR/NCEP reanalysis data and rainfall over 160 weather stations in China, investigation is conducted into the difference of summer rainfall in China (hereafter referred to as the “CS rainfall”) between the years with the Indian Ocean Dipole (IOD) occurring independently and those with IOD occurring along with ENSO so as to study the effects of El Niño - Southern Oscillation (ENSO) on the relationship between IOD and the CS rainfall. It is shown that CS rainfall will be more than normal in South China (centered in Hunan province) in the years of positive IOD occurring independently; the CS rainfall will be less (more) than normal in North China (Southeast China) in the years of positive IOD occurring together with ENSO. The effect of ENSO is offsetting (enhancing) the relationship between IOD and summer rainfall in Southwest China, the region joining the Yangtze River basin with the Huaihe River basin (hereafter referred to as the “Yangtze-Huaihe basin”) and North China (Southeast China). The circulation field is also examined for preliminary causes of such an influence.
STATISTICAL CHARACTERISTICS OF TROPICAL CYCLONES MAKING LANDFALLS AND PASSING THROUGH LAKES IN CHINA
2009, 15(1): 63-67.
Abstract:
By using the data of 1949 –C 2001 (53 years) of Tropical Cyclone (TC) Yearbooks, statistical analyses are performed to study the climatic features of TCs making landfall and then passing through lakes (hereafter referred to as “L-TCs”) in China. Results show that L-TCs can sustain a long time over land and the intensity is very strong during the course of landfall. Lakes can noticeably slow down the reduction of TC intensity, with the minimum pressure mostly maintained or decreased and the maximum velocity increased. The middle reach of the Yangtze River has the biggest TC dissipating rate as compared with the other areas where the TC is active.
By using the data of 1949 –C 2001 (53 years) of Tropical Cyclone (TC) Yearbooks, statistical analyses are performed to study the climatic features of TCs making landfall and then passing through lakes (hereafter referred to as “L-TCs”) in China. Results show that L-TCs can sustain a long time over land and the intensity is very strong during the course of landfall. Lakes can noticeably slow down the reduction of TC intensity, with the minimum pressure mostly maintained or decreased and the maximum velocity increased. The middle reach of the Yangtze River has the biggest TC dissipating rate as compared with the other areas where the TC is active.
2009, 15(1): 68-72.
Abstract:
Samples of fog water collected in the area of Guangzhou during February, March and April of 2005 are used in this work to study the chemical composition of fog water in polluting fog there. Three typical episodes of polluting fog are analyzed in terms of ionic concentration and their possible sources. It is found that the concentration of various ions in fog water is much higher than those in rainwater. Fog not only blocks visual range but contains liquid particles that result in high degree of pollution and are very harmful to human health. SO4= is the anion with the highest concentration in fog water, followed by NO3-.For the cation, Ca++ and NH4+ are the highest in concentration. It is then known that rainwater is more acidic than fog water, indicating that ionic concentration of fog water is much higher than that of rainwater, but there are much more buffering materials in fog water, like NH4+ and Ca++. There is significant enrichment of Ca++, SO4=, and Mg++ in fog water. In the Guangzhou area, fog water from polluting fog is mainly influenced continental environment and human activity. The episodes of serious fog pollution during the time have immediate relationships with the presence of abundant water vapor and large amount of polluting aerosol particles.
Samples of fog water collected in the area of Guangzhou during February, March and April of 2005 are used in this work to study the chemical composition of fog water in polluting fog there. Three typical episodes of polluting fog are analyzed in terms of ionic concentration and their possible sources. It is found that the concentration of various ions in fog water is much higher than those in rainwater. Fog not only blocks visual range but contains liquid particles that result in high degree of pollution and are very harmful to human health. SO4= is the anion with the highest concentration in fog water, followed by NO3-.For the cation, Ca++ and NH4+ are the highest in concentration. It is then known that rainwater is more acidic than fog water, indicating that ionic concentration of fog water is much higher than that of rainwater, but there are much more buffering materials in fog water, like NH4+ and Ca++. There is significant enrichment of Ca++, SO4=, and Mg++ in fog water. In the Guangzhou area, fog water from polluting fog is mainly influenced continental environment and human activity. The episodes of serious fog pollution during the time have immediate relationships with the presence of abundant water vapor and large amount of polluting aerosol particles.
