The impact of topography on heavy rainfall during two rain seasons was investigated in order to explain their mechanisms on rainfall distribution over Rwanda. Weather Research and Forecasting (WRF-ARW) model was used ...The impact of topography on heavy rainfall during two rain seasons was investigated in order to explain their mechanisms on rainfall distribution over Rwanda. Weather Research and Forecasting (WRF-ARW) model was used to study two historical cases of heavy rainfall which took place over Rwanda during two rain seasons, March to May (MAM) and September to December (SOND), from April 7 to 9, 2012 (for MAM) and from October 29 to 31, 2012 (during SOND). The control experiment was done with actual topography, whereas sensitivity experiment was carried out with topography reduced by half. Results show that rainfall distribution over Rwanda significantly changes when topography is reduced. The reduction in topography leads to a decrease in rainfall amounts in both MAM and SOND seasons, with varying magnitudes. This reveals the importance of orography in determining rainfall amounts and distribution over the region. The accumulated rainfall amount from WRF underestimate or overestimate rain gauge stations data by region and by season, but there is good agreement especially in altitude below 1490 m and above 1554 m during April and October respectively. The results may motivate modelling carters to further improve parameterization schemes in the mountainous regions.展开更多
This study evaluates the vertical profiles of aerosol and cloud optical properties in 40 dominated dust and smoke regions in Western-Northern Africa (WNA) and Central-Southern Africa (CSA), respectively, from the surf...This study evaluates the vertical profiles of aerosol and cloud optical properties in 40 dominated dust and smoke regions in Western-Northern Africa (WNA) and Central-Southern Africa (CSA), respectively, from the surface to 10km and from 2008 to 2011 based on LIVAS (LIdar climatology of Vertical Aerosol Structure for space-based lidar simulation studies). Aerosol extinction (AE), aerosol backscatter (AB), and aerosol depolarization (AD) generally increase from the surface to 1.2 km and decrease from 1.2 km to the upper layers in both WNA and CSA. AE and AB in CSA (maximum of 0.13 km<sup>-1</sup>, 0.14 km<sup>-1</sup>, 0.0021 km<sup>-1</sup>‧sr<sup>-1</sup>, 0.0033 km<sup>-1</sup>‧sr<sup>-1</sup>) are higher than in WNA (maximum of 0.07 km<sup>-1</sup>, 0.08 km<sup>-1</sup>, 0.0017 km<sup>-1</sup>‧sr<sup>-1</sup>, 0.0015 km<sup>-1</sup>‧sr<sup>-1</sup>) at 532 and 1064 nm respectively. AD in WNA (maximum of 0.25) is significantly higher than in CSA (maximum of 0.05). There is a smooth change with the height of cloud extinction and backscatter in WNA and CSA, while there is a remarkable increase of cloud depolarization with height, whereby it is high in CSA and low in WNA due to high and low fraction of cirrus respectively. Altocumulus has the highest extinction in NA (0.0139 km<sup>-1</sup>), CA (0.058 km<sup>-1</sup>), WA (0.013 km<sup>-1</sup>), while low overcast transparent (0.76 km<sup>-1</sup>) below 1 km in SA. The major findings of this study may contribute to the improvement of our understanding of aerosol-cloud interaction studies in dominated dust and smoke aerosol regions.展开更多
文摘The impact of topography on heavy rainfall during two rain seasons was investigated in order to explain their mechanisms on rainfall distribution over Rwanda. Weather Research and Forecasting (WRF-ARW) model was used to study two historical cases of heavy rainfall which took place over Rwanda during two rain seasons, March to May (MAM) and September to December (SOND), from April 7 to 9, 2012 (for MAM) and from October 29 to 31, 2012 (during SOND). The control experiment was done with actual topography, whereas sensitivity experiment was carried out with topography reduced by half. Results show that rainfall distribution over Rwanda significantly changes when topography is reduced. The reduction in topography leads to a decrease in rainfall amounts in both MAM and SOND seasons, with varying magnitudes. This reveals the importance of orography in determining rainfall amounts and distribution over the region. The accumulated rainfall amount from WRF underestimate or overestimate rain gauge stations data by region and by season, but there is good agreement especially in altitude below 1490 m and above 1554 m during April and October respectively. The results may motivate modelling carters to further improve parameterization schemes in the mountainous regions.
文摘This study evaluates the vertical profiles of aerosol and cloud optical properties in 40 dominated dust and smoke regions in Western-Northern Africa (WNA) and Central-Southern Africa (CSA), respectively, from the surface to 10km and from 2008 to 2011 based on LIVAS (LIdar climatology of Vertical Aerosol Structure for space-based lidar simulation studies). Aerosol extinction (AE), aerosol backscatter (AB), and aerosol depolarization (AD) generally increase from the surface to 1.2 km and decrease from 1.2 km to the upper layers in both WNA and CSA. AE and AB in CSA (maximum of 0.13 km<sup>-1</sup>, 0.14 km<sup>-1</sup>, 0.0021 km<sup>-1</sup>‧sr<sup>-1</sup>, 0.0033 km<sup>-1</sup>‧sr<sup>-1</sup>) are higher than in WNA (maximum of 0.07 km<sup>-1</sup>, 0.08 km<sup>-1</sup>, 0.0017 km<sup>-1</sup>‧sr<sup>-1</sup>, 0.0015 km<sup>-1</sup>‧sr<sup>-1</sup>) at 532 and 1064 nm respectively. AD in WNA (maximum of 0.25) is significantly higher than in CSA (maximum of 0.05). There is a smooth change with the height of cloud extinction and backscatter in WNA and CSA, while there is a remarkable increase of cloud depolarization with height, whereby it is high in CSA and low in WNA due to high and low fraction of cirrus respectively. Altocumulus has the highest extinction in NA (0.0139 km<sup>-1</sup>), CA (0.058 km<sup>-1</sup>), WA (0.013 km<sup>-1</sup>), while low overcast transparent (0.76 km<sup>-1</sup>) below 1 km in SA. The major findings of this study may contribute to the improvement of our understanding of aerosol-cloud interaction studies in dominated dust and smoke aerosol regions.
