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Effects of sector structure of the interplanetary magnetic field on the upper mesosphere–lower thermosphere dynamics
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ScienceDirect Advances in Space Research 52 (2013) 1959–1965 www.elsevier.com/locate/asr
Effects of sector structure of the interplanetary magnetic field on the upper mesosphere–lower thermosphere dynamics A.N. Fahrutdinova, S.V. Maksyutin, M.V. Elakhov ⇑ Institute of Physics, Kazan (Volga Region) Federal University, 18 Kremlevskaya st., Kazan 420008, Russia Received 16 December 2012; received in revised form 28 August 2013; accepted 29 August 2013 Available online 6 September 2013
Abstract In this paper we study the influence of the interplanetary magnetic field (IMF) polarity changes caused by the Earth passing through the IMF sector boundary on the dynamic processes taking place in neutral atmosphere within the altitude interval of the upper mesosphere–lower thermosphere (83–101 km). The analysis has revealed the influence of the IMF sector structure on dynamics of the upper mesosphere–lower thermosphere. There has been a significant seasonal variation of the wind reaction to the IMF polarity changes observed. The influence of the IMF polarity changes on neutral atmosphere dynamics within the altitude range of 83–101 km is most pronounced in the zonal component of neural wind when the IMF polarity changes from negative to positive in all the seasons except for spring and when IMF polarity changes from positive to negative – in spring only. Ó 2013 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Neutral wind; Interplanetary magnetic field; IMF sector structure; Geomagnetic disturbance; Upper mesosphere–lower thermosphere; Seasonal wind variation
1. Introduction During the past decades study of the influence of the Earth passing through IMF sector boundary on the magnetosphere, ionosphere and neutral atmosphere has been conducted by a number of scientists. Mansurov et al. (1969) and Svalgaard (1968) have found out that the IMF polarity changes in the circumpolar regions of the Earth (Vostok, geomagnetic latitude F = 88° and Resolute Bay, F = 84°, Thule, F = 87°) were accompanied by simultaneous antiphase changes in the vertical component of the Earth’s magnetic field. These antiphase variations were reaching 90–150c in summer, according to Mansurov et al. (1969), which was much higher than the IMF itself. Mansurov has established Mansurov et al. (1969) an increase of Ap index values when the Earth was passing ⇑ Corresponding author. Tel.: +7 9172716223.
E-mail addresses: [email protected] (A.N. Fahrutdinova), [email protected] (S.V. Maksyutin), [email protected] (M.V. Elakhov).
through the IMF sector boundary, with its maximum falling on the day following the boundary passing through day. Veselovsky et al. (2008) has made a linear approximation of Dst index values with Bz component of the IMF. Davis et al. (1997) has reported decrease in Dst index values (down to 60 nT) and increase in Kp index values (from 2 to 5.6) at the moments of the IMF polarity changes. Thus, if we take into account the effects of the IMF sector structure, this will permit us to more thoroughly study solar and geomagnetic effects produced on the atmosphere and ionosphere of the Earth. A number of researchers have observed an effect produced by the sector structure of the interplanetary magnetic field on F2 ionospheric layer (Davis et al., 1997; Bremer et al., 1996; Tulunay, 1994, 1996). They explained the decrease in foF2 values namely by the IMF polarity changes. A number of researchers have also studied an effect produced by the IMF sector structure on the thermodynamic regime of the neutral atmosphere (Ivanov and Harshiladse,
0273-1177/$36.00 Ó 2013 COSPAR. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.asr.2013.08.031
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A.N. Fahrutdinova et al. / Advances in Space Research 52 (2013) 1959–1965
2011; Troshichev et al., 2008; Lyashenko, 2003; Bokov, 2009; Rees et al., 1986). Several papers were devoted to studies of the IMF influence on meteorological parameters of the troposphere. For example, Bokov (2009) reported about dependence between spatial distribution of the atmospheric pressure and the IMF polarity. The IMF polarity influence on cloud thickness in Antarctica was described by Troshichev et al. (2008) — cloud thickness variations were also accompanied by surface temperature variations (up to ±5° C). Atmospheric pressure and temperature correlation with the IMF sector structure (see Ivanov and Harshiladse, 2011) has been studied in central Russia (IZMIRAN, Troitsk, 55°N, 37°E). Some researches into influence of the IMF polarity changes on dynamic processes taking place in the neutral atmosphere at thermospheric altitudes have been carried out, as well. For example, Lyashenko (2003) has revealed a close relationship between phases of planetary waves with a period of 7 days and the IMF sector structure. Rees et al. (1986) reported about correlation existing between speed and direction of thermospheric winds blowing in the circumpolar region and polarity changes of By component of the IMF, based on satellite data (Dynamics Explorer-2 satellite) and ground-based measurements data (Fabry–Perot interferometer, Kiruna, 68°N, 20°E). However, lack of investigations of the effect produced by the IMF sector structure on parameters of the neutral middle-latitude upper mesosphere–lower thermosphere should be noted. A study of influence exerted by geomagnetic disturbances on the neutral wind dynamics within the altitude range of 80–110 km has been presented by Fahrutdinova et al. (1999). The influence of the IMF polarity changes on the geomagnetic field is well known (Svalgaard, 1968). This paper is an attempt to study the influence of the IMF sector structure (exerted by geomagnetic disturbances) on the wind prevailing at the altitudes of the upper mesosphere–lower thermosphere (83–101 km), based on measurements by the radiometeor radar of Kazan State University (Kazan, 55°N, 49°F) (see Sidorov and Fahrudinova, 1991; Fahrutdinova, 2004). To achieve this purpose the authors considered temporal variations of Kp index as indicator of geomagnetic perturbations.
