Magnetopause position as an important index of the space weather

Phys.Chem. Earth (C), Vol. 25, No. 5-6, pp. 495-498,2000 Q 2000 Elsevier Science Ltd. All rights reserved 1464-1917/00/S - see front matter

Pergamon

PII: s1464-1917(00)00064-7

Magnetopause Position as an Important Index of the Space Weather L. N. Makarova and A. V. Shirochkov ,4--c:_a11u _-A~IIlsLIc;LIc; A-&_--c:_ n__,.-__L111s111u1t;, T-^L:L.L-31. cI*r~l~rsoul-g, n_L___~.._-IYYJY rnn?n?I, lulSSIii n..__:_ fuL;LIL; ncstwcu Received

31 October 1999; accepted

I5 March 2000

Abstract. We studied long-term variability of the solar wind dynamic pressure (p,) for the period of satellite observations from 1960 to 1996. The solar wind dynamic pressure is a crucial parameter determining the position of the magnetopause relative to the Earth. The latter parameter is thought to be an indicator of the amount of energy transferred from the solar wind to the near-Earth space. Therefore, we explored the connection between the solar wind dynamic pmssure variations and some climatic characteristics such as the middle atmosphere thermal regime and the sea ice cover area Unexpectedly high degree of correlation has been found between these parameters. We consider it as an evidence of the direct impact of the solar wind dynamics on the Earth’s climate chamcteristics. Preliminary discussion of the probable physical mechanism responsible for these connections is made. Q 2000 Elsevier Science Ltd. All rights reserved

1 Introduction The ____

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to alTectthe Earth’s weather and climate has been studied for many years (Herman and Goldberg, 1978, and references therein). Almost all of these studies dealt with the most powerful solar parameter- its UV radiation, which is expressed as the sunspot number W value. The achievements and failures of such an approach are well known. The contemporary state of the problem is still uncertain, and the necessity of searching new approaches tn &~.a .Y ;r m&bnt L” th-t uuu &n-d uayv~un.r *yuuv “.1Y111&. Thn II.W .nlw uv.yL w&d “alma ia ‘a nnnthar al.“UI~a source of the energy, which directly enters into the Earth’s magnetosphere-ionosphere-atmosphere system. A. D. Sytinsky (1987) probably was one of the first persons who managed to demonstrate a direct impact of the solar wind parameters (velocity and density) on the Earth’s atmosphere dynamics. Makarova et al. (1997) showed that the solar wind dynamic pressure variations could change significantly the thermal regime of the polar middle atmnmhmw P “‘ *““y”*~’ ” -in winter . . *-.-a fi \..“.,

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illumination). Makarova et al. (1998) proposed a physical Correspondence to:

mechanism capable to explain a’direct im_pactof the solar wind dynamic pressure on the middle atmospheric state. It was suggested that a modified version of the global electric circuit with the Earth3 magnetopause as its external element could be such a mechanism. It is well known that the solar wind dynamic pressure is a crucial factor determining the position of the magnetopause. Therefore, the subsolar distance between the magnetopause and the Eatth expressed in units of the Earth’s radius Rx could be taken as an energetically mean@@ index of the amotmt of electromagnetic energy tmnsfened from the solar wind into the dayside part of the “magnetosphere- ionosphereatmosphere” system. It was showu by Makarova et al., (1998) that a decrease oftheindexRgfrom12to6means transferring an energy equal to 4.10.‘5J into the Earth’s magnetosphere. Such an amount of energy is capable to change the atmospheric temperature by several degrees. This paper is aimed to present the new evidences on a global scale. In this case it will be possible to state about an influence of the solar wind on the Earth’s climate A special attention will be given to an important climatic parameter - the area of the ice cover in the Arctic seas. Lassen and Friis- Christensen (1991) reported that there is a similarity between the long-term variations of the polar sea-ice cover in the Greenland Sea, global mean temperature, and solar activity expressed as the sunspot number. Intriguing aspect of their report is that the icecovered area in different parts of the Greenland Sea demonstrates an opposite way of correlation with the solar activity level. These findings and ideas will be expanded further on a new level. Strong connection of the long-term variations of other parameters of the polar atmosphere with the P, value dynamics will also be shown here. 2. Long-term variations of the solar wind dynamic pressure c-e s&r Wka nn Q mmth,W #V-fxk.+;..~ ..lllW&n.xni~ u,‘uuSU”_rnEO.IP y~ruuulr a0 IauLYI6UN&-*lrrU*r

parameter has been evaluated only recently Its value is expressed by the equation P,= mnV

L. N. Makarova 495

496

L.N.

