Planetary Layer Lapse Rate Comparison of Tropical,Montane and hot Semi-Arid Climates of Nigeria

This study assessed the pattern of planetary layer lapse rate across the major climate belts of Nigeria. Six years’ data (2010-2015) for air temperature values between 1000 mbar and 850 mbar atmospheric pressure levels were acquired from Era-Interim Re-analysis data centre. The data was retrieved at 6-hourly synoptic hours: 0000H, 0600H, 1200H and 1800H at 0.125o grid resolution. Results showed that the lower tropospheric layers throughout the various climate belts has a positive lapse rate. Findings also revealed that the average annual lapse rate condition were: Tropical wet zone (Port Harcourt) -5.6 oC/km; Bi-modal Tropical continental zone (Enugu) 5.8 oC/km; Montane zone (Jos) -6.5 oC/km; Mono-modal Tropical continental zone (Kano) -6.6 oC/km; and Hot semi-arid zone (Maiduguri) -6.6 oC/km. This average values presents the lapse rates to be close to the Saturated Adiabatic Lapse Rate (SALR). Average diurnal results for the climate belts showed that lapse rate is higher during the afternoon and transition periods than the rest periods and increases from the coastal areas northward. The seasonal periods of highest lapse rates during the day time are from December – May (i.e. 5.8-9.5 oC/km) with slight decrease from June – November. The positive lapse rate of range -1.8 –    -5.9 oC/km observed during the period of dawn across the entire region showed that infrared radiation was still being released and modified by less energetic mechanical turbulence that characterizes the surface layer across Nigeria. This also indicates that global warming is real and in substantial effect. The study findings imply that conditional instability prevailed over the entire region, therefore, the planetary layer environment will be of slow to moderate dispersive potential and will require forceful mechanism to lift emissions are introduced into it. It is recommended that industrial stacks are above 50 m to enhance the dispersion of emissions aloft.