Previous statistical analyses of a large number of SOHO/MDI full disk longitudinal magnetograms provided a result that demonstrated how responses of solar flares to photospheric magnetic properties can be fitted with ...Previous statistical analyses of a large number of SOHO/MDI full disk longitudinal magnetograms provided a result that demonstrated how responses of solar flares to photospheric magnetic properties can be fitted with sigmoid functions. A logistic model reveals that these fitted sigmoid functions might be related to the free energy storage process in solar active regions. Although this suggested model is rather simple, the free energy level of active regions can be estimated and the probability of a solar flare with importance over a threshold can be forecast within a given time window.展开更多
From the observed vector magnetic fields by the Solar Optical Telescope/ Spectro-Polarimeter aboard the satellite Hinode, we have examined whether or not the quiet Sun magnetic fields are non-potential, and how the G-...From the observed vector magnetic fields by the Solar Optical Telescope/ Spectro-Polarimeter aboard the satellite Hinode, we have examined whether or not the quiet Sun magnetic fields are non-potential, and how the G-band filigrees and Ca II network bright points （NBPs） are associated with the magnetic non-potentiality. A sizable quiet region in the disk center is selected for this study. The new findings by the study are as follows. （1） The magnetic fields of the quiet region are obviously non-potential. The region-average shear angle is 40°, the average vertical current is 0.016A m^-2, and the average free magnetic energy density, 2.7× 10^2erg cm^-3. The magnitude of these non-potential quantities is comparable to that in solar active regions. （2） There are overall correlations among current helicity, free magnetic energy and longitudinal fields. The magnetic non-potentiality is mostly concentrated in the close vicinity of network elements which have stronger longitudinal fields. （3） The filigrees and NBPs are magnetically characterized by strong longitudinal fields, large electric helicity, and high free energy density. Because the selected region is away from any enhanced network, these new results can generally be applied to the quiet Sun. The findings imply that stronger network elements play a role in high magnetic non-potentiality in heating the solar atmosphere and in conducting the solar wind.展开更多
We present properties of intensity oscillations of a sunspot in the photo- sphere and chromosphere using G band and Ca u H filtergrams from Hinode. Intensity power maps as function of magnetic field strength and frequ...We present properties of intensity oscillations of a sunspot in the photo- sphere and chromosphere using G band and Ca u H filtergrams from Hinode. Intensity power maps as function of magnetic field strength and frequency reveal reduction of power in the G band with an increase in photospheric magnetic field strength at all frequencies. In Ca II H, however, stronger fields exhibit more power at high frequen- cies, particularly in the 4.5-8.0 mHz band. Power distributions in different locations of the active region show that the oscillations in Ca II H exhibit more power compared to that of the G band. We also relate the power in intensity oscillations with differ- ent components of the photospheric vector magnetic field using near simultaneous spectro-polarimetric observations of the sunspot from the Hinode spectropolarime- ter. The photospheric umbral power is strongly anti-correlated with the magnetic field strength and its line-of-sight component but there is a good correlation with the trans- verse component. A reversal of this trend is observed in the chromosphere except at low frequencies （V≤ 1.5 mHz）. The power in sunspot penumbrae is anti-correlated with the magnetic field parameters at all frequencies （1.0 ≤ v ≤ 8.0 mHz） in both the photosphere and chromosphere, except that the chromospheric power shows a strong correlation in the frequency range 3-3.5 mHz.展开更多
Using the Hilbert-Huang transform and the Lomb-Scargle method, we investigate periodicities in the daily solar radius data during the time interval from February 1978 to October 1999 derived from Caleru Observatory. T...Using the Hilbert-Huang transform and the Lomb-Scargle method, we investigate periodicities in the daily solar radius data during the time interval from February 1978 to October 1999 derived from Caleru Observatory. The following prominent periods are found： （1） the rotation cycle signal; （2） several mid-term periods including 122, 162.9 and 225 days, annual-variation periodicities （319 and 359 days）, quasi-triennial oscillations （3.46 and 3.94 years）; （3） the 11-year Schwabe cycle, which is in anti-phase with solar activity. This result indicates that the strong magnetic field associated with the Sun has a greater inhibitive effect on the radius variation.展开更多
