2017 Vol. 23, No. 1
2017, 23(1): 1-14.
doi: 10.16555/j.1006-8775.2017.01.001
Abstract:
Cloud profiling radar (CPR) onboard CloudSat allows for deep penetration into dense clouds/precipitation. In this study, tropical cyclones (TCs) are classified into three stages as developing, mature, and decaying. The circular TC area with the radius of 500 km is divided into five regions. The vertical structure characteristics of 94 Western Pacific TCs at different stages in different regions from June 2006 to February 2014 are statistically quantified using the CloudSat tropical cyclone overpass product (the CSTC Product). Contoured frequency by altitude diagrams (CFADs) of radar reflectivity show an arc-like feature and exhibit opposite distributions with a boundary at 5 km. Bright bands are found at this altitude, indicating melting layers. Deep convective (DC) clouds have the largest occurrence probability in the inner region, while Ci clouds occur more frequently in the outer region at 10-15 km. As clouds have the second largest vertical scale after DC clouds. Distributions of Ac, Cu, and Ns clouds at different stages have few distinctions. As the altitude increases, the ice effective radius and the distribution width parameter decrease while the particle number concentration increases. Moist static energy (MSE), cloud thickness (CT), liquid water path (LWP), ice water path (IWP), water vapor (WV), and rain rate (RR) all diminish along the radial direction and are significantly larger at the mature stage. The average value of MSE at the developing stage is larger than that at the decaying stage.
Cloud profiling radar (CPR) onboard CloudSat allows for deep penetration into dense clouds/precipitation. In this study, tropical cyclones (TCs) are classified into three stages as developing, mature, and decaying. The circular TC area with the radius of 500 km is divided into five regions. The vertical structure characteristics of 94 Western Pacific TCs at different stages in different regions from June 2006 to February 2014 are statistically quantified using the CloudSat tropical cyclone overpass product (the CSTC Product). Contoured frequency by altitude diagrams (CFADs) of radar reflectivity show an arc-like feature and exhibit opposite distributions with a boundary at 5 km. Bright bands are found at this altitude, indicating melting layers. Deep convective (DC) clouds have the largest occurrence probability in the inner region, while Ci clouds occur more frequently in the outer region at 10-15 km. As clouds have the second largest vertical scale after DC clouds. Distributions of Ac, Cu, and Ns clouds at different stages have few distinctions. As the altitude increases, the ice effective radius and the distribution width parameter decrease while the particle number concentration increases. Moist static energy (MSE), cloud thickness (CT), liquid water path (LWP), ice water path (IWP), water vapor (WV), and rain rate (RR) all diminish along the radial direction and are significantly larger at the mature stage. The average value of MSE at the developing stage is larger than that at the decaying stage.
2017, 23(1): 15-24.
doi: 10.16555/j.1006-8775.2017.01.002
Abstract:
Fifty-eight extratropical transition (ET) cases in the years 2000-2008, including 2,021 observations (at 6-hour intervals), over the western North Pacific are analyzed using the cyclone phase space (CPS) method, in an effort to get the characteristics of the structure evolution and environmental conditions of tropical cyclones (TCs) during ET over this area. Cluster analysis of the CPS dataset shows that strong TCs are more likely to undergo ET. ET begins with the increment of thermal asymmetry in TCs, along with the generation and intensification of an upper-level cold core, and ends with the occurrence of a lower-level cold core. ET lasts an average duration of about 28 hours. Dynamic composite analysis of the environmental field of different clusters shows that, in general, when TCs move northward, they are gradually embedded in the westerlies and gradually transform into extratropical cyclones under the influence of the mid- and higher-latitude baroclinic systems. As for those TCs which complete ET, there is always much greater potential vorticity gradient in the northwest of them and obvious water vapor transport channels in the environment.
Fifty-eight extratropical transition (ET) cases in the years 2000-2008, including 2,021 observations (at 6-hour intervals), over the western North Pacific are analyzed using the cyclone phase space (CPS) method, in an effort to get the characteristics of the structure evolution and environmental conditions of tropical cyclones (TCs) during ET over this area. Cluster analysis of the CPS dataset shows that strong TCs are more likely to undergo ET. ET begins with the increment of thermal asymmetry in TCs, along with the generation and intensification of an upper-level cold core, and ends with the occurrence of a lower-level cold core. ET lasts an average duration of about 28 hours. Dynamic composite analysis of the environmental field of different clusters shows that, in general, when TCs move northward, they are gradually embedded in the westerlies and gradually transform into extratropical cyclones under the influence of the mid- and higher-latitude baroclinic systems. As for those TCs which complete ET, there is always much greater potential vorticity gradient in the northwest of them and obvious water vapor transport channels in the environment.
