2016 Vol. 22, No. 3
2016, 22(3): 265-276.
doi: 10.16555/j.1006-8775.2016.03.001
Abstract:
The distribution of precipitation field from the typhoon Haitang (2005) during its landing on Fujian province shows obvious asymmetric feature. Based on the NCEP/NCAR FNL (Final Analysis) data, this study reveals the contributions of atmospheric factor to the asymmetrical distribution characteristics of precipitation associated with the typhoon, through the analysis of water vapor condition, vertical ascending motion condition, the calculation of the dry Q vector and its decomposition, and adiabatic heating in the air column of 1000hPa -600hPa (lower atmosphere) and 500hPa-100hPa (upper atmosphere). The results are as follows: (1) In the lower atmosphere, the humidity on both sides of typhoon path can be equivalent, while it is more wet on the right side than left in the upper atmosphere, which obviously presents asymmetric distribution characteristics. (2) Both range and intensity of the vertical motion on the right side are wider and stronger than counterparts on the left side no matter in the lower or upper atmosphere. (3) In the upper atmosphere, forcing role of atmosphere in vertical upward motion on the right side of typhoon path is the same as that on the left, while it is significantly different in the lower atmosphere, which is significantly broader in scope and stronger in the intensity, along with obvious asymmetric distribution characteristics. In addition, the further analysis of the Q vector decomposition indicates that the forcing effect of mesoscale weather systems on vertical upward motion is stronger than that of large scale weather systems in the lower atmosphere. (4) The adiabatic heating always exists on both lower and upper atmosphere, and the range and intensity of the adiabatic heating forcing showed asymmetric distribution on both lower and upper atmosphere. (5) In a summary, the upper atmosphere humidity conditions, the forcing role of lower atmosphere in vertical upward motion, especially, to mesoscale weather system, and adiabatic heating in the lower atmosphere, all show similar asymmetric distribution characteristics to that of precipitation field from the typhoon Haitang (2005), that is to say, the atmospheric factors as mentioned above are all contributed to genesis of the asymmetric distribution characteristics of precipitation.
The distribution of precipitation field from the typhoon Haitang (2005) during its landing on Fujian province shows obvious asymmetric feature. Based on the NCEP/NCAR FNL (Final Analysis) data, this study reveals the contributions of atmospheric factor to the asymmetrical distribution characteristics of precipitation associated with the typhoon, through the analysis of water vapor condition, vertical ascending motion condition, the calculation of the dry Q vector and its decomposition, and adiabatic heating in the air column of 1000hPa -600hPa (lower atmosphere) and 500hPa-100hPa (upper atmosphere). The results are as follows: (1) In the lower atmosphere, the humidity on both sides of typhoon path can be equivalent, while it is more wet on the right side than left in the upper atmosphere, which obviously presents asymmetric distribution characteristics. (2) Both range and intensity of the vertical motion on the right side are wider and stronger than counterparts on the left side no matter in the lower or upper atmosphere. (3) In the upper atmosphere, forcing role of atmosphere in vertical upward motion on the right side of typhoon path is the same as that on the left, while it is significantly different in the lower atmosphere, which is significantly broader in scope and stronger in the intensity, along with obvious asymmetric distribution characteristics. In addition, the further analysis of the Q vector decomposition indicates that the forcing effect of mesoscale weather systems on vertical upward motion is stronger than that of large scale weather systems in the lower atmosphere. (4) The adiabatic heating always exists on both lower and upper atmosphere, and the range and intensity of the adiabatic heating forcing showed asymmetric distribution on both lower and upper atmosphere. (5) In a summary, the upper atmosphere humidity conditions, the forcing role of lower atmosphere in vertical upward motion, especially, to mesoscale weather system, and adiabatic heating in the lower atmosphere, all show similar asymmetric distribution characteristics to that of precipitation field from the typhoon Haitang (2005), that is to say, the atmospheric factors as mentioned above are all contributed to genesis of the asymmetric distribution characteristics of precipitation.
2016, 22(3): 277-286.
doi: 10.16555/j.1006-8775.2016.03.002
Abstract:
To quantitatively study the role of tropical cyclone precipitation (TCP) on alleviating the drought in the southeast coastal region of China (SCR) during summer and autumn, the objective synoptic analysis technique (OSAT), improved for consistency and rationality, was used to separate the TCP data on the summers and autumns of 1963–C2005 on the basis of daily precipitation data from stations and tropical cyclone best track data. After defining the season drought index, the actual drought distribution and the assumed drought distribution without TCP were acquired. The results showed that within 1 000 km from the southeast coastline of China, TCP accounted for 11.3% of natural precipitation (NP). Without TCP, the drought index in the SCR during summer would have increased from 0.2 to 0.6 or even above 1.0 in some regions whereas the drought index during autumn would have increased from 0.4 to 0.6 or above 1.2 in some regions. The impact of TCP on drought decreases progressively from the southeast coastline to the inland regions. The TCP proportion (TCPP) showed a significant negative correlation with the drought index in many regions of the southeast, and the significant region is wider in autumn than in summer. TCP relieved the drought most significantly within a range of 0–C500 km from the southeast coastline. This drought relief showed different characteristics for the interannual variability in summer and autumn, and the cross wavelet transform indicated that the impact of TCP on drought mainly lies in 2–C4-year time scales. In particular, there was a significant effect during the summers of 1977–C1985 and in the autumns following that of 1985. Therefore, TCP has indeed largely alleviated drought in the SCR during summer and autumn.