The solar active region NOAA 11719 produced a large two-ribbon flare on 2013 April 11. We have investigated sudden variations in the photospheric magnetic fields in this active region during the flare by employing mag...The solar active region NOAA 11719 produced a large two-ribbon flare on 2013 April 11. We have investigated sudden variations in the photospheric magnetic fields in this active region during the flare by employing magnetograms obtained in the spectral line Fe I 6173 A acquired by the Helioseismic and Magnetic Imager （HMI） onboard the Solar Dynamics Observatory （SDO） spacecraft. The analysis of the line-of-sight magnetograms from HMI show sudden and persistent magnetic field changes at different locations of the active region before the onset of the flare and during the flare. The vector magnetic field observations available from HMI also show coincident variations in the total magnetic field strength and its inclination angle at these locations. Using the simultaneous Dopplergrams obtained from HMI, we observe perturbations in the photospheric Doppler signals following the sudden changes in the magnetic fields in the aforementioned locations. The power spectrum analysis of these velocity signals shows enhanced acoustic power in these affected locations during the flare as compared to the pre-flare condition. Accompanying these observations, we have also used nearly simultaneous chromospheric observations obtained in the spectral line Ha 6562.8 A by the Global Oscillation Network Group （GONG） to study the evolution of flare- ribbons and intensity oscillations in this active region. The Ha intensity oscillations also show enhanced oscillatory power during the flare in the aforementioned locations. These results indicate that the transient Lorentz force associated with sudden changes in the magnetic fields could drive localized photospheric and chromospheric oscillations, like the flare-induced oscillations in the solar atmosphere.展开更多
Observations indicate that Ellerman bombs （EBs） and chromospheric microflares both occur in the lower solar atmosphere,and share many common features,such as temperature enhancements,accompanying jet-like mass motio...Observations indicate that Ellerman bombs （EBs） and chromospheric microflares both occur in the lower solar atmosphere,and share many common features,such as temperature enhancements,accompanying jet-like mass motions,short life-time,and so on.These strongly suggest that EBs and chromospheric microflares could both probably be induced by magnetic reconnection in the lower solar atmosphere.With gravity,ionization and radiation considered,we perform two-dimensional numerical simulations of magnetic reconnection in the lower solar atmosphere.The influence of different parameters,such as intensity of the magnetic field and anomalous resistivity,on the results are investigated.Our result demonstrates that the temperature increases are mainly due to the joule dissipation caused by magnetic reconnection.The spectral profiles of EBs and chromospheric microflares are calculated with the non-LTE radiative transfer theory and compared with observations.It is found that the typical features of the two phenomena can be qualitatively reproduced.展开更多
Solar flares strongly influence space weather and human activities, and their prediction is highly complex. The existing solutions such as data based approaches and model based approaches have a common shortcoming whi...Solar flares strongly influence space weather and human activities, and their prediction is highly complex. The existing solutions such as data based approaches and model based approaches have a common shortcoming which is the lack of human engagement in the forecasting process. An image-case-based reasoning method is introduced to achieve this goal. The image case library is com- posed of SOHO/MDI longitudinal magnetograms, the images from which exhibit the maximum hori- zontal gradient, the length of the neutral line and the number of singular points that are extracted for retrieving similar image cases. Genetic optimization algorithms are employed for optimizing the weight assignment for image features and the number of similar image cases retrieved. Similar image cases and prediction results derived by majority voting for these similar image cases are output and shown to the forecaster in order to integrate his/her experience with the final prediction results. Experimental results demonstrate that the case-based reasoning approach has slightly better performance than other methods, and is more efficient with forecasts improved by humans.展开更多
Ellerman bombs （EBs） are small brightening events in the solar lower atmosphere. By their original definition, the main characteristic of EBs is the two emission bumps in both wings of chro- mospheric lines, such a...Ellerman bombs （EBs） are small brightening events in the solar lower atmosphere. By their original definition, the main characteristic of EBs is the two emission bumps in both wings of chro- mospheric lines, such as Hα and Ca II 8542A lines. Up to now, most authors have found that the temperature increase of EBs around the temperature minimum region is in the range of 600-3000 K. However, with recent IRIS observations, some authors proposed that the temperature increase of EBs could be more than 10 000 K. Using non-LTE semi-empirical modeling, we investigate the line profiles, continuum emission and radiative losses for EB models with different temperature increases, and com- pare them with observations. Our result indicates that if the EB maximum temperature reaches more than 10000K around the temperature minimum region, then the resulting Hα and Call 8542A line profiles and the continuum emission would be much stronger than those of EB observations. Moreover, due to the high radiative losses, a high temperature EB compatible with observations. Thus, our study does not higher than 10 000 K. would have a very short lifetime, which is not support the proposal that EB temperatures are higher than 10 000 K.展开更多