2017, 23(1): 25-36.
doi: 10.16555/j.1006-8775.2017.01.003
Abstract:
Three typhoons, Goni, Morakot and Etau which were generated in Western Pacific in 2009, are successfully simulated by the WRF model. The horizontal and vertical vorticity and their interaction are analyzed and diagnosed by using the simulation results. It is shown that their resultant vectors had a fixed pattern in the evolution process of the three typhoons: The horizontal vorticity converged to the tropical cyclone (TC) center below 900 hPa level, flowed out from it at around 900 to 800 hPa, and flowed in between 800 hPa and 700 hPa. If multiple maximum wind speed centers showed up, the horizontal vorticity converged to the center of the typhoon below the maximum wind speed center and diverged from the TC center above the maximum wind speed center. At low levels, the three typhoons interacted with each other through vertical circulation generated by the vortex tube. This circulation was mainly generated by the eastward or westward horizontal vorticity vectors. Clouds and precipitation were generated on the ascending branch of the vertical circulation. The vortex tubes often flowed toward the southwest of the right TC from the northeast of the left TC. According to the full vorticity equation, the horizontal vorticity converted into the vertical vorticity near the maximum wind speed center below 850 hPa level, and the period of most intense conversion was consistent with the intensification period of TC, while the vorticity advection was against the intensification. The vertical vorticity converted into the horizontal vorticity from 800 hPa to 600 hPa, and the wind speed decreased above the maximum wind speed region at low levels.
Three typhoons, Goni, Morakot and Etau which were generated in Western Pacific in 2009, are successfully simulated by the WRF model. The horizontal and vertical vorticity and their interaction are analyzed and diagnosed by using the simulation results. It is shown that their resultant vectors had a fixed pattern in the evolution process of the three typhoons: The horizontal vorticity converged to the tropical cyclone (TC) center below 900 hPa level, flowed out from it at around 900 to 800 hPa, and flowed in between 800 hPa and 700 hPa. If multiple maximum wind speed centers showed up, the horizontal vorticity converged to the center of the typhoon below the maximum wind speed center and diverged from the TC center above the maximum wind speed center. At low levels, the three typhoons interacted with each other through vertical circulation generated by the vortex tube. This circulation was mainly generated by the eastward or westward horizontal vorticity vectors. Clouds and precipitation were generated on the ascending branch of the vertical circulation. The vortex tubes often flowed toward the southwest of the right TC from the northeast of the left TC. According to the full vorticity equation, the horizontal vorticity converted into the vertical vorticity near the maximum wind speed center below 850 hPa level, and the period of most intense conversion was consistent with the intensification period of TC, while the vorticity advection was against the intensification. The vertical vorticity converted into the horizontal vorticity from 800 hPa to 600 hPa, and the wind speed decreased above the maximum wind speed region at low levels.
2017, 23(1): 37-46.
doi: 10.16555/j.1006-8775.2017.01.004
Abstract:
Using 1°×1° final analysis (FNL) data from the National Centers for Environmental Prediction (NCEP), precipitation data from the Tropical Rainfall Measuring Mission (TRMM) and the best-track tropical cyclone (TC) dataset provided by the Japan Meteorological Agency (JMA) for June-August of 2000-2009, we comprehensively consider the two factors low-level moisture channel and interaction between TCs and mid-latitude systems and implement a statistical analysis of remote precipitation in East Asia to the north of 0° and to the west of 150°E. 48 cases of remote precipitation occurred in this period, which are categorized into five classes. After a composite analysis of the different classes, the main systems at 850 hPa and 500 hPa that impact the remote precipitation are as follows: TC, mid-latitude trough, subtropical high and water vapor channel. In particular, the water vapor channel which usually connects with Indian monsoon has the most significant impact on remote heavy rainfall. Another important factor is the mid-latitude trough. The type of north trough/vortex-south TC remote precipitation events happen most frequently, accounting for 68.8% of the total incidence. Most remote precipitation events occur on the right side of the TC path (representing 71% of the total number). At 200 hPa, the remote precipitation events usually occur on the right rear portion of a high-altitude jet stream, and there is an anti-cyclonic vortex to the east and west of the TCs. When there is no anti-cyclonic vortex to the east of the TC, the TC is relatively weak. When the remote precipitation occurs to the northwest of the TC and there is a trough in the northwest direction, the TC is relatively strong. Numerical experiments are carried out using Weather Research and Forecast (WRF) model. The results shows that the TC plays a main role in producing the heavy precipitation and results in the enhancement of precipitation by impacting the water vapor channel.