for the altitude interval of 80–110 km and the periods 1986–1989, 1993–1995, 1998–2001 with the help of a radiometeor radar with an altimeter available in Kazan (56°N, 49°E) (see Sidorov and Fahrudinova, 1991; Fahrutdinova et all, 2001; Fahrutdinova, 2004). The main technical characteristics of the meteor radar are as follows: carrier frequency 32 MHz; duration of pulse 100 mcs; pulse repetition frequency 400 Hz; pulse power of the transmitter 100–150 kW (1993–2001–20 kW); baselines of phases interferometer, equal to 4 and 4.5 are oriented along the North–South, the East–West directions; rootmean-square error of height is 1 km; root-mean-square error of radial velocity is 3 m/s. Using the method of harmonic decomposition of time series we have determined speed values for prevailing zonal and meridional wind, amplitude and phase of the diurnal, semidiurnal and eight-hour tide. Altitude profiles of the wind velocity have been constructed with an altitude step of 3 km for the altitude interval of 80–110 km. In this article the wind data beyond the altitude interval of 83–101 km was excluded for the reason of their statistical unreliability. In such a way, 20 meteors per hour fell at each 3-km altitude interval, on the average. The influence exerted by the IMF polarity change on the altitudinal profiles of the neutral wind velocity has been analyzed for the time interval of 7 days (3 days before the IMF polarity change, the day of the event and 3 days after; the passing through day has not been taken into consideration) using the epoch superposition method. Such a wind data averaging for three-day prior before and after the event has been chosen in order to eliminate influence exerted by quasi-two-day variations of wind parameters. The analysis has been carried out individually for each of the four seasons of the year. Temporal variations of geomagnetic Kp index have been analyzed in a similar way with a time interval of 7 days (3 days before the Earth passing through the IMF sector boundary, the day of the event (change of the IMF polarity) and 3 days after the event; the passing through day has not been taken into consideration) using the epoch superposition method, when the impact of the IMF polarity changes on the condition of the geomagnetic field was considered.
2. Methods for analyzing the IMF sector structure effects on the prevailing wind within the altitude interval of 80–110 km
3. Effect of the IMF polarity changes on the Earth’s geomagnetic field
Data about the interplanetary magnetic field polarity and values of Kp index of geomagnetic activity for the period from 1986 to 2001 was taken from the web-sites of Svalgaard (http://www.leif.org/research/spolar.txt) and World Data Center for Geomagnetism, Kyoto (http:// wdc.kugi.kyoto-u.ac.jp/kp/index.html), respectively. Dates of the Earth passing through the IMF sector boundaries were determined by Svalgaard and presented on the same web-site (http://www.leif.org/research/sblist.txt). Data on prevailing wind in the neutral atmosphere were obtained
Earlier studies (Mansurov and Mansurova, 1971; Svalgaard, 1968; Veselovsky et al., 2008; Burch, 1974; Rusanov and Petrukovich, 2004; Fung and Shao, 2008) showed the IMF influence on condition of the geomagnetic field, that is why we analyzed the time variations of Kp index at the moment when the Earth was passing through the IMF sector boundary for the periods 1986–1990, 1993– 1995, 1998–2001. The analysis of the effect produced by the IMF on the condition of the geomagnetic field has been carried out separately for each of the four seasons in order
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to establish a direct relation with the results of analysis of the influence exerted by the IMF on the neutral wind. The data on the quantity of the IMF polarity change events by seasons is given in Table 1. Kp index variations caused by the IMF polarity changes have been studied using the epoch superposition method. We have found out that the IMF polarity changes occurring when the Earth was passing through the IMF sector boundary were followed by increase of the Kp index value averaged for 3 days by 5–6 points, i.e. by increase in the level of the geomagnetic field disturbance. This result is consistent with the data of previously conducted investigations (see Mansurov and Mansurova, 1971; Davis et al., 1997 – for the period 1967–1989 and Veselovsky et al., 2008 in 1997–2006). 4. Effect of the IMF polarity changes on the prevailing movements observed in the neutral atmosphere within the altitude interval of 80–110 km There has been an investigation of an effect produced by the IMF polarity change on the zonal (U) and meridional (V) components of the prevailing wind carried out. Altitude profiles of the zonal component of the prevailing wind U(h) revealed by the epoch superposition method for the time interval of 7 days (3 day before the Earth passing through the IMF sector boundary, the day of the event (the IMF polarity change from negative to positive) and 3 day after the event) are shown in Fig. 1, and the IMF polarity changes from positive to negative are sown in Fig. 3. Data have been averaged over three days prior to the event and over 3 days after the event to eliminate quasi-two-day variations in prevailing wind parameters. Altitude wind profile for a day of the event (a sector boundary passing through by the Earth) has not been taken into consideration due to impossibility to determine the exact time of such a sector border passing through by the Earth. The zonal prevailing wind changes its direction in summer at the height of about 88 km, as evident from Figs. 1 and 3. When the IMF polarity changed from negative to positive, the zonal prevailing wind component directed westward was observed for all seasons except for spring. Thus, the western direction of the zonal wind component strengthened, while the eastern direction weakened, when the IMF polarity was changing. This effect was much less pronounced in summer – below 98 km. During the IMF Table 1 The number of IMF polarity change events considered for all seasons. Season
Winter Spring Summer Autumn
Events count during IMF polarity’s changing Positive to negative
Negative to positive
Before
After
Before
After
73 47 55 52
74 47 57 45
73 34 69 58
82 39 62 50
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polarity changes from positive to negative zonal wind component directed westwards was less pronounced. An increase in velocity of the prevailing wind’s zonal component in winter (up to 4 m/s) has been detected for the altitude interval of 86–101 km, when polarity changed from negative to positive. Such an increase observed for the altitude interval of 89–98 km is statistically important. Decrease in the value of the zonal prevailing wind’s velocity for the interval of 98–101 km was also observed, but was less significant. In summer variations of the zonal component of the prevailing wind were insignificant below 98 km. A decrease in the average wind velocity in autumn (reaching 7 m/s) was observed for the zonal component of the prevailing wind within the whole altitude interval of 83–101 km as a result of the IMF polarity change from negative to positive. Furthermore, variations of the zonal component of the prevailing wind were almost unnoticeable in spring when the IMF polarity was changing from negative to positive. Spring variations of the average seasonal zonal component of the prevailing wind are conditioned by the IMF polarity change from positive to negative; they have a component directed to the west and change with the altitude (Fig. 3). Variations reach 5–7 m/s in the interval of 89– 98 km. Change of the zonal wind component’s direction in other seasons was almost unnoticeable, when the IMF polarity changed from