In this study,the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) is used to simulate Typhoon Mindulle (2004) at high resolution (3-km grid size...In this study,the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) is used to simulate Typhoon Mindulle (2004) at high resolution (3-km grid size).The data from measurements show that in the upper atmosphere the existence of an upper jet is important to the transition cyclone.When Mindulle moved to the area of the upper jet entrance,where high-altitude divergence existed, the pumping of the high-altitude divergence would enhance the vertical motion and low-level cyclone convergence. The enhanced vertical motion was confirmed by the simulation results and indicated that the existence of upper divergence enhanced the vertical motion which was favorable for the maintenance of Typhoon Mindulle.The process of extratropical transition (ET) and re-intensification always accompanies the process of cold air invasion. This process enhances the baroclinicity of the atmosphere and the formation of front at high altitudes, which converts baroclinic potential energy into kinetic energy and strengthens the cyclone vortex.The distributions of equivalent potential temperature (θe) and temperature anomalies show that the warm-core of the typhoon at the tropopause aids the re-intensification of the system. As the typhoon reenters the ocean, latent heat flux (LHF) increases in the north and west and the strong reflectivity and vertical motion occur in the east and southeast,and the west.With the re-intensification of the typhoon the wind field evolves from an oval to a circle at the lower atmosphere, the area coverage by high winds increases, and the distribution of the tangential wind shows an asymmetric pattern.展开更多
In order to investigate the global distributions of temporal variations of OH and O2 nightglow emissions,we statistically analyzed their variations with altitude,local time,and season,using the OH and O2 airglow emiss...In order to investigate the global distributions of temporal variations of OH and O2 nightglow emissions,we statistically analyzed their variations with altitude,local time,and season,using the OH and O2 airglow emission rate data observed by the TIMED satellite between 2002 and 2009.The results indicated that the OH nightglow emission was stronger than dayglow emission and the O2 nightglow emission was weaker than dayglow emission.In the tropics,the OH nightglow intensity reached its maximum near midnight;at higher latitudes,the OH nightglow intensities after sunset and before sunrise were much strong.At the equinoxes,the O2 nightglow intensity in the tropics decreased with local time;at the solstices,the local time-latitude distribution of the O2 nightglow intensity had a valley(with weak emission).As for the altitude-latitude distributions of nightglow emission rates,the distribution for OH nightglow at the equinoxes had one peak(with strong emission)at the equator,with a peak height around 85 km;the peak for the March equinox was stronger than that for the September equinox.The distribution for O2 nightglow at the equinoxes had three peaks,lying at 30°in the spring and autumn hemispheres and at the equator,and the peak height at the equator was the lowest.The distributions for both OH and O2 nightglow emissions at the solstices had three peaks.Both nightglow intensities in the tropics had obvious annual and semi-annual variations,the peaks and valleys for semi-annual variations appeared near the equinoxes and solstices,respectively,and the peak at the March equinox was larger than that at the September equinox.The distributions of both OH and O2 nightglow intensities showed a hemispheric asymmetry.展开更多
基金supported by the National Natural Science Foundation of China(Nos.40876004,40890155 and 40675060)National 973 Project(Nos.2009CB-421500 and 2007CB411801)
文摘In this study,the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) is used to simulate Typhoon Mindulle (2004) at high resolution (3-km grid size).The data from measurements show that in the upper atmosphere the existence of an upper jet is important to the transition cyclone.When Mindulle moved to the area of the upper jet entrance,where high-altitude divergence existed, the pumping of the high-altitude divergence would enhance the vertical motion and low-level cyclone convergence. The enhanced vertical motion was confirmed by the simulation results and indicated that the existence of upper divergence enhanced the vertical motion which was favorable for the maintenance of Typhoon Mindulle.The process of extratropical transition (ET) and re-intensification always accompanies the process of cold air invasion. This process enhances the baroclinicity of the atmosphere and the formation of front at high altitudes, which converts baroclinic potential energy into kinetic energy and strengthens the cyclone vortex.The distributions of equivalent potential temperature (θe) and temperature anomalies show that the warm-core of the typhoon at the tropopause aids the re-intensification of the system. As the typhoon reenters the ocean, latent heat flux (LHF) increases in the north and west and the strong reflectivity and vertical motion occur in the east and southeast,and the west.With the re-intensification of the typhoon the wind field evolves from an oval to a circle at the lower atmosphere, the area coverage by high winds increases, and the distribution of the tangential wind shows an asymmetric pattern.
基金supported by the National Natural Science Foundation of China(Grant Nos.40874080,40890165,40911120063,41004062)the National Basic Research Program of China("973"Project)(Grant No.2006CB806306)+1 种基金China Postdoctoral Science Foundation Funded Project(Grnat No.20100481450)the Specialized Research Fund for State Key Laboratories
文摘In order to investigate the global distributions of temporal variations of OH and O2 nightglow emissions,we statistically analyzed their variations with altitude,local time,and season,using the OH and O2 airglow emission rate data observed by the TIMED satellite between 2002 and 2009.The results indicated that the OH nightglow emission was stronger than dayglow emission and the O2 nightglow emission was weaker than dayglow emission.In the tropics,the OH nightglow intensity reached its maximum near midnight;at higher latitudes,the OH nightglow intensities after sunset and before sunrise were much strong.At the equinoxes,the O2 nightglow intensity in the tropics decreased with local time;at the solstices,the local time-latitude distribution of the O2 nightglow intensity had a valley(with weak emission).As for the altitude-latitude distributions of nightglow emission rates,the distribution for OH nightglow at the equinoxes had one peak(with strong emission)at the equator,with a peak height around 85 km;the peak for the March equinox was stronger than that for the September equinox.The distribution for O2 nightglow at the equinoxes had three peaks,lying at 30°in the spring and autumn hemispheres and at the equator,and the peak height at the equator was the lowest.The distributions for both OH and O2 nightglow emissions at the solstices had three peaks.Both nightglow intensities in the tropics had obvious annual and semi-annual variations,the peaks and valleys for semi-annual variations appeared near the equinoxes and solstices,respectively,and the peak at the March equinox was larger than that at the September equinox.The distributions of both OH and O2 nightglow intensities showed a hemispheric asymmetry.
