Chung‐Chieh Wang, G. T. Chen, Chi Hong Ngai, K. Tsuboki
There exists a minor, secondary earlymorning peak in meiyu rainfall along the western coast of Taiwan, and this work investigates one such event on June 8, 2012 in southwestern Taiwan under weak synoptic conditions through both observational analysis and numerical modeling, with the main focus on the triggering mechanism of the convection. Observations indicate that the convection developed offshore around midnight near the leading edge of a moderate lowlevel southwesterly wind surge of 15 – 20 kts and intensified and moved onshore to pro duce rainfall. The cold outflow from precipitation also led to new cell development at the backside, and the rain thus lasted for several hours until approximately 07:00 LST. Numerical simulation using a cloudresolving model at a grid size of 0.5 km successfully reproduced the event development in close agreement with the observations, once a time delay in the arrival of the southwesterly wind surge in initial/boundary conditions (from global analyses) was corrected. Aided by two sensitivity tests, the mod el results indicate that the convection breaks out between two advancing boundaries, one from the onshore surge of the prevailing southwesterly wind and the other from the offshore land/mountain breeze, when they move approximately 40 km apart. Additionally, both boundaries are required, as either one alone does not provide suf ficient forcing to initiate deep convection in the model. These findings on the initiation of offshore convection in the meiyu season, notably, are qualitatively similar to some cases in Florida with two approaching seabreeze fronts (in daytime over land).
{"title":"Case study of a morning convective rainfall event over southwestern Taiwan in the Mei-Yu season under weak synoptic conditions","authors":"Chung‐Chieh Wang, G. T. Chen, Chi Hong Ngai, K. Tsuboki","doi":"10.2151/JMSJ.2018-051","DOIUrl":"https://doi.org/10.2151/JMSJ.2018-051","url":null,"abstract":"There exists a minor, secondary earlymorning peak in meiyu rainfall along the western coast of Taiwan, and this work investigates one such event on June 8, 2012 in southwestern Taiwan under weak synoptic conditions through both observational analysis and numerical modeling, with the main focus on the triggering mechanism of the convection. Observations indicate that the convection developed offshore around midnight near the leading edge of a moderate lowlevel southwesterly wind surge of 15 – 20 kts and intensified and moved onshore to pro duce rainfall. The cold outflow from precipitation also led to new cell development at the backside, and the rain thus lasted for several hours until approximately 07:00 LST. Numerical simulation using a cloudresolving model at a grid size of 0.5 km successfully reproduced the event development in close agreement with the observations, once a time delay in the arrival of the southwesterly wind surge in initial/boundary conditions (from global analyses) was corrected. Aided by two sensitivity tests, the mod el results indicate that the convection breaks out between two advancing boundaries, one from the onshore surge of the prevailing southwesterly wind and the other from the offshore land/mountain breeze, when they move approximately 40 km apart. Additionally, both boundaries are required, as either one alone does not provide suf ficient forcing to initiate deep convection in the model. These findings on the initiation of offshore convection in the meiyu season, notably, are qualitatively similar to some cases in Florida with two approaching seabreeze fronts (in daytime over land).","PeriodicalId":17476,"journal":{"name":"Journal of the Meteorological Society of Japan","volume":"96 1","pages":"461-484"},"PeriodicalIF":3.1,"publicationDate":"2018-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2151/JMSJ.2018-051","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43723980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The combination of three visible bands of the Advanced Himawari Imager (AHI) aboard Japan Meteorological Agency’s (JMA) new-generation Himawari-8 and Himawari-9 geostationary meteorological satellites enables the production of true color imagery. True color is intuitively understandable to human analysts and beneficial for monitoring surface and atmospheric features. It is particularly useful when applied to frequent observations from a geostationary platform. In this article, we report on an application of a color reproduction approach based on the International Commission on Illumination (CIE) 1931 XYZ color system to imagery rendering. This approach allows the consideration of primary color (RGB) differences among satellite and output devices, which in turn cause differences in the colors reproduced. The RGB signals observed by the AHI are converted to XYZ tristimulus values, which are independent of the devices themselves, and then reconverted to RGB signals for output devices via the application of 3 × 3 conversion matrices. This article also covers an objective technique for the evaluation of the accuracy of XYZ values. The evaluation indicated that the combination of AHI native RGB bands is suboptimal for obtaining XYZ values as is, whereas a combination in which the green band is replaced by a pseudo band with a central wavelength of around 0.555 µm is optimal. The pseudo band is generated via regression with existing visible and near-infrared bands as predictor variables. The imagery produced using this approach was termed True Color Reproduction (TCR). This approach is applicable to other satellites that have several bands in the visible to near-infrared spectral range, and it has the potential for development toward the production of standardized sensor-independent true color imagery.