Using 1°×1° final analysis (FNL) data from the National Centers for Environmental Prediction (NCEP), precipitation data from the Tropical Rainfall Measuring Mission (TRMM) and the best-track tropical cyclone (TC) dataset provided by the Japan Meteorological Agency (JMA) for June-August of 2000-2009, we comprehensively consider the two factors low-level moisture channel and interaction between TCs and mid-latitude systems and implement a statistical analysis of remote precipitation in East Asia to the north of 0° and to the west of 150°E. 48 cases of remote precipitation occurred in this period, which are categorized into five classes. After a composite analysis of the different classes, the main systems at 850 hPa and 500 hPa that impact the remote precipitation are as follows: TC, mid-latitude trough, subtropical high and water vapor channel. In particular, the water vapor channel which usually connects with Indian monsoon has the most significant impact on remote heavy rainfall. Another important factor is the mid-latitude trough. The type of north trough/vortex-south TC remote precipitation events happen most frequently, accounting for 68.8% of the total incidence. Most remote precipitation events occur on the right side of the TC path (representing 71% of the total number). At 200 hPa, the remote precipitation events usually occur on the right rear portion of a high-altitude jet stream, and there is an anti-cyclonic vortex to the east and west of the TCs. When there is no anti-cyclonic vortex to the east of the TC, the TC is relatively weak. When the remote precipitation occurs to the northwest of the TC and there is a trough in the northwest direction, the TC is relatively strong. Numerical experiments are carried out using Weather Research and Forecast (WRF) model. The results shows that the TC plays a main role in producing the heavy precipitation and results in the enhancement of precipitation by impacting the water vapor channel.
2017, 23(1): 47-57.
doi: 10.16555/j.1006-8775.2017.01.005
Abstract:
The NCEP/NCAR reanalysis, Japan Meteorological Agency (JMA) tropical cyclone tracks and intensive surface observations are used to diagnose the features of moisture transport of tropical storm Bilis (No. 0604), which is simulated by the WRF (weather research and forecasting) mesoscale numerical model. It is shown that the Bilis was linked with the moisture channel in the lower latitudes after its landing. Meanwhile, the cross-equatorial flows over 80°–C100°E and Somali were active and brought abundant water vapor into the tropical storm, facilitating the maintenance of the landing storm with intensified heavy rainfall along its path. The simulation suggested that the decreased water vapor from lower latitudes prevents the maintenance of Bilis and the development of rainfall. While the cross-equatorial flows over 80°–C100°E and Somali were in favor of keeping the cyclonic circulation over land. If the moisture supply from the Somali jet stream was reduced, the strength and area of heavy rainfall in tropical cyclone would be remarkably weakened. Consequently, the decreased water vapor from lower latitudes can remarkably suppress the deep convection in tropical storm, then Bilis was damped without the persistent energy support and the rainfall was diminished accordingly.
The NCEP/NCAR reanalysis, Japan Meteorological Agency (JMA) tropical cyclone tracks and intensive surface observations are used to diagnose the features of moisture transport of tropical storm Bilis (No. 0604), which is simulated by the WRF (weather research and forecasting) mesoscale numerical model. It is shown that the Bilis was linked with the moisture channel in the lower latitudes after its landing. Meanwhile, the cross-equatorial flows over 80°–C100°E and Somali were active and brought abundant water vapor into the tropical storm, facilitating the maintenance of the landing storm with intensified heavy rainfall along its path. The simulation suggested that the decreased water vapor from lower latitudes prevents the maintenance of Bilis and the development of rainfall. While the cross-equatorial flows over 80°–C100°E and Somali were in favor of keeping the cyclonic circulation over land. If the moisture supply from the Somali jet stream was reduced, the strength and area of heavy rainfall in tropical cyclone would be remarkably weakened. Consequently, the decreased water vapor from lower latitudes can remarkably suppress the deep convection in tropical storm, then Bilis was damped without the persistent energy support and the rainfall was diminished accordingly.
