2011 Vol. 17, No. 4
2011, 17(4): 317-325.
Abstract:
Experiments of forecasting daily bi-variate index of the tropical atmospheric Madden–CJulian Oscillation (MJO) are performed in the context of adaptive filtering prediction models by combining the singular spectrum analysis (SSA) with the autoregressive (AR) methods. the MJO index, a pair of empirical orthogonal function (EOF) time series, called RMM1 and RMM2, predicts by the combined statistical SSA and AR models: firstly, according to the index of historic observation decomposed by SSA and then reconstructed by selecting the first several components based on prominent variance contributions; after that, established an AR prediction model from the composite (scheme A) or built the forecast models for each of these selected reconstructed components, separately (Scheme B). Several experimental MJO index forecasts are performed based on the models. The results show that both models have useful skills of the MJO index forecast beyond two weeks. In some cases, the correlation coefficient between the observed and predicted index series stays above 0.5 in 20 leading days. The SSA-AR model, based on the reconstructed composite series, has better performance on MJO forecast than the AR model, especially for the leading time longer than 5 days. Therefore, if we build a real-time forecast system by the SSA-AR model, it might provide an applicable tool for the operational prediction of the MJO index.
Experiments of forecasting daily bi-variate index of the tropical atmospheric Madden–CJulian Oscillation (MJO) are performed in the context of adaptive filtering prediction models by combining the singular spectrum analysis (SSA) with the autoregressive (AR) methods. the MJO index, a pair of empirical orthogonal function (EOF) time series, called RMM1 and RMM2, predicts by the combined statistical SSA and AR models: firstly, according to the index of historic observation decomposed by SSA and then reconstructed by selecting the first several components based on prominent variance contributions; after that, established an AR prediction model from the composite (scheme A) or built the forecast models for each of these selected reconstructed components, separately (Scheme B). Several experimental MJO index forecasts are performed based on the models. The results show that both models have useful skills of the MJO index forecast beyond two weeks. In some cases, the correlation coefficient between the observed and predicted index series stays above 0.5 in 20 leading days. The SSA-AR model, based on the reconstructed composite series, has better performance on MJO forecast than the AR model, especially for the leading time longer than 5 days. Therefore, if we build a real-time forecast system by the SSA-AR model, it might provide an applicable tool for the operational prediction of the MJO index.
2011, 17(4): 326-334.
Abstract:
Comparative analysis is carried out by using finite-domain power spectrum and lagged regression methods for the propagating characteristics and air-sea interaction processes of intraseasonal oscillations (ISOs) in the Asia to western Pacific (AWP) region during the boreal summer between the active and inactive tropical cyclone (TC) years from 79 2004. The results show as follows. (1) There exist more significant eastward propagating characteristics of the ISO in the active TC years over the whole AWP region. The ISOs of convection propagate zonally with more eastward extension in the years with active tropical cyclone activities, during which the 20-60-day period is strengthened,western Pacific becomes an area with evident characteristics of the propagation that is closely related to TC activities. (2) The air-sea interaction processes are the same in both active and inactive TC years, and the energy exchanges between the air and the sea play a role in maintaining the northwestward propagation of ISOs. (3) The air-sea interaction is more intensive in the active TC years than in the inactive ones. It is particularly true for the latent heat release by condensation as the result of convection, which may be one of the reasons resulting in significant differences in characteristics of ISOs between the active and inactive TC years.
Comparative analysis is carried out by using finite-domain power spectrum and lagged regression methods for the propagating characteristics and air-sea interaction processes of intraseasonal oscillations (ISOs) in the Asia to western Pacific (AWP) region during the boreal summer between the active and inactive tropical cyclone (TC) years from 79 2004. The results show as follows. (1) There exist more significant eastward propagating characteristics of the ISO in the active TC years over the whole AWP region. The ISOs of convection propagate zonally with more eastward extension in the years with active tropical cyclone activities, during which the 20-60-day period is strengthened,western Pacific becomes an area with evident characteristics of the propagation that is closely related to TC activities. (2) The air-sea interaction processes are the same in both active and inactive TC years, and the energy exchanges between the air and the sea play a role in maintaining the northwestward propagation of ISOs. (3) The air-sea interaction is more intensive in the active TC years than in the inactive ones. It is particularly true for the latent heat release by condensation as the result of convection, which may be one of the reasons resulting in significant differences in characteristics of ISOs between the active and inactive TC years.