Makarova and A. V Shiiochkov: Magnetopause Position

withm-protonmassandnandvartthtsolarwinddenshy and velocity, respectively. Its magnitude is usually given in nanoPascals @Pa). Newell and Meng (1994) showed that the enhanced solar wind dynamic pressure causes significant spatial displacement of the magnetospheric regions of particle precipitation. Contribution of the other IMF and solar wind parameters (including B $ to this process was negiigibie. Makarova et al. (1997) presented the experimental data showing a direct impact of the solar wind dynamic pressure variations on the thermal regime of the polar middle atmosphere. Makarova et al. (1998) showed that the Earth’s magnetopause position relative to the Earth strongly influences the ionization level in the dayside highlatitude ionosphere. If one takes into account that the magnetopause position strongly depends on the solar wind dynamic pressure it will be obvious that this solar wind parameter is capable to influence many processes in the Earth’s magnetosphere, ionosphere, and atmosphere. Therefore, it is worth to trace long-term temporal variations of P,,,, values and compare it with the correspondent variations of the standard index of the solar activity-sunspotmm&e! W.

Psw, nPa 4.0

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196819731978198319881993

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catalogues.The annually averaged values of both P w and W are presented. Obviously the data in Fig. 1 are presented only for the period of satellite observations. Several features of the data (see Fig-l) are worth mentioning. During the solar cycle 20 and during a part of the cycle 21 (1964-)980) P, and W values vary in the opposite phases (correlation coefficient r =-0.60) while during the _ __ following years this tendency disappears (correiation coefficient r =-0.33). A notable enhancement of the annually averaged values of P,w occurred after 1980. The average level of Pswfor the period of 1964-1980was equal to 2,4 nPa, while for the period of 1980-1996 this value increased to 3,35 nPa with small deviations from this level since 1980.The sunspot munber values continue to vary in its usual cyclic manner. One can conclude from Fig. 1: the temporal variations of P, and W have no close mutual coupling. However, it is clear that the possible influence of P,,,, dynamics on the .near-Earth space could be more evident in periods of minimal solar activity.

3 The solar wind dynamic pressure and the temperaturevariations in the polar atmosphere Mfxova et mve t!c3 kqgrhmga! ~kkmces of __-.al I1 \---9971 ., -.the direct influence of the P, variations on the thermal regime of the polar middle atmosphere. They used the data of the rocket measurements at Heiss Island in the Arctic (80.62oN,58.05”E).It was found that the variability of the temperature in the stratosphere and lower mesosphere could be as great as 20”C when P,, increased above 2 nPa. The accuracy of these temperature measurements was 2 K at h=40 km and 5 K at h=60 km. These phenomena occur rl~rinu winter (the rL.-nnlnr pjuht mnI?t_h_s gnd w-- cnnditinns~ _“__~_‘__~, ..u’“‘p . ..a.._* \“_ under Eastern QBO (quasi-biennaloscillations) conditions. Some notable temperature changes were also revealed at the tropospheric altitudes (8-12 km) under enhanced P, magnitudes In order to check the situation in the troposphere at conditions of increased P, the huge archive of the atmosphere baloon measurements made by Russian scientists at different Arctic observatories was used for ,-,f yI.“ICu WVWO~ I_” ima _Yuu~ ArXtkn CuuuJum. Then L1aua “1

nnnlxroio

ii8 40 20 0 196819731978198319881993

Years F&l. Long-term variations of the solar wind dynamic pressure P.. and sunspot number W for the given period of satellite observations (19601996)

Fig.1 demonstrates these data. The P ,w values were calculated using the solar wind data published by King (1978, 1986, 1993) and by the Internet, the latter covering the period from 1994 to 19%. All calculations were made in the limits of the data accuracy given in the King

~&LvI~ “Nrwth YLuU”.W I.V.Y.

PnW A”.”

included for the period of 1954-1991. The data are described in details in Nagurny (1998). The results of our analysis are presented in Fig.2. Dependence of the vertical temperature gradient within a tropopause layer expressed as a change of temperature for a distance of 100 m (CYlOOm)on the concurrent value of the solar wind dynamic pressure (in nPa) is presented here. Comparatively high coefficient of correlation (r =0.668) IXJ-X c&c f’ nrrdatinn rlmrlv v”I*-.I~“I. “w..., WAS ..l.u.3 nhtaind ““UIIaLVU fnr I”1 there u.ww turn . ..” data w... “VW. made for 26 samples with standard deviation for all measurements equal to 0,04821 of C/100 m. We checked statistical confidence of this dependence by the Students tdistribution [panofsky and Brier, 19581. We defined t value for 90 % of confidence level and for our number of the samples and consequently got the confidence interval for our data sets. It is shown in Fig. 2 by a vertical line. are

