452 Journal of the Meteorological Society of Japan Vol. 48, No. 5. Observations of the Atmospheric Electric Field. at Syowa Station, Antarctica*

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1 452 Journal of the Meteorological Society of Japan Vol. 48, No. 5 Observations of the Atmospheric Electric Field at Syowa Station, Antarctica* By Katsuhiro Kikuchi Department of Geophysics, Hokkaido University, Sapporo (Manuscript received 8 April 1970, in revised form 13 June 1970) Abstract An observation of the atmospheric electric field strength was carried out by means of a Field Mill type electrometer at Syowa Station (69*00'S, 39*35'E), Antarctica, from the beginning of Feb to the end of Jan As a result, the following interesting data were obtained: (i) no remarkable diurnal variations in undisturbed electric field, (ii) a positive correlation between the positive electric field and wind velocity, (iii) undisturbed electric field accompanied by southerly winds, (iv) an electric field accompanied by drifting and blowing snow, (v) a difference of the commencementime of the increase of a positive electric field and the increase of wind velocity, (vi) a serrated pattern of positive electric field and (vii) a disturbance of the electric field as influenced by the aurora. 1. Introduction It is well known that the first observer of atmospheric electricity at Antarctica was Simpson (1919). Except for Simpson's observations, however, it is generally accepted that no observation have been carried out at Antarctica till the present. Recently, however, Wishart and Radok (1966) observed the electric current in five antenna wires of 20m in length which were stretched between two masts of 8m in height on the snow cover during blizzard conditions mainly at Mawson Station (67*36'S, 62*52'E) of ANARE. Further, Buis (1968) observed the atmospheric electric potential gradient near the surface and as function of height by means of electric sondes as a member of Expedition Antarctique Belgo- Neerlandaise 1964 at Roi Baudouin Base (70*26'S, 24*19'E). However, it was considered that the above two observations were not sufficient. The author made observations in the field of Cloud Physics and Atmospheric Electricity when the author was a member of the wintering party of the 9th Japanese Antarctic Research Expedition ( ) at Syowa Station (69*00'S, 39*35'E) (Kikuchi, 1970). Especially, in relation * This work was done when the author was a member of the Meteorological Research Section, Wintering Party, the 9th JARE ( ). to Atmospheric Electricity, the atmospheric electric potential gradient near the surface and charges on falling and drifting snow particles were observed in parallel. In this paper, typical patterns of the atmospheric electric potential gradient near the surface will be dealt with alone. 2. Topography and Equipment "Syowa Station" is located on the coast on the north side of East Ongul Island which is part of the Antarctic continent and is approximately at a distance of 5 km from the main land as shown in Fig. 1. Although the coast of the station is mainly formed by rocks, in the winter season, from March to Nov., most of the rocks are covered by blowing and drifting snow from the northeast side which is the prevailing direction of wind. The control hut for the helicopter used in the transportation operation was used as the laboratory but for Cloud Physics and Atmospheric Electricity. The but was separated from the main building and engine room in the station at a distance of approximately 100m and was built at right angles to the prevailing wind direction, so the air was not polluted by the station (Fig. 2). In the summer season, the Ongul Strait remained open by violent storms and the tidal currents. But, permanent

