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

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

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

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

also to chemical [2] and microphysical [3] processes in the atmosphere, character-

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

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

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

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 Archi-

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

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

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

ized by different timescales.

Antarctica - A Key to Global Change

region of the atmosphere.

timescales of several weeks (e.g., [2, 4–6]).

can affect atmospheric dynamics [12].

(http://apps.ecmwf.int/datasets).

val and Retrieval System at ECMWF.

6

produced by the ULF geomagnetic activity [15].


#### Table 1.

ULF wave classification and the characteristic timescales for the three types of trapped particle motion (see also [37]).

origin of the Pc1-2 waves, observed at �80° latitude, appears to be due to substorm/storm-related instabilities and, in the dayside, to solar wind compressions of the magnetopause [44]. After conversion into Alfvén (shear) waves, ULF waves propagate along the geomagnetic field lines and can be observed on the ground at high latitudes [45, 46]. An example of energetic electron flux enhancements observed at geosynchronous orbit (L � 6.6) associated to Pc5 power fluctuations measured on the ground and in the magnetosphere is shown in Figure 1, [42]; the electron flux seems to be delayed by �2 days with respect to pulsation power.

### 2.2 The roles of relativistic electron precipitation and the polar cap electrodynamics in the global electric circuit model at high latitudes

As discussed by Tinsley and Yu [48], the galactic cosmic rays (GCR) flux is responsible for almost all the production of ionization below 15 km of altitude, which determines the conductivity in that region and at high latitudes. However, the MeV electrons and their associated X-rays produce ionization in the stratosphere and higher troposphere, which can affect the local conductivity (see also [7]). Moreover, due to electric potential difference between the ionospheric layer and the ground, a vertical current density is present:

$$J\_{\mathbf{z}} = \sigma E\_{\mathbf{z}}.\tag{1}$$

changes arise in addition to the day-to-day variability in Jz, caused by thunderstorm

(Top) The relativistic electron flux (>600 keV) measured by GOES 12 satellite at geosynchronous orbit (red) and the geomagnetic power at TNB (black). (Bottom) The cross-correlation of the >600 keV (solid) and >2 MeV (dashed) electron flux with the Pc5 power at TNB, at low latitude station of L'Aquila AQU, and at GOES 12 during 2007–2008, together with the 95% confidence levels (dashed, gray lines). Figure adapted from [42]. It clearly emerges a higher correlation with the >600 keV electron flux at a shorter-time delay (1.8– 2 days) with respect to the >2 MeV electrons (2–2.4 days), with an approximately 9 h difference, probably due

ULF Geomagnetic Activity Signatures in the Atmospheric Parameters in Antarctica

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

In particular, the B<sup>y</sup> (dawn-dusk) and B<sup>z</sup> (south-north) components of the IMF represent the main parameters controlling the electrodynamics in the upper atmosphere (i.e., the ionosphere): B<sup>z</sup> is important in the reconnection process in the dayside magnetopause, while B<sup>y</sup> affects the latitudinal dawn-dusk electrostatic

An example of polar cap electric potential in the southern hemisphere is show in Figure 2, obtained using the Weimer [50, 51] ionospheric electrodynamic model. In this example, we assigned values of 5 nT for B<sup>y</sup> and Bz, assuming a solar wind speed of VSW = 450 km/s and a solar wind number density of nSW = 3 cm<sup>3</sup>

clearly seen that two regions of polar cap potential, characterized by positive (dawnward) and negative (duskward) values of approximately 40 kV, are emerging during periods characterized by SW-magnetosphere coupling (i.e., during B<sup>z</sup> < 0), indicating higher dawn-dusk polar cap potential drop. Conversely, during closed magnetosphere (B<sup>z</sup> > 0, left panels), lower polar cap potential difference is obtained. It implies that E<sup>z</sup> increases at high latitudes during IMF-magnetosphere reconnection (B<sup>z</sup> < 0) conditions. Furthermore, both σ and E<sup>Z</sup> in Eq. (1) can be significantly influenced by geomagnetic activity. In this regard, ULF activity could play an important role in the GEC model, leading to the clouds' physical changes and radiative properties. Indeed, the ULF activity in general is associated to storms and substorms, i.e., to the occurrence of a southward IMF and, at high latitudes, polar cap electric field; therefore, ULF activity can be regarded also as a proxy of the

. It is

activity and present at all latitudes.

to the timescales of the acceleration processes, in agreements with [47].

polar cap potential difference [52, 53].