2011, 17(4): 335-344.
Abstract:
Using the 1949-2007 western North Pacific tropical cyclones (TCs) best-track data archived at the Shanghai Typhoon Institute of China Meteorological Administration for the western North Pacific from 1949 to 2007, both the characteristics of binary and multiple TCs and samples of interactions among TCs and multi-TCs are identified and statistically analyzed. According to the various features of individual TC tracks and interacting tracks, seven distinct types are proposed to describe the binary system of TCs and their interaction samples. The mean trajectories of the west and east component of binary TCs in each type are obtained using a new cluster analysis technique. These types are then analyzed in terms of landfall process, occurrence seasonality, coexistent lifetime, especially the large-scale patterns of atmospheric circulation. Finally, typical steering flows and conceptual models of the binary TCs at different phases are established based on six-hourly flow maps of the binary system and the averages are determined of the mean steering flow of ten representative binary TCs. Then, typical steering flows and conceptual models at the beginning, middle and final phase in each type are established to describe the large-scale circulation patterns of the binary system interaction types.
Using the 1949-2007 western North Pacific tropical cyclones (TCs) best-track data archived at the Shanghai Typhoon Institute of China Meteorological Administration for the western North Pacific from 1949 to 2007, both the characteristics of binary and multiple TCs and samples of interactions among TCs and multi-TCs are identified and statistically analyzed. According to the various features of individual TC tracks and interacting tracks, seven distinct types are proposed to describe the binary system of TCs and their interaction samples. The mean trajectories of the west and east component of binary TCs in each type are obtained using a new cluster analysis technique. These types are then analyzed in terms of landfall process, occurrence seasonality, coexistent lifetime, especially the large-scale patterns of atmospheric circulation. Finally, typical steering flows and conceptual models of the binary TCs at different phases are established based on six-hourly flow maps of the binary system and the averages are determined of the mean steering flow of ten representative binary TCs. Then, typical steering flows and conceptual models at the beginning, middle and final phase in each type are established to describe the large-scale circulation patterns of the binary system interaction types.
2011, 17(4): 345-351.
Abstract:
In order to understand the role of East Asian subtropical westerly jet (EASWJ) in forecasting summer precipitation in East China, interseasonal pentad characteristics of the EASWJ and their relation to summer precipitation in East China are analyzed with the daily reanalysis data provided by National Centers for Environmental Prediction (NCEP, USA) and daily precipitation data from 714 Chinese meteorological stations during the period 1960–C2009. In addition, the daily evolution of the EASWJ and objective quantification of the EASWJ are investigated for the Meiyu season over the middle and lower reaches of the Yangtze River valley. It is found that the EASWJ and summer precipitation bands in East China move simultaneously. Especially, the stationary state and northward shift of the EASWJ are closely associated with the beginning, ending and stabilization of the annually first raining season in South China and Meiyu over these reaches. Analysis on the characteristics of the EASWJ in typical (atypical) Meiyu years over these reaches shows that the EASWJ swings steadily around its climatological position in meridional orientation (with large amplitude). Numerical experiments on an example in 2005 shows that indexes proposed in this study can depict the EASWJ well and should be valuable for application in the operation.
In order to understand the role of East Asian subtropical westerly jet (EASWJ) in forecasting summer precipitation in East China, interseasonal pentad characteristics of the EASWJ and their relation to summer precipitation in East China are analyzed with the daily reanalysis data provided by National Centers for Environmental Prediction (NCEP, USA) and daily precipitation data from 714 Chinese meteorological stations during the period 1960–C2009. In addition, the daily evolution of the EASWJ and objective quantification of the EASWJ are investigated for the Meiyu season over the middle and lower reaches of the Yangtze River valley. It is found that the EASWJ and summer precipitation bands in East China move simultaneously. Especially, the stationary state and northward shift of the EASWJ are closely associated with the beginning, ending and stabilization of the annually first raining season in South China and Meiyu over these reaches. Analysis on the characteristics of the EASWJ in typical (atypical) Meiyu years over these reaches shows that the EASWJ swings steadily around its climatological position in meridional orientation (with large amplitude). Numerical experiments on an example in 2005 shows that indexes proposed in this study can depict the EASWJ well and should be valuable for application in the operation.
2011, 17(4): 352-362.
