O.A. Troshichev

Variations of the atmospheric electric field in the near‐pole region related to the interplanetary magnetic field

Variations in the atmospheric, near-surface vertical electric field component Ez measured at the Russian Antarctic station Vostok in 1998 are analyzed in conjunction with changes of the interplanetary magnetic field (IMF). A total of 134 days were selected which satisfied the “fair weather” conditions, that is, days with absence of high winds, falling or drifting snow, clouds, and electric field “pollution” from the stations power plant. It is shown that the average diurnal variation of Ez for these days follows the global geoelectric field “fair - weather” diurnal variation: the “Carnegie” curve, which describes the global electric circuit formed by the thunderstorm activity occurring mostly over equatorial regions. The Ez diurnal variation shows strong seasonal dependence: it is maximal (∼40% of the average daily magnitude) in summer but gradually reduces through the equinoctial months and is almost negligible during the austral winter. Ez at Vostok is strongly affected by variations in both the IMF By and Bz components. The influence of By is dominant during geomagnetic daytime hours (1100–1400 UT at Vostok): Ez increases with By in the range from −10 to +10 nT. The IMF Bz effect is mainly seen at dawn (Ez decreases with Bz) and dusk (Ez increases with Bz).

Atmospheric circuit influences on ground-level pressure in the Antarctic and Arctic

[1]xa0Pressure variations at 11 Antarctic sites and 7 Arctic sites have been examined and show significant correlations with a daily proxy for the output of the meteorological generators of the global atmospheric circuit. This proxy is derived from vertical electric field measurements made at Vostok on the Antarctic ice plateau. Taken with the finding of proportionate pressure variations correlated with atmospheric circuit changes owing to coupling with the interplanetary electric field, particularly for the Antarctic plateau (magnetic latitude > 83°) region, this provides experimental evidence that a small portion of the surface pressure variations are due to the influence of the global atmospheric circuit. The response to the interplanetary electric field is an example of Sun-weather coupling. To evaluate it, the daily average interplanetary magnetic field (IMF) east-west component (By) is used as a proxy for the north–south interplanetary electric field, which produces opposite ionospheric potential changes in the northern and southern polar caps. The correlation with IMF By for the pressure variations for the Antarctic sites for a solar cycle (1995–2005) is small (0.9% average covariance for the magnetic latitude > 83° sites) but significant (99.7% confidence level). The Arctic stations show a negative regression between pressure variations and IMF By, a relationship expected if the linkage process operates by the atmospheric circuit, but it is only found when the interval is restricted to the peak of the sunspot cycle (1999–2002).

Relation of PC index to the solar wind parameters and substorm activity in time of magnetic storms

The PC index has been put forward with the general aim of funding a key parameter that (1) would estimate the current state of the Earth’s magnetic 4eld, and (2) would be readily calculated from routine ground-based measurements at all time. The concept of convection in the near-pole region controlled by the solar wind parameters provides the basis of the method of calculation of the index. The PC index has been derived as a dimensionless quantity parametrized by season, UT, and hemisphere, and calibrated for interplanetary electric 4eld, merging with the magnetosphere. The results of former statistical analyses suggest that the PC index is useful in nowcasting the intensity of the auroral substorms. Twelve strong magnetic disturbances occurring in 2000 have been analyzed to verify this a8rmation under speci4c conditions. Our results show that the PC index, being a measure of the solar wind electric 4eld merging with the magnetosphere, basically follows, with a time delay of about 50 min, variations of the interplanetary electric 4eld observed in the point of libration. Distinctions in details between these quantities, typical of examined events, indicate that characteristics of the solar wind can change on the way from the point L1 to the Earth. Sharp increase of PC index indicates conclusively that auroral substorm will be developed in a matter of minutes. Correlation between the PC and AE indices turned out to be much higher in the absence of Dst variation than in the course of magnetic storm. This regularity suggests that magnetosphere responds in di:erent ways to the same changes in the solar wind parameters, and, therefore, the preceding state of the magnetosphere would be taken into account to foresee its reaction to the solar wind in;uence. c � 2002 Published by Elsevier Science Ltd.

