2006 Vol. 12, No. 1
2006, 12(1): 1-8.
Abstract:
Results of the definition of South China Sea summer monsoon onset date and East Asian summer monsoon index in recent years are summarized in this paper. And more questions to be resolved are introduced later.
Results of the definition of South China Sea summer monsoon onset date and East Asian summer monsoon index in recent years are summarized in this paper. And more questions to be resolved are introduced later.
2006, 12(1): 9-15.
Abstract:
Due to the decrease in grid size associated with the convergence of meridians toward the poles in spherical coordinates, the time steps in many global climate models with finite-difference method are restricted to be unpleasantly small. To overcome the problem, a reduced grid is introduced to LASG/IAP world ocean general circulation models. The reduced grid is implemented successfully in the coarser resolutions version model L30T63 at first. Then, it is carried out in the improved version model LICOM with finer resolutions. In the experiment with model L30T63, under time step unchanged though, execution time per single model run is shortened significantly owing to the decrease of grid number and filtering execution in high latitudes. Results from additional experiments with L30T63 show that the time step of integration can be quadrupled at most in reduced grid with refinement ratio 3. In the experiment with model LICOM and with the model’s original time step unchanged, the model covered area is extended to the whole globe from its original case with the grid point of North Pole considered as an isolated island and the results of experiment are shown to be acceptable.
Due to the decrease in grid size associated with the convergence of meridians toward the poles in spherical coordinates, the time steps in many global climate models with finite-difference method are restricted to be unpleasantly small. To overcome the problem, a reduced grid is introduced to LASG/IAP world ocean general circulation models. The reduced grid is implemented successfully in the coarser resolutions version model L30T63 at first. Then, it is carried out in the improved version model LICOM with finer resolutions. In the experiment with model L30T63, under time step unchanged though, execution time per single model run is shortened significantly owing to the decrease of grid number and filtering execution in high latitudes. Results from additional experiments with L30T63 show that the time step of integration can be quadrupled at most in reduced grid with refinement ratio 3. In the experiment with model LICOM and with the model’s original time step unchanged, the model covered area is extended to the whole globe from its original case with the grid point of North Pole considered as an isolated island and the results of experiment are shown to be acceptable.
2006, 12(1): 16-23.
Abstract:
By using data of serially numbered typhoons in northwestern Pacific and NOAA OLR data and NCEP/NCAR reanalysis data of wind field, based on the statistics and study of the relationship between the calendar years with more (or fewer) summer typhoons and ENSO events, we compared the composites of OLR eigenvectors and tropical summer wind fields during El Nino and La Nina events with more or fewer than normal summer typhoons, respectively. The results show that, in summer, without remarkable systematic anomalies of Mascarene High and Australia High in South Hemisphere, the anomaly of Walker circulation will dominate and follow the rule of ENSO impacts to atmospheric circulation and typhoon frequency. Otherwise, when systematic anomalies of Australia High appear during the El Nino events, circulation anomalies in the South Hemisphere will dominate, and many more typhoons will occur. In 1999, which is a special year of La Nina events, northward and eastward monsoon was induced by the stronger Mascarene High, and fewer typhoons arose. The typhoon source are regions where weak vertical wind shear, warm pool in western Pacific and the area with monsoon troughs are overlapping with each other. Finally, this paper analyzes and compares the source locations and ranges of more (fewer) typhoons in the events of El Nino and La Nina, respectively.
By using data of serially numbered typhoons in northwestern Pacific and NOAA OLR data and NCEP/NCAR reanalysis data of wind field, based on the statistics and study of the relationship between the calendar years with more (or fewer) summer typhoons and ENSO events, we compared the composites of OLR eigenvectors and tropical summer wind fields during El Nino and La Nina events with more or fewer than normal summer typhoons, respectively. The results show that, in summer, without remarkable systematic anomalies of Mascarene High and Australia High in South Hemisphere, the anomaly of Walker circulation will dominate and follow the rule of ENSO impacts to atmospheric circulation and typhoon frequency. Otherwise, when systematic anomalies of Australia High appear during the El Nino events, circulation anomalies in the South Hemisphere will dominate, and many more typhoons will occur. In 1999, which is a special year of La Nina events, northward and eastward monsoon was induced by the stronger Mascarene High, and fewer typhoons arose. The typhoon source are regions where weak vertical wind shear, warm pool in western Pacific and the area with monsoon troughs are overlapping with each other. Finally, this paper analyzes and compares the source locations and ranges of more (fewer) typhoons in the events of El Nino and La Nina, respectively.