Dynamic processes occurring in solar active regions are dominated by the solar magnetic field. As of now, observations using a solar magnetograph have supplied us with the vector components of a solar photospheric mag...Dynamic processes occurring in solar active regions are dominated by the solar magnetic field. As of now, observations using a solar magnetograph have supplied us with the vector components of a solar photospheric magnetic field. The two transverse components of a photospheric magnetic field allow us to compute the amount of electric current. We found that the electric current in areas with positive （negative） polarity due to the longitudinal magnetic field have both positive and neg- ative signs in an active region, however, the net current is found to be an order-of- magnitude less than the mean absolute magnitude and has a preferred sign. In particu- lar, we have statistically found that there is a systematic net electric current from areas with negative （positive） polarity to areas with positive （negative） polarity in solar ac- tive regions in the northern （southern） hemisphere, but during the solar minimum this tendency is reversed over time at some latitudes. The result indicates that there is weak net electric current in areas of solar active regions with opposite polarity, thus provid- ing further details about the hemispheric helicity rule found in a series of previous studies.展开更多
Accurate measurement of magnetic fields is very important for understanding the formation and evolution of solar magnetic fields.Currently,there are two types of solar magnetic field measurement instruments:filter-bas...Accurate measurement of magnetic fields is very important for understanding the formation and evolution of solar magnetic fields.Currently,there are two types of solar magnetic field measurement instruments:filter-based magnetographs and Stokes polarimeters.The former gives high temporal resolution magnetograms and the latter provides more accurate measurements of magnetic fields.Calibrating the magnetograms obtained by filter-based magnetographs with those obtained by Stokes polarimeters is a good way to combine the advantages of the two types.Our previous studies have shown that,compared to the magnetograms obtained by the Spectro-Polarimeter(SP)on board Hinode,those magnetograms obtained by both the filter-based Solar Magnetic Field Telescope(SMFT)of the Huairou Solar Observing Station and by the filter-based Michelson Doppler Imager(MDI)aboard SOHO have underestimated the flux densities in their magnetograms and systematic center-to-limb variations present in the magnetograms of both instruments.Here,using a sample of 75 vector magnetograms of stable alpha sunspots,we compare the vector magnetograms obtained by the Helioseismic and Magnetic Imager(HMI)aboard Solar Dynamics Observatory(SDO)with co-temporal vector magnetograms acquired by SP/Hinode.Our analysis shows that both the longitudinal and transverse flux densities in the HMI/SDO magnetograms are very close to those in the SP/Hinode magnetograms and the systematic center-to-limb variations in the HMI/SDO magnetograms are very minor.Our study suggests that using a filter-based magnetograph to construct a low spectral resolution Stokes profile,as done by HMI/SDO,can largely remove the disadvantages of the filter-type measurements and yet still possess the advantage of high temporal resolution.展开更多
The Full-disk vector Magneto Graph(FMG)instrument will carry out polarization observations at one wavelength position of the Fe I 5324.179?spectral line.This paper describes how to choose this single wavelength positi...The Full-disk vector Magneto Graph(FMG)instrument will carry out polarization observations at one wavelength position of the Fe I 5324.179?spectral line.This paper describes how to choose this single wavelength position,the relevant data-processing and the magnetic field calibrations based on the measured polarization signals at one single wavelength position.It is found that solar radial Doppler velocity,which can cause the spectral line to shift,is a disadvantageous factor for the linear calibration at one wavelength position.Observations at two symmetric wavelength positions may significantly reduce the wavelength shift effect(~75%),but simulations show that such polarization signals located at the solar limbs(e.g.,beyond the longitude range of±30°)are not free from the effect completely.In future work,we plan to apply machine learning techniques to calibrate vector magnetic fields,or employ full Stokes parameter profile inversion techniques to obtain accurate vector magnetic fields,in order to complement the linear calibration at the single wavelength position.展开更多
It is reported that ultra-fine dynamic ejections along magnetic loops of an active region origi- nate from intergranular lanes and they are associated with subsequent heating in the corona. As continu- ing work, we an...It is reported that ultra-fine dynamic ejections along magnetic loops of an active region origi- nate from intergranular lanes and they are associated with subsequent heating in the corona. As continu- ing work, we analyze the same set of data but focus on a quiet region and the overlying EUV/UV emis- sion as observed by the Atmospheric Imaging Assembly （AIA） on board Solar Dynamics Observatory （SDO）. We find that there appear to be dark patches scattered across the quiet region and the dark patches always stay along intergranular lanes. Over the dark patches, the average UV/EUV emission at 131, 17 1, 304 and 1600 A （middle temperature） is more intense than that of other regions and EUV brightness is negatively correlated with 10830A intensity, though, such a trend does not exist for high temperature lines at 94, 193, 211 and 335 A. For the same quiet region, where both TiO 7057 A broad band images and 10830A filtergrams are available, contours for the darkest lane areas on TiO images and clark patches on 10830A filtergrams frequently differ in space. The results