2006 Vol. 12, No. 2
2006, 12(2): 105-112.
Abstract:
Based on daily NCEP reanalysis data, OLR and satellite rainfall data, the characteristic of the activities of South China Sea summer monsoon(SCSSM) in 2004 were analyzed. The results showed that the establishment of SCSSM was little later than normal and the intensity was stronger than normal. Influenced by the location of the northwest Pacific subtropical high, which was much northward and westward than normal, SCSSM was active mainly in the South China Sea areas. There existed obvious intraseasonal oscillation and two significant periods of SCSSM, one was about 20-30 days and the other about 40-50 days. The transportation of moisture was concentrated on the South China Sea and the northwest Pacific regions, reducing the northward transportation and resulting in drought in southern China
Based on daily NCEP reanalysis data, OLR and satellite rainfall data, the characteristic of the activities of South China Sea summer monsoon(SCSSM) in 2004 were analyzed. The results showed that the establishment of SCSSM was little later than normal and the intensity was stronger than normal. Influenced by the location of the northwest Pacific subtropical high, which was much northward and westward than normal, SCSSM was active mainly in the South China Sea areas. There existed obvious intraseasonal oscillation and two significant periods of SCSSM, one was about 20-30 days and the other about 40-50 days. The transportation of moisture was concentrated on the South China Sea and the northwest Pacific regions, reducing the northward transportation and resulting in drought in southern China
2006, 12(2): 113-120.
Abstract:
Using NCEP/NCAR daily reanalysis data and SCSMEX data, an investigation is carried out of the relationship between the position variation of the west Pacific subtropical high (WPSH) and the apparent heating in June 1998 based on the complete vertical vorticity equation. It is found that the non-adiabatic heating plays an important role in the position variation of WPSH. In comparison with climatic mean status, the vertical change of non-adiabatic heating is stronger in the north side of WPSH in June 1998, but weaker in the south side of WPSH. The anomalous non-uniform heating induces anomalous cyclonic vorticity in South China, areas to the south of the Yangtze and its mid-lower valleys, but anomalous anticyclonic vorticity in the Indo-China Peninsula and South China Sea areas lead to the more southward position of WPSH than the mean.
Using NCEP/NCAR daily reanalysis data and SCSMEX data, an investigation is carried out of the relationship between the position variation of the west Pacific subtropical high (WPSH) and the apparent heating in June 1998 based on the complete vertical vorticity equation. It is found that the non-adiabatic heating plays an important role in the position variation of WPSH. In comparison with climatic mean status, the vertical change of non-adiabatic heating is stronger in the north side of WPSH in June 1998, but weaker in the south side of WPSH. The anomalous non-uniform heating induces anomalous cyclonic vorticity in South China, areas to the south of the Yangtze and its mid-lower valleys, but anomalous anticyclonic vorticity in the Indo-China Peninsula and South China Sea areas lead to the more southward position of WPSH than the mean.
2006, 12(2): 121-129.
Abstract:
Guangzhou spring rainfall mainly exhibits interannual variation of Quasi-biannual and interdecadal variation of 30 yrs, and is in the period of weak rainfall at interdecadal time scale. SST anomalies (SSTA) of Nino3 are the strongest precursor of Guangzhou spring rainfall. They have significant positive correlation from previous November and persist stably to April. Nino3 SSTA in the previous winter affects Guangzhou spring rainfall through North Pacific subtropical high and low wind in spring. When Nino3 SSTA is positive in the previous winter, spring subtropical high is intense and westward, South China is located in the area of ascending airflow at the edge of the subtropical high, and water vapor transporting to South China is intensified by anticyclone circulation to the east of the Philippines. So Guangzhou spring rainfall is heavy. When Nino3 SSTA is negative, the subtropical high is weak and eastward, South China is far away from the subtropical high and is located in the area of descending airflow, and water vapor transporting to South China is weak because low-level cyclonic circulation controls areas to the east of the Philippines and north wind prevails in South China. So Guangzhou spring rainfall is weak and spring drought is resulted.