2017, 23(1): 58-67.
doi: 10.16555/j.1006-8775.2017.01.006
Abstract:
The intraseasonal oscillation (ISO) of the South China Sea (SCS, 105-120°E, 5-20°N) convection and its influences on the genesis and track of the western North Pacific (WNP) tropical cyclones (TCs) were explored, based on the daily average of NCEP/NCAR reanalysis data, the OLR data and the western North Pacific tropical cyclone best-track data from 1979 to 2008. The mechanism of the influences of ISO on TC movement and the corresponding large-scale circulation were discussed by a trajectory model. It was found as follows. (1) During the SCS summer monsoon, the SCS convection exhibits the ISO features with active phases alternating with inactive phases. The monsoon circulation patterns are significantly different during these two phases. When the SCS convection is active (inactive), the SCS-WNP monsoon trough stretches eastward (retreats westward) due to the activity (inactivity) of SCS monsoon, and the WNP subtropical high retreats eastward (stretches westward), which enhances (suppresses) the monsoon circulation. (2) The amount of TC genesis in the active phase is much more than that in the inactive phase. A majority of TCs form west of 135 °E during the active phases but east of 135 °E in the inactive phases. (3) The TCs entering the area west of 135 °E and south of 25 °N would move straight into the SCS in the active phase, or recurve northward in the inactive phase. (4) Simulation results show that the steering flow associated with the active (inactive) phases is in favor of straight-moving (recurving) TCs. Meanwhile, the impacts of the locations of TC genesis on the characteristics of TC track cannot be ignored. TCs that occurred father westward are more likely to move straight into the SCS region.
The intraseasonal oscillation (ISO) of the South China Sea (SCS, 105-120°E, 5-20°N) convection and its influences on the genesis and track of the western North Pacific (WNP) tropical cyclones (TCs) were explored, based on the daily average of NCEP/NCAR reanalysis data, the OLR data and the western North Pacific tropical cyclone best-track data from 1979 to 2008. The mechanism of the influences of ISO on TC movement and the corresponding large-scale circulation were discussed by a trajectory model. It was found as follows. (1) During the SCS summer monsoon, the SCS convection exhibits the ISO features with active phases alternating with inactive phases. The monsoon circulation patterns are significantly different during these two phases. When the SCS convection is active (inactive), the SCS-WNP monsoon trough stretches eastward (retreats westward) due to the activity (inactivity) of SCS monsoon, and the WNP subtropical high retreats eastward (stretches westward), which enhances (suppresses) the monsoon circulation. (2) The amount of TC genesis in the active phase is much more than that in the inactive phase. A majority of TCs form west of 135 °E during the active phases but east of 135 °E in the inactive phases. (3) The TCs entering the area west of 135 °E and south of 25 °N would move straight into the SCS in the active phase, or recurve northward in the inactive phase. (4) Simulation results show that the steering flow associated with the active (inactive) phases is in favor of straight-moving (recurving) TCs. Meanwhile, the impacts of the locations of TC genesis on the characteristics of TC track cannot be ignored. TCs that occurred father westward are more likely to move straight into the SCS region.
2017, 23(1): 68-80.
