极地研究

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On aurora australis research

Tschu Kangkun, Hong Minghua

1999, 10 (2-English): 75-80.

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This paper consists of two parts. The first part gives an account of reviewing the work already done for the aurora borealis, dealing with arctic explorers and observing station. since International Geophysical Year (IGY) in Antarctic,together with aurora height, brightness, forms and structures, colors and spectroscopy. The second part enumerates six modern problems of aurora australis to be undertaken for Chinese scientific workers during forthcoming years; these are aurora conjugacy, aurora ovals, aurora substorms, methods of treating large amount of data, study of shock-aurora and comparative planetology.

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Simultaneous observations of Syowa East HF radar and Zhongshan Station optical aurora associated with the solar wind negative pressure impulse

N. Sato, Y. Murata, H. Yamagishi, A. S. Yukimatu, M. Kikuchi, K. Makita, Yang Huigen, Liu Ruiyuan

1999, 10 (2-English): 81-87.

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The field of views of the Syowa East HF radar covers over Zhongshan Station (magnetic latitude ~ 74. 5°S). We examined the relation between HF radar signatures and optical aurora by using the data obtained on 3 Augusl 1997. A geomagnetic negative sudden impulse (SI^- ) occurred at ~ 1432 UT on 3 August 1997associated with the sudden decrease of solar wind plasma density. From the behavior of the optical aurora observed by all-sky TV camera and scanning photometers at Zhongshan Station, a sudden enhancement of auroral emission intensity and poleward moving signature occurred associated with the negative SI. It is intcresting that the temporal and spatial variations of the HF radar backscatter power showed one to one correlations with optical aurora data. The details of this event are examined and compared with the data onboard WIND sate1lite and from ground based magnetometers.

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Determination of apparent bulk velocity of auroral images

Xu Wenyao, Wei Zigang, Zhang Beichen, Hu Hongqiao, Liu Ruiyuan

1999, 10 (2-English): 89-94.

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In this paper we use a correlation analysis technique of random pattern to calculation of shift velocity of auroral image. The velocity thus obtained is a kind of apparent "average" velocity of whole image. instead of the velocity of some certain points or parts in the auroral pattern. The technique is used to an example of aurora australis recorded at Zhongshang Station of Antarctica in 1997. The typical velocity of the auroral pattern for the studied cases is about 3 km/s.

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Aurora morphology in the dayside

Masaru Ayukawa, Kazuo Makita, Natsuo Sato, Masayuki Kikuchi, Yang Huigen, Liu Ruiyuan, Hu Hongqiao

1999, 10 (2-English): 95-100.

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Day-side aurora phenomena are examined by using TV image data obtained at Ny-Alesund in Svalbard, Godhavn in Greenland and Zhongshan Station, Antarctica. Results are summarized as follows. During the quiet period, in the pre-and post-noon sectors: (1) Weak arc (Sun-aligned arc), (2) Corona aurora and (3) Band aurora are observed in these stations. During disturbed period,Corona aurora and Band aurora are also observed in the pre- and post-noon sectors. However, bright discrete aurora instead of weak are (Sun-aligned arc) develops from thc night side oval in the dawn and dusk sectors. Pre-noon corona and post-noon band aurora are observed in the lower latitude as compared with the location of those auroras during the quiet period.

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The auroral occurrence over Zhongshan Station, Antarctica

Hu Hongqiao, Liu Ruiyuan, Yang Huigen, Kazuo Makita, Natsuo Sato

1999, 10 (2-English): 101-109.

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The auroral data observed by all sky TV camera during 1995 and 1997 at Zhongshan Station of Antarctica are used to analyze the statistic characteristics of the aurora over Zhongshan Station. Around postnoon (1200 - 1600UT ) and midnight (2000 - 0100 UT ), the aurora appears more frequently and stronger than those in evening (1600- 2000UT ). The corona type auroras mainly occur at poleward and overhead of Zhongshan Station during postnoon and around midnight. The hand type auroras mainly appear during postnoon. while during evening and around midnight only appear at equatorward. The active surges mostly appear around midnight,while the transpolar arcs mainly occur after midnight. Except for the transpolar arcs. the occurrences of the other three type auroras are related with Kp index. Usually Zhongshan Station enters the auroral oval at postnoon,the exact time depends on Kp index.