Guangzhou spring rainfall mainly exhibits interannual variation of Quasi-biannual and interdecadal variation of 30 yrs, and is in the period of weak rainfall at interdecadal time scale. SST anomalies (SSTA) of Nino3 are the strongest precursor of Guangzhou spring rainfall. They have significant positive correlation from previous November and persist stably to April. Nino3 SSTA in the previous winter affects Guangzhou spring rainfall through North Pacific subtropical high and low wind in spring. When Nino3 SSTA is positive in the previous winter, spring subtropical high is intense and westward, South China is located in the area of ascending airflow at the edge of the subtropical high, and water vapor transporting to South China is intensified by anticyclone circulation to the east of the Philippines. So Guangzhou spring rainfall is heavy. When Nino3 SSTA is negative, the subtropical high is weak and eastward, South China is far away from the subtropical high and is located in the area of descending airflow, and water vapor transporting to South China is weak because low-level cyclonic circulation controls areas to the east of the Philippines and north wind prevails in South China. So Guangzhou spring rainfall is weak and spring drought is resulted.
2006, 12(2): 130-138.
Abstract:
Multiple equilibria and their stability in tropical atmosphere are investigated through β-plane barotropic models with consideration of heating and dissipation. We have derived the solutions of the model equations corresponding to the multiple equilibria or the steady flows first, and then establish the criteria for the stability of steady flow by use of the Liapunov direct Method. When these criteria are applied to the solutions of equilibria obtained, stable flows, which are closely related to the different patterns of quasi-stationary circulation in the tropical region, are found. The configurations of these stable flows and the shift between two of them as season changes provide quite reasonable explanations to many fundamental problems of tropical circulation features such as the catastrophe mechanism of the onset and the break-active cycle of the Asian summer monsoon. It follows that the onset or the abrupt transition of the Asian summer monsoon could be attributed to the multiple equilibrium property of the tropical circulation resulted from the advective nonlinearity, which provide another explanation among others.
Multiple equilibria and their stability in tropical atmosphere are investigated through β-plane barotropic models with consideration of heating and dissipation. We have derived the solutions of the model equations corresponding to the multiple equilibria or the steady flows first, and then establish the criteria for the stability of steady flow by use of the Liapunov direct Method. When these criteria are applied to the solutions of equilibria obtained, stable flows, which are closely related to the different patterns of quasi-stationary circulation in the tropical region, are found. The configurations of these stable flows and the shift between two of them as season changes provide quite reasonable explanations to many fundamental problems of tropical circulation features such as the catastrophe mechanism of the onset and the break-active cycle of the Asian summer monsoon. It follows that the onset or the abrupt transition of the Asian summer monsoon could be attributed to the multiple equilibrium property of the tropical circulation resulted from the advective nonlinearity, which provide another explanation among others.
2006, 12(2): 139-149.
Abstract:
Identifying the Northern Hemisphere (NH) temperature reconstruction and instrumental data for the past 1000 years shows that climate change in the last millennium includes long-term trends and various oscillations. Two long-term trends and the quasi-70-year oscillation were detected in the global temperature series for the last 140 years and the NH millennium series. One important feature was emphasized that temperature decreases slowly but it increases rapidly based on the analysis of different series. Benefits can be obtained of climate change from understanding various long-term trends and oscillations. Millennial temperature proxies from the natural climate system and time series of nonlinear model system are used in understanding the natural climate change and recognizing potential benefits by using the method of wavelet transform analysis. The results from numerical modeling show that major oscillations contained in numerical solutions on the interdecadal timescale are consistent with that of natural proxies. It seems that these oscillations in the climate change are not directly linked with the solar radiation as an external forcing. This investigation may conclude that the climate variability at the interdecadal timescale strongly depends on the internal nonlinear effects in the climate system.