9

potential asymmetry [49].

Figure 1.

It is directed along the stratosphere-troposphere-ground direction z, and it varies horizontally, due to variations in the local vertical column resistance represented by its resistivity σ and by variations in the local ionospheric potential φ(E). While σ is affected by the GCR and precipitating MeV electron fluxes from the outer radiation belt into the atmosphere, φ(E) is strongly dependent on SW-magnetosphere coupling process. In particular, the potential increases in the polar cap where geomagnetic field lines map to magnetospheric regions characterized by coupling processes with the interplanetary magnetic field (IMF); because Jz, flowing through clouds in the troposphere, responds to conductivity and potential changes occurring up to 120 km altitude, it is very effective in linking stratosphere and ionosphere with clouds. Recent reviews by Lam and Tinsley [3] and Mironova et al. [7] well discuss the atmosphere response to current density changes near the poles caused by the interaction of the solar wind with the geomagnetic field; such

ULF Geomagnetic Activity Signatures in the Atmospheric Parameters in Antarctica DOI: http://dx.doi.org/10.5772/intechopen.81106

#### Figure 1.

origin of the Pc1-2 waves, observed at �80° latitude, appears to be due to

ULF waves Magnetically trapped particles

Pc4 7–22 45–150 —— — Pc3 22–100 10–45 —— — Pc2 100–200 5–10 —— — Pc1 200–5000 0.2–5 10�<sup>1</sup> 10<sup>0</sup> Bounce

periodicity (s)

Electrons Protons

–10�<sup>4</sup> 10�<sup>1</sup>

–10<sup>3</sup> 102 Drift

–10�<sup>2</sup> Gyro

Motion type

Pulsation type Frequency range (mHz) Period range (s) Characteristic

Pc5 2–7 150–600 10<sup>2</sup>

Antarctica - A Key to Global Change

— —— 10�<sup>3</sup>

Table 1.

[37]).

8

Periodicity correspondence between relativistic electrons and ULF waves is marked in bold.

2.2 The roles of relativistic electron precipitation and the polar cap

and the ground, a vertical current density is present:

electrodynamics in the global electric circuit model at high latitudes

As discussed by Tinsley and Yu [48], the galactic cosmic rays (GCR) flux is responsible for almost all the production of ionization below 15 km of altitude, which determines the conductivity in that region and at high latitudes. However, the MeV electrons and their associated X-rays produce ionization in the stratosphere and higher troposphere, which can affect the local conductivity (see also [7]). Moreover, due to electric potential difference between the ionospheric layer

It is directed along the stratosphere-troposphere-ground direction z, and it varies horizontally, due to variations in the local vertical column resistance represented by its resistivity σ and by variations in the local ionospheric potential φ(E). While σ is affected by the GCR and precipitating MeV electron fluxes from the outer radiation belt into the atmosphere, φ(E) is strongly dependent on SW-magnetosphere coupling process. In particular, the potential increases in the polar cap where geomagnetic field lines map to magnetospheric regions characterized by coupling processes with the interplanetary magnetic field (IMF); because Jz, flowing through clouds in the troposphere, responds to conductivity and potential changes occurring up to 120 km altitude, it is very effective in linking stratosphere and ionosphere with clouds. Recent reviews by Lam and Tinsley [3] and Mironova et al. [7] well discuss the atmosphere response to current density changes near the poles caused by the interaction of the solar wind with the geomagnetic field; such

J<sup>z</sup> ¼ σEz: (1)

substorm/storm-related instabilities and, in the dayside, to solar wind compressions of the magnetopause [44]. After conversion into Alfvén (shear) waves, ULF waves propagate along the geomagnetic field lines and can be observed on the ground at high latitudes [45, 46]. An example of energetic electron flux enhancements observed at geosynchronous orbit (L � 6.6) associated to Pc5 power fluctuations measured on the ground and in the magnetosphere is shown in Figure 1, [42]; the electron flux seems to be delayed by �2 days with respect to pulsation power.