{"title":"True Color Imagery Rendering for Himawari-8 with a Color Reproduction Approach Based on the CIE XYZ Color System","authors":"Hidehiko Murata, Kotaro Saitoh, Yasuhiko Sumida","doi":"10.2151/JMSJ.2018-049","DOIUrl":"https://doi.org/10.2151/JMSJ.2018-049","url":null,"abstract":"The combination of three visible bands of the Advanced Himawari Imager (AHI) aboard Japan Meteorological Agency’s (JMA) new-generation Himawari-8 and Himawari-9 geostationary meteorological satellites enables the production of true color imagery. True color is intuitively understandable to human analysts and beneficial for monitoring surface and atmospheric features. It is particularly useful when applied to frequent observations from a geostationary platform. In this article, we report on an application of a color reproduction approach based on the International Commission on Illumination (CIE) 1931 XYZ color system to imagery rendering. This approach allows the consideration of primary color (RGB) differences among satellite and output devices, which in turn cause differences in the colors reproduced. The RGB signals observed by the AHI are converted to XYZ tristimulus values, which are independent of the devices themselves, and then reconverted to RGB signals for output devices via the application of 3 × 3 conversion matrices. This article also covers an objective technique for the evaluation of the accuracy of XYZ values. The evaluation indicated that the combination of AHI native RGB bands is suboptimal for obtaining XYZ values as is, whereas a combination in which the green band is replaced by a pseudo band with a central wavelength of around 0.555 µm is optimal. The pseudo band is generated via regression with existing visible and near-infrared bands as predictor variables. The imagery produced using this approach was termed True Color Reproduction (TCR). This approach is applicable to other satellites that have several bands in the visible to near-infrared spectral range, and it has the potential for development toward the production of standardized sensor-independent true color imagery.","PeriodicalId":17476,"journal":{"name":"Journal of the Meteorological Society of Japan","volume":"1 1","pages":"211-238"},"PeriodicalIF":3.1,"publicationDate":"2018-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2151/JMSJ.2018-049","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46037770","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
On July 13, 2012, a bow echo was observed over the lee side of the Mt. Halla (1,950 m above sea level) on Jeju Island, Korea. Three-dimensional (3D) wind-field and surface observation analyses were carried out to understand the structure and evolution of convective systems with a bow echo on a bell-shaped terrain. A northeastward-moving convective system passed over the approximately bell-shaped isolated mountain with a mean speed of 17 m s. On the windward side of the mountain, the convective system developed by the inflow of unstable warm air from the ocean and terrain-induced upward motion, even with a low convective available potential energy value of 511 J kg. When passing the lee side of the mountain, a bow echo was formed in the convective system by the strongest winds behind the bow echo. Behind the leading edge of the bow echo, the strengthened rear-inflow jet descended with relatively dry air along the surface, resulting in enhancing evaporative cooling. The precipitation-induced downdrafts generated a cold pool on the lee side of the mountain. The development of an rear-inflow jet and cold pool formation both contributed to the evolution of the bow echo. In addition, the isolated bell-shaped terrain had a major indirect influence on the evolution of the convective system with a bow echo in this event.