suggest that the dark patches do not simply reflect the areas with the darkest lanes but are associated with a kind of enhanced absorption （EA） at 10830A,. A strict definition for EA with narrow band 10830A filtergrams is found to be difficult. In this paper, we define enhanced absorption patches （EAPs） of a quiet region as the areas where emission is less than ,-90% of the mean intensity of the region. The value is equivalent to the average intensity along thin dark loops connecting two moss regions of the active region. A more strict definition for EAPs, say 88%, gives even more intense UV/EUV emission over those in the middle temperature range. The results provide further observational evidence that energy for heating the upper solar atmosphere comes from the intergranular lane area where the magnetic field is constantly brought in by convection motion in granules.展开更多
An algorithm was developed for identifying and tracking a magnetic bright point, or bright point （BP） for short, observed in both the photosphere （G-band） and chromosphere （Ca II H）, as well as for pairing a pho...An algorithm was developed for identifying and tracking a magnetic bright point, or bright point （BP） for short, observed in both the photosphere （G-band） and chromosphere （Ca II H）, as well as for pairing a photospheric BP （PBP） with its conjugate chromospheric BP （CBP）. Two sets of data observed by Hinode/SOT in the quiet Sun near the disk center were analyzed. About 278 PBP-CBP pairs were identified and tracked. Lifetimes of both the PBPs and CBPs follow an exponential distribution with average lifetimes of 174 s and 163 s, respectively. We found that the differences in appearance time, in disappearance time and in lifetime of the two kinds of BPs all follow Gaussian distributions,which may indicate that the mechanisms of PBP and CBP formation/disintegration are different. However, the lifetimes of PBPs and CBPs are positively correlated with one another, with a correlation coefficient of 0.8. Furthermore, we calculated the horizontal displacement between the PBP and its conjugate CBP, which follows a Gaussian function with an average and standard deviation of （67.7 ± 38.5）km. We also calculated the amplitude of the flux tube shape change which might be caused by MHD waves propagating along the flux tube, and found that it follows an exponential distribution very well.展开更多
Light bridges(LBs)are bright lanes that divide one sunspot umbra into two or more parts.Though frequently observed in sunspots,their formation mechanisms have rarely been studied and thus are not well understood.Here ...Light bridges(LBs)are bright lanes that divide one sunspot umbra into two or more parts.Though frequently observed in sunspots,their formation mechanisms have rarely been studied and thus are not well understood.Here we present results from the first statistical investigation on the formation of LBs.Using observations with the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory,we identified 144 LBs within 71 active regions(ARs)over the whole year of 2014.The formation processes of these LBs can be categorized into three groups:penumbral intrusion(type-A),sunspot merging(typeB)and umbral-dot emergence(type-C).The numbers of events in these three categories are 74,57 and 13,respectively.The duration of the LB formation process is mostly less than 40 hours,with an average of~20 hours.Most LBs have a maximum length of less than 20.For type-A LBs,we found a positive correlation between the LB length and the duration of the LB formation process,suggesting a similar speed of penumbral intrusion in different sunspots.展开更多
A multi-model integration method is proposed to develop a multi-source and heterogeneous model for short-term solar flare prediction. Different prediction models are constructed on the basis of extracted predictors fr...A multi-model integration method is proposed to develop a multi-source and heterogeneous model for short-term solar flare prediction. Different prediction models are constructed on the basis of extracted predictors from a pool of observation databases. The outputs of the base models are normal- ized first because these established models extract predictors from many data resources using different prediction methods. Then weighted integration of the base models is used to develop a multi-model integrated model （MIM）. The weight set that single models assign is optimized by a genetic algorithm. Seven base models and data from Solar and Heliospheric Observatory/Michelson Doppler Imager lon- gitudinal magnetograms are used to construct the MIM, and then its performance is evaluated by cross validation. Experimental results showed that the MIM outperforms any individual model in nearly every data group, and the richer the diversity of the base models, the better the performance of the MIM. Thus, integrating more diversified models, such as an expert system, a statistical model and a physical model, will greatly improve the performance of the MIM.展开更多
基金Supported by the National Natural Science Foundation of China
文摘Previous statistical analyses of a large number of SOHO/MDI full disk longitudinal magnetograms provided a result that demonstrated how responses of solar flares to photospheric magnetic properties can be fitted with sigmoid functions. A logistic model reveals that these fitted sigmoid functions might be related to the free energy storage process in solar active regions. Although this suggested model is rather simple, the free energy level of active regions can be estimated and the probability of a solar flare with importance over a threshold can be forecast within a given time window.