positive to negative. Effect of the IMF polarity changes from negative to positive (see Fig. 2) produced on the meridional component of the prevailing wind V was more pronounced in spring in the lower part of the studied altitude interval (below 90 km). During other seasons variations of the meridional component of the prevailing wind V caused by the IMF polarity changes from negative to positive were weak and statistically insignificant within the whole altitude interval. For autumn and spring influence of the IMF polarity changes from positive to negative (see Fig. 4) led to increase in the value of the meridional component of the prevailing wind directed northwards within the altitude interval of 83–90 km. Such variations reached 6–7 m/s. A weak increase of the meridional component of the prevailing wind was observed within the altitude interval of 90–110 km, but it was not statistically significant. In winter and summer variations of the meridional component of the prevailing wind V caused by the IMF polarity changes from positive to negative were weak and statistically insignificant within the whole altitude interval studied. The basis of the proposed mechanism of the IMF influence on the neutral wind in the upper mesosphere–lower thermosphere has been suggested in Pudovkin and Raspopov, 1992. According to this work, variations and heterogeneity of the Interplanetary Magnetic Field, as well as of geomagnetic disturbances and other solar activity manifestations connected with it lead to modulation of sun and
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Fig. 1. Zonal prevailing wind altitude profiles during negative to positive IMF polarity changing events.
Fig. 2. Meridional prevailing wind altitude profiles during negative to positive IMF polarity changing events.
cosmic rays flux. Variations of cosmic rays intensity, in their turn, lead to changes in the atmosphere transparency and, consequently, influence changes of solar energy flux getting into the lower atmosphere. This energy presumably may get into the MLT region by force of the wave interaction with troposphere (Forbes, 2000). The proposed vari-
ant of the mechanism of interaction between the IMF changes and velocity of the prevailing neutral MLT wind blowing in the upper mesosphere–lower thermosphere requires further studies. Since the IMF polarity changes accompanied by the Earth passing through the sector boundary disturb the
A.N. Fahrutdinova et al. / Advances in Space Research 52 (2013) 1959–1965
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Fig. 3. Zonal prevailing wind altitude profiles during positive to negative IMF polarity changing events.
Fig. 4. Meridional prevailing wind altitude profiles during positive to negative IMF polarity changing events.
geomagnetic field, the results have been compared with those previously published in the study of the influence of geomagnetic field disturbances on the neutral wind dynamics observed for the Kazan station (56°N, 49°E) for the alti-
tude interval of 80–110 km within the periods 1986–1990, 1993–1995 (Fahrutdinova et al., 1999). Geomagnetic conditions were considered as disturbed if the daily sum of Kp index values RKp > 20 and as quiet – if RKp < 20,
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regardless of the cause of the geomagnetic field disturbance (see Fahrutdinova et al., 1999). Subsequently, calculation of average seasonal vertical profiles of zonal and meridional components of the prevailing wind have been separately made for quiet and disturbed geomagnetic conditions. There has been a different method of obtained data used in this paper. There has been the epoch superposition method chosen for analysis of low-observable effects (effect of geomagnetic disturbances caused by the Earth passing through the IMF sector boundaries, produced on the neutral wind within the altitude interval of 83–101 km). The following differences have been revealed when comparing the results of the present study with the results previously got by Fahrutdinova et al. (1999) for reaction of the prevailing wind on the geomagnetic field changes, which were observed within the altitude interval of 80–110 km in Kazan region: 1. Fahrutdinova et al. (1999) described a noticeable weakening of the zonal component of the prevailing wind in summer and winter within the whole altitude interval (from 10–12 m/s to 6 m/s and from 12–16 m/s to 6– 12 m/s, respectively). These variations were caused by geomagnetic disturbances accompanied by increase in Kp index values. According to the results obtained in this paper, the IMF polarity changes from negative to positive, which were also accompanied by increase in Kp index values, did not lead to significant changes in the velocity profile of the prevailing zonal wind (Fig. 1) within the whole altitude interval in winter and within the altitude interval of about 98 km only – in autumn. The significant changes of the zonal wind component have not been detected during the IMF polarity changes from positive to negative in winter and summer. Results obtained by Fahrutdinova et al. (1999) for autumn and spring seasons have not testified any significant changes of the zonal component of the prevailing wind connected with disturbed geomagnetic conditions, while the present study has established presence of the zonal component of the prevailing wind directed westwards in autumn (during the IMF polarity changes from negative to positive) and in spring (during the IMF polarity changes from positive to negative). 2. There have been some discrepancies detected between the results of the present study and the results previously obtained by Fahrutdinova et al., 1999, for the meridional component of the prevailing wind, as well. For example, a weak meridional component of the prevailing wind directed to the north has been detected for disturbed geomagnetic conditions in all seasons (see Fahrutdinova et al., 1999). In autumn these variations were more powerful and led to wind direction changes from south to north under disturbed geomagnetic conditions. According to the results obtained in this paper, influence exerted by the IMF polarity changes was most pronounced in autumn (strengthening of the meridional component of the prevailing wind directed northwards),
but only in the lower part of the studied altitude interval (83–89 km) and only when the IMF polarity changed from positive to negative. The meridional wind component directed northwards has also been detected for the altitude interval of 83–90 km in spring. The studied discrepancy between the response of dynamic parameters of the neutral wind, observed within the altitude interval of 80–110 km in Kazan (56°N 49°E) during the Earth passing through the IMF sector boundary and accompanied by increase in geomagnetic activity level, and the results of the influence exerted by geomagnetic disturbances on the parameters of the neutral wind, previously obtained for shorter time series, can be explained by the following reasons: 1. Geomagnetic disturbances caused by the Earth passing through the IMF sector boundary are weak (difference in RKp values between the disturbed and weekly disturbed geomagnetic conditions does not exceed 7 points if averaged by the epoch superposition method). 2. Source data were different – in this study we supplemented this data with measurement results obtained for the period 1998–2001. 3. Data processing methods differ. In this paper the epoch superposition method was used for analyzing dependence of the wind speed variations on the Earth passing through the IMF sector boundary, while Fahrutdinova et al. (1999) were not taking the effects of specific disturbances into consideration in their work and the results were based on the magnitude of the daily RKp value sum only.
