2017 Vol. 23, No. 4
2017, 23(4): 345-356.
doi: 10.16555/j.1006-8775.2017.04.001
Abstract:
This study investigates the long-term spatiotemporal variability of diurnal temperature range (DTR) in East Africa (EA). The study carries out non-parametric trend analysis of gridded DTR monthly data sourced from Climatic Research Unit (CRU). The DTR exhibits mixed signals in space and time over EA. The DTR correlates negatively with rainfall over EA. Reduction in DTR coincides with the summer season in the northern and southern hemispheres respectively, suggesting the influence of cloud cover on it. There was a non-uniform pattern of DTR changes across the region with time. Lake Victoria basin recorded the highest warming rates. The Indian Ocean coast recorded the least spatiotemporal variability in DTR. A reduction in DTR is evident in the two seasons: hot and cold. The start of the study period; 1921–C1930, was the coolest decade in the study period. Most parts of EA recorded negative DTR anomalies in 1961–C1970. The overall reduction in DTR throughout the study period highlights the ongoing warming which is a global phenomenon. There remains need for investigating the causation of the observed DTR variability for effective monitoring of the variability in future.
This study investigates the long-term spatiotemporal variability of diurnal temperature range (DTR) in East Africa (EA). The study carries out non-parametric trend analysis of gridded DTR monthly data sourced from Climatic Research Unit (CRU). The DTR exhibits mixed signals in space and time over EA. The DTR correlates negatively with rainfall over EA. Reduction in DTR coincides with the summer season in the northern and southern hemispheres respectively, suggesting the influence of cloud cover on it. There was a non-uniform pattern of DTR changes across the region with time. Lake Victoria basin recorded the highest warming rates. The Indian Ocean coast recorded the least spatiotemporal variability in DTR. A reduction in DTR is evident in the two seasons: hot and cold. The start of the study period; 1921–C1930, was the coolest decade in the study period. Most parts of EA recorded negative DTR anomalies in 1961–C1970. The overall reduction in DTR throughout the study period highlights the ongoing warming which is a global phenomenon. There remains need for investigating the causation of the observed DTR variability for effective monitoring of the variability in future.
2017, 23(4): 357-367.
doi: 10.16555/j.1006-8775.2017.04.002
Abstract:
RegCM4.3, a high-resolution regional climate model, which includes five kinds of aerosols (dust, sea salt, sulfate, black carbon and organic carbon), is employed to simulate the East Asian summer monsoon (EASM) from 1995 to 2010 and the simulation data are used to study the possible impact of natural and anthropogenic aerosols on EASM. The results show that the regional climate model can well simulate the EASM and the spatial and temporal distribution of aerosols. The EASM index is reduced by about 5% by the natural and anthropogenic aerosols and the monsoon onset time is also delayed by about a pentad except for Southeast China. The aerosols heat the middle atmosphere through absorbing solar radiation and the air column expands in Southeast China and its offshore areas. As a result, the geopotential height decreases and a cyclonic circulation anomaly is generated in the lower atmosphere. Northerly wind located in the west of cyclonic circulation weakens the low-level southerly wind in the EASM region. Negative surface radiative forcing due to aerosols causes downward motion and an indirect meridional circulation is formed with the low-level northerly wind and high-level southerly wind anomaly in the north of 25°N in the monsoon area, which weakens the vertical circulation of EASM. The summer precipitation of the monsoon region is significantly reduced, especially in North and Southwest China where the value of moisture flux divergence increases.