基金supported by the National Natural Science Foundation of China (10873020, 10703007, G10573025, 40674081, 10603008, 10733020 and 40890161)the Chinese Academy of Sciences Project KJCX2-YW-T04the National Basic Research Program of China(G2006CB806303)
文摘From the observed vector magnetic fields by the Solar Optical Telescope/ Spectro-Polarimeter aboard the satellite Hinode, we have examined whether or not the quiet Sun magnetic fields are non-potential, and how the G-band filigrees and Ca II network bright points （NBPs） are associated with the magnetic non-potentiality. A sizable quiet region in the disk center is selected for this study. The new findings by the study are as follows. （1） The magnetic fields of the quiet region are obviously non-potential. The region-average shear angle is 40°, the average vertical current is 0.016A m^-2, and the average free magnetic energy density, 2.7× 10^2erg cm^-3. The magnitude of these non-potential quantities is comparable to that in solar active regions. （2） There are overall correlations among current helicity, free magnetic energy and longitudinal fields. The magnetic non-potentiality is mostly concentrated in the close vicinity of network elements which have stronger longitudinal fields. （3） The filigrees and NBPs are magnetically characterized by strong longitudinal fields, large electric helicity, and high free energy density. Because the selected region is away from any enhanced network, these new results can generally be applied to the quiet Sun. The findings imply that stronger network elements play a role in high magnetic non-potentiality in heating the solar atmosphere and in conducting the solar wind.
基金Support for the post-launch operation is provided by JAXA and NAOJ (Japan), STFC (UK), NASA (USA), ESA and NSC (Norway)financial the German Science Foundation (DFG) under grant DE 787/3-1
文摘We present properties of intensity oscillations of a sunspot in the photo- sphere and chromosphere using G band and Ca u H filtergrams from Hinode. Intensity power maps as function of magnetic field strength and frequency reveal reduction of power in the G band with an increase in photospheric magnetic field strength at all frequencies. In Ca II H, however, stronger fields exhibit more power at high frequen- cies, particularly in the 4.5-8.0 mHz band. Power distributions in different locations of the active region show that the oscillations in Ca II H exhibit more power compared to that of the G band. We also relate the power in intensity oscillations with differ- ent components of the photospheric vector magnetic field using near simultaneous spectro-polarimetric observations of the sunspot from the Hinode spectropolarime- ter. The photospheric umbral power is strongly anti-correlated with the magnetic field strength and its line-of-sight component but there is a good correlation with the trans- verse component. A reversal of this trend is observed in the chromosphere except at low frequencies （V≤ 1.5 mHz）. The power in sunspot penumbrae is anti-correlated with the magnetic field parameters at all frequencies （1.0 ≤ v ≤ 8.0 mHz） in both the photosphere and chromosphere, except that the chromospheric power shows a strong correlation in the frequency range 3-3.5 mHz.
基金Supported by the National Natural Science Foundation of China
文摘Using the Hilbert-Huang transform and the Lomb-Scargle method, we investigate periodicities in the daily solar radius data during the time interval from February 1978 to October 1999 derived from Caleru Observatory. The following prominent periods are found： （1） the rotation cycle signal; （2） several mid-term periods including 122, 162.9 and 225 days, annual-variation periodicities （319 and 359 days）, quasi-triennial oscillations （3.46 and 3.94 years）; （3） the 11-year Schwabe cycle, which is in anti-phase with solar activity. This result indicates that the strong magnetic field associated with the Sun has a greater inhibitive effect on the radius variation.
