Vostok (Antarctica) Polar Cap Index

Contact Person: Oleg Troshichev at olegtro@aari.nw.ru
Web Page: http://www.aari.nw.ru where recent PCI data are plotted.
Web Page for Thule PCI data (1975-present): http://web.dmi.dk/projects/wdcc1/pcn/pcn.html
PDF file of the official description of the PC-index adopted by IAGA at the IUGG in Birmingham in 1999.

ACKNOWLEDGMENTS: The Vostok Polar Cap Index was provided by the Arctic and Antarctic Research Institute of St. Petersburg, Russia via the CEDAR Database. (Please send a courtesy copy of any publications using the Vostok PCI to Dr. Oleg Troshichev.).

  1. Data Description
  2. References
  3. 15 min Plots (1978-1992)
  4. 1 min Plots (1992-present)
NOTE 01/29/03: Hourly data from Oct 2001 to Dec 2002, and 1 min data from May-Dec 2002 (plotted) will be added to the DB soon.

Data Description

The Vostok ground magnetometer station is located in Antarctica (-78.463 S, 106.826 E) and has been operated by the Arctic and Antarctic Research Institute of St. Petersburg since 1958. The analog data have been digitized for 1978 and 1979, and for 1983-1995. A 1-sec digital magnetometer was installed in 1996. The station is part of the former Soviet Union's scientific exploration of Antarctica, which started in 1957 during the International Geophysical Year (IGY). It is located near the center of the Antarctic ice sheet, about 3488 m above mean sea level, and about 1250 km from McMurdo and about 1500 km from Mirny on the coast.

Vostok is located in the polar cap at a high magnetic latitude. In 1978, the magnetic field at the surface was about 60950 nT, with an inclination angle of -77.682 degrees, a declination angle of -11.835 degrees, and an apex magnetic location of (-83.30, 53.56). In 2001, the magnetic field at the surface was about 59470 nT, with an inclination angle of -76.807 degrees, a declination angle of -12.019 degrees, and an apex magnetic location of (-83.31, 55.11). The apex magetic location of -83.3 is very close to the corrected geomagnetic (cgm) location of -83.4 cgmlat used for Vostok.

Magnetometer stations sense the currents flowing in the ionosphere. Magnetic activity in the polar cap is caused mainly by changes in the IMF southward component (Bz) and the solar wind velocity. Numerous investigations have showed that the IMF southward component drives ionospheric convection over the polar caps, which is sensed by ground magnetometers responding to the two-cell system of currents flowing in the ionosphere. As the Earth rotates under this two-cell current system, a near-pole station is always located under the sun-aligned part of the system (i.e. under a transpolar current).

The transpolar current allows a Polar Cap magnetic activity Index (PCI) to be derived from a single near-pole station by simply calculating a magnetic horizontal component disturbance along the dawn-dusk meridian. The new magnetic activity index PC was introduced and studied by Troshichev and Andrezen [1985] and Troshichev et al. [1988] using data from two near-pole stations at Thule (Greenland, 85.4 cgmlat) and Vostok (Antarctica, -83.4 cgmlat).

The algorithm to derive the Vostok PC index is based on a statistical analysis of the relationship between the IMF and the magnetic disturbances observed at near-pole stations. Since the stations are located under the sunward transpolar current, the magnetic perturbations at such a station will be approximately in the duskward direction. The latter is slightly modified because the two-cell equivalent current system is skewed with respect to the noon-midnight meridian. The transverse magnetic perturbation caused by the transpolar current is:

  • DHpc(nT) = DH(nT) * sin(gamma) +/- DD(nT) * cos(gamma)
    where
  • gamma = glon +/- Decl + UTdeg + phi
  • DH = deviation in the H magnetic field component from the quiet level in nT
  • DD = deviation in the D magnetic field component from the quiet level, converted from angles to nT
  • Decl = is the station's average declination angle in degrees
  • glon = geographic longitude in degrees
  • UTdeg = Universal Time (UT) hour expressed in degrees (UTdeg = UT(hr) * 15 deg/hr)
  • phi = an angle between the transpolar current and the noon-midnight meridian for a given UT
    The "plus" sign is for the south pole (Vostok) while the "minus" sign if for the north pole (Thule or Eureka). The quiet levels are determined from quiet days from a particular month, and the method of determining the quiet level differs in the calculation of PCI at Vostok and Thule. For Vostok, a quiet daily variation from quiet days of the previous month is used, except for the month of March when the sun sets where the quiet level must be recalculated from the quiet days during the month of March. The final PC Vostok values are thus nearly real time except during March when the final values are adjusted after the end of the month. For Thule, a constant daily quiet level is used which is an interpolation between the nighttime quiet levels from two consecutive winter periods to characterize the secular variation. Daily quiet variations are ignored.