RegCM4.3, a high-resolution regional climate model, which includes five kinds of aerosols (dust, sea salt, sulfate, black carbon and organic carbon), is employed to simulate the East Asian summer monsoon (EASM) from 1995 to 2010 and the simulation data are used to study the possible impact of natural and anthropogenic aerosols on EASM. The results show that the regional climate model can well simulate the EASM and the spatial and temporal distribution of aerosols. The EASM index is reduced by about 5% by the natural and anthropogenic aerosols and the monsoon onset time is also delayed by about a pentad except for Southeast China. The aerosols heat the middle atmosphere through absorbing solar radiation and the air column expands in Southeast China and its offshore areas. As a result, the geopotential height decreases and a cyclonic circulation anomaly is generated in the lower atmosphere. Northerly wind located in the west of cyclonic circulation weakens the low-level southerly wind in the EASM region. Negative surface radiative forcing due to aerosols causes downward motion and an indirect meridional circulation is formed with the low-level northerly wind and high-level southerly wind anomaly in the north of 25°N in the monsoon area, which weakens the vertical circulation of EASM. The summer precipitation of the monsoon region is significantly reduced, especially in North and Southwest China where the value of moisture flux divergence increases.
2017, 23(4): 368-379.
doi: 10.16555/j.1006-8775.2017.04.003
Abstract:
The spatial and temporal variations of daily maximum temperature (Tmax), daily minimum temperature (Tmin), daily maximum precipitation (Pmax) and daily maximum wind speed (WSmax) were examined in China using Mann–CKendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15 °C per decade, 0.45 °C per decade and 0.58 mm per decade, respectively, while WSmax had decreased significantly at 1.18 m?s-1 per decade during 1959–C2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China (SC), northwestern North China (NC), northeastern Northeast China (NEC), eastern Northwest China (NWC) and eastern Southwest China (SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley (YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes, such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics
The spatial and temporal variations of daily maximum temperature (Tmax), daily minimum temperature (Tmin), daily maximum precipitation (Pmax) and daily maximum wind speed (WSmax) were examined in China using Mann–CKendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15 °C per decade, 0.45 °C per decade and 0.58 mm per decade, respectively, while WSmax had decreased significantly at 1.18 m?s-1 per decade during 1959–C2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China (SC), northwestern North China (NC), northeastern Northeast China (NEC), eastern Northwest China (NWC) and eastern Southwest China (SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley (YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes, such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics
2017, 23(4): 380-395.
doi: 10.16555/j.1006-8775.2017.04.004
Abstract:
Using National Centers for Environmental Prediction/Department of Energy (NCEP/DOE) monthly reanalysis data and an extended reconstruction of the sea surface temperature data provided by National Oceanic and Atmospheric Administration, the basic characteristics of the interannual variation in the wintertime Middle East subtropical westerly jet stream (MEJ) and its possible physical factors are studied. The results show that the climatological mean MEJ axis extends southwestward-northeastward and that its center lies in the northwest part of the Arabian Peninsula. The south-north shift of the MEJ axis and its intensity show obvious interannual variations that are closely related to the El Niño-Southern Oscillation (ENSO) and the mid-high latitude atmospheric circulation. The zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing causes the MEJ axis shift, and the Arctic Oscillation (AO) causes the middle-western MEJ axis shift. Due to the influences of both the zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing and the dynamical role of the AO, an east-west out-of-phase MEJ axis shift is observed. Furthermore, the zonal asymmetric response to the ENSO-related tropical convective forcing can lead to an anomalous Mediterranean convergence (MC) in the high troposphere. The MC anomaly excites a zonal wave train along the Afro-Asian jet, which causes the middle-western MEJ axis shift. Under the effects of both the zonal symmetric response to the ENSO-related tropical convective forcing and the wave train along the Afro-Asian jet excited by the MC anomaly, an east-west in-phase MEJ axis shift pattern is expressed. Finally, the AO affects the MEJ intensity, whereas the East Atlantic (EA) teleconnection influences the middle-western MEJ intensity. Under the dynamical roles of the AO and EA, the change in the MEJ intensity is demonstrated.