Abstract:
The 1979-2001 ERA-40 monthly mean meridional winds are used to calculate the mass streamfunctions in the monsoon region (60–C140? E) and Niño zone (160? E–C120? W), with which the climate characteristics and intensity variation of the localized Hadley circulation (LHC) are analyzed over the two regions and the linkage of this LHC to Pacific SST is explored. Evidence suggests as follows. 1) The climatological LHC is stronger in the monsoon than in the Niño zone, with its position in the former northward of the latter, especially in the summer half-year. The resulting difference is due mainly to the land-sea heterogeneous distribution and the existence of a cold pool in the equatorial eastern Pacific. 2) The LHC experiences a distinct interannual variability in intensity and during 1979–C2001 the LHC strength of the two regions changes broadly in an anti-phase manner. 3) The LHC has its intensity associated closely with Pacific SST in such a way that its strength anomaly in the monsoon (Niño) band in January is correlated negatively (positively) with the SSTA over the all-Niño (1–C4) zone (ANZ) in the equatorial middle and eastern Pacific but positively (negatively) correlated to SSTA in the C-shaped area that surrounds the ANZ. The pattern of July is in rough agreement with that of January, except for more feeble correlativity in July, especially over the monsoon region; 4) The ENSO episode has different impacts on the LHC vigor in the two regions. With the occurrence of an El Niño, the LHC is weakened (strengthened) in the monsoon (Niño) region, and the reversal takes place during the La Niña year, with greater anomaly in the Niño area.
The 1979-2001 ERA-40 monthly mean meridional winds are used to calculate the mass streamfunctions in the monsoon region (60–C140? E) and Niño zone (160? E–C120? W), with which the climate characteristics and intensity variation of the localized Hadley circulation (LHC) are analyzed over the two regions and the linkage of this LHC to Pacific SST is explored. Evidence suggests as follows. 1) The climatological LHC is stronger in the monsoon than in the Niño zone, with its position in the former northward of the latter, especially in the summer half-year. The resulting difference is due mainly to the land-sea heterogeneous distribution and the existence of a cold pool in the equatorial eastern Pacific. 2) The LHC experiences a distinct interannual variability in intensity and during 1979–C2001 the LHC strength of the two regions changes broadly in an anti-phase manner. 3) The LHC has its intensity associated closely with Pacific SST in such a way that its strength anomaly in the monsoon (Niño) band in January is correlated negatively (positively) with the SSTA over the all-Niño (1–C4) zone (ANZ) in the equatorial middle and eastern Pacific but positively (negatively) correlated to SSTA in the C-shaped area that surrounds the ANZ. The pattern of July is in rough agreement with that of January, except for more feeble correlativity in July, especially over the monsoon region; 4) The ENSO episode has different impacts on the LHC vigor in the two regions. With the occurrence of an El Niño, the LHC is weakened (strengthened) in the monsoon (Niño) region, and the reversal takes place during the La Niña year, with greater anomaly in the Niño area.
2011, 17(4): 363-374.
Abstract:
Based on tropical cyclone datasets from Shanghai Typhoon Institute of China Meteorological Administration, the National Centers for Environmental Prediction (NCEP, USA) reanalysis data and the rainfall records from 743 stations in China, the impacts of cyclogenesis number over the South China Sea and the western Pacific are studied on the 30-60-day oscillations in the precipitation of Guangdong during the flooding period. The year with more-than-normal (less-than-normal) tropical cyclogenesis is defined as a ‘high year’ (‘low year’). In light of the irregular periodic oscillations, the method used to construct the composite life cycle is based on nine consecutive phases in each of the cycles. Phases 1, 3, 5, and 7 correspond to, respectively, the time when precipitation anomalies reach the minimum, a positive transition (negative-turning-to-positive) phase, the maximum, and a negative transition phase. The results showed that the precipitation of the 30-60-day oscillations is associated with the interaction between a well-organized eastward propagation system from the Arabian Sea/Bay of Bengal and a westward-propagating system (with cyclonic and anticyclonic anomalies in the northwest-southeast direction) from the South China Sea to western Pacific during the high years, whereas the precipitation is affected during a low year by the circulation over the South China Sea and western Pacific (with cyclonic and anticyclonic anomalies in the northeast-southwest direction). During the high year, the warm and wet air mass from the ocean to the west and south are transported to Guangdong by westerly anomalies and an enclosed latitudinal cell, which ascends in the Northern Hemisphere low latitudes and descends in the Southern Hemisphere low latitudes. During the low year, the warm and wet air mass from the ocean to the south is transported to Guangdong by southwesterly wind anomalies and local ascending movements. Because the kinetic energy, westerly, easterly shift, vertical velocity and vapor transportation averaged over (109–C119° E, 10–C20° N) is stronger in high years than those in low years, the precipitation of the 30-60-day oscillations in Guangdong is higher in high years than that in low years.