2009, 15(1): 73-77.
Abstract:
In order to understand the impact of initial conditions upon prediction accuracy of short-term forecast and nowcast of precipitation in South China, four experiments i.e. a control, an assimilation of conventional sounding and surface data, testing with nudging rainwater data and the assimilation of radar-derived radial wind, are respectively conducted to simulate a case of warm-sector heavy rainfall that occurred over South China, by using the GRAPES_MESO model. The results show that (1) assimilating conventional surface and sounding observations helps improve the 24-h rainfall forecast in both the area and order of magnitude; (2) nudging rainwater contributes to a significant improvement of nowcast, and (3) the assimilation of radar-derived radial winds distinctly improves the 24-h rainfall forecast in both the area and order of magnitude. These results serve as significant technical reference for the study on short-term forecast and nowcast of precipitation over South China in the future.
In order to understand the impact of initial conditions upon prediction accuracy of short-term forecast and nowcast of precipitation in South China, four experiments i.e. a control, an assimilation of conventional sounding and surface data, testing with nudging rainwater data and the assimilation of radar-derived radial wind, are respectively conducted to simulate a case of warm-sector heavy rainfall that occurred over South China, by using the GRAPES_MESO model. The results show that (1) assimilating conventional surface and sounding observations helps improve the 24-h rainfall forecast in both the area and order of magnitude; (2) nudging rainwater contributes to a significant improvement of nowcast, and (3) the assimilation of radar-derived radial winds distinctly improves the 24-h rainfall forecast in both the area and order of magnitude. These results serve as significant technical reference for the study on short-term forecast and nowcast of precipitation over South China in the future.
2009, 15(1): 78-82.
Abstract:
As an approach to the technological problem that the wind data of QuikSCAT scatterometer cannot accurately describe the zone of typhoon-level strong wind speed, some objective factors such as the typhoon moving speed, direction and friction are introduced in this study to construct the asymmetric strengthening of the QuikSCAT wind field. Then by adopting a technology of four-dimensional data assimilation, an experiment that includes both the assimilation and forecasting phases is designed to simulate Typhoon Rananim numerically. The results show that with model constraints and adjustment, this technology can incorporate the QuikSCAT wind data to the entire column of the model atmosphere, improve greatly the simulating effects of the whole-column wind, pressure field and the track as well as the simulated typhoon intensity covered by the forecast phase, and work positively for the forecasting of landfall locations.
As an approach to the technological problem that the wind data of QuikSCAT scatterometer cannot accurately describe the zone of typhoon-level strong wind speed, some objective factors such as the typhoon moving speed, direction and friction are introduced in this study to construct the asymmetric strengthening of the QuikSCAT wind field. Then by adopting a technology of four-dimensional data assimilation, an experiment that includes both the assimilation and forecasting phases is designed to simulate Typhoon Rananim numerically. The results show that with model constraints and adjustment, this technology can incorporate the QuikSCAT wind data to the entire column of the model atmosphere, improve greatly the simulating effects of the whole-column wind, pressure field and the track as well as the simulated typhoon intensity covered by the forecast phase, and work positively for the forecasting of landfall locations.
2009, 15(1): 83-88.
Abstract:
Because of the difficulty in deciding on the structure of BP neural network in operational meteorological application and the tendency for the network to transform to an issue of local solution, a hybrid Particle Swarm Optimization Algorithm based on Artificial Neural Network (PSO-BP) model is proposed for monthly mean rainfall of the whole area of Guangxi. It combines Particle Swarm Optimization (PSO) with BP, that is, the number of hidden nodes and connection weights are optimized by the implementation of PSO operation. The method produces a better network architecture and initial connection weights, trains the traditional backward propagation again by training samples. The ensemble strategy is carried out for the linear programming to calculate the best weights based on the “east sum of the error absolute value” as the optimal rule. The weighted coefficient of each ensemble individual is obtained. The results show that the method can effectively improve learning and generalization ability of the neural network.
