Ionospheric scintillation refers to rapid radio signal amplitude and phase fluctuations due to small-scale irregularities in the ionosphere.Occurring primarily at equatorial and low latitudes,scintillation is linked t...Ionospheric scintillation refers to rapid radio signal amplitude and phase fluctuations due to small-scale irregularities in the ionosphere.Occurring primarily at equatorial and low latitudes,scintillation is linked to equatorial plasma bubbles(EPBs),regions of depleted plasma density that form after sunset.Ionospheric scintillation typically occurs from post-sunset hours until midnight.Post-sunset EPBs can be enhanced or suppressed during geomagnetic storms,depending on local sunset timing and how it relates to the storm's main or recovery phases.This study analyzes ionospheric scintillation in Indonesia,located at low geomagnetic and geographic latitudes,during geomagnetic events from 2003 to 2024.Using the S4 index,scintillation was examined with data from seven observation stations during geomagnetic storm events.Geomagnetic activity was evaluated using Dst,SYM-H,and AE indices,employing Superposed Epoch Analysis(SEA)to assess scintillation occurrence linked to minimum SYM-H,defined as epoch 0 to represent the storm peak or the onset of recovery phase in each event.The analysis categorized geomagnetic storms into weak-moderate(–100 nT<min.Dst≤–30 nT)and strong(min.Dst≤–100 nT),and examined their dependence on the local time of minimum SYM-H.Results indicate that scintillation first appears~6 hours after epoch 0 in weak-moderate geomagnetic storms,and~12 hours after epoch 0 in strong geomagnetic storms.The average AE index returns to its baseline value(quiet condition)~6 and~12 hours after epoch 0 for weak-moderate and strong geomagnetic storms,respectively.Further analysis based on the classification of the local time of epoch 0 shows that scintillation occurrence is not observed in post-sunset hours when epoch 0 falls between 16:00 and 19:00 LT for weak-moderate geomagnetic storms.In strong geomagnetic storms,scintillation occurrence during post-sunset hours is absent when epoch 0 is between 10:00 and 19:00 LT.Notably,when the minimum SYM-H(epoch 0)nearly coincides with local sunset,scintillation activity occurs around sunset in both weak-moderate and strong geomagnetic storms.Furthermore,when epoch 0 falls within midnight until early morning,scintillation can be generated in the post-sunset hours before epoch 0.Still,post-midnight scintillation is not observed in the equatorial region during the recovery phase of either weak-moderate and strong storm events.Our findings show that when sunset falls before or coincide with epoch 0,the likelihood of post-sunset EPB and scintillation increases,due to the prompt-penetration electric field(PPEF)in the main phase of storm.The disturbance dynamo electric field(DDEF)in the recovery phase driven by equatorward winds from auroral Joule heating operates for at least 6-and 12-hours post-epoch 0 in the cases of weak-moderate and strong geomagnetic storms,respectively.When the local sunset falls within these operational DDEF periods,post-sunset EPBs will likely be suppressed,inhibiting ionospheric scintillation during post-sunset hours.Finally,this study provides essential information for developing more accurate ionospheric scintillation prediction models in space weather services in equatorial regions.展开更多
Flash drought is characterized by a period of rapid drought intensification with impacts on agriculture,water resources,ecosystems,and human environment.In the Qilian Mountains,northwestern China,flash droughts are be...Flash drought is characterized by a period of rapid drought intensification with impacts on agriculture,water resources,ecosystems,and human environment.In the Qilian Mountains,northwestern China,flash droughts are becoming more frequently due to the global climate warming.However,the spatiotemporal variations and their driving factors of flash droughts are not clear in this region.In this study,the European Centre for Medium-range Weather Forecasts(ECMWF)Reanalysis v5-Land(ERA5-Land)dataset was utilized to identify two types of flash drought events(heatwave-induced and water scarcity-induced