Significant impacts of radiation physics in the Weather Research and Forecasting model on the precipitation and dynamics of the West African Monsoon

Li, R.; Jin, Jiming; Wang, S.-Y.; Gillies, Robert R.

doi:10.1007/s00382-014-2294-2

Cited by 18 publications

(15 citation statements)

References 33 publications

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“…This is consistent with large low cloud errors in the previous generation of climate models over southern West Africa identified by Knippertz et al [] and indeed with a more general climate model bias, where low cloud occurrence in the tropics is systematically underestimated [ Nam et al , ]. This is likely to have significant impacts on the surface radiation budget [ Knippertz et al , ] and consequently the broader circulation [ Li et al , ]; it is planned to examine this in detail using radiation calculations in a future study. High‐level and mid‐level cloud cover errors are smaller, but there are deficiencies in the representation of their diurnal cycle and also that of precipitation, which are linked to convection parametrization in the models [ Pearson et al , ].…”

Section: Discussionsupporting

confidence: 79%

“…Even numerical weather prediction models at convection‐permitting resolution can have large cloud errors in SWA; Stein et al [] showed that the Met Office Unified Model overestimates low cloud cover and underestimates anvil cloud cover at all resolutions from 40 to 1.5 km. Cloud errors in SWA can have a large impact on radiation [ Knippertz et al , ], which in turn may affect the broader circulation [ Li et al , ; Marsham et al , ]. In light of these problems simulating present‐day climate, it is perhaps unsurprising that projections of future precipitation in West Africa show large diversity, for both regional [ Paeth et al , ] and global coupled [ Cook and Vizy , ] models.…”

Section: Introductionmentioning

confidence: 99%

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A multisatellite climatology of clouds, radiation, and precipitation in southern West Africa and comparison to climate models

2016

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Southern West Africa (SWA) has a large population that relies on highly variable monsoon rainfall, yet climate models show little consensus over projected precipitation in this region. Understanding of the current and future climate of SWA is further complicated by rapidly increasing anthropogenic emissions and a lack of surface observations. Using multiple satellite observations, the ERA‐Interim reanalysis, and four climate models, we document the climatology of cloud, precipitation, and radiation over SWA in June–July, highlight discrepancies among satellite products, and identify shortcomings in climate models and ERA‐Interim. Large differences exist between monthly mean cloud cover estimates from satellites, which range from 68 to 94%. In contrast, differences among satellite observations in top of atmosphere outgoing radiation and surface precipitation are smaller, with monthly means of about 230 W m−2 of longwave radiation, 145 W m−2 of shortwave radiation, and 5.87 mm d−1 of precipitation. Both ERA‐Interim and the climate models show less total cloud cover than observations, mainly due to underestimating low cloud cover. Errors in cloud cover, along with uncertainty in surface albedo, lead to a large spread of outgoing shortwave radiation. Both ERA‐Interim and the climate models also show signs of convection developing too early in the diurnal cycle, with associated errors in the diurnal cycles of precipitation and outgoing longwave radiation. Clouds, radiation, and precipitation are linked in an analysis of the regional energy budget, which shows that interannual variability of precipitation and dry static energy divergence are strongly linked.

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Section: Discussionsupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

A multisatellite climatology of clouds, radiation, and precipitation in southern West Africa and comparison to climate models

2016

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“…Not limited to West Africa, Noda et al (2009) show that sub-grid cloud processes in the Non-Hydrostatic Icosahedral Atmospheric Model (NICAM) influence not only the development of low-level cloudiness but also middle and higher clouds, even at horizontal grid scales of 14 and 7 km, due to differences in turbulent transport. Also, different radiation schemes have been found to impact precipitation and the north-south gradient of surface temperature, which affects the strength of the monsoon flow (Li et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

The role of low-level clouds in the West African monsoon system

2019

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Abstract. Realistically simulating the West African monsoon system still poses a substantial challenge to state-of-the-art weather and climate models. One particular issue is the representation of the extensive and persistent low-level clouds over southern West Africa (SWA) during boreal summer. These clouds are important in regulating the amount of solar radiation reaching the surface, but their role in the local energy balance and the overall monsoon system has never been assessed. Based on sensitivity experiments using the ICON model for July 2006, we show for the first time that rainfall over SWA depends logarithmically on the optical thickness of low clouds, as these control the diurnal evolution of the planetary boundary layer, vertical stability and finally convection. In our experiments, the increased precipitation over SWA has a small direct effect on the downstream Sahel, as higher temperatures due to increased surface radiation are accompanied by decreases in low-level moisture due to changes in advection, leading to almost unchanged equivalent potential temperatures in the Sahel. A systematic comparison of simulations with and without convective parameterization reveals agreement in the direction of the precipitation signal but larger sensitivity for explicit convection. For parameterized convection the main rainband is too far south and the diurnal cycle shows signs of unrealistic vertical mixing, leading to a positive feedback on low clouds. The results demonstrate that relatively minor errors, variations or trends in low-level cloudiness over SWA can have substantial impacts on precipitation. Similarly, they suggest that the dimming likely associated with an increase in anthropogenic emissions in the future would lead to a decrease in summer rainfall in the densely populated Guinea coastal area. Future work should investigate longer-term effects of the misrepresentation of low clouds in climate models, e.g. moderated through effects on rainfall, soil moisture and evaporation.

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“…Li et al (2015) have shown that WAM precipitation patterns are very sensitive to the radiation scheme, and the most realistic patterns were obtained with the Rapid Radiative Transfer Model for General Circulation Models (RRTMG) with the Monte-Carlo Independent Column Approximation (McICA) method of random cloud overlap from Mlawer et al (1997). The planetary boundary layer physics are computed using the Yonsei University scheme .…”

Section: Meteorological Fields With the Wrf Modelmentioning

confidence: 99%

Interactions of atmospheric gases and aerosols with the monsoon dynamics over the Sudano-Guinean region during AMMA

et al. 2018

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Abstract. Carbon monoxide, CO, and fine atmospheric particulate matter, PM 2.5 , are analyzed over the Guinean Gulf coastal region using the WRF-CHIMERE modeling system and observations during the beginning of the monsoon 2006 (from May to July), corresponding to the Africa Multidisciplinary Monsoon Analysis (AMMA) campaign period.Along the Guinean Gulf coast, the contribution of longrange pollution transport to CO or PM 2.5 concentrations is important. The contribution of desert dust PM 2.5 concentration decreases from ∼ 38 % in May to ∼ 5 % in July. The contribution of biomass burning PM 2.5 concentration from Central Africa increases from ∼ 10 % in May to ∼ 52 % in July. The anthropogenic contribution is ∼ 30 % for CO and ∼ 10 % for PM 2.5 during the whole period.

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Significant impacts of radiation physics in the Weather Research and Forecasting model on the precipitation and dynamics of the West African Monsoon

Cited by 18 publications

References 33 publications

A multisatellite climatology of clouds, radiation, and precipitation in southern West Africa and comparison to climate models

A multisatellite climatology of clouds, radiation, and precipitation in southern West Africa and comparison to climate models

The role of low-level clouds in the West African monsoon system

Interactions of atmospheric gases and aerosols with the monsoon dynamics over the Sudano-Guinean region during AMMA

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