Because of the difficulty in deciding on the structure of BP neural network in operational meteorological application and the tendency for the network to transform to an issue of local solution, a hybrid Particle Swarm Optimization Algorithm based on Artificial Neural Network (PSO-BP) model is proposed for monthly mean rainfall of the whole area of Guangxi. It combines Particle Swarm Optimization (PSO) with BP, that is, the number of hidden nodes and connection weights are optimized by the implementation of PSO operation. The method produces a better network architecture and initial connection weights, trains the traditional backward propagation again by training samples. The ensemble strategy is carried out for the linear programming to calculate the best weights based on the “east sum of the error absolute value” as the optimal rule. The weighted coefficient of each ensemble individual is obtained. The results show that the method can effectively improve learning and generalization ability of the neural network.
2009, 15(1): 89-92.
Abstract:
In order to research possible influences of the adjustment of plant distribution on the development frequency of thunderstorms over the Leizhou Peninsula, mathematic statistic methods, including correlation analyses, 11 kinds of fitting models and all-variable regression methods, were used for analyses and research. The results show that the average trend of the number of annual thunderstorm days is descending obviously, and there are thunderstorms in all seasons, in which warm post-midday thunderstorms have taken up the most part, and high frequency is found from May to September, and the starting and ending dates of thunderstorms have a great annual discrepancy. The vegetation structure has been improved along with the reduction of rice fields and the area increment of sugarcane and fruits planting, which results in the decrease of the number of thunderstorm days; the change in the characteristics of winter spare fields, which is caused by the planting of vegetables, limits the formation of thunderstorms in early winter and late spring. Meanwhile, the area adjustment of peanut planting has little influence on the variation of thunderstorm days. The adjustment of principal crop distribution, such as rice, sugarcane, fruits and vegetables, may have obvious influence on the formation of thunderstorms, and sugarcane has the largest effect, followed in turn by rice, vegetables and fruits, and the adjustment of crop distribution has little influence on the starting and ending dates of thunderstorms.
In order to research possible influences of the adjustment of plant distribution on the development frequency of thunderstorms over the Leizhou Peninsula, mathematic statistic methods, including correlation analyses, 11 kinds of fitting models and all-variable regression methods, were used for analyses and research. The results show that the average trend of the number of annual thunderstorm days is descending obviously, and there are thunderstorms in all seasons, in which warm post-midday thunderstorms have taken up the most part, and high frequency is found from May to September, and the starting and ending dates of thunderstorms have a great annual discrepancy. The vegetation structure has been improved along with the reduction of rice fields and the area increment of sugarcane and fruits planting, which results in the decrease of the number of thunderstorm days; the change in the characteristics of winter spare fields, which is caused by the planting of vegetables, limits the formation of thunderstorms in early winter and late spring. Meanwhile, the area adjustment of peanut planting has little influence on the variation of thunderstorm days. The adjustment of principal crop distribution, such as rice, sugarcane, fruits and vegetables, may have obvious influence on the formation of thunderstorms, and sugarcane has the largest effect, followed in turn by rice, vegetables and fruits, and the adjustment of crop distribution has little influence on the starting and ending dates of thunderstorms.
2009, 15(1): 93-96.
Abstract:
To understand how temperature varies in urban Shanghai under the background of global climate change and how it is affected by urbanization, the Shanghai temperature responses to global warming were analyzed, and then the temperature trends of urban and suburb stations under different climatic backgrounds were obtained. The urbanization effects on temperature were studied by comparing urban stations to suburb stations, the relationship between urbanization variables and temperature components were obtained, and observation data of surface and high level were combined to assess the contribution of urbanization effect. In the last part of the paper, the cause of urbanization effects on temperature was discussed. The results indicated: The long term change trend of Shanghai annual mean temperature is 1.31/100a from 1873 to 2004, the periods of 1921 –C 1948 and 1979 –C 2004 are warmer, and the 1979 –C 2004 period is the warmest; compared to suburb stations, the representative urban station has slower decreases in the cool period and faster increases in the warm one; the urban and suburb temperatures have distinct differences resulting from urbanization and the differences are increasing by the year, with the difference of mean temperature and minimum temperature being the greatest in fall and that of maximum temperature being the largest in summer between the urban and suburban areas. The urbanization process accelerates the warming speed, with the minimum temperature being the most obvious; the urbanization effect contributes a 0.4°C increase in 1980s and 1.1°C in 1990s to the annual mean temperature.