    The "true" transpolar current direction (phi) is derived through a linear correlation analysis relating the IMF and the horizontal perturbations projected onto various directions. The direction that shows the maximum correlation with the IMF parameter is then used for derivation of the PC index. Troshichev and Andrezen [1985] found that the highest correlation with the PC index was with the "merging electric field" (Em) in the magnetosphere suggested by Kan and Lee [1979], where

  • Em (mV/m) = 1.e-3 * Vsw * sqrt(By**2+Bz**2) * [sin(theta/2)]**2
    and
  • Vsw = solar wind velocity in km/s
  • By = IMF azimuthal component in nT
  • Bz = IMF vertical component in nT
  • theta = angle between the Earth's magnetic field and the IMF
    The correlation is optimal when there is about a 20 minute (satellite to earth transit time) delay between the IMF/SW parameters and the polar cap disturbances. The magnitude of DHpc indicates the response of the ground magnetic activity to the interplanetary electric field imparted to the magnetosphere.

    The optimal directions (phi) vary with UT and season [Troshichev et al., 1988; Vennerstroem et al., 1991]. To take into account the diurnal and seasonal variations, the projected horizontal perturbation (DHpc) have been normalized with respect to the parameter Em as:

  • DHpc(nT) = alpha * Em(mV/m) + beta
  • PC(dimensionless) = eta * (DHpc(nT) - beta) / alpha
    where
  • alpha, beta = regression coefficients in UT and month
  • eta = 1 mV/m, normalization to make PCI dimensionless
    The original alpha and beta regression coefficients and phi angles were calculated separately for Vostok and Thule using data from 1977 to 1979 for every UT hour and every month (24x12 arrays). (See the description in Vennerstroem et al., 1994). The Vostok regression coefficients and phi angles were recalculated in 1997 using the original 1978-1979 data for every 5 minutes of UT and every month (288x12 arrays). These 5-min regression coefficients are interpolated inbetween every 5-min to calculate 1-min Vostok PC indices, while the original 60-min Thule regression coefficients are interpolated and smoothed between every hour to calculate the 1-min Thule PC indices. The greater time frequency of these coefficients for the Vostok PCI in combination with the greater time frequency and daily variation in the calculation of the quiet levels removed from the Vostok data result in a larger range of positive and negative values for the Vostok 1-min PCI compared to the Thule 1-min PCI. For 15-min indices, the differences are not great. The recommended basic reference is Troshichev et al [1988].

    The dimensionless PC index is roughly equivalent to the merging electric field Em at the magnetopause in mV/m if there were a perfect correlation between the two parameters. Em varies between near zero and about 30 mV/m, while the PC index is mostly positive, but can be negative. Large positive values of the PC index indicate a disturbed state of of the magnetosphere (large merging electric field Em) whereas low or negative PC index values corresponds to a quiet magnetosphere.

    The Vostok PC index is available starting in 1978. The 15-minute averages are available in 1978 and 1979, and in 1983-1991. Starting in 1992 there are 1-minute values. Hourly averages are available for both periods. Gaps in the record are from 1980-1982; February and April 1993 (Perestroika); November 1993 through December 1994 (station closed); 21 January to 31 December 1996 (station closed). The 1993 data are of questionable quality and users should contact Dr. Troshichev before using them.

    Please use the following acknowledgement when using Vostok PC index data: "The PC index from Vostok station (Antarctica) used in this paper was provided by R. Y. Lukianova and O. A. Troshichev (http://www.aari.nw.ru)". Please provide reprints of refereed papers in international journals to maintain the list of the Vostok PC index related publications at the Arctic and Antarctic Research Institute in St. Petersburg.

    Descriptions of this polar cap index may be found in:

    J. R. Kan and L. C. Lee, Energy coupling function and solar wind-magnetosphere cynamo, Geophys. Res. Lett., 6, 577-580, 1979.
    O. A. Troshichev and G. V. Andrezen, The relationship between interplanetary quantities and magnetic activity in the wouthern polar cap, Planet. Space Sci., 33, 415-419, 1985.
    O. A. Troshichev, V. G. Andrezen, S. Vennerstroem, and E. Friis-Christensen, Magnetic activity in the Polar Cap - a new index, Planet. Space Sci., 36, 1095-1102, 1988.
    S. Vennerstroem, E. Friis-Christensen, O. A. Troshichev, and V. G. Andrezen, Comparison between the polar cap index, PC, and the auroral electrojet indices AE, AL, and AU, J. Geophys. Res., 96, 101-113, 1991.
    S. Vennerstroem, E. Friis-Christensen, O. A. Troshichev and V. G. Andrezen, Geomagnetic Polar Cap (PC) Index 1975-1993, Report UAG-103, WDC-A for Solar-Terrestrial Physics, NOAA/NGDC, Boulder, Colorado, 274 pp, 1994.