ULF wave classification and the characteristic timescales for the three types of trapped particle motion (see also

(Top) The relativistic electron flux (>600 keV) measured by GOES 12 satellite at geosynchronous orbit (red) and the geomagnetic power at TNB (black). (Bottom) The cross-correlation of the >600 keV (solid) and >2 MeV (dashed) electron flux with the Pc5 power at TNB, at low latitude station of L'Aquila AQU, and at GOES 12 during 2007–2008, together with the 95% confidence levels (dashed, gray lines). Figure adapted from [42]. It clearly emerges a higher correlation with the >600 keV electron flux at a shorter-time delay (1.8– 2 days) with respect to the >2 MeV electrons (2–2.4 days), with an approximately 9 h difference, probably due to the timescales of the acceleration processes, in agreements with [47].

changes arise in addition to the day-to-day variability in Jz, caused by thunderstorm activity and present at all latitudes.

In particular, the B<sup>y</sup> (dawn-dusk) and B<sup>z</sup> (south-north) components of the IMF represent the main parameters controlling the electrodynamics in the upper atmosphere (i.e., the ionosphere): B<sup>z</sup> is important in the reconnection process in the dayside magnetopause, while B<sup>y</sup> affects the latitudinal dawn-dusk electrostatic potential asymmetry [49].

An example of polar cap electric potential in the southern hemisphere is show in Figure 2, obtained using the Weimer [50, 51] ionospheric electrodynamic model. In this example, we assigned values of 5 nT for B<sup>y</sup> and Bz, assuming a solar wind speed of VSW = 450 km/s and a solar wind number density of nSW = 3 cm<sup>3</sup> . It is clearly seen that two regions of polar cap potential, characterized by positive (dawnward) and negative (duskward) values of approximately 40 kV, are emerging during periods characterized by SW-magnetosphere coupling (i.e., during B<sup>z</sup> < 0), indicating higher dawn-dusk polar cap potential drop. Conversely, during closed magnetosphere (B<sup>z</sup> > 0, left panels), lower polar cap potential difference is obtained. It implies that E<sup>z</sup> increases at high latitudes during IMF-magnetosphere reconnection (B<sup>z</sup> < 0) conditions. Furthermore, both σ and E<sup>Z</sup> in Eq. (1) can be significantly influenced by geomagnetic activity. In this regard, ULF activity could play an important role in the GEC model, leading to the clouds' physical changes and radiative properties. Indeed, the ULF activity in general is associated to storms and substorms, i.e., to the occurrence of a southward IMF and, at high latitudes, polar cap electric field; therefore, ULF activity can be regarded also as a proxy of the polar cap potential difference [52, 53].

Figure 2.

Computed polar cap electric potential, obtained using Weimer [50, 51] ionospheric electrodynamic model at the equinoctial day 100 of the year 2000 in the southern hemisphere, for open (B<sup>z</sup> < 0, left panels) and closed (B<sup>z</sup> > 0, right panels) magnetospheric conditions. The meridians are separated by 2 h (MLT) and the geomagnetic parallels by 15°. The morning (afternoon) side corresponds to the right (left) side of each panel.

Figure 3.

Figure 4.

11

marked with vertical lines. Figure adapted from [54].

The normalized global wavelet (GW) analysis during the summer (first column) and winter (second column) in 2007 (top panels); the GW, normalized to the corresponding variances, of the ULF activity indexes logPc5 and logPc1-2 at TNB, and of φcap (bottom panels). The three first maximum values of the normalized GW are

ULF Geomagnetic Activity Signatures in the Atmospheric Parameters in Antarctica

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

Time averaged cross-wavelet amplitude (Wxy) between temperature T and zonal wind U with (top) logPc1-2, (middle) logPc5, and (bottom) polar cap potential difference φcap during summer and winter months in 2007, as a function of period and altitude h. In each panel, the black contour lines mark the 90% (thin) and 95% (bold) significance level of time-averaged wavelet coherence. Vertical lines indicate the periodicities observed in

solar wind and geomagnetic activity (Figure 3). Figure adapted from [54].