To quantitatively study the role of tropical cyclone precipitation (TCP) on alleviating the drought in the southeast coastal region of China (SCR) during summer and autumn, the objective synoptic analysis technique (OSAT), improved for consistency and rationality, was used to separate the TCP data on the summers and autumns of 1963–C2005 on the basis of daily precipitation data from stations and tropical cyclone best track data. After defining the season drought index, the actual drought distribution and the assumed drought distribution without TCP were acquired. The results showed that within 1 000 km from the southeast coastline of China, TCP accounted for 11.3% of natural precipitation (NP). Without TCP, the drought index in the SCR during summer would have increased from 0.2 to 0.6 or even above 1.0 in some regions whereas the drought index during autumn would have increased from 0.4 to 0.6 or above 1.2 in some regions. The impact of TCP on drought decreases progressively from the southeast coastline to the inland regions. The TCP proportion (TCPP) showed a significant negative correlation with the drought index in many regions of the southeast, and the significant region is wider in autumn than in summer. TCP relieved the drought most significantly within a range of 0–C500 km from the southeast coastline. This drought relief showed different characteristics for the interannual variability in summer and autumn, and the cross wavelet transform indicated that the impact of TCP on drought mainly lies in 2–C4-year time scales. In particular, there was a significant effect during the summers of 1977–C1985 and in the autumns following that of 1985. Therefore, TCP has indeed largely alleviated drought in the SCR during summer and autumn.
2016, 22(3): 287-295.
doi: 10.16555/j.1006-8775.2016.03.003
Abstract:
Based on 6-hourly sensible heat flux and latent heat flux from the NCEP Climate Forecast System Reanalysis (CFSR) and circulation data from the Japanese 25-year Reanalysis (JRA-25), the initial developing process of tropical cyclone Mindulle (1005) in 2010 has been diagnosed to reveal the impact of air-sea interaction over the South China Sea (SCS) on the genesis of its incipient vortex. The results show that the incipient vortex first occurred east of the Luzon Island on 0000 UTC 20 August, suggesting that the topographic forcing of the Luzon Island for easterly winds over the western Pacific might be one of the factors responsible for the formation of the incipient vortex. During the formation stage of the incipient vortex, strong southeasterlies over the SCS caused warm water of the middle and eastern SCS to flow toward the Luzon Island due to Ekman transport resulting from wind stress, leading to an increase of the sea surface temperature and sensible heat flux into the atmosphere. Although the anomalous sensible heating favored surface pressure to reduce, it was not conducive to the increase of local vorticity associated with the vortex above the heating area because, according to the atmospheric thermal adaptation theory, the anticyclonic vorticity would be created in the lower troposphere due to the decreased vertical gradient of the sensible heating. However, the ascending motions occurred over the eastern area of the anomalous sensible heating due to the augmentation of the vorticity advection with increasing height, causing water vapor to condense in the middle and upper troposphere. In turn, cyclonic vorticity was generated in the lower troposphere due to the increased vertical gradient of the condensation latent heating, resulting in the formation and further growth of the incipient vortex. Therefore, the vorticity creation due to the condensation heating played a dominant role during the subsequent enhancing stage of the incipient vortex.
Based on 6-hourly sensible heat flux and latent heat flux from the NCEP Climate Forecast System Reanalysis (CFSR) and circulation data from the Japanese 25-year Reanalysis (JRA-25), the initial developing process of tropical cyclone Mindulle (1005) in 2010 has been diagnosed to reveal the impact of air-sea interaction over the South China Sea (SCS) on the genesis of its incipient vortex. The results show that the incipient vortex first occurred east of the Luzon Island on 0000 UTC 20 August, suggesting that the topographic forcing of the Luzon Island for easterly winds over the western Pacific might be one of the factors responsible for the formation of the incipient vortex. During the formation stage of the incipient vortex, strong southeasterlies over the SCS caused warm water of the middle and eastern SCS to flow toward the Luzon Island due to Ekman transport resulting from wind stress, leading to an increase of the sea surface temperature and sensible heat flux into the atmosphere. Although the anomalous sensible heating favored surface pressure to reduce, it was not conducive to the increase of local vorticity associated with the vortex above the heating area because, according to the atmospheric thermal adaptation theory, the anticyclonic vorticity would be created in the lower troposphere due to the decreased vertical gradient of the sensible heating. However, the ascending motions occurred over the eastern area of the anomalous sensible heating due to the augmentation of the vorticity advection with increasing height, causing water vapor to condense in the middle and upper troposphere. In turn, cyclonic vorticity was generated in the lower troposphere due to the increased vertical gradient of the condensation latent heating, resulting in the formation and further growth of the incipient vortex. Therefore, the vorticity creation due to the condensation heating played a dominant role during the subsequent enhancing stage of the incipient vortex.