flash drought events)that occurred in the growing season(April‒September)during 1981-2020 in this area.The results showed that the frequency of heatwave-induced flash droughts has decreased since 2010,while the frequency of water scarcity-induced flash droughts has declined markedly.Spatially,heatwave-induced flash droughts were predominantly concentrated in the western Qilian Mountains,whereas water scarcity-induced flash droughts were primarily concentrated in the central and eastern Qilian Mountains.A significantly increasing temporal trend in both types of flash droughts in the eastern Qilian Mountains was found.Meanwhile,there was a decreasing temporal trend of heatwave-induced flash droughts in the southwestern part of the region.Additionally,the influence of two major atmospheric modes,i.e.,the El Niño‒Southern Oscillation(ENSO)and North Atlantic Oscillation(NAO),on these two types of flash droughts was explored by the Superposed Epoch Analysis.The ENSO mainly influences flash droughts in the central and eastern parts of the Qilian Mountains by altering the strength of the East Asian monsoon,while the NAO mainly affects flash droughts in the entire parts of the Qilian Mountains by inducing anomalous westerlies activity.Our findings have important implications for predicting the evolution of flash drought events in the Qilian Mountains region under continued climate warming.展开更多
Based on the data from the Medium-Energy Proton and Electron Detector （MEPED） onboard NOAA-17, 141 anomalies of a Chinese Sun-Synchronous satellite （SSO-X） that occurred between 02/01/2010 and 09/31/2012 were stud...Based on the data from the Medium-Energy Proton and Electron Detector （MEPED） onboard NOAA-17, 141 anomalies of a Chinese Sun-Synchronous satellite （SSO-X） that occurred between 02/01/2010 and 09/31/2012 were studied statistically. About 26 out of the 52 anomalies that occurred outside the South Atlantic Anomaly （SAA） were accompanied by energetic electron storms. Superposed Epoch Analysis （SEA） was used to analyze the properties of the anomalies and the dynamics of the space environments during these 26 events. Then, a Monte Carlo method was utilized to simulate the electron deposition and the interactions of the injected electrons with an aluminum shield and polyethylene dielectric. The average, median, and 75tb percentile values of the maximum electric field strength inside the dielectric were calculated. The results showed the tbl- lowing. （1） SSO-X anomalies are more likely to occur within the SAA, as 89 out of 141 anomalies （63%） occurred there. （2） Twenty-six of the anomalies that occurred outside the SAA during energetic electron storms were located near the outer boundaries of the outer radiation belts, and these were more frequent in the Southern Hemisphere than in the Northern Hemi- sphere. （3） Electron flux enhancements occurred around the failure time at all energy levels but were more profound in the lower energy channels. The maximum fluxes of electrons 〉30 keV, 〉100 keV, and 〉300 keV were 106, 3.5x10s, and 1.2×10^6 cm 2 s^-1 · sr ^-1, respectively. （4） The average, median, and 75th percentile values of the maximum electric field strengths inside the dielectric for the aforementioned 26 events remained in the range from 106 to 107 V/m for long time periods, which sug- gests that the ＇potential hazards＇ of internal discharges cause SSO-X anomalies. The above results can provide useful infor- mation for the design and protection of sun-synchronous spacecraft.展开更多
Based on the magnetic field and plasma data obtained by GEOTAIL in 1992-1995 and WIND in1994-2009, the magnetic field and plasma properties in the magnetotail near lunar orbit were studied statistically using the supe...Based on the magnetic field and plasma data obtained by GEOTAIL in 1992-1995 and WIND in1994-2009, the magnetic field and plasma properties in the magnetotail near lunar orbit were studied statistically using the superposed epoch analysis. The results showed that near the 0° sector the plasma density was negatively correlated with Dst index while the temperature was positively correlated with Dst index. The plasma velocity and magnetic field strength had little correlation with Dst