doi: 10.16555/j.1006-8775.2017.01.007
Abstract:
The influence of the interannual variation of cross-equatorial flow (CEF) on tropical cyclogenesis over the western North Pacific (WNP) is examined in this paper by using the tropical cyclone (TC) best track data from the Joint Typhoon Warning Center and the JRA-25 reanalysis dataset. The results showed that the number of TCs forming to the east of 140°E over the southeastern part of the western North Pacific (WNP) is in highly positive correlation with the variation of the CEF near 125°E and 150°E, i.e., the number of tropical cyclogeneses increases when the cross-equatorial flows are strong. Composite analyses showed that during the years of strong CEF, the variations of OLR, vertical wind shear between 200-850 hPa, 850 hPa relative vorticity and 200 hPa divergence are favorable for tropical cyclogenesis to the east of 140°E over the tropical WNP, and vice versa. Moreover, it is also discussed from the view of barotropic energy conversion that during the years of strong CEF, an eastward-extended monsoon trough leads to the rapid growth of eddy kinetic energy over the eastern part of WNP, which is favorable for tropical cyclogenesis; but during the years of weak CEF, the monsoon trough is located westward in the western part of the WNP, consistent with the growth area of eddy kinetic energy. As a result, there are fewer TC geneses over the eastern part of WNP. Besides, the abrupt strengthening of a close-by CEF 2-4 days before tropical cyclogenesis may be the one of its triggers.
The influence of the interannual variation of cross-equatorial flow (CEF) on tropical cyclogenesis over the western North Pacific (WNP) is examined in this paper by using the tropical cyclone (TC) best track data from the Joint Typhoon Warning Center and the JRA-25 reanalysis dataset. The results showed that the number of TCs forming to the east of 140°E over the southeastern part of the western North Pacific (WNP) is in highly positive correlation with the variation of the CEF near 125°E and 150°E, i.e., the number of tropical cyclogeneses increases when the cross-equatorial flows are strong. Composite analyses showed that during the years of strong CEF, the variations of OLR, vertical wind shear between 200-850 hPa, 850 hPa relative vorticity and 200 hPa divergence are favorable for tropical cyclogenesis to the east of 140°E over the tropical WNP, and vice versa. Moreover, it is also discussed from the view of barotropic energy conversion that during the years of strong CEF, an eastward-extended monsoon trough leads to the rapid growth of eddy kinetic energy over the eastern part of WNP, which is favorable for tropical cyclogenesis; but during the years of weak CEF, the monsoon trough is located westward in the western part of the WNP, consistent with the growth area of eddy kinetic energy. As a result, there are fewer TC geneses over the eastern part of WNP. Besides, the abrupt strengthening of a close-by CEF 2-4 days before tropical cyclogenesis may be the one of its triggers.
2017, 23(1): 81-90.
doi: 10.16555/j.1006-8775.2017.01.008
Abstract:
Spatio-temporal variation of actual evapotranspiration (ETa) in the Pearl River basin from 1961 to 2010 are analyzed based on daily data from 60 national observed stations. ETa is calculated by the Advection-Aridity model (AA model) in the current study, and Mann–CKendall test (MK) and Inverse Distance Weighted interpolation method (IDW) were applied to detect the trends and spatial variation pattern. The relations of ETa with climate parameters and radiation / dynamic terms are analyzed by Person correlation method. Our findings are shown as follows: 1) Mean annual ETa in the Pearl River basin is about 665.6 mm/a. It has significantly decreased in 1961–C2010 at a rate of -24.3 mm/10a. Seasonally, negative trends of summer and autumn ETa are higher than that of spring and winter. 2) The value of ETa is higher in the southeast coastal area than in the northwest region of the Pearl River basin, while the latter has shown the strongest negative trend. 3) Negative trends of ETa in the Pearl River basin are most probably due to decreasing radiation term and increasing dynamic term. The decrease of the radiation term is related with declining diurnal temperature range and sunshine duration, and rising atmospheric pressure as well. The contribution of dynamic term comes from increasing average temperature, maximum and minimum temperatures in the basin. Meanwhile, the decreasing average wind speed weakens dynamic term and finally, to a certain extent, it slows down the negative trend of the ETa.
Spatio-temporal variation of actual evapotranspiration (ETa) in the Pearl River basin from 1961 to 2010 are analyzed based on daily data from 60 national observed stations. ETa is calculated by the Advection-Aridity model (AA model) in the current study, and Mann–CKendall test (MK) and Inverse Distance Weighted interpolation method (IDW) were applied to detect the trends and spatial variation pattern. The relations of ETa with climate parameters and radiation / dynamic terms are analyzed by Person correlation method. Our findings are shown as follows: 1) Mean annual ETa in the Pearl River basin is about 665.6 mm/a. It has significantly decreased in 1961–C2010 at a rate of -24.3 mm/10a. Seasonally, negative trends of summer and autumn ETa are higher than that of spring and winter. 2) The value of ETa is higher in the southeast coastal area than in the northwest region of the Pearl River basin, while the latter has shown the strongest negative trend. 3) Negative trends of ETa in the Pearl River basin are most probably due to decreasing radiation term and increasing dynamic term. The decrease of the radiation term is related with declining diurnal temperature range and sunshine duration, and rising atmospheric pressure as well. The contribution of dynamic term comes from increasing average temperature, maximum and minimum temperatures in the basin. Meanwhile, the decreasing average wind speed weakens dynamic term and finally, to a certain extent, it slows down the negative trend of the ETa.