2012年7月13日，在济州岛汉罗山背风面(海拔1950米)观测到弓形回波。通过三维风场和地面观测分析，了解了钟形地形上弓形回波对流系统的结构和演化。一股向东北移动的对流系统以17 m s的平均速度掠过近钟形孤立山。在山的迎风侧，对流系统由海洋不稳定暖空气流入和地形诱导的上升运动发展而来，对流有效位能较低，为511 J kg。当经过山的背风面时，弓形回波背后最强的风在对流系统中形成弓形回波。在弓形回波前缘后，增强的后流入射流带着表面相对干燥的空气下降，导致蒸发冷却增强。降水引起的下降气流在山的背风面形成了一个冷池。后入流射流的发展和冷池的形成都促进了弓形回波的演化。此外，孤立的钟形地形对弓形回波对流系统的演化具有重要的间接影响。
{"title":"Structure and Evolution of a Convective System with Bow Echo Associated with Terrain on Jeju Island, Korea","authors":"Kang Yunhee, Jong‐Hoon Jeong, C. You, Dong-In Lee","doi":"10.2151/JMSJ.2018-050","DOIUrl":"https://doi.org/10.2151/JMSJ.2018-050","url":null,"abstract":"On July 13, 2012, a bow echo was observed over the lee side of the Mt. Halla (1,950 m above sea level) on Jeju Island, Korea. Three-dimensional (3D) wind-field and surface observation analyses were carried out to understand the structure and evolution of convective systems with a bow echo on a bell-shaped terrain. A northeastward-moving convective system passed over the approximately bell-shaped isolated mountain with a mean speed of 17 m s. On the windward side of the mountain, the convective system developed by the inflow of unstable warm air from the ocean and terrain-induced upward motion, even with a low convective available potential energy value of 511 J kg. When passing the lee side of the mountain, a bow echo was formed in the convective system by the strongest winds behind the bow echo. Behind the leading edge of the bow echo, the strengthened rear-inflow jet descended with relatively dry air along the surface, resulting in enhancing evaporative cooling. The precipitation-induced downdrafts generated a cold pool on the lee side of the mountain. The development of an rear-inflow jet and cold pool formation both contributed to the evolution of the bow echo. In addition, the isolated bell-shaped terrain had a major indirect influence on the evolution of the convective system with a bow echo in this event.","PeriodicalId":17476,"journal":{"name":"Journal of the Meteorological Society of Japan","volume":"96 1","pages":"447-460"},"PeriodicalIF":3.1,"publicationDate":"2018-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43438406","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Background error covariance (BEC) is one of the key components in data assimilation systems for numerical weather prediction. Recently, a scheme of using an inhomogeneous and anisotropic BEC estimated from historical forecast error samples has been tested by utilizing the extended alpha control variable approach (BEC-CVA) in the framework of the variational Data Assimilation system for the Weather Research and Forecasting model (WRFDA). In this paper, the BEC-CVA approach is further examined by conducting single observation assimilation experiments and continuous-cycling data assimilation and forecasting experiments covering a 3-week period. Additional benefits of using a blending approach (BEC-BLD), which combines a static, homogeneous BEC and an inhomogeneous and anisotropic BEC, are also assessed. Single observation experiments indicate that the noise in the increments in BEC-CVA can be somehow reduced by using BEC-BLD, while the inhomogeneous and multivariable correlations from BEC-CVA are still taken into account. The impact of BEC-CVA and BEC-BLD on short-term weather forecasts is compared with the threedimensional variational data assimilation scheme (3DVar) and also compared with the hybrid ensemble transform Kalman filter and 3DVar (ETKF-3DVar) in WRFDA. The results show that BEC-CVA and BEC-BLD outperform the use of 3DVar. BEC-CVA and BEC-BLD underperform ETKF-3DVar, as expected. However, the computational cost of BEC-CVA and BEC-BLD is considerably less expensive because no ensemble forecasts are required. Journal of the Meteorological Society of Japan Vol. 96, No. 5 430