文摘The solar active region NOAA 11719 produced a large two-ribbon flare on 2013 April 11. We have investigated sudden variations in the photospheric magnetic fields in this active region during the flare by employing magnetograms obtained in the spectral line Fe I 6173 A acquired by the Helioseismic and Magnetic Imager （HMI） onboard the Solar Dynamics Observatory （SDO） spacecraft. The analysis of the line-of-sight magnetograms from HMI show sudden and persistent magnetic field changes at different locations of the active region before the onset of the flare and during the flare. The vector magnetic field observations available from HMI also show coincident variations in the total magnetic field strength and its inclination angle at these locations. Using the simultaneous Dopplergrams obtained from HMI, we observe perturbations in the photospheric Doppler signals following the sudden changes in the magnetic fields in the aforementioned locations. The power spectrum analysis of these velocity signals shows enhanced acoustic power in these affected locations during the flare as compared to the pre-flare condition. Accompanying these observations, we have also used nearly simultaneous chromospheric observations obtained in the spectral line Ha 6562.8 A by the Global Oscillation Network Group （GONG） to study the evolution of flare- ribbons and intensity oscillations in this active region. The Ha intensity oscillations also show enhanced oscillatory power during the flare in the aforementioned locations. These results indicate that the transient Lorentz force associated with sudden changes in the magnetic fields could drive localized photospheric and chromospheric oscillations, like the flare-induced oscillations in the solar atmosphere.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10221001,10333040,10403003,10620150099,10610099 and 10673004)by the Major State Basic Research Development Program (973 project 2006CB806302)
文摘Observations indicate that Ellerman bombs （EBs） and chromospheric microflares both occur in the lower solar atmosphere,and share many common features,such as temperature enhancements,accompanying jet-like mass motions,short life-time,and so on.These strongly suggest that EBs and chromospheric microflares could both probably be induced by magnetic reconnection in the lower solar atmosphere.With gravity,ionization and radiation considered,we perform two-dimensional numerical simulations of magnetic reconnection in the lower solar atmosphere.The influence of different parameters,such as intensity of the magnetic field and anomalous resistivity,on the results are investigated.Our result demonstrates that the temperature increases are mainly due to the joule dissipation caused by magnetic reconnection.The spectral profiles of EBs and chromospheric microflares are calculated with the non-LTE radiative transfer theory and compared with observations.It is found that the typical features of the two phenomena can be qualitatively reproduced.
基金supported by the National Natural Science Foundation of China (Grant No. 11078010)
文摘Solar flares strongly influence space weather and human activities, and their prediction is highly complex. The existing solutions such as data based approaches and model based approaches have a common shortcoming which is the lack of human engagement in the forecasting process. An image-case-based reasoning method is introduced to achieve this goal. The image case library is com- posed of SOHO/MDI longitudinal magnetograms, the images from which exhibit the maximum hori- zontal gradient, the length of the neutral line and the number of singular points that are extracted for retrieving similar image cases. Genetic optimization algorithms are employed for optimizing the weight assignment for image features and the number of similar image cases retrieved. Similar image cases and prediction results derived by majority voting for these similar image cases are output and shown to the forecaster in order to integrate his/her experience with the final prediction results. Experimental results demonstrate that the case-based reasoning approach has slightly better performance than other methods, and is more efficient with forecasts improved by humans.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11533005,11025314,13001003,11203014 and 11103075)NKBRSF(Grant 2014CB744203)
文摘Ellerman bombs （EBs） are small brightening events in the solar lower atmosphere. By their original definition, the main characteristic of EBs is the two emission bumps in both wings of chro- mospheric lines, such as Hα and Ca II 8542A lines. Up to now, most authors have found that the temperature increase of EBs around the temperature minimum region is in the range of 600-3000 K. However, with recent IRIS observations, some authors proposed that the temperature increase of EBs could be more than 10 000 K. Using non-LTE semi-empirical modeling, we investigate the line profiles, continuum emission and radiative losses for EB models with different temperature increases, and com- pare them with observations. Our result indicates that if the EB maximum temperature reaches more than 10000K around the temperature minimum region, then the resulting Hα and Call 8542A line profiles and the continuum emission would be much stronger than those of EB observations. Moreover, due to the high radiative losses, a high temperature EB compatible with observations. Thus, our study does not higher than 10 000 K. would have a very short lifetime, which is not support the proposal that EB temperatures are higher than 10 000 K.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11273034, 11178005,41174153, 11173033 and 11103037)the National Basic Research Program of China (973 program,2011CB811401)Chinese Academy of Sciences under Grant KJCX2-EW-T07
文摘Dynamic processes occurring in solar active regions are dominated by the solar magnetic field. As of now, observations using a solar magnetograph have supplied us with the vector components of a solar photospheric magnetic field. The two transverse components of a photospheric magnetic field allow us to compute the amount of electric current. We found that the electric current in areas with positive （negative） polarity due to the longitudinal magnetic field have both positive and neg- ative signs in an active region, however, the net current is found to be an order-of- magnitude less than the mean absolute magnitude and has a preferred sign. In particu- lar, we have statistically found that there is a systematic net electric current from areas with negative （positive） polarity to areas with positive （negative） polarity in solar ac- tive regions in the northern （southern） hemisphere, but during the solar minimum this tendency is reversed over time at some latitudes. The result indicates that there is weak net electric current in areas of solar active regions with opposite polarity, thus provid- ing further details about the hemispheric helicity rule found in a series of previous studies.
