Memoirs of the British Astronomical Association, Vol. 45 Aurora Section

MESOSPHERIC CLOUDS 2002: Papers given at the meeting in Perth, Scotland, 2002 August 19-22 M. Gadsden & N. D. James (editors)

2002 September © 2002 The British Astronomical Association Burlington House Piccadilly LONDON W1J 0DU U.K. http://www.britastro.org/

ISBN 0-902749-14-5

CCD imaging of NLCs in South America and Russia since 1998

T. Sugiyama1, R.M.Mac-Mahon2, N. Ueno3, P. Ammosov4, G.A. Gavrilyeva5, S. Nikolashkin5, A. M. Zadorozhny6, A. Semmenov7, N. Persev7, and V. Sukhodoev7 1Univ. Ryukyu ([email protected]), Japan. 2Univ. Magallanes (rmonreal@ ona.fi.mag.cl), Chile. 3Ushuaia, Argentina, 4Yakute State Univ. Russia, 5Institute of Cosmophysical Research and Aeronomy ([email protected]), Russia, 6Novosibirsk

State Univ. ([email protected]), Laboratory (meso @omega.ifaran.ru), Russia.

Russia

7Upper

Atmospheric

Abstract: We are operating automatic CCD cameras for observations of noctilucent clouds(NLCs) at the both hemispheres since 1998. We have taken over 10,000 pictures of the polar summer nights. Our objectives of the recording of the polar night sky are to confirm the intervallic occurrences of NLCs, to investigate the longitudinal distribution of NLCs and to start researches of the southern hemispheric NLCs. In this article some results of the observations are shown and the interest to research longitudinal distributions of NLCs is stressed.

1. Introduction Due to the limited observational regions for NLCs, around some 50 degree to 65 degree in latitude, characteristics of the southern NLCs are not yet investigated at all [Fogle, 1965]. Thus the difference of occurrences in comparison with the northern ones is not yet clear at all. Gadsden [1985] has found a 5 day periodicity in bright NLCs, which was lately confirmed in West-Europe NLC data during 29 years by Sugiyama [1998]. Sugiyama et al. [1996] have found a 5.5 day periodicity in polar mesospheric summer echoes(PMSE) observed at Alaska. Kirkwood and Rechou [1998] have found the 5 day periodicity in PMSE at Scandinavia. They tested the origin of the 5 day periodicity as due to the temperature variations induced by planetary waves [Gadsden, 1986] through investigation of mesospheric temperature variations. Sugiyama [1994] has suggested that the periodic occurrences of NLCs with intervals of several days should be brought about by the limited amount of water vapour at the mesosphere, because condensation of ice particles results in freezed-dry atmosphere and newly production of nuclei for condensation pause until the water vapour will diffuse back to the mesopause after evaporation of ice particles at the bottom of NLCs. Because the spatial wave number of the dominant planetary waves is 1 along longitude, investigation of NLC distributions along longitude should be crucial for the discussion of the origin of the periodic displays. At present, however, no systematic observations of world wide NLC distributions have been carried out. In this short article we show some results of our CCD imaging of NLCs in South

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America since 1998 and in Russia since 1999.

2. Observations We are executing recording of images of NLCs with CCD cameras (KODAK DC120) with automatic operation in the both hemispheres: Punta Arenas (53.1S, 70.9W, since 1998), Ushuaia (54.9S, 78.3W, since 1998), Yakutsk (63.0N, 129.5E, since 1999), Novosibirsk (55.1N, 83.0E, since 2000), and Moscow (55.7N, 36.8E, since 2000). Images of polar night sky are taken throughout summers at every 10 minutes in southern hemisphere and at every 15 minutes in the northern hemisphere. We have taken over 10,000 pictures. Because of weather conditions, especially in the southern hemisphere, an automatic operation is a necessary method to find rare events of NLCs. Our aims of this project are to inspect: 1) southern hemispheric NLCs in comparison with the northern ones, 2) bright NLC occurrences with interval of several days, 3) longitudinal distributions of NLC displays by comparing other world wide data, 4) variations of NLC occurrences by long-term recordings.

3. Southern Hemispheric NLCs in 1998/1999 We have set CCD imagers at both Punta Arenas and Ushuaia since the summer of 1998/1999. Figure 1 shows the performance of simultaneous NLC observations at the two sites throughout in the summer. As the weather conditions are very severe for NLC observations positive results of NLCs are very limited, succeeding in taking only a few of NLC pictures in every summer. Figure 2 shows the NLCs on 27 December in 1998 simultaneously observed at the both stations. From these images we determine cloud height as to be around 80 km, poor height resolution due to the angular linearity of the camera being not enough in the corner of the images. Anyway we can conclude that the highest clouds on the earth surely exist in the southern hemisphere.