2017, 23(1): 91-102.
doi: 10.16555/j.1006-8775.2017.01.009
Abstract:
The impacts of soil moisture (SM) on heavy rainfall and the development of Mesoscale Convection Systems (MCSs) are investigated through 24-h numerical simulations of two heavy rainfall events that occurred respectively on 28 March 2009 (Case 1) and 6 May 2010 (Case 2) over southern China. The numerical simulations were carried out with WRF and its coupled Noah LSM (Land Surface Model). First, comparative experiments were driven by two different SM data sources from NCEP-FNL and NASA-GLDAS. Secondary, with the run driven by NASA-GLDAS data as a control one, a series of sensitivity tests with different degree of (20%, 60%) increase or decrease in the initial SM were performed to examine the impact of SM on the simulations. Comparative experiment results show that the 24-h simulated cumulative rainfall distributions are not substantially affected by the application of the two different SM data, while the precipitation intensity is changed to some extent. Forecast skill scores show that simulation with NASA-GLDAS SM data can lead to some improvement, especially in the heavy rain (–R50 mm) forecast, where there is up to 5% increase in the TS score. Sensitivity test analysis found that a predominantly positive feedback of SM on precipitation existed in these two heavy rain events but not with completely the same features. Organization of the heavy rainfall-producing MCS seems to have an impact on the feedback process between SM and precipitation. For Case 1, the MCS was poorly organized and occurred locally in late afternoon, and the increase of SM only caused a slight enhancement of precipitation. Drier soil was found to result in an apparent decrease of rainfall intensity, indicating that precipitation is more sensitive to SM reduction. For Case 2, as the heavy rain was caused by a well-organized MCS with sustained precipitation, the rainfall is more sensitive to SM increase, which brings more rainfall. Additionally, distinctive feedback effects were identified from different stages and different organization of MCS, with strong feedback between SM and precipitation mainly appearing in the early stages of the poorly organized MCS and during the late period of the well-organized MCS.
The impacts of soil moisture (SM) on heavy rainfall and the development of Mesoscale Convection Systems (MCSs) are investigated through 24-h numerical simulations of two heavy rainfall events that occurred respectively on 28 March 2009 (Case 1) and 6 May 2010 (Case 2) over southern China. The numerical simulations were carried out with WRF and its coupled Noah LSM (Land Surface Model). First, comparative experiments were driven by two different SM data sources from NCEP-FNL and NASA-GLDAS. Secondary, with the run driven by NASA-GLDAS data as a control one, a series of sensitivity tests with different degree of (20%, 60%) increase or decrease in the initial SM were performed to examine the impact of SM on the simulations. Comparative experiment results show that the 24-h simulated cumulative rainfall distributions are not substantially affected by the application of the two different SM data, while the precipitation intensity is changed to some extent. Forecast skill scores show that simulation with NASA-GLDAS SM data can lead to some improvement, especially in the heavy rain (–R50 mm) forecast, where there is up to 5% increase in the TS score. Sensitivity test analysis found that a predominantly positive feedback of SM on precipitation existed in these two heavy rain events but not with completely the same features. Organization of the heavy rainfall-producing MCS seems to have an impact on the feedback process between SM and precipitation. For Case 1, the MCS was poorly organized and occurred locally in late afternoon, and the increase of SM only caused a slight enhancement of precipitation. Drier soil was found to result in an apparent decrease of rainfall intensity, indicating that precipitation is more sensitive to SM reduction. For Case 2, as the heavy rain was caused by a well-organized MCS with sustained precipitation, the rainfall is more sensitive to SM increase, which brings more rainfall. Additionally, distinctive feedback effects were identified from different stages and different organization of MCS, with strong feedback between SM and precipitation mainly appearing in the early stages of the poorly organized MCS and during the late period of the well-organized MCS.