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A theory for the formation of weak double layer

Hong Minghua, Wang Xianmin, Tang Keyun

1999, 10 (2-English): 111-116.

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Solitary electrostatic waves with ion acoustic speed were frequently observed by satellites in the auroral acceleration region. In this paper, the nonlinear ion acoustic waves are studied in the plasma which is composed of warm electrons with the Boltzman distribution and cold ions of equal density. The characteristics of solitary-likc structure in the ion acoustic frequency range are derived with the methods of reductive perturbation and phase plane analysis. The results show that nonlinear ion acoustic waves may develop to a symmetric solitary structure which is compressive and no net potential drop when dissipation does not exist, and in the case with dissipation it may evolve to compressive solitary-like structure with asymmetric shape. produce net potential drop and form weak double layer. The above theoretical results are consistent with observations.

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A simulation study of the influence of soft precipitating electrons on the polar ionosphere

Zhang Beichen, Liu Ruiyuan, Liu Shunlin, He Longsong

1999, 10 (2-English): 117-124.

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Calculation of the influence of soft precipitating electrons on the polar ionosphere was carried out. The primary results are: (1) During summer time when the sunlight is the main source of upper atmosphere ionization, the additional soft electron precipitation can increase the N_mF₂. The daily variation of N_mF₂ is mainly controlled by solar EUV radiation. (2) At wintertime, when only soft electron precipitation ionization is considered, a peak at the height of F₂ layer also appears. The altitude profile of electron density is different frorn that when the sunlit ionization is taken into account.

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Post-noon ionospheric absorption observed by the imaging riometers at polar cusp/cap conjugate stations

M. Nishino, H. Yamagishi, N. Sato, Y. Murata, Liu Ruiyuan, Hu Hongqiao, P. Stauning, J. A. Holtet

1999, 10 (2-English): 125-132.

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An example of post-noon ionospheric absorption observed by the imaging riometers at Ny-Alesund/Danmarkshavn in the arctic region and Zhongshan Station in Antarctic is presented. The post-noon absorption observed simultaneously between the hemispherical stations was a spike-type with weak intensity (<1 dB) during the high solar wind dynamic pressure. The absorption spikes might be caused by precipitation of highrenergy electrons (30 - 300 keV) in the closed dayside magnetosphere. It should be noted that the precipitation region of the absorption spike associated with the steep pressure increase (~ 13 nPa) was localized and shifted equatorward.

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Ionospheric absorption at Zhongshan Station, Antarctica during magnetic storms in early May, 1998

Liu Ruiyuan, He Longsong, Hu Hongqiao, Liu Yonghua

1999, 10 (2-English): 133-140.

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In the paper the high latitude ionospheric absorption events, monitored by an imaging riometer at Zhongshan Station, Antarctica, are examined during magnetic storms in early May, 1998. The storm absorption at ~0 639 UT on May 2 was mainly an equatorward progressing absorption event, which were associated with a strong negative bay of the magnetic H component and with a large Pc3 range pulsation. There was a time lag of about 1. 5 hours between the onset of the ionospheric disturbance and the IMF southward turning in the solar wind. The event at 2 222 UT on May 2 was a typical midnight absorption spike event. The absorption region took the form of an elongated strip with the length of 100 - 150 km and the width of 30 - 40 km. The absorption during 0 830-1 200 UT on May 6 was a polar cap absorption (PCA) event,caused by intense precipitation of high-energy protons erupted after a large solar flare explosion.

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The high-latitude ionospheric phenomena observed by DPS-4 at Zhongshan Station, Antarctica

Liu Shunlin, Liu Ruiuan, He Longsong

1999, 10 (2-English): 141-148.

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Ionograms, which were obtained from February 1995 to January 1999 by a Digisonde Portable Sounder-4 (DPS-4) at Zhongshan Station in Antarctica, have been scaled. The ionograms interpretation has shown various ionosphcric phcnomena occurred in the cusp region. They are particle precipitation effects in the E region. F region magnetic noon phenomena, slant Es phenomena and lacuna. F layer irregularity zone (FLIZ) phenomena, and auroral oval identification. Typical examples of ionograms and ionogram sequences observed at Zhongshan Station are displayed in this paper.