Based on tropical cyclone datasets from Shanghai Typhoon Institute of China Meteorological Administration, the National Centers for Environmental Prediction (NCEP, USA) reanalysis data and the rainfall records from 743 stations in China, the impacts of cyclogenesis number over the South China Sea and the western Pacific are studied on the 30-60-day oscillations in the precipitation of Guangdong during the flooding period. The year with more-than-normal (less-than-normal) tropical cyclogenesis is defined as a ‘high year’ (‘low year’). In light of the irregular periodic oscillations, the method used to construct the composite life cycle is based on nine consecutive phases in each of the cycles. Phases 1, 3, 5, and 7 correspond to, respectively, the time when precipitation anomalies reach the minimum, a positive transition (negative-turning-to-positive) phase, the maximum, and a negative transition phase. The results showed that the precipitation of the 30-60-day oscillations is associated with the interaction between a well-organized eastward propagation system from the Arabian Sea/Bay of Bengal and a westward-propagating system (with cyclonic and anticyclonic anomalies in the northwest-southeast direction) from the South China Sea to western Pacific during the high years, whereas the precipitation is affected during a low year by the circulation over the South China Sea and western Pacific (with cyclonic and anticyclonic anomalies in the northeast-southwest direction). During the high year, the warm and wet air mass from the ocean to the west and south are transported to Guangdong by westerly anomalies and an enclosed latitudinal cell, which ascends in the Northern Hemisphere low latitudes and descends in the Southern Hemisphere low latitudes. During the low year, the warm and wet air mass from the ocean to the south is transported to Guangdong by southwesterly wind anomalies and local ascending movements. Because the kinetic energy, westerly, easterly shift, vertical velocity and vapor transportation averaged over (109–C119° E, 10–C20° N) is stronger in high years than those in low years, the precipitation of the 30-60-day oscillations in Guangdong is higher in high years than that in low years.
2011, 17(4): 375-384.
Abstract:
Researchers have paid much attention to the influence of the tropical zonal wind quasi-biennial oscillation (QBO) on tropical methane, while generally ignoring the change in extra-tropical methane. The present study analyzed the interannual changes in the methane mixing ratio in extra-tropics of both the Southern Hemisphere (SH) and Northern Hemisphere (NH) using Halogen Occultation Experiment (HALOE) satellite data. The results show that interannual changes in extra-tropical methane exhibit QBO features in both hemispheres that are obviously different from those in the tropics. The extra-tropical methane QBO perturbations usually occur in two layers and are longitudinally asymmetrical about the equator. The amplitude of the methane QBO disturbance in the extra-tropics is smaller than that in the tropics from 10 to 1 hPa but much larger in the layer from 30 to 10 hPa. The interannual relative changes in the methane mixing ratio are similar in both the NH extra-tropics and the tropics in the middle and upper stratosphere. Using the National Center for Atmospheric Research two-dimensional, interactive chemical dynamical radiative model (SOCRATES), simulation was conducted to investigate the mechanism of the extra-tropical methane QBO. The results indicate that the tropical stratospheric zonal wind QBO results in the QBO of the induced residual circulation. It is the transport of methane by the induced residual circulation that causes the methane QBO in the extra-tropics. The induced residual circulations in the middle and upper stratosphere are not always longitudinally symmetrical about the equator, resulting in different distribution of the methane QBO in the SH and NH extra-tropics.