## 3. Experimental evidence of signatures of solar wind effects in the atmospheric parameters

In their study, Francia et al. [15] examined surface air temperature measured at the automatic weather station ENEIDE, located at TNB, during 2007–2008, while signatures of ULF activity and polar cap potential difference were found by [54] in the stratosphere and troposphere, using the ERA-Interim reanalysis dataset.

Figure 3 shows the global wavelet (GW), i.e., the time-averaged wavelet [55, 56], separately for summer and winter months, of Pc5 and Pc1-2 powers at TNB and of the polar cap potential difference φcap [54].

Common power peaks emerge at 27 days, the Sun synodic rotation period, and its first subharmonics (13.5 and 9 days), in the SW-related parameter φcap and correspondingly in the ULF activity. In particular, in Figure 4 signatures of ULF activity and polar cap potential difference in temperature T and zonal wind U at tropospheric and stratospheric heights above TNB are observed. In their work [54], cross-wavelet Wxy and wavelet coherence γ<sup>2</sup> [56] are computed between SW-driven and atmospheric parameters; the analysis was supported by the Monte Carlo test for the estimation of significance levels.

In can be seen from Figure 4 that the correspondence at 27 days is high and statistically significant in both the troposphere and the stratosphere during winter months, while at 13.5 days it is restricted to h < 10 km. During summer, the crosswavelet Wxy for T shows very low values and an ambiguous correspondence at the ULF Geomagnetic Activity Signatures in the Atmospheric Parameters in Antarctica DOI: http://dx.doi.org/10.5772/intechopen.81106

#### Figure 3.

3. Experimental evidence of signatures of solar wind effects in the

Computed polar cap electric potential, obtained using Weimer [50, 51] ionospheric electrodynamic model at the equinoctial day 100 of the year 2000 in the southern hemisphere, for open (B<sup>z</sup> < 0, left panels) and closed (B<sup>z</sup> > 0, right panels) magnetospheric conditions. The meridians are separated by 2 h (MLT) and the geomagnetic parallels by 15°. The morning (afternoon) side corresponds to the right (left) side of each panel.

In their study, Francia et al. [15] examined surface air temperature measured at the automatic weather station ENEIDE, located at TNB, during 2007–2008, while signatures of ULF activity and polar cap potential difference were found by [54] in the stratosphere and troposphere, using the ERA-Interim reanalysis dataset. Figure 3 shows the global wavelet (GW), i.e., the time-averaged wavelet [55, 56], separately for summer and winter months, of Pc5 and Pc1-2 powers at TNB

Common power peaks emerge at 27 days, the Sun synodic rotation period, and

its first subharmonics (13.5 and 9 days), in the SW-related parameter φcap and correspondingly in the ULF activity. In particular, in Figure 4 signatures of ULF activity and polar cap potential difference in temperature T and zonal wind U at tropospheric and stratospheric heights above TNB are observed. In their work [54], cross-wavelet Wxy and wavelet coherence γ<sup>2</sup> [56] are computed between SW-driven and atmospheric parameters; the analysis was supported by the Monte Carlo test for

In can be seen from Figure 4 that the correspondence at 27 days is high and statistically significant in both the troposphere and the stratosphere during winter months, while at 13.5 days it is restricted to h < 10 km. During summer, the crosswavelet Wxy for T shows very low values and an ambiguous correspondence at the

atmospheric parameters

Antarctica - A Key to Global Change

Figure 2.

10

the estimation of significance levels.

and of the polar cap potential difference φcap [54].

The normalized global wavelet (GW) analysis during the summer (first column) and winter (second column) in 2007 (top panels); the GW, normalized to the corresponding variances, of the ULF activity indexes logPc5 and logPc1-2 at TNB, and of φcap (bottom panels). The three first maximum values of the normalized GW are marked with vertical lines. Figure adapted from [54].