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Seasonal characteristics of F region in lower solar activity period at Zhongshan Station, Antarctica

He Longsong, Liu Ruiyuan, Liu Shunlin, Liu Yonghua

1999, 10 (2-English): 149-154.

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Based on data of Digisonde Portable Sounder-4 (DPS-4 ) in 1995 -1997. we have analyzed the seasonal variations of F region at Zhongshan Station (69. 4°S,76. 4°E ). During the summer of Zhongshan Station, F region ionization is mainly controlled by the solar ultraviolet radiation. Similar to the phenomena in mid-latitude area, the value f₀F₂ is changed with local time. During equinox scasons, soft electron precipitation from the cusp/cleft region seems significant, f₀F₂is changed with rnagnetic local time, and shows the magnetic noon phenomenon. In winter, the effect of the solar radiation on the F region is less than that of summer. Instead, F region is affected by particle precipitation from cusp/cleft region as well as polar plasma convection, therefore, the diurnal variation of f₀F₂is more complex and shows two peaks. F region occurs all day in summer. and seldom appears at midnight in equinox. In winter, F region shows two minimums, one is at midnight and the other is at afternoon cusp. Further analysis of the F region spread indicates that in winter the aurora oval passes over the Zhongshan Station is at 1 100 UT - 1 500 UT.

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Polarization characteristics of Pc3 pulsations at Zhongshan Station of Antarctica

Yang Shaofeng, Liu Yonghua

1999, 10 (2-English): 155-162.

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In this paper the data of geomagnetic pulsations at Zhongshan Station from February 3 to Novernber 30 in 1996 are analyzed in ordcr to study polarization characteristics of Zhongshan Station Pc3 pulsations which comprises the cusp Pc3 pulsation and the nightside Pc3 pulsation. For the cusp Pc3 pulsation. the right-handed polarization is always dominant. But their orientation of major axes of polarizations changes with season, NW-SE is dominant in summer and NE-SW in winter. For the nightside Pc3 pulsation,the right-handed with NE-SW is always dominant before midnight. But the left-handed with the mixing orientation of major axes is dominant in summer and the NE-SW with the mixing polarization sense is dominant in winter after midnight. It means that the two types of Zongshan Station Pc3 pulsations have different sources.

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Propagation characteristics of the Pc3 frequency range pulsations in the cusp latitudes

Liu Yonghua, Liu Ruiyuan, Yang Shaofeng, He Longsong, B. J. Fraser

1999, 10 (2-English): 163-170.

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Two induction magnetometers have been installed at Zhongshan Station and Davis Station, Antarctica respectively. We adopt with cross-spectral analysis technique to analyze the data of the two induction magnetometers, in June, September,December 1996 and March 1997. to investigate the Pc3 frequency range pulsation occurrence and propagation characteristics in the cusp latitudes. The results are summarized as following: At Zhongshan-Davis Stations, the Pc3 frequency range pulsations occur mainly around the local noon/ local magnetic noon and local magnetic midnight respectively. In daytime, the pulsations have a seasonal variation in amplitude, occurrence and temporal range, all of them are sma1lest in winter. But in nighttime, the pulsations have no such a variation. The pu1sation amplitude in nighttime is much larger than the one in daytime all oveI the year. The pulsation propagating direction is mainly western in daytime and irregularly in nighttime. It can be thought that the different sources of the pulsation and the ionospheric electric conductivity are mainly responsible for these characteristics.

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The characteristics of Pi2 pulsations at Zhongshan Station of Antarctica

Du Aimin, Yang Shaofeng, Xiao Fuhui

1999, 10 (2-English): 171-175.

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In this paper Pi2 pulsations at Zhongshan Station of Antarctica are analyzed from October 1-31, 1996. Their characteristics e. g. occurrence frequency, frequency, and polarization are studied. The characteristics of Pi2 pulsations are summerized as follows: (1) Pi2 pulsations at Zhongshan Station usually take place from 2000 MLT to 0200 MLT; the main frequencies are between 6.79 mHz and 13.58mHZ; (2) Pi2 pulsations with low frequencies are dominent. The range of main frequencies becomes narrow at midnight; (3) The Polarization of Pi2 pulsations are almost linear; (4) About the orientation of major axes the NW-SE direction is dominent before 2200 MLT and NE-SW is dominent after 2200 MLT. The generation mechanism of Pi2 pulsations at Zhongshan Station is discussed theoretically.

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