Читать книгу Congo Basin Hydrology, Climate, and Biogeochemistry - Группа авторов - Страница 63

The regional atmospheric circulation of Central Africa is governed by low‐level westerly winds, the northern and southern components of the African Easterly Jet (AEJ) and the Tropical Easterly Jet (TEJ). These winds are some of the most important factors related to the convective activity of precipitation through moisture transport from the Atlantic and Indian Oceans to the continent (Dyer et al., 2017; Nicholson & Grist, 2003; Pokam et al., 2014). Figure 4.8 shows the low‐level wind (at 925 hPa) for the period from 2001 to 2006. In this figure, we observe that the regional circulation over the Atlantic and Indian Oceans is well represented by ERA 5 during all seasons. The different experiments capture this regional circulation reasonably well but with an overestimation of the zonal wind at the eastern border, which is well marked during the JJA season and across the Atlantic Ocean. However, the direction and intensity of the wind are well represented by the different experiments. It is across the Atlantic Ocean that the direction was not well simulated by the experiments. Convergence towards the continent was not well represented.

Figure 4.8 Spatial and seasonal distributions at 925 hPa of zonal wind in colour (m/s) and wind intensity (in m/s vector) for the period 2001–2006 of ERA5 (a–d) and the different experiments (e–l).

Figure 4.9 Spatial and seasonal distributions at 200 hPa of zonal wind in colour (m/s) and wind intensity (in m/s vector) for the period 2001–2006 of ERA5 (a–d) and the different experiments (e–l).

Figure 4.9 shows wind at 200 hPa pressure level. We observe that ERA 5 has the TEJ located between 5°S–5°N latitude, which extends from the Indian Ocean to the Atlantic Ocean during the DJF, MAM, and SON seasons. The experiments tend to reasonably reproduce this TEJ but with an overestimation of the intensity and spatial extent. As far as wind direction and intensity are concerned, the experiments manage to represent them during the DJF, MAM, and SON seasons. A comparative analysis of the different experiments reveals that performance is similar, but there are important differences.