The separate contributions of line squalls, thunderstorms and the monsoon to the total rainfall in nigeria

Abstract

Using thunderstorm and rainfall information from five Nigerian stations for a five year period, the separate contributions of line squalls, thunderstorms and ordinary monsoons to the total rainfall and their variations with latitude are investigated. Total and thunderstorm rainfall decreases with increasing latitude but monsoon precipitation decreases exponentially while line squall rainfall is at a maximum around 9"N. Rainfall from thunderstorms shows a single annual peak in July/August at stations north of about 8"N whereas line squall precipitation exhibits a double maximum for all stations south of 12"N. It is also shown that, in the mean, line squalls are the most important rain producing systems, giving 47.6 per cent of the mean total annual precipitation compared with 39 per cent and 13.4 per cent from thunderstorms and ordinary monsoon rain, respectively.

Pre‐rainy season moisture build‐up and storm precipitation delivery in the West African Sahel

“…The disparity may be due partly to the fact that their rain events did not discriminate between precipitating and non-precipitating storms. Also, Omotosho (1985) showed that in August, there is some contribution to rainfall from the 'monsoon rain' (meso-scale convective systems with only an occasional thunder over a period consisting of 945 several hours) over areas north of 11°N. The difference between the raindays and storms may also be due to this effect.…”

“…The long-term data for evaluating the anomalies were obtained from Aspliden and Adefolalu (1976), which was based on actual radiosonde observations over West Africa. Omotosho (1985Omotosho ( , 1987 distinguished between two groups of storms in Nigeria -in situ and slow-moving storms (maximum gusts <12 ms −1 ) and squall lines with gusts greater than 12 ms −1 . The first group occurs mostly between 1200 and 2400 h while squall lines affect Kano after 2400 h (Omotosho, 1987).…”

“…For the total annual number of storms, the monthly totals were simply added together for each year and used to obtain Tables II and IV. However, in order to investigate the intraseasonal and interannual variations of the storms and their characteristics, the method of Omotosho (1985) was followed. The most common phenomenon at Kano is for storms to occur between 1200 and 2400 h (Omotosho, 1987).…”

“…It is equally well-known that at least 95% of this Sahelian precipitation is delivered by the deep convective systems (squall lines and thunderstorms, hereafter together termed storms) which traverse the sub-region from May to October (Omotosho, 1985). Omotosho (1987) showed that these storms, housed within zone C of West African weather zones about 200 km south of the intertropical discontinuity (ITD), are strongly dependent on the vertical wind shear associated with the African easterly jet (AEJ) located around 700 mb level.…”

Climate Variability Impact on the Frequency of Occurrence of Mesoscale Convective Systems in Northern Nigeria

“…Unsurprisingly, Ochei et al [7] also showed that the occurrence of thunderstorms tends to be greatly reduced over Maiduguri (North-eastern Nigeria) than over Sokoto (North-western Nigeria). However, further studies [8][9][10][11] have revealed the occurrence of upper-level downdrafts at the sides of the upper portion of updrafts.Most works on mesoscale convective systems ranges from its contribution to total precipitation [2,6,12], frequency of occurrences of such systems [7] to the damages it has caused over-time [13][14][15], but none has been written explicitly on the implication of the changing climate on the frequency of occurrence of these mesoscale convective systems. This is an area where changing climate variables, have the tendency of affecting either negatively (positively), by decreasing (increasing) the number of occurrence of thunderstorm in a given time frame.…”