Using National Centers for Environmental Prediction/Department of Energy (NCEP/DOE) monthly reanalysis data and an extended reconstruction of the sea surface temperature data provided by National Oceanic and Atmospheric Administration, the basic characteristics of the interannual variation in the wintertime Middle East subtropical westerly jet stream (MEJ) and its possible physical factors are studied. The results show that the climatological mean MEJ axis extends southwestward-northeastward and that its center lies in the northwest part of the Arabian Peninsula. The south-north shift of the MEJ axis and its intensity show obvious interannual variations that are closely related to the El Niño-Southern Oscillation (ENSO) and the mid-high latitude atmospheric circulation. The zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing causes the MEJ axis shift, and the Arctic Oscillation (AO) causes the middle-western MEJ axis shift. Due to the influences of both the zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing and the dynamical role of the AO, an east-west out-of-phase MEJ axis shift is observed. Furthermore, the zonal asymmetric response to the ENSO-related tropical convective forcing can lead to an anomalous Mediterranean convergence (MC) in the high troposphere. The MC anomaly excites a zonal wave train along the Afro-Asian jet, which causes the middle-western MEJ axis shift. Under the effects of both the zonal symmetric response to the ENSO-related tropical convective forcing and the wave train along the Afro-Asian jet excited by the MC anomaly, an east-west in-phase MEJ axis shift pattern is expressed. Finally, the AO affects the MEJ intensity, whereas the East Atlantic (EA) teleconnection influences the middle-western MEJ intensity. Under the dynamical roles of the AO and EA, the change in the MEJ intensity is demonstrated.
2017, 23(4): 396-407.
doi: 10.16555/j.1006-8775.2017.04.005
Abstract:
Planetary boundary layer height (PBLH) is an important input parameter for any boundary layer study or model, either climate or atmospheric. The variation of the PBLH is also of great significance to the physical processes of numerical prediction, diagnosis of weather forecasting and monitoring urban pollutants. However, effective ways to monitor the PBLH continuously are lack. Wind profilers are commonly used in monitoring PBLH continuously because of its high temporal and spatial resolution, coupled with capability of continuous detection. In this paper, the covariance wavelet transform (CWT) is used to analyze the range-corrected signal-to-noise ratio (SNR) of the wind profiler to determine the PBLH, which is then compared with the results measured by the gradient method and the radiosonde. The conclusions are as follows: (1) The scaling parameter a and translation parameter b of the wavelet are critical in determination of the PBLH by applying the CWT as different values may get completely different results, which requires to select appropriate values in the calculation carefully. (2) Quality control is crucial in determining the PBLH because good quality control can help remove mutation points, which makes the determined PBLH more consistent with the actual situation. (3) In clear-air, the gradient method is not applicable if the boundary layer turbulence is inhomogeneous and the impact of noise is large for that it is easy to be impacted by the mutation of SNR caused by the atmosphere turbulence instability and other factors, which will cause large errors, while the CWT method as an improvement of the gradient method can determine the PBLH quite well. (4) Through quality control, the PBLHs determined by the CWT are consistent with those of radiosonde, and the correlation coefficient between them is 0.87.
Planetary boundary layer height (PBLH) is an important input parameter for any boundary layer study or model, either climate or atmospheric. The variation of the PBLH is also of great significance to the physical processes of numerical prediction, diagnosis of weather forecasting and monitoring urban pollutants. However, effective ways to monitor the PBLH continuously are lack. Wind profilers are commonly used in monitoring PBLH continuously because of its high temporal and spatial resolution, coupled with capability of continuous detection. In this paper, the covariance wavelet transform (CWT) is used to analyze the range-corrected signal-to-noise ratio (SNR) of the wind profiler to determine the PBLH, which is then compared with the results measured by the gradient method and the radiosonde. The conclusions are as follows: (1) The scaling parameter a and translation parameter b of the wavelet are critical in determination of the PBLH by applying the CWT as different values may get completely different results, which requires to select appropriate values in the calculation carefully. (2) Quality control is crucial in determining the PBLH because good quality control can help remove mutation points, which makes the determined PBLH more consistent with the actual situation. (3) In clear-air, the gradient method is not applicable if the boundary layer turbulence is inhomogeneous and the impact of noise is large for that it is easy to be impacted by the mutation of SNR caused by the atmosphere turbulence instability and other factors, which will cause large errors, while the CWT method as an improvement of the gradient method can determine the PBLH quite well. (4) Through quality control, the PBLHs determined by the CWT are consistent with those of radiosonde, and the correlation coefficient between them is 0.87.
