Polar mesosphere summer echoes(PMSEs)are very strong radar echoes in the polar mesopause in local summer.Here we present the frequency dependence of the volume reflectivity and the effect of energetic particle precipi...Polar mesosphere summer echoes(PMSEs)are very strong radar echoes in the polar mesopause in local summer.Here we present the frequency dependence of the volume reflectivity and the effect of energetic particle precipitation on modulated PMSEs by using PMSEs observations carried out by European Incoherent SCATter(EISCAT)heating equipment simultaneously with very high frequency(VHF)radar and ultra high frequency(UHF)radar on 12 July 2007.According to the experimental observations,the PMSEs occurrence rate at VHF was much higher than that at UHF,and the altitude of the PMSEs maximum observed at VHF was higher than that at UHF.Overlapping regions were observed by VHF radar between high energetic particle precipitation and the PMSEs.In addition,highfrequency heating had a very limited impact on PMSEs when the UHF electron density was enhanced because of energetic particle precipitation.In addition,an updated qualitative method was used to study the relationship between volume reflectivity and frequency.The volume reflectivity was found to be inversely proportional to the fourth power of radar frequency.The theoretical and experimental results provide a definitive data foundation for further analysis and investigation of the physical mechanism of PMSEs.展开更多
For the first time,the effect of ions on complex conductivity and permittivity of dusty plasma at Polar Mesosphere Summer Echoes(PMSE)altitude is analyzed.Because of ions higher mass and smaller thermal velocity,gener...For the first time,the effect of ions on complex conductivity and permittivity of dusty plasma at Polar Mesosphere Summer Echoes(PMSE)altitude is analyzed.Because of ions higher mass and smaller thermal velocity,generally,their effects are not considered in the study of electromagnetic properties of dusty plasmas.In this study,we modified the equations of conductivity and permittivity by adding the effect of ions.In the PMSE altitude region between 80 and 90 km,a local reduction in electron density(i.e.,an electron biteout),is produced by electron absorption onto dust particles.The bite-out condition contains high dust density and smaller electron density.From simulation results in comparatively strong bite-out conditions,we found that the ion effects on conductivity become significant with smaller dust size,lower electron temperature,and lower neutral density.For comparatively weak bite-out conditions,the ion effects on conductivity become significant with larger dust size,higher electron temperature,and higher neutral density.On the other hand,for different dust sizes,electron temperatures and neutral density,the ion effects on complex permittivity become significant only in very strong bite-out conditions.Based on these simulation results,we conclude that,in the absence of electron bite-out conditions,the effect of ions on complex conductivity and permittivity is not significant and can be ignored.However,during bite-out conditions,the effect of ions becomes significant and cannot be ignored because it significantly changes the conductivity and permittivity of dusty plasmas.展开更多
In this work,for the first time,we have analyzed and compared the responses of polar mesosphere winter echoes(PMWE)and their summer counterpart,polar mesosphere summer echoes(PMSE),to high-frequency(HF)heating in term...In this work,for the first time,we have analyzed and compared the responses of polar mesosphere winter echoes(PMWE)and their summer counterpart,polar mesosphere summer echoes(PMSE),to high-frequency(HF)heating in terms of modulated characteristics(i.e.,backscatter intensity reduction,recovery,and overshoot).Both PMWE and PMSE observations were from the same site(Tromsφ,Norway;69.6°N,19.2°E)and radar(EISCAT[European Incoherent Scatter Scientific Association]very high frequency,224 MHz).The heating patterns of both PMWE and PMSE were found to be similar;however,PMSE was more greatly affected by HF heating.Polar mesosphere summer echoes showed recovery and overshoot more frequently than did PMWE.In addition,the mean recovery and overshoot of PMSE were greater than those of PMWE.The associated electron temperature enhancement was estimated for both PMWE and PMSE and showed that,compared with PMWE,the electron temperature enhancement was more significant in PMSE.The strong heating effects on PMSE may be due to the considerable increase in electron temperature.展开更多