index. Around the current sheet near the lunar orbit, the Bx varied between -15-15 nT, the plasma density was less than 0.4 cm^-3, the median of plasma density for all events was less than 0.1 cm^-3, the temperature varied from 0.016 to 8.98 keV, the median of the plasma temperature for all the events was -3 keV, the median of speed was about 200 km/s and the maximum speed was up to 1500 km/s. The tailward and earthward flows could be observed accompanied with the current sheet. For the current sheet cases with tailward flow, the Bx varied from -15 to 15 nT, the upper quartile of plasma velocity was more than 400 krn/s, the maximum speed was up to 1500 km/s. For the current sheet cases with tailward flow, the Bx varied from -10 to 10 nT, the upper quartile of plasma velocity was less than 400 km/s, the maximum speed was up to 1200 km/s. The median of plasma density, temperature and velocity were similar for the two categories. This paper discussed the relationship between above results and magnetic reconnection at magnetic tail, compared the above results with the observation in the far magnetotail. We fitted the statistical results according to the Harris current sheet model, and the observation was consistent with Harris current sheet model. The above results can provide useful information for the design and protection of lunar-orbiting spacecraft and can be used as the background magnetic field and plasma parameters in the numerical simulation of mid-magnetotail reconnection.展开更多
Hot Flow Anomalies (HFAs) are phenomena that frequently appear in the vicinity of the Earth's bow shock. We have identified 765 HFA events with Cluster spacecraft data from 2003 to 2009. We study the plasma and ma...Hot Flow Anomalies (HFAs) are phenomena that frequently appear in the vicinity of the Earth's bow shock. We have identified 765 HFA events with Cluster spacecraft data from 2003 to 2009. We study the plasma and magnetic field variations during typical HFAs. Then we study the average structure of HFAs using the superposed epoch method during a 200 s time interval, with the HFA onset time as the epoch time. The results show that HFAs can be classified into four classes based on variations of the dynamic pressure over time, namely "-+" (down-up), "+-" (up-down), "M" (up-down-up) and "W" (up-down-up-down-up), where the letters represent similar shapes with the variation trends of the dynamic pressure. Trends of other parameters are highly related to those of the dynamic pressure with obvious characteristics of the classification. Moreover, statistical results suggest that the number of HFA events varies in years. Compared with the speed of solar wind and sunspot number, the number of HFA events in each year has positive correlation with the former, while it has little relation with the latter. The result of this paper will provide data base for further studies on the mechanisms of the formation, the structural evolution and other relative questions of HFAs.展开更多
基金supported by the National Research and Innovation Agency(BRIN),Indonesia.
文摘Ionospheric scintillation refers to rapid radio signal amplitude and phase fluctuations due to small-scale irregularities in the ionosphere.Occurring primarily at equatorial and low latitudes,scintillation is linked to equatorial plasma bubbles(EPBs),regions of depleted plasma density that form after sunset.Ionospheric scintillation typically occurs from post-sunset hours until midnight.Post-sunset EPBs can be enhanced or suppressed during geomagnetic storms,depending on local sunset timing and how it relates to the storm's main or recovery phases.This study analyzes ionospheric scintillation in Indonesia,located at low geomagnetic and geographic latitudes,during geomagnetic events from 2003 to 2024.Using the S4 index,scintillation was examined with data from seven observation stations during geomagnetic storm events.Geomagnetic activity was evaluated using Dst,SYM-H,and AE indices,employing Superposed Epoch Analysis(SEA)to assess scintillation occurrence linked to minimum SYM-H,defined as epoch 0 to represent the storm peak or the onset of recovery phase in each event.The analysis categorized geomagnetic storms into weak-moderate(–100 nT<min.Dst≤–30 nT)and