Researchers have paid much attention to the influence of the tropical zonal wind quasi-biennial oscillation (QBO) on tropical methane, while generally ignoring the change in extra-tropical methane. The present study analyzed the interannual changes in the methane mixing ratio in extra-tropics of both the Southern Hemisphere (SH) and Northern Hemisphere (NH) using Halogen Occultation Experiment (HALOE) satellite data. The results show that interannual changes in extra-tropical methane exhibit QBO features in both hemispheres that are obviously different from those in the tropics. The extra-tropical methane QBO perturbations usually occur in two layers and are longitudinally asymmetrical about the equator. The amplitude of the methane QBO disturbance in the extra-tropics is smaller than that in the tropics from 10 to 1 hPa but much larger in the layer from 30 to 10 hPa. The interannual relative changes in the methane mixing ratio are similar in both the NH extra-tropics and the tropics in the middle and upper stratosphere. Using the National Center for Atmospheric Research two-dimensional, interactive chemical dynamical radiative model (SOCRATES), simulation was conducted to investigate the mechanism of the extra-tropical methane QBO. The results indicate that the tropical stratospheric zonal wind QBO results in the QBO of the induced residual circulation. It is the transport of methane by the induced residual circulation that causes the methane QBO in the extra-tropics. The induced residual circulations in the middle and upper stratosphere are not always longitudinally symmetrical about the equator, resulting in different distribution of the methane QBO in the SH and NH extra-tropics.
2011, 17(4): 385-391.
Abstract:
Using the 1970–C2005 annual precipitation and evaporation data at 80 gauge stations across Hunan province, this work analyzes the spatial distribution and variation tendency of the local droughts and floods using linear regression, wavelet analysis, abrupt change, clusters, Empirical Orthogonal Function (EOF) and rotated EOF (REOF). Results show that there are four dry areas and three wet areas in Hunan. The whole province exhibits a moistening trend except some small areas in western, eastern and southern Hunan. The most prominent feature of annual precipitation is that the whole province basically displays a consistent variation tendency, as far as the dominant EOF mode is concerned. In addition, the spatial features of the other EOF modes include dry-wet differences, e.g. wet (or dry) in the north versus dry (or wet) in the south, wet (or dry) in the center and dry (or wet) in the surrounding areas. The distribution of the ratios of evaporation to precipitation exhibits both common features as well as spatial differences, which can be classified into four types: South Hunan, North Hunan, Northeast Hunan, and Central Hunan. There is an abrupt change from dry to wet patterns in the early 1990s. Generally, the drought-flood distribution presents variations of three periods. In the late 2000s, Hunan province will be in a period of drought, followed by a period of flood.
Using the 1970–C2005 annual precipitation and evaporation data at 80 gauge stations across Hunan province, this work analyzes the spatial distribution and variation tendency of the local droughts and floods using linear regression, wavelet analysis, abrupt change, clusters, Empirical Orthogonal Function (EOF) and rotated EOF (REOF). Results show that there are four dry areas and three wet areas in Hunan. The whole province exhibits a moistening trend except some small areas in western, eastern and southern Hunan. The most prominent feature of annual precipitation is that the whole province basically displays a consistent variation tendency, as far as the dominant EOF mode is concerned. In addition, the spatial features of the other EOF modes include dry-wet differences, e.g. wet (or dry) in the north versus dry (or wet) in the south, wet (or dry) in the center and dry (or wet) in the surrounding areas. The distribution of the ratios of evaporation to precipitation exhibits both common features as well as spatial differences, which can be classified into four types: South Hunan, North Hunan, Northeast Hunan, and Central Hunan. There is an abrupt change from dry to wet patterns in the early 1990s. Generally, the drought-flood distribution presents variations of three periods. In the late 2000s, Hunan province will be in a period of drought, followed by a period of flood.
2011, 17(4): 392-398.
Abstract:
By means of the regional boundary layer model (RBLM), a study on the influences of the urban planning and construction on the summer urban heat island (UHI) in the metropolis of Shenzhen is performed. In the study, the current summer UHI distribution, the influences of the increasing high-density construction and the energy consumption on the summer air temperature distribution, and the influences of the urban ventilation corridor on the summer air temperature distribution are numerically analyzed. Some conclusions are drawn in the light of the study: (1) The summer UHI is more obvious in day time than that in night time in the summer of Shenzhen, and the maximum values of UHI intensity in the day time appear in the areas with high-density construction, which are located in Nanshan, Futian and Luohu and western Bao′an districts. (2) The increase of construction density and energy consumption in the urban area will lead to the increase of temperature near the ground, and the increase of temperature at nighttime is more obvious than that at daytime. (3) The ventilation corridor can effectively reduce the UHI intensity and can be taken as a method to eliminate the negative climatic effect caused by the increase of high-density construction and energy consumption in the future.