To understand how temperature varies in urban Shanghai under the background of global climate change and how it is affected by urbanization, the Shanghai temperature responses to global warming were analyzed, and then the temperature trends of urban and suburb stations under different climatic backgrounds were obtained. The urbanization effects on temperature were studied by comparing urban stations to suburb stations, the relationship between urbanization variables and temperature components were obtained, and observation data of surface and high level were combined to assess the contribution of urbanization effect. In the last part of the paper, the cause of urbanization effects on temperature was discussed. The results indicated: The long term change trend of Shanghai annual mean temperature is 1.31/100a from 1873 to 2004, the periods of 1921 –C 1948 and 1979 –C 2004 are warmer, and the 1979 –C 2004 period is the warmest; compared to suburb stations, the representative urban station has slower decreases in the cool period and faster increases in the warm one; the urban and suburb temperatures have distinct differences resulting from urbanization and the differences are increasing by the year, with the difference of mean temperature and minimum temperature being the greatest in fall and that of maximum temperature being the largest in summer between the urban and suburban areas. The urbanization process accelerates the warming speed, with the minimum temperature being the most obvious; the urbanization effect contributes a 0.4°C increase in 1980s and 1.1°C in 1990s to the annual mean temperature.
2009, 15(1): 97-101.
Abstract:
With correlation analysis and factor analysis methods, the effects of preceding Pacific SSTs on subtropical high indexes of main raining seasons are discussed. The results of correlation analysis show that the effects of SSTs on five subtropical high indexes differ in seasons and regions. The variation of SSTs mostly affects the area and intensity indexes of the subtropical high, followed by the western ridge index, and the effect on the ridge line index is more remarkable than on the north boundary index. The results of factor analysis reveals that the first common factor of SST of each season reflected mainly the inverse relation of SSTs variation between the central and eastern part of equatorial Pacific and the western Pacific, which correlates better with the subtropical high indexes in the main raining seasons than other common factors of SST. The analysis of interdecadal variation indicated that the variation of SSTs was conducive to the emergence of the La Niña event before the end of 1970s, such that in the summer the subtropical high is likely to be weaker and smaller and located eastward and northward. After the 1980s, the opposite characteristics prevailed.
With correlation analysis and factor analysis methods, the effects of preceding Pacific SSTs on subtropical high indexes of main raining seasons are discussed. The results of correlation analysis show that the effects of SSTs on five subtropical high indexes differ in seasons and regions. The variation of SSTs mostly affects the area and intensity indexes of the subtropical high, followed by the western ridge index, and the effect on the ridge line index is more remarkable than on the north boundary index. The results of factor analysis reveals that the first common factor of SST of each season reflected mainly the inverse relation of SSTs variation between the central and eastern part of equatorial Pacific and the western Pacific, which correlates better with the subtropical high indexes in the main raining seasons than other common factors of SST. The analysis of interdecadal variation indicated that the variation of SSTs was conducive to the emergence of the La Niña event before the end of 1970s, such that in the summer the subtropical high is likely to be weaker and smaller and located eastward and northward. After the 1980s, the opposite characteristics prevailed.
2009, 15(1): 102-105.
Abstract:
A nested-model system is constructed by embedding the regional climate model RegCM3 into a general circulation model for monthly-scale regional climate forecast over East China. The systematic errors are formulated for the region on the basis of 10-yr (1991-2000) results of the nested-model system, and of the datasets of the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) and the temperature analysis of the National Meteorological Center (NMC), U.S.A., which are then used for correcting the original forecast by the system for the period 2001-2005. After the assessment of the original and corrected forecasts for monthly precipitation and surface air temperature, it is found that the corrected forecast is apparently better than the original, suggesting that the approach can be applied for improving monthly-scale regional climate dynamical forecast.
