Acta Geophysicavol. 59, no. 5, Oct. 2011, pp. 1044-1056

DOI: 10.2478/s11600-011-0029-x

© 2011 Institute of Geophysics, Polish Academy of Sciences

Climate Changes Associated withHigh-Amplitude Sq Geomagnetic Variations

Taha RABEH1, Joao CARVALHO2, Ahmed KHALIL3

Esmat A. EL-AAL3, and Ibrahim EL-HEMALY3

1IGIDL, Lisbon University, Portugale-mail: taharabeh@yahoo.com (corresponding author)

2Laboratório Nacional de Energia e Geologia (LNEG), Portugal3National Research Institute of Astronomy and Geophysics, Helwan, Egypt

A b s t r a c t

When the solar irradiance propagates between the outer mag-netospheric regions and the ionosphere, dynamic processes of themagnetosphere-ionosphere-thermosphere system are affected at the lowerend of their paths by the interaction of radiation with the neutral troposphere.The main target of this work is to investigate the relationship between thediurnal magnetic field variations resulting from solar activities and the vari-ation in the troposphere temperature. Meteorological and geomagnetic dataacquired from different observatories located in Egypt, Portugal and Slo-vakia in a long-term and daily-term scales were analyzed.

The long-term results show that there is a close relationship betweenthe diurnal Sq magnetic field variations and the tropospheric temperature.The rate of temperature increase at mid-latitude areas is higher than athigh-latitude. During the period of investigation, it is found that the tropo-sphere temperature has increased by about 0.033 °C/year at Helwan, Egypt,0.03 °C/year at Coimbra, Portugal, and 0.028 °C/year in Hurbanovo/StaráLesná, Slovakia. The Sq geomagnetic variations depend on the intensity ofthe electric currents generated by the effect of solar radiation in the iono-sphere.

Key words: Earth’s climate, diurnal magnetic field variation, meteorologi-cal data, geomagnetic data, solar radiation.

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1. INTRODUCTIONThe idea of the existence of a close relationship between the lower tropo-sphere and solar activity is accepted by many scientists (Brown and John 1979,Houghton et al. 1992, Bucha and Bucha 1998, Donarummo et al. 2002, Hoytand Schatten 1997, Hurrell 1996, Kelly 1977, Kondratyev and Nikolsky 1983,Ram and Stolz 1999, Svensmark and Friis-Christensen 1997). Eddy (1976)indicated in his study a very strong link between the weather changes and thesolar irradiance. Sharma (2002) studied variations in solar magnetic activity.He stated that the cosmic ray influx, in turn, is affected by the solar surfacemagnetic activity and the geomagnetic dipole strength. He suggested that vari-ations in solar activity control the 100 000 year (100 ka) glacial-interglacialcycles. Haigh and Lundstedt (2007) show the solar variability influences thetropospheric climate. Also, they postulated the existence of thermosphere-ionosphere-mesosphere-stratosphere coupling process. This result was sup-ported by many scientists (Cubasch et al. 1997, Dickinson 1975, Haigh 2003,Hartley et al. 1998, Keckhut et al. 2005, Thompson et al. 2005). Based onthis hypothesis, we started to analyze relationships between the variations inthe magnetic field due to the solar radiation and the tropospheric temperature.

To do so, we investigated a relationship between the Sq magnetic field andthe temperature variations. We used the horizontal magnetic component, H,and the temperature, °C, data from different observatories around the globe.We present in this study the data from three different ground stations (geo-magnetic and meteorological observatories) in Egypt (29°51’N and 31°20’E),Portugal (40°22’N and 8°42’W) and Slovakia (latitudes 47°87’N and 49°09’N,longitudes 20°17’E and 18°19’E). The tropospheric temperature was registered2 m above the ground at meteorological observatories sites. Additionally, datafor sunspot numbers, flares and aa-index from NOAA data center have beenused. Furthermore, a computer software package was constructed at the Cen-tre of Geophysics (IGIDL), Lisbon, Portugal, to calculate the magnetic field Sq

variations in order to reveal the process of the temperature and geomagneticinteraction.

Analyses of the changes of weather activity in many places around theglobe and the geomagnetic variations in two time domains have been carriedout in terms of the diurnal range and long term variations. Only a few typicalresults are presented here to illustrate the process.