2016, 22(3): 296-304.
doi: 10.16555/j.1006-8775.2016.03.004
Abstract:
Based on NCEP/CFSR 0.5° reanalysis data and the best track data from the Japan Tokyo Typhoon Center, composite and comparative analyses demonstrate the asymmetrical structures of the temperature and humidity in tropical cyclones over the Western North Pacific and the South China Sea from 1979 to 2010. The results are shown as follows. (1) With intensifying tropical cyclones, the flow field tends to become gradually more axisymmetric; however, the asymmetry of the specific humidity in the outer regions is more obvious. (2) In general, tropical cyclones have a non-uniform, vertical, “double warm-core” structure. The “warm-cores” in the lower level of weak tropical cyclones and in the higher level of strong tropical cyclones are the stronger of the two. (3) The distribution area of a “warm-core” is enhanced with cyclone intensification and tends to become more axisymmetric. At 200 hPa, the “warm-core” of a weak cyclone has a weak anticyclone in the center, whereas that of a strong cyclone has a weak cyclone in the center. (4) The “wet-core” of a tropical cyclone is primarily located in the lower level (700–C850 hPa). With the cyclone’s intensification, the intensity of the “wet-core” increases and the scope of the 0.8 g?kg?1 specific humidity anomaly tends to expand to higher levels. (5) With the cyclone’s deepening, the pseudo-equivalent potential temperature at different levels in different regions increases. In addition, the largest warming rates at each intensity level in the different regions occur in the core area, followed in turn by the envelope and outer areas.
Based on NCEP/CFSR 0.5° reanalysis data and the best track data from the Japan Tokyo Typhoon Center, composite and comparative analyses demonstrate the asymmetrical structures of the temperature and humidity in tropical cyclones over the Western North Pacific and the South China Sea from 1979 to 2010. The results are shown as follows. (1) With intensifying tropical cyclones, the flow field tends to become gradually more axisymmetric; however, the asymmetry of the specific humidity in the outer regions is more obvious. (2) In general, tropical cyclones have a non-uniform, vertical, “double warm-core” structure. The “warm-cores” in the lower level of weak tropical cyclones and in the higher level of strong tropical cyclones are the stronger of the two. (3) The distribution area of a “warm-core” is enhanced with cyclone intensification and tends to become more axisymmetric. At 200 hPa, the “warm-core” of a weak cyclone has a weak anticyclone in the center, whereas that of a strong cyclone has a weak cyclone in the center. (4) The “wet-core” of a tropical cyclone is primarily located in the lower level (700–C850 hPa). With the cyclone’s intensification, the intensity of the “wet-core” increases and the scope of the 0.8 g?kg?1 specific humidity anomaly tends to expand to higher levels. (5) With the cyclone’s deepening, the pseudo-equivalent potential temperature at different levels in different regions increases. In addition, the largest warming rates at each intensity level in the different regions occur in the core area, followed in turn by the envelope and outer areas.
ENSEMBLE PREDICTION EXPERIMENTS OF TYPHOON TRACK BASED ON THE STOCHASTIC TOTAL TENDENCY PERTURBATION
2016, 22(3): 305-317.
doi: 10.16555/j.1006-8775.2016.03.005
Abstract:
The GRAPES-TCM is used to make ensemble prediction experiments for typhoon track. Three kinds of ensemble schemes are designed for the experiments. A total of 109 experiments are made for the nine typhoons in 2011 and the integral time is 72 h. The experiment results are shown as follows. In the three ensemble schemes, on the whole, scheme 1 has the best track prediction. Its average absolute track error and overall deviations of typhoon moving speed and moving direction are all the smallest in the three schemes. For both scheme 1 and scheme 2, they are all smaller than those of their control predictions. Both of their ensemble predictions show superiority to their deterministic predictions. Overall, compared with the observations, the typhoon moving directions of the three schemes mainly skew to the right, and in the late integration they mainly tend to be relatively slow. In the three schemes, the track dispersion of scheme 1 is the largest and that of scheme 3 the smallest. In scheme 1 it is much larger than in schemes 2 and 3. The difference of dispersion between scheme 2 and scheme 3 is small. The track dispersions of the three schemes are all much smaller than their rational dispersions. Compared with the eight domestic and overseas operational numerical weather prediction (NWP) models, scheme 1 has better predictions than the other seven operational models except ECMWF NWP model. Scheme 1 has the value of operational application.
The GRAPES-TCM is used to make ensemble prediction experiments for typhoon track. Three kinds of ensemble schemes are designed for the experiments. A total of 109 experiments are made for the nine typhoons in 2011 and the integral time is 72 h. The experiment results are shown as follows. In the three ensemble schemes, on the whole, scheme 1 has the best track prediction. Its average absolute track error and overall deviations of typhoon moving speed and moving direction are all the smallest in the three schemes. For both scheme 1 and scheme 2, they are all smaller than those of their control predictions. Both of their ensemble predictions show superiority to their deterministic predictions. Overall, compared with the observations, the typhoon moving directions of the three schemes mainly skew to the right, and in the late integration they mainly tend to be relatively slow. In the three schemes, the track dispersion of scheme 1 is the largest and that of scheme 3 the smallest. In scheme 1 it is much larger than in schemes 2 and 3. The difference of dispersion between scheme 2 and scheme 3 is small. The track dispersions of the three schemes are all much smaller than their rational dispersions. Compared with the eight domestic and overseas operational numerical weather prediction (NWP) models, scheme 1 has better predictions than the other seven operational models except ECMWF NWP model. Scheme 1 has the value of operational application.