By means of the regional boundary layer model (RBLM), a study on the influences of the urban planning and construction on the summer urban heat island (UHI) in the metropolis of Shenzhen is performed. In the study, the current summer UHI distribution, the influences of the increasing high-density construction and the energy consumption on the summer air temperature distribution, and the influences of the urban ventilation corridor on the summer air temperature distribution are numerically analyzed. Some conclusions are drawn in the light of the study: (1) The summer UHI is more obvious in day time than that in night time in the summer of Shenzhen, and the maximum values of UHI intensity in the day time appear in the areas with high-density construction, which are located in Nanshan, Futian and Luohu and western Bao′an districts. (2) The increase of construction density and energy consumption in the urban area will lead to the increase of temperature near the ground, and the increase of temperature at nighttime is more obvious than that at daytime. (3) The ventilation corridor can effectively reduce the UHI intensity and can be taken as a method to eliminate the negative climatic effect caused by the increase of high-density construction and energy consumption in the future.
2011, 17(4): 399-408.
Abstract:
Observational data of the severe typhoon Hagupit are obtained by a 3-dimensional ultrasonic anemometer which is installed on a 100-meter-high meteorological tower located at an islet off the coast of Guangdong. The characteristics of the extreme wind load parameters for offshore wind turbines under the influence of extreme winds at severe typhoon intensity are analyzed. By comparing the observed data with the results derived from the International Electrotechnical Commission (IEC) standard 61400-1, the applicability of the methods computing extreme wind load parameters in the IEC standard are investigated under typhoon conditions. The results are as follows. (1) The changes of both the offshore extreme gust wind speeds and the extreme wind directions render a “M” shape bi-modal distribution with peak values in the eyewall region of Hagupit. (2) There are significant differences of amplitudes of the observed extreme operating gust wind speeds and extreme wind direction from the results calculated from the IEC standard. (3) The amplitudes of both the extreme operating gust wind speeds and the extreme directions exceed the upper limits of the IEC standard for three standard classes of wind turbines, and the values calculated by IEC standard are much significantly larger than the measured ones. (4) The observed extreme operating gust wind speeds are consistent with the results calculated by the IEC standard when wind turbines are under full or partial workload or cut-off conditions, although the amplitude of extreme wind directions calculated in terms of the IEC standard is larger than that of direct measurements. Measured extreme operating gust wind speeds sometimes exceed the IEC design criteria.
Observational data of the severe typhoon Hagupit are obtained by a 3-dimensional ultrasonic anemometer which is installed on a 100-meter-high meteorological tower located at an islet off the coast of Guangdong. The characteristics of the extreme wind load parameters for offshore wind turbines under the influence of extreme winds at severe typhoon intensity are analyzed. By comparing the observed data with the results derived from the International Electrotechnical Commission (IEC) standard 61400-1, the applicability of the methods computing extreme wind load parameters in the IEC standard are investigated under typhoon conditions. The results are as follows. (1) The changes of both the offshore extreme gust wind speeds and the extreme wind directions render a “M” shape bi-modal distribution with peak values in the eyewall region of Hagupit. (2) There are significant differences of amplitudes of the observed extreme operating gust wind speeds and extreme wind direction from the results calculated from the IEC standard. (3) The amplitudes of both the extreme operating gust wind speeds and the extreme directions exceed the upper limits of the IEC standard for three standard classes of wind turbines, and the values calculated by IEC standard are much significantly larger than the measured ones. (4) The observed extreme operating gust wind speeds are consistent with the results calculated by the IEC standard when wind turbines are under full or partial workload or cut-off conditions, although the amplitude of extreme wind directions calculated in terms of the IEC standard is larger than that of direct measurements. Measured extreme operating gust wind speeds sometimes exceed the IEC design criteria.
2011, 17(4): 409-417.
Abstract:
The conventional observations data, NCAR/NCEP-2 reanalysis data, and NOAA outgoing longwave radiation data are used to investigate different characteristics of Leo and Neoguri, two April typhoons that ever made landfall on the continent of China over the past 60 years. The results showed that both Leo and Neoguri occurred during the La Nina events. Strong convective activity, weak vertical wind shear and upper-level divergence were in favor of the formation of these April typhoons. Leo originated from a monsoon depression and Neoguri evolved from an easterly wave. The meandering moving track of Leo attributed to strong northeast monsoon and a weak and changeable subtropical high; the steady moving track of Neoguri was governed by a strong and stable subtropical high. Leo and Neoguri had similar terrain conditions and intensities during landfall but were different in precipitation as water vapor transport and duration of kinetic uplifting resulted in apparent discrepancies between them.