498

L. N. Makarova and A. V Shiiochkov: Magnetopause Position

and vice versa. These results are quite reasonable, since an increase of P, causes warming up of the polar atmosphere (Makarova et. al., 1997). The data in Fig. 3 confirm the results published by Lassen and Friis-Christensen (1991) showing different response of the ice-cover area in the Davis Straigt to the solar activity level. The data in Fig 3 are a clear demonstration of ability of the solar wind to influence the Earths climatic system. 5 Discussion and conclusion A strong comtection between the dynamics of the solar wind dynamic pressure and the two reliable sets of the hydrometeorological parameters was found by means of a quantitative study. A choice of these latter parameters is explained by the long temporal rows of these original data of excellent quality. The results of this study together with previous findings reported by Makarova et al. (1997) and by Makarova et al. (1998) provide solid reasons to suggest that the solar wind dynamic pressure is an important universal factor, strongly affecting the long-term variations in the dayside ionosphere, middle- and low atmosphere. These conclusions are derived from purely quantitative studies. Their statistical signilicance seems to be very reliable. In this case a problem to identity a physical mechanism responsible for these connections arises immediately. As a possible candidate a modified version of the global electric circuit is proposed. In this version the main source of energy (electromotive force dynamo) is located at the dayside magnetopause instead of the tropical thunderstorm dynamo proposed in the original scheme [Bering, 19951. In this interpretation the global electric circuit is suggested as a giant spherical condenser where its external plate is the magnetopause while its internal plate is the Earth’s surface. The energy accumulated by this condenser increases with a decreasing distance between the plates. This way, a subsolar distance between the magnetopause and the Earth could be the universal geophysical index bearing quantitative information about amount of energy transferred from the solar wind to the near-Earth space. It is known that a magnetopause position depends on both, P m and B, values lBoelof and Sibeck, 19941. This study deals with the long-term climate variations. It seems that in this case it is possible to take into account the iong-term variations of P, only, since it is a more slowly changing parameter Furthemore, if one takes into account non-uniformity of the ground surface conductivity, it will be possible to explain the local character of the effects, produced by the solar wind dynamic pressure in the Earth atmosphere. For example, different response of the sea ice-cover in the Greenland Sea and in the Davis Straigt (see Fig.3) could be explained by different conductivity of these both arcas. If the big ice-free areas in the Greeland Sea represent a region of the enhanced conductivity, the area of the

Eastern Canada coast is primarily permafrost soil with very low conductivity. Obviously, the intensities of the airground currents in these areas will be quite different More detailed discussions of the modified version of the global electric circuit together with other phenomena confirming its reality are given by Makarova ,et al. (1998). It is not the purpose of this paper to present a description of all elements of the proposed version of the global electric circuit, because some of them must be elaborated more carefully. The prime intention of this study is to demonstrate that the solar wind dynamic pressure is capable to control the processes occurring in the whole thickness of the Earth air envelope: from the magnetosphere down to the lower atmosphere. Of course, further investigations are needed to get the new evidences of the direct solar wind impact on the Earth ionosphere and atmosphere. Probably, additional physical models could be proposed to explain these phenomena Still, it is impossible to ignore a real contribution of the solar wind energy to the processes in the Earth%climatic system. The main task of future investigations is to try to evaluate this contribution quantitatively with higher accuracy and to find the conditions when these factors become evident to be taken into account in the climatic models.

References Bering, E. A. III, The global circuit: Global thermometer, weather byproduct,or climate mcderator7,U.SNational Report to International Union of Geodev and Geophysics. 1991-1994, p.845, American Geophysical Union, Washington,DC, 1995. Herman, J. R, and R A Goldberg Sun, Weather, and Climate, NASA SP-426, Washington,DC, 1978. King, J. H., InterplanetatyMedirm DataBook, NASA, 1977,1986,1993. Lassen, K., and E. Friis-Christensen, Similarity between long-term variationsof polar sea-ice cover, global mean temperature,and solar activity,Paper, presented atXLI EGS General Assembly, Wiesbaden, 22-26Apri1, 1991. Makarova,L. N., A V. Shirochkov, J. A Grigor’evs,and DMVolobuev, Gn the connection of the processes in the solar wind with the polar Russian), regime varations (in atmosphere thermal GeomagAerorwmy, wL 37,158- 164,1997 Makarova, L. N., A V. Sbirochkov, and K. V. Koptjaeva, The Eatth’s magnetosphere magnetopause as an element of the global elect& circuit (m Russian), Geomagn.Aeronomy, wL 38,159 - 162,199s. Nagurny, AP., Climatic chsmcteristics of the tropopause over the Arctic Basin, Ann. Geophystcae 16,110 - 115,1998. Newell, P. T. and C.-I. Meng, Ionospheric projection of magnetospheric regions under low and high solar wind pressure conditions, J. Geophys. Res., 99 (Al), 273.286,1994. Panofsky, HA.. and G.W. Brie-r, Some applications of statistics to meteorology, University Park, PA 1958. Roelof, E.C., and D.G. Sibeck, Magnetopause shape as a bivariate limction of interplanetarymagnetic field B z and solar wind dynamic pressure,J.Geophys.Res.,98. (A12). 21421-21450.1993. Sytinsky, A D, Connection of the Earth’s seismicfeatures with the solar activity and with the atmosphertc processes (in Russian), Hydrometeoizdat.Leningrad, 1987. Zskbarov, V. F., The sea ice in the climatic system (in Russian), Hydrometeoizdat. St. Petersburg. 1996.