strong(min.Dst≤–100 nT),and examined their dependence on the local time of minimum SYM-H.Results indicate that scintillation first appears~6 hours after epoch 0 in weak-moderate geomagnetic storms,and~12 hours after epoch 0 in strong geomagnetic storms.The average AE index returns to its baseline value(quiet condition)~6 and~12 hours after epoch 0 for weak-moderate and strong geomagnetic storms,respectively.Further analysis based on the classification of the local time of epoch 0 shows that scintillation occurrence is not observed in post-sunset hours when epoch 0 falls between 16:00 and 19:00 LT for weak-moderate geomagnetic storms.In strong geomagnetic storms,scintillation occurrence during post-sunset hours is absent when epoch 0 is between 10:00 and 19:00 LT.Notably,when the minimum SYM-H(epoch 0)nearly coincides with local sunset,scintillation activity occurs around sunset in both weak-moderate and strong geomagnetic storms.Furthermore,when epoch 0 falls within midnight until early morning,scintillation can be generated in the post-sunset hours before epoch 0.Still,post-midnight scintillation is not observed in the equatorial region during the recovery phase of either weak-moderate and strong storm events.Our findings show that when sunset falls before or coincide with epoch 0,the likelihood of post-sunset EPB and scintillation increases,due to the prompt-penetration electric field(PPEF)in the main phase of storm.The disturbance dynamo electric field(DDEF)in the recovery phase driven by equatorward winds from auroral Joule heating operates for at least 6-and 12-hours post-epoch 0 in the cases of weak-moderate and strong geomagnetic storms,respectively.When the local sunset falls within these operational DDEF periods,post-sunset EPBs will likely be suppressed,inhibiting ionospheric scintillation during post-sunset hours.Finally,this study provides essential information for developing more accurate ionospheric scintillation prediction models in space weather services in equatorial regions.
基金supported by the National Natural Science Foundation of China(42477481,42477483)the Science and Technology Program in Gansu Province(23JRRA599)the Chinese Academy of Sciences(CAS)"Light of West China"Program.
文摘Flash drought is characterized by a period of rapid drought intensification with impacts on agriculture,water resources,ecosystems,and human environment.In the Qilian Mountains,northwestern China,flash droughts are becoming more frequently due to the global climate warming.However,the spatiotemporal variations and their driving factors of flash droughts are not clear in this region.In this study,the European Centre for Medium-range Weather Forecasts(ECMWF)Reanalysis v5-Land(ERA5-Land)dataset was utilized to identify two types of flash drought events(heatwave-induced and water scarcity-induced flash drought events)that occurred in the growing season(April‒September)during 1981-2020 in this area.The results showed that the frequency of heatwave-induced flash droughts has decreased since 2010,while the frequency of water scarcity-induced flash droughts has declined markedly.Spatially,heatwave-induced flash droughts were predominantly concentrated in the western Qilian Mountains,whereas water scarcity-induced flash droughts were primarily concentrated in the central and eastern Qilian Mountains.A significantly increasing temporal trend in both types of flash droughts in the eastern Qilian Mountains was found.Meanwhile,there was a decreasing temporal trend of heatwave-induced flash droughts in the southwestern part of the region.Additionally,the influence of two major atmospheric modes,i.e.,the El Niño‒Southern Oscillation(ENSO)and North Atlantic Oscillation(NAO),on these two types of flash droughts was explored by the Superposed Epoch Analysis.The ENSO mainly influences flash droughts in the central and eastern parts of the Qilian Mountains by altering the strength of the East Asian monsoon,while the NAO mainly affects flash droughts in the entire parts of the Qilian Mountains by inducing anomalous westerlies activity.Our findings have important implications for predicting the evolution of flash drought events in the Qilian Mountains region under continued climate warming.