{"title":"Refinement of the Use of Inhomogeneous Background Error Covariance Estimated from Historical Forecast Error Samples and its Impact on Short-Term Regional Numerical Weather Prediction","authors":"Yaodeng Chen, Jia Wang, Yufang Gao, Xiaomeng Chen, Hongli Wang, Xiangyu Huang","doi":"10.2151/JMSJ.2018-048","DOIUrl":"https://doi.org/10.2151/JMSJ.2018-048","url":null,"abstract":"Background error covariance (BEC) is one of the key components in data assimilation systems for numerical weather prediction. Recently, a scheme of using an inhomogeneous and anisotropic BEC estimated from historical forecast error samples has been tested by utilizing the extended alpha control variable approach (BEC-CVA) in the framework of the variational Data Assimilation system for the Weather Research and Forecasting model (WRFDA). In this paper, the BEC-CVA approach is further examined by conducting single observation assimilation experiments and continuous-cycling data assimilation and forecasting experiments covering a 3-week period. Additional benefits of using a blending approach (BEC-BLD), which combines a static, homogeneous BEC and an inhomogeneous and anisotropic BEC, are also assessed. Single observation experiments indicate that the noise in the increments in BEC-CVA can be somehow reduced by using BEC-BLD, while the inhomogeneous and multivariable correlations from BEC-CVA are still taken into account. The impact of BEC-CVA and BEC-BLD on short-term weather forecasts is compared with the threedimensional variational data assimilation scheme (3DVar) and also compared with the hybrid ensemble transform Kalman filter and 3DVar (ETKF-3DVar) in WRFDA. The results show that BEC-CVA and BEC-BLD outperform the use of 3DVar. BEC-CVA and BEC-BLD underperform ETKF-3DVar, as expected. However, the computational cost of BEC-CVA and BEC-BLD is considerably less expensive because no ensemble forecasts are required. Journal of the Meteorological Society of Japan Vol. 96, No. 5 430","PeriodicalId":17476,"journal":{"name":"Journal of the Meteorological Society of Japan","volume":"96 1","pages":"429-446"},"PeriodicalIF":3.1,"publicationDate":"2018-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2151/JMSJ.2018-048","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43237902","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hongli Wang, L. Qiu, Xiaoning Xie, Zhiyuan Wang, Xiao-dong Liu
The climate variability in monsoon and arid regions attributable to dynamic vegetation is investigated using NCAR’s Community Earth System Model with the Dynamic Global Vegetation Model. Two present climate simulations, one using dynamics and the other using fixed vegetation cover, are carried out. A comparative analysis of the two simulations reveals that the climate in monsoon and arid regions exhibits different responses to dynamic vegetation. On the hemispheric scale, precipitation mainly increases in the Northern Hemisphere and decreases in the Southern Hemisphere in response to dynamic vegetation, while the surface temperature exhibits a consistent decrease. On the regional scale, precipitation decreases caused by dynamic vegetation are the main trend in monsoon regions except for the Asian monsoon region, while precipitation responses to vegetation change are weak in arid regions relative to monsoon regions. The surface temperature increases significantly because of dynamic vegetation only in the boreal winter Asian monsoon region, while the rest of the monsoon and arid regions mainly exhibit reduced surface temperatures. Therefore, the climate variability in the Asian monsoon Journal of the Meteorological Society of Japan Vol. 96, No. 4 392
{"title":"Climate Variability in Monsoon and Arid Regions Attributable to Dynamic Vegetation in a Global Climate Model","authors":"Hongli Wang, L. Qiu, Xiaoning Xie, Zhiyuan Wang, Xiao-dong Liu","doi":"10.2151/JMSJ.2018-047","DOIUrl":"https://doi.org/10.2151/JMSJ.2018-047","url":null,"abstract":"The climate variability in monsoon and arid regions attributable to dynamic vegetation is investigated using NCAR’s Community Earth System Model with the Dynamic Global Vegetation Model. Two present climate simulations, one using dynamics and the other using fixed vegetation cover, are carried out. A comparative analysis of the two simulations reveals that the climate in monsoon and arid regions exhibits different responses to dynamic vegetation. On the hemispheric scale, precipitation mainly increases in the Northern Hemisphere and decreases in the Southern Hemisphere in response to dynamic vegetation, while the surface temperature exhibits a consistent decrease. On the regional scale, precipitation decreases caused by dynamic vegetation are the main trend in monsoon regions except for the Asian monsoon region, while precipitation responses to vegetation change are weak in arid regions relative to monsoon regions. The surface temperature increases significantly because of dynamic vegetation only in the boreal winter Asian monsoon region, while the rest of the monsoon and arid regions mainly