#### Figure 4.

Time averaged cross-wavelet amplitude (Wxy) between temperature T and zonal wind U with (top) logPc1-2, (middle) logPc5, and (bottom) polar cap potential difference φcap during summer and winter months in 2007, as a function of period and altitude h. In each panel, the black contour lines mark the 90% (thin) and 95% (bold) significance level of time-averaged wavelet coherence. Vertical lines indicate the periodicities observed in solar wind and geomagnetic activity (Figure 3). Figure adapted from [54].

27 day periodicity for all input parameters. Interestingly, a Wxy and γ<sup>2</sup> attenuation can be seen, especially during winter months, near to the tropopause position (7– 10 km). Regarding U, high and significant Wxy and γ<sup>2</sup> values are found mostly in the stratosphere, at 27 and 13.5 day periodicities, during winter months. During summer the pattern is similar but with lower values.

able to produce changes in the atmospheric parameters, such as temperature. In particular, the accumulation of charge on droplets and aerosol particles, most importantly the interstitial cloud condensation nuclei (CCN) and ice-forming

ULF Geomagnetic Activity Signatures in the Atmospheric Parameters in Antarctica

heat, and the amount of water vapor released into the troposphere.

Scavenging is due to collisions between the nuclei and droplets, entailing sizedependent collection of nuclei and changes in their size distribution and overall concentration. It affects a number of microphysical processes, which cause changes in macroscopic cloud properties and in turn partitioning of energy flow in the system. In particular, the charge can increase or decrease the scavenging rates, depending on size, changing the concentrations and size distributions. Size distribution changes in CCN produce size distribution changes in droplets, affecting coagulation, precipitation, latent heat transfer, and cloud cover. Scavenging of iceforming nuclei by supercooled droplets promotes contact ice nucleation, releasing latent heat. The latent heat changes cause storm invigoration [59] and in winter storms can cause changes in the amplitude of Rossby waves and blocking. Since the typical lifetime of CCN in an air mass can be up to 10 days, the change in their properties can affect also later cycle of evaporation/condensation, flux of latent

Figure 6 shows the results of superposed epoch analysis (SEA) conducted by

Composites of the zonal mean of temperature C<sup>T</sup> and specific humidity C<sup>Q</sup> at the epoch for different orientations of the IMF, where N represents the number of cases. Solid and dashed lines indicate the 90% confidence levels. The gray region represents the longitudinally averaged Antarctic icy surface profile. Figure adapted from [57].

[57] on Q and T at the epoch for different orientations of the IMF. It shows correspondence in T and Q, more evident during the IMF B<sup>z</sup> < 0 and B<sup>y</sup> > 0 conditions, i.e., when the interplanetary electric field is efficiently transmitted into the high-latitude ionosphere and the dawn-dusk polar cap potential difference φcap, due to E<sup>y</sup> = VSWBz, as well as the vertical E<sup>z</sup> = VSWBy, increases (see also Figure 2). In particular, the vertical electric field during southward IMF conditions can be directly transferred in the ionospheric polar cap in the southern hemisphere,

nuclei (IFN), directly affects scavenging rates.

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

Figure 6.

13

Analyzing the tropospheric temperature, specific humidity Q and cloud cover (CC) in Antarctica, Regi et al. [57] found further experimental evidence of SWatmosphere coupling. In particular, the authors analyzed 54 high geomagnetic activity time intervals, by using the superposed epoch analysis with the Monte Carlo test [58].

The results, shown in Figure 5, revealed a clear correspondence between Pc1-2 and variations in temperature, specific humidity, and cloud cover. The most significant correspondence is found at latitudes higher than 85°S in both T and Q parameters. Positive variations occurred at the epoch and 1 day after, suggesting that Pc1-2 power affects the specific humidity and the tropospheric temperature within 1 day; negative variations occurred at 2 days after the epoch.

Regarding the cloud cover (zonal mean) composite averages, computed at low (LCC, h < 3 km), medium (MCC, 3 < h < 6 km), and high (HCC, h > 6 km) altitudes, (see Figure 5, bottom panels), we found that the main effect of the ULF activity on these parameters consists in an increase in the HCC and MCC at the epoch. Moreover, we also found a significant variation at 1 day after and a decrease at 2 days after the epoch.

