1. Introduction

In the latest years, the Sun-Earth environment is studied to explain observed physical phenomena in the context of space weather/climate, such as climate changes. It is well known that the Sun continuously transfers its energy to the Earth's environment through radiation and solar wind (SW). Although the Sun's radiation represents the main source affecting the Earth's atmosphere, the SW energy plays an important role during high geomagnetic activity time intervals [1]. On this regard, the magnetosphere-ionosphere represents a complex system able to partially convert SW impacting energy through nonlinearly related physical processes. Such effects are more evident at high latitudes where reconnection processes between interplanetary magnetic field (IMF), carried out by the solar wind, and magnetospheric field occur, making the polar cap an important laboratory to study the SW-atmosphere interactions. Solar wind-driven electrodynamic processes and ultralow frequency (ULF, 1 mHz–5 Hz) waves seem to lead to both diffusion and precipitation processes of energetic electrons in the outer radiation belts, leading

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*Antarctica - A Key to Global Change*

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also to chemical [2] and microphysical [3] processes in the atmosphere, characterized by different timescales.

radiation belt, leading particle precipitations, as well as polar cap potential difference related with SW parameters; in Section 3, we present the experimental evidence of SW effects on the atmospheric parameters in Antarctica at stratospheric and tropospheric heights; finally, in Section 4, we discuss the estimated timescale response of atmospheric parameters and the possible physical processes involved in SW-atmosphere coupling processes. For greater clarity, we described data analysis

ULF Geomagnetic Activity Signatures in the Atmospheric Parameters in Antarctica

2. The solar wind-magnetosphere coupling processes at high latitudes

2.1 ULF interaction with relativistic electrons in the outer radiation belts

ULF magnetohydrodynamic waves received particular attention in the past decades [18–23], since they provide a convenient probe of the magnetosphere, by means of ground [24–26] and/or satellites magnetic field measurements [22, 27–30]

Generated by a variety of instabilities, ULF waves transport energy throughout the magnetosphere and are observed on the ground as continuous pulsations (Pc, Table 1). They can play important roles in the energization and loss of radiation belt particles (see [34] for a review). In particular, ULF waves can interact with the relativistic electrons (>300 keV) magnetically trapped in the radiation belts (L 5–7 Re, λ 60–70°, where L is the McIlwain parameter). In that regions, the charged particle is subject to gyro, bounce, and drift periodic motions (see Table 1),

In particular, wave-particle interactions are theoretically predicted [37, 38] because drift and bounce motion frequencies of trapped electrons are in the Pc5 (1–7 mHz) and Pc1-2 (100 mHz–5 Hz) frequency range, respectively. Experimental evidence confirms diffusion/acceleration of energetic electrons by Pc5 magnetospheric waves [39–42] and their precipitations after pitch angle scattering, due to gyro-resonant interaction with electromagnetic ion cyclotron (EMIC) waves [38–41]. Such waves are in the Pc1-2 frequency range and are generated at the magnetic equator by unstable distributions of ring current ions during geomagnetic storms [43]. Moreover, recent investigations show that Pc5 waves have their origin also in the leading edge of the corotating interaction regions (CIR) [42], while the

The estimation of the Earth's surface temperature and lower atmosphere energy budget significantly changes due to small amount, distribution, or radiative properties of clouds [16]: therefore, they represent one of the largest sources of uncertainty in predictions of climate change [17]. Even small atmospheric electrical modulations can affect aerosol nucleation processes and cloud condensation nuclei production in troposphere and thus modify cloud properties. In this regard, the polar cap electrodynamics and the energetic particle precipitation seem to be important SW-atmosphere coupling mechanisms, responsible for atmospheric changes on timescales from several weeks to days. It is also known that a global electric current flows in the global electric circuit. It is generated mainly by charge separation in clouds at the tropics and maintains the global ionosphere at a potential of about 250 kV. Variations above and below this value occur in the high-latitude regions due to SW-magnetosphere-ionosphere coupling processes. In this section, we briefly discuss the solar wind-magnetosphere coupling processes, which could produce observable effects in the stratospheric and tropospheric dynamics due to energetic particle precipitation from the outer radiation belt, as well as to the polar

and methods in each section.