2017, 23(1): 103-112.
doi: 10.16555/j.1006-8775.2017.01.010
Abstract:
Climatic characteristics of tropical stratospheric methane have been well researched using various satellite data, and numerical simulations have furtherly conducted using chemical climatic models, while the impact of tropica1 stratospheric methane oxidation on tropical distribution of water vapor is not paid enough attention in general circulation models. Parameterization of methane oxidation is taken into account to deal with the chemical moisturizing action due to the methane oxidation in this paper. Numerical simulation and analysis of the influence of stratospheric methane on the prediction of tropical stratospheric moisture and temperature fields using general circulation model is conducted using heavy storm cases including a heavy rain in South China and a typhoon caused tropical storm. The results show obvious impact of methane oxidation on the forecasting precipitation. It is demonstrated that the stratospheric water vapor in the tropic is significantly remedied by introducing of parameterization of methane oxidation. And prediction of stratospheric temperature is accordingly modified, especially in the lower stratosphere within 30oN. The verification of monthly mean of forecast anomaly correlation (ACC) and root mean square (RMS) errors over the tropics indicated that the impact of stratospheric methane is neutral as to the forecast of geopotential height, and positive to the forecast of temperature and winds over the tropics.
Climatic characteristics of tropical stratospheric methane have been well researched using various satellite data, and numerical simulations have furtherly conducted using chemical climatic models, while the impact of tropica1 stratospheric methane oxidation on tropical distribution of water vapor is not paid enough attention in general circulation models. Parameterization of methane oxidation is taken into account to deal with the chemical moisturizing action due to the methane oxidation in this paper. Numerical simulation and analysis of the influence of stratospheric methane on the prediction of tropical stratospheric moisture and temperature fields using general circulation model is conducted using heavy storm cases including a heavy rain in South China and a typhoon caused tropical storm. The results show obvious impact of methane oxidation on the forecasting precipitation. It is demonstrated that the stratospheric water vapor in the tropic is significantly remedied by introducing of parameterization of methane oxidation. And prediction of stratospheric temperature is accordingly modified, especially in the lower stratosphere within 30oN. The verification of monthly mean of forecast anomaly correlation (ACC) and root mean square (RMS) errors over the tropics indicated that the impact of stratospheric methane is neutral as to the forecast of geopotential height, and positive to the forecast of temperature and winds over the tropics.
2017, 23(1): 113-120.
doi: 10.16555/j.1006-8775.2017.01.011
Abstract:
Based on the tropical cyclone (TC) observations in the western North Pacific from 2000 to 2008, this paper adopts the particle swarm optimization (PSO) algorithm of evolutionary computation to optimize one comprehensive classification rule, and apply the optimized classification rule to the forecasting of TC intensity change. In the process of the optimization, the strategy of hierarchical pruning has been adopted in the PSO algorithm to narrow the search area, and thus to enhance the local search ability, i.e. hierarchical PSO algorithm. The TC intensity classification rule involves core attributes including 12-HMWS, MPI, and Rainrate which play vital roles in TC intensity change. The testing accuracy using the new mined rule by hierarchical PSO algorithm reaches 89.6%. The current study shows that the novel classification method for TC intensity change analysis based on hierarchic PSO algorithm is not only easy to explain the source of rule core attributes, but also has great potential to improve the forecasting of TC intensity change.
Based on the tropical cyclone (TC) observations in the western North Pacific from 2000 to 2008, this paper adopts the particle swarm optimization (PSO) algorithm of evolutionary computation to optimize one comprehensive classification rule, and apply the optimized classification rule to the forecasting of TC intensity change. In the process of the optimization, the strategy of hierarchical pruning has been adopted in the PSO algorithm to narrow the search area, and thus to enhance the local search ability, i.e. hierarchical PSO algorithm. The TC intensity classification rule involves core attributes including 12-HMWS, MPI, and Rainrate which play vital roles in TC intensity change. The testing accuracy using the new mined rule by hierarchical PSO algorithm reaches 89.6%. The current study shows that the novel classification method for TC intensity change analysis based on hierarchic PSO algorithm is not only easy to explain the source of rule core attributes, but also has great potential to improve the forecasting of TC intensity change.
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