Influence of variations of the cosmic rays on atmospheric pressure and temperature in the Southern geomagnetic pole region

Abstract Daily data of pressure, temperature, and wind observations at Antarctic station Vostok in 1981–1991 have been analyzed with regard to the cosmic-rays variations. Case study and statistical treatment of the data provide the following results. The beginning of the Forbush decrease of galactic cosmic rays is followed within one day by significant warming of the atmosphere (about 10°) at altitudes h km in the near-pole region. The duration of warming is about 1 day, then the atmosphere quickly reverted to previous temperature conditions. The Forbush decrease is accompanied by reduction of atmospheric pressure at all altitudes below 20 km, the magnitude of reduction being maximal at higher altitudes. The reduction of atmospheric pressure can develop synchronously with the Forbush decrease or can be delayed for 1–5 days depending on the preceding trends in the meteorological processes, occurrence of the solar proton spikes, and intensity of the Forbush decrease. Spikes of solar cosmic rays affect within 0–2 days the increase of atmospheric pressure at altitudes of 10–15 km. The troposphere warming and reduction of the pressure in low stratosphere and troposphere is followed within 0–6 days by reconstruction of the whole wind system above the near-pole region.

Monthly Diurnal Global Atmospheric Circuit Estimates Derived from Vostok Electric Field Measurements Adjusted for Local Meteorological and Solar Wind Influences

AbstractLocal temperature, wind speed, pressure, and solar wind–imposed influences on the vertical electric field observed at Vostok, Antarctica, are evaluated by multivariate analysis. Local meteorology can influence electric field measurements via local conductivity. The results are used to improve monthly diurnal averages of the electric field attributable to changes in the global convective storm contribution to the ionosphere-to-earth potential difference. Statistically significant average influences are found for temperature (−0.47 ± 0.13% V m−1 °C−1) and wind speed [2.1 ± 0.5% V m−1 (m s−1)−1]. Both associations are seasonally variable. After adjusting the electric field values to uniform meteorological conditions typical of the Antarctic plateau winter (−70°C, 4.4 m s−1, and 623 hPa), the sensitivity of the electric field to the solar wind external generator influence is found to be 0.80 ± 0.07 V m−1 kV−1. This compares with the sensitivity of 0.82 V m−1 kV−1 to the convective meteorology generato...

Influence of short-term changes in solar activity on baric field perturbations in the stratosphere and troposphere

Abstract Influence of short-term changes in solar activity on baric (pressure) field perturbations is studied using such characteristics as the Sazonov index (IS), describing the intensity of meridional transfer, the Blinova index (IB), describing the intensity of zonal transfer, and ‘vorticity area index’ (VAI) describing the tropospheric cyclonic perturbations. The epoch superposition method is used to reveal effects of the solar central meridian (CM) passage of active regions, the Forbush decreases (FD) in galactic cosmic rays, and the solar proton (SP) events. The results of the analysis show that influence of short-term changes in the solar activity on baric field perturbations is the most evident in the stratosphere (30 mbar-level). The meridional circulation in case of the FD and SP events begin to increase about 5–7 days before the key date, reaches maximum nearby the key date and decays after the key date. The meridional circulation in case of the solar CM passage of active regions starts to increase after the key date and reaches the maximum by 5–6 days. Fluctuations of baric field within periods of 5–7 days typical of meridional and zonal transfers in troposphere (500 mbar-level) are evidently connected with internal dynamics of the atmosphere, not with the effects of solar activity. VAI characterizing cyclonic activity in the troposphere, shows the striking correspondence to changes of the meridional circulation in the stratosphere. Comparison of changes in the stratospheric perturbations with behavior of the UV irradiance in course of the FD and SP events show their full correspondence at the initial stage of these processes. The conclusion is made that growth of baric perturbations observed in the stratosphere in associations with the FD and SP events before the key date is caused by the solar UV irradiance increase, whereas decay of the baric perturbations after the key date is related to direct influence of the solar energetic corpuscular fluxes on the stratosphere.