Polar mesosphere summer echoes(PMSE)are observed simultaneously with Digisonde and EISCAT VHF radar.The phenomenon of irregular Es layers is called PMSE-like or PMSE-Es(Polar Mesosphere Summer Echoes-Es)and has some r...Polar mesosphere summer echoes(PMSE)are observed simultaneously with Digisonde and EISCAT VHF radar.The phenomenon of irregular Es layers is called PMSE-like or PMSE-Es(Polar Mesosphere Summer Echoes-Es)and has some relationship with real PMSE.In this paper,the characteristics of irregular Es layers at 80–100 km were observed by Digisonde at Tromsøduring 2003–2014 are statistically analyzed with ionograms.The diurnal,day-to-day and year-to-year variations and discrepancies of occurrence rate between PMSE and PMSE-Es are compared with the statistical results observed by Esrange MST radar(ESRAD),and the reasons are discussed.The results show that the trends in the occurrence rate of PMSE-Es are similar to the trends in the occurrence rate of PMSE,but there are some notable differences.The occurrence rate of PMSE-Es is much lower than the occurrence rate of PMSE.The minimum value of PMSE-Es appears 1–2 hours earlier than the minimum value of the PMSE occurrence rate,while PMSE-Es appear earlier than PMSE in the year.In addition,there is a significant positive correlation between the annual average occurrence rates of PMSE and PMSE-Es.PMSEEs is a relatively important occurrence in the polar mesopause.Analysis of its characteristics can provide new ideas and methods for studying the formation mechanism of PMSE.展开更多
Polar Mesosphere Summer Echoes(PMSEs)are very strong radar echoes observed at altitudes near the polar summer mesopause.One of the essential properties of these radar echoes is that they can give useful diagnostic inf...Polar Mesosphere Summer Echoes(PMSEs)are very strong radar echoes observed at altitudes near the polar summer mesopause.One of the essential properties of these radar echoes is that they can give useful diagnostic information about the physics of the scattering process.In this paper,the related characteristics of PMSEs measured with the European Incoherent SCATter Very High Frequency(EISCAT VHF)224 MHz radar on 13–15 July 2010 are studied at different elevation angles from 78°to 90°.It is found that the PMSEs peak power and strongest PMSEs average power occur at the same elevation angles.Also interesting is that the strongest PMSEs occur at off-vertical angles when a PMSEs has a layered(multilayer)structure.And reflection may have more significant effects on PMSEs when there are double or multilayer PMSEs.Possible explanations regarding these observations are discussed.展开更多
基金This research was funded by the Sichuan Science and Technology Program(no.2019YJ0188)the National Natural Science Foundation of China(nos.61671116,61771096,11905026)+2 种基金the National Key Research and Development Program of China(no.2019YFA0210202)Fundamental Research Funds for the Central Universities(nos.ZYGX2019Z006,ZYGX2019J012)We are grateful to the EISCAT Scientific Association for providing the PMSE experimental data(http://portal.eiscat.se/schedule/schedule.cgi).The EISCAT Scientific Association is supported by China(China Research Institute of Radio Wave Propagation),Finland(Suomen Akatemia of Finland),Japan(the National Institute of Polar Research of Japan and Institute for Space-Earth Environmental Research at Nagoya University),Norway(Norges Forskningsråd of Norway),Sweden(the Swedish Research Council),and the UK(the Natural Environment Research Council).We also acknowledge the China Scholarship Council.
文摘Polar mesosphere summer echoes(PMSEs)are very strong radar echoes in the polar mesopause in local summer.Here we present the frequency dependence of the volume reflectivity and the effect of energetic particle precipitation on modulated PMSEs by using PMSEs observations carried out by European Incoherent SCATter(EISCAT)heating equipment simultaneously with very high frequency(VHF)radar and ultra high frequency(UHF)radar on 12 July 2007.According to the experimental observations,the PMSEs occurrence rate at VHF was much higher than that at UHF,and the altitude of the PMSEs maximum observed at VHF was higher than that at UHF.Overlapping regions were observed by VHF radar between high energetic particle precipitation and the PMSEs.In addition,highfrequency heating had a very limited impact on PMSEs when the UHF electron density was enhanced because of energetic particle precipitation.In addition,an updated qualitative method was used to study the relationship between volume reflectivity and frequency.The volume reflectivity was found to be inversely proportional to the fourth power of radar frequency.The theoretical and experimental results provide a definitive data foundation for further analysis and investigation of the physical mechanism of PMSEs.
基金supported by the National Natural Science Foundation of China(No.61671116,61771096,11905026)National Key Research and Development Program of China(No.2019YFA0210202)Fundamental Research Funds for the Central Universities(No.ZYGX2019Z006,ZYGX2019J012).