2. SOLAR RADIATION AND GEOMAGNETIC FIELDReid (1987) used in his correlation the global mean value of sea surface tem-perature (SST) (see Fig. 1) for the period from 1860 to 1980. He shows a closerelationship between the changing rate in the solar activities and the changingrate of the Earth’s tropospheric temperature. It can be noticed that the 11-year

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Fig. 1. Variations of (a) the mean values of sunspot numbers and (b) the sea surfacetemperature (SST), for the period 1860 to 1980. The solid line represents the yearlyaverage values variations and the doted line the running mean average variations.

smoothed annual mean sunspot numbers (SSN) increased from about 45 duringthe year 1860 to about 80 for the year 1985, while the sea surface temperatureincreased by about 0.45 °C during the specified period. The correlation showsmatching between the maxima and minima of the sea surface temperatures andthe mean values of the sunspot number curves.

This result encouraged us to examine this relationship. Therefore, we ex-amined the relationship between the sunspot numbers and the aa-index of geo-magnetic field in terms of 11/22 year cycle. The data for the period 1860 to 2000(Fig. 2) shows that sunspot numbers are smoothly correlated with aa-index interms of 11-year solar cycles. The aa-index does show the 11-year cycle but twomain differences between sunspot numbers and aa-index are clearly noticeable(see Fig. 2). The difference concerns the long-term variation between aa-indexand sunspot numbers, in particular in the level at solar activity minima. Weshow this correlation to illustrate the relation between the solar activity and themagnetic field. Cliver et al. (1998) showed that the variability of the Earth’smagnetic field is related to the incoming solar radiation. Fluteau et al. (2006)indicated that the solar flux of energy and particles can jointly explain parallelvariations in temperature and external magnetic field. However, Kerr (2006),explained this graph (Fig. 3) based on NASA’s scientists analyses, in which theyhave discovered a positive trend in the intensity of the solar activity since 1980.They found the factor of variability of about 0.06 flares per year. This is similarto the annual variability of the tropospheric temperature on the Earth, which hasbeen 0.05 per year. He also noticed that the trend in fluctuations of the solaractivity and the trend in variability of the tropospheric temperature on the Earthare almost parallel to one another. Simultaneously, both trends are separated byan equalized interval. He thought that the steadiness of the difference betweenthe two trends corresponds to a difference between the intensity of solar irradi-

Sq VARIATIONS AND TROPOSPHERE TEMPERATURE 1047

Fig. 2. Relationship between yearly averages of sunspot numbers and aa-index of geo-magnetic field variations in terms of 11-year solar cycles. They show a general similar-ity between SSN and aa-index in time of variations.

Fig. 3. Correlation between variations in the tropospheric temperature and solar flareswith respect to the last two solar cycles.

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ance and the tropospheric temperature (0.06−0.05 = 0.01). He concluded thatit is evident that the equivalences between the variability of the tropospherictemperature and the variability of the solar irradiance are directly related to theintensity of the incoming solar radiation. The latter includes all forms of radi-ation emitted by the Sun, for example, the infrared radiation (heat), light, UVradiation, X-rays, Gamma rays, etc. At present, we are experiencing a largersolar cycle (lasting about 100 years) that includes 10 cycles of 11 years each.

The correlation between the flares with respect to the tropospheric temper-ature variations and sunspot numbers along twenty years from 1985 to 2005(see Fig. 3) shows that the variability of the flares is parallel to the variability ofthe tropospheric temperature. The increase in the flares rate and the incomingsolar radiation are corresponding to the increase in the troposheric temperature.The largest flare and highest tropospheric temperature are correlated with thebeginning of maxima of the solar cycles. It is evident that the equivalencesbetween the variability of the tropospheric temperature and the variability ofthe solar irradiance/solar activities are directly related to the intensity of theincoming solar radiation and also the variability of the geomagnetic field.

3. THE GEOMAGNETIC FIELD VARIATIONS ANDTHE INCREASE IN THE TROPOSPHERE TEMPERATURE

In this work we use data from different observatories around the globe. Wewill present data from three sites located in Egypt, Portugal and Slovakia tostudy and analyze the relationship between the tropospheric temperature andgeomagnetic variations. The temperature data (°C) and geomagnetic data(H-component) acquired by Helwan, Coimbra and Hurbanovo/Stará Lesná,Meteorological and Geomagnetic Observatories are used.