DOI: http://dx.doi.org/10.5772/intechopen.81106

cap electrodynamics at high latitudes.

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as well as inspect ground conductivity [31–33].

each one characterized by different timescales [35–36].

The longer-term response, characterized by timescales of several weeks, is usually attributed to the odd nitrogen (NOx) production, due to precipitating energetic electrons, in the mesosphere and lower thermosphere. During the polar winter, NOx can live long enough to be transported downward into the stratosphere where it chemically perturbs the ozone distribution, altering the radiative balance in that region of the atmosphere.

This can in turn affect the overall circulation in the stratosphere, and such changes can propagate to the surface level, eventually leading to detectable changes in surface air temperatures, through dynamical coupling processes occurring on timescales of several weeks (e.g., [2, 4–6]).

Conversely, the shorter-time response (<1 day) of the atmosphere to the SWmagnetosphere coupling processes is probably related to changes in the atmospheric electrodynamics. It can be attributed to electric conductivity variations in the lower atmosphere by ionization mechanisms and/or to changes of the polar cap electric potential induced by SW perturbations [7]. The consequent modulation of the current density which flows from the upper boundary (being as low as 60 km, [8]) through the troposphere to the ground in the global electric circuit (GEC) [3, 9–11] could influence cloud formation through the release of latent heat, which in turn can affect atmospheric dynamics [12].

This work represents a review of our investigations on the experimental observation of the possible short (within 1 day) timescale response of the atmosphere to the SW dynamics, observed during 2003–2010, which correspond to the solar cycle 23 and the beginning of solar cycle 24. We analyzed the geomagnetic field variations monitored at the Mario Zucchelli station, at Terra Nova Bay (TNB, AACGM latitude λ = 80.01°S and longitude φ = 306.94°E) in Antarctica, and atmospheric parameters at tropospheric and stratospheric heights, provided by ERA-Interim and Monitoring Atmospheric Composition and Climate (MACC) reanalysis archives (http://apps.ecmwf.int/datasets).

The ERA-Interim is a global atmospheric reanalysis dataset, continuously updated in real time (see [13] and references therein). Global atmospheric and surface parameters from 1 January 1979 are available from the surface up to 0.1 hPa as atmospheric fields on model levels and pressure levels, with a temporal resolution of 6 h, and as surface fields with a temporal resolution of 3 h. The data assimilation system used to produce ERA-Interim is based on a 2006 release of the ECMWF Integrated Forecast Model (IFS Cy31r2). The MACC dataset is a global reanalysis dataset of atmospheric composition data, produced by assimilating satellite data into a global model and data assimilation system (see [14] and references therein). The system includes a four-dimensional variational analysis (4D-Var) with a temporal resolution of 12 h analysis window. The ERA-Interim and MACC data, at 1 day resolution used for our studies, have been retrieved from the Meteorological Archival and Retrieval System at ECMWF.

Solar wind parameters and interplanetary magnetic field are monitored by using OMNI data, time-shifted to the bow shock nose (i.e., the subsolar position of the supersonic-to-subsonic transition regions) and collected on CDAWeb (http:// cdaweb.gsfc.nasa.gov). Geomagnetic activity was monitored by using a triaxial search-coil magnetometer data, recorded at TNB, at a sampling rate of 1 s.

The atmospheric parameters must be whitened to filter the longer period components (essentially 1 year and 6 months), which would obscure the weak effects produced by the ULF geomagnetic activity [15].

This review is structured as follows: in Section 2, we shortly introduce the interactions occurring between ULF waves and the energetic electrons in the outer ULF Geomagnetic Activity Signatures in the Atmospheric Parameters in Antarctica DOI: http://dx.doi.org/10.5772/intechopen.81106

radiation belt, leading particle precipitations, as well as polar cap potential difference related with SW parameters; in Section 3, we present the experimental evidence of SW effects on the atmospheric parameters in Antarctica at stratospheric and tropospheric heights; finally, in Section 4, we discuss the estimated timescale response of atmospheric parameters and the possible physical processes involved in SW-atmosphere coupling processes. For greater clarity, we described data analysis and methods in each section.