The conventional observations data, NCAR/NCEP-2 reanalysis data, and NOAA outgoing longwave radiation data are used to investigate different characteristics of Leo and Neoguri, two April typhoons that ever made landfall on the continent of China over the past 60 years. The results showed that both Leo and Neoguri occurred during the La Nina events. Strong convective activity, weak vertical wind shear and upper-level divergence were in favor of the formation of these April typhoons. Leo originated from a monsoon depression and Neoguri evolved from an easterly wave. The meandering moving track of Leo attributed to strong northeast monsoon and a weak and changeable subtropical high; the steady moving track of Neoguri was governed by a strong and stable subtropical high. Leo and Neoguri had similar terrain conditions and intensities during landfall but were different in precipitation as water vapor transport and duration of kinetic uplifting resulted in apparent discrepancies between them.
2011, 17(4): 418-429.
Abstract:
The coastal area of southern China is frequently affected by marine meteorological disasters, and is also one of the key areas that influence the short-term climate change of China. Due to a lack of observational facilities and techniques, little has been done in this area in terms of operational weather monitoring and scientific research on atmospheric and marine environment. With the support of China Meteorological Administration (CMA) and Guangdong Meteorological Bureau (GMB), the Marine Meteorological Science Experiment Base (MMSEB) at Bohe, Maoming has been jointly established by Guangzhou Institute of Tropical and Marine Meteorology (GITMM) and Maoming Meteorological Bureau (MMB) of Guangdong Province after three years of hard work. It has become an integrated coastal observation base that is equipped with a complete set of sophisticated instruments. Equipment maintenance and data quality control procedures have been implemented to ensure the long-term, steady operation of the instruments and the availability of high quality data. Preliminary observations show that the data obtained by the MMSEB reveal many interesting features in the boundary layer structure and air-sea interaction in such disastrous weather as typhoons and sea fog. The MMSEB is expected to play an important role in the scientific research of disastrous weather related to marine meteorology.
The coastal area of southern China is frequently affected by marine meteorological disasters, and is also one of the key areas that influence the short-term climate change of China. Due to a lack of observational facilities and techniques, little has been done in this area in terms of operational weather monitoring and scientific research on atmospheric and marine environment. With the support of China Meteorological Administration (CMA) and Guangdong Meteorological Bureau (GMB), the Marine Meteorological Science Experiment Base (MMSEB) at Bohe, Maoming has been jointly established by Guangzhou Institute of Tropical and Marine Meteorology (GITMM) and Maoming Meteorological Bureau (MMB) of Guangdong Province after three years of hard work. It has become an integrated coastal observation base that is equipped with a complete set of sophisticated instruments. Equipment maintenance and data quality control procedures have been implemented to ensure the long-term, steady operation of the instruments and the availability of high quality data. Preliminary observations show that the data obtained by the MMSEB reveal many interesting features in the boundary layer structure and air-sea interaction in such disastrous weather as typhoons and sea fog. The MMSEB is expected to play an important role in the scientific research of disastrous weather related to marine meteorology.
2011, 17(4): 430-440.
Abstract:
El Niño or La Niña manifest in December over the Pacific and will serve as an index for the forecasting of subsequent Indian summer monsoon, which occurs from June to mid-September. In the present article, an attempt is made to study the variation of latent heat flux (LHF) over the north Indian Ocean during strong El Niño and strong La Niña and relate it with Indian monsoon rainfall. During strong El Niño the LHF intensity is higher and associated with higher wind speed and lower cloud amount. During El Niño all India rainfall is having an inverse relation with LHF. Seasonal rainfall is higher in YY+1 (subsequent year) than YY (year of occurrence). However there is a lag in rainfall during El Niño YY+1 from June to July when compared with the monthly rainfall.
El Niño or La Niña manifest in December over the Pacific and will serve as an index for the forecasting of subsequent Indian summer monsoon, which occurs from June to mid-September. In the present article, an attempt is made to study the variation of latent heat flux (LHF) over the north Indian Ocean during strong El Niño and strong La Niña and relate it with Indian monsoon rainfall. During strong El Niño the LHF intensity is higher and associated with higher wind speed and lower cloud amount. During El Niño all India rainfall is having an inverse relation with LHF. Seasonal rainfall is higher in YY+1 (subsequent year) than YY (year of occurrence). However there is a lag in rainfall during El Niño YY+1 from June to July when compared with the monthly rainfall.
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