2017, 23(4): 408-416.
doi: 10.16555/j.1006-8775.2017.04.006
Abstract:
One-dimensional retrieval was performed on Typhoon Haiyan utilizing the advanced technology microwave sounder onboard the satellite Suomi NPP to retrieve the temperature and water vapor profiles of the typhoon. Comparisons of the retrieved profiles and ECMWF reanalysis were made to assess the results. The main conclusions are as follows. (1) The results have high spatial resolution and therefore can precisely represent the temperature and humidity distribution of the typhoon. (2) The retrieved temperature is low in the areas of low temperature and high in the areas of high temperature; similar patterns are observed for humidity. This means that systematic revision may be needed during routine application. (3) The results of the retrieved temperature and humidity profiles are generally accurate, which is quite important for typhoon monitoring.
One-dimensional retrieval was performed on Typhoon Haiyan utilizing the advanced technology microwave sounder onboard the satellite Suomi NPP to retrieve the temperature and water vapor profiles of the typhoon. Comparisons of the retrieved profiles and ECMWF reanalysis were made to assess the results. The main conclusions are as follows. (1) The results have high spatial resolution and therefore can precisely represent the temperature and humidity distribution of the typhoon. (2) The retrieved temperature is low in the areas of low temperature and high in the areas of high temperature; similar patterns are observed for humidity. This means that systematic revision may be needed during routine application. (3) The results of the retrieved temperature and humidity profiles are generally accurate, which is quite important for typhoon monitoring.
2017, 23(4): 417-425.
doi: 10.16555/j.1006-8775.2017.04.007
Abstract:
Based on observed rainfall data, this study makes a composite analysis of rainfall asymmetry in tropical cyclones (TCs) after making landfall in Guangdong province (GD) during 1998–C2015. There are 3.0 TCs per year on average making landfall in GD and west of GD (WGD) has the most landfall TCs. Most of TCs make landfall in June, July, August, and September at the intensities of TY, STS, and TS. On average, there is more rainfall in the southwest quadrant of TC in CGD (center of GD), WGD, and GD as a whole, and the maximum rainfall is located in the southwest near the TC center. The mean TC rainfall in the east of GD (EGD) leans to the eastern side of TC. The TC rainfall distributions in June, July, August, and September all lean to the southwest quadrant and the maximum rainfall is located in the southwest near the TC center. The same features are found in the mean rainfall of TD, TS, STS, TY, and STY. The maximum rainfall is mainly in the downshear of vertical wind shear. Vertical wind shear is probably the dominate factor that determines asymmetric rainfall distribution of TCs in GD. Storm motion has little connection with TC rainfall asymmetry in GD.
Based on observed rainfall data, this study makes a composite analysis of rainfall asymmetry in tropical cyclones (TCs) after making landfall in Guangdong province (GD) during 1998–C2015. There are 3.0 TCs per year on average making landfall in GD and west of GD (WGD) has the most landfall TCs. Most of TCs make landfall in June, July, August, and September at the intensities of TY, STS, and TS. On average, there is more rainfall in the southwest quadrant of TC in CGD (center of GD), WGD, and GD as a whole, and the maximum rainfall is located in the southwest near the TC center. The mean TC rainfall in the east of GD (EGD) leans to the eastern side of TC. The TC rainfall distributions in June, July, August, and September all lean to the southwest quadrant and the maximum rainfall is located in the southwest near the TC center. The same features are found in the mean rainfall of TD, TS, STS, TY, and STY. The maximum rainfall is mainly in the downshear of vertical wind shear. Vertical wind shear is probably the dominate factor that determines asymmetric rainfall distribution of TCs in GD. Storm motion has little connection with TC rainfall asymmetry in GD.
