THE INFLUENCE OF THE COSMIC RAY FORBUSH DECREASE ON THE LOW IONOSPHERE IN THE POLAR REGION

Used the ionization theory of the cosmic ray charged particles in the polar ionosphere, the influence of the cosmic ray Forbush decrease on the low ionosphere in the polar region is studied in this paper. The relationship between the Forbush decrease and the cosmic noise absorption during the polar night is analysed based on the data recorded by a Riometer at Antarctic Zhongshan Station (69° 22'24'S, 76°22'40'E). The relation of between the cosmic ray Forbush decrease and the cosmic noise absorption is well interpreted by means of the ionizaiotn theory.

Recent progress in Chinese polar upper-atmospheric physics research: review of research advances supported by the Chinese Arctic and Antarctic expeditions

It has been more than 30 years since the first Chinese Antarctic Expedition took place. Polar upper atmospheric observations started at this time. First began at Great Wall Station and then at Zhongshan Station in Antarctica, and later in the Arctic at Yellow River Station, Kjell Henriksen Observatory on Svalbard, and at the China-Iceland Joint Aurora Observatory in Iceland. In this paper, we reviewed the advances in polar upper atmosphere physics （UAP） based on the Chinese national Arctic and Antarctic research over the last five years. These included newly deployed observatories and research instruments in the Arctic and Antarctic; and new research findings, from grotmd-based observations, about polar ionosphere dynamics, aurora and particle precipitation, polar plasma convection, geomagnetic pulsations and space plasma waves, space weather in the polar regions, simulations of the polar ionosphere-magnetosphere. In conclusion, suggestions were made for future polar upper atmosphere physics research in China.

A conjugate study of the polar ionospheric F2-layer and IRI-2007 at 75 ° magnetic latitude for solar minimum

Long-duration conjugate observations by the EISCAT Svalbard Radar （ESR） and the ionosonde at Zhongshan station from the International Polar Year （IPY） during solar minimum conditions are analyzed, with respect to variability in the F2-1ayer peak parameters. A comparison between International Reference Ionosphere- 2007 （IRI-2007） and observation data clearly demonstrates good agreement in summer, but greater deviations in winter. The IRI model reproduces the F2 peak parameters dominated by solar photoionization reasonably well, but it does not address the effect of electron precipitation. Hence, the discrepancies become large in the winter auroral ionosphere.

A case study based on ground observations of the conjugate ionospheric response to interplanetary shock in polar regions

Data acquired by imaging relative ionospheric opacity meters(riometers),ionospheric total electron content(TEC)monitors,and three-wavelength auroral imagers at the conjugate Zhongshan station(ZHS)in Antarctica and Yellow River station(YRS)in the Arctic were analyzed to investigate the response of the polar ionosphere to an interplanetary shock event induced by solar flare activity on July 12,2012.After the arrival of the interplanetary shock wave at the magnetosphere at approximately 18:10 UT,significantly enhanced auroral activity was observed by the auroral imagers at the ZHS.Additionally,the polar conjugate observation stations in both hemispheres recorded notable evolution in the two-dimensional movement of cosmic noise absorption.Comparison of the ionospheric TEC data acquired by the conjugate pair showed that the TEC at both sites increased considerably after the interplanetaryshock wave arrived,although the two stations featured different sunlight conditions(polar night in July in the Antarctic region and polar day in the Arctic region).However,the high-frequency(HF)coherent radar data demonstrated that different sourcesmight be responsible for the electron density enhancement in the ionosphere.During the Arctic polar day period in July,the increased electron density over YRS might have been caused by anti-sunward convection of the plasma irregularity,whereas in Antarctica during the polar night,the increased electron density over ZHS might have been caused by energetic particle precipitation from the magnetotail.These different physical processes might be responsible for the different responses of the ionosphere at the two conjugate stations in response to the same interplanetary shock event.

Simultaneous optical and radar observations of poleward moving auroral forms under different IMF conditions

Using high temporal resolution optical data obtained from three-wavelength all-sky imagers at Chinese Yellow River Station in the Arctic, together with the EISCAT Svalbard radar （ESR） and SuperDARN radars, we investigated the dayside pole- ward moving auroral forms （PMAFs） and the associated plasma features in the polar ionosphere under difibrent interplanetary magnetic field （1MF） conditions, between 0900 and 1010 UT on 22 December 2003. Simultaneous optical and ESR observations revealed that all PMAFs were clearly associated with pulsed particle precipitations. During northward IMF, particles can precipi- tate into lower altitudes and reach the ionospheric E-region, and there is a reverse convection cell associated with these PMAFs. This cell is one of the typical signatures of the dayside high-latitude （lobe） reconnection in the polar ionosphere. These results indicate that the PMAFs were associated with the high-latitude reconnection. During southward IMF, the PMAFs show larger lati- tudinal motion, indicating a longer mean lifetime, and the associated ionospheric features indicate that the PMAFs were generated by the dayside low-latitude reconnection.