2006, 12(1): 24-28.
Abstract:
Based on the 1973 –C 2003 temperature data of Guangzhou meteorological station and 1980 –C 2000 temperature data of Foshan airport, the variations of urbanization effect on temperature of Pearl River Delta (PRD) and Guangzhou city were analyzed. It was found that the temperature has increased significantly due to the PRD’s urbanization. During the last 20 years, Foshan airport’s temperature has increased by 0.7°C, and the Guangzhou city’s temperature increased by about 1.1°C during last 30 years. The heat island of Guangzhou city is obvious but has some differences from other big Chinese cities.
Based on the 1973 –C 2003 temperature data of Guangzhou meteorological station and 1980 –C 2000 temperature data of Foshan airport, the variations of urbanization effect on temperature of Pearl River Delta (PRD) and Guangzhou city were analyzed. It was found that the temperature has increased significantly due to the PRD’s urbanization. During the last 20 years, Foshan airport’s temperature has increased by 0.7°C, and the Guangzhou city’s temperature increased by about 1.1°C during last 30 years. The heat island of Guangzhou city is obvious but has some differences from other big Chinese cities.
2006, 12(1): 29-33.
Abstract:
Using the new formula of moist available energy (MAE), the value of the MAE’s key terms of three heavy rainfall cases in Guangdong province in 1998 was calculated. The energetic aggregation and energetic discharge are analyzed. It shows that the value of the key terms in the formula appears different feature clearly in the different precipitation period, as well as the function of each term presents in the heavy rain region.
Using the new formula of moist available energy (MAE), the value of the MAE’s key terms of three heavy rainfall cases in Guangdong province in 1998 was calculated. The energetic aggregation and energetic discharge are analyzed. It shows that the value of the key terms in the formula appears different feature clearly in the different precipitation period, as well as the function of each term presents in the heavy rain region.
2006, 12(1): 34-40.
Abstract:
Datasets of equivalent temperature of black body (TBB) and sea surface temperature (SST) ranging from 1980 to 1997 are used to diagnose and analyze the characteristics of frequency spectrum and strength of intraseasonal variation of convection. The relationship between the strength of intraseasonal oscillation of convection, strength of convection itself and SST in the South China Sea (SCS) is studied. It is shown that, there are distinguishable annual, interannual and interdecadal variations in both strength and frequency spectrum of intraseasonal variation of convection in SCS. There are connections between strength of convection, strength of ISO1 in the summer half (s.h.) year and SST in ensuing winter half (w.h.) year in SCS. The strong (weak) convection and strong (weak) ISO1 are associated with negative (positive) bias of SST in ensuing w.h. year in SCS.
Datasets of equivalent temperature of black body (TBB) and sea surface temperature (SST) ranging from 1980 to 1997 are used to diagnose and analyze the characteristics of frequency spectrum and strength of intraseasonal variation of convection. The relationship between the strength of intraseasonal oscillation of convection, strength of convection itself and SST in the South China Sea (SCS) is studied. It is shown that, there are distinguishable annual, interannual and interdecadal variations in both strength and frequency spectrum of intraseasonal variation of convection in SCS. There are connections between strength of convection, strength of ISO1 in the summer half (s.h.) year and SST in ensuing winter half (w.h.) year in SCS. The strong (weak) convection and strong (weak) ISO1 are associated with negative (positive) bias of SST in ensuing w.h. year in SCS.
2006, 12(1): 41-45.
