Characterization of Surface Layer Turbulence across a West African Tropical Climate Belt

• 作者: Precious N. Ede
• 来源期刊: 大气和气候科学(英文)
• 学科: 物理学
• 关键词: TURBULENCE Richardson Number West Africa Nigeria Coastal Area Air Pollution
• 年，卷（期）: 2020,（3）
• 页码范围: 405-420
• 页数: 16页
• 分类号: O35

摘要

This study surveyed the levels of boundary layer surface turbulence across a West African climate region. Five years (2011-2015) temperature and wind speed data at synoptic hours 0000 Hr, 0600 Hr, 1200 Hr and 1800 Hr within 0.125<span style="white-space:nowrap;">&deg;</span> grid resolution was sourced from Era-Interim Reanalysis platform at 1000 mbar pressure level. Using the Richardson (Ri) number technique, results showed that mechanical turbulence of Ri range 0.04 - 0.57 dominates across the surface layer for study locations of Port Harcourt, Enugu, Jos, Kano and Maiduguri than thermal turbulence. However, the least turbulent area was the coastal zone of surveyed region. Results also indicated that the vertical height (L) at which thermal turbulence replaces mechanical turbulence across study locations ranged from 20 - 250 m with lowest replacement levels (20 - 50 m) occurring mainly in the coastal area of Port Harcourt during periods of dawn. The most turbulent periods in the southern coastal location of study region were during key rainy periods from June-August while that for the rest far northern inland areas occur during the dry season/early rainy periods i.e. November-May. The implication of the lower surface turbulence/replacement level within coastal domains most especially during periods of dawn is that emission releases near surface layer will be dispersed after initial rise due to buoyancy at horizontal levels thereby increasing ground level pollutants concentration across sensitive receptors that are close to emission source. At heights of thermal turbulence replacement, emission releases will be transported vertically and then dispersed further away from emission sources, thus impacting sensitive receptors at farther distances. This is the atmospheric boundary layer dynamics that makes ground level pollution worse in the coastal city of Port Harcourt in recent times during periods of dawn. Efforts must be made by concerned Stakeholders towards ensuring that emissions are reduced during the period