A nested-model system is constructed by embedding the regional climate model RegCM3 into a general circulation model for monthly-scale regional climate forecast over East China. The systematic errors are formulated for the region on the basis of 10-yr (1991-2000) results of the nested-model system, and of the datasets of the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) and the temperature analysis of the National Meteorological Center (NMC), U.S.A., which are then used for correcting the original forecast by the system for the period 2001-2005. After the assessment of the original and corrected forecasts for monthly precipitation and surface air temperature, it is found that the corrected forecast is apparently better than the original, suggesting that the approach can be applied for improving monthly-scale regional climate dynamical forecast.
2009, 15(1): 106-110.
Abstract:
Madden-Julian Oscillations (MJO) in six integrations using an AGCM with different cumulus parameterization schemes and resolutions are examined to investigate their impacts on the MJO simulation. Results suggest that the MJO simulation can be affected by both resolution and cumulus parameterization, though the latter, which determines the fundamental ability of the AGCM in simulating the MJO and the characteristics of the simulated MJO, is more crucial than the former. Model resolution can substantially affect the simulated MJO in certain aspects. Increasing resolution cannot improve the simulated MJO substantially, but can significantly modulate the detailed character of the simulated MJO; meanwhile, the impacts of resolution are dependent on the cumulus parameterization, determining the basic features of the MJO. Changes in the resolution do not alter the nature of the simulated MJO but rather regulate the simulation itself, which is constrained by cumulus parameterization schemes. Therefore, the vertical resolution needs to be increased simultaneously. The vertical profile of diabatic heating may be a crucial factor that is responsible for these different modeling results. To a large extent, it is determined by the cumulus parameterization scheme used.
Madden-Julian Oscillations (MJO) in six integrations using an AGCM with different cumulus parameterization schemes and resolutions are examined to investigate their impacts on the MJO simulation. Results suggest that the MJO simulation can be affected by both resolution and cumulus parameterization, though the latter, which determines the fundamental ability of the AGCM in simulating the MJO and the characteristics of the simulated MJO, is more crucial than the former. Model resolution can substantially affect the simulated MJO in certain aspects. Increasing resolution cannot improve the simulated MJO substantially, but can significantly modulate the detailed character of the simulated MJO; meanwhile, the impacts of resolution are dependent on the cumulus parameterization, determining the basic features of the MJO. Changes in the resolution do not alter the nature of the simulated MJO but rather regulate the simulation itself, which is constrained by cumulus parameterization schemes. Therefore, the vertical resolution needs to be increased simultaneously. The vertical profile of diabatic heating may be a crucial factor that is responsible for these different modeling results. To a large extent, it is determined by the cumulus parameterization scheme used.
2009, 15(1): 111-115.
Abstract:
It is generally thought that the influence of comparable track typhoons is approximately similar, but in fact their wind and especially their rainstorm distribution are often very different. Therefore, a contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604), which are of a similar track, is designed to help understand the mechanism of the TC rainstorm and to improve forecasting skills. The daily rainfall of TC Haitang (0505) and Bilis (0604) is diagnosed and compared. The result indicates that these two TCs have similar precipitation distribution before landfall but different precipitation characteristics after landfall. Using NCEP/GFS analysis data, the synoptic situation is analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence. The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang (0505) and Bilis (0604) before landfall results from a peripheral easterly wind, a combination of the tropical cyclone and the terrain. After landfall and moving far inland of the storm, the precipitation of Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in the coastal area. One of the important contributing factors to heavy rainstorms in southeast Zhejiang is a southeast jet stream, which is maintained over the southeast coast. In contrast, the South China Sea monsoon circulation transports large amounts of water vapor into Bilis –C when a water-vapor transport belt south of the tropical cyclone significantly strengthens –C which strengthens the transport. Then, it causes water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much stronger on the south side than that on the north side. After Bilis travels far inland, the cold air guided by a north trough travels into the TC and remarkably enhances precipitation. In summary, combining vertical wind shear with water vapor transportation is a good way to predict rainstorms associated with landing tropical cyclones.