Identifying the Northern Hemisphere (NH) temperature reconstruction and instrumental data for the past 1000 years shows that climate change in the last millennium includes long-term trends and various oscillations. Two long-term trends and the quasi-70-year oscillation were detected in the global temperature series for the last 140 years and the NH millennium series. One important feature was emphasized that temperature decreases slowly but it increases rapidly based on the analysis of different series. Benefits can be obtained of climate change from understanding various long-term trends and oscillations. Millennial temperature proxies from the natural climate system and time series of nonlinear model system are used in understanding the natural climate change and recognizing potential benefits by using the method of wavelet transform analysis. The results from numerical modeling show that major oscillations contained in numerical solutions on the interdecadal timescale are consistent with that of natural proxies. It seems that these oscillations in the climate change are not directly linked with the solar radiation as an external forcing. This investigation may conclude that the climate variability at the interdecadal timescale strongly depends on the internal nonlinear effects in the climate system.
2006, 12(2): 150-158.
Abstract:
With the data from the Tropical Cyclone Yearbooks between 1970 and 2001, statistical analyses were performed to study the climatic features of landfall TCs (noted as TCs hereafter) in China with particular attention focused on landfall frequency, locations, sustaining, decaying, transition, intensification and dissipation etc. The results indicate that the sustaining periods of TC over land are quite different for different landfall spots, and increased from Guangxi to Zhejiang. The most obvious decreasing of TC intensity occurs mainly within 12 hours after landfall. The stronger a TC is，the more it decays. The areas over which TCs are dissipated can be in Heilongjiang, the northernmost, and Yunnan, the westernmost. Besides, Guangxi is an area with high dissipating rate and subject to TC dissipation as compared with the other coastal regions.
With the data from the Tropical Cyclone Yearbooks between 1970 and 2001, statistical analyses were performed to study the climatic features of landfall TCs (noted as TCs hereafter) in China with particular attention focused on landfall frequency, locations, sustaining, decaying, transition, intensification and dissipation etc. The results indicate that the sustaining periods of TC over land are quite different for different landfall spots, and increased from Guangxi to Zhejiang. The most obvious decreasing of TC intensity occurs mainly within 12 hours after landfall. The stronger a TC is，the more it decays. The areas over which TCs are dissipated can be in Heilongjiang, the northernmost, and Yunnan, the westernmost. Besides, Guangxi is an area with high dissipating rate and subject to TC dissipation as compared with the other coastal regions.
2006, 12(2): 159-164.
Abstract:
A new method, BDA perturbing, is used in ensemble forecasting of typhoon track. This method is based on the Bogus Data Assimilation scheme. It perturbs the initial position and intensity of typhoons and gets a series of bogus vortex. Then each bogus vortex is used in data assimilation to obtain initial conditions. Ensemble forecast members are constructed by conducting simulation with these initial conditions. Some cases of typhoon are chosen to test the validity of this new method and the results show that: using the BDA perturbing method to perturb initial position and intensity of typhoon for track forecast can improve accuracy, compared with the direct use of the BDA assimilation scheme. And it is concluded that a perturbing amplitude of intensity of 5 hPa is probably more appropriate than 10 hPa if the BDA perturbing method is used in combination with initial position perturbation.
A new method, BDA perturbing, is used in ensemble forecasting of typhoon track. This method is based on the Bogus Data Assimilation scheme. It perturbs the initial position and intensity of typhoons and gets a series of bogus vortex. Then each bogus vortex is used in data assimilation to obtain initial conditions. Ensemble forecast members are constructed by conducting simulation with these initial conditions. Some cases of typhoon are chosen to test the validity of this new method and the results show that: using the BDA perturbing method to perturb initial position and intensity of typhoon for track forecast can improve accuracy, compared with the direct use of the BDA assimilation scheme. And it is concluded that a perturbing amplitude of intensity of 5 hPa is probably more appropriate than 10 hPa if the BDA perturbing method is used in combination with initial position perturbation.
2006, 12(2): 165-173.
Abstract:
By using regular meteorological data, physical quantity fields, satellite pictures and Doppler radar echo data, we analyze the mesoscale features and the conditions of 4 successive heavy precipitation processes in Yunnan aroused by the storm over the Bay in the early summer. The results show that the life of the storm over the Bay is usual 2 or 3 days and the cloud top temperature of the storm is always below -65°C. The storm over the Bay affects Yunnan by mesoscale convective cloud clusters, cloud system in peripheral or weaken itself moving to the northeast. The Tibetan Plateau shear lines and vortexes, NE-SW convergence channels and southwest wind convergence supply favorable circulation background and dynamical conditions. There are many common features about Doppler radar echoes, the flocculent echoes with intensity about 35-45 dBZ move to the east to produce successive precipitation in Yunnan, and the mesoscale features of southwest jet and wind veering with altitude not only are favorable to transport warm and moist airflow brought to the north by the storm over the Bay, but also are favorable to convective development.