As discussed in the Introduction, GEC affects atmospheric parameters, such as cloud cover through several proposed microphysical processes (e.g., [3, 10, 48])

#### Figure 5.

(Top and middle panels) Composites of the zonal mean of temperature C<sup>T</sup> and specific humidity C<sup>Q</sup> of 54 selected epochs (corresponding to geomagnetic active periods) as a function of latitude and altitude. Solid and dashed lines indicate the 90% confidence levels. The gray region represents the longitudinally averaged Antarctic icy surface profile. (Bottom panels) Composite mean of cloud cover at different altitudes CLCC (h < 3 km), CMCC (3 < h < 6 km), and CHCC (h > 6 km) as a function of latitude; the bold lines mark composites statistically relevant. Figure adapted from [57].

#### ULF Geomagnetic Activity Signatures in the Atmospheric Parameters in Antarctica DOI: http://dx.doi.org/10.5772/intechopen.81106

able to produce changes in the atmospheric parameters, such as temperature. In particular, the accumulation of charge on droplets and aerosol particles, most importantly the interstitial cloud condensation nuclei (CCN) and ice-forming nuclei (IFN), directly affects scavenging rates.

Scavenging is due to collisions between the nuclei and droplets, entailing sizedependent collection of nuclei and changes in their size distribution and overall concentration. It affects a number of microphysical processes, which cause changes in macroscopic cloud properties and in turn partitioning of energy flow in the system. In particular, the charge can increase or decrease the scavenging rates, depending on size, changing the concentrations and size distributions. Size distribution changes in CCN produce size distribution changes in droplets, affecting coagulation, precipitation, latent heat transfer, and cloud cover. Scavenging of iceforming nuclei by supercooled droplets promotes contact ice nucleation, releasing latent heat. The latent heat changes cause storm invigoration [59] and in winter storms can cause changes in the amplitude of Rossby waves and blocking. Since the typical lifetime of CCN in an air mass can be up to 10 days, the change in their properties can affect also later cycle of evaporation/condensation, flux of latent heat, and the amount of water vapor released into the troposphere.

Figure 6 shows the results of superposed epoch analysis (SEA) conducted by [57] on Q and T at the epoch for different orientations of the IMF. It shows correspondence in T and Q, more evident during the IMF B<sup>z</sup> < 0 and B<sup>y</sup> > 0 conditions, i.e., when the interplanetary electric field is efficiently transmitted into the high-latitude ionosphere and the dawn-dusk polar cap potential difference φcap, due to E<sup>y</sup> = VSWBz, as well as the vertical E<sup>z</sup> = VSWBy, increases (see also Figure 2). In particular, the vertical electric field during southward IMF conditions can be directly transferred in the ionospheric polar cap in the southern hemisphere,

Composites of the zonal mean of temperature C<sup>T</sup> and specific humidity C<sup>Q</sup> at the epoch for different orientations of the IMF, where N represents the number of cases. Solid and dashed lines indicate the 90% confidence levels. The gray region represents the longitudinally averaged Antarctic icy surface profile. Figure adapted from [57].

27 day periodicity for all input parameters. Interestingly, a Wxy and γ<sup>2</sup> attenuation can be seen, especially during winter months, near to the tropopause position (7– 10 km). Regarding U, high and significant Wxy and γ<sup>2</sup> values are found mostly in the stratosphere, at 27 and 13.5 day periodicities, during winter months. During

Analyzing the tropospheric temperature, specific humidity Q and cloud cover (CC) in Antarctica, Regi et al. [57] found further experimental evidence of SWatmosphere coupling. In particular, the authors analyzed 54 high geomagnetic activity time intervals, by using the superposed epoch analysis with the Monte

The results, shown in Figure 5, revealed a clear correspondence between Pc1-2 and variations in temperature, specific humidity, and cloud cover. The most significant correspondence is found at latitudes higher than 85°S in both T and Q parameters. Positive variations occurred at the epoch and 1 day after, suggesting that Pc1-2 power affects the specific humidity and the tropospheric temperature within

