This study investigates the variability and periodicity of minimum temperature, maximum temperature and sunspot number—a solar activity index in selected synoptic stations across Nigeria from 1946 to 2010. Annual and semiannual effect of solar activity on minimum temperature was observed in all the six stations. This was indicated in the occurrence of modal periodicities of 6-month and 12-month observed across the six synoptic stations. The synoptic stations are Sokoto (13.01°N, 5.15°E), Ilorin (8.29°N, 4.35°E), Ikeja (6.35°N, 3.20°E), Enugu (6.28°N, 7.33°E), Port-Harcourt (4.51°N, 7.01°E) and Maiduguri (11.51°N, 13.05°E). Similarly, the trends of inter-decadal va-riability of minimum and maximum temperature show a non-uniformity increase over the analyzed period with a slight decrease before 1960. The long term behavior of minimum and maximum temperature shows a warming rate which ranges from 0.1°C/decade to 0.2°C/ decade across the six stations except for maximum temperature at Ilorin and minimum temperature at Sokoto which is at -0.2°C/decade and 0.3°C/decade respectively.
The amount of energy reaching the earth from the sun is the main driver of weather and climate. Temperature differences from day to night and from season to season are the consequences of the intensity of sunlight falling to the surface and into the earth’s atmosphere.
The impact of solar activity on Earth’s terrestrial environment is propagated from the heliosphere via the in- terplanetary medium to the lower atmosphere which has troposphere at its lower end. However, sunspots are the most easily observed features of the solar photosphere, while at the same time they are important manifestations of solar activity [
A full understanding of the influence of solar variability on the Earth’s climate requires knowledge of the short and long term solar variability, solar-terrestrial interactions, and the mechanisms determining the response of the Earth’s climate system to these interactions [
Nigeria’s climate is characterized by strong latitudinal zones becoming progressively drier and hotter as one travels from the coast to the north. Temperatures throughout Nigeria are generally high; diurnal variations are much more pronounced than seasonal variations. Although average temperatures vary little from coastal to in- land areas, inland areas especially in the northeast have greater extremes.
The aim of this study is to improve knowledge on the potential localized effect of solar activity on tempera- ture in selected cities across Nigeria. This was achieved by investigating the trend pattern of temperature, a cli- matic variable with respect to sunspot number—a solar index. Similarly, attribution of periodic variation of temperature to solar effect is also investigated.
Nigeria is located approximately within latitude 4 degrees and 14 degrees north of the equator and between 2 degrees and 14 degree east of the Greenwich Meridian (
The six synoptic stations chosen in this study takes into account the major climatic zones in the country. So- koto (13.01˚N, 5.15˚E) and Maiduguri (11.51˚N, 13.05˚E) are in the highland semi-arid zone of Nigeria. Ilorin (8.29˚N, 4.35˚E) and Enugu (6.28˚N, 7.33˚E) are from the sub-humid zone while Ikeja (6.35˚N, 3.20˚E) and Port Harcourt (4.51˚N, 7.01˚E) are in the lowland warm and humid forest zone.
A brief description of some of the selected cities across Nigeria whose data is utilized in this research is given below:
Sokoto (13.01˚N, 5.15˚E) is one of the cities in the Sahel region of Nigeria. The influence of increase in tem- perature has resulted in increased evapotranspiration, drought as well as desertification [
Ilorin (8.29˚N, 4.35˚E) is located in the transition zone between the dry savanna of northern Nigeria and de- ciduous woodlands of southern Nigeria [
Ikeja (6.35˚N, 3.20˚E) is located in the South Western region of Nigeria. It is a coastal area with a characteris- tic warm humid climate. The three major wind currents that influence the climate of this area are the maritime tropical (mT) air mass, the continental tropical (cT) air mass and the equatorial easterlies [
Port Harcourt (4.51˚N, 7.01˚E) is a coastal city located in the Niger Delta region of Nigeria. It falls within the humid tropical rain forest belt of Southeastern Nigeria. It has two seasons, the wet season and the dry season. During the wet and dry seasons the mean temperature varies from about 20.30˚C to about 32.16˚C respectively.