2016, 22(3): 318-329.
doi: 10.16555/j.1006-8775.2016.03.006
Abstract:
The relationship between the tropical intra-seasonal oscillation (ISO) and tropical cyclones (TCs) activities over the South China Sea (SCS) is investigated by utilizing the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) global reanalysis data and tropical cyclone best-track data from 1949 to 2009. The main conclusions are: (1) A new ISO index is designed to describe the tropical ISO activity over the SCS, which can simply express ISO for SCS. After examining the applicability of the index constructed by the Climate Prediction Center (CPC), we find that the convection spatial scale reflected by this index is too large to characterize the small-scale SCS and fails to divide the TCs activities over the SCS into active and inactive categories. Consequently, the CPC index can’t replace the function of the new ISO index; (2) The eastward spread process of tropical ISO is divided into eight phases using the new ISO index, the phase variation of which corresponds well with the TCs activities over the SCS. TCs generation and landing are significantly reduced during inactive period (phase 4-6) relative to that during active period (phase 7-3); (3) The composite analyses indicate distinct TCs activities over the SCS, which is consistent with the concomitant propagation of the ISO convective activity. During ISO active period, the weather situations are favorable for TCs development over the SCS, e.g., strong convection, cyclonic shear and weak subtropical high, and vice versa; (4) The condensation heating centers, strong convection and water vapor flux divergence are well collocated with each other during ISO active period. In addition, the vertical profile of condensation heat indicates strong ascending motion and middle-level heating over the SCS during active period, and vice versa. Thus, the eastward propagation of tropical ISO is capable to modulate TCs activities by affecting the heating configuration over the SCS.
The relationship between the tropical intra-seasonal oscillation (ISO) and tropical cyclones (TCs) activities over the South China Sea (SCS) is investigated by utilizing the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) global reanalysis data and tropical cyclone best-track data from 1949 to 2009. The main conclusions are: (1) A new ISO index is designed to describe the tropical ISO activity over the SCS, which can simply express ISO for SCS. After examining the applicability of the index constructed by the Climate Prediction Center (CPC), we find that the convection spatial scale reflected by this index is too large to characterize the small-scale SCS and fails to divide the TCs activities over the SCS into active and inactive categories. Consequently, the CPC index can’t replace the function of the new ISO index; (2) The eastward spread process of tropical ISO is divided into eight phases using the new ISO index, the phase variation of which corresponds well with the TCs activities over the SCS. TCs generation and landing are significantly reduced during inactive period (phase 4-6) relative to that during active period (phase 7-3); (3) The composite analyses indicate distinct TCs activities over the SCS, which is consistent with the concomitant propagation of the ISO convective activity. During ISO active period, the weather situations are favorable for TCs development over the SCS, e.g., strong convection, cyclonic shear and weak subtropical high, and vice versa; (4) The condensation heating centers, strong convection and water vapor flux divergence are well collocated with each other during ISO active period. In addition, the vertical profile of condensation heat indicates strong ascending motion and middle-level heating over the SCS during active period, and vice versa. Thus, the eastward propagation of tropical ISO is capable to modulate TCs activities by affecting the heating configuration over the SCS.
2016, 22(3): 330-340.
doi: 10.16555/j.1006-8775.2016.03.007
Abstract:
Multisatellite data is used to analyze the characteristics of three eyewall replacement cycles (ERCs) during the lifetime of Typhoon Muifa (1109). Spiral rainbands evolutions, concentric eyewall (CE) structure modes, CE durations, and intensity changes are discussed in detail. In addition, an ERC evolution model of Typhoon Muifa is given. There are four main findings. (1) The outer spiral rainband joins end to end to form the outer eyewall after it disconnects from the original (inner) eyewall. The inner eyewall weakens as the outer eyewall becomes axisymmetric and is intensified. The contraction of the outer eyewall causes the inner eyewall to dissipate rapidly. Finally, the ERC ends with an annular eyewall or spiral rainbands. (2) Although the CE duration times of Typhoon Muifa’s three ERCs covered a large range, the CE structures were all maintained for approximately 5 h from the formation of the axisymmetric outer eyewall to the end of the cycle. (3) There is no obvious precipitation reflectivity in the eye or moat region for the subsidence flow. The convection within the two eyewalls is organized as a radially outward slope with increasing height. (4) Typhoon intensity estimation results based on ADT may not explain the intensity variations associated with ERC correctly, while the typhoon’s warm core data retrieved from AMSU-A works well.