5. Conclusion The following basic regularities of the effect produced by the IMF polarity changes on dynamic processes taking place in the upper mesosphere–lower thermosphere within the altitude interval of 83–101 km have been determined as a result of analysis of the radiometeor observations in Kazan (56°N, 49°E) for the periods 1986–1989, 1993– 1995, 1998–2001: The Earth passing through the IMF sector boundary is accompanied by the geomagnetic field disturbance and Kp index value increase. The average daily value of RKp grows by 5–7 points. The effect which the IMF polarity changes (caused by the Earth passing through the IMF sector boundaries) were producing on the dynamic processes, observed in the neutral middle-latitude atmosphere (prevailing wind) within the altitude interval of 83–101 km, has been revealed. Effect of the IMF polarity changes on the neutral wind blowing in the upper mesosphere–lower thermosphere is most pronounced for the zonal wind component in
A.N. Fahrutdinova et al. / Advances in Space Research 52 (2013) 1959–1965
winter and autumn, when the IMF polarity changes from negative to positive, and in spring, when the IMF polarity changes from positive to negative. For the meridional component of the prevailing wind the effect of the IMF polarity changes has been revealed in spring and autumn seasons when the IMF polarity changed from positive to negative only.
Acknowledgements This research has been supported by the grant “Research into thermodynamical regime of the lower and middle atmosphere, wave structure and Geo-solar factors influence on a temporary and altitude structure of neutral and charged atmosphere parameters”, which was awarded within the framework of the Federal Program of the Ministry of Education and Science of the Russian Federation. References Bokov, V.N., 2009. Trigger effect of spatial and temporal variability of atmospheric circulation in the occurrence of earthquakes. Abstract of thesis doctor geographical sciences, Saint Petersburg, 48s. (in Russian). Bremer, J., Lastovicka, J., Tulunay, Y., 1996. Influence of the interplanetary magnetic field on the variability of the mid-latitude F2 layer. Annali di Geofisica 39 (4), 721–727. Burch, J.L., 1974. Observations of interactions between interplanetary and geomagnetic fields. Rev. Geophys. Space Phys. 12, 193. Davis, C.J., Wild, M.N., Lockwood, M., Tulunay, Y.K., 1997. Ionospheric and geomagnetic responses to changes in IMF BZ: a superposed epoch study. Ann. Geophys. 15, 217–230. Fahrutdinova, A.N., 2004. The circulation of the mesosphere–lower thermosphere in middle latitudes. Kasan State Univercity, Kazan, 167p. (in Russian). Fahrutdinova, A.N., Stepanov, A.M., Fedorov, D.V., Yasnitsky, D.S., 2001. Time variations of dynamical processes in the midlatitude upper mesosphere–lower thermosphere. Adv. Space Res. 27 (6–7), 1115– 1120. Fahrutdinova, A.N., Sherstyukov, O.N., Maksyutin, S.V., 1999. The effect of geomagnetic activity on the upper mesosphere-lower thermosphere and on parameters of the Es-layer. Adv. Space Res. 24 (11), 1499– 1502.