Abstract:
Taking Tropical Cyclone (TC) No.9806 (Todd) as an example, the effects of Zhoushan archipelago terrain on landfall TC are investigated by use of numerical simulation. Results show that, under topographic influences of Zhoushan Islands, the westward-moving landfall TC deflects. And, small orographic highs and enhanced rainfall caused by climbing airflow on the windward slope of main mountains of these islands are a result of effects of Zhoushan Islands. These results display some particular laws of effects of small-sized islands on the landfall of TC.
Taking Tropical Cyclone (TC) No.9806 (Todd) as an example, the effects of Zhoushan archipelago terrain on landfall TC are investigated by use of numerical simulation. Results show that, under topographic influences of Zhoushan Islands, the westward-moving landfall TC deflects. And, small orographic highs and enhanced rainfall caused by climbing airflow on the windward slope of main mountains of these islands are a result of effects of Zhoushan Islands. These results display some particular laws of effects of small-sized islands on the landfall of TC.
2006, 12(1): 46-54.
Abstract:
The 2.5。×2.52。 gridded ECMWF reanalysis data are used to diagnose the genesis, development and dissipation of typhoon Dan by calculated stream function, velocity potential and vapor budget. It is shown in the result that when typhoon Dan moved westwards, water vapor mainly came from the eastern and western boundaries, with most of it was transferred by the easterly flow south of the western North Pacific subtropical high; after Dan swerved northwards, water vapor mainly came from western boundary of the typhoon, and the vapor came from the South China Sea and the Indian Ocean. The transfer of water vapor was mainly concentrated on the mid-lower troposphere, especially the level of 925hPa, at which the most intensive transfer belt was located. During the different period of typhoon Dan, there was great water vapor change as indicated by stream function, velocity potential and vapor budget, which suggest the importance of water vapor in the development of typhoon Dan.
The 2.5。×2.52。 gridded ECMWF reanalysis data are used to diagnose the genesis, development and dissipation of typhoon Dan by calculated stream function, velocity potential and vapor budget. It is shown in the result that when typhoon Dan moved westwards, water vapor mainly came from the eastern and western boundaries, with most of it was transferred by the easterly flow south of the western North Pacific subtropical high; after Dan swerved northwards, water vapor mainly came from western boundary of the typhoon, and the vapor came from the South China Sea and the Indian Ocean. The transfer of water vapor was mainly concentrated on the mid-lower troposphere, especially the level of 925hPa, at which the most intensive transfer belt was located. During the different period of typhoon Dan, there was great water vapor change as indicated by stream function, velocity potential and vapor budget, which suggest the importance of water vapor in the development of typhoon Dan.
2006, 12(1): 55-58.
Abstract:
Based on a barotropic vortex model, generalized energy-conserving equation was derived and two necessary conditions of basic flow destabilization are gained. These conditions correspond to generalized barotropic instability and super speed instability. They are instabilities of vortex and gravity inertial wave respectively. In order to relate to practical situation, a barotropic vortex was analyzed, the basic flow of which is similar to lower level basic wind field of tropical cyclones and the maximum wind radius of which is 500 km. The results show that generalized barotropic instability depending upon the radial gradient of relative vorticity can appear in this vortex. It can be concluded that unstable vortex Rossby wave may appear in barotropic vortex.
Based on a barotropic vortex model, generalized energy-conserving equation was derived and two necessary conditions of basic flow destabilization are gained. These conditions correspond to generalized barotropic instability and super speed instability. They are instabilities of vortex and gravity inertial wave respectively. In order to relate to practical situation, a barotropic vortex was analyzed, the basic flow of which is similar to lower level basic wind field of tropical cyclones and the maximum wind radius of which is 500 km. The results show that generalized barotropic instability depending upon the radial gradient of relative vorticity can appear in this vortex. It can be concluded that unstable vortex Rossby wave may appear in barotropic vortex.
2006, 12(1): 67-75.