Multisatellite data is used to analyze the characteristics of three eyewall replacement cycles (ERCs) during the lifetime of Typhoon Muifa (1109). Spiral rainbands evolutions, concentric eyewall (CE) structure modes, CE durations, and intensity changes are discussed in detail. In addition, an ERC evolution model of Typhoon Muifa is given. There are four main findings. (1) The outer spiral rainband joins end to end to form the outer eyewall after it disconnects from the original (inner) eyewall. The inner eyewall weakens as the outer eyewall becomes axisymmetric and is intensified. The contraction of the outer eyewall causes the inner eyewall to dissipate rapidly. Finally, the ERC ends with an annular eyewall or spiral rainbands. (2) Although the CE duration times of Typhoon Muifa’s three ERCs covered a large range, the CE structures were all maintained for approximately 5 h from the formation of the axisymmetric outer eyewall to the end of the cycle. (3) There is no obvious precipitation reflectivity in the eye or moat region for the subsidence flow. The convection within the two eyewalls is organized as a radially outward slope with increasing height. (4) Typhoon intensity estimation results based on ADT may not explain the intensity variations associated with ERC correctly, while the typhoon’s warm core data retrieved from AMSU-A works well.
2016, 22(3): 341-351.
doi: 10.16555/j.1006-8775.2016.03.008
Abstract:
Typhoon KROSA in 2007 is simulated using GRAPES, a mesoscale numerical model, in which a two-parameter mixed-phase microphysics scheme is implanted. A series of numerical experiments are designed to test the sensitivity of landfalling typhoon structure and precipitation to varying cloud microphysics and latent heat release. It is found that typhoon track is sensitive to different microphysical processes and latent heat release. The cloud structures of simulated cyclones can be quite different with that of varying microphysical processes. Graupel particles play an important role in the formation of local heavy rainfall and the maintenance of spiral rainbands. Analysis reveals that the feedback of latent heat to dynamic fields can significantly change the content and distribution of cloud hydrometeors, thus having an impact on surface precipitation.
Typhoon KROSA in 2007 is simulated using GRAPES, a mesoscale numerical model, in which a two-parameter mixed-phase microphysics scheme is implanted. A series of numerical experiments are designed to test the sensitivity of landfalling typhoon structure and precipitation to varying cloud microphysics and latent heat release. It is found that typhoon track is sensitive to different microphysical processes and latent heat release. The cloud structures of simulated cyclones can be quite different with that of varying microphysical processes. Graupel particles play an important role in the formation of local heavy rainfall and the maintenance of spiral rainbands. Analysis reveals that the feedback of latent heat to dynamic fields can significantly change the content and distribution of cloud hydrometeors, thus having an impact on surface precipitation.
2016, 22(3): 352-361.
doi: 10.16555/j.1006-8775.2016.03.009
Abstract:
Using the National Center for Environmental Prediction reanalysis data on 1.0° × 1.0° grids and data from the Tropical Cyclone yearbook (2000), a diagnostic analysis and numerical simulation were performed to investigate the characteristics and mechanism underlying the rapid weakening of typhoon Xangsane. The results show that a sharp decline in the intensity of typhoon Xangsane resulted from its movement into the cool sea surface temperature area in the East China Sea, the intrusion of cold air from the mainland into the typhoon, and a rapid increase of the vertical wind shear in the surrounding environment. An important factor that led to the demise of the typhoon was a significant decrease in the moisture transport into the typhoon. Furthermore, the results of the numerical simulation and sensitivity experiments indicate that sea surface temperature largely modulated the rapid weakening of typhoon Xangsane.
Using the National Center for Environmental Prediction reanalysis data on 1.0° × 1.0° grids and data from the Tropical Cyclone yearbook (2000), a diagnostic analysis and numerical simulation were performed to investigate the characteristics and mechanism underlying the rapid weakening of typhoon Xangsane. The results show that a sharp decline in the intensity of typhoon Xangsane resulted from its movement into the cool sea surface temperature area in the East China Sea, the intrusion of cold air from the mainland into the typhoon, and a rapid increase of the vertical wind shear in the surrounding environment. An important factor that led to the demise of the typhoon was a significant decrease in the moisture transport into the typhoon. Furthermore, the results of the numerical simulation and sensitivity experiments indicate that sea surface temperature largely modulated the rapid weakening of typhoon Xangsane.
2016, 22(3): 362-373.
doi: 10.16555/j.1006-8775.2016.02.010
Abstract:
Global gridded daily mean data from the NCEP/NCAR Reanalysis (1948–C 2012) are used to obtain the onset date, retreat date and duration time series of the South China Sea summer monsoon (SCSSM) for the past 65 years. The summer monsoon onset (retreat) date is defined as the time when the mean zonal wind at 850 hPa shifts steadily from easterly (westerly) to westerly (easterly) and the pseudo-equivalent potential temperature at the same level remains steady at greater than 335 K (less than 335 K) in the South China Sea area [110–C120° E (10–C20° N)]. The clockwise vortex of the equatorial Indian Ocean region, together with the cross-equatorial flow and the subtropical high, plays a decisive role in the burst of the SCSSM. The onset date of the SCSSM is closely related to its intensity. With late (early) onset of the summer monsoon, its intensity is relatively strong (weak), and the zonal wind undergoes an early (late) abrupt change in the upper troposphere. Climate warming significantly affects the onset and retreat dates of the SCSSM and its intensity. With climate warming, the number of early-onset (-retreat) years of the SCSSM is clearly greater (less), and the SCSSM is clearly weakened.