It is generally thought that the influence of comparable track typhoons is approximately similar, but in fact their wind and especially their rainstorm distribution are often very different. Therefore, a contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604), which are of a similar track, is designed to help understand the mechanism of the TC rainstorm and to improve forecasting skills. The daily rainfall of TC Haitang (0505) and Bilis (0604) is diagnosed and compared. The result indicates that these two TCs have similar precipitation distribution before landfall but different precipitation characteristics after landfall. Using NCEP/GFS analysis data, the synoptic situation is analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence. The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang (0505) and Bilis (0604) before landfall results from a peripheral easterly wind, a combination of the tropical cyclone and the terrain. After landfall and moving far inland of the storm, the precipitation of Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in the coastal area. One of the important contributing factors to heavy rainstorms in southeast Zhejiang is a southeast jet stream, which is maintained over the southeast coast. In contrast, the South China Sea monsoon circulation transports large amounts of water vapor into Bilis –C when a water-vapor transport belt south of the tropical cyclone significantly strengthens –C which strengthens the transport. Then, it causes water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much stronger on the south side than that on the north side. After Bilis travels far inland, the cold air guided by a north trough travels into the TC and remarkably enhances precipitation. In summary, combining vertical wind shear with water vapor transportation is a good way to predict rainstorms associated with landing tropical cyclones.
2009, 15(1): 116-120.
Abstract:
The National Centers for Environmental Prediction (NCEP) reanalysis data, Climate Diagnostics Center Merged Analysis of Precipitation (CMAP) results, and NOAA Extended Reconstructed Sea Surface Temperature (SST), have been utilized in this paper to study the quasi-biennial variations in Asia-Pacific monsoon subsystems and associated SST anomalies (SSTA) and wind anomalies. Four monsoon indices are computed from NCEP/ National Center for Atmospheric Research (NCAR) reanalysis to represent the South Asian monsoon (SAM), South China Sea summer monsoon (SCSSM), Western North Pacific monsoon (WNPM) and East Asian monsoon (EAM), respectively. The quasi-biennial periods are very significant in Asia-Pacific monsoons (as discovered by power spectrum analysis), and for SAM and EAM---with moderate effects by El Niño-Southern Oscillation (ENSO)---the quasi-biennial periods are the most important factor. For SCSSM and WNPM (once again due to the effects of ENSO), the quasi-biennial periods are of secondary durations. There are obvious interdecadal variations in the quasi-biennial modes of the Asia-Pacific monsoon, so in the negative phase the biennial modes will not be significant or outstanding. The wind anomalies and SSTA associated with the biennial modes are very different in the SAM, WNPM and EAM regions. Since the WNPM and SCSSM are very similar in the biennial modes, they can be combined into one subsystem, called SCS/WNPM.
The National Centers for Environmental Prediction (NCEP) reanalysis data, Climate Diagnostics Center Merged Analysis of Precipitation (CMAP) results, and NOAA Extended Reconstructed Sea Surface Temperature (SST), have been utilized in this paper to study the quasi-biennial variations in Asia-Pacific monsoon subsystems and associated SST anomalies (SSTA) and wind anomalies. Four monsoon indices are computed from NCEP/ National Center for Atmospheric Research (NCAR) reanalysis to represent the South Asian monsoon (SAM), South China Sea summer monsoon (SCSSM), Western North Pacific monsoon (WNPM) and East Asian monsoon (EAM), respectively. The quasi-biennial periods are very significant in Asia-Pacific monsoons (as discovered by power spectrum analysis), and for SAM and EAM---with moderate effects by El Niño-Southern Oscillation (ENSO)---the quasi-biennial periods are the most important factor. For SCSSM and WNPM (once again due to the effects of ENSO), the quasi-biennial periods are of secondary durations. There are obvious interdecadal variations in the quasi-biennial modes of the Asia-Pacific monsoon, so in the negative phase the biennial modes will not be significant or outstanding. The wind anomalies and SSTA associated with the biennial modes are very different in the SAM, WNPM and EAM regions. Since the WNPM and SCSSM are very similar in the biennial modes, they can be combined into one subsystem, called SCS/WNPM.
粤公网安备 4401069904700002号