2 October 1970 Katsuhiro Kikuchi 453 amplifier and recorder were placed in the observation hut. Usually the recorder was kept running at a speed of 50mm per hour and 300mm per hour during disturbed and interesting phenomena in weather conditions. 3. Results Fig. 1 Syowa Station and its neighboring topography 3.1. Undisturbed electric field The atmospheric electric field was in general quite stable when the wind velocity was below a few meters per second. On the other handy disturbed electric fields were recorded when the wind velocity was more than a few meters per second. Except for a short period in the summer season, a semi permanent snow cover was seen around the station. Thus, the drifting and blowing snow were observed when the wind velocity was more than a few meters per second according to the conditions of the surface of the snow cover. As may be expected violent disturbed fields were recorded during blizzards and undisturbed electric fields were observed for relatively long duration of several days or more in calm weather conditions. Fig. 2 Map around Syowa Station fast ice was present near the Island. For the observations of the atmospheric electric potential gradient, an atmospheric field meter of the "Field Mill" type was used. To obtain undisturbed observations, the field meter was set up on the north side of the helicopter port. This was the flattest place around the station and the distance from the observation but was about 20m. The height of the but roof was about 3m. An automatic voltage regulator, an Fig. 3 Record of the undisturbed electric field Fig. 3 shows a typical example of the undisturbed and stable electric field from 1500 LMT (LMT at Syowa Station=Universal time+ 3hrs) to 2200 LMT on 6th June, One of the characteristics of the observed undisturbed fields was that it showed no remarkable diurnal variations. Furthermore, the phenomenon of the undisturbed field had a duration of a few days. As seen in the figure, no remarkable maximum electric field appeared around 2100LMT, that is

3 454 Journal of the Meteorological Society of Japan Vol. 48, No UT as in the Carnegie's observation 1915/ 1921 (Mauchly, 1926). And in this case, it continued for about 50 hours. In almost any duration, no wind velocity was observed as seen on the middle part of the figure. And the lower part in the figure shows the wind direction. In the middle and the lower figures, the instantaneous and the mean wind velocity and the wind direction are shown respectively. The scales of the mean wind velocity and the mean direction are shown by the parenthesized numbers in velocity.and the parenthesized directions. Namely, the scale of the vertical axis of the instantaneous and the mean wind velocity is shifted by 10 meters per second and the angle between the instantaneous and the mean wind direction is shifted by 90 degrees. The axes of the time of the mean wind velocity and the mean wind direction were delayed by 5 minutes as compared with each instantaneous velocity and direction, respectively. According to routine meteorological observations at 1500, the amount of clouds, cloud forms, direction and velocity of clouds and the height of cloud base were 2ScXX15 and 5AcXX25, respectively, and the wind velocity was calm. At 2100LMT, no clouds were observed and a very gentle wind noted. Although a report concerning to the diurnal variation of the undisturbed electric field will be made in the near future, the mean maximum value of the undisturbed electric fields which were observed in the duration from May to the following January was 103.4v/m at 2000U.T. and this value was only 13% greater than the minimum value at 0600 U.T.. The difference between the maximum and minumum values was very smaller than that of the observations of Carnegie (Mauchly, 1926) and of Roi Baudouin Base (Buffs, 1968) Increasing of the positive electric field accompanied by increasing wind velocity Fig. 4 shows the most generalized pattern observed at Syowa Station. As a whole, the variation of the positive electric field shows a good correlation with that of the wind velocity and also, a number of small variations of the electric fields correspond to that of the instantaneous wind velocities. Almost all cases having a good correlation between the increasing of the positive electric field and the increasing of wind velocity were limited strictly when the wind Fig. 4 Record showing increasing of the positive electric field accompanied by increasing wind velocity directions were from northeast to east The undisturbed electric field accompanied by southerly winds Fig. 5 shows one of the typical patterns which was observed when the prevailing wind direction was southerly. As may be seen in this figure, the electric field pattern showed the same trends as seen in the undisturbed electric field as described previously as a whole, in spite of the mean wind velocity was higher than 5m per second. Furthermore, in the case of this phenomenon, and inverse relation between the variation of the electric field and that of the wind velocity was seen for instance, around 0840, a small variation in the electric field as against no variation in the wind velocity was seen while around Fig. 5 Record of the undisturbed electric field accompanied by southerly winds