    Summary Plots for Vostok Polar Cap Incex

     Plots are for every 60 days of polar cap indices calculated from Vostok, Antarctica. The 15-min values are plotted between 1978-1991, and the 1-min values are plotted from 1992 to the present.


    Summary Plots for 15-min Vostok Polar Cap Index

  • Jan 01, 1978-Mar 01, 1978 All data for this period
  • Mar 02, 1978-Apr 30, 1978 All data for this period
  • May 01, 1978-Jun 29, 1978 All data for this period
  • Jun 30, 1978-Aug 28, 1978 All data for this period
  • Aug 29, 1978-Oct 27, 1978 All data for this period
  • Oct 28, 1978-Dec 26, 1978 All data for this period
  • Dec 27, 1978-Feb 24, 1979 All data for this period
  • Feb 25, 1979-Apr 25, 1979 All data for this period
  • Apr 26, 1979-Jun 24, 1979 All data for this period
  • Jun 25, 1979-Aug 23, 1979 All data for this period
  • Aug 24, 1979-Oct 22, 1979 All data for this period
  • Oct 23, 1979-Dec 21, 1979 All data for this period
  • Dec 22, 1979-Feb 19, 1980 All data for this period
  • Jan 01, 1983-Mar 01, 1983 All data for this period
  • Mar 02, 1983-Apr 30, 1983 All data for this period
  • May 01, 1983-Jun 29, 1983 All data for this period
  • Jun 30, 1983-Aug 28, 1983 All data for this period
  • Aug 29, 1983-Oct 27, 1983 All data for this period
  • Oct 28, 1983-Dec 26, 1983 All data for this period
  • Dec 27, 1983-Feb 24, 1984 All data for this period
  • Feb 25, 1984-Apr 24, 1984 All data for this period
  • Apr 25, 1984-Jun 23, 1984 All data for this period
  • Jun 24, 1984-Aug 22, 1984 All data for this period
  • Aug 23, 1984-Oct 21, 1984 All data for this period
  • Oct 22, 1984-Dec 20, 1984 All data for this period
  • Dec 21, 1984-Feb 18, 1985 All data for this period
  • Feb 19, 1985-Apr 19, 1985 All data for this period
  • Apr 20, 1985-Jun 18, 1985 All data for this period
  • Jun 19, 1985-Aug 17, 1985 All data for this period
  • Aug 18, 1985-Oct 16, 1985 All data for this period
  • Oct 17, 1985-Dec 15, 1985 All data for this period
  • Dec 16, 1985-Feb 13, 1986 All data for this period
  • Feb 14, 1986-Apr 14, 1986 All data for this period
  • Apr 15, 1986-Jun 13, 1986 All data for this period
  • Jun 14, 1986-Aug 12, 1986 All data for this period
  • Aug 13, 1986-Oct 11, 1986 All data for this period
  • Oct 12, 1986-Dec 10, 1986 All data for this period
  • Dec 11, 1986-Feb 08, 1987 All data for this period
  • Feb 09, 1987-Apr 09, 1987 All data for this period
  • Apr 10, 1987-Jun 08, 1987 All data for this period
  • Jun 09, 1987-Aug 07, 1987 All data for this period
  • Aug 08, 1987-Oct 06, 1987 All data for this period
  • Oct 07, 1987-Dec 05, 1987 All data for this period
  • Dec 06, 1987-Feb 03, 1988 All data for this period
  • Feb 04, 1988-Apr 03, 1988 All data for this period
  • Apr 04, 1988-Jun 02, 1988 All data for this period
  • Jun 03, 1988-Aug 01, 1988 All data for this period
  • Aug 02, 1988-Sep 30, 1988 All data for this period
  • Oct 01, 1988-Nov 29, 1988 All data for this period
  • Nov 30, 1988-Jan 28, 1989 All data for this period
  • Jan 29, 1989-Mar 29, 1989 All data for this period
  • Mar 30, 1989-May 28, 1989 All data for this period
  • May 29, 1989-Jul 27, 1989 All data for this period
  • Jul 28, 1989-Sep 25, 1989 All data for this period
  • Sep 26, 1989-Nov 24, 1989 All data for this period
  • Nov 25, 1989-Jan 23, 1990 All data for this period
  • Jan 24, 1990-Mar 24, 1990 All data for this period
  • Mar 25, 1990-May 23, 1990 All data for this period
  • May 24, 1990-Jul 22, 1990 All data for this period
  • Jul 23, 1990-Sep 20, 1990 All data for this period
  • Sep 21, 1990-Nov 19, 1990 All data for this period
  • Nov 20, 1990-Jan 18, 1991 All data for this period
  • Jan 19, 1991-Mar 19, 1991 All data for this period
  • Mar 20, 1991-May 18, 1991 All data for this period
  • May 19, 1991-Jul 17, 1991 All data for this period
  • Jul 18, 1991-Sep 15, 1991 All data for this period
  • Sep 16, 1991-Nov 14, 1991 All data for this period
  • Nov 15, 1991-Jan 13, 1992 All data for this period