Global gridded daily mean data from the NCEP/NCAR Reanalysis (1948–C 2012) are used to obtain the onset date, retreat date and duration time series of the South China Sea summer monsoon (SCSSM) for the past 65 years. The summer monsoon onset (retreat) date is defined as the time when the mean zonal wind at 850 hPa shifts steadily from easterly (westerly) to westerly (easterly) and the pseudo-equivalent potential temperature at the same level remains steady at greater than 335 K (less than 335 K) in the South China Sea area [110–C120° E (10–C20° N)]. The clockwise vortex of the equatorial Indian Ocean region, together with the cross-equatorial flow and the subtropical high, plays a decisive role in the burst of the SCSSM. The onset date of the SCSSM is closely related to its intensity. With late (early) onset of the summer monsoon, its intensity is relatively strong (weak), and the zonal wind undergoes an early (late) abrupt change in the upper troposphere. Climate warming significantly affects the onset and retreat dates of the SCSSM and its intensity. With climate warming, the number of early-onset (-retreat) years of the SCSSM is clearly greater (less), and the SCSSM is clearly weakened.
2016, 22(3): 374-381.
doi: 10.16555/j.1006-8775.2016.03.011
Abstract:
This study analyzes the Ishii 700 m heat content (HC) in the South China Sea (SCS). During the 1978–C2012 period, the HC in the SCS changed dramatically on interannual timescales. Three main findings emerged from the analysis. 1) The first spatial pattern of the empirical orthogonal function (EOF1) was consistently distributed over most of the SCS, whereas that of the second empirical orthogonal function (EOF2) showed a dipole signal. 2) The HC anomalies in the SCS were closely related to the SCS summer monsoon intensity. When the HC over most of the SCS increased (decreased) in previous winter, the SCS summer monsoon was strengthened (weakened). Therefore, the HC behavior in the SCS during previous winter can well predict the intensity of the SCS summer monsoon. 3) HC anomalies in the SCS largely influence the monsoon and Walker circulations, in turn affecting the western Pacific subtropical high and finally the SCS summer monsoon.
This study analyzes the Ishii 700 m heat content (HC) in the South China Sea (SCS). During the 1978–C2012 period, the HC in the SCS changed dramatically on interannual timescales. Three main findings emerged from the analysis. 1) The first spatial pattern of the empirical orthogonal function (EOF1) was consistently distributed over most of the SCS, whereas that of the second empirical orthogonal function (EOF2) showed a dipole signal. 2) The HC anomalies in the SCS were closely related to the SCS summer monsoon intensity. When the HC over most of the SCS increased (decreased) in previous winter, the SCS summer monsoon was strengthened (weakened). Therefore, the HC behavior in the SCS during previous winter can well predict the intensity of the SCS summer monsoon. 3) HC anomalies in the SCS largely influence the monsoon and Walker circulations, in turn affecting the western Pacific subtropical high and finally the SCS summer monsoon.
2016, 22(3): 382-392.
doi: 10.16555/j.1006-8775.2016.02.012
Abstract:
Climate effect caused by urbanization has been an indispensable anthropogenic factor in the research on regional climate change. Based on daily precipitation data, possible effects of precipitation on the development of three city groups in eastern China are discussed. With three classification methods (TP, PD and MODIS land cover), urban and rural stations are identified. The main findings are as follows. Climate effects caused by urbanization are different from place to place. In 1960 to 2009, the urbanization brought more precipitation to the Yangtze River Delta and Pearl River Delta city groups but had no obvious effect on the precipitation of the Beijing-Tianjin-Tangshan city group. The difference of precipitation is slight between urban and suburban areas during slow period of the urbanization from 1960 to 1979. It is more evident in the rapid period (1980 to 2009) that urbanization has positive effects on precipitation in every city group. The difference of precipitation between urban and rural stations is sensitive to the ways of distinguishing rural from urban area, which may cause uncertainties in 1960 to 1979, while it is very different in 1980 to 2009 in which urbanization favors more precipitation in all city groups and their differences in precipitation are not sensitive to the division methods.
Climate effect caused by urbanization has been an indispensable anthropogenic factor in the research on regional climate change. Based on daily precipitation data, possible effects of precipitation on the development of three city groups in eastern China are discussed. With three classification methods (TP, PD and MODIS land cover), urban and rural stations are identified. The main findings are as follows. Climate effects caused by urbanization are different from place to place. In 1960 to 2009, the urbanization brought more precipitation to the Yangtze River Delta and Pearl River Delta city groups but had no obvious effect on the precipitation of the Beijing-Tianjin-Tangshan city group. The difference of precipitation is slight between urban and suburban areas during slow period of the urbanization from 1960 to 1979. It is more evident in the rapid period (1980 to 2009) that urbanization has positive effects on precipitation in every city group. The difference of precipitation between urban and rural stations is sensitive to the ways of distinguishing rural from urban area, which may cause uncertainties in 1960 to 1979, while it is very different in 1980 to 2009 in which urbanization favors more precipitation in all city groups and their differences in precipitation are not sensitive to the division methods.