4 October 1970 Katsuhiro Kikuchi and 1000, an unchanged electric field as against a small variation in the wind velocity. And also, the pattern of the wind velocity from ;southerly direction differed from that of northeasterly winds, namely, the frequency and the intensity of the gustiness of wind which affect the electric field was more smaller and weaker in southerly winds than in northeasterly winds. The strength of the electric field in southerly wind nearly the same as that in the case of the undisturbed electric fields Electric field accompanied by drifting and blowing snow The upper half in Fig. 6 shows an example of moderate blowing snow. The mean maximum wind velocity in duration as shown in the figure was 20m per second. Accompanying the increase of concentration of blowing snow particles, But, the ranges of amplitude and the periods of cycle are narrower and longer than that of the above described example. In this case, the horizontal visibility decreased at 1014 with the increase of the concentration of blowing snow particles and recovered at The phenomena of the commencement and the end of drifting and blowing snow appear quite abruptly. Fig. 7 shows the chart of the commencement of drifting snow. A sudden increase of the positive electric field from the undisturbed electric field to an off scale range occurred at On the other hand, the time of changes of wind velocity and wind direction occurred at The difference of the commencement time of the electric field and the wind velocity and direction, in this case, approximately 20 minutes, will be described in the following section. The phenomenon of Fig. 6 Record of the electric field accompanied by drifting and blowing snow gradually the electric field increases to positive as seen at around A further increase of the concentration of blowing snow particles with the increase of the wind velocity and the intensity of gustiness shows the following sudden violent fluctuations of the electric field, namely, a wider range of amplitude and shorter period of cycle as seen from 1110 to The record around 1140 shows the recovery of the horizontal visibility for lower concentration of blowing snow particles and decrease of the intensity of gustiness. The lower half in the same figure shows an example of weak blowing snow. The electric field increased in the positive region with the same intensity as seen in the upper figure. Fig. 7 Record of the electric field when the drifting snow began

5 456 Journal of the Meteorological Society of Japan Vol. 48, No. 5 commencement time of the increase of the electric current and the wind velocity coincided with each other in almost all cases of their observations. Figs. 9 to 11 show examples of the precedence of about 5, 10 and 15 minutes, respectively. An example of the precedence of about 20 minutes is shown in Fig. 7. Especially, it is of interest to note that the preceding time of 10 and 15 minutes of the electric fields as seen in Figs. 10 and 11 correspond strictly in almost all increases of the wind velocities in certain disturbance periods Serrated pattern of electric field Figs. 12 and 13 show a distinctive pattern of the electric field. In Fig. 12, the pattern was Fig. 8 Record of the electric field when the drifting snow terminated the end of drifting snow is shown in Fig. 8. The change of electric field is of special interest around In this case, the increase of the positive electric field means the decreasing of the concentration of drifting snow particles accompanied by the sudden decrease of the wind velocity at the same time. In the case of violent snow storms, namely blizzards, the electric fields vary more severely in the regions from negative to positive, and positive to negative. As a result, the white recording chart was colored by the red recording ink spreading almost over the chart during the blizzard. 3.5 Difference of the commencement time of electric field and wind velocity Throughout the observational period, a full one year, it was observed frequently that the commencement time of the increasing of positive electric field preceded that of the increase in wind velocity. According to the observation of the electric currents in the stretching antenna wires in blizzards by Wishart and Radok (1966), the Fig. 9 Record of the electric field preceding the wind velocity by 5 minutes

6 October 1970 Katsuhiro Kikuchi 457 halves in Figs. 12 and 13. The serrated pattern was observed at a rate of 1 to 2 times per month. Fig. 10 Record of the electric field preceding the wind velocity by 10 minutes 3.7. Disturbed electric field influenced by auroras As described previously, the electric field was in general quite stable when the wind velocity was below a few meters per second. However, sometimes there were sudden changes, i.e. disturbances, in the electric field when no meteorological circumstances were changed, that is, under very calm weather conditions. At times some of these unknown phenomena seemed to be related to auroral activity. Example is shown in Fig. 14. Fig. 14 shows an example of 7th Sept, According to a routine observation by a Fig. 11 Record of the electric field preceding the wind velocity by 15 minutes recorded around 1200 and 1320 and the cycle of the pattern was approximately 5 to 10 minutes. And also, in Fig. 13, a typical pattern was recorded around From these distinctive patterns, the author has attempted to call them "serrated patterns of electric field". At time the pattern was observed, the serrated patterns were also recognized on the charts of the wind velocity and the wind direction as seen in the lower Fig. 12 Record of the serrated pattern of the ctric field ele