The data derived from Helwan, Egypt (29°51’N, 31°20’E), covers the pe-riod from 1860 to 1960. The results (see Fig. 4) show good correlation betweenthe variations of the magnetic field and the tropospheric temperature. It can benoticed that during the period from 1860 to 1910, the tropospheric temperaturevaried in the range of 0.6 °C while the magnetic field varied in the range of250 nT, whereas during the period from 1910 to 1960 the variations are nearlytwo times bigger. Also, the analyses illustrate that the increasing rate of the tro-pospheric temperature reaches about 0.033 °C per year. The data derived fromCoimbra, Portugal, site covered measurements from 1895 to 1948. It can benoticed that there is a good correlation between the tropospheric temperatureand magnetic field variations (see Fig. 5). It is obvious that the rate of varia-tion during the period from 1892 to 1910 is twice the values during the periodfrom 1910 to 1950. Also, we find that the rate of increase in the tropospherictemperatures reaches about 0.03 °C per year.

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Fig. 4. Correlation between variations of the monthly averages of magnetic field, H ,and monthly averages of temperature at Helwan, Egypt.

Fig. 5. Correlation between variations of the monthly averages of magnetic field, H ,and monthly averages of temperature at Coimbra, Portugal.

The data from Hurbanovo/Stará Lesná, Slovakia, contained measurementsfrom 1980 to 2005. The results (see Fig. 6) show a good correlation betweenvariations of the tropospheric temperature and magnetic field, whereas the rateof increase of the tropospheric temperatures reaches about 0.028 °C per year.

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Fig. 6. Correlation between variations of the monthly averages of magnetic field, H ,and monthly averages of temperature at Hurbanovo/Stará Lesná, Slovakia.

Also, they show that the tropospheric temperature varied in the range of 0.4 °C,while the magnetic field varied in the range of 50 nT during the previouslymentioned period.

4. MAGNETIC FIELD VARIATIONS, Sq, AND THE DIURNALVARIATIONS OF THE TROPOSPHERE TEMPERATURE

The diurnal magnetic variations, commonly known as Sq variations or “mag-netic quiet-day solar variations” (Chapman and Bartels 1940), are generatedin the Earth’s ionosphere, mainly by solar radiation and tidal forces, which acton the neutral and ionized particles at heights between 70 and 120 km. Cor-responding to the solar position, an electric current system is generated whichcovers about 1/3 of the Earth’s northern hemisphere. The dayside ionosphericcurrents are of considerable size, up to ten thousands of amperes close to thecenters. The nightside current systems “regeneration currents” are smaller inamplitude, but extend over a larger area.

The geomagnetic variations resulting from these dynamo systems aresafely observed at each magnetic observatory, day by day, with amplitudesof ± some tens of nT maximum in the magnetic components D, H, Z. Theshape and amplitude of these diurnal Sq variations depend strongly on the geo-graphic latitude of the observatory site. The intensities vary with local time ina prevailing cycle period of 24 h. Other parts of the variation, such as the lunarcomponent, or induction effects resulting from special conductivity conditions

Sq VARIATIONS AND TROPOSPHERE TEMPERATURE 1051

in the Earth’s crust or upper mantle are not considered here, as they are of minorrelevance for this study.

We used in our analyses the calculated Sq magnetic field at each observa-tory and the tropospheric temperature (°C) derived from the same location orwith a maximum distance of about ±2 longitudes. The Sq variations were com-puted by removing the absolute values of the horizontal magnetic field from themean values of the horizontal magnetic component H along the daytime. Theresulting ∆h/Sq represents the magnetic quiet-day solar variations.

We used the yearly averages values for Sq to correlate them with the yearlyaverages mean values of the tropospheric temperature along the day for the cor-responding durations for Helwan site. On looking to the diurnal variations anal-yses of the 100 years at Helwan, Egypt (see Fig. 7) we can notice a good cor-relation between the maxima/minima of the magnetic Sq and the tropospherictemperature, °C. The maximum values for Sq and °C can be found at 12 hwhile the minimum values can be found at 18 h for Sq and at 24 h for °C. Ingeneral view, there is a parallel similarity between Sq and °C variations alongthe duration of the daytime.

The correlation between the Sq magnetic field and the tropospheric tem-perature, °C, for October 2008 at Coimbra, Portugal (see Fig. 8), shows thatthere is a general and parallel similarity for Sq and °C variations along the du-ration of 24 hours. The maximum values for Sq and °C can be found at 13 hwhile the minimum values can be found at 6 h for Sq and °C.

Fig. 7. Correlation between hourly averages of Sq magnetic field and the tropospherictemperature variations at Helwan, Egypt, along the daytime for the period 1880 to 1960.