2016, 22(3): 393-401.
doi: 10.16555/j.1006-8775.2016.02.013
Abstract:
The spatio-temporal variation of surface sensible heat flux (SHF) in southern China (SC) is studied based on the data evaluated from conventional observational meteorological data. There exist prominent increasing trends in all seasonal surface sensible heat fluxes in the western SC and decreasing trends in the central-eastern part of southern China. The variations of surface sensible heat flux in all seasons are dominant on interannual time-scales. The land-air temperature difference and the near-surface wind speed are two key factors for the interannual variations of SHF, but the former is more important. The first two major anomalous patterns of SHF are presented as the region-wide in-phase anomalies and the east-west dipole anomalies, respectively, based on the EOF analysis results.
The spatio-temporal variation of surface sensible heat flux (SHF) in southern China (SC) is studied based on the data evaluated from conventional observational meteorological data. There exist prominent increasing trends in all seasonal surface sensible heat fluxes in the western SC and decreasing trends in the central-eastern part of southern China. The variations of surface sensible heat flux in all seasons are dominant on interannual time-scales. The land-air temperature difference and the near-surface wind speed are two key factors for the interannual variations of SHF, but the former is more important. The first two major anomalous patterns of SHF are presented as the region-wide in-phase anomalies and the east-west dipole anomalies, respectively, based on the EOF analysis results.
2016, 22(3): 402-412.
doi: 10.16555/j.1006-8775.2016.02.014
Abstract:
In the context of global warming, apparent decdal-interdecdal variabilities can be detected in summer precipitation in southern China. Especially around the 1990s, precipitation in South China experienced a phase transition from a deficiency regime to an abundance regime in the early 1990s, while the Yangtze River Valley witnessed a phase shift of summer precipitation from abundance to deficiency in the late 1990s. Pertinent analyses reveal a close relationship between such decadal precipitation shifts and moisture budgets, which is mainly modulated by the meridional component. This relationship can be attributed to large-scale moisture transport anomalies. Further, the HYSPLIT model is utilized to quantitatively evaluate relative moisture contributions from diverse sources during different regimes. It can be found that during the period with abundant precipitation in South China, the moisture contribution from the source of Indochina Peninsula-South China Sea increased significantly, while during the deficient precipitation regime in the Yangtze River Valley, moisture from local source, western Pacific and Indochina Peninsula-South China Sea contributed less to precipitation. It means some new features of relative moisture contributions from diverse sources to precipitation anomaly in southern China took shape after 1990s.
In the context of global warming, apparent decdal-interdecdal variabilities can be detected in summer precipitation in southern China. Especially around the 1990s, precipitation in South China experienced a phase transition from a deficiency regime to an abundance regime in the early 1990s, while the Yangtze River Valley witnessed a phase shift of summer precipitation from abundance to deficiency in the late 1990s. Pertinent analyses reveal a close relationship between such decadal precipitation shifts and moisture budgets, which is mainly modulated by the meridional component. This relationship can be attributed to large-scale moisture transport anomalies. Further, the HYSPLIT model is utilized to quantitatively evaluate relative moisture contributions from diverse sources during different regimes. It can be found that during the period with abundant precipitation in South China, the moisture contribution from the source of Indochina Peninsula-South China Sea increased significantly, while during the deficient precipitation regime in the Yangtze River Valley, moisture from local source, western Pacific and Indochina Peninsula-South China Sea contributed less to precipitation. It means some new features of relative moisture contributions from diverse sources to precipitation anomaly in southern China took shape after 1990s.
2016, 22(3): 413-425.
doi: 10.16555/j.1006-8775.2016.02.015
Abstract:
The present study designs experiments on the direct assimilation of radial velocity and reflectivity data collected by an S-band Doppler weather radar (CINRAD WSR-98D) at the Hefei Station and the reanalysis data produced by the United States National Centers for Environmental Prediction using the Weather Research and Forecasting (WRF) model, the WRF model with a three-dimensional variational (3DVAR) data assimilation system and the WRF model with an ensemble square root filter (EnSRF) data assimilation system. In addition, the present study analyzes a Meiyu front heavy rainfall process that occurred in the Yangtze -Huaihe River Basin from July 4 to July 5, 2003, through numerical simulation. The results show the following. (1) The assimilation of the radar radial velocity data can increase the perturbations in the low-altitude atmosphere over the heavy rainfall region, enhance the convective activities and reduce excessive simulated precipitation. (2) The 3DVAR assimilation method significantly adjusts the horizontal wind field. The assimilation of the reflectivity data improves the microphysical quantities and dynamic fields in the model. In addition, the assimilation of the radial velocity and reflectivity data can better adjust the wind fields and improve the intensity and location of the simulated radar echo bands. (3) The EnSRF assimilation method can assimilate more small-scale wind field information into the model. The assimilation of the reflectivity data alone can relatively accurately forecast the rainfall centers. In addition, the assimilation of the radial velocity and reflectivity data can improve the location of the simulated radar echo bands. (4) The use of the 3DVAR and EnSRF assimilation methods to assimilate the radar radial velocity and reflectivity data can improve the forecast of precipitation, rain-band areal coverage and the center location and intensity of precipitation.