基金supported by the National Natural Science Foundation of China(Grant No.41421003)the Major Project of Chinese National Programs for Fundamental Research and Development(Grant No.2012CB825603)
文摘Based on the data from the Medium-Energy Proton and Electron Detector （MEPED） onboard NOAA-17, 141 anomalies of a Chinese Sun-Synchronous satellite （SSO-X） that occurred between 02/01/2010 and 09/31/2012 were studied statistically. About 26 out of the 52 anomalies that occurred outside the South Atlantic Anomaly （SAA） were accompanied by energetic electron storms. Superposed Epoch Analysis （SEA） was used to analyze the properties of the anomalies and the dynamics of the space environments during these 26 events. Then, a Monte Carlo method was utilized to simulate the electron deposition and the interactions of the injected electrons with an aluminum shield and polyethylene dielectric. The average, median, and 75tb percentile values of the maximum electric field strength inside the dielectric were calculated. The results showed the tbl- lowing. （1） SSO-X anomalies are more likely to occur within the SAA, as 89 out of 141 anomalies （63%） occurred there. （2） Twenty-six of the anomalies that occurred outside the SAA during energetic electron storms were located near the outer boundaries of the outer radiation belts, and these were more frequent in the Southern Hemisphere than in the Northern Hemi- sphere. （3） Electron flux enhancements occurred around the failure time at all energy levels but were more profound in the lower energy channels. The maximum fluxes of electrons 〉30 keV, 〉100 keV, and 〉300 keV were 106, 3.5x10s, and 1.2×10^6 cm 2 s^-1 · sr ^-1, respectively. （4） The average, median, and 75th percentile values of the maximum electric field strengths inside the dielectric for the aforementioned 26 events remained in the range from 106 to 107 V/m for long time periods, which sug- gests that the ＇potential hazards＇ of internal discharges cause SSO-X anomalies. The above results can provide useful infor- mation for the design and protection of sun-synchronous spacecraft.
基金supported by the National Natural Science Foundation ofChina (Grant No. 40831061)the National Key Laboratory Special Fund and the Open Research Foundation of Science and Technology on Aerospace Flight Dynamics Laboratory (Grant No. 2012afd1034)
文摘Based on the magnetic field and plasma data obtained by GEOTAIL in 1992-1995 and WIND in1994-2009, the magnetic field and plasma properties in the magnetotail near lunar orbit were studied statistically using the superposed epoch analysis. The results showed that near the 0° sector the plasma density was negatively correlated with Dst index while the temperature was positively correlated with Dst index. The plasma velocity and magnetic field strength had little correlation with Dst index. Around the current sheet near the lunar orbit, the Bx varied between -15-15 nT, the plasma density was less than 0.4 cm^-3, the median of plasma density for all events was less than 0.1 cm^-3, the temperature varied from 0.016 to 8.98 keV, the median of the plasma temperature for all the events was -3 keV, the median of speed was about 200 km/s and the maximum speed was up to 1500 km/s. The tailward and earthward flows could be observed accompanied with the current sheet. For the current sheet cases with tailward flow, the Bx varied from -15 to 15 nT, the upper quartile of plasma velocity was more than 400 krn/s, the maximum speed was up to 1500 km/s. For the current sheet cases with tailward flow, the Bx varied from -10 to 10 nT, the upper quartile of plasma velocity was less than 400 km/s, the maximum speed was up to 1200 km/s. The median of plasma density, temperature and velocity were similar for the two categories. This paper discussed the relationship between above results and magnetic reconnection at magnetic tail, compared the above results with the observation in the far magnetotail. We fitted the statistical results according to the Harris current sheet model, and the observation was consistent with Harris current sheet model. The above results can provide useful information for the design and protection of lunar-orbiting spacecraft and can be used as the background magnetic field and plasma parameters in the numerical simulation of mid-magnetotail reconnection.
文摘Hot Flow Anomalies (HFAs) are phenomena that frequently appear in the vicinity of the Earth's bow shock. We have identified 765 HFA events with Cluster spacecraft data from 2003 to 2009. We study the plasma and magnetic field variations during typical HFAs. Then we study the average structure of HFAs using the superposed epoch method during a 200 s time interval, with the HFA onset time as the epoch time. The results show that HFAs can be classified into four classes based on variations of the dynamic pressure over time, namely "-+" (down-up), "+-" (up-down), "M" (up-down-up) and "W" (up-down-up-down-up), where the letters represent similar shapes with the variation trends of the dynamic pressure. Trends of other parameters are highly related to those of the dynamic pressure with obvious characteristics of the classification. Moreover, statistical results suggest that the number of HFA events varies in years. Compared with the speed of solar wind and sunspot number, the number of HFA events in each year has positive correlation with the former, while it has little relation with the latter. The result of this paper will provide data base for further studies on the mechanisms of the formation, the structural evolution and other relative questions of HFAs.