2017, 23(4): 426-439.
doi: 10.16555/j.1006-8775.2017.04.008
Abstract:
In order to study the spatial structure and dynamical mechanism of extreme precipitation in East Asia, a corresponding climate network is constructed by employing the method of event synchronization. It is found that the area of East Asian summer extreme precipitation can be separated into two regions: one with high area-weighted connectivity receiving heavy precipitation mostly during the active phase of the East Asian Summer Monsoon (EASM), and another one with low area-weighted connectivity receiving heavy precipitation during both the active and the retreating phase of the EASM. Besides, a new way for the prediction of extreme precipitation is also developed by constructing a directed climate networks. The simulation accuracy in East Asia is 58% with a 0-day lead, and the prediction accuracy is 21% and average 12% with a 1-day and an n-day (2≤n≤10) lead, respectively. Compared to the normal EASM year, the prediction accuracy is low in weak years and high in strong years, which is relevant to the differences of correlations and extreme precipitation rates in different EASM situations. Recognizing and indentifying these effects is good for understanding and predicting extreme precipitation in East Asia.
In order to study the spatial structure and dynamical mechanism of extreme precipitation in East Asia, a corresponding climate network is constructed by employing the method of event synchronization. It is found that the area of East Asian summer extreme precipitation can be separated into two regions: one with high area-weighted connectivity receiving heavy precipitation mostly during the active phase of the East Asian Summer Monsoon (EASM), and another one with low area-weighted connectivity receiving heavy precipitation during both the active and the retreating phase of the EASM. Besides, a new way for the prediction of extreme precipitation is also developed by constructing a directed climate networks. The simulation accuracy in East Asia is 58% with a 0-day lead, and the prediction accuracy is 21% and average 12% with a 1-day and an n-day (2≤n≤10) lead, respectively. Compared to the normal EASM year, the prediction accuracy is low in weak years and high in strong years, which is relevant to the differences of correlations and extreme precipitation rates in different EASM situations. Recognizing and indentifying these effects is good for understanding and predicting extreme precipitation in East Asia.
2017, 23(4): 440-449.
doi: 10.16555/j.1006-8775.2017.04.009
Abstract:
Based on NCEP / NCAR daily reanalysis data, climate trend rate and other methods are used to quantitatively analyze the change trend of China’s summer observed temperature in 1983-2012. Moreover, a dynamics-statistics-combined seasonal forecast method with optimal multi-factor portfolio is applied to analyze the impact of this trend on summer temperature forecast. The results show that: in the three decades, the summer temperature shows a clear upward trend under the condition of global warming, especially over South China, East China, Northeast China and Xinjiang Region, and the trend rate of national average summer temperature was 0.27°C per decade. However, it is found that the current business model forecast (Coupled Global Climate Model) of National Climate Centre is unable to forecast summer warming trends in China, so that the post-processing forecast effect of dynamics-statistics-combined method is relatively poor. In this study, observed temperatures are processed first by removing linear fitting trend, and then adding it after forecast to offset the deficiency of model forecast indirectly. After test, ACC average value in the latest decade was 0.44 through dynamics-statistics-combined independent sample return forecast. The temporal correlation (TCC) between forecast and observed temperature was significantly improved compared with direct forecast results in most regions, and effectively improved the skill of the dynamics-statistics-combined forecast method in seasonal temperature forecast.