The present study designs experiments on the direct assimilation of radial velocity and reflectivity data collected by an S-band Doppler weather radar (CINRAD WSR-98D) at the Hefei Station and the reanalysis data produced by the United States National Centers for Environmental Prediction using the Weather Research and Forecasting (WRF) model, the WRF model with a three-dimensional variational (3DVAR) data assimilation system and the WRF model with an ensemble square root filter (EnSRF) data assimilation system. In addition, the present study analyzes a Meiyu front heavy rainfall process that occurred in the Yangtze -Huaihe River Basin from July 4 to July 5, 2003, through numerical simulation. The results show the following. (1) The assimilation of the radar radial velocity data can increase the perturbations in the low-altitude atmosphere over the heavy rainfall region, enhance the convective activities and reduce excessive simulated precipitation. (2) The 3DVAR assimilation method significantly adjusts the horizontal wind field. The assimilation of the reflectivity data improves the microphysical quantities and dynamic fields in the model. In addition, the assimilation of the radial velocity and reflectivity data can better adjust the wind fields and improve the intensity and location of the simulated radar echo bands. (3) The EnSRF assimilation method can assimilate more small-scale wind field information into the model. The assimilation of the reflectivity data alone can relatively accurately forecast the rainfall centers. In addition, the assimilation of the radial velocity and reflectivity data can improve the location of the simulated radar echo bands. (4) The use of the 3DVAR and EnSRF assimilation methods to assimilate the radar radial velocity and reflectivity data can improve the forecast of precipitation, rain-band areal coverage and the center location and intensity of precipitation.
2016, 22(3): 426-432.
doi: 10.16555/j.1006-8775.2016.02.016
Abstract:
In order to understand the activity characteristics of low-level jets in the Nanjing area, statistical analysis and comparative study are carried out on their monthly and diurnal variations, characteristics of their cores and accompanying weather conditions using wind profile data in 2005―2008 collected by two wind profilers. The results show that low-level jets have significant monthly and diurnal variations. They occur more frequently in spring and summer than in autumn and winter and are more active in early morning and at night, with the maximum wind speed usually occurring at midnight. The central part of the low-level jet occurs mainly at the height of less than 1400 meters, and the enhancement of central speed is beneficial to the appearance of precipitation. Meanwhile, when the low-level jet appears in summer, it helps cause heavy rain. The statistical results of the boundary wind profiler are well consistent with those of the tropospheric wind profiler. Two kinds of wind profilers also have the capability of continuously detecting the development of low-level jets.
In order to understand the activity characteristics of low-level jets in the Nanjing area, statistical analysis and comparative study are carried out on their monthly and diurnal variations, characteristics of their cores and accompanying weather conditions using wind profile data in 2005―2008 collected by two wind profilers. The results show that low-level jets have significant monthly and diurnal variations. They occur more frequently in spring and summer than in autumn and winter and are more active in early morning and at night, with the maximum wind speed usually occurring at midnight. The central part of the low-level jet occurs mainly at the height of less than 1400 meters, and the enhancement of central speed is beneficial to the appearance of precipitation. Meanwhile, when the low-level jet appears in summer, it helps cause heavy rain. The statistical results of the boundary wind profiler are well consistent with those of the tropospheric wind profiler. Two kinds of wind profilers also have the capability of continuously detecting the development of low-level jets.
2016, 22(3): 433-444.
doi: 10.16555/j.1006-8775.2016.02.017
Abstract:
According to the characteristics of organized cumulus convective precipitation in China, a cumulus parameterization scheme suitable for describing the organized convective precipitation in East Asia is presented and modified. The Kain–CFristch scheme is chosen as the scheme to be modified based on analyses and comparisons of simulated precipitation in East Asia by several commonly-used mesoscale parameterization schemes. A key dynamic parameter to dynamically control the cumulus parameterization is then proposed to improve the Kain–CFristch scheme. Numerical simulations of a typhoon case and a Mei-yu front rainfall case are carried out with the improved scheme, and the results show that the improved version performs better than the original in simulating the track and intensity of the typhoons, as well as the distribution of Mei-yu front precipitation.
According to the characteristics of organized cumulus convective precipitation in China, a cumulus parameterization scheme suitable for describing the organized convective precipitation in East Asia is presented and modified. The Kain–CFristch scheme is chosen as the scheme to be modified based on analyses and comparisons of simulated precipitation in East Asia by several commonly-used mesoscale parameterization schemes. A key dynamic parameter to dynamically control the cumulus parameterization is then proposed to improve the Kain–CFristch scheme. Numerical simulations of a typhoon case and a Mei-yu front rainfall case are carried out with the improved scheme, and the results show that the improved version performs better than the original in simulating the track and intensity of the typhoons, as well as the distribution of Mei-yu front precipitation.
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