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Forbes, J.M., 2000. Wave coupling between the lower and upper atmosphere: case study of an ultra-fast Kelvin wave. J. Atmos. Sol. Terr. Phys. 62 (17–18), 1603–1621. Ivanov, K.G., Harshiladse, A.Ph., 2011. The dynamics of solar activity and abnormal summer weather in 2010. 1. Sectoral boundaries: the formation and destruction of the anticyclone. Geomagn. Aeron. 51 (4), 450–455 (in Russian). Lyashenko, M.V., 2003. Wave disturbances in the thermosphere according to the Kharkov incoherent scatter radar and global network of ionosondes during 1997–2002. In: Proceedings of the VI Session of Young Scientists, Wave Processes in the Problem Space Weather, BAYSIS-2003, Irkutsk, pp. 49–51. (in Russian). Mansurov, S.M., 1969. New evidences for an association between magnetic fields of Earth and Space. Geomagn. Aeron. 9 (4), 768–770 (in Russian). Mansurov, S.M., Mansurova, L.G., 1971. The association between magnetic fields of Earth and Space. Geomagn. Aeron. 11 (1), 115– 118 (in Russian). Pudovkin, M.I., Raspopov, O.M., 1992. Mechanism of solar activity influence on low atmosphere condition and meteorological parameters (review). Geomagn. Aeron. 32 (5), 1–22 (in Russian). Rees, D., Fuller-Rowell, T.J., Gordon, R., Smith, M.F., Maynard, N.C., Heppner, J.P., Spencer, N.W., Wharton, L., Hays, P.B., Killeen, T.L., 1986. A theoretical and empirical study of the response of the high latitude thermosphere to the sense of the “Y” component of the interplanetary magnetic field. Planet. Space Sci. 34 (1), 1–40. Rusanov, A.A., Petrukovich, A.A., 2004. Influence of solar wind parameters on the level of geomagnetic field fluctuations. Cosmic Res. 42 (4), 354–361. Fung, Shing F., Shao, Xi, 2008. Specification of multiple geomagnetic responses to variable solar wind and IMF input. Ann. Geophys. 26, 639–652. Sidorov, V.V., Fahrutdinova, A.N., 1991. Earth middle atmosphere research according to MAP program. Handbook MAP 32, 211–212. Svalgaard, L., 1968. Sector structure of the interplanetary magnetic field and daily variations of the geomagnetic field of high latitudes. Sc. Rep., Danish Meteorological Inst., 11p. Troshichev, O., Vovk, V., Egorova, L., 2008. IMF-associated cloudiness above near-pole station Vostok: impact on wind regime in winter Antarctica. J. Atmos. Sol. Terr. Phys. 70, 1289–1300. Tulunay, Y., 1996. Interplanetary magnetic field and its possible effects on the mid-latitude ionosphere III. Annali di Geofisica 39 (4), 853–862. Tulunay, Y., 1994. Interplanetary magnetic field and its possible effects on the mid-latitude ionosphere II. Annali di Geofisica 37 (2), 193–200. Veselovsky, I.S., Shugai, Yu.S., Yakovchuk, O.S., 2008. The relationship between Dst and Bz for geomagnetic storms in 23th solar cycle. Sol. Terr. Phys. 1 (12), 172–173 (in Russian).
ScienceDirect Advances in Space Research 52 (2013) 1959–1965 www.elsevier.com/locate/asr
Effects of sector structure of the interplanetary magnetic field on the upper mesosphere–lower thermosphere dynamics A.N. Fahrutdinova, S.V. Maksyutin, M.V. Elakhov ⇑ Institute of Physics, Kazan (Volga Region) Federal University, 18 Kremlevskaya st., Kazan 420008, Russia Received 16 December 2012; received in revised form 28 August 2013; accepted 29 August 2013 Available online 6 September 2013
Abstract In this paper we study the influence of the interplanetary magnetic field (IMF) polarity changes caused by the Earth passing through the IMF sector boundary on the dynamic processes taking place in neutral atmosphere within the altitude interval of the upper mesosphere–lower thermosphere (83–101 km). The analysis has revealed the influence of the IMF sector structure on dynamics of the upper mesosphere–lower thermosphere. There has been a significant seasonal variation of the wind reaction to the IMF polarity changes observed. The influence of the IMF polarity changes on neutral atmosphere dynamics within the altitude range of 83–101 km is most pronounced in the zonal component of neural wind when the IMF polarity changes from negative to positive in all the seasons except for spring and when IMF polarity changes from positive to negative – in spring only. Ó 2013 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Neutral wind; Interplanetary magnetic field; IMF sector structure; Geomagnetic disturbance; Upper mesosphere–lower thermosphere; Seasonal wind variation
1. Introduction During the past decades study of the influence of the Earth passing through IMF sector boundary on the magnetosphere, ionosphere and neutral atmosphere has been conducted by a number of scientists. Mansurov et al. (1969) and Svalgaard (1968) have found out that the IMF polarity changes in the circumpolar regions of the Earth (Vostok, geomagnetic latitude F = 88° and Resolute Bay, F = 84°, Thule, F = 87°) were accompanied by simultaneous antiphase changes in the vertical component of the Earth’s magnetic field. These antiphase variations were reaching 90–150c in summer, according to Mansurov et al. (1969), which was much higher than the IMF itself. Mansurov has established Mansurov et al. (1969) an increase of Ap index values when the Earth was passing ⇑ Corresponding author. Tel.: +7 9172716223.
E-mail addresses: [email protected] (A.N. Fahrutdinova), [email protected] (S.V. Maksyutin), [email protected] (M.V. Elakhov).
through the IMF sector boundary, with its maximum falling on the day following the boundary passing through day. Veselovsky et al. (2008) has made a linear approximation of Dst index values with Bz component of the IMF. Davis et al. (1997) has reported decrease in Dst index values (down to 60 nT) and increase in Kp index values (from 2 to 5.6) at the moments of the IMF polarity changes. Thus, if we take into account the effects of the IMF sector structure, this will permit us to more thoroughly study solar and geomagnetic effects produced on the atmosphere and ionosphere of the Earth. A number of researchers have observed an effect produced by the sector structure of the interplanetary magnetic field on F2 ionospheric layer (Davis et al., 1997; Bremer et al., 1996; Tulunay, 1994, 1996). They explained the decrease in foF2 values namely by the IMF polarity changes. A number of researchers have also studied an effect produced by the IMF sector structure on the thermodynamic regime of the neutral atmosphere (Ivanov and Harshiladse,
0273-1177/$36.00 Ó 2013 COSPAR. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.asr.2013.08.031
1960
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2011; Troshichev et al., 2008; Lyashenko, 2003; Bokov, 2009; Rees et al., 1986). Several papers were devoted to studies of the IMF influence on meteorological parameters of the troposphere. For example, Bokov (2009) reported about dependence between spatial distribution of the atmospheric pressure and the IMF polarity. The IMF polarity influence on cloud thickness in Antarctica was described by Troshichev et al. (2008) — cloud thickness variations were also accompanied by surface temperature variations (up to ±5° C). Atmospheric pressure and temperature correlation with the IMF sector structure (see Ivanov and Harshiladse, 2011) has been studied in central Russia (IZMIRAN, Troitsk, 55°N, 37°E). Some researches into influence of the IMF polarity changes on dynamic processes taking place in the neutral atmosphere at thermospheric altitudes have been carried out, as well. For example, Lyashenko (2003) has revealed a close relationship between phases of planetary waves with a period of 7 days and the IMF sector structure. Rees et al. (1986) reported about correlation existing between speed and direction of thermospheric winds blowing in the circumpolar region and polarity changes of By component of the IMF, based on satellite data (Dynamics Explorer-2 satellite) and ground-based measurements data (Fabry–Perot interferometer, Kiruna, 68°N, 20°E). However, lack of investigations of the effect produced by the IMF sector structure on parameters of the neutral middle-latitude upper mesosphere–lower thermosphere should be noted. A study of influence exerted by geomagnetic disturbances on the neutral wind dynamics within the altitude range of 80–110 km has been presented by Fahrutdinova et al. (1999). The influence of the IMF polarity changes on the geomagnetic field is well known (Svalgaard, 1968). This paper is an attempt to study the influence of the IMF sector structure (exerted by geomagnetic disturbances) on the wind prevailing at the altitudes of the upper mesosphere–lower thermosphere (83–101 km), based on measurements by the radiometeor radar of Kazan State University (Kazan, 55°N, 49°F) (see Sidorov and Fahrudinova, 1991; Fahrutdinova, 2004). To achieve this purpose the authors considered temporal variations of Kp index as indicator of geomagnetic perturbations.