基金supported by the National Natural Science Foundation of China(NSFC,grant No.11973056)the National Key R&D Program of China(grant No.2021YFA1600500)。
文摘Accurate measurement of magnetic fields is very important for understanding the formation and evolution of solar magnetic fields.Currently,there are two types of solar magnetic field measurement instruments:filter-based magnetographs and Stokes polarimeters.The former gives high temporal resolution magnetograms and the latter provides more accurate measurements of magnetic fields.Calibrating the magnetograms obtained by filter-based magnetographs with those obtained by Stokes polarimeters is a good way to combine the advantages of the two types.Our previous studies have shown that,compared to the magnetograms obtained by the Spectro-Polarimeter(SP)on board Hinode,those magnetograms obtained by both the filter-based Solar Magnetic Field Telescope(SMFT)of the Huairou Solar Observing Station and by the filter-based Michelson Doppler Imager(MDI)aboard SOHO have underestimated the flux densities in their magnetograms and systematic center-to-limb variations present in the magnetograms of both instruments.Here,using a sample of 75 vector magnetograms of stable alpha sunspots,we compare the vector magnetograms obtained by the Helioseismic and Magnetic Imager(HMI)aboard Solar Dynamics Observatory(SDO)with co-temporal vector magnetograms acquired by SP/Hinode.Our analysis shows that both the longitudinal and transverse flux densities in the HMI/SDO magnetograms are very close to those in the SP/Hinode magnetograms and the systematic center-to-limb variations in the HMI/SDO magnetograms are very minor.Our study suggests that using a filter-based magnetograph to construct a low spectral resolution Stokes profile,as done by HMI/SDO,can largely remove the disadvantages of the filter-type measurements and yet still possess the advantage of high temporal resolution.
基金supported by the Strategic Priority Research Program on Space Science, the Chinese Academy of Sciences (Grant Nos. XDA15320302, XDA15052200 and XDA15320102)the National Natural Science Foundation of China (Grant Nos. 11773038, 11703042, U1731241, 11427901, 11427803, 11473039 and U1831107)the 13th Fiveyear Informatization Plan of the Chinese Academy of Sciences (Grant No. XXH13505-04)
文摘The Full-disk vector Magneto Graph(FMG)instrument will carry out polarization observations at one wavelength position of the Fe I 5324.179?spectral line.This paper describes how to choose this single wavelength position,the relevant data-processing and the magnetic field calibrations based on the measured polarization signals at one single wavelength position.It is found that solar radial Doppler velocity,which can cause the spectral line to shift,is a disadvantageous factor for the linear calibration at one wavelength position.Observations at two symmetric wavelength positions may significantly reduce the wavelength shift effect(~75%),but simulations show that such polarization signals located at the solar limbs(e.g.,beyond the longitude range of±30°)are not free from the effect completely.In future work,we plan to apply machine learning techniques to calibrate vector magnetic fields,or employ full Stokes parameter profile inversion techniques to obtain accurate vector magnetic fields,in order to complement the linear calibration at the single wavelength position.
