By use of the 2-m Mcmath-Pierce telescope at Kitt Peak, the high-quality spectra of a plage with moderate brightness near the center of solar disk were obtained. The data include seven spectral lines, which are Hα, H...By use of the 2-m Mcmath-Pierce telescope at Kitt Peak, the high-quality spectra of a plage with moderate brightness near the center of solar disk were obtained. The data include seven spectral lines, which are Hα, Hβ, Call H and K lines and the infrared triplet. With the con- sideration of fine structures of solar plages, a two-component atmospheric model is constructed by keeping the cool component to be the quiet atmosphere. Three cases of the hot component are given for different filling factors where the temperature and density distribution are adjusted in or- der to reproduce the seven observed spectral profiles. We also briefly discuss the influence of the column density at the base of the corona, m_0, and the macro-turbulent velocity on the required filling factor and computed profiles. The two-component model is compared with precious one-component semi-empirical models. The limitation of the model is pointed out and further im- provement is indicated.展开更多
By use of the 2-m McMath-Pierce telescope at Kitt Peak, the high-quality spectra of a moderate-brightness plage near the center of solar disk were obtained. The data include seven spectral lines: Hα, Hβ, Call H and ...By use of the 2-m McMath-Pierce telescope at Kitt Peak, the high-quality spectra of a moderate-brightness plage near the center of solar disk were obtained. The data include seven spectral lines: Hα, Hβ, Call H and K lines and infrared triplet. Under the assumption of plane-parallel atmosphere, the hydrostatic, transfer and statistic equilibrium equations were solved iteratively and the semi-empirical model of the plage has been obtained. It can well reproduce the observed seven line profiles. The model has been compared with two existing plage models. Further improvement has also been discussed.展开更多
In order to evaluate how much Total Solar Irradiance(TSI)has influenced Northern Hemisphere surface air temperature trends,it is important to have reliable estimates of both quantities.Sixteen different estimates of t...In order to evaluate how much Total Solar Irradiance(TSI)has influenced Northern Hemisphere surface air temperature trends,it is important to have reliable estimates of both quantities.Sixteen different estimates of the changes in TSI since at least the 19th century were compiled from the literature.Half of these estimates are"low variability"and half are"high variability".Meanwhile,five largely-independent methods for estimating Northern Hemisphere temperature trends were evaluated using:1)only rural weather stations;2)all available stations whether urban or rural(the standard approach);3)only sea surface temperatures;4)tree-ring widths as temperature proxies;5)glacier length records as temperature proxies.The standard estimates which use urban as well as rural stations were somewhat anomalous as they implied a much greater warming in recent decades than the other estimates,suggesting that urbanization bias might still be a problem in current global temperature datasets-despite the conclusions of some earlier studies.Nonetheless,all five estimates confirm that it is currently warmer than the late 19th century,i.e.,there has been some"global warming"since the 19th century.For each of the five estimates of Northern Hemisphere temperatures,the contribution from direct solar forcing for all sixteen estimates of TSI was evaluated using simple linear least-squares fitting.The role of human activity on recent warming was then calculated by fitting the residuals to the UN IPCC’s recommended"anthropogenic forcings"time series.For all five Northern Hemisphere temperature series,different TSI estimates suggest everything from no role for the Sun in recent decades(implying that recent global warming is mostly human-caused)to most of the recent global warming being due to changes in solar activity(that is,that recent global warming is mostly natural).It appears that previous studies(including the most recent IPCC reports)which had prematurely concluded the former,had done so because they failed to adequately consider all the relevant estimates of TSI and/or to satisfactorily address the uncertainties still associated with Northern Hemisphere temperature trend estimates.Therefore,several recommendations on how the scientific community can more satisfactorily resolve these issues are provided.展开更多
Investigating the length scales of granules could help understand the dynamics of granules in the photosphere.In this work,we detected and identified granules in an active region near disk center observed at wavelengt...Investigating the length scales of granules could help understand the dynamics of granules in the photosphere.In this work,we detected and identified granules in an active region near disk center observed at wavelength of TiO(7057?)by the 1.6 m Goode Solar Telescope(GST).By a detailed analysis of the size distribution and flatness of granules,we found a critical size that divides the granules in motions into two regimes:convection and turbulence.The length scales of granules with sizes larger than 600 km follow Gauss function and demonstrate“flat”in flatness,which reveal that these granules are dominated by convection.Those with sizes smaller than 600 km follow power-law function and behave power-law tendency in flatness,which indicate that the small granules are dominated by turbulence.Hence,for the granules in active regions,they are originally convective in large length scale,and directly become turbulent once their sizes turn to small,likely below the critical size of 600 km.Comparing with the granules in quiet regions,they evolve with the absence of the mixing motions of convection and turbulence.Such a difference is probably caused by the interaction between fluid motions and strong magnetic fields in active regions.The strong magnetic fields make high magnetic pressure which creates pressure walls and slows down the evolution of convective granules.Such walls cause convective granules extending to smaller sizes on one hand,and cause wide intergranular lanes on the other hand.The small granules isolated in such wide intergranular lanes are continually sheared,rotated by strong downflows in surroundings and hereby become turbulent.展开更多
基金the National Natural Science Foundation of China (Grant No. 10025315) NKBRSF (Grant No. G2000078402) TRAPOYT.