for the altitude interval of 80–110 km and the periods 1986–1989, 1993–1995, 1998–2001 with the help of a radiometeor radar with an altimeter available in Kazan (56°N, 49°E) (see Sidorov and Fahrudinova, 1991; Fahrutdinova et all, 2001; Fahrutdinova, 2004). The main technical characteristics of the meteor radar are as follows: carrier frequency 32 MHz; duration of pulse 100 mcs; pulse repetition frequency 400 Hz; pulse power of the transmitter 100–150 kW (1993–2001–20 kW); baselines of phases interferometer, equal to 4 and 4.5 are oriented along the North–South, the East–West directions; rootmean-square error of height is 1 km; root-mean-square error of radial velocity is 3 m/s. Using the method of harmonic decomposition of time series we have determined speed values for prevailing zonal and meridional wind, amplitude and phase of the diurnal, semidiurnal and eight-hour tide. Altitude profiles of the wind velocity have been constructed with an altitude step of 3 km for the altitude interval of 80–110 km. In this article the wind data beyond the altitude interval of 83–101 km was excluded for the reason of their statistical unreliability. In such a way, 20 meteors per hour fell at each 3-km altitude interval, on the average. The influence exerted by the IMF polarity change on the altitudinal profiles of the neutral wind velocity has been analyzed for the time interval of 7 days (3 days before the IMF polarity change, the day of the event and 3 days after; the passing through day has not been taken into consideration) using the epoch superposition method. Such a wind data averaging for three-day prior before and after the event has been chosen in order to eliminate influence exerted by quasi-two-day variations of wind parameters. The analysis has been carried out individually for each of the four seasons of the year. Temporal variations of geomagnetic Kp index have been analyzed in a similar way with a time interval of 7 days (3 days before the Earth passing through the IMF sector boundary, the day of the event (change of the IMF polarity) and 3 days after the event; the passing through day has not been taken into consideration) using the epoch superposition method, when the impact of the IMF polarity changes on the condition of the geomagnetic field was considered.
2. Methods for analyzing the IMF sector structure effects on the prevailing wind within the altitude interval of 80–110 km
3. Effect of the IMF polarity changes on the Earth’s geomagnetic field
Data about the interplanetary magnetic field polarity and values of Kp index of geomagnetic activity for the period from 1986 to 2001 was taken from the web-sites of Svalgaard (http://www.leif.org/research/spolar.txt) and World Data Center for Geomagnetism, Kyoto (http:// wdc.kugi.kyoto-u.ac.jp/kp/index.html), respectively. Dates of the Earth passing through the IMF sector boundaries were determined by Svalgaard and presented on the same web-site (http://www.leif.org/research/sblist.txt). Data on prevailing wind in the neutral atmosphere were obtained
Earlier studies (Mansurov and Mansurova, 1971; Svalgaard, 1968; Veselovsky et al., 2008; Burch, 1974; Rusanov and Petrukovich, 2004; Fung and Shao, 2008) showed the IMF influence on condition of the geomagnetic field, that is why we analyzed the time variations of Kp index at the moment when the Earth was passing through the IMF sector boundary for the periods 1986–1990, 1993– 1995, 1998–2001. The analysis of the effect produced by the IMF on the condition of the geomagnetic field has been carried out separately for each of the four seasons in order
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to establish a direct relation with the results of analysis of the influence exerted by the IMF on the neutral wind. The data on the quantity of the IMF polarity change events by seasons is given in Table 1. Kp index variations caused by the IMF polarity changes have been studied using the epoch superposition method. We have found out that the IMF polarity changes occurring when the Earth was passing through the IMF sector boundary were followed by increase of the Kp index value averaged for 3 days by 5–6 points, i.e. by increase in the level of the geomagnetic field disturbance. This result is consistent with the data of previously conducted investigations (see Mansurov and Mansurova, 1971; Davis et al., 1997 – for the period 1967–1989 and Veselovsky et al., 2008 in 1997–2006). 4. Effect of the IMF polarity changes on the prevailing movements observed in the neutral atmosphere within the altitude interval of 80–110 km There has been an investigation of an effect produced by the IMF polarity change on the zonal (U) and meridional (V) components of the prevailing wind carried out. Altitude profiles of the zonal component of the prevailing wind U(h) revealed by the epoch superposition method for the time interval of 7 days (3 day before the Earth passing through the IMF sector boundary, the day of the event (the IMF polarity change from negative to positive) and 3 day after the event) are shown in Fig. 1, and the IMF polarity changes from positive to negative are sown in Fig. 3. Data have been averaged over three days prior to the event and over 3 days after the event to eliminate