SOLAR RADIATIVE VARIABILITY FORCING OF CLIMATE CHANGE ON SEASONAL TO DECADAL SCALES IN KENYA

Abstract

The study focused on solar forcing of the Earth’s climate by looking at how indices ofthe various solar spheres relate to the climatic parameters measured on the Earth.The daily meteorological data for nine climatic parameters: Relative Humidity,Maximum Temperature, Minimum Temperature, Wind speed, Sunshine duration, SolarRadiation, Evaporation, Rainfall and Average Temperature obtained from the KenyaMeteorological Department (KMD) for the five representative synoptic meteorologicalstations covering the period 1986 to 2005 were filtered and reduced to Monthly means.The same procedure was done to the solar indices (Sunspot numbers, F10.7 cm solarradio flux and Mg II core-to-wing ratio) data obtained from NGDC, Boulder, Coloradothrough their website. The cross-correlation method was applied to calculate thecorrelation coefficients between the various meteorological variables and solar indices ateach station. Significant periodicities in the meteorological variables at each station weredetermined from the periodograms that were obtained by applying the Fourier transformtechnique Scargle periodogram (Scargle, 1982) to the monthly means of themeteorological variables. Modeling of the meteorological and solar indices was doneusing the proposed linear Multivariate model, and the empirical coefficients determinedby applying least square fittings. Validity of the models was tested using the statisticalindicators: The Mean Bias Error (MBE) and Root Mean Square Error (RMSE).Periodicities in the drought occurrences were determined. Employing the stepwisemultivariate regression analysis in SPSS, the proposed model was then applied to thecases where solar indices were lagged.Results show that above 95% level of statistically significant correlations exist betweenwind speed and sunspot numbers in Kericho; between minimum temperature andsunspot numbers in Kisumu; between sunshine duration and sunspot numbers in Garissa;and between solar radiation and sunspot numbers in Garissa. Above 95% level ofstatistically significant correlations exist between relative humidity and F10.7 cm radiosolar flux in Mombasa; between wind speed and F10.7 cm radio solar flux in Kericho,Kisumu, Mombasa and Garrisa; between solar radiation and F10.7 cm radio solar flux inNairobi and Kisumu; between evaporation and F10.7 cm radio solar flux in Garissa; andbetween average temperature and F10.7 cm radio solar flux in Kericho. Also above 95%level of statistically significant correlations exist between relative humidity and Mg IIcore-to-wing ratio in Mombasa; between wind speed and Mg II core-to-wing ratio inKericho, Mombasa and Garissa; between solar radiation and Mg II core-to-wing ratio inNairobi; and between evaporation and Mg II core-to-wing ratio in Kericho.Modal periodicities of 6 and 12 months are detected in climatic parameters in all themeteorological stations apart from Kericho.The models from the Fast Fourier analysis technique, show variations of solar forcingon climatic parameters at different locations in Kenya. Periodicities of 3.5 and 11 yearsin drought occurrences obtained in some meteorological stations in the droughtoccurrences are also comparable to the literature reports on solar activity periodicities,thus confirming solar signature on the Kenyan climate. Stepwise regression modelsmanifest in specific meteorological stations, and for different climatic parameters. Theseare seen from the above 95% level of statistically significant correlations between theobserved and predicted values from the Fast Fourier analysis models. Solar control isevident on the climate of Kenya