Based on NCEP / NCAR daily reanalysis data, climate trend rate and other methods are used to quantitatively analyze the change trend of China’s summer observed temperature in 1983-2012. Moreover, a dynamics-statistics-combined seasonal forecast method with optimal multi-factor portfolio is applied to analyze the impact of this trend on summer temperature forecast. The results show that: in the three decades, the summer temperature shows a clear upward trend under the condition of global warming, especially over South China, East China, Northeast China and Xinjiang Region, and the trend rate of national average summer temperature was 0.27°C per decade. However, it is found that the current business model forecast (Coupled Global Climate Model) of National Climate Centre is unable to forecast summer warming trends in China, so that the post-processing forecast effect of dynamics-statistics-combined method is relatively poor. In this study, observed temperatures are processed first by removing linear fitting trend, and then adding it after forecast to offset the deficiency of model forecast indirectly. After test, ACC average value in the latest decade was 0.44 through dynamics-statistics-combined independent sample return forecast. The temporal correlation (TCC) between forecast and observed temperature was significantly improved compared with direct forecast results in most regions, and effectively improved the skill of the dynamics-statistics-combined forecast method in seasonal temperature forecast.
2017, 23(4): 450-461.
doi: 10.16555/j.1006-8775.2017.04.010
Abstract:
By employing the singular value decomposition (SVD) analysis, we have investigated in the present paper the covariations between circulation changes in the Northern (NH) and Southern Hemispheres (SH) and their associations with ENSO by using the NCEP/NCAR reanalysis, the reconstructed monthly NOAA SST, and CMAP precipitation along with NOAA Climate Prediction Center (CPC) ENSO indices. A bi-hemispheric covariation mode (hereafter BHCM) is explored, which is well represented by the first mode of the SVD analysis of sea surface pressure anomaly (SLPA-SVD1). This SVD mode can explain 57.36% of the total covariance of SLPA. BHCM varies in time with a long-term trend and periodicities of 3–C5 years. The long term trend revealed by SVD1 shows that the SLP increases in the equatorial central and eastern Pacific but decreases in the western Pacific and tropical Indian Ocean, which facilitates easterlies in the lower troposphere to be intensified and El Niño events to occur with lower frequency. The spatial pattern of the BHCM looks roughly symmetric about the equator in the tropics, whereas it is characterized by zonal disturbances in the mid-latitude of NH and is highly associated with AAO in the mid-latitude of SH. On inter-annual time scales, the BHCM is highly correlated with ENSO. The atmosphere in both the NH and SH responds to sea surface temperature anomalies in the equatorial region, while the contemporaneous circulation changes in the NH and SH in turn affect the occurrence of El Niño/La Niña. In boreal winter, significant temperature and precipitation anomalies associated with the BHCM are found worldwide. Specifically, in the positive phase of the BHCM, temperature and precipitation are anomalously low in eastern China and some other regions of East Asia. These results are helpful for us to better understand interactions between circulations in the NH and SH and the dynamical mechanisms behind these interactions
By employing the singular value decomposition (SVD) analysis, we have investigated in the present paper the covariations between circulation changes in the Northern (NH) and Southern Hemispheres (SH) and their associations with ENSO by using the NCEP/NCAR reanalysis, the reconstructed monthly NOAA SST, and CMAP precipitation along with NOAA Climate Prediction Center (CPC) ENSO indices. A bi-hemispheric covariation mode (hereafter BHCM) is explored, which is well represented by the first mode of the SVD analysis of sea surface pressure anomaly (SLPA-SVD1). This SVD mode can explain 57.36% of the total covariance of SLPA. BHCM varies in time with a long-term trend and periodicities of 3–C5 years. The long term trend revealed by SVD1 shows that the SLP increases in the equatorial central and eastern Pacific but decreases in the western Pacific and tropical Indian Ocean, which facilitates easterlies in the lower troposphere to be intensified and El Niño events to occur with lower frequency. The spatial pattern of the BHCM looks roughly symmetric about the equator in the tropics, whereas it is characterized by zonal disturbances in the mid-latitude of NH and is highly associated with AAO in the mid-latitude of SH. On inter-annual time scales, the BHCM is highly correlated with ENSO. The atmosphere in both the NH and SH responds to sea surface temperature anomalies in the equatorial region, while the contemporaneous circulation changes in the NH and SH in turn affect the occurrence of El Niño/La Niña. In boreal winter, significant temperature and precipitation anomalies associated with the BHCM are found worldwide. Specifically, in the positive phase of the BHCM, temperature and precipitation are anomalously low in eastern China and some other regions of East Asia. These results are helpful for us to better understand interactions between circulations in the NH and SH and the dynamical mechanisms behind these interactions
2017, 23(4): 462-470.