Monthly data of maximum temperature and minimum temperature were obtained from The Nigerian Meteoro- logical Agency (NIMET), Oshodi, Lagos Nigeria. The data were obtained for six weather stations representing
the three main climatic zones (humid, sub-humid and semi-arid) within Nigeria for the period 1946-2010 (65 years). They are Sokoto (13.01˚N, 5.15˚E), Ilorin (8.29˚N, 4.35˚E), Ikeja (6.35˚N, 3.20˚E), Enugu (6.28˚N, 7.33˚E) Port Harcourt (4.51˚N, 7.01˚E) and Maiduguri (11.51˚N, 13.05˚E). The solar index used was sunspot number (SSN) from 1946-2010 obtained from the National Geophysical Data Center (NGDC), Boulder, Colo- rado, USA. Missing monthly data was filled up by taking the means of the monthly value of the two preceding and following years. The linear trends in the climate time series between the years 1946-2010 were calculated by means of least-square linear fitting. Time series anomalies of temperature from 1951-2010 were obtained as deviations to the annual mean of 1981-2010. The relationships between time series of temperature and sunspot number were analyzed by means of parametric correlations. The statistical significance of the trend and correla- tion was estimated with the t-student test. T-test is preferentially used on data that is not serially correlated or seasonally cyclic or skewed. In order to test the confidence on the regression trend, it is important to set the con- fidence limits on the slope of the regression line. In this analysis, the statistical significance in the trend and cor- relation coefficients are considered significance only at least at 95% level. Finally, the periodicity of temperature for each of the six meteorological stations was analyzed.
The annual variation of minimum temperature, maximum temperature is compared to the annual variation of sunspot number in all the six meteorological stations under consideration in this research. This is presented in
trend of 0.18˚C/decade, 0.16˚C/decade, 0.13˚C/decade, 0.12˚C/decade, 0.15˚C/decade was obtained for maxi- mum temperature at Port Harcourt, Enugu, Ikeja, Maiduguri and Sokoto respectively between the years 1946- 2010. However, at Ilorin a slight decreasing trend of −0.02˚C/decade was observed. The long-term behavior of maximum and minimum temperature time series are similar to the global increase in mean air temperature, al- though the rate of warming in the selected cities across Nigeria is approximately twice the global mean surface temperatures which have risen by 0.074/decade over the last century [
It can be observed from the periodicity analysis of minimum temperature in
SSN | Sokoto | Maidu | Ilorin | Ikeja | Port | Enugu | |||
---|---|---|---|---|---|---|---|---|---|
SSN | 1.00 | ||||||||
Sokoto | −0.01 | 1.00 | |||||||
Maidu | 0.00 | 0.89 | 1.00 | ||||||
Ilorin | 0.07 | 0.18 | 0.16 | 1.00 | |||||
Ikeja | 0.01 | 0.21 | 0.03 | 0.12 | 1.00 | ||||
Port | 0.01 | 0.56 | 0.49 | 0.16 | 0.45 | 1.00 | |||
Enugu | 0.01 | 0.60 | 0.55 | 0.20 | 0.36 | 0.62 | 1.00 | ||
SSN | Sokoto | Maidu | Ilorin | Ikeja | Port | Enugu | ||
---|---|---|---|---|---|---|---|---|
SSN | 1.00 | |||||||
Sokoto | 0.01 | 1.00 | ||||||
Maidu | −0.03 | 0.76 | 1.00 | |||||
Ilorin | −0.06 | 0.45 | 0.35 | 1.00 | ||||
Ikeja | −0.04 | 0.41 | 0.32 | 0.86 | 1.00 | |||
Port | −0.07 | 0.36 | 0.26 | 0.80 | 0.86 | 1.00 | ||
Enugu | −0.06 | 0.40 | 0.29 | 0.90 | 0.88 | 0.86 | 1.00 |
(March 22nd and September 22nd). Gazis et al. (1995) [
The recent climate change in Nigeria may not be attributed to solar activity. However, influence of geomagnetic effect on temperature has been demonstrated at Sokoto, Maiduguri, Ilorin, Port Harcourt, Ikeja and Enugu in pe- riodicity of 6-month/cycle and 12-month/cycle. This provides an evidence of solar terrestrial connection in the earth’s atmosphere and has an important effect on communication and navigation systems.