exhibit reduced surface temperatures. Therefore, the climate variability in the Asian monsoon Journal of the Meteorological Society of Japan Vol. 96, No. 4 392","PeriodicalId":17476,"journal":{"name":"Journal of the Meteorological Society of Japan","volume":"96 1","pages":"391-403"},"PeriodicalIF":3.1,"publicationDate":"2018-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47340659","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study investigated the absolute values of column-integrated water vapor (precipitable water; PW) in the climate models used in the Coupled Model Intercomparison Project Phase 5 (CMIP5), in terms of the relation ships between PW and precipitation characteristics. We identified that global mean PW values are systematically much lower in CMIP5 models than in observations. This dry bias is most profound over the tropical ocean. The dry bias is partly due to biases in sea surface temperatures in the CMIP5-coupled climate models. However, the dry bias is also present in Atmospheric Model Intercomparison Project (AMIP) experiments, which implies the existence of other factors. The relationship between PW and rainfall characteristics shows that rainfall occurs when water vapor levels are lower than in observations, particularly in models with a relatively strong dry bias. This suggests that the reproducibility of rainfall characteristics may be associated with the dry bias.
{"title":"A Systematic Tropospheric Dry Bias in the Tropics in CMIP5 Models: Relationship between Water Vapor and Rainfall Characteristics","authors":"H. Takahashi","doi":"10.2151/JMSJ.2018-046","DOIUrl":"https://doi.org/10.2151/JMSJ.2018-046","url":null,"abstract":"This study investigated the absolute values of column-integrated water vapor (precipitable water; PW) in the climate models used in the Coupled Model Intercomparison Project Phase 5 (CMIP5), in terms of the relation ships between PW and precipitation characteristics. We identified that global mean PW values are systematically much lower in CMIP5 models than in observations. This dry bias is most profound over the tropical ocean. The dry bias is partly due to biases in sea surface temperatures in the CMIP5-coupled climate models. However, the dry bias is also present in Atmospheric Model Intercomparison Project (AMIP) experiments, which implies the existence of other factors. The relationship between PW and rainfall characteristics shows that rainfall occurs when water vapor levels are lower than in observations, particularly in models with a relatively strong dry bias. This suggests that the reproducibility of rainfall characteristics may be associated with the dry bias.","PeriodicalId":17476,"journal":{"name":"Journal of the Meteorological Society of Japan","volume":"96 1","pages":"415-423"},"PeriodicalIF":3.1,"publicationDate":"2018-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45495740","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, the response of tropical cyclone (TC) activity to El Niño-Southern Oscillation (ENSO) and coherent sea surface temperature anomaly (SSTA) in the Indian Ocean (IO) is investigated, with a particular focus on the decaying phase of El Niño. The TC anomalies are obtained from the database for Policy Decision making for Future climate change (d4PDF). This dataset is based on 100-member ensemble simulations for the period of 1951 – 2010 using the state-of-the-art atmospheric general circulation model (AGCM) forced with the observed SST as well as the historical radiative forcing. The AGCM utilized in the d4PDF is the Meteorological Research Institute Atmospheric General Circulation Model (MRI-AGCM) with about 60 km horizontal resolution. Our analysis revealed a prolonged decrease in TC frequency (TCF) over the tropical Western Pacific during the postEl Niño years until the boreal fall. Dominance of anomalous anticyclone (AAC) over the Western Pacific induced by the delayed warming in the tropical IO is the main factor for the suppressed TC activity rather than the local SST change. In contrast, the TC number over the South China Sea tends to increase during the post-El Niño fall (September to November). The physical reason can be ascribed to the weakening of the AAC associated with the termination of IO warming. Thus, we demonstrate that the effect of the IO warming should be taken into account when the ENSO is considered as an environmental factor for predicting TC activity.