基金supported by NSFC grants (Nos. 11333009, 11428309 and 11573012)supported by NJIT, US NSF AGS 1250818 and NASA NNX13AG14G grants+1 种基金partly supported by the strategic priority research program of CAS under Grant No. XDB09000000by the Korea Astronomy and Space Science Institute and Seoul National University
文摘It is reported that ultra-fine dynamic ejections along magnetic loops of an active region origi- nate from intergranular lanes and they are associated with subsequent heating in the corona. As continu- ing work, we analyze the same set of data but focus on a quiet region and the overlying EUV/UV emis- sion as observed by the Atmospheric Imaging Assembly （AIA） on board Solar Dynamics Observatory （SDO）. We find that there appear to be dark patches scattered across the quiet region and the dark patches always stay along intergranular lanes. Over the dark patches, the average UV/EUV emission at 131, 17 1, 304 and 1600 A （middle temperature） is more intense than that of other regions and EUV brightness is negatively correlated with 10830A intensity, though, such a trend does not exist for high temperature lines at 94, 193, 211 and 335 A. For the same quiet region, where both TiO 7057 A broad band images and 10830A filtergrams are available, contours for the darkest lane areas on TiO images and clark patches on 10830A filtergrams frequently differ in space. The results suggest that the dark patches do not simply reflect the areas with the darkest lanes but are associated with a kind of enhanced absorption （EA） at 10830A,. A strict definition for EA with narrow band 10830A filtergrams is found to be difficult. In this paper, we define enhanced absorption patches （EAPs） of a quiet region as the areas where emission is less than ,-90% of the mean intensity of the region. The value is equivalent to the average intensity along thin dark loops connecting two moss regions of the active region. A more strict definition for EAPs, say 88%, gives even more intense UV/EUV emission over those in the middle temperature range. The results provide further observational evidence that energy for heating the upper solar atmosphere comes from the intergranular lane area where the magnetic field is constantly brought in by convection motion in granules.
基金supported by the CAS grants(XDA17010507,XDA15010900 and QYZDJ-SSWSLH012)the NationalBasic Research Program of China(973 Program,2013CBA01503)+1 种基金the National Natural Science Foundation of China(Grant Nos.U1631130,11333007 and 11763004)supported by a grant associated with the Project of the Group for Innovation of Yunnan Province
文摘An algorithm was developed for identifying and tracking a magnetic bright point, or bright point （BP） for short, observed in both the photosphere （G-band） and chromosphere （Ca II H）, as well as for pairing a photospheric BP （PBP） with its conjugate chromospheric BP （CBP）. Two sets of data observed by Hinode/SOT in the quiet Sun near the disk center were analyzed. About 278 PBP-CBP pairs were identified and tracked. Lifetimes of both the PBPs and CBPs follow an exponential distribution with average lifetimes of 174 s and 163 s, respectively. We found that the differences in appearance time, in disappearance time and in lifetime of the two kinds of BPs all follow Gaussian distributions,which may indicate that the mechanisms of PBP and CBP formation/disintegration are different. However, the lifetimes of PBPs and CBPs are positively correlated with one another, with a correlation coefficient of 0.8. Furthermore, we calculated the horizontal displacement between the PBP and its conjugate CBP, which follows a Gaussian function with an average and standard deviation of （67.7 ± 38.5）km. We also calculated the amplitude of the flux tube shape change which might be caused by MHD waves propagating along the flux tube, and found that it follows an exponential distribution very well.
基金supported by the National Natural Science Foundation of China(Grant Nos.11803002,11825301 and 11790304)the Strategic Priority Research Program of Chinese Academy of Sciences(XDA17040507)。
文摘Light bridges(LBs)are bright lanes that divide one sunspot umbra into two or more parts.Though frequently observed in sunspots,their formation mechanisms have rarely been studied and thus are not well understood.Here we present results from the first statistical investigation on the formation of LBs.Using observations with the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory,we identified 144 LBs within 71 active regions(ARs)over the whole year of 2014.The formation processes of these LBs can be categorized into three groups:penumbral intrusion(type-A),sunspot merging(typeB)and umbral-dot emergence(type-C).The numbers of events in these three categories are 74,57 and 13,respectively.The duration of the LB formation process is mostly less than 40 hours,with an average of~20 hours.Most LBs have a maximum length of less than 20.For type-A LBs,we found a positive correlation between the LB length and the duration of the LB formation process,suggesting a similar speed of penumbral intrusion in different sunspots.
基金supported by the National Natural Science Foundation of China(Grant No.11078010)SOHO is a project of international cooperation between the European Space Agency(ESA) and NASA
文摘A multi-model integration method is proposed to develop a multi-source and heterogeneous model for short-term solar flare prediction. Different prediction models are constructed on the basis of extracted predictors from a pool of observation databases. The outputs of the base models are normal- ized first because these established models extract predictors from many data resources using different prediction methods. Then weighted integration of the base models is used to develop a multi-model integrated model （MIM）. The weight set that single models assign is optimized by a genetic algorithm. Seven base models and data from Solar and Heliospheric Observatory/Michelson Doppler Imager lon- gitudinal magnetograms are used to construct the MIM, and then its performance is evaluated by cross validation. Experimental results showed that the MIM outperforms any individual model in nearly every data group, and the richer the diversity of the base models, the better the performance of the MIM. Thus, integrating more diversified models, such as an expert system, a statistical model and a physical model, will greatly improve the performance of the MIM.