文摘For the first time,the effect of ions on complex conductivity and permittivity of dusty plasma at Polar Mesosphere Summer Echoes(PMSE)altitude is analyzed.Because of ions higher mass and smaller thermal velocity,generally,their effects are not considered in the study of electromagnetic properties of dusty plasmas.In this study,we modified the equations of conductivity and permittivity by adding the effect of ions.In the PMSE altitude region between 80 and 90 km,a local reduction in electron density(i.e.,an electron biteout),is produced by electron absorption onto dust particles.The bite-out condition contains high dust density and smaller electron density.From simulation results in comparatively strong bite-out conditions,we found that the ion effects on conductivity become significant with smaller dust size,lower electron temperature,and lower neutral density.For comparatively weak bite-out conditions,the ion effects on conductivity become significant with larger dust size,higher electron temperature,and higher neutral density.On the other hand,for different dust sizes,electron temperatures and neutral density,the ion effects on complex permittivity become significant only in very strong bite-out conditions.Based on these simulation results,we conclude that,in the absence of electron bite-out conditions,the effect of ions on complex conductivity and permittivity is not significant and can be ignored.However,during bite-out conditions,the effect of ions becomes significant and cannot be ignored because it significantly changes the conductivity and permittivity of dusty plasmas.
基金supported by the National Natural Science Foundation of China(No.62271113,62201529)the National Key Laboratory of Electromagnetic Environment(No.202102010)the Natural Science Foundation of Sichuan Province(No.2022NSFSC1848).
文摘In this work,for the first time,we have analyzed and compared the responses of polar mesosphere winter echoes(PMWE)and their summer counterpart,polar mesosphere summer echoes(PMSE),to high-frequency(HF)heating in terms of modulated characteristics(i.e.,backscatter intensity reduction,recovery,and overshoot).Both PMWE and PMSE observations were from the same site(Tromsφ,Norway;69.6°N,19.2°E)and radar(EISCAT[European Incoherent Scatter Scientific Association]very high frequency,224 MHz).The heating patterns of both PMWE and PMSE were found to be similar;however,PMSE was more greatly affected by HF heating.Polar mesosphere summer echoes showed recovery and overshoot more frequently than did PMWE.In addition,the mean recovery and overshoot of PMSE were greater than those of PMWE.The associated electron temperature enhancement was estimated for both PMWE and PMSE and showed that,compared with PMWE,the electron temperature enhancement was more significant in PMSE.The strong heating effects on PMSE may be due to the considerable increase in electron temperature.
基金supported by the National Natural Science Foundation of China(No.61671116,61771096,11905026)National Key Research and Development Program of China(No.2019YFA 0210202)Fundamental Research Funds for the Central Universities(No.ZYGX2019Z006,ZYGX2019J012).
文摘Polar mesosphere summer echoes(PMSE)are observed simultaneously with Digisonde and EISCAT VHF radar.The phenomenon of irregular Es layers is called PMSE-like or PMSE-Es(Polar Mesosphere Summer Echoes-Es)and has some relationship with real PMSE.In this paper,the characteristics of irregular Es layers at 80–100 km were observed by Digisonde at Tromsøduring 2003–2014 are statistically analyzed with ionograms.The diurnal,day-to-day and year-to-year variations and discrepancies of occurrence rate between PMSE and PMSE-Es are compared with the statistical results observed by Esrange MST radar(ESRAD),and the reasons are discussed.The results show that the trends in the occurrence rate of PMSE-Es are similar to the trends in the occurrence rate of PMSE,but there are some notable differences.The occurrence rate of PMSE-Es is much lower than the occurrence rate of PMSE.The minimum value of PMSE-Es appears 1–2 hours earlier than the minimum value of the PMSE occurrence rate,while PMSE-Es appear earlier than PMSE in the year.In addition,there is a significant positive correlation between the annual average occurrence rates of PMSE and PMSE-Es.PMSEEs is a relatively important occurrence in the polar mesopause.Analysis of its characteristics can provide new ideas and methods for studying the formation mechanism of PMSE.
基金the National Natural Science Foundation of China(No.s 61671116,61771096,11905026)National Key Research and Development Program of China(No.2019YFA0210202)Fundamental Research Funds for the Central Universities(No.s ZYGX2019Z006,ZYGX2019J012).
文摘Polar Mesosphere Summer Echoes(PMSEs)are very strong radar echoes observed at altitudes near the polar summer mesopause.One of the essential properties of these radar echoes is that they can give useful diagnostic information about the physics of the scattering process.In this paper,the related characteristics of PMSEs measured with the European Incoherent SCATter Very High Frequency(EISCAT VHF)224 MHz radar on 13–15 July 2010 are studied at different elevation angles from 78°to 90°.It is found that the PMSEs peak power and strongest PMSEs average power occur at the same elevation angles.Also interesting is that the strongest PMSEs occur at off-vertical angles when a PMSEs has a layered(multilayer)structure.And reflection may have more significant effects on PMSEs when there are double or multilayer PMSEs.Possible explanations regarding these observations are discussed.