{"title":"Seasonal Modulation of Tropical Cyclone Occurrence Associated with Coherent Indo-Pacific Variability during Decaying Phase of El Niño","authors":"H. Ueda, Kana Miwa, Y. Kamae","doi":"10.2151/JMSJ.2018-044","DOIUrl":"https://doi.org/10.2151/JMSJ.2018-044","url":null,"abstract":"In this paper, the response of tropical cyclone (TC) activity to El Niño-Southern Oscillation (ENSO) and coherent sea surface temperature anomaly (SSTA) in the Indian Ocean (IO) is investigated, with a particular focus on the decaying phase of El Niño. The TC anomalies are obtained from the database for Policy Decision making for Future climate change (d4PDF). This dataset is based on 100-member ensemble simulations for the period of 1951 – 2010 using the state-of-the-art atmospheric general circulation model (AGCM) forced with the observed SST as well as the historical radiative forcing. The AGCM utilized in the d4PDF is the Meteorological Research Institute Atmospheric General Circulation Model (MRI-AGCM) with about 60 km horizontal resolution. Our analysis revealed a prolonged decrease in TC frequency (TCF) over the tropical Western Pacific during the postEl Niño years until the boreal fall. Dominance of anomalous anticyclone (AAC) over the Western Pacific induced by the delayed warming in the tropical IO is the main factor for the suppressed TC activity rather than the local SST change. In contrast, the TC number over the South China Sea tends to increase during the post-El Niño fall (September to November). The physical reason can be ascribed to the weakening of the AAC associated with the termination of IO warming. Thus, we demonstrate that the effect of the IO warming should be taken into account when the ENSO is considered as an environmental factor for predicting TC activity.","PeriodicalId":17476,"journal":{"name":"Journal of the Meteorological Society of Japan","volume":"96 1","pages":"381-390"},"PeriodicalIF":3.1,"publicationDate":"2018-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42891040","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Kawabata, H. Bauer, T. Schwitalla, V. Wulfmeyer, A. Adachi
In the preparation for polarimetric radar data assimilation, it is essential to examine the accuracy of forward operators based on different formulations. For this purpose, four forward operators that focus on warm rain conditions are compared both with each other and actual observations with respect to their performance for C-band dual polarimetric radars. These operators mutually consider radar beam broadening and climatological beam bending. The first operator derives polarimetric parameters assuming an exponential raindrop size distribution obtained by the models and is based on fitting functions against scattering amplitudes. The other three converters estimate the mixing ratio of rainwater from the measured polarimetric parameters. The second converter uses both the horizontal reflectivity (ZH) and the differential reflectivity (ZDR), the third uses the specific differential phase (KDP), and the fourth uses both KDP and ZDR, respectively. Comparisons with modeled measurements show that the accuracy of the third converter is superior to the other two. Another evaluation with actual observations shows that the first converter has slightly higher fractions skill scores than the other three. Considering the attenuation effect, the fitting function and the operator only with KDP are found to be the most suitable for data assimilation at C-band.