Evidence for influence of the solar wind variations on atmospheric temperature in the southern polar region

Abstract Detailed analysis of meteorological and aerological data from Vostok station (Antarctica) for 1978–1992 made it possible to conclude that dramatic changes of the troposphere temperature, observed in the southern polar region, are related to the variations of the interplanetary magnetic field (IMF). The warming is observed at ground level and cooling at h>10 km if the IMF vertical component decreases (Δ B Z h>10 km ) is observed for Δ B Z >0. There is a linear relationship between the value of change in the interplanetary electric field (Δ E SW ) and ground temperature at Vostok station: the larger is the leap in the E SW the stronger is the temperature deviation. The effect reaches maximum within 1 day and is damped equally quickly. The tropospheric pressure and horizontal winds respond to the E SW fluctuations as well. It is suggested that the interplanetary electric field affects the katabatic system of atmospheric circulation typical of the ice dome in winter Antarctic.

Ionospheric Pc5 plasma oscillations observed by the King Salmon HF radar and their comparison with geomagnetic pulsations on the ground and in geostationary orbit

[1]xa0We analyzed Pc5 (1.7–6.7 mHz) oscillations of ionospheric Doppler plasma velocity observed on a westward pointing beam 3 of the SuperDARN King Salmon HF radar in Alaska during the solar maximum in 2002 and the minimum in 2007. Local time distributions of the ionospheric Pc5 oscillations showed peculiar asymmetric characteristics in both years; that is, the occurrence probability had a maximum around the magnetic midnight, whereas backscatter echoes exhibited almost no oscillation on the dayside. We compared these ionospheric Pc5 events with magnetic field variations on the ground under the radar beam at Pebek and King Salmon and the geostationary ETS-8 satellite at almost conjugate longitude. We found only a few nightside events where both the radar and magnetometers detected similar sinusoidal oscillations. On the other hand, from statistical spectral analyses we found that there were positive correlations between the integrated Pc5 range spectral power of velocity oscillations and the geomagnetic pulsations both on the ground and in geostationary orbit although the pulsation powers were quite low. For these ionospheric Pc5 events, we found that both solar wind bulk flow speed and dynamic pressure showed no correlation with the spectral power and more than half of the Pc5 events were observed when the geomagnetic activities were low as inferred from the AE and Dst indices. These results indicate that the azimuthal Pc5 oscillation in the ionospheric plasma flow does not represent well-known characteristics of Pc5 pulsations driven by solar wind changes. We consider that the nightside occurrence peak of the ionospheric Pc5 oscillation might be related to diurnal changes in the ionospheric conductivity, which controls the amplitude of wave electric fields in the ionosphere. Therefore, the Pc5 wave power distributions obtained by radar observations provide features different from those obtained from magnetic field observations.

PC index as a proxy of the solar wind energy that entered into the magnetosphere: Development of magnetic substorms

The Polar Cap (PC) index has been approved by the International Association of Geomagnetism and Aeronomy (IAGA XXII Assembly, Merida, Меxico, 2013) as a new index of magnetic activity. The PC index can be considered to be a proxy of the solar wind energy that enters the magnetosphere. This distinguishes PC from AL and Dst indices that are more related to the dissipation of energy through auroral currents or storage of energy in the ring current during magnetic substorms or storms. The association of the PC index with the direct coupling of the solar wind energy into the magnetosphere is based upon analysis of the relationship of PC with parameters in the solar wind, on the one hand, and correlation between the time series of PC and the AL index (substorm development), on the other hand. This paper (the first of a series) provides the results of statistical investigations that demonstrate a strong correlation between the behavior of PC and the development of magnetic substorms. Substorms are classified as isolated and expanded. We found that (1) substorms are preceded by growth in the РС index, (2) sudden substorm expansion onsets are related to “leap” or “reverse” signatures in the PC index which are indicative of a sharp increase in the PC growth rate, (3) substorms start to develop when PC exceeds a threshold level 1.5u2009±u20090.5u2009mV/m irrespective of the length of the substorm growth phase, and (4) there is a linear relation between the intensity of substorms and PC for all substorm events.