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Figure 1. Southern hemispheric NLC observations in 1998/1999. The horizontal axis is the date from the beginning of 1998. NLCs are ranked from 1 to 5 according to their brightness. The negative night with no NLCs in the clear sky is labeled by –2, –1 denotes the bad weather conditions, and no data no operations.

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4.. NLCs in Russia in 2000 Figure 3 shows the results of NLC observations in 3 stations in Russia in 2000 summer. At Yakutsk NLCs are not observed in the high summer due to its high latitude (63 degree north) as well as the OH ariglow [Gavrilyeva et al. 2001]. In Figure 3 we can see some nature of the NLC occurring with variable intervals around several days including negative nights of NLCs among the interval. Figure 4 shows the periodic analysis for the data of Figure 3. In Figure 4, brightness of NLCs are evaluated with the power of 2 to the brightness level(1 to 5) and the negative night is given values of minus 8 in brightness. The autocorrelations are independently obtained at the 3 stations only when pairs of the data are found, missing data including bad weather being fully excluded in calculation, and they are accumulated with weight assigned by the standard deviation of the mean value. The error bars in Figure 4 show the compiled standard deviations of the mean values of the 3 correlations at 3 stations. Due to variable intervals of NLC displays as shown in Figure 3 with limited numbers of occurrences only a weak oscillatory correlation is seen in Figure 4.

Figure 2a. NLC at Ushuaia on 27 December 1998. The sea is the Beagle Channel.

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Figure 2b. Same as Figure 2a except for at Punta Arenas. Figure 3. (next page) Simultaneous observations for NLCs at 3 stations in Russia in 2000 summer.

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To see the longitudinal distribution of NLCs we redraw the NLC nights both at Moscow and Novosibirsk in Figure 5, where 2 nights are correlated with positive NLCs, 9 nights with negative NLCs, 3 nights being anti-correlated in NLC occurrences.

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Figure 4. Autocorrelation function for NLC displays obtained at 3 Russian stations.

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Figure 5. Details for occurrence correlations of NLC displays at Moscow and Novosibirsk.

5. Comparison of our Russian 2000 data with the internet NLC data As shown in the former sections the NLC occurrences are events not so frequent, and we can not get some statistical conclusions within the data of one summer. Then we compare our data with those given in Noctilucent clouds observer’s homepage (http://www.personal.u-net.com/~kersland/nlc/nlchome.htm). Figure 6 shows an autocorrelatioin function for NLC observations in Europe in 2000 obtained from the homepage data Some 6 day periodicity is seen in Figure 6.

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Figure 6. An autocorrelation function for NLC observations in Europe in 2000 made from the data given by the internet net.com/~kersland/ nlc/nlchome.htm).

homepage

(http://www.personal.u-

An cross correlation of NLC occurrences between Europe and Siberia (Novosibirsk and Yakutsk) are shown in Figure 7. A one day delay of NLC occurrence in Europe against in Siberia is seen in Figure 7. This must be simply due to the difference of local time by the rotation of the earth, which suggests that we may see the same NLC occurrence at the different local night, NLCs having broad distributions along longitudes at a time. In concluding this article we stress the need of the world wide systematic network for NLC observations, including airplane observations every night through a summer.

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Figure 7. Spatial cross-correlation of NLC occurrence between Siberia and Europe in 2000 (see text).

Acknowledgements: One of the authors (A. M. Zadorozhny) is supported under Grant No. 00-05-65187 of the Russian Foundation for Basic Research. References Fogle B., Noctilucent Clouds over Punta Arenas, Chile, Nature, 207, 66, 1965. Gadsden M., Observations of Noctilucent clouds form North-West Europe, Ann. Geophys., 3, 1190126, 1985. Gavrilyeva G. P.P.Ammosov, S.V. Nikolashkin, T.Sugiyama, A.P.Ammosov, Preliminary results of registration of the Noctilucent clouds in Yakutsk, IAGA-IASPEI Joint Scientific Assembly, p103, 2001 Kirkwood S., and A.Rechou, Planetary wave modulation of PMSE, Geophys. Res. Letters, 25, 4509-4512, 1998. Sugiyama T, J. Ion-recombination nucleation and growth of ice particles in noctilucent clouds, J. Geophys. Res., 99, 3915-3929, 1994 Sugiyama T., Y.Muraoka, H.Sogawa, S.Fukao, Oscillations in polar mesospheric summer echoes and bifurcation of noctilucent clouds formation, Geophys. Res. Letters, 23, 653-656, 1996 Sugiyama T., Statistical study of Noctilucent cloud occurrence in Western Europe, Proceedings of the NIPR Symposium on Upper Atmosphere Physics, 11, 81087, 1998.

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