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Fig. 8. Correlation between hourly averages of Sq magnetic field and the tropospherictemperature variations at Coimbra, Portugal, along the daytime for October 2008.

We also show a good correlation between Sq and °C variations for January2008 at Hurbanovo/Stará Lesná, Slovakia (see Fig. 9). The lowest values for°C are found at 6 to 8 h and at 18 h for Sq variations. The correlations arein agreement with the maximum values at midday during the daytime period

Fig. 9. Correlation between hourly averages of Sq magnetic field and the tropospherictemperature variations at Hurbanovo/Stará Lesná, Slovakia, along the daytime for Jan-uary 2008.

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Fig. 10. Correlation between the global Sq magnetic field and the Earth’s temperaturefor about 95 years at northern Atlantic area.

while they are showing shifts for the corresponding minimum values. However,the shape of the curves depends on the solar zenith angle as well as the site’slocations; therefore, the variations would be different but in general they showa parallel similarity along the corresponding periods.

Figure 10 shows a general correlation between the global Sq magneticfield from Cheltenham/Fredericksburg geomagnetic observatories and the tro-posphere temperature for about 95 years in USA. The variations in the Sq mag-netic field agree with the tropospheric temperature changes.

5. THE RELATION BETWEEN THE SOLAR RADIATIONAND Sq MAGNETIC VARIATIONS

From the previously mentioned analysis, it can be noticed that the Sq magneticfield is strongly connected with the solar radiation where it is directly propor-tional with the sunspot numbers and intensity/numbers of solar flares.

The long term changes of magnetic intensity exhibit amplitudes of severaltenths of nT within a few decades, which is very well correlated with the so-lar radiation and the tropospheric temperature. The solar comprises ultraviolet,X-rays and Gamma rays which have an ability to ionize and generate electriccurrent in the atmosphere (Parkhomov et al. 2006). This current producesadditional magnetic field, ∆h, added to horizontal magnetic component. Themagnitude of ∆h is proportional to the intensity of solar radiation. The value

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of additional magnetic field, ∆h, depends on the increase of the electric cur-rent, I, that is mainly based on the solar radiation and ionization process in theionosphere.

6. CONCLUSIONSAn analysis of the relationship between the magnetic field and the tropospherictemperature changes has been conducted using the horizontal magnetic com-ponent, H, and tropospheric temperature, °C, as well as Sq magnetic field.The correlation between H and °C for the 100 year recorded data proves theirclose relationship in terms of 11-year solar cycle and the diurnal variations (seeTable 1). This is apparent from the correlation between the °C and aa-indexand sunspot numbers. Obviously the magnetic field is produced from the elec-tric current in the ionosphere deduced from the solar radiation/solar plasma.The existence of a close relationship of solar activity with the lower tropo-sphere is due to the close distance between the location of the ionosphere andthe lower troposphere where the coupling process of thermosphere-ionosphere-mesosphere-stratosphere exists. The mechanism of the thermal heating in thetroposphere by cosmic rays, storms and flares induces electric currents wherea permanent layer of heavy ion-clusters is produced. The currents in this layercontrol the electric fields and hence the magnetic field. The heating occursdue to this process (Baker 2000). This process has a direct effect on the tropo-sphere temperature. The rate of the temperature increase at mid-latitude areasis higher than that at high-latitude areas. The geomagnetic variations reflectthe fact that an additional magnetic field, ∆h, depends on the intensity of theelectric current, I, deduced from the solar radiation. Hence, the Sq magneticfield variations are mainly affected by the intensity of the solar radiation andtherefore are correlated with the changes in the tropospheric temperature.

T a b l e 1

The rate of increase in tropospheric temperature and horizontalmagnetic component during the investigated periods

LocationRate of increase

temperature magnetic field[oC/year] H[nT]

Helwan Observatory 0.033 5.6Coimbra Observatory 0.03 3.7Hurbanovo/Stará Lesná 0.028 1.5

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The troposphere temperature increases by about 0.033 °C/year at Hel-wan, Egypt; 0.03 °C/year at Coimbra, Portugal; and 0.028 °C/year in Hur-banovo/Stará Lesná, Slovakia. Also, a close relationship can be noticed be-tween the diurnal Sq magnetic field and the troposphere temperature variations(see Table 1).

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Received 14 October 2009Received in revised form 18 March 2011

Accepted 23 March 2011