Regarding the cloud cover (zonal mean) composite averages, computed at low

As discussed in the Introduction, GEC affects atmospheric parameters, such as cloud cover through several proposed microphysical processes (e.g., [3, 10, 48])

(Top and middle panels) Composites of the zonal mean of temperature C<sup>T</sup> and specific humidity C<sup>Q</sup> of 54 selected epochs (corresponding to geomagnetic active periods) as a function of latitude and altitude. Solid and dashed lines indicate the 90% confidence levels. The gray region represents the longitudinally averaged Antarctic icy surface profile. (Bottom panels) Composite mean of cloud cover at different altitudes CLCC (h < 3 km), CMCC (3 < h < 6 km), and CHCC (h > 6 km) as a function of latitude; the bold lines mark composites

(LCC, h < 3 km), medium (MCC, 3 < h < 6 km), and high (HCC, h > 6 km) altitudes, (see Figure 5, bottom panels), we found that the main effect of the ULF activity on these parameters consists in an increase in the HCC and MCC at the epoch. Moreover, we also found a significant variation at 1 day after and a decrease

summer the pattern is similar but with lower values.

Antarctica - A Key to Global Change

1 day; negative variations occurred at 2 days after the epoch.

Carlo test [58].

at 2 days after the epoch.

Figure 5.

12

statistically relevant. Figure adapted from [57].

leading to a vertical current J<sup>z</sup> = σE<sup>z</sup> from the ionosphere to the ground through the stratospheric and tropospheric layers.

However, the different time delays in different years could be due to variations in

ULF Geomagnetic Activity Signatures in the Atmospheric Parameters in Antarctica

In this work we presented a short review of our experimental results regarding the possible relationship between SW and atmospheric parameters at high latitude, in Antarctica, at Terra Nova Bay. Examining possible relationship between geomagnetic activity in the Pc1-2 and Pc5 frequency range and the polar cap potential difference with stratospheric and tropospheric parameters, the results provided in

• Common power peaks emerge at 27 days, the synodic Sun rotation period, and its first subharmonics (13.5 and 9 days), in the polar cap potential

zonal wind at tropospheric and stratospheric altitudes (Figure 4).

in the stratosphere it appears mostly at the 27 day periodicity.

• The correspondence is more evident during winter, when solar radiation-

difference φcap and in the ULF activity (Figure 3) and in the temperature and

• Around the tropopause, approximately at 8 km, the correspondence is low, and

Further investigations [57] at tropospheric heights at high latitudes indicate that SW-driven electrodynamic processes and energetic particle precipitation related with enhancement of Pc1-2 activity can affect tropospheric temperature, specific humidity, and cloud cover. The response is quick (within 1 day) at ground and in the troposphere. These results suggest that the electrodynamics modulate the physical properties of clouds, probably through electron scavenging microphysical mechanism. It is a matter of fact that electron scavenging is strongly dependent on vertical tropospheric-stratospheric conductivity variations, due to energetic particle precipitation driven by ULF waves, and on the vertical electric current, modulated by polar cap potential, associated to SW-magnetosphere reconnection processes. More recently, evidence of an SW signature in the mesosphere [62] has been published, indicating that the SW can affect the atmosphere through the whole atmospheric column. As discussed by [63], the processes involved in each atmospheric layer are almost certainly different, and transport phenomena could be

Our conclusions are supported by the observed short (<1–2 days) delay response in the atmospheric parameters at troposphere altitudes and at ground with respect to the much longer delay expected for chemical mechanism [15, 57]. However, this matter should be further investigated as underlined by [63] in particular through the examination of the time delays at stratospheric and mesospheric altitudes and at lower latitudes; the study of the dependence on different interplanetary conditions might be also useful for a more deep understanding of the atmosphere response to

The authors acknowledge J. H. King and N. Papatashvilli at NASA and CDAWeb

for solar wind data (http://cdaweb.gsfc.nasa.gov) and Daniel Weimer at Space

large-scale transport pattern (see [57] for details).

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

5. Summary and conclusions

[54] can be summarized as follows:

driven processes are absent.

important.

the SW.

15

Acknowledgements