    • Summary Plots for 1-min Vostok Polar Cap Index

     Both 1-min and 1-hour data are available for this period.
  • Jan 01, 1992-Feb 29, 1992 All data for this period
  • Mar 01, 1992-Apr 29, 1992 All data for this period
  • Apr 30, 1992-Jun 28, 1992 All data for this period
  • Jun 29, 1992-Aug 27, 1992 All data for this period
  • Aug 28, 1992-Oct 26, 1992 All data for this period
  • Oct 27, 1992-Dec 25, 1992 All data for this period
  • Dec 26, 1992-Feb 23, 1993 All data for this period
  • Feb 24, 1993-Apr 24, 1993 All data for this period
  • Apr 25, 1993-Jun 23, 1993 All data for this period
  • Jun 24, 1993-Aug 22, 1993 All data for this period
  • Aug 23, 1993-Oct 21, 1993 All data for this period
  • Oct 22, 1993-Dec 20, 1993 All data for this period
  • Oct 17, 1994-Dec 15, 1994 All data for this period
  • Dec 16, 1994-Feb 13, 1995 All data for this period
  • Feb 14, 1995-Apr 14, 1995 All data for this period
  • Apr 15, 1995-Jun 13, 1995 All data for this period
  • Jun 14, 1995-Aug 12, 1995 All data for this period
  • Aug 13, 1995-Oct 11, 1995 All data for this period
  • Oct 12, 1995-Dec 10, 1995 All data for this period
  • Dec 11, 1995-Feb 08, 1996 All data for this period
  • Dec 05, 1996-Feb 02, 1997 All data for this period
  • Feb 03, 1997-Apr 03, 1997 All data for this period
  • Apr 04, 1997-Jun 02, 1997 All data for this period
  • Jun 03, 1997-Aug 01, 1997 All data for this period
  • Aug 02, 1997-Sep 30, 1997 All data for this period
  • Oct 01, 1997-Nov 29, 1997 All data for this period
  • Nov 30, 1997-Jan 28, 1998 All data for this period
  • Jan 29, 1998-Mar 29, 1998 All data for this period
  • Mar 30, 1998-May 28, 1998 All data for this period
  • May 29, 1998-Jul 27, 1998 All data for this period
  • Jul 28, 1998-Sep 25, 1998 All data for this period
  • Sep 26, 1998-Nov 24, 1998 All data for this period
  • Nov 25, 1998-Jan 23, 1999 All data for this period
  • Jan 24, 1999-Mar 24, 1999 All data for this period
  • Mar 25, 1999-May 23, 1999 All data for this period
  • May 24, 1999-Jul 22, 1999 All data for this period
  • Jul 23, 1999-Sep 20, 1999 All data for this period
  • Sep 21, 1999-Nov 19, 1999 All data for this period
  • Nov 20, 1999-Jan 18, 2000 All data for this period
  • Jan 19, 2000-Mar 18, 2000 All data for this period
  • Mar 19, 2000-May 17, 2000 All data for this period
  • May 18, 2000-Jul 16, 2000 All data for this period
  • Jul 17, 2000-Sep 14, 2000 All data for this period
  • Sep 15, 2000-Nov 13, 2000 All data for this period
  • Nov 14, 2000-Jan 12, 2001 All data for this period
  • Jan 13, 2001-Mar 13, 2001 All data for this period
  • Mar 14, 2001-May 12, 2001 All data for this period
  • May 13, 2001-Jul 11, 2001 All data for this period
  • Jul 12, 2001-Sep 09, 2001 All data for this period
  • Sep 10, 2001-Nov 08, 2001 All data for this period
  • Nov 09, 2001-Jan 07, 2002 All data for this period
  • Jan 08, 2002-Mar 08, 2002 All data for this period
  • Mar 09, 2002-May 07, 2002 All data for this period
  • May 08, 2002-Jul 06, 2002 All data for this period
  • Jul 07, 2002-Sep 04, 2002 All data for this period
  • Sep 05, 2002-Nov 03, 2002 All data for this period
  • Nov 04, 2002-Jan 02, 2003 All data for this period

    • -Revised 29 Jan 2003 by emery@ucar.edu