Abstract:
With simultaneous observed sea surface temperature anomaly (SSTA), the difference between NCEP/NCAR 925hPa reanalysis wind stress anomaly (NCEPWSA) and FSU wind stress anomaly (FSUWSA) is analyzed, and the prediction abilities of Zebiak-Cane coupled ocean-atmosphere model (ZC coupled model) with NCEPWSA and FSUWSA serving respectively as initialization wind are compared. The results are as follows. The distribution feature of NCEPWSA matches better with that of the observed SSTA than counterpart of FSUWSA both in 1980s and in 1990s; The ZC ocean model has a better skill under the forcing of NCEPWSA than that of FSUWSA, especially in 1990s. Meanwhile, the forecast abilities of the ZC coupled model in 1990s as well as in 1980s have been improved employing NCEPWSA as initialization wind instead of FSUWSA. Particularly, it succeeded in predicting 1997/1998 El Niño 6 to 8 months ahead; further analysis shows that on the antecedent and onset stages of the 1997/1998 El Niño event, the horizontal cold and warm distribution characteristics of the simulated SSTA from ZC ocean model, with NCEPWSA forcing compared to FSUWSA forcing, match better with counterparts of the corresponding observed SSTA, whereby providing better predication initialization conditions for ZC coupled model, which, in turn, is favorable to improve the forecast ability of the coupled model.
With simultaneous observed sea surface temperature anomaly (SSTA), the difference between NCEP/NCAR 925hPa reanalysis wind stress anomaly (NCEPWSA) and FSU wind stress anomaly (FSUWSA) is analyzed, and the prediction abilities of Zebiak-Cane coupled ocean-atmosphere model (ZC coupled model) with NCEPWSA and FSUWSA serving respectively as initialization wind are compared. The results are as follows. The distribution feature of NCEPWSA matches better with that of the observed SSTA than counterpart of FSUWSA both in 1980s and in 1990s; The ZC ocean model has a better skill under the forcing of NCEPWSA than that of FSUWSA, especially in 1990s. Meanwhile, the forecast abilities of the ZC coupled model in 1990s as well as in 1980s have been improved employing NCEPWSA as initialization wind instead of FSUWSA. Particularly, it succeeded in predicting 1997/1998 El Niño 6 to 8 months ahead; further analysis shows that on the antecedent and onset stages of the 1997/1998 El Niño event, the horizontal cold and warm distribution characteristics of the simulated SSTA from ZC ocean model, with NCEPWSA forcing compared to FSUWSA forcing, match better with counterparts of the corresponding observed SSTA, whereby providing better predication initialization conditions for ZC coupled model, which, in turn, is favorable to improve the forecast ability of the coupled model.
2006, 12(1): 76-82.
Abstract:
There was a new concept of ‘adaptive or targeting observation’ in recent years, which is an additional and targeting observation based on the existing and fixed observing network for the atmosphere on the impacted region. Dropsonde is one of the important observing instruments in the adaptive or targeting observation. In this paper, GRAPES, the next generation of numerical weather prediction system of China has been used. The impacts on the typhoon Dujuan (No.200315) forecast in experiments with dropsonde have been studied and experiments on sensitivity have also been done. It was found that the forecasts of the elements have been improved obviously with the use of dropsonde, such as the path, the center location, and the intensity of typhoon. It was also found in the sensitivity studies that the setting of deviation structure also has obvious impacts on the forecast for typhoons. It is not true that the simulation is better when the proportion of the data of dropsonde is larger in the course to modify the background.
There was a new concept of ‘adaptive or targeting observation’ in recent years, which is an additional and targeting observation based on the existing and fixed observing network for the atmosphere on the impacted region. Dropsonde is one of the important observing instruments in the adaptive or targeting observation. In this paper, GRAPES, the next generation of numerical weather prediction system of China has been used. The impacts on the typhoon Dujuan (No.200315) forecast in experiments with dropsonde have been studied and experiments on sensitivity have also been done. It was found that the forecasts of the elements have been improved obviously with the use of dropsonde, such as the path, the center location, and the intensity of typhoon. It was also found in the sensitivity studies that the setting of deviation structure also has obvious impacts on the forecast for typhoons. It is not true that the simulation is better when the proportion of the data of dropsonde is larger in the course to modify the background.
2006, 12(1): 83-84.
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