7 458 Journal of the Meteorological Society of Japan Vol. 48, No. 5 meteorologist, no clouds and calm circumstances were recorded at 0300 and aurora displays were recorded from 0100 to On the other hand, an observer of aurora reported the first maximum of the aurora at 0138 to The reported time coincided with the peaks of disturbed electric field. Furthermore, the peaks of brightness of the aurora were reported at 0248, 0345 and 0520 to 0530, respectively. The electric field strength showed 5 fold or over values of the undisturbed electric field and the values were larger than those recorded by Buis (1968) who reported that the influence of aurora was approximately two times that of the undisturbed electric field. Moreover, from 0203 to 0206, a corona type aurora was observed. But the characteristic peak corresponding to the corona type was not recognized. Fig. 13 Record of the serrated pattern of the electric field Fig. 14 Record of the electric field during auroral display 4. Considerations Throughout the entire one year observation, various kinds of characteristic electric field patterns were obtained. In relation to the undisturbed electric field, the author is positive that no diurnal variations were observed but because of the importance of this phenomenon, it may be worthy of future discussions following continuous observations over the next few years and after sufficient data accumulation related to the phenomenon is made. The increase of the positive electric field accompanied by the increase in wind velocity may be interpreted as increase of concentration of charged particles of falling and blowing snow accompanied by increasing wind velocity. In general, an inverse relation between the sign of charged precipitation particles and the sign of the electric field was noted in Antarctica, likewise, that is, the precipitation particles which were detected by means of a vacuum tube electrometer were charged negative when the electric fields were positive. Although, the opposite inverse relation, namely, positive charged raindrops and negative electric fields were not observed because of the lack of rainfall in Antarctica, the same phenomenon with regard to the inverse relation during snowfall was observed by Magono and Orikasa (1966) in Sapporo, Japan and Reiter in West Germany (1969). Within the limitation of the phenomenon in which the wind direction was constantly from northeast to east, the prevailing wind directions in both cases either low pressure

8 October 1970 Katsuhiro Kikuchi 459 or katabatic winds were limited strictly from the northeast to east at Syowa Station. The author cannot recall any cases of strong westerly winds throughout the observation at the station. It is considered that the undisturbed electric field accompanied by a southerly wind direction is due to the topographic conditions around Syowa Station where the southerly wind velocity was weaker than that of northeasterly winds by as much as 10m per second. There is a gradual slope between the station and the seashore approximately 100m towards the prevailing wind direction and the sea surface is covered by old fast ice on the station side of the coast and by new ice on the Ongul Strait. And further this continues on to a gradual upgrade of the Antarctic continent covered by permanent snow and ice. On the other hand, the southern side of the station is covered mostly by rocks to the south end of the East Ongul Island for approximately 2 km which further connects to the new ice on the open sea. Consequently, it is surmised that the southerly wind less carries charged particles as compared against the northeasterly winds which has little influence on the electric field. Regarding the electric field accompanied by drifting and blowing snow, as a whole, this may be explained by the inverse relation described previously. However, in relation to the observation of the electric field in the weather conditions of the time changes of the concentration of the solid precipitation particles and of wind velocity are required with the previous observation and because we do not at present have adequate continuous instruments for the detection of the concentration of solid precipitation particles such as drifting and blowing snow further discussion cannot be made. The difference of the commencement time of the abrupt increase of the electric field and the wind velocity may be depend on the vertical distribution of the wind velocity, that is to say, the wind in which a number of charged snow particles are contained arrives earlier over the field mill equipment than the wind velocity at the height of the anemometer level and thus a space charge is formed over the equipment first. This phenomenon is remarkable when a katabatic wind hits the station. The typical vertical distribution of a katabatic wind velocity at the station has its maximum value at a height of m (Morita; 1968, Yamazaki et al; 1969). It thus appears that the height of the space charge area affecting the electric field is m at the highest. When the serrated pattern of electric field was recorded on the chart, similar patterns were recorded on the charts of the wind velocity and the wind direction. Considering the space charge influencing the electric field, it may be expected that the changes of wind velocity compared with that of the wind direction have some effect on the changes of the electric field. The exact time of peak to peak between the electric field and the wind velocity could not be clarified because the chart speed of wind of a routine meteorological observation was constant at such low rates of 30mm per hour. As described above in section 3.7., at times there were sudden changes in the electric field when no meteorological circumstances were changes. And some of these unknown phenomena may be attributed to auroral activity. Moreover, the values observed at Syowa Station were approximately five times that of the undisturbed electric field. This shows a higher activity than that observed at Roi Baudouin Base by Buis (1968), who reported that the value influenced by the aurora was approximately two times that of the undisturbed electric field. However, there are some contradictions concerning the influence of auroras on the electric field. Scholz (1935) reported results that show the same changes in the electric field as mentioned above. On the other hand, Wait (1923) did not find a clear correlation. According to Chamberlain (1961) and Swift (1965), it is possible that this contradiction may be solved if the type of aurora is taken into account. It may be surely such example that the peak of the electric field corresponding with the corona type of aurora was not recognized in the example given in Fig. 14. We have, however, insufficient data for a discussion on the relation with the aurora. Various interesting phenomena were noted throughout the one year observation. Thus, the author hopes that a continuation of the observations of the electric field, air-earth currents and ionic conductivities, together at least a few or more years will be made. Acknowledgments The author expresses his hearty thanks to Prof. N. Kikagawa, Saitama University and Dr. M.