{"title":"Evaluation of Forward Operators for Polarimetric Radars Aiming for Data Assimilation","authors":"T. Kawabata, H. Bauer, T. Schwitalla, V. Wulfmeyer, A. Adachi","doi":"10.2151/JMSJ.2018-017","DOIUrl":"https://doi.org/10.2151/JMSJ.2018-017","url":null,"abstract":"In the preparation for polarimetric radar data assimilation, it is essential to examine the accuracy of forward operators based on different formulations. For this purpose, four forward operators that focus on warm rain conditions are compared both with each other and actual observations with respect to their performance for C-band dual polarimetric radars. These operators mutually consider radar beam broadening and climatological beam bending. The first operator derives polarimetric parameters assuming an exponential raindrop size distribution obtained by the models and is based on fitting functions against scattering amplitudes. The other three converters estimate the mixing ratio of rainwater from the measured polarimetric parameters. The second converter uses both the horizontal reflectivity (ZH) and the differential reflectivity (ZDR), the third uses the specific differential phase (KDP), and the fourth uses both KDP and ZDR, respectively. Comparisons with modeled measurements show that the accuracy of the third converter is superior to the other two. Another evaluation with actual observations shows that the first converter has slightly higher fractions skill scores than the other three. Considering the attenuation effect, the fitting function and the operator only with KDP are found to be the most suitable for data assimilation at C-band.","PeriodicalId":17476,"journal":{"name":"Journal of the Meteorological Society of Japan","volume":"1 1","pages":"157-174"},"PeriodicalIF":3.1,"publicationDate":"2018-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2151/JMSJ.2018-017","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47715254","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"The Outer-Core Wind Structure of Tropical Cyclones","authors":"Kelvin T. F. Chan, J. Chan","doi":"10.2151/JMSJ.2018-042","DOIUrl":"https://doi.org/10.2151/JMSJ.2018-042","url":null,"abstract":"","PeriodicalId":17476,"journal":{"name":"Journal of the Meteorological Society of Japan","volume":"96 1","pages":"297-315"},"PeriodicalIF":3.1,"publicationDate":"2018-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2151/JMSJ.2018-042","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42494591","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The dependence of intensification rate (IR) of a tropical cyclone (TC) on its initial structure, 14 including the radius of maximum wind (RMW) and the radial decay rate of tangential wind 15 outside the RMW, is examined based on ensemble of simulations using a nonhydrostatic 16 axisymmetric cloud-resolving model. It is shown that the initial spinup period is shorter and the 17 subsequent IR is larger for the storm with the initially smaller RMW or with the initially more 18 rapid radial decay of tangential wind outside the RMW. The results show that the longevity of 19 the initial spinup period is determined by how quickly the inner-core region becomes nearly 20 saturated in the middle and lower troposphere and thus deep convection near the RMW is 21 initiated and organized. Because of the larger volume and weaker Ekman pumping, the 22 inner-core of the initially larger vortex takes longer time to become saturated and thus 23 experiences a longer initial spinup period. The vortex initially with the larger RMW (with the 24 slower radial decay of tangential wind outside the RMW) has lower inertial stability inside the 25 RMW (higher inertial stability outside the RMW) develops more active convection in the 26 outer-core region and weaker boundary-layer inflow in the inner-core region and thus 27 experiences lower IR during the primary intensification stage. vortices -1 day
{"title":"Effect of the Initial Vortex Structure on Intensification of a Numerically Simulated Tropical Cyclone","authors":"Jing Xu, Yuqing Wang","doi":"10.2151/JMSJ.2018-014","DOIUrl":"https://doi.org/10.2151/JMSJ.2018-014","url":null,"abstract":"The dependence of intensification rate (IR) of a tropical cyclone (TC) on its initial structure, 14 including the radius of maximum wind (RMW) and the radial decay rate of tangential wind 15 outside the RMW, is examined based on ensemble of simulations using a nonhydrostatic 16 axisymmetric cloud-resolving model. It is shown that the initial spinup period is shorter and the 17 subsequent IR is larger for the storm with the initially smaller RMW or with the initially more 18 rapid radial decay of tangential wind outside the RMW. The results show that the longevity of 19 the initial spinup period is determined by how quickly the inner-core region becomes nearly 20 saturated in the middle and lower troposphere and thus deep convection near the RMW is 21 initiated and organized. Because of the larger volume and weaker Ekman pumping, the 22 inner-core of the initially larger vortex takes longer time to become saturated and thus 23 experiences a longer initial spinup period. The vortex initially with the larger RMW (with the 24 slower radial decay of tangential wind outside the RMW) has lower inertial stability inside the 25 RMW (higher inertial stability outside the RMW) develops more active convection in the 26 outer-core region and weaker boundary-layer inflow in the inner-core region and thus 27 experiences lower IR during the primary intensification stage. vortices -1 day","PeriodicalId":17476,"journal":{"name":"Journal of the Meteorological Society of Japan","volume":"96 1","pages":"111-126"},"PeriodicalIF":3.1,"publicationDate":"2018-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2151/JMSJ.2018-014","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46177951","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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