A Theoretic Model for the Shock Observed in Geo-space

An electrostatic model for the shock observed in the earth's polar region is established by deriving the 'Sagdeev potential' from the magnetohydrodynamic equations in a cylindrical coordinate system. The results show that the shock can develop from the ion acoustic wave or ion cyclotron wave in the polar region, and can exist when the Mach number M and the initial electric field E-0 satisfy the condition of vertical bar(a/M-2-1)E(0)vertical bar = 1. Also, some features of the shock wave are discussed. The result can interpret the electrostatic shock observed in the earth's polar region.

The extremely intense CNA events observed at Zhongshan Station in July, 2000

Using the ground observation data at Zhongshan Station of Antarctica during July 13 to 17, 2000, the intense absorption events associated with the activities of the solar active region R9077 are analyzed. It was shown that an intense polar cap absorption event lasted more than 3 days, which was caused by the solar proton event associated with the X5/3B major flare at 1024 UT on July 13. The polar cap event started at about 1040 UT on July 14, and lasted to about 1940 UT on July 17, with a typical day night variation. At the same time, the intense solar activities extremely disturbed the magnetosphere, therefore aurora substorms occurred frequently. The energetic particle precipitation from the magnetosphere caused several absorption spikes superposing on the background of polar cap absorption. One distinct event is the absorption enhancement that started at about 0300 UT on July 15, reached its peak of 26 dB at about 0645 UT and recovered at about 1110 UT on the same day, which was the strongest absorption event observed at Zhongshan Station since the imaging riometer installed in February, 1997. Another outstanding absorption spike with pulsation occurred at about 1753 UT on 14th, its peak reached to 6 dB.

Statistical characteristics of the polar ionospheric scale height around the peak height of F_2 layer with observations of the ESR radar: Quiet days

The ionospheric scale height around the peak height of F2 layer(HmF2)is a very important parameter defining the profile of topside ionosphere.Based on observations of the EISCAT ESR radar,we statistically study the HmF2 at high latitudes.In order to derive the HmF2,a least square method is adopted to fit the electron density profile above the peak height of F2 layer(hmF2)from observations of the ESR radar.The result shows that it is in well agreement between the topside profiles deduced from the fitted HmF2 and the actual measuring topside profile with a height range from hmF2 to 300 km above the hmF2.Therefore,HmF2 can be considered as a constant in this range.With observations of the ESR between 1997 and 2008,we analyze the statistical characteristics of polar HmF2 with local time,season,and solar activity under quiet geomagnetic conditions(Kp≤2),respectively.Variations of HmF2 in quiet days show a diurnal trend with a maximum in the morning and a minimum in the afternoon.The HmF2 always has the highest seasonal amplitude in summer under three kinds of solar activities.The seasonal magnitude of the HmF2 in winter remains between that in spring and that in autumn under low solar activity,while it is the lowest under moderate and high solar activities.We also compare measured HmF2 with those derived by IRI2007,which indicates that IRI2007 model can only approximately provide the average values of polar HmF2 in quiet days but is limited in presenting diurnal and solar activity variations of HmF2.

Multiple ground-based observations at Zhongshan Station during the April/May 1998 solar events

Simultaneous observations at Zhongshan Station, Antarctica, during May 1-7, 1998 are presented to show the responses of the polar ionosphere to the April/May 1998 solar events. One of the main geo-effects of the solar events resulted in the major magnetic storm on May 4. At the storm onset on May 2 the ionosphere F2 layer abruptly increased in altitude, the geomagnetic H-component started negative deviation and the spectral amplitude of the ULF wave intensified. Both large isolated riometer absorption and large negative deviation of the geomagnetic H-component occurred at about 0639UT. There was a time lag of about one hour and ten minutes between the storm onset and the IMF southward turning, as measured by the WIND satellite. The polar ionosphere was highly disturbed, as shown by frequent large deviations of the geomagnetic H-component, large riometer absorption events and strong ULF waves in all the courses of the storm. The absorption increased greatly causing the digisonde to be blackout most of the time. However, the data still showed a substantial decrease in the F2 electron density and oscillation of the F2 layer peak height with an amplitude exceeding 200 km.