doi: 10.16555/j.1006-8775.2017.04.011
Abstract:
Snow cover on the Tibetan Plateau (TP) has been shown to be essential for the East Asian summer monsoon. In this paper, we demonstrate that tropical cyclone (TC) 04B (1999) in the northern Indian Ocean, which made landfall during the autumn of 1999, may have contributed to climate anomalies over East Asia during the following spring and summer by increasing snow cover on the TP. Observations indicate that snow cover on the TP increased markedly after TC 04B (1999) made landfall in October of 1999. Sensitivity experiments, in which the TC was removed from a numerical model simulation of the initial field, verified that TC 04B (1999) affected the distribution as well as increased the amount of snow on the TP. In addition, the short-term numerical modeling of the climate over the region showed that the positive snow cover anomaly induced negative surface temperature, negative sensible heat flux, positive latent heat flux, and positive soil temperature anomalies over the central and southern TP during the following spring and summer. These climate anomalies over the TP were associated with positive (negative) summer precipitation anomalies over the Yangtze River valley (along the southeastern coast of China).
Snow cover on the Tibetan Plateau (TP) has been shown to be essential for the East Asian summer monsoon. In this paper, we demonstrate that tropical cyclone (TC) 04B (1999) in the northern Indian Ocean, which made landfall during the autumn of 1999, may have contributed to climate anomalies over East Asia during the following spring and summer by increasing snow cover on the TP. Observations indicate that snow cover on the TP increased markedly after TC 04B (1999) made landfall in October of 1999. Sensitivity experiments, in which the TC was removed from a numerical model simulation of the initial field, verified that TC 04B (1999) affected the distribution as well as increased the amount of snow on the TP. In addition, the short-term numerical modeling of the climate over the region showed that the positive snow cover anomaly induced negative surface temperature, negative sensible heat flux, positive latent heat flux, and positive soil temperature anomalies over the central and southern TP during the following spring and summer. These climate anomalies over the TP were associated with positive (negative) summer precipitation anomalies over the Yangtze River valley (along the southeastern coast of China).
2017, 23(4): 471-480.
doi: 10.16555/j.1006-8775.2017.04.012
Abstract:
On the basis of NCEP/NCAR reanalysis data and yearbooks of CMA tropical cyclones, statistical analysis is performed for 1949–C2013 offshore typhoons subjected to rapid decay (RD). This analysis indicates that RD typhoons are small-probability events, making up about 2.2% of the total offshore typhoons during this period. The RD events experience a decadal variation, mostly in the 1960s and 1970s (maximal in the 1970s), rapidly decrease in the 1980s and 1990s and quickly increase from 2000. Also, RD typhoons show remarkable seasonal differences: they arise mainly in April and July–CDecember, with the prime stage being in October–CNovember. The offshore RD typhoons occur mostly in the South China Sea (SCS) and to a lesser extent in the East China Sea (ECS); however, none are observed over the Huang Sea and Bo Sea.
On the basis of NCEP/NCAR reanalysis data and yearbooks of CMA tropical cyclones, statistical analysis is performed for 1949–C2013 offshore typhoons subjected to rapid decay (RD). This analysis indicates that RD typhoons are small-probability events, making up about 2.2% of the total offshore typhoons during this period. The RD events experience a decadal variation, mostly in the 1960s and 1970s (maximal in the 1970s), rapidly decrease in the 1980s and 1990s and quickly increase from 2000. Also, RD typhoons show remarkable seasonal differences: they arise mainly in April and July–CDecember, with the prime stage being in October–CNovember. The offshore RD typhoons occur mostly in the South China Sea (SCS) and to a lesser extent in the East China Sea (ECS); however, none are observed over the Huang Sea and Bo Sea.
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