9 460 Journal of the Meteorological Society of Japan Vol. 48, No. 5 Kobayashi, Meteorological Research Institute, they prepared a set of Field Mill electrometer and gave some advices about the observation to him and to Prof. R. Muhleisen, Astronomisches Institut, Universitat Tubingen, for his discussions of this study. And the author expresses his sincere gratitude to Mr. M. Murayama, the leader of the 9th Japanese Antarctic Research Expedition and to Mr. T. Sekino, one of the engineer of the expedition for their kind cooperation in the field of the logistics at Syowa Station. The expense of this study was defrayed from the Antarctic Office, the Educational Ministry of Japan. References Buis, P.M., 1968: Expedition Antarctique Belgo- Neerlandaise 1964, "Atmospheric Electricity", Exantar, Bruxelles, Chamberlain, J.W., 1961: Physics of Aurora and Airglow, Acandemic press, New York. Kikuchi, K., 1970: Observations of the Cloud Physics and the Atmospheric Electricity at Syowa Station, Antarctica. (In Japanese) Tenki, 17, Magono, C. and K. Orikasa, 1966: On the disturbance of surface electric field caused by snowfall. J. Meteor. Soc. Japan, Ser. II, 44, Mauchly, S.J., 1926: Studies in atmospheric electricity based on observations made on the Carnegie, Carnegie Inst. Res. Dept. Terr. Magn., 5, Morita, Y., 1968: Winds of katabatic origin observed at Syowa Station (I). (In Japanese with English abstract), Antarctic Record, No. 31, Reiter, R., 1969: A contribution to the atmosphericelectric phenomenology of nonthunderstorm clouds and precipitation. Planetary Electrodynamics, Vol. 1, Gordon and Breach. Scholz, J., 1935: Polarlichtuntersuchungen auf Franz- Josephs-Land. Gerl. Beitr. Geophys., 44, Simpson, G.C., 1919: Brit. Antarc. Exped Meteorology. 1, Swift, D.W., 1965: An interpretation of the auroral breakup. Geophysical Institute, Univ, of Alaska. NSF G Wait, G.R., 1923: Magnetic and atmospheric-electric disturbances and auroral displays, Western Australia, January Terr. Magn., 28, 49. Wishart, E.R, and U. Radok, 1966: Electrostatic changing of aerial wires during antarctic blizzards. University of Melbourne, Meteorology Department. Publication No Yamazaki, M., R. Ibe and H. Fukutani, 1969: On the weather and meteorological observation at Syowa Base, Antarctica. (In Japanese) Tenki, 16,