quasi-two-day variations in prevailing wind parameters. Altitude wind profile for a day of the event (a sector boundary passing through by the Earth) has not been taken into consideration due to impossibility to determine the exact time of such a sector border passing through by the Earth. The zonal prevailing wind changes its direction in summer at the height of about 88 km, as evident from Figs. 1 and 3. When the IMF polarity changed from negative to positive, the zonal prevailing wind component directed westward was observed for all seasons except for spring. Thus, the western direction of the zonal wind component strengthened, while the eastern direction weakened, when the IMF polarity was changing. This effect was much less pronounced in summer – below 98 km. During the IMF Table 1 The number of IMF polarity change events considered for all seasons. Season
Winter Spring Summer Autumn
Events count during IMF polarity’s changing Positive to negative
Negative to positive
Before
After
Before
After
73 47 55 52
74 47 57 45
73 34 69 58
82 39 62 50
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polarity changes from positive to negative zonal wind component directed westwards was less pronounced. An increase in velocity of the prevailing wind’s zonal component in winter (up to 4 m/s) has been detected for the altitude interval of 86–101 km, when polarity changed from negative to positive. Such an increase observed for the altitude interval of 89–98 km is statistically important. Decrease in the value of the zonal prevailing wind’s velocity for the interval of 98–101 km was also observed, but was less significant. In summer variations of the zonal component of the prevailing wind were insignificant below 98 km. A decrease in the average wind velocity in autumn (reaching 7 m/s) was observed for the zonal component of the prevailing wind within the whole altitude interval of 83–101 km as a result of the IMF polarity change from negative to positive. Furthermore, variations of the zonal component of the prevailing wind were almost unnoticeable in spring when the IMF polarity was changing from negative to positive. Spring variations of the average seasonal zonal component of the prevailing wind are conditioned by the IMF polarity change from positive to negative; they have a component directed to the west and change with the altitude (Fig. 3). Variations reach 5–7 m/s in the interval of 89– 98 km. Change of the zonal wind component’s direction in other seasons was almost unnoticeable, when the IMF polarity changed from positive to negative. Effect of the IMF polarity changes from negative to positive (see Fig. 2) produced on the meridional component of the prevailing wind V was more pronounced in spring in the lower part of the studied altitude interval (below 90 km). During other seasons variations of the meridional component of the prevailing wind V caused by the IMF polarity changes from negative to positive were weak and statistically insignificant within the whole altitude interval. For autumn and spring influence of the IMF polarity changes from positive to negative (see Fig. 4) led to increase in the value of the meridional component of the prevailing wind directed northwards within the altitude interval of 83–90 km. Such variations reached 6–7 m/s. A weak increase of the meridional component of the prevailing wind was observed within the altitude interval of 90–110 km, but it was not statistically significant. In winter and summer variations of the meridional component of the prevailing wind V caused by the IMF polarity changes from positive to negative were weak and statistically insignificant within the whole altitude interval studied. The basis of the proposed mechanism of the IMF influence on the neutral wind in the upper mesosphere–lower thermosphere has been suggested in Pudovkin and Raspopov, 1992. According to this work, variations and heterogeneity of the Interplanetary Magnetic Field, as well as of geomagnetic disturbances and other solar activity manifestations connected with it lead to modulation of sun and
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Fig. 1. Zonal prevailing wind altitude profiles during negative to positive IMF polarity changing events.
Fig. 2. Meridional prevailing wind altitude profiles during negative to positive IMF polarity changing events.
cosmic rays flux. Variations of cosmic rays intensity, in their turn, lead to changes in the atmosphere transparency and, consequently, influence changes of solar energy flux getting into the lower atmosphere. This energy presumably may get into the MLT region by force of the wave interaction with troposphere (Forbes, 2000). The proposed vari-
ant of the mechanism of interaction between the IMF changes and velocity of the prevailing neutral MLT wind blowing in the upper mesosphere–lower thermosphere requires further studies. Since the IMF polarity changes accompanied by the Earth passing through the sector boundary disturb the
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Fig. 3. Zonal prevailing wind altitude profiles during positive to negative IMF polarity changing events.
Fig. 4. Meridional prevailing wind altitude profiles during positive to negative IMF polarity changing events.
