Acta Physica Academiae Scientiarum Hungaricae, Tomus 45 (3), pp. 243-275 (1978) OST THE DIURNAL VARIATION COEFFICIENTS OF THE NUCLEONIC COMPONENT OF COSMIC RAYS By M. F. TOLBA, S. A. WAHAB and A. M. SALEM COSb{IC RAY GROUP, PHYSICS DEPARTMENT, FACULTY OF SCIENCE, AIN SHAMS UNIVERSITY, CAIRO, EGYPT (Reeeived in revised form 24. X. 1978) The expected amplitudes, as well as the time shift due to geomagnetic bending, of the diurnal waves have been calculated for 27 cosmic ray nentron monitors for the recent shapes of the diurnal, semidiurnal and tridiurnal anisotropies. The calculations areperformed for latitude dependenee of the form, cosn )t and rigidity dependence of the form R t~ exp [(1-R)/Ro] where ~ is the asymptotie latitude, R is the rigidity in GV, and n, ~ and R O are constants. For the diurnal anisotropy, the ealculations are given for n = 1, ~ = --0.4, 0.0, +0.4, +0.8, R o -~ ~o and maximum cutoff rigidity ~-- 90 GV, while for semidiurnal and tridiurnal aniso- tropies the results are given for n = 1, 2, {~ = 1, 2 and R o = 50, 90 GV. Moreover, the cal- culation of the attenuation 91 to the Iatitude effect, the smoothing effcct, and the mean latitude and mean eone broadening are given for the different concerned anisotropies. The presently caleulated coeffieients for diurnal variation are significantly smaller than those cal- eulated previonsly due to the carcful selection of the used parameters. A considerable increase in the time shift due to geomagnetic bending is only found in the wide cone stations. The relation between the mean latitude, the cone broadening, the time shift, and the expected amplitude for all diurnal components and the minimum cutoff rigidity of the different sta- tions are discussed. 1. Introduetion The information about the different modulation mechanisms of cosmic rays in the interplanetary space can be obtained by the investigation of the different components of solar diurnal variations. I-Iowever, the accurate characteristics of the anisotropies that produce these variations can only be obtained by a careful calculation of the coefficients transforming the shape of the va¡ recorded on the surface of the earth to the corresponding free space anisotropy. Several calculations have been carried out by different authors for the coefficients of the first and second components of diurnal variation using different methods of calculation and shapes of anisotropy [1, 2, 3, 4, 5]. McCRACKEN et al [2] have calculated the coefficients and the shift in the asymptotic time due to geomagnetic bending for both dirunal and semidiurnal anisotropies, where the rigidity dependence of the anisotropy is used in the form R a up to rigidity 500 GV and latitude dependence of the form cos 4. In later investigation, FujII et al [5] and NAGASHIMA et al [6] showed that the semidiurnal anisotropy is reasonably assumed to have the rigidity dependence of the form R ~ exp (--R/Ro), where R is the rigidity in GV, Acta Physica Academiae Sr Hungarirne 45, 197~