文摘By use of the 2-m Mcmath-Pierce telescope at Kitt Peak, the high-quality spectra of a plage with moderate brightness near the center of solar disk were obtained. The data include seven spectral lines, which are Hα, Hβ, Call H and K lines and the infrared triplet. With the con- sideration of fine structures of solar plages, a two-component atmospheric model is constructed by keeping the cool component to be the quiet atmosphere. Three cases of the hot component are given for different filling factors where the temperature and density distribution are adjusted in or- der to reproduce the seven observed spectral profiles. We also briefly discuss the influence of the column density at the base of the corona, m_0, and the macro-turbulent velocity on the required filling factor and computed profiles. The two-component model is compared with precious one-component semi-empirical models. The limitation of the model is pointed out and further im- provement is indicated.
基金This work was partly supported by a key project from the Ministry of Science and Technology ofChina and by the National Natural Science Foundation of China (Grant No. 49990451) from the Doctoral Program of the Ministry of Education of China.
文摘By use of the 2-m McMath-Pierce telescope at Kitt Peak, the high-quality spectra of a moderate-brightness plage near the center of solar disk were obtained. The data include seven spectral lines: Hα, Hβ, Call H and K lines and infrared triplet. Under the assumption of plane-parallel atmosphere, the hydrostatic, transfer and statistic equilibrium equations were solved iteratively and the semi-empirical model of the plage has been obtained. It can well reproduce the observed seven line profiles. The model has been compared with two existing plage models. Further improvement has also been discussed.
基金financial support from the Center for Environmental Research and Earth Sciences(CERES)support from NASA+2 种基金NSFTennessee State Universitythe State of Tennessee through its Centers of Excellence program。
文摘In order to evaluate how much Total Solar Irradiance(TSI)has influenced Northern Hemisphere surface air temperature trends,it is important to have reliable estimates of both quantities.Sixteen different estimates of the changes in TSI since at least the 19th century were compiled from the literature.Half of these estimates are"low variability"and half are"high variability".Meanwhile,five largely-independent methods for estimating Northern Hemisphere temperature trends were evaluated using:1)only rural weather stations;2)all available stations whether urban or rural(the standard approach);3)only sea surface temperatures;4)tree-ring widths as temperature proxies;5)glacier length records as temperature proxies.The standard estimates which use urban as well as rural stations were somewhat anomalous as they implied a much greater warming in recent decades than the other estimates,suggesting that urbanization bias might still be a problem in current global temperature datasets-despite the conclusions of some earlier studies.Nonetheless,all five estimates confirm that it is currently warmer than the late 19th century,i.e.,there has been some"global warming"since the 19th century.For each of the five estimates of Northern Hemisphere temperatures,the contribution from direct solar forcing for all sixteen estimates of TSI was evaluated using simple linear least-squares fitting.The role of human activity on recent warming was then calculated by fitting the residuals to the UN IPCC’s recommended"anthropogenic forcings"time series.For all five Northern Hemisphere temperature series,different TSI estimates suggest everything from no role for the Sun in recent decades(implying that recent global warming is mostly human-caused)to most of the recent global warming being due to changes in solar activity(that is,that recent global warming is mostly natural).It appears that previous studies(including the most recent IPCC reports)which had prematurely concluded the former,had done so because they failed to adequately consider all the relevant estimates of TSI and/or to satisfactorily address the uncertainties still associated with Northern Hemisphere temperature trend estimates.Therefore,several recommendations on how the scientific community can more satisfactorily resolve these issues are provided.
基金the National Natural Science Foundation of China(Nos.41822404,11973083,42074205,11763004,11729301,11803005,12111530078 and 12173012)Shenzhen Technology Project(JCYJ20190806142609035 and GXWD 20201230155427003-20200804151658001)。
文摘Investigating the length scales of granules could help understand the dynamics of granules in the photosphere.In this work,we detected and identified granules in an active region near disk center observed at wavelength of TiO(7057?)by the 1.6 m Goode Solar Telescope(GST).By a detailed analysis of the size distribution and flatness of granules,we found a critical size that divides the granules in motions into two regimes:convection and turbulence.The length scales of granules with sizes larger than 600 km follow Gauss function and demonstrate“flat”in flatness,which reveal that these granules are dominated by convection.Those with sizes smaller than 600 km follow power-law function and behave power-law tendency in flatness,which indicate that the small granules are dominated by turbulence.Hence,for the granules in active regions,they are originally convective in large length scale,and directly become turbulent once their sizes turn to small,likely below the critical size of 600 km.Comparing with the granules in quiet regions,they evolve with the absence of the mixing motions of convection and turbulence.Such a difference is probably caused by the interaction between fluid motions and strong magnetic fields in active regions.The strong magnetic fields make high magnetic pressure which creates pressure walls and slows down the evolution of convective granules.Such walls cause convective granules extending to smaller sizes on one hand,and cause wide intergranular lanes on the other hand.The small granules isolated in such wide intergranular lanes are continually sheared,rotated by strong downflows in surroundings and hereby become turbulent.