geomagnetic field, the results have been compared with those previously published in the study of the influence of geomagnetic field disturbances on the neutral wind dynamics observed for the Kazan station (56°N, 49°E) for the alti-
tude interval of 80–110 km within the periods 1986–1990, 1993–1995 (Fahrutdinova et al., 1999). Geomagnetic conditions were considered as disturbed if the daily sum of Kp index values RKp > 20 and as quiet – if RKp < 20,
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regardless of the cause of the geomagnetic field disturbance (see Fahrutdinova et al., 1999). Subsequently, calculation of average seasonal vertical profiles of zonal and meridional components of the prevailing wind have been separately made for quiet and disturbed geomagnetic conditions. There has been a different method of obtained data used in this paper. There has been the epoch superposition method chosen for analysis of low-observable effects (effect of geomagnetic disturbances caused by the Earth passing through the IMF sector boundaries, produced on the neutral wind within the altitude interval of 83–101 km). The following differences have been revealed when comparing the results of the present study with the results previously got by Fahrutdinova et al. (1999) for reaction of the prevailing wind on the geomagnetic field changes, which were observed within the altitude interval of 80–110 km in Kazan region: 1. Fahrutdinova et al. (1999) described a noticeable weakening of the zonal component of the prevailing wind in summer and winter within the whole altitude interval (from 10–12 m/s to 6 m/s and from 12–16 m/s to 6– 12 m/s, respectively). These variations were caused by geomagnetic disturbances accompanied by increase in Kp index values. According to the results obtained in this paper, the IMF polarity changes from negative to positive, which were also accompanied by increase in Kp index values, did not lead to significant changes in the velocity profile of the prevailing zonal wind (Fig. 1) within the whole altitude interval in winter and within the altitude interval of about 98 km only – in autumn. The significant changes of the zonal wind component have not been detected during the IMF polarity changes from positive to negative in winter and summer. Results obtained by Fahrutdinova et al. (1999) for autumn and spring seasons have not testified any significant changes of the zonal component of the prevailing wind connected with disturbed geomagnetic conditions, while the present study has established presence of the zonal component of the prevailing wind directed westwards in autumn (during the IMF polarity changes from negative to positive) and in spring (during the IMF polarity changes from positive to negative). 2. There have been some discrepancies detected between the results of the present study and the results previously obtained by Fahrutdinova et al., 1999, for the meridional component of the prevailing wind, as well. For example, a weak meridional component of the prevailing wind directed to the north has been detected for disturbed geomagnetic conditions in all seasons (see Fahrutdinova et al., 1999). In autumn these variations were more powerful and led to wind direction changes from south to north under disturbed geomagnetic conditions. According to the results obtained in this paper, influence exerted by the IMF polarity changes was most pronounced in autumn (strengthening of the meridional component of the prevailing wind directed northwards),
but only in the lower part of the studied altitude interval (83–89 km) and only when the IMF polarity changed from positive to negative. The meridional wind component directed northwards has also been detected for the altitude interval of 83–90 km in spring. The studied discrepancy between the response of dynamic parameters of the neutral wind, observed within the altitude interval of 80–110 km in Kazan (56°N 49°E) during the Earth passing through the IMF sector boundary and accompanied by increase in geomagnetic activity level, and the results of the influence exerted by geomagnetic disturbances on the parameters of the neutral wind, previously obtained for shorter time series, can be explained by the following reasons: 1. Geomagnetic disturbances caused by the Earth passing through the IMF sector boundary are weak (difference in RKp values between the disturbed and weekly disturbed geomagnetic conditions does not exceed 7 points if averaged by the epoch superposition method). 2. Source data were different – in this study we supplemented this data with measurement results obtained for the period 1998–2001. 3. Data processing methods differ. In this paper the epoch superposition method was used for analyzing dependence of the wind speed variations on the Earth passing through the IMF sector boundary, while Fahrutdinova et al. (1999) were not taking the effects of specific disturbances into consideration in their work and the results were based on the magnitude of the daily RKp value sum only.
5. Conclusion The following basic regularities of the effect produced by the IMF polarity changes on dynamic processes taking place in the upper mesosphere–lower thermosphere within the altitude interval of 83–101 km have been determined as a result of analysis of the radiometeor observations in Kazan (56°N, 49°E) for the periods 1986–1989, 1993– 1995, 1998–2001: The Earth passing through the IMF sector boundary is accompanied by the geomagnetic field disturbance and Kp index value increase. The average daily value of RKp grows by 5–7 points. The effect which the IMF polarity changes (caused by the Earth passing through the IMF sector boundaries) were producing on the dynamic processes, observed in the neutral middle-latitude atmosphere (prevailing wind) within the altitude interval of 83–101 km, has been revealed. Effect of the IMF polarity changes on the neutral wind blowing in the upper mesosphere–lower thermosphere is most pronounced for the zonal wind component in
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winter and autumn, when the IMF polarity changes from negative to positive, and in spring, when the IMF polarity changes from positive to negative. For the meridional component of the prevailing wind the effect of the IMF polarity changes has been revealed in spring and autumn seasons when the IMF polarity changed from positive to negative only.
Acknowledgements This research has been supported by the grant “Research into thermodynamical regime of the lower and middle atmosphere, wave structure and Geo-solar factors influence on a temporary and altitude structure of neutral and charged atmosphere parameters”, which was awarded within the framework of the Federal Program of the Ministry of Education and Science of the Russian Federation. References Bokov, V.N., 2009. Trigger effect of spatial and temporal variability of atmospheric circulation in the occurrence of earthquakes. Abstract of thesis doctor geographical sciences, Saint Petersburg, 48s. (in Russian). Bremer, J., Lastovicka, J., Tulunay, Y., 1996. Influence of the interplanetary magnetic field on the variability of the mid-latitude F2 layer. Annali di Geofisica 39 (4), 721–727. Burch, J.L., 1974. Observations of interactions between interplanetary and geomagnetic fields. Rev. Geophys. Space Phys. 12, 193. Davis, C.J., Wild, M.N., Lockwood, M., Tulunay, Y.K., 1997. Ionospheric and geomagnetic responses to changes in IMF BZ: a superposed epoch study. Ann. Geophys. 15, 217–230. Fahrutdinova, A.N., 2004. The circulation of the mesosphere–lower thermosphere in middle latitudes. Kasan State Univercity, Kazan, 167p. (in Russian). Fahrutdinova, A.N., Stepanov, A.M., Fedorov, D.V., Yasnitsky, D.S., 2001. Time variations of dynamical processes in the midlatitude upper mesosphere–lower thermosphere. Adv. Space Res. 27 (6–7), 1115– 1120. Fahrutdinova, A.N., Sherstyukov, O.N., Maksyutin, S.V., 1999. The effect of geomagnetic activity on the upper mesosphere-lower thermosphere and on parameters of the Es-layer. Adv. Space Res. 24 (11), 1499– 1502.
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