By using regular meteorological data, physical quantity fields, satellite pictures and Doppler radar echo data, we analyze the mesoscale features and the conditions of 4 successive heavy precipitation processes in Yunnan aroused by the storm over the Bay in the early summer. The results show that the life of the storm over the Bay is usual 2 or 3 days and the cloud top temperature of the storm is always below -65°C. The storm over the Bay affects Yunnan by mesoscale convective cloud clusters, cloud system in peripheral or weaken itself moving to the northeast. The Tibetan Plateau shear lines and vortexes, NE-SW convergence channels and southwest wind convergence supply favorable circulation background and dynamical conditions. There are many common features about Doppler radar echoes, the flocculent echoes with intensity about 35-45 dBZ move to the east to produce successive precipitation in Yunnan, and the mesoscale features of southwest jet and wind veering with altitude not only are favorable to transport warm and moist airflow brought to the north by the storm over the Bay, but also are favorable to convective development.
2006, 12(2): 174-178.
Abstract:
Typhoon Maggie (1999) interacted with another tropical depression system and moved along a west-southwest track that is somewhat abnormal during its pre-landing stage. Two numerical experiments are carried out in this paper to study the effect of the interaction on the track of typhoon Maggie using the mesoscale numerical weather prediction model system with a tropical cyclone bogusing scheme developed by Center for Coastal and Atmospheric Research, the Hong Kong University of Science and Technology. Results show that the cyclone system interacting with Maggie is the main factor for the abnormal track of Maggie.
Typhoon Maggie (1999) interacted with another tropical depression system and moved along a west-southwest track that is somewhat abnormal during its pre-landing stage. Two numerical experiments are carried out in this paper to study the effect of the interaction on the track of typhoon Maggie using the mesoscale numerical weather prediction model system with a tropical cyclone bogusing scheme developed by Center for Coastal and Atmospheric Research, the Hong Kong University of Science and Technology. Results show that the cyclone system interacting with Maggie is the main factor for the abnormal track of Maggie.
2006, 12(2): 179-185.
Abstract:
The MM5, which is the PSU/NCAR mesoscale nonhydrostatic limited-area model, and its adjoining modeling system are used in this paper. Taking T106 analysis data as background field the authors generate an optimal initial condition of a typhoon by using two bogus data assimilation schemes, and conduct some numerical simulating experiments. The results of No.9608 typhoon (Gloria) show that the optimal initial field have some dramatic improvements, such as inaccurate position of typhoon center, weaker typhoon circulation and incomplete inner structure of the typhoon, which are caused by shortage of data over the sea. Some improvements have been made in the track forecast. Through several comparing experiments, the initialization optimized by BDA scheme is found to be more reasonable than GFDL scheme and its typhoon track forecast is better.
The MM5, which is the PSU/NCAR mesoscale nonhydrostatic limited-area model, and its adjoining modeling system are used in this paper. Taking T106 analysis data as background field the authors generate an optimal initial condition of a typhoon by using two bogus data assimilation schemes, and conduct some numerical simulating experiments. The results of No.9608 typhoon (Gloria) show that the optimal initial field have some dramatic improvements, such as inaccurate position of typhoon center, weaker typhoon circulation and incomplete inner structure of the typhoon, which are caused by shortage of data over the sea. Some improvements have been made in the track forecast. Through several comparing experiments, the initialization optimized by BDA scheme is found to be more reasonable than GFDL scheme and its typhoon track forecast is better.
2006, 12(2): 184-188.
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2006, 12(2): 189-192.
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2006, 12(2): 193-196.
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2006, 12(2): 197-200.
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2006, 12(2): 201-204.
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2006, 12(2): 205-208.
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